THE SYNTHESIS AND CHARACTERIZATION
OF SOME N-SUBSTITUTED
CYCLOSILOXAZANES AND
CYCLODISILAZANES

Thesis for the Degree of M., S.
MICHIGAN. STATE UNIVERSITY
TERENCE I. SWIHART
1959

 
 
   
   

 
 

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THESIS

    
 
 

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ABSTRACT

THE SYNTHESIS AND CHARACTERIZATION OF SOME
N-SUBSTITUTED CYCLOSILOXAZANES
AND CYCLODISILAZANES

BY

Terence J. Swihart

In recent years reports concerning attempts to prepare
N-alkali cyclosiloxanes and their silyl derivatives have
appeared. These reports list attempted reactions of sodium
amide or phenyllithium with cyclosiloxazanes. This approach
was unsuccessful and resulted in the indiscriminate cleavage
of siloxane bonds.

This work describes the preparation of some N-lithium
salts of polydimethylcyclosiloxazanes and their rearrange—
ment in tetrahydrofuran to form cyclodisilazanes. Also
described is the preparation of some silyl derivatives of
cyclosiloxazanes and cyclodisilazanes.

It has been found that stoichiometric conversion of
polydimethylcyclosiloxazanes to the N-substituted lithium
salt proceeds at 25° with g-butyllithium in prhexane.
Further, the lithium salt, 2,2,4,4,6,6-hexamethyl-5-lithio-
1,5-dioxa-5-aza-2,4,6-trisilacyclohexane, has been shown

to react with triorganohalosilanes in a mixture of

Terence J. Swihart

tetrahydrofuran (THF) and nfhexane at 250 to yield the

N-substituted triorganosilyl derivative, reaction (1).

 

 

 

Me2$I:OSiMe2)-21\IH + fl-BuLi n_:::ane.>- MegsL;1(OSiMeg)-211—Li
+ Butane
44THF, nrhexane‘ (i)

 

L1Cl + Me2§1(081Me2}2?—81Megvi —‘ViMegSiCl

 

While the reaction of triorganohalosilanes with 2,2,4,4,6,6,—
8,8—octamethyl-5,7-dilithio-1,5-dioxa—5,7-diaza-2,4,6,8-
tetrasilacyclooctane, or with 2,2,4,4,6,6,8,8—octamethyl-7-
lithio-1,5,5-trioxa-7-aza—2,4,6,8-tetrasilacyclooctane
results in a ring contraction according to the reactions

(ii) and (iii) below.

 

 

M92 .
Megsi-O-SiMeg e2 $1 reg
Ll-IN N-L1 + 2 R351Cl mfggxane >: R381031-N: /N81OSJ.R3 +
MeZSi-O—SiMeg ‘25 f1 2 LiCl
Meg
(ii)
ea
Megsi-O-SiMeg M62 I4.
. I l . THF . I. /Sl'°\
Ll-N ? + R3$lCl n-hsxane >= R351081-N I’81Me2
Megsi-O-SiMeg ’25 sl-o
Meg (iii)

It has further been shown that the reaction of 2,2,4,4,6,6,8,8-
octamethyl-S,7-dilithio-1,5-dioxa-5,7-diaza-2,4,6,8-tetra-
silacyclooctane with dimethyldichlorosilane yields a crystal-
line polymer of low molecular weight containing cyclodisila-

zane units along the backbone of the polymer. The reaction

Terence J. Swihart
and prOposed structure is presented below.
Megsi-o-siMeg

Li-§ T-Li + MegsiClg
MGQSi-O-SiMeg

THFl 25°
__ $e2 _T
Si Me Me
. / \ I2 .2 .
-—-O-Sl-N NL-Si-O- 1 *———- + 2 L1Cl
I \\ ,,/
M82 fl
Meg X
L— _

 

 

THE SYNTHESIS AND CHARACTERIZATION OF SOME
N-SUBSTITUTED CYCLOSILOXAZANES

AND CYCLODISILAZANES

BY

. I“
Terence J£“Swihart

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Chemistry

1969

Dedication
To My Grandparents,

John and Angeline Kowalczyk

ACKNOWLEDGEMENT

I wish to acknowledge Dr. W. E. Weibrecht for his
suggestions and guidance, and Dr. R. N. Hammer for his aid
in the completion of this thesis.

Also, I wish to thank Dr. J. F. Hyde for his encour-
agement, and the Dow Corning Corporation for the use of
some materials and equipment.

Finally, I am eSpecially grateful for the love,
patience and understanding of my wife, Romaine, during the

completion of this thesis.

 

ii

TABLE OF CONTENTS

I. INTRODUCTION. . . . . . . . . . . . . . . . . .

II.

III.

IV.

RESEARCH OBJECTIVES . . . . . . . . . . . . . .
PART I. THE PREPARATION OF a,w-DICHLOROPOLY-
DIMETHYLSILOXANES AND THE CONVERSION OF THESE
MATERIALS TO POLYDIMETHYLCYCLOSILOXAZANES . . .

A. EXperimental . . . . . . . . . . . . . . . .

1. Preparation of onakDichloropolydimethyl-

siloxanes . . . . . . . . . . . . . . .
a. Materials. . . . . . . . . . . . .
b. Synthesis and Characterization . .
2. The Preparation of Some Polydimethyl-
cyclosiloxazanes. . . . . . . . . . . .
a. Materials. . . . . . . . . . . . .
b. Synthesis and Characterization . .
B. General Discussion . . . . . . . . . . . . .
1. H1 Nuclear Magnetic Resonance Character
ization Data. . . . . . . . . . . . . .
2. Infrared Characterization Data. . . . .

PART II. THE PREPARATION OF SOME N-SUBSTITUTED
LITHIUM SALTS OF POLYDIMETHYLCYCLOSILOXAZANES .

A. Experimental . . . . . . . . . . . . . . . .
1. Materials . . . . . . . . . . . . . . .
2. Synthesis and Characterization. . . . .
B. General Discussion . . . . . . . . . . . . .
C. Infrared Spectrosc0pic Analysis of the N-
Substituted Lithium Salts of Polydimethyl-
cyclosiloxazanes . . . . . . . . . . . . . .
D. The Determination of the Stoichiometry of
the Metallation of Cyclostiloxazanes with
Butyllithium . . . . . . . . . . . . . . .
E. The Ring Contraction of Some N-Substituted
Lithium Salts of Polydimethylcyclosiloxa-
zanes. . . . . . .... . . . . . . . . . . .

iii

44

44
44
44
46

56

59

62

TABLE OF CONTENTS-~continued Page

V.

VI.

PART III. THE PREPARATION OF SOME N-SILYL

DERIVATIVES OF POLYDIMETHYLCYCLOSILOXAZANES

AND OF POLYDIMETHYLCYCLODISILAZANES. . . . . . 68

A. Experimental. . . . . . . . . . . . . . . . 68
1. Materials. . . . . . . . . . . . . . . 68
2. Synthesis and Purification . . . . . . 68

B. Preparation-—Procedure II . . . . . . . . . 71

C. General Discussion. . . . . . . . . . . . 71

D. A Discussion of the Spectral Data of 2, 2, 4-
4,6,6-Hexamethyl- S-dimethylvinylsilyl-1, 5-
dioxa- S-aza— 2, 4, 6- -trisilacyclohexane (3:11) 85
E. Infrared and H1 Nuclear Magnetic Resonance
Structure Confirmation of 2,2, 4,4, 6, 6-Hexa-
methyl-5-[(dimethylvinylsiloxy)dimethyl—
silyl]-1, S-dioxa-S-aza-2,4,6-trisilacyclo-
hexane (XIV). . . . . . . . . . . . . . . . 85
F. Infrared and H1 Nuclear Magnetic Resonance
Structure Confirmation of 2, 2,4, 4-Tetra-
methyl-1,3-bis[(dimethylvinylsiloxy)di-
methylsilyl]-1,5-diaza-2,4-disilacyclo-
butane and of 2,2,4,4-tetramethyl-1,5-bis-
[(trimethylsiloxy)dimethylsilyl]-1,5—diaza-
2,4-disilacyclobutane (£2)(XVI) . . . . . . 86

PART IV. THE PREPARATION OF SOME LINEAR POLY-
MERIC MATERIALS CONTAINING ALTERNATING
SILOXANE AND CYCLODISILAZANE UNITS AS THE BACK-

BONE OF THE POLYMER. . . . . . . . . . . . . . 89
A. Experimental. . . . . . . . . . . . . . . . 89
1. Materials. . . . . . . . . . . . . . . 89
2. Preparation. . . . . . . . . . . . . . 89
B. General Discussion. . . . . . . . . . . . 96

C. Spectrosc0pic Confirmation of a,w-Dimethyl-
vinylsilylpoly[1, 1, 5, 3, 5, S-hexamethyl-2,4-
dioxa-1,5,5-trisilapentane-1,5-(2,2,4,4-
tetramethyl-1,3-diaza-2,4-disilacyclo-
butane)], Polymer A; and of d,w~Dimethyl-
vinylsilyl-poly[1,1,5,3,5,5,7,7-octamethyl-
2,4,6-trioxa-1,3,5,7-tetrasilaheptane-1,5-
(2,2,4,4—tetramethyl-1,5-diaza-2,4-disila-
cyclobutane)], Polymer B. . . . . . . . . . 97

D. Some Physical PrOperties of the Prepared
Polymers. . . . . . . . . . . . . . . . . 101

1. Thermal Stability. . . . . . . . . . . 101

iv

TABLE OF CONTENTS--continued Page

2. Microscopic Identification of the

Prepared Polymers. . . . . . . . . . . 105
3. Molecular Weight Determinations. . . . 105
4. Hydrolyzability. . . . . . . . . . . . 104

VII. SOME MISCELLANEOUS PHYSICAL PROPERTIES OF THE
N-SUBSTITUTED LITHIUM POLYDIMETHYLCYCLOSILOXA-
MES . O O O O I O O O O O O O C O O O O C O O 106

VIII. MISCELLANEOUS. . . . . . . . . . . . . . . . . 107

A. Analytical Methods. . . . . . . . . . . . 107
1. Carbon, Hydrogen, Silicon and Nitrogen
Analyses . . . . . . . . . . . . 107

2. Chlorine Analysis. . . . . . . . . . . 107
5. Hydrolyzable Nitrogen. . . . . . . . . 107
4. Lithium Analysis . . . . . . . . . . . 108
5. Molecular Weight . . . . . . . . . . . 108
6. Spectrosc0pic Data . . . . . . . . . . 108
7. Photomicrographs . . . . . . . . . . . 109
8. Thermal Gravimetric Analyses . . . . . 109

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . 111

TABLE

II.

III.

IV.

VI.

VII.

VIII.

IX.

XI.

XII.

XIII.

LIST OF TABLES

Characterization Data of Some a,w—Dichloropoly-
dimethylsiloxanes. . . . . . . . . . . . . . .

Structure Representation of the Polydimethyl-
cyclosiloxazanes Prepared and Isolated . . . .

Characterization Data of the Polydimethylcyclo-
siloxazanes Prepared . . . . . . . . . . . . .

Some Physical Properties of the Polydimethyl-
cyclosiloxazanes Prepared. . . . . . . . . . .

Hl Nuclear Magnetic Resonance Data of Some
Prepared Polydimethylcyclosiloxazanes. . . . .

Hl Nuclear Magnetic Resonance Data of Some
Known Cyclosiloxazanes and'Siloxanes . . . . .

The Assignment of Chemical Shifts to Specific
Methyl Protons for Polydimethylcyclosiloxa-
zanes. . . . . . . . . . . . . . . . . . . . .

A Comparison of the Infrared Siloxane Absorp-
tion Frequencies for Some Polydimethylcyclo-
siloxazanes. . . . . . . . . . . . . . . . . .

Accumulated Infrared Spectra of Some Cyclo-
siloxazanes. . . . . . . . . . . . . . . . . .

Structure Representation of the N-Lithium
Polydimethylcyclosiloxazanes Prepared. . . . .

Characterization Data of the N-Lithium Polydi-
methylcyclosiloxazanes Prepared. . . . . . . .

Infrared Spectra of Some N-Substituted Lithio-
cyclosiloxazanes . . . . . . . . . . . . . . .

Moles of Butane Evolved for the Reaction of

Butyllithium with Various Polydimethylcyclo-
siloxazanes. . . . . . . . . . . . . . . . . .

vi

Page

12

19

21

22

33

55

36

41

42

47

49

58

61

LIST OF TABLES--continued

TABLE Page

XIV. Hl Nuclear Magnetic Resonance Data of Some N-
Substituted Lithium Cyclosiloxazanes. . . . . . 66

XV. Structure Representation of Some N-Silyl Deriva-
tives of Cyclosiloxazanes and Cyclodisilazanes. 72

XVI. Correlation Chart of Starting Materials and
Products Formed from the Attempted Silylations
of Various Cyclosiloxazanes . . . . . . . . . . 75

XVII. Characterization Data for the N-Silyl Deriva-
tives of Cyclosiloxazanes and Cyclodisilazanes. 74

XVIII. Characteristic Infrared GrOUp Absorptions for
Compounds XIII-XVI; . . . . . . . . . . . . . . 75

XIX. Hl Nuclear Magnetic Resonance Characterization

XX. Moles of Reactants Used in the Preparation of
Polymer A; a,weDimethylvinylsilyl-poly[1,1,5,5-
5,5-hexamethyl-2,4-dioxa-1,5,S-trisilapentane-
1,5-(2,2,4,4,tetramethyl-1,5-diaza-2,4-disila-
cyclobutaneIJ, and of Polymer B; d,w-Dimethyl-
vinylsilyl-poly(1,1,5,5,5,5,7,7-octamethyl-2,4—
6-trioxa-1,5,5,7-tetrasilaheptane-1,5-(2,2,-
4,4-tetramethyl-1,5-diaza-2,4-disilacyclo-
butane)]. . . . . . . . . . . . . . . . . . . . 91

XXI. Infrared Spectra of Polymer A and Polymer B . . 92

-XXII. H1 Nuclear Magnetic Resonance Spectra of
Polymer A and Polymer B . . . . . . . . . . . . 95

XXIII. Thermal Gravimetric Analysis of Polymer A and
of Polymer B in Helium and in Air . . . . . . . 102

vii

LIST OF FIGURES

FIGURE Page
1. Vapor phase chromatograph of 1,5-dichloro-
1,1,5,5-tetramethyl-2-oxa-1,5—disilapropane. . 15
2. Vapor phase chromatograph of 1,5—dichloro-

10.

