THE REACTION OF l-METHYL-l,
2 - DICARBACLOSD - DODECABORANE (12)
AND 1,2-BIS (DIPHENYLPHOSPHINO)
CARBORANEUZ) WITH PLATINUM SALTS

Thesis for the Degree of Ph. D.
MICHIGAN STATE UNIVERSITY
RONALD MICHAEL ROGOWSKI

197 l

"WL 5- ’3

This is to certify that the

thesis entitled

THE REACTION OF l—METHYL-l , 2-D ICARBACLOSO-
DODECABORANE (12) AND 1 , Z-BIS (D IPHENYLPHOSPHINO) CARBORANE (12)
WITH PLATINUM SALTS

presented by

Ronald Michael Rogowski

has been accepted towards fulfillment
of the requirements for

Ph-D- degree in Chemistry

Kc. QA.

Major professor

Date g‘q‘q’

0-7689

    
  

 

 
 

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THE REACTION OF l-METHYL-I,2-DICARBACLOSO-DODECABORANE(12)
AND 1,Z-BIS(DIPHENYLPHOSPHINO)CARBORANE(12)
WITH PLATINUM SALTS

BY

Ronald Michael Rogowski

A THESIS

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

DOCTOR OF PHILOSOPHY
Department of Chemistry

1971

ACKNOWLEDGMENTS

The author is deeply indebted to Dr. Kim Cohn for his
competent guidance and personal interest throughout the
course of this research.

The author is grateful to Mr. Eric Roach for obtaining
31F and 11B nmr spectral data.

The author wishes to express his gratitude to the
Department of Chemistry, Michigan State University, and
especially to the Inorganic Division faculty members for
their tutelage and for the financial aid and experience
gained as a Graduate Teaching Assistant.

The author also wishes to express his deepest appreci-
ation to Dr. RObert N. Hammer and Dr. Wilma N. Bradley for

their encouragement and friendship.

ii

TABLE OF CONTENTS

 

Page

INTRODUCTION . . . . . . . . . . . . . . . . . . . . 1
EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . 6
A. Experimental Methods . . . . . . . . . . . 6

B. Materials . . . . . . . . . . . . . . . . . 7

C. Synthesis: General Reaction Procedures . 7

1. Synthesis of the cis-Platinum Phosphine
Complexes . . . . . . . . . . . . . .

2. The Reaction of 1-Methyl-1,2-dicarbacloso-
dodecaborane(12) with cis—Platinum
Phosphine Complexes . . . . . . . . . 14

a. The Preparation of
QfPt[P(C6H5)3]2[-C c-CH3]2 . . 14

B10H1o
b. The Preparation of
SrPt[P(CeH5)2(CH3)]2[-c C-CH3]2 16

BIOHIO

c. The preparation of
ngt[P(C5H5)(CH3)2]2[-C c—CH3]2 20

BIOHIO

d. The Preparation of
QfPt[P(CH3)3]2[-C C-CH3]2 . . . 24

BioHio

3. The Reaction of l-Methyl-l,2—dicarbacloso-
dodecarborane(12) with gig and trans-Di-
chlorobis(tri-gfbutylphosphine)platinum-
(II) . . . . . . . . . . . . . . . . 26

4. The Preparation of 1,2-bis(diphenyl-
phosphino)carborane(12) . . . . . . . 30

iii

TABLE OF CONTENTS (Cont.)

Page

a. The Reaction of 1,2'bis(diphenyl-
phosphino)carborane(12) with Potas-
sium Tetrachloroplatinite(11) . . 30

D. Attempted Syntheses . . . . . . . . . . . . 39

1. The Reaction of 1,2—Dicarbacloso-dodeca-
borane(12) with Titanium and Vanadium
Dicyclopentadienyldichlorides . . . . 39

2. The Reaction of 1<Methyl-1,2-dicar—
bacloso-dodecaborane(12) with
Palladium and Nickel Chlorides . . . . 42

DISCUSSION . . . . . . . . . . . . . . . . . . . . . 44

REFERENCES . . . . . . . . . . . . . . . . . . . . . 55

iv

Table

II.

III.

LIST OF TABLES

Page

Characterization data of the
cis-Pt(C1)2(L)2 Complexes . . . . . . . . . 10

Characterization data of the
cis-Pt(-C C-CH3)2(L)2 Complexes . . . . . 18

BIOH10

Mass spectrum of (C5H5)2P-C C-P(C6H5)2 . 34

B10H10

LIST OF FIGURES

Figure Page

1. Infrared spectrum of cis-PtC12[P(C6H5)(CH3)212
run as a Nujol mull . . . . . . . . . . . . . 11

2. 1H nmr spectrum of cis-PtC12[P(C6H5)(CH3)2]2
iDCDzClz..................12

3. 31F nmr spectrum of cis—PtC12[P(CGH5)(CH3)2]2
in CD2C12 . o o o o o o o o . o o . o o o o o 13

4. 1H nmr spectrum of cis-Pt[P(C6H5)3]2[-C C-CH312
in CS . . . . . . . . . . .'. . . . 15
2 B10H10
5. Infrared spectrum of
cis-Pt[P(C3H5)3]2[-CV§7C -CH3]2 run as a Nujol

mull . . . . . . . . . . . . . . 17

BlOHIO

6. 1H nmr spectrum of cis-
Pt[P(C6H5)2(CH3)]2[-C c-CH3]2 in cs2 . . . 19

BloHlo

7. Infrared spectrum of cis—
Pt[P(C5H5) 2(CH3) ]2[—c —C-CH3]2 run as a Nujol
mull . . . . . . . . . . . . . . . . 21

BlOHlo

8. 31F and 1H nmr Spectra of cis-
Pt[P(C6H5)(CH3)2]2[-C C-CH3] in cs2 . . . . 22

 

10

9. 11B nmr spectrum of cis—
Pt[P(C6H5)(CH3)2]2[-C C-CH3]2 in CH2C12 . . 23

B10H1o

10. Infrared spectrum of cis-
Pt[P(C6H5)(CH3)2]2[-C— C-CH3]2 run as a Nujol
mull . . . . . . . . . . . . . . . . 25

B10H10

vi

LIST OF FIGURES (Cont.)

Figure

11.

12.

13.

14.

15.

16.

17.

18.

Page

Infrared spectrum of cis-
Pt[P(CH3)3i2[-c C-CH3]2 run as a Nujol mull 27

B10310

Infrared spectrum of trans—
Pt[P(C4H4)3]2[-C C-CH312 run as a Nujol mull 29

B10H10

Infrared spectrum of (C6H5)2P-C C-P(C6H5)2
run as a Nujol mull . . . . . . . . 31

B10H10

118 nmr spectrum of (C6H5)2P-C C-P(C6H5)2
in C52 . o . . . . . . . . . . . . o 32
B10H10

31P and 1H nmr spectra of (CsflsfiP-C C-P(C6H5)2
in C32 0 o o o o 9 o o o o o o o o o
BioH1o

Infrared spectrum of [(C6H5)2P-C C-P(C6H5)2]2-

PtClz run as a Nujol mull . . .
B10H10

Infrared spectrum of [(C6H5)2P—C C-P(C6H5)2]-

PtC12 run as a Nujol mull . . . 39
BioHio

Schematic representation of predicted spectrum

for QfBioczHlo unit and the schematic representa-
tion of spectrum resulting from selective over-
lapping in (C6H5)2P-C C-P(C6H5)2 . . . . . . 51

BlOHIO

vii

NOMENCLATURE

The rapid development of research in the area of
boron cage compounds was in part responsible for the
development of a complete set of rules governing the
nomenclature of such systems (1,2). This nomenclature
will be employed in naming all compounds in this manu-
script with the exception of references to compounds
which have been reported previously by other authors.
These references will retain the nomenclature used in the
original publication. In all work contained in the ex-
perimental section of this thesis, the CH3-B10C2H10-H
unit will be referred to as 1-methyl-1,2-dicarbocloso-

dodecaborane(12) or by the common name methyl carborane(12).

