A SWDY OF THE ENFRARED SPECTRA OF THE
TREMETHYLPLATINUM HAUDES
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TIME: fat tho Dsgm M’ Na. D.

MICHlGAN STATE UNEVERSEYY

Michael N. Hamhsfefier‘
195$

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MICHIGAN STATE UNIVERSITY

or AGRICULTURE AND APPLIED SCIENCE
DEPARTI‘AEIIT OF CH EMTSTRY
EAST LANSING, MICHIGAN

A STUDY OF
THE INFRARED SPECTRA OF THE
TRIMETHYLPLATINUM HALIDES
AND SOME OF THEIR SQMPLEXES

By

flichael N. hoechstetter

A THESIS

Submitted to the School for.Advanced Graduate Studies of
Michigan State University of Agriculture and Applied Science
in partiel fulfillment of the requirements
for the degree of

DOCTOR OF.PHILOSOPHY

Department of Chemistry

1960

ACKNOWLEDGEmEflT

The author gives grateful acknowledgement to Associate Professor
Carl B. Brubaker for his many helpful suggestions. his guidance. and
encouragement during the course of this project.

Sincere thanks are proffered as well to other departmental staff
members for their assistance and advice, and to the Atomic Energy
Commission for financial support of this work.

Much appreciation is given to the author's wife, Florence, for
the typing of this thesis, and for the patience and understanding
which helped to make this entire project possible.

VITA

Michael N. Hoechstetter was born in Lowell, Massachusetts, on
February I, 1931. After attending public schools in Dwight, Illinois;
Des Hoines, Iowa; and Worcester, Massachusetts; he received under-
graduate education at Worcester Polytechnic Institute and graduated
with a 3.5. Degree in chemistry in 1953. In 1955 he obtained an
“.8. Degree in chemistry from Lehigh.University in Bethlehem, Penn-
sylvania. That same year he began graduate work at Michigan State
University, and later became a candidate for the Ph.D. Degree in
Chemistry. His major field is inorganic chemistry with minor fields
of study in physical chemistry and physics.

His professional eXperience includes two years as a Research
Assistant in Printing Ink Chemistry at Lehigh University, two and one
half years as a Graduate Teaching Assistant at nichigan State Univer—
sity, and one and one half years as a Special Graduate Research
Assistant at Michigan State. He is a.member of the American Chemical
Society. and of the Society of Sigma 11.

He is married and is the father of one child.

A STUDY OF
THE INFEARED SPECTRA OF THE
TBIMETHYLPLATINUM HALIDES
AND SOuE OF THEIR COMPLEXES

By

Michael N. Hoechstetter

AN ABSTRACT

Submitted to the School for Advanced Graduate Studies of
Michigan State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Chemistry

1960

Approved ‘69 h g [i 9 lgiihubl"? “n %:! I

t

ABSTRACT

The trimethylplatinum halides, hydroxide, the ammonia and pyridine
complexes, and their equivalent deutero-trimethylplatinum compounds
were all prepared for study of their infrared spectra.

It was hoped that the observed spectra could be correlated with
the known structures of the compounds or possibly be used to help
determine the configurations of the complexes. Neither of these
objectives could be accomplished because the observed spectra of the
trimethylplstinum halides consisted only of the vibrations of the methyl
group alone as though it were attached to a single heavy atom as in the
case of the methyl halides. The spectra of the ammonia and pyridine
complexes showed only the uncoupled vibrations of the methyls and of the
ligands themselves. In these latter instances there were shifts in some
of the absorption peaks of the ligands upon complex formation, but there
were essentially no shifts in the methyl peaks under the same conditions.
Also, no peaks were observed which could be classified as vibrations of
whole molecules.

The reason for this may be the fact that the very stable hexa-
coordinate platinum compounds most likely have such very rigid bonds
between the platinum and the carbons, halogens, or nitrogens that the
relatively low energy infrared radiation can not cause these atoms to
Vibrate. The one exception to this is the Pt — O vibration which occurs
in trimethylplatinum hydroxide. It is not known why this one vibration

can occur while Pt — C and Pt - N vibrations can not.