11.

1,1,5,5,5,5-hexamethyl-2,4-dioxa-1,5,5-

trisilapentane . . . . . . . . . . . . . . . . 14
Vapor phase chromatograph of 1,7—dichloro-
1,1,5,5,4,4,7,7-octamethyl-2,4,6-trioxa-1,5,5-
7-tetrasilaheptane . . . . . . . . . . . . . . 15
Vapor phase chromatograph of 1,9—dichloro-

1,1,5,5,5,5,7,7,9,9-decamethyl-1,2,4,6,8-
tetraoxa-1,5,5,7,9-pentasilanonane . . . . . . 16

. Infrared spectrum of 2,2,4,4,6,6-hexamethyl-

1,5-dioxa-5-aza-2,4,6-trisilacyclohexane . . . 25

Infrared Spectrum of 2,2,4,4,6,6,8,8-octa-
methyl-1,5,5-trioxa—7-aza—2,4,6,8-tetrasila—
cycloéctane. . . . . . . . . . . . . . . . . . 24

Infrared spectrum of 2,2,4,4,6,6,8,8,10—10-
decamethyl-1,5,5,7-tetraoxa-9-aza-2,4,6,8-10-
pentasilacyclodecane . . . . . . . . . . . . . 25

Infrared spectrum of 2,2,4,4,6,6,8,8-octa-
methyl-1,5—dioxa-5,7—diaza-2,4,6,8-tetrasila-
cycloéctane. . . . . . . . . . . . . . . . . . 26

Infrared spectrum of 2,2,4,4,6,6,8,8,10,10,12-
12-dodecamethyl-1,5,7,9-tetraoxa-5,11-diaza-
2,4,6,8,10,12-hexasilacyclododecane. . . . . . 27

Infrared spectrum of 2,2,4,4,6,6,8,8,10,10,12,
12-dodecamethyl-1,5,9-trioxa-5.6,11-triaza-
2,4,6,8,10,12—hexasilacyclododecane. . . . . . 28

Vapor phase chromatograph of the ammination

products of 1,5—dichloro-1,1,5,5,5,5—hexa-
methyl-2,4-dioxa-1,5,5-trisilapentane. . . . . 51

viii

LIST OF FIGURES--continued

FIGURE Page

12. Infrared spectrum of 2,2,4,4,6,6-hexamethyl—
5-lithio-1,5-dioxa-5-aza-2,4,6-trisilacyclo-
hexane. . . . . . . . . . . . . . . . . . . . . 50

15. Infrared spectrum of 2,2,4,4,6,6,8,8-octa-
methyl-7—lithio—1,5,5-trioxa—7-aza-tetrasila-
cycloéctane . . . . . . . . . . . . . . . . . . 51

14. Infrared spectrum of 2,2,4,4,6,6,8,8,10,10—
decamethyl—9-lithio-1,5,5,7-tetraoxa-9-aza-
2,4,6,8,10-pentasilacyclodecane . . . . . . . . 52

15. Infrared spectrum of 2,2,4,4,6,6,8,8-octa—
methyl-5,7-dilithio-1,5-dioxa-5,7-diaza-2,4,6,8-
tetrasilacycloéctane. . . . . . . . . . . . . . 55

16. Infrared Spectrum of 2,2,4,4,6,6,8,8,10,10,12,-
12-dodecamethyl-5,7,11-trilithio-1,5,9-trioxa-
5,7,11-triaza-2,4,6,8,10,12-hexasilacyclo-
dodecane. . . . . . . . . . . . . . . . . . . . 54

17. Infrared spectrum of the reaction product of
chlorotrimethylsilane and 2,2,4,4,6,6,8,8-octa-
methyl-5,7-dilithio-1,5-dioxa-5,7-diaza-2,4,6,8-
tetrasilacycloéctane. . . . . . . . . . . . . . 67

18. Infrared spectrum of 2,2,4,4,6,6-hexamethyl-5-
(dimethylvinylsilyl)—1,5-dioxa-5-aza-2,4,6-tri—
silacyclohexane . . . . . . . . . . . . . . . . 77

19. Infrared Spectrum of 2,2,4,4,6,6-hexamethyl—5—
[(dimethylvinylsiloxy)dimethylsilyl]-1,5-dioxa-
5-aza-2,4,6—trisilacyclohexane. . . . . . . . . 78

20. Infrared spectrum of 2,2,4,4—tetramethyl-1,5—
bis[(dimethylvinylsiloxy)dimethylsilyl]-1,5—
diaza-2,4-disilacyclobutane . . . . . . . . . . 79

21. Infrared spectrum of 2,2,4,4-tetramethyl-1,5-
bis[(trimethylsiloxy)dimethylsilyl]—1,5—diaza-

2,4-disilacyclobutane . . . . . . . . . . . . . 80
22. Infrared Spectrum of Polymer A. . . . . . . . . 95
25. Infrared spectrum of Polymer B. . . . . . . . . 94

ix

NOMENCLATURE

The organosilicone compounds reported herein are named
according to the ACS draft No. 10, of July 5, 1968, which
is based on IUPAC Comptes undus de la Quinzieme Conference,
Amsterdam (1949), pages 127—152. Rule D-421 was followed
which describes the use of replacement nomenclature in sub-
section C-0.6 (cf. rule B-4).

Examples:

Linear chains

7 8 5 4 3. 2\l.
H33i-NH-NH-CHg-Sng-S-Sng

2-Thia-5,6-diaza—1,5,7—trisilaheptane
Rings

01\\
o=c2 ?Si(CH3)2

H2C5 3CH2
\\\ 4,/

S
2,2—Dimethyl-1—oxa-4-thia—2-silacyclohexane-G-one
Si(CH3)3
§s

/’ \\\
(CH3)2Si4 6 i(CH3)2
3g) 1

//
‘\\Sia
(CH3)2

2,2,4,4,6,6-Hexamethyl-S-trimethylsilyl—1,5—dioxa-5-aza-

2,4,6-trisilacyclohexane.

I. INTRODUCTION

As it would be impractical to survey the entire field
of silicon-nitrogen chemistry, reference is given to
R. Fessenden and J. S. Fessenden who present an excellent
review article in the area of Silicon—nitrogen chemistry
through December of 1959 (1). The silicon-nitrogen chemis-
try which does, however, relate to this thesis is outlined
in the following paragraphs.

Silicon-nitrogen chemistry had been, until the late
1950's, an area of neglect. This is surprising when one
considers the abundant possibilities inherent in silicon-
nitrogen chemistry. The recent upsurge of research in this
area is due in large part to the advent of commercially
available Siloxane materials, which require as starting
materials large quantities of various chlorosilanes.
Chlorosilanes are also the chief starting materials used in
the preparation of silicon-nitrogen compounds.

Silicon-nitrogen compounds are most generally prepared

by the reaction of an ESiCl group with an H-N= group.
RasiC]. +- 2 R'NHa"—'—_Ah RssiNHR' + R'NHsCl.

This reaction is reversible, the halosilane being obtainable

from the silylamine and the amine salt (2,5). It has been

shown that the bromo- and iodo-silanes are more reactive
towards a given amine than the correSponding chlorosilane (4).
It is interesting to note that the silicon-nitrogen bond
is unique in the sense that a mesomeric equilibrium involving
the dw-pw orbitals of silicon and nitrogen, reSpectively, is
established (5).
This interaction of dw-pw orbitals imparts a type of

double bond character to the Silicon—nitrogen bond (6).

 

I // 9 /’
-Si-N <5 > —%ie= N
I \

The extent of this dw-pw interaction is in large measure
dependent upon the nature of the substituents on Silicon
(7,8,9,10).

The type and degree of organic or halide substitution
on silicon also affects the chemical reactivity of chlorine
on Silicon (11). Normally halosilanes react rapidly with
secondary and primary amines, with the exception of fluoro-
silanes which have been found to react only with metallated
amines (12,15).

Tertiary amines do not react with halosilanes but do,
however, interact with the tri— and tetra-halogenated silanes
to form various complexes (14,15,16,17).

Ammonia reacts with most halosilanes to form silylamines.

 

R381X + 2 NH3 >- RgsiNHg + NH4X

The stability of silylamines towards silazane formation

appears to be very dependent upon steric factors. For
example.
assiCI + 2 NH3 ———4>- essiNHg + NH4C1 (18)
MessiCl + 2 NH3 ————>- 1/2MeBSigNH + 1/2NH3 + NH4C1 (19,
20,21)

H3$iCl + 2 NH3-————>- 1/5(HgSi)3N + 2/5NH3 + NH4C1 (22).

Silazane formation is generally thought to occur by way

of condensation of the silylamines (6).
2RgSiNH2 ———4+- (R331)2NH + NH3

Krfiger and Rochow capitalized on the condensation be-
havior of silylamines to prepared cyclopolydimethylsiloxazanes

from a,w-dichlorOpolydimethylsiloxanes (25).

Me
I
ClSi(OSiMe2)XCl + NH3 (excess)

e Mel

HaNsi(OSiMe2)XNH2
Me

Meg

NH4Cl + Si(OSiMe2+;—NH
I

T

A more recent paper by J. G. Murray and R. K. Griffith
describes the preparation of dimethyl and phenylmethyl homo-
polymer and diphenyldimethyl c0polymer cyclic siloxazanes

(24).

0f the many reactions which silazanes and siloxazanes
undergo, that of metallation of the nitrogen linked to
silicon iS especially interesting. These materials, silyl
substituted alkali metal amides, are easily prepared by
the metallation of bis(silyl)amines with organic alkali

metal compounds, alkali amides and alkali hydrides (25-29).

(R351) 2NH + NaNHg ——'>' (R351) gNNa + NH3
(R381)2NH + NaH ————+- (R381(2NNa + H2
(R381)2NH + R'Li ————r- (R381)2NL1 + in

(where R' = propyl, butyl or phenyl)

The alkali metals themselves will also function as metal-
lating agents for bis(silyl)amines in special cases (12,50).
This approach requires a suspension of the alkali metal in
styrene or inainaphthalene-tetrahydrofuran mixture.

These metallated silyl-substituted alkali metal amides
are unique intermediates which are used primarily for the
synthesis of materials otherwise made with great difficulty
(51-55).

W. Fink of Monsanto extended the techniques developed
for the preparation of linear silyl-substituted alkali
metal amides to the preparation of mono-, di-, tri-, or
tetra-N-lithio cyclosilazanes (56). The addition of the
appropriate amount of chlorotrimethylsilane to these materials

yielded N-Silyl—Substituted cyclosilazanes (56,57).

H .Li
N N

. . . ‘~ .
I \‘S1Me2 + 5 ButL1 n-hexaneTT Me281/' S1Me2

HN NH LiN Li
‘\\Sf/ \\‘Si/N

Meg Meg

 

+5M€351C1
Shaking autoclave
150-200O

 

\r

LiCl + N—Silyl-Substituted
cyclosilazane.
Breed and Elliot, and at a later date W. Fink, used

this approach to prepare some N-chlorodimethylsilyl deriva-

tives of cyclosilazanes (57,58). Upon further exploration of

this chemistry, W. Fink found the reaction of dichlorodimethyl—

silane with the dilithiated cyclotrisilazane to yield 1,5-

bis(chlorodimethylsilyl)-2,2,4,4-tetramethylcyclodisilazane

rather than the eXpected silylated cyclotrisilazane.

H Mea

Si
‘ MegsI/I \\SiMe2 + 3 Me231c12 ——#- ClMegsi-N \\N—S1Me2Cl
LIN ‘/NLi \\3:
S1 2
I...
+ [Cl-Megsi]2NH + 2 LiCl

It is interesting to note that 1,5-bis(chlorodimethylsilyl)-
2,2,4,4,-tetramethylcyclodisilazane can be prepared directly

from the reaction of hexamethylcyclotrisilazane with

dichlorodimethylsilane (59).

48 hrs. \_

12 MegsiC12 + 8 (MeQSiNH)3 1750 /

Meg

Meg M62

1
9 ClSi-N< \ N-SiCl + 6 NH4C1

S1
1462
(54%)

Related to the work of Breed, Elliot, and Fink, is the
attempt by Rochow and Krfiger to metallate cyclosiloxazanes.
Rochow and Krfiger report that attempted metallation of cyclo-
siloxazanes with phenyllithium and sodium amide in refluxing
n-hexane results in the cleavage of the silozane bond (22).
In support of these findings Wannagat reports the cleavage
of the 81—0 bond in attempts to metallate bis(alkoxysilyl)-
amines with organolithium compounds (40). J. F. Hyde has
also reported the cleavage of Siloxane bonds with sodium
amide under rather drastic conditions (41). Until very re-
cently there was no literature information which outlined
the metallation of a linear or cyclic siloxazane. The first
report of the successful metallation and Silylation of
cyclosiloxazanes was made at the 1968 Spring American Chemical
Society Meeting in San Francisco. The reported work was
drawn from a portion of this thesis and was reported by this

author.

Shortly thereafter a brief communication was published
by R. P. Buch, N. C. Lloyd and C. A. Pearce which indicates
the reaction of butyllithium with some cyclosiloxazanes, as
did we, and also indicates the disproportionation and subse-
quent ring contraction of some of these salts during their
reaction with monochlorosilanes to yield cyclodisilazane
structures (42). No characterization data is presented.
Also no mention is made of the preparation of polymeric
materials from the lithiated cyclosiloxazanes, which is out-

lined in this thesis.

II. RESEARCH OBJECTIVES

The primary purpose of this research was to describe
a technique which would facilitate the metallation of
siloxazanes. These metallated siloxazanes could serve as
reactive intermediates from which new compounds could be
synthesized.

The possible reaction of metallated siloxazanes with

various Chlorosilanes would be of particular interest.