1. R. Adams, Inorg. Chem., , 1087 (1962).

 

.2.
Z.

2. R. Adams, Inorg. Chem., , 1945 (1968).

 

viii

INTRODUCTION

The ability of boron to bond with itself and form a
series of hydrides was first recognized by Alfred Stock (1).
The first boron hydrides to be isolated were the compounds
Bszv B4H10, B5H9, B5H11, B6H10, and B10H14. Decaborane—14
(B10H14) is the only member of this group that can be
handled in air without spontaneous ignition or hydrolysis.
It was the high reactivity displayed by these boron hydrides,
coupled with their relative scarcity, that led Stock to
develop special high-vacuum techniques for their manipu-
lation. These compounds were considered to be mere chemi-
cal curiosities. They presented unusual valency problems
because their formulation in terms of normal two-electron
bonds proved impossible. Most of these structural and
bonding problems were resolved during the last twenty years
(2). The boron hydrides are characterized by structures
that can be recognized as fragments of the icosahedron or
the octahedron. Recently, extremely stable polyhedral boron
ions and icosahedral carboranes have been prepared (3).

The polyhedral boranes encompass molecules or ions in
which boron atoms alone or in combination with other atoms,

describe a closed polyhedron ranging from the tetrahedron

2
to the icosahedron (4). Subsequent investigations of these
polyhedral boranes revealed an aromatic character manifest
not only in an extraordinary thermal stability, but also
in a substitution chemistry centered on the polyhedral
boron-hydrogen or carbon—hydrogen bonds. These highly
symmetrical species are stabilized by three-dimensional
electron delocalization and may be considered to be the
aromatic members of the boron hydride series. The low
toxicity (5) of these polyhedral boranes and their high
stability toward acid and base attack is surprising in view
of the toxicity and instability of other boron hydrides (6).
The icosahedral carboranes share this stability, but are
less stable to basic degradation than 312H122‘.

The discovery of this new class of compounds, "aromatic"
polyhedral boranes, has resulted in broad areas of research
with a variety of synthetic and theoretical problems. Re—
ports on the derivative chemistry have suggested that this
class of compounds may rival that of aromatic hydrocarbons.
Several reviews on the chemistry of some of these materials,

. 2 a-
particularly Ban

and Bn-zcan are available (7-14).

In the late sixties significant developments (15)
occurred in the field of research which combines polyhedral
carboranes and transition metal chemistries in much the
same way as the first metallocenes were synthesized from
aromatic organic species and transition metal derivatives.

Several groups of polyhedral species are known in which a

transition metal resides in the polyhedral surface. Their

3
remarkable stability suggests that they are stabilized by
some degree of electron delocalization similar to that
found in the Ban2_ ions (3), the carboranes (3), and the
more stable metallocenes. This area is of interest since
rather unusual formal oxidation states of transition metals
may be attained.

The original work in this area of chemical synthesis
involved the preparation of the B9C2H112- ligand (15-17),
which resembles the well known w-bonding cyc10pentadienide
ion. The B9C2H112- ion (or dicarbollide ion) is known in
two isomeric forms, each of which constitutes an eleven
particle icosahedral fragment capable of regenerating an
icosahedral surface upon coordination of a transition metal
at the open vertex. Later work has demonstrated that bonding
of this type is not restricted to the B9C2H112- ions, but
can be extended to the BloCHlla- (18-19) and BlosHloz- (20)
icosahedral fragment ions and the B7C1H92- (21) and BEC2H32-
(22) ions of different geometry. The B9C2H112- ion, which
can be produced by strong base degradation of 1,2- and 1,7-
dicarbacloso-dodecaborane(12), has been employed to generate
a series of ferrocene-like "sandwich" compounds (23-29).
Various transition metals have been inserted in the open
face of the dicarbollide (B9C2H112‘) ion to form a series
of w-complexes (23-29). The structures of some of these
compounds have been determined by means of X-ray diffraction

(30-31).

4

In all of these systems the bonding is of w-character
in which d orbitals of the transition metal can overlap
with the five nearly equivalent sp3 atomic orbitals (3,9,15),
of the Open pentagonal face of the eleven particle icosa-
hedral fragment. The research described in this thesis was
undertaken with the purpose of synthesizing a sigma-bonded
transition metal carborane complex. As of 1968 no sigma-
bonded complex had been reported in the chemical literature.
After the start of this project, the first literature re-
ports of sigma-bonded transition metal-carborane complexes
appeared in the chemical literature (32-34). Hawthorne
synthesized 1-[(w-c5H5)Ee(co)2]-2-(CH3)-(o-1,2-Bloc2H10)

‘yig the interaction of the lithium salt (35) of the 1-(CH3)-
1,2-B10C2H10-ion with v-(C5H5)Fe(CO)ZI in 1,2-dimethoxy-
ethane solvent (32). These initial results were followed

by several other reports of transition metal-carborane com-
plexes containing a sigma bond (34,36). Compounds of copper,
gold, and platinum were reported to give sigma-bonded car-
borane complexes.

Another area of interest is the synthetic investigation
of the derivative chemistry which is based on the substitu-
tion at the two carbon atoms of 1,2-dicarbacloso-dodecar-
borane(12) (13). In general, groups which are so substituted
act as if they were attached to a very bulky, electron with-
drawing moiety (9,11). With the appropriate groups substi-
tuted at these two carbon atoms, it is possible to prepare

a bifunctional ligand. Very little information is available

5
regarding the steric and electronic properties of the
carborane cage when present in such a ligand.

H. D. Smith (37) has reported that the reaction of
nickel(II) chloride 6-hydrate with 1,2-bis(diphenyl-
phosphine)—gfcarborane(12), as well as with the corre-
sponding derivatives containing one, two, and three bromine
atoms attached to the carborane nucleus, produced complexes
which contain one or two molecules of the bisphosphino
ligand and one of nickel(II) chloride. Zaborowski and Cohn
reported the preparationand characterization of the
analogous arsino-l,2-dicarbacloso-dodecarborane(12) (38).
They were able to use this compound as a bidentate ligand.

It was of interest to attempt the synthesis of new
transition metal carborane complexes. New information
about the electron delocalization about the carborane cage
system would be of value in attempts to elucidate the simi-
larity of the reaction chemistry between benzene and car-
borane. The preparation and characterization of stable,
inert, transition complexes of platinum was also of interest
because of recent work in which platinum complexes were
shown to possess potential medical value as anti-tumor

agents (39).

EXPERIMENTAL

A. Experimental Methods

A Perkin-Elmer 457 grating spectrophotometer was used
to obtain the infrared spectra. Solid spectra were run
either as Nujol or as Fluorolube mulls between CsI plates.