EABLE OF CONTthS

Page
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8

nESULTS.......................................................
DISCUSSION.................................................... 50
sumussr...............................................I ....... 66
BIBLIOGRAPHY...... ........ ............. ...... ...... ........ ... s7

”PEK'DICESOIOO ...... ......l......... 000000 C ....... .0... 000000 D '70

Table

1.

to

10.
ll.
12.
13.
14.
lb.
16.
17.
18.

19.

20.

31.

Wavelength
Absorption
Absorption
Absorption
Absorption

Absorption

LIST OF $ABLn§

Corrections for Perkinadlmer Spectrograph .........

Peaks

Peaks

Peaks

Peaks

Peaks

of
of
of
of

of

Absorption Peaks of
[wetness]
Absorption Peaks of

Absorption Peaks of

Assignments for Absorption Peaks
Assignments for Absorption Peaks of (CH3)3PtOH.

Assignments for Absorption Peaks of [(053 )3Pt(NHS)3 I. . . . . . .

(333)3Pt1 and (CD5)3PtI....

(Cii5 )SPtBr and (CD5 )5PtBr.

(CHE)3PtCl and (005)3PtC1...

(035 )sPtOH and (C05)3Pt01i. .

(CH3)3PtOD and (CD3)3PtOD.

[(033)3Pt(1€k13)3] I and

OOOOOOOOOOOOOOOOOOOOOOO

OOOOOOOOOOOOOO

OOOOOOOOOOOOOO

Pyridine and cis—(py)2PtCl4. .............

(013.3)3Pt1(py)2and (CD3)SPtI(py)z . . . . . . . . .

of (CUS)3PtI.. ........... ...

Assignments for Absorption Peaks of (033)3Pt(py)21.... ...... .

Comparison of Observed and Calculated Peaks of

Comparison of Observed and Calculated Peaks of

Comparison of Observed and Calculated Peaks of

Comparison of Observed and Calculated Peaks of

Comparison of Observed and Calculated Peaks of

Comparison of Observed and Calculated Peaks of

(CD3)3PtI. .
(OJ-)3 )sptBr. . e .

(ugh—5mm. . . .
(CD3)3PtOD....

CD301 .........

[(CD3)3Pt(NHB)3] I... eeeeee eseeeee oooooooooooooooooooooooooo
Comparison of Observed and Calculated Peeks of
(CD3)3Pt(py)21 ...............................................

Comparison of X~nay "d“ Spacings ior \Cds )4Pt and
(6%)8Pt0deeeeee eeeeeee a eeeeeeeee e eeeeeeeeeeeeeeeeeeeeeeeeeee

Page

28

30

34

76

76

77

b4

LIST OF EIuUde

Blouse

l.

10.

ll.

12.

13.

14.

15.

16.

Configuration of Trimethylplatinum halides............ .....

Configuration of [(C33)3Pt(NHg)3] "1 with 03v Symmetry. . . .

.

Configuration of I:(Cd3)3Pt(Niié)3] '1 wi th (38 Sy.:unetr;,'. . . . . .

Configuration of (CH3)3Pt(py)21. ...........................

Configuration of cis-tpy)thCl4... ......... .................

Apparatus Used for Preparation of PtCl4.... ........ . ........

Apparatus used for Preparation of (CH3)3PtI....... ....... ...

Calibration Curve for Perkin-almer Model 21 Spectrograph....

spectra of (C33)3Pt1 and (CDé)3PtI... ............ . ........ ..
Spectra of (Ch3)32t3r and (CD3)3Ptdr ...... .. ..... ...........
Spectra of (033)3Pt01 and (CD3)3PtCl................... .....

Spectra of (C83)3PtOH and (CD3)3PtOB.......................

Spectra of (Ch3)3PtOh + -OD and (Ch3)3PtGH + «00.. ....... ...

H

Spectra o

Spectra of Pyridine and cis-(py)2PtCl4.....................