./ \ ./ \./ \ ./
sl-o-si Si—o-Ei
p NLi + R3Sic1-——> o -SiR3 + LiCl
31-0-31 Si-o7gi
/ \ / \ / ‘\ \

If it could be demonstrated that this reaction occurs with a
high degree of specificity, new areas of research would be
Opened.
Should the following two factors established;
(1) that the metal salts of the siloxazanes can be
prepared,
(2) that the metal salts of the siloxazanes react

specifically in the manner,

(ESi)gNLi + ClSiE ——->- (ESi)3N + LiCl,

then a reaction of the following type, to demonstrate the

possibility of preparing block copolymers would be attempted.

 

\ ,/\ ./
S1-O-S1
x + 1 Li-I: N-Li + x ClgSiRg >
'ifO-SI _
I \ / \ \ l \ / T. \ / \ A

Si-O-Si R2 Si-O-Si

I I
Li? ?——4 31-h ¥——'—Li
Si-O-Si Si-O-Si
/ \ I \ - / \ / \' x

 

 

The possibility of being able to exercise very exact struc-
tural control in the preparation of new polymers and true
block copolymer systems via the above reaction is immediately
apparent. The preparation of such materials is the sug—

gested third phase of this research.

A : rm“; :f

III. PART I. THE PREPARATION OF a,w-DICHLOROPOLY-

DIMETHYLSILOXANES AND THE CONVERSION OF THESE
MATERIALS TO POLYDIMETHYLCYCLOSILOXAZANES

A. Experimental

1. Preparation of a,w-DichlorOpolydimethylsiloxanes

a. Materials

 

Polydimethylcyclosiloxanes obtained from the Dow Corn-
ing Corporation were used without further treatment. The
hydrogen chloride was a product of the Mathieson Company and
was of 99% minimum purity.

b. Synthesis and Characterization

The d,w—dichloropolydimethylsiloxanes were prepared
according to the method of J. F. Hyde and P. L. Brown (45).
This is a high pressure equilibration technique. Eight
liters of a mixture of polydimethylcyclosiloxanes was added
to two liters of distilled water and allowed to react under
250 p.s.i. of HCl for seven hours at 250 in a sixteen liter
glass-lined pressure kettle. The pressure kettle was
equipped with a pressure and temperature gauge. The pres-
sure and temperature were recorded automatically as a function
of time. The pressure kettle was stirred continuously during
the seven hour reaction time. The stirrer was sealed with a

mechanical rotating seal produced by the Durasal Company.

10

11

After the materials had been equilibrated for seven hours
stirring was discontinued. The aqueous phase was then
separated from the Siloxane phase, under pressure, through
a drain attached to the bottom of the kettle. The pressure
on the kettle was relieved through a vent valve and the
chlorosiloxane phase was drained into two four liter glass
containers. A partial vacuum was applied to each container
to remove any dissolved HCl. A five liter ground glass one-
necked flask, equipped with a thermometer well, was charged
with 5450 grams of the prepared a,w-dichlorOpolydimethyl-
siloxanes. This charged flask was attached to a five-foot
distillation column, 7.5 cm inner diameter; packed with
porcelein saddles. The distillation column was equipped
with a distillation head, an automatic take off device, and
a fraction cutter.

The boiling point, per cent Cl as an indication of
stoichiometry, and the calculated and found molecular weight
based on the end group analysis, was compiled in Table I.
Figures 1-4 represent the vapor phase chromatographs of the
distilled fractions which were used as intermediates. The
per cent hydrolyzable chlorine was determined by titration
to the phenolphthalein end point with 0.1 N alcoholic KOH
in a 50/50 ethanol-water hydrolysis medium.

The vapor phase chromatograph used in this work and in
the identification of all of the volatile compounds was an

F and M 500, equipped with a 2' x 1/4" column packed with

12

.mcfinoano
manmumaouown ucmu Hem you mammamcm msoum cam co Ummmn ma chom uanmB Hoasomaoz
*

 

 

 

 

mus mme mm.ma 0s.ma as m.» um om.maa e n x

awn amm om.om mm.om as we um oaoa m u x

mew hem mm.mm mm.mm as we um om.ms m n x

mom mom mm.¢m sm.¢m as am um om.~¢ a n x
*ocsom c.0Hmo canoe 6.0Hmo ucflom Hox+mmzflmovflmmmzao

unmmmz umHsomHoz Ho been new mcHHHom

 

 

mmZdNOAHmAMmBMZHQMAOmOMOAmUHQIS.d mzom m0 484G ZOHBdNHfiMBOdeEO

H mflmfifi

 

Figure 1.

15

 

 

01_._=.=.=J Le

 

m l

Vapor phase chromatograph of 1,5-dichloro—1,1,5,5-
tetramethyl-Z-oxa-1,5-disilapr0pane.

14

2...

1-4- I

 

 

 

o v L

 

Figure 2. Vapor phase chromatograph of 1,5-dichloro-
1,1,5,5,5,5-hexamethyl-2,4-dioxa—1,5,5-
trisilapentane.

15

8?

 

 

 

. '  . I1.

Figure 5. Vapor phase chromatograph of 1,7-dichloro-
1,1,5,5,4,4,7,7-octamethyl-2,4,6-trioxa-1,5,5,7-
tetrasilaheptane.

91

64

14

 

16

 

 

 

 

 

 

Figure 4.

Vapor phase chromatograph of 1,9-dichloro-
1,1,5,5,5,5,7,7,9,9-decamethyl-2,4,6,8-tetraoxa-
1,5,5,7,9-pentasilanonane.

17

chromosorp W. The conditions were kept constant throughout
the research reported herein. Sample size = 1 - 10 ul.
heating rate = 210/min., flow rate = 60 ml. of Ng/min, 100

milliamps, temperature range 75—500+O.

2. The Preparation of Some Polydimethylcyclosiloxazanes

a. Materials

The preparation, identification and purification of the
starting materials, the d,w-dichloropolydimethylsiloxaneS,
is outlined in Part I experimental section A. ngexane,
dried over sodium metal, was used as a solvent without any
further treatment. -Ammonia gas obtained from the Mathieson
Company was dried over alkaline earth hydroxides prior to
being used.

b. Synthesis and Characterization

The general procedure used for the preparation of the
polydimethylcyclosiloxazanes is outlined below. The appara-
tus used was a three liter, three necked flask equipped
with a reflux condenser, stirrer, sparger and addition funnel.
The d,w-dichloropolydimethylsiloxanes in prhexane were con-
verted to poleimethylcyClosiloxazanes by treatment with
ammonia gas at atmospheric pressure. The gfhexane solution
containing the starting material was Slowly added to a large
volume of gfhexane which was constantly swept with ammonia
gas. After the addition of the starting material was com-
pleted the flow of ammonia gas was discontinued and the re-

action mixture was filtered to remove the ammonium chloride.

18

The ammonium chloride and the product, is formed according

to the following reaction:

Me
I

Cl-Si(OSiMe2+kCl + excess NH3 (9.)
Me

nfhexane

2 NH4C1 + M62Si(OSiMeg)Xf—'

L—II—J

The reaction temperature during the ammination process was
maintained below 50°C by controlling the rate of addition of
the d,w-dichloropolydimethylsiloxane. After the product was
filtered, the filtrate was vacuum distilled at less than 250
to remove the volatile ammonia gas and prhexane. The ma-
terials were then purified by vacuum distillation. Table II
lists the compounds which were isolated. Table III lists
the calculated and found per cent C, H, N and Si. Some of
the physical properties of the pure materials are listed in
Table IV. The distilled yield of the prepared materials is
also listed in Table IV and is based on the amount of start-
ing a,w-dichlorOpolydimethylsiloxane. Infrared spectra were
obtained on each pure material and is presented in Figures
5-10. The infrared and H1 nuclear magnetic resonance (H1 nmr)
data obtained on these materials is discussed in the follow;

ing sections.

19

TABLE II

STRUCTURE REPRESENTATION OF THE POLYDIMETHYLCYCLO-
SILOXAZANES PREPARED AND ISOLATED

 

 

(CH3)2 (CH3)2 (CH3)2
s’ s‘ s‘
/ l\ / l\ / l\
o o o I . 0
(CH3) géi Si (CH3) 2 (CH3) 281 1 (CH3) 2 (CH3) géi 1(CH3) 2
\\ // I I I i A
E o\\ //N-H o
Si. (CH3)2Si Si<CH3)2
(CH3)2 \I-lq
H
(I) (II)
(III)
(CH3)2 (CH3)2 (CH3)2
//Si\\ //SL\\ //Sl\\
H’I“ ? ? e-H
(CH3)2S1 Si(CH3)2 (CH3)2Si si(CH3)2 (CH3)2Si Si(CH3)2
\\ 'H T T H”? 9
Si// , (CH3)2Si Si(CH3)2 (CH3)2$i Si(CH3)2
(CH3)2 o\ ./ -H \ ./N-H
(IV) S1 S1
(CH3)2 (CH3)2
(v) (VI)

(I) 2,2,4,4,6,6-Hexamethyl—1,5-dioxa-5-aza-2,4,6—trisila-
cyclohexane.

(II) 2,2,4,4,6,6,8,8-Octamethyl-1,5,5-trioxa-7-aza—2,4,6,8-
tetrasilacycloéctane.

(III) 2,2,4,4,6,6,8,8,10,10-Decamethyl—1,5,5,7-tetraoxa—9-
aza-2,4,6,8,10-pentasilacyclodecane.

(IV) 2,2,4,4,6,6,8,8-0ctamethyl-1,5-dioxa-5,7-diaza-2,4,6,8-
tetrasilacycloéctane.

continued‘

20

(V) 2,2,4,4,6,6,8,8,10,10,12,12-Dodecamethyl-1,5,7,9-
tetraoxa-5,11-diaza-2,4,6,8,10,12-hexasilacyclododecane.

(VI) 2,2,4,4,6,6,8,8,10,10,12,12-Dodecamethyl—1,5,9-trioxa-
5,7,11-triaza-2,4,6,8,10,12-hexasilacyclododecane.

 

21

 

 

 

 

o.mm mm.m Hm.m m.mm .II
mm.m mfi.m >.mm o.mm mm.m 4m.m mm.mm AH>V
m.>m S¢.m m>.m «.mm .1
m¢.m mm.m m.mm a.mm mm.m mm.m sm.mm A>v
.. mfi.m Sm.m m.mm .II
I- mm.m om.m m.mm In mm.m «m.m mm.mm A>HV
mm.m mm.m m.mm .III
.. Nm.m os.m m.mm I- m>.m oe.m mm.mm AHHHC
In me.¢ em.m >.mm II.
I- me.¢ m>.m m.mm .. «s.« He.m em.mm AHHV
In om.m oe.w m.>m .I
In ww.m mm.m m.>m In mm.m ow.m wm.mm AHV
IIIIIIIII mmmucmummmlllllllll IIIIIIIIIImmmucmoummllllllll
Hm z m o Hmv z m o pcsomsoo
chom UmumHDUHMU

 

mwmhamcd Hmucmfimam

 

II

HHH mflmda

Qmm¢mmmm mWZ<N€NOAHmOAUMUQNmBQZHQMAOm NEE m0 ¢B¢Q ZOHBdNHMHBUdemU

 

22

Own ma A>HV mo ucflom mcHunE

.mnsumummEmp Eoou um pwaom ma >H USSOQEOU .nflswfia Umaooouummsm so can xmocw m>Huomnmmm
.x.

 

 

m6. mummmeé as 3.0 am 0% Age
Noe. TONS; as 3.0 um omeums ed
9mm *mummmeé as 8.0 t. 0H AID
9mm 9.34 as m.o 2... 08 films
ET. @1934 as fio um cow films
«.9. mmoeé as Hm u... can a
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mwfluumaoum HMUflmwsm

 

 

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>H MAM¢B

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Amaouoflzv zumcmam>m3
0.0N 0.9“ 0.3” 03v.“ 0...: 0.0.“ o.m o.m m.m

_ . b . S p L! — I.

A

 

 

 

 

 

25

 

 

 

 

 

 

 

 

 

 

 

 

 

 

aw _ _ _ _ .~ _
com com com ooos coma ooom

HIEU hocmskum

.mcmDonoHumomHHmmuump
Im.m.¢.mlmumnnlmonHUIm.m.aua>£uwfimu00|m.m.m.m.¢.¢.m.m mo Esuuowmm pwumumcH .m musmwm

Amcouuwzv Sumcmam>m3

0.0N o.wH o.ma o.¢a O.Nfi 0.0d O.m~ O.m
Ir P p F p . p
u

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00m 00m 00m 000d coma 000m

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Amsouoflzv numcmam>m3
0.0N o.ma o.ma o.¢d oumd 0.0H o.m nfim

L p . . p

3 %

 

 

 

25

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_ _ _ _ a \ _
00m OOm 00m OOOH OOMH 000m.

H(EU mocmsvmhm

 

Alvfldqu

 

 

 

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Im.m.¢.NImnmfl©I>.mlmonolm.alamnumfivaOIm.m.m.m.¢.¢.m.m mo Esuuommm UmumumsH .m musmflm
AmSOHUHZV numcmaw>m3

0.0N 0.0d 0.06 0.¢d 0.NH 0.0fi 0.0 0.0
b . . _ . r . % L

 

 

26

 

 

 

 

 

 

 

 

 

 

 

 

 

 

II 4 _ . _
com 08 com oooa coma ooom

HIEo mocmsvmum

.mcmomsonoaomumaflmmxmaIma.oa.m.m.¢.mImaneIda.m
ImxomuumpIm.S.m.HIHSHumSHUmuonINH.NH.oa.oa.m.m.m.m.«.«.m.m «0 asnuommm omumumcH .m musmflm
Amcouoazv numcma m>m3
o.om o.mfi o.ma o.wa ouma 0.0a o.m a p.m

b —

P n — ~

 

 

27

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_ 4 _ 4 sh <_ I
000 000 000 000d 00min 000m.

HIEU hucmflvmuh

I In

AJAJ.

.:.~.~

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........

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o.om o.ma o.ma O.HH o.md o.wa ohm a. 0mm
- n p Q

 

 

28

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

H q _ _ .4 4
00m 000 000 0006 OOMH 000m

HIEU hocoswmnh

29

B. General Discussion

 

The class of compounds known as cyclosiloxazanes have
steadily attracted the attention of an increasing number of
scientists since the first cyclosiloxazane was prepared in

1959 by Sokolov'(44).