Proton nmr spectra were observed by means of a Varian
Model 56/60 nuclear magnetic resonance spectrometer oper-
ating at the ambient temperature of the instrument. Tetra-
methylsilane was employed as an internal standard. Phos-
phorus and boron nmr absorptions were obtained on an NMR
Specialties MP1000 pulsed spectrometer with an operating
frequency of 65 MHz, and a field strength of 47.6 and 28.0
kilogauss respectively. Solutions of P406 and B(OCH3)3
were employed as internal references, by the capillary
insertion technique.

Mass spectral data were obtained by means of an
Hitachi-RMU—G Spectrometer operating with an ionizing
voltage of 56V.

The preparations were carried out under an atmosphere
of dry nitrogen. Analyses were performed by Spang Labora—
tories, Ann Arbor, Michigan or by Chemalytics, Inc., Tempe,
Arizona. -Melting points were obtained by the use of a
Thomas-Hoover Capillary Melting Point Apparatus.

6

7

B. Materials

 

Methyl carborane [1-methyl-1,2-dicarbacloso-dodeca-

borane(12)]. was prepared from purified propargyl bromide

 

(3-bromopropyne), acetonitrile, and decaborane (U. S.
Department of the Air Force) by the use of a method pre-
viously described (40-41). The procedure was modified in
the following manner. Both the number of sulfuric acid-
containing traps and the number of empty safety traps in
the purification train was increased from the suggested
value of one (40) to three traps. Second, the white solid,
CH3-B10C2H10-H was dried in vacuo over P205 rather than at
atmospheric pressure. The identity of the product was
established by its melting point (found, 211 1 2°, lit.
(40) 211-213°) and by a comparison of the 1H nmr with the
reported values. The 1H nmr spectrum (C82) exhibits ab—
sorptions at a 3.50 (broad singlet, intensity 1, due to the
C-H on methyl carborane(12)), and o 2.00 (broad singlet,
intensity 3, due to the C-methyl protons) (lit. (40) a

3.48 and 1.98 respectively). The puresmethyl carborane(12)
was stored in an evacuated desiccator over P205 prior to
use. The potassium tetrachloroplatinite (K2PtCl4) and 2f
butyllithium were used as supplied by Alfa Inorganics

Company.
C. Synthesis: General Reaction Procedures

All reactions which use 1-methyl-1,2—dicarbacloso—

dodecarborane(12) as a monodentate ligand were performed in

8
an analogous manner. Any variation in the experimental
procedure for a specific preparation will be mentioned.

The general reactions are Shown below:

0
CH3 "C C‘H + £‘C4H9Li 0 > CH3 "C C‘Li + n-C4H10
(C235)20 Vii '—

 

B10H1o BioHio

 

. 0°
2CH3—C C-Ll + PtClzL > PtL -c C-CH )
$07 2 (C2H5 >20 2( V 3 2

+ 2LiCl
BioHio B10H10

where L is a phosphine ligand. The slurry of lithiomethyl-

carborane(12), CHa-CN67C-Li was freshly prepared by charging

BlOHlo
a nitrogen purged 100-ml three—necked flask with 1-methyl-

1,2-dicarbacloso-dodecarborane(12) (2 mmol) which contained
50 ml of dry diethyl ether. The flask was fitted with a
magnetic stirrer, a nitrogen inlet, and an addition funnel
with a nitrogen outlet. This flask was then cooled to 0°

and a solution of nfbutyllithium (2 mmol) in 10 ml of dry
diethyl ether was added over a period of 10 minutes yi§_the
addition funnel. The solution was maintained at 0° and was
stirred during this addition procedure. The reaction was
allowed to proceed for 30 min at 0°. At the end of this

time a 1 mmol sample of the phosphinoplatinumdichloro com-
plex in a suitable solvent was added over a period of 15 min.
(An insoluble platinum complex was added as a suspension in
solvent.) The stirred solution was maintained at 0° for

45 min and then was allowed to warm to room temperature (25°)

over a period of one hr. That a reaction took place was

9
indicated either by a color change or by the disappearance
of the insoluble platinum slurry. Sometimes the mixture
was allowed to reflux for 15 min. The solvent was then
removed by distillation in vacuo. The products were re-
crystallized from appropriate solvents and then dried in_

vacuo .

1. Synthesis of the cis-Platinum Phosphine Complexes

The following platinum compounds, gigfdichlorobis-
(trimethylphosphine)platinum(II) [QfPtC12[P(CH3)3]2]: gig-
dichlorobis(dimethylphenylphosphine)platinum(II)
[ngtClz[P(CH3)2(C6H5)]2]: gisfdichlorobis(methyldiphenyl-
phosphine)platinum(II) [ngtClz[P(CH3)(C6H5)2]2]; and SEE-
dichlorobis(triphenylphosphine)platinum(II)
[ngtClz[P(C6H5)3]2] were prepared and characterized ac—
cording to previously described methods (42-44). Character-
ization data are found in Table I. A typical ir spectrum,
as well as 1H and 31F nmr spectra for Sigfdichlorobis-
(methyldiphenylphosphine)platinum(II) is shown in Figures
1-3. No nmr was obtained for the gisfdichlorobis(tri-
phenylphosphine)platinum(II) complex because the compound

was insoluble.

 

 

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2. The Reaction of 1-Methyl-1,2-dicarbaclosododecaborane(12)

with cis—Platinum Phosphine Complexes

 

a. The Preparation of C -Pt[P(C6H5) 3]2[ -C C-CHsiz

 

 

BioH

The reaction was carried out as previously described.
After the 1ithiomethylcarborane(12) (2 mmol) was prepared,
a slurry of gisfdichlorobis(triphenylphosphine)platinum(II)
in dry diethyl ether was added to the stirred 1ithiomethyl-
carborane(12) solution maintained at 0°. This addition took
10 min. The reaction was then allowed to proceed at 0° for
one hr after which time it was allowed to warm to 25° over
a one hr period. The disappearance of the insoluble platinum
slurry and the appearance of a clear yellow solution was
evidence that a reaction took place. The solvent was then
removed by distillation in vacuo. The yellow solid, which
remained in the reaction flask, was recrystallized from a
70:30 mixture of carbon disulfide and methylene chloride. A
small amount of nfpentane was employed to initiate the pre—
cipitation of the product from solution. The amber solid
was then filtered and dried in vacuo.

The 60 MHz 1H nmr (CS2) spectrum exhibited two peaks
at a 2.1 (broad singlet, relative intensity 1, due to C-
methyl protons of methyl carborane(12)), and 6 7.3 (broad
multiplet, relative intensity 5, due to the triphenylphos—
phine protons). The 1H nmr spectrum is shown in Figure 4.
We could not obtain 31P and 11B nmr spectra because of the

low solubility of this product.