Ha

Spectra o

[(cupspumpz] 1 and [(CD333PtCNH5)3] 1.....

(083)3Pt(py)21 and (025)3Pt(py)21......... ..... ..

12

lb

29

61

46

49

INTRODUCTION AND HISTORICAL BACKGROUND

The chemistry of platinum is concerned mostly with its numerous
complex compounds which are either of platinum (II)or of platinum (IV).
In the former group the stability of the complexes is achieved by the
formation of a tetracovalent square planar arrangement around the
platinum. 0n the other hand the platinum (IV)comp1exes are stabilized
by octahedral hexacoordination.

Among the octahedral platinum compounds are the trimethylplatinum
halides which are formally platinum (1) compounds since the methyl
groups are very covalent rather than ionic, extremely stable to
oxidation. and unreactive. These compounds were first reported by
Pepe and Peachy (2) who prepared trimethlyplatinum iodide by the
reaction:

3 CHSMgI + stair—s (CH3)3PtI + 2 lg612 .. 11313
From this compound trimethylplatinum hydroxide was prepared by reaction
with moist silver oxide, and subsequently the other halides were formed
by the reaction of the hydroxide with the appropriate acids. The
halides were found to be tetrameric in solution (3) and in the solid
state as well. according to Bundle (4) who elucidated the cubic tetra»
neric structure of both the trimethylplatinum chloride and of tetra-
methylplatinum (1). ( See noun: 1,)
In this type of structure each platinum is surrounded octahedrally by
three aethyls and three halides which results in a very stable and un-

reactive molecule. Upon the addition of complexing agents such as

pyridine, amonia, ethylenediamine, 2,2'-bipyridine, and acetylacetone,
the ha10gen bridging is disrupted and simple units are formed which are
octahedral, hexacoordinated complexes in which the halogen may be in
the coordination sphere as in (033)3?t(py)21 or completely removed as
an ion in [(033)3Pt(flfls)311 (5)(6).
till these compounds, with the exception of tetramethylplatinum
(see appendix), are easily prepared, and most of them were during the
course of numerous unsuccessful attempts to prepare tetramethylplatinum.
It was during this time that it was decided to carry out a study of the
infrared epectra of the trimethylplatinum halides and some of their
complexes. This was done in order to correlate, if possible, the
observed epectra with the known structures of the compounds.
The.application of infrared spectroscopy to inorganic compounds is
very recent, and has been used mainly in the study of coordination
complexes (7) because many ligands exhibit well defined infrared spectra.
By comparison of the spectra of the free ligand with that of the complex,
information concerning the structure of the complex can be obtained.
This technique has been used to great advantage by Quagliano (7g), for
example, in showing the structural isomerism of nitro— and nitritopent—

Ruminecobalt (Ill) chlorides.

 

 

 

 

 

 

 

 

 

 

 

 

 

CH3
l “3
H3O Et/ 1
l
I I 033
I u
' I
x ' Pt— 05/
/|‘ /
use :I
.. :1? ..
,/: /°Hs
/ X, ————————— Pt—Gfls
/ //
/ ///
//// | CH
// 3
H30 -—Pt’/ x
830
033

... .. = axes of two-fold symmetry

 

 

X :3 halogen, Mdroxide, or methyl

FIGURE 1

THEORETICAL

The absorption of infrared radiation by a molecule depends upon
whether the individual bond vibrations and] or entire group vibrations
show frequency of change of dipole moment equal to the nbmrbed fre-
quencies. The individual vibrations can be treated mathematically as
simple harmonic oscillations in which the frequency is given by the

expression:

1

where 7/: frequency in cm. , c t: velocity of light in cm/sec., k = the

bond force constant in dyne/cm, and p: the reduced mass in grams.
= m “2 ~24
”' (11";55)(l.66110 gm)

m1 and me are the masses of the vibrating atoms, and 1.66110'24gm is
the actual mass of the hydrogen atom in grams.