An extension of this interest in the use of polydimethyl- M

cyclosiloxazanes as intermediates for the preparation of
N-substituted organosilylcyclosiloxazanes, prompted the syn-
thesis of a series of known and new polydimethylcyclosiloxa-
zanes for use as reactive intermediates.

These materials were prepared according to Rochow (25)
wherein the a,w—dichloropolydimethylsiloxanes were amminated
in an organic solvent. The desired cyclosiloxazanes were

produced in fair yields.

He
x Clsi(OSiMeg+zC1 + 5x NH3
e
O
25 Behexane
we
-Si (OSiMe2)z + 2x NH4C1
e Y

The cyclosiloxazanes which were prepared from the apprOpriate
a,w-dichlorOpolydimethylsiloxane are shown in Table II.

It is interesting to note that, although ammination of
1,5-dichloro-1,1,5,5,5,5-hexamethyl-2,4-dioxa-1,5,5—tri-

silapentane produced compound (I) in a distilled yield of 40%,

50

the next highest homolog (2) could not, at first, be iso-
lated from the same reaction mixture. AS can be seen in
Figurefifi.the presence of this compound or of compound (VII)
shown below was indicated by the vapor phase chromatograph

of the reaction mixture.

I‘ee 1%
HgNSi(OSiMe2)2N(OSiMe2)3NH2

(VII)

It is felt that the increased temperature required to
effect distillation, did in fact effect the polymerization
of compound (2) due to the presence of NH4Cl as a trace
contaminant.

Rochow and Kruger have reported that NH4Cl is a catalyst

for the polymerization of cyclosiloxazanes to polysiloxazanes

 

(25).
M62
Si
I \\¥-H N§$C1->: H Me
M8231 ’/,SiMe2 A 2
X) -Si-(OSiMeg)2

Thus, in the second attempt to prepare compound (2)
extreme care was taken, by more thorough filtration, to
eliminate trace amounts ammonium chloride. This resulted
in the successful isolation of compound (y), and later

compound (2;) by distillation.

 

 

 

 

51

 

 

 

 

. n-hexane
4
Compound (I)
5
21
1.
m Compound (31
04g A
Figure 11. Vapor phase chromatograph of the ammination

products of 1,5-dichloro-1,1,5,5,5,5-hexamethyl-
2,4-dioxa-1,5,5-trisilapentane.

52

1. H1 Nuclear Magnetic Resonance Characterization Data

The prepared cyclosiloxazanes listed in Table II were
characterized by H1 nuclear magnetic resonance (Hlnmr) and
by infrared. The Spectroscopic data was found to be in
complete agreement with the prOposed structures for com-
pounds (1:21).

The Hlnmr data is presented in Table V, and are without
any peculiarity.

The accumulated Hlnmr data on the cyclosiloxazanes
allows some assignment of T values. The absorption in the
range from 9.08 to 9.11 T in compounds (II), (III), and (y)
is attributed to the methyl groups near adjacent Siloxane
and silazane groups. This premise is based primarily on the
Hlnmr analyses of compounds (III) and (2). As can be seen

from the structure of compound (III), a 2 to 5 proton mole

ratio of Me1 to Meg, respectively, is expected. The experi—
mentally measured proton ratio is 12.2 to 17.8 as expected,
at T values of 9.910 and 9.945, respectively. This yields

a 2 to 5 molar ratio of Me1 to Me2 as predicted by theory.

55

TABLE V

H1 NUCLEAR MAGNETIC RESONANCE DATA OF SOME
PREPARED POLYDIMETHYLCYCLOSILOXAZANES

 

 

Hydrogen Proton Ratios

 

 

 

compound Theory Found T
*
1462
’,Si\\
O 'X-
‘ ** E. '. Me 6
(l) M82 I\ ,/’SlM —fiE¢; ='I§ 1 peak 9.900
E
** *
Megfii-O-?iMe2
1 Me* _ Ig' 12.2 9.947*
ill) *E‘? ? * Me** ” 12 11.8 9.911**
MeESi—O-SiMeg
* -)(-
M82Si-O-SiM82
Me* _ I§_ 17.8 9.945*
(331) *? ** Me** ' 12 12.2 9.910**
M82?i iM82
o [\Il-H
\sf’
**
M82
M82 $82
I
gig) Si-O-fii
H-fi N-H 1 peak 1 peak 9.950
I
?i-O-gi
M82 fi82
** M * 96*
$82 '82 M82
(V) Si-O-Si—O- £\
" I Me* _ 12. 11.7 9.953
H 1‘} /N'H Me** ‘ 4 24.5 9.908
Si-O-Si-O-Si
** l | * 1 **

M82 M82 M82

continued

54

TABLE V--continued

 

 

Compound Hydroqgn Proton Ratios T
Theory Found

$82 M82 H M82

S'- _ .__ _ .
( ) i O 1 1\\ 1 1 2
VI H-N eak eak 9.9 4
.__ ‘\ . . .//0 P P

Si-O-Si——N-Si

U l l
M82 M82 H &82

 

55

The assignment of the T values in the range of 9.908-
9.911 to the methyl protons adjacent to a silazane and
Siloxane group is in direct contradiction to a similar assign-
ment made by Rochow and Kruger (45). Based on the available
data at that time, Rochow and Kruger quite appropriately
assigned the higher frequency absorption, at 9.950 T, to the
methyl protons adjacent to the silazane functions, and the
lower frequency absorption at 9.915 T to the methyl protons
in a pure Siloxane environment. These assignments were made

based on the Hlnmr spectrum of the following compounds.

TABLE VI

Hl NUCLEAR MAGNETIC RESONANCE DATA OF SOME
KNOWN CYCLOSILOXAZANES AND SILOXANES

 

 

 

Compounds T
(Measio)3 9.885
(MegsiNH)3 9.947
(MegsiNH)4 9.955
H
Megsi-N-SiMeg 9.915, 9.950 (equal inten-
' ' sities, Rochow)
9 <3
Megsi-O-SiM82 9.911, 9.947 (equal inten-

sities this thesis)

 

Compounds (IX) and (XI) which contain only methyl groups

adjacent to Siloxane and silazane groups exhibit a Hlnmr

56

absorption value which is intermediate (9.924-50) to com—

pounds containing methyl silicon groups bordered by silazane

or siloxane grOUPS on both sides.

TABLE VII

THE ASSIGNMENT OF CHEMICAL SHIFTS TO SPECIFIC METHYL
PROTONS FOR POLYDIMETHYLCYCLOSILOXAZANES

 

 

Compound Class Grouping

T value of

 

H on C
H M82 Me H Me Me
-I '. I, ‘\ \./
I N-Si-O-Si ’,N-—Si-—O- 9.924-9.950
x=2,5
M82 H Me Me
EL. \\1
II -Sl(OSlMea)y‘ // —-Sl-—O- 9.908—9.911
x
Me Me
\\ /
for; y = 5, x = 1 -O——Si——O- 9.945-9.955
y = 4, x = 1
y = 2, x = 2

 

An exception to the above assignments is observed in the

Hlnmr spectrum of compound (I).

H
Me\\ | ‘/.Me

Si-PN-—Si
Me/’| I \‘Me
0 ,0

\\'Si

/ \.
Me Me

57

Based on the assignments in Table VII, a two to one proton
ratio would be predicted at T values of nJ9.908 and rv9.948,
respectively. Instead, this compound exhibits no splitting
of its signal at 9.900 T, which is near the expected absorp-

H Me Me
tion frequency for a \SN-:S{;—O grouping from compound
Class II. Compound.g)would be the first in the homologous

series of compound class II where x = 1.

2. Infrared Characterization Data

The infrared data is consistent with the proposed struc—
tures (45). However, some peculiarities exist which hereto-
fore have never been recognized in silicon chemistry, but
are, however, quite common to carbon chemistry. This is dis—
cussed below.

Compounds (V) and (VI) exhibit an unusual double N—H
stretching vibration at 5578 and 5547 cm-1. Whereas com-
pounds (I-IV) exhibit but one absorption, at 5410-5580 cm'l,
as eXpected. A splitting of the N-H stretching frequencies
would normally be interpreted as an indication of the
presence of ESi-NH2, which exhibits two hydrogen stretching
frequencies between 5570 and 5580 cm'l.

However the -NH2 deformation at 1540 cm-1, which is
normally quite strong, is absent or at the best is very
weak in compounds (2) and (XI). These results, in conjunc-
tion with the excellent structure confirmation of compounds
(2) and (XI) by Hlnmr and by elemental analysis, would

indicate the total absence of ESiNH2.

58

The splitting of the N-H vibrational frequency must
then be interpreted as an indication of some form of hydrogen
bonding of the hydrogen on nitrogen.

Either inter- or intra-molecular hydrogen bonding could
be responsible for the splitting of the N-H vibrational
frequency. This type of phenomenon is observed in many
organic secondary amines, wherein splitting of the N-H vibra-
tion occurs because of hydrogen bonding.

Since this phenomenon seems to be unique to silicone
chemistry, it was felt that it would be worthwhile to estab-
lish the form of the hydrogen bonding involved in compounds
(39 and (VI). Compound (2) was therefore run by infrared
at 0.1, 1.0 and 10.0 weight per cent concentrations in CCl4.

The absorption ratio of the free to the hydrogen bonded
N-H stretching vibrations at 5580 cm‘1 and 5540 cm-1
reSpectively, were found to remain relatively constant (”1.58)
over the entire concentration range. This ratio was found
to decrease to 1.1 for compound (XI) at a ten weight per cent

concentration in CC14.

5‘
N
Mezsi/ SiMeg
0 <3
I
M8231 $1M82 (2;)
I
H-N N-H

l
M8231 éiM82
\ /

59

This implies an increase in the amount of hydrogen bonding
relative to compound (2). No attempt was made to determine
the form or forms of hydrogen bonding existent in compound
(11) .

These data indicate some form of intramolecular hydrogen
bonding as being largely reSponsible fbr the splitting of
the N-H vibrational frequency in compound (2). The construc-

tion of a molecular model from, Prentice-Hall, Molecular

 

Framework Models, also indicates a favorable grometry for

intramolecular hydrogen bonding in compounds (2) and (XI).

”(lee

Si
0/ \o

./ EiM82
M8281
H i5\\\ .
\th H [SIMeg (y)
M82Si/ O
/
0 8i

M82

 

The geometry of compound (Iy) as indicated by the
Molecular Framework Models is unfavorable for the type of
interaction displayed by compound (2). Compound (I!) as a
result exhibits only the unassociated N-H vibrational fre-
quency at 5400 cm-1, as a ten weight per cent solution in
cc14.

Based on these analysis it is concluded that the Split-
ting of the N-H vibrational frequency of compound (2) at
5580 cm'1 and 5540 cm"1 is in fact largely due to intra-

molecular hydrogen bonding of the hydrogen on nitrogen to

40

to the W electrons of another nitrogen atom in the ring.

The dodecamethylcyclohexasiloxazanes, exhibit but one
very strong siloxane alborbance at 1062-1066 cm‘l. This is
in contrast to dodecamethylcyclohexasiloxane (Me23i0)6,which
is the first member in the series of permethylcyolosiloxanes
to exhibit splitting of the siloxane absorbance at 1097 cm‘1
(weak) and 1068 cm"1 (strong). Splitting of the siloxane
vibration is, however, exhibited by compounds (II) and (III),
respectively.

Rochow and Kruger also reported a splitting of the
SiOSi vibration for compound (II) (44). This phenomenon
was explained as due to two different SiOSi angles in the
same compound. The calculated values for some silazane and
siloxane angles as reported by Rochow are presented in
Table VIII along with other literature values. 9Compound (II)
is included for comparison. Based on the shift to higher
frequencies for compound (III) relative to compound (II) it
is apparent that the two different siloxane bonds in com-
pound (III) are much less strained than in compound (II).

This is to be expected since any ring strain in com-
pound.(II) would be relieved by a ring expansion via the
insertion of a fM82SiO- group into compound (II) to yield

compound (III).

“on. u d- <--.

41

 

 

 

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42

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45

 

 

 

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szNmIzIHmI m: szAmIzIH I m: szHmIzIA I 8:

 

 

UchHuGOUIIXH mqm¢a

IV. PART II. THE PREPARATION OF SOME N-SUBSTITUTED
LITHIUM SALTS OF POLYDIMETHYLCYCLOSILOXAZANES

A. Experimental

 

1. Materials

The preparation and purification of the polydimethyl-
cyclosiloxazane starting materials is described in Part I.
Reagent grade gfhexane obtained from the Fisher Scientific
Company was used as a solvent without further treatment.
Butyllithium was obtained from the Foote Chemical Company
and was used without any further treatment. It is sold as
15.18% butyllithium in gfhexane, the specific gravity being

approximately 0.68 g./ml. at 25°.

2. Synthesis and Characterization

The general technique used for the preparation of
lithium salts of the polydimethylcyclosiloxazanes is outlined
below. A sample of distilled cyclosiloxazane was weighed in
a 60 ml. flask. A rubber stopper, containing a piece of
glass tubing and equipped with a septum, was inserted into
the neck opening of the flask. The system was then purged
with dry nitrogen gas, with the septum removed, through a
vent leading from the side of the neck of the flask. Upon

completion of the nitrogen gas purge, the system was vented

44

45

to the atmosphere by connecting some tubing to the side arm
on the flask. A tube filled with Drierite was attached to
the tubing.

The appropriate number of moles of butyllithium was
introduced through the septum with a calibrated syringe.

The following reaction took place.

Reaction I

H

. I _/' . -
>si-N--si- + CH3(CH2)3L1 9— hexane;
/ \

CH3(CH2)2CH3 +

 

ESi—st 1:
L1
The reaction is quite exothermic. However, it was possible
to maintain the temperature below 500 by controlling the
rate of addition of butyllithium, the lithium salt of the
cyclic siloxazane precipitated from solution as a finely
divided white solid. ,After the addition of butyllithium
was completed, the reaction mixture was cooled to -600C by
using dry ice. The sample was then vacuum filtered at that
temperature under a nitrogen atmosphere. The solid product
was washed twice with small portions of g-hexane, cooled to
-60°C, and once with g-hexane at 250. The precipitate was'
then transferred to a glass container, sealed and weighed

immediately to determine the amount of product obtained.