15

 

 

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16

The infrared spectrum obtained as a Nujol mull and
shown in Figure 5, exhibits characteristic absorptions at
740 (m) and 2550 (s) cm—l. The absorption at 740 cm"1 is
attributed to the B-H cage structure and the one at 2550
cm- is ascribed to the 8-H stretching mode. Other ab-
sorptions appear at 510 (s), 545 (ms), 670 (s), 993 (w),
1020 (mw), 1090 (ms), 1115 (w), 1180 (w), 1305 (w), 1570
(w), and 2720 (w) cm-l. The bands tentatively assigned to
Pt-Cl stretches present in the starting material (300, 320
cm-1) were absent from the product. The analytical data
for this compound and the subsequent alkylphenylphosphine
platinum complexes of methyl carborane(12) are represented
in Table II. The compound was slightly soluble in carbon

disulfide, methylene chloride, and benzene. It is stable

in air.

 

b. The Preparation of Q-Pt[P(C6H5)2(CH3)]2[-CVc-CH3]2
B10H1o

The reaction procedure was identical to the one pre-
viously described for the preparation of the triphenylphos-
phine platinum complex. An amber solid was isolated. The
1H nmr spectrum (CS2) exhibited three peaks at o 1.9
(doublet J = 12 Hz, due to the methyl protons attached to
phosphorus), 2.05 (singlet, due to C-methyl protons of the
carborane), 7.3 multiplet, due to the phenyl protons of the
phosphine ligand). The overlap of peaks at a 1.9 and 2.05
made the accurate determination of relative peak areas im-

possible. The 1H nmr spectrum is shown in Figure 6. This

 

17

 

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20
product was too insoluble to obtain 31P nmr Spectral data.
The 118 signal consisted of a broad doublet at 629.4 up-
field from B(OCH3)3.

The infrared spectrum of this compound mulled in Nujol
is shown in Figure 7. The characteristic absorptions due
to the carborane were present, (740 and 2550 cm-1) while
the Pt-Cl stretches were absent (320 cm—l).

The solubility of this complex was similar to that
described for the triphenylplatinum carborane complex. See

Table II for the analytical data obtained from this complex.

 

c. The Preparation of g-Pt[P(C6H5)(CH3)2]2[-CVc-CH3]2
BioHlo

The reaction was carried out in an analogous manner to
that previously described, however, the reaction mixture
was allowed to reflux for 15 min at 36°. The 1H nmr spec-
trum (C82) exhibited three peaks 5 2.0 (doublet J = 11 Hz,
due to the methyl protons attached to phosphorus), 2.1
(singlet overlapped with a 2.0 doublet, due to the C-methyl
protons of the carborane), 7.4 (multiplet, due to the phenyl
protons of the phosphine ligand). The nmr spectra are
shown in Figures 8 and 9. The 31P nmr (CH2C12) 5 120.4
(broad singlet). The 118 nmr (CH2C12) 5 21.4, 22.6, 23.8
(three broad absorptions, intensity 1), 27.7 (broad singlet,
intensity 3), 29.4 (broad singlet, intensity 4), 31.0 (broad

singlet, intensity 4), 33.4 (broad singlet, intensity 3).

 

21

 

camcam .Hohsz ou opp mCOHumHOQO ozu monocmc x

 

 

.HHSE Hohsz m mm can «mmmUiUKWVUIH«MAmmuvuAmmmuvmmumimflo mo Esuuoomm commumaH .b Tuscan

AaiEov mocosvoum
cmm ccv com com cccH ccmH cch cccH cccm ccmm cccm ccmm
. b F b ~ _ - _ p _ p P

 

 

 

 

 

 

 

 

 

 

22

 

 

OHmOHm

.mmo CH m_mmUIUN©VUIHm_mAmmUVAnmmUVmHDmimHo mo mnuommm HEC me can mam .m musmflm

 

am

AAA

 

 

 

 

 

 

 

 

 

 

v.cmH o

 

 

23

 

 

.mocmnmmmn Hmcnmuxo cm mm com: mmB «Ammuovm
OHmOHm

 

.mHUmmU CH mammUlUbulammmnmmUVAmmcUVmHumlmHO m0 EDHuomflsm HES mHH

o.am e.ea e.aa am
Tam _e.am_ mam _ v.3 a AIIIII .
. _ _

 

 

. "Ammoovm

.m onsmflm

 

 

24
The infrared spectrum of this compound mulled in Nujol,
is shown in Figure 10. Again the two absorptions character-
istic of the carborane cage are present (740 and 2550 cm-l).
See Table II for the analytical data. This complex was
slightly more soluble in organic solvents than the previous
phenylphosphineplatinum carborane complex, but was less

stable in air, presumably because of hydrolysis.

d. The Preparation of ngt[P(CH3)3]2[-C C-CH312

 

 

B10H1o

The general reaction procedure described previously was
employed. After allowing the reaction vessel to warm to
250 for two hours, some of the insoluble trimethylphosphine
platinum complex began to dissolve. After the solution was
allowed to reflux for 15 min, it became cloudy and slightly
yellow in color. After removal of the diethyl ether sol-
vent by distillation in vacuo, a yellow residue remained in
the flask. A buff colored solid was isolated after recrys—
tallization. This solid decomposed when moist. Precise
analytical data could not be obtained.

The 1H nmr spectrum (C82) consisted of two resonances,
a 2.0 (broad overlapping singlet and doublet, due to the
methyl protons of the phosphine and the C-methyl protons of
the carborane). After two hrs the upfield peak decreased
and a new resonance 6 3.5 [broad singlet, due to the start-
ing material, 1-methyl-1,2—dicarbacloso-dodecarborane(12)]

appeared.

 

25

 

.Hoflsz ou osc mcoflumuomnm on» monocmp x
OHmOHm

. .HHSE
Hoflsz m mm can «HmmUiukmvoiH«HmfimmUVAnmmovmuumimHo mo Esuuommm cmHMHMCH .cH musmflm

 

AaiEov mocmsvmum
cmm com com com cccH ccmfi cch cccH ccwH ccmm cccm ccmm

. p p _ F F _ _ _ P _ p

3

 

 

 

 

 

 

 

26
The infrared spectrum of this compound exhibited the
characteristic absorptions of the carborane cage. The ap-
pearance of strong bands at 1630 and 3400 cm"1 (OH vibra-
tional modes) suggests that hydrolysis and decomposition
of the product had occurred. The infrared spectrum is shown

in Figure 11.

3. The Reaction of l-Methyl-l,2-dicarbacloso-dodecarborane(12)

 

with cis and trans—Dichlorobis(tri—Efbutylphosphine)-

platinum(II)

 

 

The gig and trans isomers of dichlorobis(tri—nfbutyl-
phosphine)platinum(II) which were used for these reactions
were prepared and characterized according to the method
described by Kauffman and Teter (45). M.P. 140-1440 and
65—660 for the gig and t£§n§_complexes respectively (lit.
(45) 142—144° and 65-66°). The reaction procedure described
in the previous section was employed. Because the trans_
complex was soluble in benzene, benzene rather than diethyl
ether was employed as a solvent. After addition of the
yellow trans complex to the reaction flask a small amount
of white precipitate appeared. The reaction was allowed to
warm to 23°. The benzene was removed by distillation in
vacuo, and a golden solid remained in the reaction vessel.
This solid was dissolved in 70:30 carbon disulfide-methylene
chloride mixture and then recrystallized from nfpentane.