Organic, organometallic, and a very few inorganic molecules ex-
hibit the necessary combination of force constants and reduced masses
to absorb infrared radiation while many inorganic molecules and ions do
not absorb because the bonds are often tee rigid to be affected by the
relatively los energies of infrared light. For this reason organic
molecules and the very light inorganic molecules are the best absorbers
Of infrared radiation.

his number of vibrations which a molecule can undergo depend both
on the number of atoms and on the symmetry properties of the molecules.

These rules are listed in great detail by Hersberg (8).!” a non-linear

molecule the total number of vibrations is given by: n = 3N - 6 where
N = the number of atoms in the molecule. In 0331 for instance Ii 2: 5
so that n = (3)(5)-6 = 9. However the number of different modes of
vibration is determined by the fact that the molecule has a symmetry
(03v) which in this case permits three A1 vibrations and three I
vibrations. The former are completely symmetric with respect to the
single three-fold axis of rotational symmetry and to the three equi-
valent vertical planes of symmetry which characterize this particular
space group. The latter group are doubly degenerate modes with respect
to the three-fold symmetry axis. This means that there are three pairs
of vibrations in which the two vibrations in each pair have the same
energy. Therefore the three totally symmetric Al vibrations and the
three doubly degenerate B vibrations make a total of nine. In addition
to these fundamental vibrations some overtone and combination vibrations
are observed. The simple molecules of the 63' space group like ammonia
and the methyl halides exhibit only the ‘1 and the 3 vibrations. Some
of the more complicated molecules can exhibit the A2 species as well.
In this case the vibrations are symmetric with respect to the three-fold
axis but antisymmetric with respect to the vertical planes of symmetry.
The trimethylplatinum halides and hydroxide belong to the D2 3 V
space group because these cubic tetramere (FIGURE 1) hare three equi-
Vedent and mutually perpendicular axes of two-fold symmetry which can
'be designated as the x, y, and s axes respectively. Using the selection

rules for this epace group (8) as applied to the halides, there are 42

vibrations of species A which are symmetric to all three axes, and 40
vibrations of species 51 which are symmetric with respect to the s axis
but antisymmetric with respect to the x and y axes. There are also 40
vibrations each for the 32 and 33 species. The former are symmetric
with respect to the y axis only while the latter are symmetric only to
the x axis. This means that there are 162 vibrations possible for the
halides. Application of the same selection rules to the hydroxide re-
sults in 45 vibrations of type A, and 43 each of species Bl, 32, and 35
for a total of 174.

The configuration of the trimethyltriammineplatinum (I) ion is
unknown. It is believed that the complexing by the ammonia does not
alter the arrangement of the methyl groups so that the three Pt -0
‘bonds would remain mutually perpendicular. Under this condition the
three Pt - N bonds would also be mutually perpendicular. This arrange-

zaent would result in a 63' space group as shown in FIGURE 2:

 

B
- - g

vertical plane of
symmetry

 

The single three-fold axis of rotational symmetry goes through the

platinum and is perpendicular to the plane of the paper.

Three equi—

valent vertical planes of symmetry can be passed through this axis and

and at the same time be passed through an ammonia and a methyl. The

selection rules for this space group give 14 totally symmetric A1

vibrations, 9 of the A2 vibrations which are symmetric to the rotational

axis but antisymmetric to the vertical planes of symmetry, and 23 of

the doubly degenerate E vibrations which are antisymmetric to the rota—

tional axis.

This gives a total of 69 vibrations.