The product was stored over CaSO4 in a vacuum desiccator.

46

A vacuum of 1 mm. was applied to the desiccator for two hours
to remove trace amounts of grhexane. The products were then
removed for analysis. The lithium salts of the cyclosiloxa-
zanes were characterized by their infrared and Hlnmr spectra
and by per cent lithium. A list of the materials prepared

is presented in Table X. The per cent yield based on the
starting amount of the cyclosiloxazane, the ratio of the
moles of butane found to moles of butane calculated accord-
ing to Reaction I, and the per cent lithium as an indication
of stoichiometry are listed in Table XI. The infrared
spectra of compounds XIIIrIII_are presented in Figures 12-16.
The Hlnmr Spectra (and infrared data) are accumulated in

Tables XIV and XII.

B. General Discussion

,A variety of reactions describing the preparation of
metallated disilazanes have been reported within recent years
(25-29). These metallated disilazanes have been used primar-
ily as reactive intermediates for the formation of tris(silyl)-

amines (51-55).

 

[RgsijgNN'a + R3SiCl > [R381]3N + NaCl

Rochow (44), attempted to extend this work to the prep-
aration of N-substituted sodium cyclosiloxazanes through the
reaction of sodium amide or phenyllithium with the respective

cyclosiloxazane in toluene or ether. These early attempts

47

TABLE X

STRUCTURE REPRESENTATION OF THE N-LITHIUM
POLYDIMETHYLCYCLOSILOXAZANES PREPARED

 

 

Di Li
MeZSi-N-SiMeg MeZSi-N-SiMeg
I l
o 0 (VIII) 0 0 (Ir)
\ 4’ I |
SlM82

Me2Si—0-SiMe2

Li
M82?i‘N-S iM82
0 (x)
M8251 éIiM82
O
\ ./
51
M82

(VIII) 2,2,4,4,6,6-Hexamethyl-5-lithio-1,5-dioxa-5-aza-2,4,6-
trisilacyclohexane.

(IE) 4,4, 6,8,8-Octamethyl—7—1ithio-1,5,5-trioxa-7-aza-
6,8

12! 6i
,4, -tetrasilacyc105ctane.

(x) 2,2,4,4,6,6,8,8,10,10-Decamethyl-9-lithio-1,5,5,7-
tetraoxa-9-aza-2,4,6,8,10-pentasilacyclodecane.

continued

48

TABLE X-—continued

 

 

Li Li

I
Measi-N-siMeg MeZSi-N-Simeg

\
3’ C.) (2;) (.3 ‘3 (xxx)

M82Si-I‘f-SiM82 M82§i SIiM82

Li Li -N /N-Li

Si—O-SI
M82 M82

(II) 2,2,4,4,6,6,8,8-Octamethyl-5,7-di1ithio-1,5-dioxa-5,7-
diaz-2,4,6,8-tetrasilacyclooctane.

(XII) 2,2,4,4,6,6,8,8,10,10,12,12—Dodecamethyl-5,7,11-
trilithio-1,5,9-trioxaé5,7,11-triaza—2,4,6,8,10,12—
hexasilacyclododecane.

 

49

 

8m IIII 3.8 $8 :53

 

 

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ucmu Hmm mcwououud Um>ao>m manusm mo mmaoz HA usmuuflMll

 

 

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HN flam¢8

50

 

 

 

 

 

 

 

 

 

80-! ,
7o - .
60 4 I.
50 - L
40 _. .
so - ,
20 . k
I

108 ..
O - I T I

1200 ,1000 800 650

Frequency (cm-1)

Figure 12. Infrared spectrum of 2,2,4,4,6,6-hexamethyl-
5-lithio-1,5-dioxa-5-aza—2,4,6-trisilacyclo-
hexane.

51

 

 

 

 

 

 

 

 

 

 

80- L
707 -
60- t
58 I»
0
404 -
50—\ " -'
209 .
10+ U .
0 , . .
1200 1000 800 650

Frequency (cm-1)

Figure 15. Infrared spectrum of 2,2,4,4,6,6,8,8-octamethyl-
7-lithio-1,5,5-trioxa-7-aza-tetrasilacyclo-
6ctane.

52

 

 

 

 

 

 

 

 

 

80- L
70 -. .
60 4 -
so— I
40 _, r
30 - -
20 -~ U -
10 - -
0 I 4r I
1200 1000 800 650

Frequency (cm'l)

Figure 14. Infrared spectrum of 2,2,4,4,6,6,8,8,10,10-
decamethyl-9-lithio-1,5,5,7-tetraoxa-9-aza-
2,4,6,8,10-pentasilacyclodecane.

55

 

 

 

 

 

 

80— ,
cl“
70- r
604 ) r
50* -
40‘ -
50~ .
20m .
10w 9
O l I l
1200 1000 800 650

Frequency (cm-l)

Figure 15. Infrared spectrum of 2,2,4,4,6,6,8,8-octamethy1-
5,7-dilithio-1,5-dioxa-5,7—diaza-2,4,6,8-tetra-
silacyclooctane.

54

 

 

 

 

 

 

 

80

60-. -

40fi .

20- -
O U

 

 

I T I
1200 1000 800 600
Frequency (cm-1)

Figure 16. Infrared Spectrum of 2,2,4,4,6,6,8,8,10,10,12,12—
dodecamethyl-5,7,11-trilithio-1,5,9-trioxa-5,7,11—
triaza-2,4,6,8,10,12-hexasilacyclododecane.

55

by Rochow were reported to result in cleavage of the siloxane
bond and the subsequent formation of polymeric material,
presumably a polysiloxazane.

Rochow and Kruger (44), further reported that there waS
no evidence for metallation of the disilazane linkage.
However, these experimenters employed only non-polar Solvents
as the reaction media in their attempts to metallate the
Silazane linkage.

Since most of the available metallating agents are salts,
it was felt that their reaction with the disilazane linkage
could be enhanced by increasing the ionizing or polar
character of the reaction medium.

Attempts to metallate compound (I) with sodium amide,
calcium hydride, sodium hydride and metallic sodium were
therefore carried out in dry acetonitrile at 500. Under
these conditions there was no evidence for metallation of
the -N- group, nor was there any evidence for cleavage of
the Siloxane bond. The dimethylcyclosiloxazanes did not
react in any manner under these conditions with any of the
aforementioned metallating reagents. Each reaction was
followed by vapor phase chromatography on a modified 710 F
and M dual column chromatograph.

The work of W. Fink (56,57), wherein N-substituted
lithiocyclosiloxazanes were prepared by treating hexamethyl-
cyclotrisilazane with butyllithium, suggested a possible

reaction between butyllithium and cyclosiloxazanes. It was

56

felt that the reaction Should be carried out at low tempera-
ture to minimize the possibility of Siloxane cleavage, which
was reported by Rochow in the reaction of phenyllithium with
cyclosiloxazanes.

The following reaction was attempted and was found to
proceed quantitatively in gfhexane at room temperature with

the evolution of butane gas:

 

 

 

_ M82
Megsi(OSiMe2-)-;NH + BuLi gogefzggfr- Megsi(0Si JIE-N-Li
L \ L \
+ Butane

This reaction is general for a large number of cyclosiloxa—
zanes. The compounds listed in Table X were prepared in
high yields.

The metallation of the cyclosiloxazanes with butyllithium.
does not appear to lead to the formation of any Species other
than the products listed in Table X. This is evidenced by
infrared, Hl nmr per cent lithium, and the high yields of
the desired Species. A discussion of the characterization

data is offered in the following sections.

C. Igfrared Spectroscopic Analysis of the N-Sub§tituted
Lithium Salts of Eolydimethylcyclogiloxazangg

1 in the

The Si-C asymmetric vibration at 800-810 cm“
N-lithio cyclosiloxazanes corresponds to the previously
reported values for related compounds such as the cyclo—

siloxazanes and cyclosiloxanes (45). The Si-CHs Symmetric

57

deformation, which commonly occurs from 1250-80 cm‘l, falls
to frequencies of 1245-1255 cm‘1 for compounds (VIII-XII):
this is unusually low for the Si-CH3 deformation absorption
frequency.

There is no indication of Si-Bu in the infrared Spectra
of compounds (XIIIfXII). This is indicated largely by the

1 which

absence of a strong absorption between 870-890 cm'
is indicative of Si-Bu. Also the absorptions normally
associated with Si-Bu at 1470 and 1590 cm‘l, which are
largely in the same range as the Nujol absorptions, are not
detectable as absorption Shoulders on the Nujol peak.

This analysis is in agreement with the contention that
no Siloxane cleavage is observed in the reaction of butyl—
lithium with the cyclosiloxazanes in g-hexane at 250.

AS in the case of the cyclosiloxazanes, the N-lithio-
cyclosiloxazanes also exhibit a splitting of the SiOSi
vibration. The position of the dual absorbancies is appar-
ently dependent upon the Size of the ring, as well aS the
position and number of nitrogen atoms having displaced the
oxygen atoms in the ring. In general the Siloxane and
silazane stretching vibrations Shift to lower frequencies
as the Size of the ring is decreased. This is indicative
of increasing ring strain aS the ring Size is reduced.

The observed dual SiOSi absorbances as a function of
structure are presented in Table XII. AS was previously

mentioned in Part I, splitting of the siloxane vibration is

also observed in high molecular permethylcyclosiloxanes.

58

 

 

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QMM¢MMZH

59

The absorption at 1140-1180 cm‘1 is difficult to explain.
This is normally the position assigned to the N-H bending
vibration. However, the N-H stretching frequency at 5540—5580
cm‘1 is extremely weak, indicating very little -SiNH- was
formed as a result of hydrolysis of -SiNLi- while preparing
the Nujol mulls. The SiBu group is known to absorb at 1190-
1

1200 cm'1 but the absorption typical of SiBu at 870-890 cm"

is absent from the infrared Spectra.

D. The Determination of the Stoichiometryiof the
Metallation of Cyclosiloxazanes
with Butyllithium

Experimental

A sample of distilled cyclosiloxazane was weighed in a
50 ml flask containing a Side arm inlet equipped with a
rubber septum. This flask was attached to a 100 ml cali—
brated gas burette. The system was purged with dry nitrogen
after which a known amount of butyllithium was introduced
through the septum from a calibrated syringe. Upon complete
addition of the butyllithium the flask was Shaken and then
allowed to stand for one hour at 24.80. The mercury levels
in the gas burette was adjusted with the mercury reservoir
during the evolution of the butane gas so as not to pressurize
the system during the reaction. The difference between the
final and the original mercury reading in ml was taken as
the volume of butane evolved at 746 mm at 24.80. The re-

sults for the cyclosiloxazanes run in this system are given

60

in Table XIII. The volume of butane evolved at 746 mm was
corrected to 760 mm using the gas law.
This data indicates the metallation of the cyclosiloxa—

zanes is quantitative and proceeds according to reaction

 

I below:

\8' \S'

— l .—

/ _ / 1\

\N-H + BuLi n hexane > N-Li + Butane

\‘ ./ \ ./

.31 ‘81

/ , /

The data also Show the following most probable side reactions
do not occur to any extent, as might be measurable by the
aforementioned technique, based on the moles of butane
evolved.
Me2$i(OSiMe2+;?H + BuLi --—>' BuMe28i(OSiMe2+;NLi
L

Wee

Me2$i(OSiMeg‘);f1H + BuLi ——> BuMegsi(OSiMe2§:—§N«(-Sio-)§Li

L
That is, the reactions above would not require the evolution
of butane--if either of these reactions were to occur in
large measure then the established stoichiometry according
to reaction I would be invalid.

The premise that the reaction is essentially quantita—

tive is further substantiated by the high yields of compounds
(Ify)and by the Spectral data which are discussed in the

following section.

61

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mom mo m0 mmaoz

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ZDHEBHAQNBDm m0 ZOHBU¢MM HEB mom Qm>flo>m HZ<BDm m0 mmfloz

HHHX mamda

62

E. The Ring Contraction of Some N-Substituted Lithium
Salts of Polydimethylcyclosiloxazanes
W. Fink and Breed and Elliot indicate the N-substituted
lithium cyclosilazanes, upon reaction with Silylating re-
agents, undergo a disproportionation and subsequent ring

contraction to yield the cyclodisilazane structure (46,47).

- M82 Me
Ll—Hi—N Li 3.2 M82 H
\ I I/ o I / K .0 ‘ I
M8231 SlM82 + 2 Me281Cl -—-)' Me381-N N-Si-—N-S1Me3
\ / \ /
E 91

M82

The recent work of Bush, Floyd and Pearce is related to
that of Breed and Elliot, wherein some N—substituted lithium
cyclosiloxazanes were reported to have undergone a ring
contraction to yield cyclodisilazane structures (42).

Compound (II) was reported to have undergone "ring contraction"
in 1,2-dimethoxyethane in Six hours at room temperature.
The reaction of this material with chlorotrimethylsilane

yielded the cyclodisilazane.

 

Li
Megsi-N-?1M82
' MeO (CH2) 20Mep .
0 0 6 hrs” R3137 + 2 Me3S1Cl ——>
M82éi-N-SIM82
I
Li M82
M82 /,Si M82

Me381081———N\ \N—SiOSiMes + 2 LiCl

Si
M82

65

These investigators attribute this ring contraction to
a transannular nucleOphilic rearrangement of the initially

formed N-lithium salt as represented below.

M82
, f} , '
Me2S1\ 1Me2 /S% _ +
\\\ '- .+ . I
H? x? L1 _____%> /0 NSiMego L1
Megsi S SiMea M8231——g——51M82

Ring contraction of this sort does not occur to any
measurable extent in p-hexane. This is evidenced by the
absence of the typical (strong infrared) cyclodisilazane
absorptions at 875—900 cm"1 and at 1025 cm"1 in the infrared
spectra of the N-substituted lithium cyclosiloxazanes
isolated from the reaction of butyllithium with the cyclo—
siloxazanes in pfihexane.

.Also, the H1 nmr data presented in Table III are con-
sistent with the proposed structures for the N-lithium
salts. The chemical Shifts typical of N,N'—bis(dimethylsilyl)-
tetramethylcyclodisilazane structures are at approximately
9.75 and 10.00 T for the ring methyls and the methyl groups
on Silicon adjacent to the ring, respectively (46).