The 1H nmr spectrum (C82) exhibited three resonances,

d 1.0 and 1.6 (broad multiplet, due to the nfbutyl groups

 

27

 

.Hoflsz on mac mcoflumnomnm mzu monococ X
OHmOHm

 

.HHSE Hohsz m mm con «HmmUIUKWVUIHNHmAmmuvmgumimflo mo Esnuoomm pmumumCH .HH ousmfim

Eov mocmsomum

.omm wow owo oww oowH oomH ooWH oowH oowH comm fiwom owmm

3

 

 

 

 

 

 

 

 

 

 

 

28

on the phosphine), and 2.1 (singlet, due to C-methyl pro-
tons of the methyl carborane).

The infrared Spectrum of the compound mullen in Nujol,
is Shown in Figure 12. The characteristic absorptions (725
and 2580 cm-1) of the carborane cage were detected. The
peaks at 1630 and 3400 cm.1 are attributed to OH stretching
modes which arise from the hydrolysis of this complex.

AQQI, Calcd. for C30H80B20P2Pt: C, 39.42; H, 8.76.

Found: C, 39.75; H, 8.30.

Molecular weight determined in benzene was 880 (theoretical
913). The melting point was 185 i 5° (decomposition). The
compound was partially soluble in methylene chloride and
carbon disulfide. It appears to be moisture sensitive and
decomposition was evident upon exposure to air for 15 min.
The gig isomer of dichlorobis(tri-nfbutylphosphine)plati-
num(II) was prepared according to the method of Kauffman
and Teter (45). The general reaction procedure described
for the Ergg§_isomer was used. The white 213 isomer was
insoluble in benzene and in most other organic solvents,
thus it was added as a slurry in benzene. Upon warming to
250 the white slurry disappeared and the solution turned
yellow. After distillation in vacuo, a yellow oily liquid
remained in the flask. After recrystallization of the liquid
from a 30:70 mixture of carbon disulfide and nfpentane a
pale yellow solid remained.

Attempts to obtain reproducible nuclear magnetic reso-

nance data from this product were unsuccessful. The complex

29

 

 

oHOflsz 0U QDU mCOHUQHOWQM $5..“ mmuocmmu um
OHmOHm

.HHSE Honsz m no son «HmmUIUN®VUi_«HnAmmeovaumimcmnu mo Eduuommm commumcH .ma onsmflh

AHIEUV mucosqoum
cmm oov coo cow oooH coma coma coca oowH ooom comm ooom comm ooov
- . p L p p b i.

P p . . L - T

N

 

 

 

 

 

30
proved to be insoluble in most organic solvents. The 1H nmr
spectrum (C82) gave three broad peaks at a 1.0, 1.6, and 2.1.
The Shifts were approximately the same as for the trans
complex. The growth of an absorption peak at a 3.5, sug-
gests the product undergoes decomposition to the starting
methyl carborane(12). The infrared Spectrum for the £35
compound Showed the characteristic carborane cage absorp-
tions as well as OH stretching modes which are attributed
to the hydrolysis of this compound. Several attempts to get
precise analyses and melting points on this gig compound

were unsuccessful.
4. The Preparation of 1,2- bis(diphenylphosphino)carborane(12)

This bidentate carborane ligand was prepared according
to the method of Alexander and Schroeder (46). The air-
stable white solid was recrystallized from petroleum ether
m.p. 217-218° (lit. (46) 2190). Infrared, 1H, 319, and 113
nuclear magnetic resonance, and mass spectral data, not pre-
viously reported for this compound, are shown in Figures 13-
15 and Table III.

flat—l. Calcd. for C26H30B10P2: C, 60.93; H, 5.86; P, 12.11.

Found: C, 60.82; H, 5.82; P, 11.10.

a. The Reaction of 1,2-bis(diphenylphosphino)carbor-
ane(12) with Potassium Tetrachloroplatinite(II)

Two complexes were obtained when 1,2-bis(diphenylphos-

phino)carborane(12) was allowed to interact with potassium

31

 

omm cow

- b

 

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OHmme

.HHDE Homsz m mm com «Ammoovmiokmvoimmfinmoov mo Esuuowmm UmumumCH .MH musmflm

ooo

 

 

 

oom
.

OOOH
L

A

Eov mocwsvoum

HI
oomH
_

oovH
p

 

oooH omwfi ooom Cmmm ooom
- — -

 

 

 

32

 

 

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0.3%on

.mmo CH «mammovmiumwwoimmnmmmov mo Eznuoomm ch maH .VH ousmflm

“Lem H.om nAri

m m
. moo m
38— Sea . 3:0 A V

 

 

 

 

iiiiillllll'lllll‘l

 

33

 

 

 

mEB

OHNOHm

.mmo CH «AmmmovaUNWVUimmAmmouv Mo mnuommm HE: ma can mam .mH musmflm

am
.AI mm.» .owé e

 

 

 

O
m. we a A m so;

 

 

 

 

.34

*-
Table III. Mass Spectrum of (C6H5)2P-CV§7C-P(C6H5)2

. . BlOHlo
(Ionization Voltage 70 eV)

 

 

 

m/e Relative Intensity Assignment
512 100 [(C6H5)2P-C ' c-P(C6H5)2]+
BioH1o
435 37.5 [(C6H5)P'C C'P(C6H5)2]+
BioHio
404 15.5 [(CSH5)-CVC-P(C6H5)2]+
BioHio
+
327 36.5 [(CsHs )2P-CVC 1
BioHio
262 14.5 [P(C6Hs)3]+
250 15.0 [(CaH5)P=CVC 1+
BioHio
216 12.5 ?
+
185 45.0 [P(C6H5)2]

 

~X-
Boron cage compounds appear as a broad distribution due to

boron isotopic effects. The center of each distribution is
the m/e value reported.

35
tetrachloroplatinite(II). Both a 2:1 and a 1:1 complex of
ligand to metal salt were prepared. To prepare the 2:1
compound, a 0.415 g (1 mmol) sample of K2PtC14 was dis—
solved in a 60:40 methanol—water mixture and to this mag—
netically stirred solution a 1.03 g (2 mmol) sample of the
1,2-bis(diphenylphosphino)carborane(12) was added. No
immediate reaction was evident so the solution was stirred
for 12 hrs at about 30°. After 12 hrs the solution was
darkened by the formation of a gray-violet precipitate.
This solution was cooled, filtered, and then washed with
three 101mlponionscfi cold 50:50 methanol-water mixture.
A white residue and a violet precipitate were observed.
The white substance was removed by washing the filtrate
with benzene. The violet solid was insoluble in carbon di-
sulfide, benzene, methylene chloride, diethyl ether, chloro—
form, and nfpentane, as well as HCl. A sample of this

solid was sublimed in vacuo at 250°. The small amount of

 

white solid sublimate which was collected was shown by

means of its 1H nmr Spectrum to be the starting bisphosphino-
carborane(12) ligand. The remaining violet solid did not
appear to be altered by the sublimation process.

A nuclear magnetic resonance Spectrum could not be ob—
tained due to the extreme insolubility of the violet solid.
An infrared spectrum of the solid mulled in Nujol is Shown
in Figure 16. The absorptions at 750 and 2540 cm"1 are
characteristic of the bisphosphinocarborane(12) ligand.