Compound (II), which is most likely to undergo ring
contraction, Shows but one peak at 9.829 T. If in fact
compound (zl) had formed the smaller ring, as in the example
below, an integrated area ratio of 12:12 would be eXpected

at T 9.75 and 9.9-10.0.

64

 

Li
M8251“—N‘"$iM82 M82
l I _g-hexane M82 Si\\ M82
0 0 71/ > LiOS i—-N N—SiOLi
' ' \ Si/
Me as i——N—s iMe 2 M
. e2
L1
XI

Further evidence for the maintenance of the basic cyclo-
siloxazane structure, after lithiation, is indicated from
the reaction of chlorodimethylvinylsilane with the isolated
N,N'-dilithium salt, compound (II), in THF at room tempera-
ture. The infrared spectrum (Figure 17) of the undistilled
reaction product doeS not display the typical strong cyclo-
disilazane absorbtions at 875-900 cm’l. Instead, it indi-

cates that the following material is the primary product:

M82§i-O’SiM82
ViMegsi-N N-SiM82Vi
M82éi-O‘éiM82

which could only be formed from the corresponding N,N'-
dilithium salt.

However, attempts to prepare the N-lithium salts of
compounds (II) and (I!) in THF, followed by an I2.§I£g
Silylation of the salts with a monochlorosilane yielded
only the Siloxysilylated cyclotrisilozane and cyclodisilazane.
The reaction scheme leading to these products of smaller

ring size is written below.

65

 

 

 

 

 

 

Li salt .
Mesi(OSiMe2+gNH BUE§F1n4>r in THF, R351C1>.
\ I] n-hexane pfhexane
_ M‘82
Megfii(OSiMe2)2NSiOSiR3
l
Li salt .
[Me2$i(OSiMeg+INH]2 BuEIFin:>: in THF R35101;=
n—hexane 'p-hexane
M82 Méa M82
/,Sl\\ .
R3SiOSiN N-SiOSle
‘\ /’

Si
M82

Only compound (I) yielded the expected silyl derivative when

the above reaction scheme was followed.

These data indicate that the lithiation reaction can be

controlled and directed by the proper choice of solvent for

the reaction medium.

.p-hexane

 

BuLi + {Me2$i(OSiMe2+NH+2

BuLi + [Measi(OSiMea)NH]2

prhexane

M82

 

THF

>r LiOSi——N

>- {Me2Si(OSiMe2)NLi+2

M82

Si M82
./,N-510L1

S1

M82

The various Silylation reactions are discussed in the

next section.

66

 

 

 

 

88m III III A a 353
mmm.m III III a 5 EMS

Uhmm.m 0wo.a .l
m¢m.m >m.a fiumum m m ANV

Q QIIII

mmmm.m moo.m

nmwm.m 9mm.o M .II

mmmm.m moo. a a a m m as;
mm>.m mm.o .

Q QTIII. .

mamm.m moo.m a m m N AHHH>V

m05a0> P chom UUHMU pcsom UUHMU ocsomaoo

 

moflumm unmfimm xmmm

 

mxmmm mo HmQEDz

 

 

mmZ¢N¢NOAHmOAUNU SDHEBHA QNBDBHBmmDmIZ mzom m0 ¢B¢Q NUZ¢ZOmmm UHEHZGéS MdmAUDZ Hm

>HN mqmfia

67

 

 

 

 

 

 

 

 

 

 

80 - -
70- .
60 — -
50 8 .
40 -» ' n -
50 4 .
20 - .
10 ~ U -
O 1 I I

1200 1000 800 650

Frequency (cm-1)

Figure 17. Infrared spectrum of the reaction product of
chlorotrimethylsilane and 2,2,4,4,6,6,8,8-
octamethyl-5,7-dilithio-1,5-dioxa-5,7—diaza-
2,4,6,8-tetrasilacyclooctane.

V. PART III. THE PREPARATION OF SOME N-SILYL DERIVATIVES
OF POLYDIMETHYLCYCLOSILOXAZANES AND OF
POLYDIMETHYLCYCLODISILAZANES

A. Experimental--Procedure I

1. Materials

Tetrahydrofuran which was used as a solvent was freshly
distilled from C3H2. The Chlorosilanes used in these re-
actions were obtained from the Dow Corning Corporation and

were distilled prior to being used.

2. Synthesis and Purification

The following technique was used for the preparation
of all the distilled silyl derivatives of the polydimethyl-
cyclosiloxazanes.

A one liter, three-necked, round-bottom flask, equipped
with a reflux condenser, stirrer, and an addition port
stoppered with a rubber septum, was charged with a weighed
amount of a cyclosiloxazane. To the cyclosiloxazane was
added 200 percent by weight of tetrahydrofuran. The system
was purged for five minutes with nitrogen gas, dried over
CaSO4. To this solution, with constant stirring, was added
the correct number of moles of butyllithium from a glass

syringe by Slow addition through the addition port containing

68

69

the rubber septum. The temperature of the medium was main-
tained below 500 by controlling the addition rate of butyl-
lithium. The reaction medium remained a homogeneous liquid
system during and after the addition of the required amount
of butyllithium for all polydimethylcyclosiloxazane systems
investigated, with one exception. In the conversion of
compound (I!) to its lithium salt, the lithium salt did not
remain completely soluble in the THF-pfhexane solvent sys-
tem. Instead, a portion or all of the lithium salt of
compound (I!) precipitated from solution as a white, finely
divided, solid.

After the addition of butyllithium was completed, the
reaction mixture was stirred for from 0.5 to 2.5 hours at
room temperature. A weighed amount of the desired monochloro—
silane was then added dropwise from a 125 ml. addition funnel
equipped with a drying tube. This reaction displayed an
apparent induction period. No exothermic reaction is
detected within the first five minutes after the addition of
five to ten percent of the chlorosilane, nor iS any lithium
chloride precipitated from the reaction mixture. However,
upon the addition of 20 to 25 per cent of the chlorosilane,
a very exothermic reaction occurs with the immediate forma-
tion of lithium chloride.

Once the reaction has started, the addition of more
chlorosilane results in the immediate formation of more

lithium chloride and an increase in the temperature of the

7O

reaction mixture. The temperature of the reaction mixture
was maintained below 550 by regulating the addition rate

of the chlorosilane. The chlorosilane was always added

in a slight excess to insure the complete reaction of all
lithium on nitrogen. After the addition of the chlorosilane
was completed, the reaction mixture was stirred for one to
two hours at room temperature. Ammonia gaS dried over
sodium hydroxide was passed into the reaction mixture to
convert any unreacted chlorosilane to the disilazane accord—

ing to the equation below.
2R3$iCl + excess NH3 (g) — NH4C1 + (R3Si)2NH

This step was necessary because hydrogen chloride which could
form from the hydrolysis of unreacted chlorosilane, would
react with ESi-NE bonds. After the reaction mixture had
been amminated, it was vacuum filtered to remove the lithium
chloride and ammonium chloride. The calculated lithium
chloride and ammonium chloride from the total reaction always
correlated well with the observed values. The filtrate was
strip distilled to remove the low boiling volatile solvents.
Distillation over a spinning band column was used to purify
the remaining high boiling product.

The silyl derivatives of the lithiated cyclosiloxazanes,
which were isolated according to procedure A, are presented
in Table XV. Table XVI lists the starting materials, pro-

cedure used, the product formed and the percent yields.

71

Other physical properties and the elemental analysis are
presented (Table XVII). The Spectral data is accumulated

in Tables XVIII and XIX, Figures 18-21.

B. Preparation--Procedure II

 

A weighed amount of compound (XI) was placed in a large
amount of THF. To this solution was immediately added the
required amount of chlorodimethylvinylsilane to yield the
N,N'-disilyl.derivativeIIfcompound (XI). The reaction was
exothermic. The reaction was allowed to proceed for one
hour at room temperature after which the THF and unreacted
chlorotrimethylsilane was removed under reduced pressure.
The product was then filtered and analyzed by infrared. The
infrared spectrum indicated the formation of the following
material.

Me 2S|i—O—-S iMe 2
ViMeZS i -1\|I N-s iMe2Vi (XXII)
Me 228 i—o—Sl iM82
The analysis of the infrared spectrum is discussed in the

following sections.

C. General Discussion

As was reported in Part II, the N-lithio derivatives of

cyclosiloxazanes can be readily prepared and isolated from

72

TABLE XV

STRUCTURE REPRESENTATION OF SOME N-SILYL DERIVATIVES
OF CYCLOSILOXAZANES AND CYCLODISILAZANES

 

 

M82
’,Si-O‘\ 2,2,4,4,6,6-Hexamethyl-5-(dimethyl-
ViMeZSi-N SiM82 binylsilyl)-1,5-dioxa-5-aza—2,4,6-
“Si-O” trisilacyclohexane.
M82
(XIII)
M82
Si-O\\ 2,2,4,4,6,6-Hexamethyl-5-[(dimethyl-
ViMeQSiOSi-N‘\ /,SiMe2 vinylsiloxy)dimethylsilyl]-1,5-
M82 Si-O dioxa-5-aza-2,4,6-trisilacyclo-
M82 hexane.
(XIV)
M82

/,S1 2,2,4,4-Tetramethyl-1,5-bis-
ViMeZSiOSi-N :TNSiOSiMeZVi [(dimethylvinylsiloxy)dimethyl

Me2 \‘Si Me2 silyl]—1,5—diaza-2,4—disila-
M82 cyclobutane.

(52)

M82

‘/Si\ 2,2,4,4-Tetramethyl-1,5-bis[(tri-

MeasiOSi-N N-SiOSiMe3 methylsiloxy)dimethylsilyl]—1,5-
M82 “Si/ M82 diaza—2,4-disilacyclobutane.
M82 ‘

Qggg

 

75

.fip wmmm 00m
.x.

 

 

 

 

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0. ms flay 4 5880: 3.3
m. E Aflv a SGmeS one
m . e A Ammo m 58%ng GE
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Umaafiumfla puspoum muspmooum mcmHHmOHOHSU mafiunmum

 

 

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20mm szmom mBUDaomm QZd mA¢HmMB¢Z OZHBM¢Bm m0 BMdEU ZOHBdAmmmOU

H>N mflmdh

74

 

 

 

 

 

 

mm.m mm.m m.mm
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mo.m mm.m m.aw .l|
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MR QR MK ZR 3& MR 0mm unwom ocsomaou
venom UUHMO um XmUCH mcwaflom
mammwmc¢ HmucmEmHm m>Huumumwm

 

 

mmZ¢N¢AHmHQQAUNU QZ< mmZ¢N¢XOAHmOQUMU
m0 mm>HB¢>HMMQ AMAHmIZ Mme mom ¢B¢Q ZOHBdNHmmEU¢M¢EO

HH>N mqm48

75

.Husu 0mo«)\um umvasonm*

 

 

 

Amvoom Amvmom mom Amvfiom Amvwom ouflm mM>
A3Vowm III In: ABQOmm A3Vomm mmv Q
A3vomm III III A3v0>m A3V0>w mmo Q
nun Amvmmm Aevm¢m nun In: va oflm >
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35mm Eomm muo
In- In: 1.: Amvomm AmVOmm Hmoflm mm>
In: Am>vmfioa Am>vmaoa In- In: ZNHm mm>
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szmmom A3Vomom szomom mum >
5.3.>V0>mm in- nu- -4- In- m:z >
filH HIE- has} 35 Aflmy @flH
vasomeoo

 

 

HH>NIHHHN mDZDOQZOU MOm mZOHEmmomm¢ mbomw QMMdmmZH UHBmHMEBU<Mde

HHH>X mflméB

76

 

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N0:

 

 

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b . . P . b L F . .

 

 

 

 

 

 

 

77

 

 

 

 

 

 

 

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78

 

 

 

 

 

 

 

 

 

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P LL I.

Jail!

 

 

 

80

 

 

 

 

 

 

81

nfhexane. However, attempts to prepare the N-lithio deriva-
tive of compounds (£1) and ($2) in THF followed by an ip.§i£g
Silylation with a monochlorosilane resulted in the rearrange-
ment of the N-lithio derivative and subsequent ring contrac-

tion according to the reactions written below.

M82

I
Megsi(OSiMe2+3NH 1) BuLi inTfifhexanej>= Megfii(OSiMe2+z?SiOSiR3

I a! 2) R331c1

 

 

+ LiCl

 

(gg)
Meg M72 M32
. . THF ~_ . . ./Sl\\ '. .
+Me231051Me2NH+2- 1) BuLi in n_hexane r R381031——N‘\S.’/N51031R3
. —' 1
2) R3SIC1 Me
(139 2
+ LiCl

Of the cyclosiloxazanes treated according to procedure I.
only the N-lithio derivative of compound (1) yielded the ex-

pected product from THF according to the reaction below.

MeafiE(OSiMe2+§NH THF Me28i(OSiMeg+§?SiR3

1) BuLi in pfhexane’ I
2) RssiCl c. v

(g) + LiCl

 

 

Ring contraction of the N-lithio-derivative of compound
(L) very probably did not occur in procedure I since this
would have necessitated the formation of a cyclodisiloxazane

of the sort:

Meg
. . r’31\~
R381051-—N / 0
Meg ‘\Si

Meg

82

The formation of this compound would be energetically un-

favored and in addition would be extremely reactive towards
+_

Li 0 Si, which would also be formed in tetrahydrofuran as a

result of a ring contraction according to the reaction below.

,+
p1
N-
/'\ Me, Mea
Megsi ' SiMeg THF _ -’- /Si\
l 1 | ‘ Li+—OSi-—N\ o
o - 0 Si"
ow
Si M82
M82
(XVIII)a

Although the formation of compound (XVIIIfiis unlikely, the
rearrangement of the N-lithio salts of cyclosiloxazanes
affords an approach that could, under the correct reaction
conditions, possibly yield a cyclodisiloxazane.

With relation to procedure II, it is important to note
that the formation of the triorganosilyl derivative of com-
pound.(;y) without ring contraction was indicated by infrared.
Procedure II was carried out by placing the N,N'-dilithio
derivative of compound (Ly), isolated from nfhexane, in THF
and immediately treating the salt with an excess of chloro-

dimethylVinylsilane.

 

M62 M82 M82 M82
Si-O-Si ,Si-o-si
I \ o THF 0
L]. -N/ N-Ll , , .. -. . . #V’iMeRSi -N \I-S lMegVi
M62 M82 M82 M82

+ 2 LiCl

85

The reaction product, freed of volatiles, showed the
typical absorption for the SiOSi assymetric vibration at
1055 cm’1 and two strong absorptions at 955 cm‘1 and 955 cm‘1
for the two forms of SigN present in compound (XXII). The
absorptions typical of the silyl-substituted cyclodisilazane
at 880-900 cm":L and at 1015-1040 cm"1 were not observed
(Table XVIII).

These data indicate a critical rate dependence of the
rearrangement of the lithiated cyclosiloxazanes to smaller
rings upon the polarity or ionizing ability of the solvent
reaction media. This explains why compound (XXII) was indi-
cated by infrared when procedure II was employed. Other
investigators have indicated that the ring contraction of
the N,N'-dilithio salt of compound (IE) to the cyclodisilazane
requires six hours in 1,2-dimethoxyethane. The ring contrac-
tion of that same salt in tetrahydrofuran is obviously much

faster (Procedure I, page 68).

D. A Discussion of the Spectral Data of 2,2,4,4,6,6-
Hexamethyl-5-dimethylvinylsilyl-l,S-dioxg-
5-aza-2,4,6-trisi1acyclohexane (XIII)

Compound (XIII) prepared according to Procedure I, was
distilled in a yield of 67 per cent and was characterized by
elemental analysis and by infrared and H1 nmr. The infrared
spectrum of compound (XIII) shows two types of siloxane

1

vibrations at absorptions of 1028 cm' and 990 cm’l. The

N—hydrogen and lithium analogs of compound (XIII) also

84

exhibit two siloxane vibrational absorbances at approximately
1020 cm‘1 and 985 cm'l. There also appears to be present
two SigN vibrational absorbances at 950 cm‘1 and 911 cm'1
which are probably due to the two forms of SigN stretching
vibrations one would expect for the more strained SigN ring
stretching vibration and for the pendant silicon-nitrogen—
silicon ring stretching vibration.

It is important to note the invariance of the double
siloxane absorptions at 1028 and 990 cm‘1 throughout the

following series: Me2%i(OSiMe2+§NrX (X = H-, Li-, ViMeZSi-).

 

This is a critical observation since it indicates that the
/Si-O\ /
unit -N /,Si has not contracted during the silylation
\Si-O .\
I x
of the lithium salt of(;). If ring contraction would have

occurred, subsequent silylation with a monochlorosilane would

have yielded the following compound:

M92
M82 /Si
ViMeasiOSi—N \o (XVIII)b
\S./ ~---—-
1
Meg

This compound should yield two siloxane vibrational absorb—

ances at approximately 1060 cm'1

and at a frequency much

less than 990 cm'1 for the pendant siloxane and ring siloxane
vibration, respectively. As was stated earlier, this be—
havior is in fact not evidenced in the infrared spectrum of
compound 0.9.3.13.)- Also the SigN vibrational frequency for the

cyclodisilazane unit is normally between 880-900 cm'l.

85

The SigN linkage in compound(§y;;;)b should also be strained.
However, no shift to a lower SigN vibrational frequency is
noted.

Further structure confirmation indicating the proposed
structure is found in the H1 nmr data° Compound XIII yields
a methyl proton ratio of 631226 at T values of 9.772, 9.807,
and 9.905, respectively (Table XIX). This is in agreement

with the structure assignment of compound (XIII).

E. Infrared and H1 Nuclear Magnetic Resonance¥Structure
Confirmation of 2,2,4L4L6,6-Hexamethyl-5-[(dimethyl-
vinylsiloxy)dimethylsilyll-1,5-dioxa—5-aggf
2,4,6-trisilacyclohexane (XIV)

The infrared Spectrum of compound (XIV) indicates two
forms of siloxane vibration which show absorbances at 1025
cm'1 and 990 cm'l° This appears to be typical of the cyclo-
trisiloxazane unit shown below.

/N\

\\ . .
1,81 81“
I I

O
‘\ ,/
Si

/ \.
A shoulder on the strong absorption peak at 1025 cm'1 occurs
at approximately 1000 cm'l. This absorbance is felt to be a
disiloxane absorbance due to the N-siloxysilyl pendant group,

/

ViMeZSiOSiMe2-—N‘\ . .As in compound (XIII), this material
1

also exhibits two absorption bands at 945 and 915 cm-

which indicates the two forms of SiaN vibrations in compound

86

l

(XIV). The absorption band at 915 cm” is very probably due

to the strained SigN vibration in the ring.

The H1 nmr data lends further credance to structure
(XIV). Chemical shifts were observed at 9.807, 9.819, 9.826,
and 9.909‘? with a methyl proton ratio of 12:6:6:6 which is
identical to the required proton ratio (Table.XIX). If
silylation of the N-lithium salt of compound (II) had pro-
ceeded without ring contraction, the required methyl proton

ratio of the resulting product below would be 6:12:12.

M82 M82
//Sl'O-§l
Si-O i

M62 M82

ViMGgSi-N

F. Infrared and H1 Nuclear Magnetic Resonance Structure
Confirmation of 2,2,4,4-Tetramethyl-1,5-bis[(dimethyl-
vinylsiloxy)dimethylsilylj-i,5-diaza—2,4-disila-
cyclobutane and of 2,2,4,4-tetramethyl-1,5—
bis[(trimethylsiloxy)dimethylsilyl]-1,5-
diaza-2,4—disilacyclobutane (XE).(XVI)
Compounds (Xy)and (XVI) both show very strong absorp-
tions at 880-900 cm-1 and at 1015-1020 cm'l. These absorp-

tion bands are indicative of a silylated cyclodisilazane

structure (47):

\ /
Si
\~ /’
/-Si-N \N-Si/

\i/ ‘

/ \
The SigN absorption bands between 900-950 cm'1 commonly

associated with silazanes and tris-silylamines are not

87

present in the infrared spectra of compounds (X2) and (XXX).
The one disiloxane vibration is observed at 1068 and 1070
cm'1 for compounds (X2) and (XXX), respectively.

The H1 nmr spectra of compound (XV) revealed chemical
shifts at 9.748, 9.875, and 10.000 T with a methyl proton
ratio of 12:12:12, which is in agreement with the proposed
structure (46). Neither of the other two possible isomeric
structures shown below would yield the correct methyl proton
ratios.

Meg Meg
ViMegsi -N /Sl-O-Sl\ N-SiMegvi (EX)

Si-o-sr’
M82 M82

M62

Me 2 / S j. ‘0 ( )
ViMe S 103 i—N iMe XX
2 \\Si-N’/S 2 '7—

Meg \‘SiMegVi

Compound (XXX) should yield a 12:24 methyl proton ratio
while compound (XX) should yield a ratio of 6:6:6:6:12.
Further evidence for the proposed structure is offered
from the work of Breed and Elliot (47) wherein they have
assigned a chemical shift of 9.76-9.79 T for silylmethyl
protons attached to a cyclodisilazane ring. Also the pendant,
N-silylmethyl protons exhibit a chemical shift of 10.000 T.
The H1 nmr spectrum of compounds (X3) and (X31) are in full

agreement with these assignments.

88

In conclusion the methyl proton ratio of compound (XVI)

is 3:2:2 which is what is predicted by theory (Table XIX).

VI. PART IV. THE PREPARATION OF SOME LINEAR POLYMERIC
MATERIALS CONTAINING ALTERNATING SILOXANE AND
CYCLODISILAZANE UNITS AS THE BACKBONE
OF THE POLYMER

A. Experimental

 

1. Materials

 

The dichlorodimethylsilane was obtained from the Dow
Corning Corporation. It was distilled before being used.
The preparation and purification of bis(chlorodimethyl)-

disiloxane is described in Part I.

2. Preparation

A general procedure used to prepare these polymeric
materials is outlined as follows.

A weighed amount of the cyclosiloxazane was placed in a
500 milliliter, three-necked flask equipped with a stirrer,
addition funnel and rubber septum. To this reaction flask was
added enough THF to yield a 40 weight per cent solution of com—
pound (l!). The system was then purged with dry nitrogen gas.
After the nitrogen gas purge was discontinued, butyllithium
in slight excess was added through the rubber septum from
a calibrated syringe to form the lithium salt.

Stirring of the reaction mixture was continued for thirty
minutes after the addition of butyllithium was completed.
The chlorosilane or chlorosiloxane was then added from the

89

 

9O

separatory funnel. Upon the addition of the chlorosilane or
chlorosiloxane the reaction medium became hazy, after which
lithium chloride began to form.

The reaction mixture did not warm until the precipitate
began to form. Only lithium chloride precipitates from
solution, as the polymer remains in solution.

The reaction mixture was stirred at 250 for two hours,
after which ten weight per cent of chlorodimethylvinylsilane
was added based on the starting amount of compound (IV).
Upon the addition of the monochlorosilane, the reaction mix-
ture was stirred for an additional thirty minutes. The
system was then purged with dry ammonia gas to convert any
unreacted monochlorosilane to the disilazane according to

the reaction below.

excess NH34(g) t
7

ViMGgSiCl [ViMGESi ] 2NH + NH4C1

Following this step, the reaction mixture was vacuum filtered
to remove the lithium chloride and any ammonium chloride that
was formed. The filtrate was devolatilized by vacuum distil-
lation. The product residue was, at this point, slightly
cloudy. It was therefore dissolved in pfhexane, pressure
filtered and strip distilled to remove the volatiles to leave
a clear product. Table XX lists the mole ratios of reactants
used to prepare the polymers. Tables XXI and XXII and

Figures 22-25 list the infrared and nuclear magnetic resonance
data, while Table XXIII, represents the thermal gravimetric

analysis data of the prepared polymers.

91

 

 

 

mmmo.o mmso.o mmmo.o m umsmaom
mmwo.o ommo.o mmao.o e umsmaom
om_flmmmzaoa maonmmmz Hqsm m+mzxmmzflmooflmmmz+ mo coflumummmum

comb muscuummm mo mmaoz

 

 

_AmzceomoqowochmHaua.muewcHaum.equmemzcmsmsuw.4
u.m.mvum.Humzcsmmm<qu<msmsus.m.m.au<onmaum.«.m

IAEBEBUOI N. . m. . m . m . m . m . H . .2 NAOMIANAHmAWZHNVQNmBmZHQlS .d

“m mmzwqom mo 62¢ .HAmzceomoqowo<AHmHon¢.mucwcHoum.aqumemzcmsme
u¢.w.m.mvnm.aumz¢ezmm¢quHmsnm.m.au¢oncn«.mnqwmemzcxmmnm.m.m.m.fi.a_wnom
quuHmnwzH>qwmsmzchs.a “d mmzwaom mo one¢m<mmmm mus zH ammo mszcsocmm mo mmqoz

XX "Manda

92

TABLE XXI

INFRARED SPECTRA OF POLYMER A AND POLYMER B

 

 

 

Polymer A Polymer B

v C-H 2960(3) 2962(5)

2902(w) 2902(w)
v C=C 1590(v.w.) 1590(V.w.)
Sas CH3 1408(m) 1408(m)
6s CH3 1255(3) 1257(5)
vas SiOSi 1075(3) 1080(5)
v SiNSi 1000(V.s.) 1005(V.s.)
v SiNSi 945(w.m.) 940(w)
v SiNSi 885(5) 887(s)
v Si-C 850(m) 850(m)

vas Si-C 802(8) 802(5)

 

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AHIEUV mucmsvmum

oom 00¢ 00m 00m oooa ooma 004a Coma coma ooom ooew 00mm oomm comm
P r p . p n P k —

IP . m r

 

 

 

 

 

 

 

 

.m umfihaom mo Esnuummm mmHMHMCH .mN musmam

AHIEUV mucmsqmnm

com cow com com coca coma ooaa coma coma oocN ooam comm comm comm
. p p p L r L H P . L t

P h

 

 

 

 

 

 

 

 

95

 

mam.m

 

 

 

o .
as. ........ 2....
u u u COM m o
Mm¢F.m o+n4 mm om gm mm A coupmom I u on m
mam.m
osmm.m
unwm.m mAxmm3va mAxMOBVa
" u u o m con m .
Mama.m o+nm mm oH am mm A a up on A u on a
mason moamo chom muamu
mosam> e mOaumm cououm amnumz mxmmm oz mo “$9852 Hmfimaom

 

 

m mgflom 92¢ fl mgflom .mO gfiummm mvgommm UHBNZG§ MdmAUDZ am

H HuOn 3&8

96

B. General Discussion

The following reaction sequence is prOposed based on

the polymeric materials, isolated and characterized by infra-

red and H1 nmr data. The structure verification of the

polymers and their physical and thermal prOperties are dis-

cussed in the following sections.

Reaction Sequence

 

 

 

 

 

 
  

M62 M62 .— M62 M62
Si-O-Si . . Si-O-Si
- /’ '\
H-N: :N-H Bum 13H? hexane? Li—N /N-Li ?
Si-O-Si \ Si-O-Si
M62 M62 Step 1 M62 M62
THF
Step 2
room
temperature
W
Step 5 M62
M62 /Si\ M62
CiMegsi(OSiMe2-)—Cl LiOSi-N N—SiOLi
y = 0, y = 1 M62
fl
M62 M62
M62 Si\~ M62 M62 M62 /,Si\\ M62
LiOSi-N Nd—Si-(OSi-i-OSi—N N iOLi
\ ./ X \ ./
Si L Si
M62 - M62
2
Step 4 excess ViMeZSiCl
M62
M62 M62 ‘ Si M62 M62 M62 Si\ M62 M62
ViSi-O-Si-N/ \N i-(OSi—)—OSi-N/ / i-O-SiVi
M62 M62

 

97

The reaction intermediate indicated in square brackets is
conjectured.

Step 5, which follows, involves the conversion of the
unreacted chlorodimethylvinylsilane to the disilazane via
ammination with ammonia gas. The step is included to elimi-
nate the possible formation of hydrogen chloride from the
hydrolysis of any unreacted chlorosilane. Hydrogen chloride,
if formed, would react with the cyclodisilazane unit in the
polymer. This is undesirable.