There was no Pt-Cl stretch observed in the appropriate

 

III. I I i 'Vi.i

36

 

 

.HOnsz ou moo mcoaumuomnm och monococ x
OHmOHm

1:58 Hohsz m mm con NHUDQNHNAnmoovmiuwoimfinmmo: mo Enuuommm commumcH .oH wusmflm

omm com com
_i P

_

oom
p

oooa
P

AHIEUV mocmsomnm
ccmH covH coca coma oflcm ommm oflom
» p b -

 

 

 

 

 

37
region of the infrared Spectrum (280 to 310 cm-l). This
fact together with the chemical analyses suggests that the
2:1 complex of ligand to platinum salt was formed.

Anal, Calcd. for C52H60B20012P4Pt: C, 48.37; H, 4.65;
CI, 5.50. Found: C, 47.66; H, 4.48; Cl, 6.57. No molecular
weight data were obtained due to the insolubility of this
compound.

The 1:1 ligand to platinum complex was first prepared
by accident in an attempt to prepare the 2:1 complex. A
1 mmol sample of KthCl4 was dissolved in a 60:40 mixture
of ethyl acetate and water. To this stirred solution, a
1 mmol sample of the 1,2-bis(diphenylphosphino)carborane(12)
was added. No immediate reaction was observed. The reac—
tion flask was cooled to 20°. After Six hours a white pre-
cipitate was observed in the reaction vessel. The mixture
was filtered; the precipitate was washed with water and
then dried in vacuo. This gray~white solid was insoluble
in carbon disulfide, benzene, methylene chloride, diethyl
ether, chloroform, and nfpentane. I was unable to recrys-
tallize the product and sublimation in vacuo at 250° left
the product unchanged.

No nmr Spectral data were obtained due to the insolu-
bility of the complex. The infrared Spectrum of this com—
plex mulled in Nujol is shown in Figure 17. The bands
characteristic of the bis(phosphino)carborane(12) at 750

1

and 2540 cm- are again present. There are also bands at

280, 290, and 310 cm‘1 which we tenatively assign to Pt-Cl

38

 

was oos

 

000
L

oom
—

ofioH

.Honsz on can mcoflumuomflm emu monococ X

OHEOHm

AaIEoV mucoswmum
ome sovfi cwofi

 

 

 

omwfi

owom

oomm

 

2:58 Homsz m mm 23H «HUDQNAmmoovmiOWUimmflmmmov mo Eduuoomm UmHmHMCH .bH ousmflm

ooom

 

 

 

39
stretches. This evidence together with the analytical data
support the suggested 1:1 formula for this complex.
Anal. Calcd. for C26H30810C12P2Pt: C, 40.10; H, 3.89:
Cl, 9.11. Found: C, 39.83; H, 3.85; CI, 8.89. No molecu-
lar weight data was obtained due to the insolubility of

this product.

D. Attempted Syntheses

 

1. The Reaction of 1,2—Dicarbacloso-dodecaborane(12) with

Dicyclopentadienyldichlorides of Titanium and Vanadium

The Similarity of carborane to benzene suggested that
(C5H5)2Ti(-C c-) or the dimer, (C5H5)2Ti(-C C)2Ti(C5H5)2,

B10H10 B10310
might be prepared through a reaction analogous to the pre-

viously reported (47) reaction.

THF

 

(C5H5)2TiC12 + 2Li-C6H5 > (C6H5)2Ti(C5H5)2 + 2LiC1

Specifically, a 1 mmol sample of 1,2-dicarbacloso-dodeca-
borane(12) was dissolved in 50 ml of dried tetrahydrofuran
solvent. A 2 mmol sample of nfbutyl lithium in pf hexane
was Slowly added,over a period of 5 min, to the stirred
reaction vessel maintained at 0°. After 30 min the white
slurry of the dilithium salt of carborane appeared. The
red titanium complex (1 mmol) was added over a 10 min
period as a suSpension in THF. Immediate evidence of reac-
tion was noted by a color change from red to dark green.

After allowing this stirred mixture to react at 0° for

40
30 min, the system was allowed to warm to 25°. The solvent
was removed by distillation in vacuo and a dark green oily
residue remained in the flask. Attempts to recrystallize
this oily product from benzene, methylene chloride, and £7
pentane proved futile.

The 1H nuclear magnetic resonance spectrum of the resi-
due taken in THF revealed peaks attributed to the cyclo—
pentadienyl protons (o 6.5) as well as the characteristic
peak (5 3.52) of 1,2-dicarbacloso—dodecaborane(12). Several
other minor peaks attributed to the unreacted titanium
complex and decomposition products were observed. After
several hours in solution the 1H nmr peak attributed to the
starting carborane (5 3.52) increased in intensity. Pre-
cise analyses were never obtained.

This reaction was repeated several times with variations
in the reaction time (30 min to 3 hrs) and temperature (0°
to 36°). All attempts to isolate a stable fraction from
the oily residues proved futile.

The vanadium analogue to titanium dicyclopentadienyl-
dichloride was then investigated. The reaction procedures
were identical to those employed in attempting to prepare
the titanium complex, however, vanadium dicyclopentadienyl-
dichloride was used as atreactant and THE as a solvent.
Again a dark oily residue was the final product and all at-
tempts at recrystallization proved unsuccessful.

The ability of titanium to polymerize may be responsible

for the difficulty in isolating a characterizable compound.

41

The two reactive sites of 1,2-dicarbacloso-dodecaborane(12)

may enhance the chance of polymerization. Thus polymers of

 

the type
(C5H5)\\ (CsHs) \;.:’,(C5H5)
T1‘\‘ ’//, 1
,/// <3‘§7C ‘\‘~Cxé7c -
BIOHIO BioHio .41“

 

may form upon reaction. To avoid this problem I used
1—methyl-1,2-dicarbacloso—dodecaborane(12) (40) instead of
1,2-dicarbaclosos—dodecaborane(12). In this moiety, one of
the active C-H Sites has been blocked by the addition of a
methyl group. This would eliminate the possibility of a
polymer involving the carborane linkage.

Reaction procedures identical to those previously
described (pp 7,8) were employed. After addition of titan—
ium or vanadium dicyclopentadienyldichloride the solution
immediately turned from the original color of the starting
material to a dark green. Removal of the solvent (THF)
by distillation in vacuo left an oily residue. All atte ts
at recrystallization were unsuccessful. The nuclear mag—
netic resonance spectrum exhibited the characteristic peaks
ascribed to the starting carborane material. The use of
diethyl ether or benzene as the solvent resulted in no
noticeable difference in the final product. No acceptable

analyses were obtained on the system.

42

2. The Reaction of l-Methyl-l,2—dicarbacloso—dodecaborane(12)
with Palladium and Nickel Chlorides

 

Following the successful preparation of platinum-
carborane compounds, reactions with palladium analogs of
platinum were attempted. The starting materials for these
reactions, gisfdichlorobis(triphenylphosphine)palladium(II)
and transfdichlorobis(tri—dimethylaminophosphine)palladium(II)
were prepared and characterized according to previously re—
ported methods (48, 49), m.p. 260—2650 and 1200 (decomp.)
(lit. (48,49) 260—270° and 119—120° respectively). The pro-
cedures used to make the palladium compounds were identical
to those described previously (pp 7—8). In a typical reac-
tion, a 2 mmol sample of the lithium salt of methyl carbor-
ane(12) was prepared under nitrogen. This was followed by
the addition of 1 mmol of the appropriate palladium complex
in diethyl ether. When Sigfdichlorobis(triphenylphosphine)-
palladium(II) and transfdichlorobis(tri-dimethylphosphine)-
palladium(II) were employed, no immediate reaction was ob-
served but dissolution of the added palladium complex occur-
red after the reaction flask was allowed to warm to 25° for
one hr. The solution underwent a gradual color change from
yellow to brown to black over this time period. An oily
black residue remained after removal of diethyl ether by
distillation in vacuo. These residues were partially sol-
uble in carbon disulfide. A 1H nuclear magnetic resonance
Spectrum revealed peaks which can be attributed to the

starting material (5 2.0 and 3.5) and other minor peaks,

43
(5—10% relative intensity) probably a result of the decompo-
sition of the unreacted palladium complexes, which increased
in intensity upon standing. Attempts to recrystallize these
products were unsuccessful. A change of the solvent from
diethyl ether to benzene had no observable effect on the
reaction.

The analogous nickel(II) system was investigated X13
the preparation and characterization of the dichlorobis-
(triphenylphosphine)nicke].CLI) (50,51) (m.p., 245-250°;
lit. m.p. (51), 247—250°) and the subsequent interaction
of this product with a 2 mmol sample of 1—methyl—1,2-di—
carbacloso-dodecaborane(12). The reaction procedure used
was identical to that described previously (pp 7—8). There
was no evidence of immediate reaction, but upon warming to
25° the solution gradually darkened. The solvent (benzene)
was removed by distillation in vacuo and a black residue
remained in the flask. A 1H nmr spectrum of the black
residue in carbon disulfide exhibited peaks which can be
ascribed to the starting methyl carborane and a very broad
resonance (6 7.3) due to the paramagnetic nickel complex.
No further attempts at synthesis of nickel(II) complexes

were carried out.

DISCUSSION

Sigma Bonded Methyl Carborane(12) Complexes

Although no o-bonded transition metal complexes of
methyl carborane(12) were reported at the start of this
study, during the time these investigations were underway,
three reports of Similar complexes appeared (32-34). In
these reports,however, detailed spectroscopic data were
not presented. In this study the results of a systematic
investigation of o—bonded complexes will be reported,
together with spectroscopic data. I was unable to obtain
sufficient data, because of experimental difficulties, to
fully characterize the influence of the carborane cage on
the metal-carbon bond.

The possibility of preparing o-bonded complexes by the
interaction of gig-platinum phosphine compounds with methyl

carborane(12) was established.

 

. . 00
sis-PtclziP(CH3)nPh3_n12 + 2CH3-C C-Li (C2H5)20 >

310310
cis-Pt[P(CH3)nPh n]2[-c C-CH3]2 + 2LiCl
— 3-

BioHio

(where Ph is a phenyl group).

44

45

Elemental analyses together with molecular weight data
suggest that all the complexes are monomeric and non—ionic
when dissolved in C82.

The 1H nmr Spectral results indicate that bis(alkyl-
phenyl)phosphinoplatinum methyl carborane(12) complexes
have been isolated. The 1H nmr spectral data Show the
presence of the methyl group on the carborane cage along
with the appropriate phenyl and or methyl groups on the
phosphine. The absence of the C-H resonance, characteristic
of the starting methyl carborane(12), suggests this linkage
has been destroyed on complexation, as expected.

The most soluble compound (C82, CH2C12, and benzene)

was cis-Pt[P(CH3)2Ph]2[-C C-CH312. The 319 nmr of this

BioHio
complex appears as a broad Singlet at 5 +120.4. Although

the 195Pt-31P coupling constant could be obtained on cis—

PtC12[(CH3)nPh ]2, they were not observed in cis-

3-n

Pt[(CH3)nPh3_ [—C -CH3]2 because of the lower solu—

n12
BioHio
bility of the latter complexes.

The 113 nmr of cis-Pt[P(CH3)2Ph]2[-C C-CH3]2 is

BioHio
Shown in Figure 9. The apparently simple low field triplet

and high field quartet may be due to overlap of the absorp-
tions or second order spectral effects. For cis-Pt[P(CH3)3]2-
[-c C-CH3]2, cis—Pt[P(CH3)Ph2]2[-C C-CH312, and

BioHio BioHio

46
cis-Pt[P(Ph)3]2[-C C-CH3]2 only very broad 118 resonance

BioHio
absorptions were obtained.

In order to understand what effects the o-bonded methyl
carborane(12) exerts in the platinum complexes, an attempt
was made to obtain the 195Pt-31P coupling constants. It
has been suggested (52) that as the value of the coupling
constant increases there is a corresponding increase in the
w-acceptor character of the phosphine ligand. Although I
was able to obtain these data for the complexes of the type

cis-PtC12[P(CH3) Ph ] extensive efforts to obtain

n 3-n 2’
Similar data for the complexes in which the chloride ligand
is replaced by methyl carborane(12) were unsuccessful be-
cause the complexes which contained the carborane ligand
were much less soluble than those which contained the chloride.
The yields for the gig—pt[P(CH3)3Ph3_n] [—c C-CH3]2

BioHio
products were about 50%, based upon the amount of methyl

.carborane(12) recovered. As the phenyl groups on phos—
phorus were replaced by methyl groups the yields decreased.
The complexes which contained greater numbers of methyl
groups were more easily hydrolyzed, which may account for
the lower yields.

It can be suggested on the basis of these observations
that methyl carborane(12) is a poorer W-acceptor than a
chloride anion when either of these are trans to phOSphines
in platinum(II) complexes. Increased stability toward

hydrolysis is observed for dichlorobis(methylphenylphosphine)

47
platinum(II) compounds as the methyl groups on the phos-
phine are replaced by phenyl groups. This stability has
been attributed to the increased r—acceptor character on
phosphine because of electron delocalization within the
phenyl groups (52,53).

The phenyl groups on phosphorus enhance the w-accep-
tor character of the phosphine. This results in greater
overall bond strength between platinum and phosphorus (53).
Methyl groups, however, act as electron donors; this
weakens the w~acceptor character of phOSphorus and the
resultant bond strength between platinum and phosphorus
is decreased.

The substitution of methyl carborane(12) for the
chloride ligand results in phosphinoplatinum(II) methyl
carborane(12) complexes which are more susceptible to
hydrolysis than the corresponding dichlorobis(phosphino)-
platinum(II) complexes. Since the phosphine groups remain
unchanged, hydrolysis apparently is made easier through
the replacement of the chloride ligand by methyl car-
borane(12). This suggests that methyl carborane(12) is a
weaker v-acceptor than a chloride ligand.

Such a result is not unreasonable. The chloride anion,
which lies in the middle of the triggfeffect series, can
function as a v-acceptor (53). On the other hand, it has
been reported that the gfcarborane(12) cage can function as
an electron donor or acceptor (54,55). Since the methyl

group attached to the boron cage acts as an electron donor

48
to the cage, the methyl carborane(12) ligand should be a
better electron donor and a poorer n-acceptor (56). No
kinetic or thermodynamic studies have been attempted on
this system.

The gi§_and trans complexes of dichlorobis(tri-nf
butylphosphine)platinum(II) formed upon interaction with
methyl carborane(12) were much more susceptible to hydrol-
ysis than the corresponding phenyl phosphine complexes of
methyl carborane(12). We suggest this because of the ap-
pearance of bands associated with CH vibrations in the
infrared spectrum (1600 and 3400 cm—1) and the appearance
of an 1H nmr resonance which can be ascribed to the start-
ing material, methyl carborane(12) (C-H resonance at 6 3.5).