Compound (XX) is listed in the reaction sequence for the
sake of convenience. The true intermediate or intermediates
formed which result in the formation of the cyclodisilazane
unit have not been identified. For the sake of simplicity
in the following sections, let Polymer A and Polymer B to be
representative of the polymer structure written above where

x = 1 and x = 2, respectively.

C. Spectrosc0pic Confirmation of a,m-Dimethylvinylsilyl-
pgiyjij1ys,5,5L5-hexgmethyl-2,4-dioxa-1,5,5-trisila-
pentane-1,5-(2,2,4L44tetrgmethyl-1JSwdiaza—Z,g-
disilacyclobutane)], Polymer A; and of d,m-
Dimethylvinylsilyl:poly[111,5,5,5,5,7,7-
octamethyl-2,4,6-trioxa-1LS,5,7-tetrg—
silaheptane—1,5-(2,2L4L4-tetggr
methyl-1L5-diaza-2,4-disilg-
cyclobutanell, PolymerXQ

Polymers A and B both show very strong absorptions at
880-890 cm.1 and at 1000-1005 cm‘l. These absorption bands
are indicative of a silylated cyclodisilazane structure.

This assignment was recently indicated by Breed and Elliot (47).

98

The Si2N absorption band, between 900 and 950 cm‘l, common
to both disilazane and tris-silylamine structures, was also
evident in the infrared spectra of Polymers A and B as a
weak band at 940-945 cm”1 (Figures 22 and 25). However, no
NH absorption was observed at 1140-1180 cm'l. This would
indicate that the infrared absorption at 940-945 cm‘1 is
due to some form of tris-silylamine structure other than
that exhibited by the N,N'-silylated cyclodisilazane.

.A form of tris-silylamine structure unlike that of the
silylated cyclodisilazane could be incorporated into Polymers
A or B if the ring contraction of the N,N'-dilithium salt of
(Iy)was incomplete, according to the partial rearrangement

listed below.

 

M62 M62 M62
Si-O-Si Si-O
Li-N N-Li THF >a Li—N’/ SlM62
\\ - ./’ room \. . //
81-0—81 tem erature Sl-N\\
M62 M62 p M62 SiOLi
M62

Thus, Upon subsequent reaction with the dichlorosilane or
dichlorosiloxane the unit indicated below would be incorpo-

rated into the polymer chain

M62
Si-O

——M62Si-N SiM62

\ /

\ SiOSi—-
M62M62

Si-N

as an "impurity" and should show a typical Si2N absorption

between 900-950 cm'l. It would appear from infrared that

99

the amount of the trimer cyclosiloxazane incorporated into
the polymer chain relative to the number of cyclodisilazen
units is small.

An alternate explanation of the absorption at 940-945
cm‘1 involves the assignment of this absorption to the out
of plane C-H bending vibration due to the vinyl group
present as the dimethylvinylsilyl endblocking unit (45).
However, the expected accompanying C=C stretching frequency
at 1590-1600 cm'1 is of too weak an intensity to compliment

i

the stronger vibration at 940 cm‘ .

Based on this analysis, it is felt that the unit

\ /
N/Sl-O\Si/
\Si-N/ ‘

/' \ \\

is indeed present in small concentrations as an impurity
in Polymers A and B.
The’Hl nmr data would be expected to yield a 2:1:2

methyl proton ratio for Polymer A indicated below

 

r a
M62 c b 2 c M62
. . . /Si\ “ewe; “:2 /Si\ ”14:2 M:2.
VlMGZSIOMegsl-N N‘“—Sl-(031+“‘OSI_“N i-OSiVi
\Si/ x \si/
M62 L M62

where x = 1. For x = 2 the expected ratio of Mea/Meb/MeC
is 2:2:2, where z = a).

These mole ratios were indeed observed (Table XXII).
The chemical shift for the methyl protons in the cyclo-

disilazane ring and the methyl protons on the adjacent silicon

100

connecting group, Mea-Mec, was I 9.74-9.75 and 9.98, respec-
tively. This is in agreement with the assignment by Breed
and Elliot of T 9.75 and 10.00 for the silylmethyl protons
attached to a cyclodisilazane ring (47), and adjacent to the
cyclodisilazane rings respectively (Table XXII). Since the
polymer was endblocked with the dimethylvinylsilyl group,
one would expect to observe a fourth weak band in the H1
nuclear magnetic resonance spectra for the methyl protons.
A peak is evident at I 9.818. However, since the infrared
barely indicates the presence of the vinyl group, it is sur-
prising that H1 nmr would pick up these methyl protons of
the endblocking group.

The correct eXplanation for the observed weak fourth
peak might be to attribute this absorption to the methyl
protons (in brackets below) of the cyclotrisiloxazane

"impurity".

 

 

r- ‘t
M62
Si—-"—O
/
— ‘\ >SiM62
Si——N
M62 [ \

It is felt that this I'impurity" can be eliminated by

allowing the N,N'-dilithium salt of compound (X!) more time
to ring contract in tetrahydrofuran, prior to reaction with

the chlorosilanes.

101

D. Some Ehysical PrOQerties of the Prepared Polymers

 

 

1. Thermal Stability

The thermal gravimetric analyses of Polymers A and B
were gathered so as to indicate qualitatively the thermal
stability of these materials under oxidative and non-
oxidative conditions. Polymers A and B both exhibited good
thermal stability relative to polydimethylsiloxanes as
evidenced by a weight loss of only 15 percent at 4250 in
air (Table XXIII). Polydimethylsiloxane fluids normally
undergo extensive siloxane rearrangement at 2500-5500C
(48,49). In air, most polydimethylsiloxanes oxidize appreci—
ably above 250°C (50).

As in the case of polydimethylsiloxanes, polymers A and
B exhibit a high weight loss (more than 95 per cent) in
helium. This indicates that Polymers A and B, like polydi-
methylsiloxanes, are subject to thermal rearrangement below
450-5000c.

The low weight loss of Polymers A and B, 52-56 per cent
at 670-7100C in air, indicates the formation of a cross-
linked polymer formed via an oxidative process. The cross-
linked material is apparently fairly resistant to thermal
rearrangement as is evidenced by the stability of these ma-
terials towards the further formation of volatile species

between 550-4500C.

102

TABLE XXIII

THERMAL GRAVIMETRIC ANALYSIS OF

POLYMER A AND OF
POLYMER B'IN HELIUM AND IN AIR

 

 

Per Cent Weight Loss

 

 

 

 

o Polymer A . Polymer B .
Temperature C Helium Air Helium Air
100 0.5 0.5 0.6 0.4
200 5.7 5.4 5.5 4.1
500 8.0 7.6 11.1 9.9
550 11.6 11.1 15.2 15.2
400 16.9 12.8 20.5 15.1
450 25.5 18.2 27.5 20.0
500 54.0 25.9 41.5 26.5
550 45.4 28.6 59.0 51.5
600 77.2 51.1 88.8 55.8
650 97.5 51.5 99.5 56.0

 

105

2. Microscopic Identification of the Preparedggglymers

Polymer A was examined in polarized light with crossed
nicols and was found to show birefringence, which is an
indication of crystallinity. Polymer A is a waxy solid
at room temperature but melts at 40-420. As would be ex—
pected, the polymer no longer exhibits birefringence under
polarized light at 420.

Polymer A was allowed to recrystallize from toluene
between two glass slides. A photomicrograph was taken of
this sample at 100X under polarized light with a 55 mm.
camera attached to the microscope. The photomicrograph
showed fern-like dendrites and an area of high polymer
concentration, containing numerous spherulites growing from
nucleation sites.

Polymer B is a liquid at room temperature. It exhibited
no birefringence as a solid at -600 under polarized light.

The presence of spherulites in high polymers has been
known since Kirchhof took the first picture of this type of
crystal formation in 1929 (51). According to Bunn (52) the
spherulite structure is the normal manner of crystallization

of high polymers.

5. Molecular Weight Determinations

The number average molecular weights of Polymers A and
B were determined by vapor phase osmometry. These measure-
ments were performed by the Dow Corning Corporation. Values

of 259015 per cent and 2,50015 per cent were found for

104

Polymers A and B, respectively. This yields the average

degree of polymerization as indicated below.

 

 

M62 M62
M62 /Si\ M62 M62 M62 /Si\ M62
ViMegsiOSi-N N———s i——(-OSi-)- OSi-N - N———s ios iMe 2v1
M62 ‘l— M62 _.

6.10

H
._i
N

N

Polymer A; x

4.55

II
N
N

II

Polymer B; x

4. Hydrgiyzability

Polymer A was titrated with 0.1 N aqueous hydrogen
chloride in an acetone-toluene-ethanol solution using a back
titration technique to yield theory per cent nitrogen based
on the proposed structure. The following procedure was
employed and is included since it qualitatively indicates
the hydrolytic stability of the polymer.

Into a 250 ml iodine flask containing 70 ml of ethanol
are placed 0.1527 grams of polymer A. The polymer was not
soluble in ethanol. To this mixture was added 15.8 ml of
0.1 N aqueous HCl. After standing for two hours, the polymer
appeared to remain intact and apparently did not dissolve.
To this mixture was added 20 ml of acetone and 50 ml of
toluene which dissolved the polymer. The solution was
allowed to stand for one-half hour after which the sample
was back titrated with 6.8 m1 of 0.1 N alcoholic KOH to

neutrality as indicated by brom—cresol purple. This analysis

105

yields 7.58 per cent nitrogen and indicates that the cyclo-
disilazane structure is subject to hydrolysis in a homo-
geneous acid solution. The theoretical amount of nitrogen
for polymer A based on the molecular weight measurement is

7.68 per cent.

VII. SOME MISCELLANEOUS PHYSICAL PROPERTIES
OF THE N-SUBSTITUTED LITHIUM
POLYDIMETHYLCYCLOSILOXAZANES

The N-lithium salts are white crystalline solids.
Crystallinity was evidenced by birefringence patterns when
the salts were exposed to polarized light under crossed
nicols. The salts are high melting materials or may de-
compose at high temperatures prior to reaching their melting
point. No obvious change could be detected when compounds
(ylglegl) were heated at 1500 in sealed vials for one hour.
The salts are not pyrophoric,but are, however, quite

hygroscopic.

106

VI I I . MI SCELLANEOUS
A. Analytical Methods

1. Carbon, Hydrogen, Silicon and Nitrogen Analyses
The carbon, hydrogen, silicon and nitrogen analyses'
in this investigation were carried out by the Dow Corning

Corporation, Midland, Michigan.

2. Chlorine Analysis.

The chlorine analysis was carried out by placing a
weighed sample of an a,m—dichlorosiloxane into a 250 ml
iodine flask containing about 100 ml of a 50/50 ethanol-
water solution.

The solution was then titrated to a phenolphthalein

endpoint with 0.1 N alcoholic potassium hydroxide.

5. Hydrolyzable Nitrogen

Hydrolyzable nitrogen was determined by placing a
weighed sample of product into a 250 ml iodine flask contain-
ing largely ethanol and some distilled water. The solution
was then acidified by adding an excess of 0.1 N aqueous
hydrochloric acid. The solution was allowed to stand for
from one-half to one hour after which the sample was titrated
to a brom-cresol purple endpoint with 0.1 N alcoholic potas-

sium hydroxide.

107

108

4. Lithium Analysis

The lithium analysis was performed by placing a weighed
sample of a N-lithio cyclosiloxazane into a 250 ml iodine
flask containing about 100 ml of‘a 50/50 ethanol-water
solution. The solution was then acidified by adding an
excess of 0.1 N aqueous hydrochloric acid. The solution
was allowed to stand for one hour after which the sample was
titrated to a brom-cresol purple endpoint with 0.1 N
alcoholic potassium hydroxide. The compound being titrated
was assumed to be pure. Thus, the amount of 0.1 N aqueous
hydrochloric acid required to titrate the theoretical amount
of nitrogen for the specific compound being analyzed was
subtracted from the total amount of 0.1 N aqueous hydrogen
chloride used. The difference was assumed to be the amount
of 0.1 N aqueous hydrogen chloride necessary to neutralize
the lithium hydroxide formed as a result of hydrolysis of

-%i-N-Li—.

5. Molecular Weight
The molecular weight of Polymers A and B was determined
on a Hewlitt-Packard 502 Vapor Pressure Osmometer which was

made available by the Dow Corning Corporation.

6. Spectrosc0pic Data
The infrared Spectra of the polydimethylcyclosiloxa—
zanes were recorded from 400-1500 cm'1 as two per cent

solutions in carbon disulfide and from 1200 to 4000 cm’1

109

as ten per cent solutions in carbon tetrachloride on a
Perkin Elmer 557 Grating Infrared SpectrOphotometer.

The infrared spectra of the N-lithium salts of the
cyclosiloxazanes were recorded as Nujol mulls on a Unicam
SP-200.

The infrared Spectra of the N—Silyl derivatives and of
Polymers A and B were recorded as ten per cent and as two
per cent solutions in carbon tetrachloride and in carbon
disulfide respectively. The instrument used was a Perkin
Elmer 521 Grating Spectrophotometer.

The H1 nmr data of the cyclosiloxazanes, the N-Silyl
derivatives, and of Polymers A and B were recorded as ten
per cent solutions in carbon tetrachloride on a Varian A-60
at 50 and 500 cycles per second. The N-lithium salts were
recorded as supersaturated solutions in benzene also

on a Varian A-60 at 50 and 5000 cycles per second.

7. Photomicrographs
The photomicrograph of Polymer A was taken with a Karl-

Zeiss 65040 Ultraphot II.

8. Thermal Gravimetric Analyses

The thermal gravimetric analyses of Polymers A and B
were performed by the Dow Corning Corporation. A heating
rate of 5O/minute was used for a 60-70 mg sample. The gas
flow rate was 50 cc/minute; the air was first dried and then

passed through a purifier before being introduced into the

110

sample area. The analysis was carried out at one atmos—

phere in a 16 mm x 4 mm deep cylindrical platinum cup.

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(1)

(2)
(3)

(4)
(5)

(6)

(7)
(8)

(9)
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(11)

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(14)

(15)

(16)

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"Fibres From Synthetic Polymers,"

 

M'((1)7111)((1111701)?!)1(Wes