The expected gig complex from the interaction of di-
chlorobis(tri-nfbutylphosphine)platinum(II) and methyl
carborane(12) was not isolated. We suggest that a reaction
similar to that described below can be used to rationalize
the difficulty we encountered in the preparation of the
gigfdichlorobis(tri-nfbutylphosphine)platinum(II) methyl
carborane(12) complex. (Where C4H8 is a butyl group which

is bonded to both phosphorus and platinum.)

00

3]2 C6H6 >

CH3-C C-Li + cis-PtC12[P(C4H9)

BioHio

(CH3-c C-)Pt[P(C4H9)3][P(C4H9)2(C4H8)] + LiCl

BloHlo

49
Turco reported similar results for the interaction of
dichlorobis(tri-ethylphosphine)platinum(II) with methyl
carborane(12) (33). He tentatively formulated the product
of this reaction as [P(C2H5)3]Pt(-C C-CH3)[P(C2H5)2(C2H4)].

B10310
(Where the C2H4 group is bonded to both phosphorus and

platinum.) The molecular weight data, which was low for
the expected methyl carborane(12) complex of dichlorobis-
(tri—gfbutylphosphine)platinum(II), is near the theoretical
molecular weight for the product shown in the reaction (687).
Precise analytical results were never obtained. No further
investigations were attempted on this system.

Magnetic susceptibility measurements of all the phos-
phino methyl carborane(12) platinum complexes isolated were
made on a Gouy balance. In every case, the compounds were

found to be diamagnetic.

Platinum Complexes with 1,2-bis(diphenylphosphino)carborane(12)

 

The bidentate ligand 1,2-bis(diphenylphosphino)car-
borane(12) was first isolated by Schroeder (46). The pre—
viously unreported 1H, 31P, and 118 nmr Spectra are shown
in Figures 12-14.

The proton spectrum (Figure 12) is unusual in that two
distinct phenyl resonance absorptions are observed. These
are located at 6 7.35 and 7.80 respectively from TMS. This
behavior generally is observed when phenyl groups are bonded

to systems which allow electron delocalization (57).

50

The 31F nmr (Figure 13) of 1,2-bis(diphenylphosphino)-
carborane(12) is a complex multiplet centered at 6 +78.8
from P406.

The 118 nmr spectrum of 1,2-bis(diphenylphosphino)car-
borane(12) (Figure 14) may be rationalized in the following
manner. In the icosahedral structure for the QfBioczHio
unit one readily recognizes the existence of four different
types of boron atoms, namely, 3(6), 8(10), 9(12), and
4(5,7,11). This would give rise to four singlets of area
2:2:2:4. These absorptions are further split by Spin-Spin
coupling due to the protons attached to the borons to give
a predicted spectrum of four doublets of relative integral
intensities, 2:2:2:4. Such a spectrum has been reported
for the 11B nmr of gfcarborane(12) at 60 MHz (58) and has
been rationalized in terms of selective overlapping of the
expected doublets (59).

The predicted spectrum of gfcarborane(12) which appears
to consist of four doublets is Shown schematically in Figure
18a. It has been suggested that the high field doublet (d)
is due to the 3(6) boron atoms located nearest to the 1
carbon atoms of the icosahedral cage of gfcarborane(12) (58).
When 1,2 bis(diphenylphosphino)carborane(12) is prepared,
the 3(6) boron atoms would probably feel the electronic
effect of the carbon-phosphorus attachment more than the
other boron atoms. A schematic reproduction of the 11B nmr
spectrum obtained at 65 MHz of 1,2 bis(diphenylphosphino)-

carborane(12) is shown in Figure 18b. It can be suggested,

51

 

 

 

 

 

"i ”—1

L i4

L___J L___.| ' u I
a b I C E

Figure 18a. Schematic representation of predicted Spectrum
for QfBioczHio unit.

 

 

 

 

 

 

 

 

 

 

Iu—i L.
2 3

I.
N

 

)—
Ho

Figure 18b. Schematic representation of spectrum resulting
from selective overlapping in
(C6H5)2P'C C‘P(C6H5)2 -

B10310

 

 

 

52
therefore, that the resonances ascribed to the 3(6) boron
atoms, (d in Figure 18a), are Shifted so as to overlap the
high field member of d with the low field member of the
resonance due to the 4(5,7,11) boron atoms, (c in Figure 18a).
The low field member of d, the resonances ascribed to the
3(6) boron atoms, then overlaps with another low field
doublet (b in Figure 18a). It is not possible to determine
from the experimental data which boron atoms correSpond to
the resonances ascribed to the 8(10) and 9(12) atoms (a and
b in Figure 18a). The resultant Spectrum consists ofia low
field 1:1 doublet and an apparent 2:3:2 triplet. This is
close to the observed 11B Spectrum for the 1,2-bis(diphenyl-
phosphino)carborane(12) ligand (Figure 14). It has been
reported that the attachment of AS(CH3)2 groups to the of
carborane(12) cage has resulted in a change of electronic
environment about the carbon atoms so as to cause such
Spectral results (55).

The mass spectral assignments for 1,2obis(diphenyl-
phosphino)carborane(12) are shown in Table III. The main
peaks occur at m/e ratios of 512, 435, 404, and 327. These
result from the loss of phenyl groups or the phenyl phos-
phine itself from the boron cage. A strong parent ion peak
is observed which suggests that the ligand is thermo-
dynamically stable.

The interaction of 1,2-bis(diphenylphosphino)carborane(12)
with potassium tetrachloroplatinite(II) (K2PtCl4) gave a

monosubstituted, PtLClZ, and a disubstituted, [PtL2]C12

53

complex (where L is 1,2—bis(diphenylphosphino)carborane(12)).
Both of these products were insoluble in carbon disulfide,
benzene, acetone, ethyl acetate, methanol, ethanol, methylene
chloride, tetrahydrofuran, and hydrochloric acid. The
identity of these products is suggested by the analytical
and infrared spectral data. Specifically, the C, H, and P
analyses agree with the proposed formulations. In addition,
the presence of platinum-chlorine stretches is observed in
the infrared spectrum of the monosubstituted product
(Figure 17), but is absent in the infrared of the disubsti-
tuted product (Figure 16). Attempts to obtain molecular
weight data by means of mass Spectral techniques were un-
successful. It is generally difficult to volatilize platinum
compounds for mass Spectral analyses (60).

I attempted to prepare o-bonded methyl carborane(12)
complexes containing titanium, vanadium, palladium, and
nickel by the use of similar techniques. The equations for

the reactions are:
00
(C235)2O

 

1- (W-C5H5)2Mcl2 + 2CH3-C C-Li —>
B10H10
(w-C5H5)2M(o-c C-CH3)2 + 2LiCl

BlOH10

(where C5H5 is the cyclopentadienyl anion and M is titanium

or vanadium).

54

00

2. cis—MC12(PPh3)2 + 2CH3-C C-Li (c H ) o >
252

 

BIOHIO
glng(PPh3)2(—C C-CH3)2 + 2LiCl
BIOHio
(where M is palladium or nickel).
However, no complexes could be isolated. Studies

on some of these systems are still in progress by other

investigators.

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