The other possibility for this ion involves an arrangement in

which the three methyl groups are no longer mutually perpendicular, but

instead two of them are trans- to each other while the third one is

cis- to both of them.

the configuration is shown in FIGURE 3:

{-

 

  
    

   

N33

330

v

‘

\\“

 
       
   
      

FIGURE 3

 

+1

The same thing holds true for the ammonia, and

+1”

::plane
of
symmetry

§

Under the above conditions the only element of symmetry possible is a
plane which can be passed through either the three methyls and one
ammonia as shown in FIGURE 3, or through three ammonias and one methyl.
Either way gives the same number of vibrations based on a 6. space
group. 'mere can be 39 vibrations of species A' which are completely
symmetric to the plane of symmetry. and 30 vibrations of type A." which
are antisymmetric to the plane. 'Diis gives a total of 69 vibrations
which is the same number which can be present using the 03' space group,
only there are no degenerate modes with the GB space group. It is
believed that the ion has the 63' symmetry because of the fact that the
trimetnylplatinum group is extremely stable and most likely does not
change the configuration of the methyl groups upon complex formation.

me molecule trimethylhis(pyridine) iodoPlatinumU) can have three
possible configurations which are shown in FIGURE 4. In each case a
total of 42 vibrations are possible excluding those of the pyridine
itself. In these instances the number of vibrations of the molecule
as a whole has been calculated by considering the pyridines as point
laesee. The configuration shown in FIGURE 4a is believed to be the
actual configuration of the molecule for the same reason as that
advanced for the trimethyltriammineplatinum(IJ ion. The other two
configurations are the other possibilities. ‘me 0. space group of the
f 1.er two configurations allows 25 vibrations of the A' type or
'ynnnetric to the plane of symmetry and l? vibrations of type A“ or
antiSymmetric to the plane. In the last case all 42 vibrations are of

Bpecies A which are symmetric to any arbitrarily chosen one-fold axis

of symmetry. The configurations of FIGURE 4a and 4c can also be

applied to the molecule trimethyl(2,2'-bipyridine)chloroplatinumfl)

P?

 

033

   

(b) (C)
C. % =plane 0, no symmetry
'of symmetry
FIGURE 4

though the same argument in favor of 4a can be applied in this case
also.
Fbr cis-bis(pyridine)tetrachloroplatinum(IV) only one configuration

is possible, and this has C, symmetry as shown in FIGURE 5:

FY

,/
,.

   
   
 

   
  

m = plane of symmetry

 

FIGUhE 5
By considering the pyridines as point masses again, a total of 15
Vibrations are possible for the molecule as a whole excluding the

Pyridine vibrations. There are 9 of the symmetric 5' vibrations and 6

10

of the antisymmetric A" vibrations.
It would appear that all of these molecules should have very

complicated spectra which.might be next to impossible to interpret;
however. many of the vibrations might be either completely inactive in

the infrared region or so weak that. for all practical purposes. they

would be non-existent. In addition some vibrations might be only Raman

active, but this could not be checked because the necessary spectro-

graph was not available. Even with these simplifying factors the

spectra can still be very complex.

Some vibrations which appear in the 2 to 7 micron region of the
infrared spectrum can easily be identified because generally they are
not very drastically affected by the presence of different substituents

on the molecule. Some of these vibrations include the O — H stretch

at 2.8a... the N - B stretch at 2.9“, the C - H stretch at 3.2». and

the pyridine C =2 N and C 5'- C stretches between 6.0 and 7.0“. In the

6 to 15 micron region the N — H deformations and numerous C - H

In addition to these vibrations many molecules
The latter

deformations occur.
exhibit single bond and skeletal vibrations in this region.
are characteristic of the molecule as a whole as the peak at 9.8;“ in

c)'<:l.0prope.ne and its derivatives (9). This latter group of frequencies

is often shifted drastically by changing substituents on the molecule.
30 that interpretation is often very difficult; however..this region is

“IOful for qualitative identification of many molecules.

II

EXPERIMENTAL

W

The starting material for this entire study consisted of 20 grams
of scrap sheet platinum which was obtained from the Baker.Platinum
Iorke in Newark, New Jersey. It was converted to the hexachloroPIatinic
(IV) acid by dissolving in about 200 ml of aqua regia which was made by
mixing 50 ml of b8% reagent grade nitric acid with 150 ml of 37%
reagent grade hydrochloric acid. Once the platinum was dissolved, the
solution was boiled down to about 100 ml on an electric hot plate,
about 200 ml of concentrated hydrochloric acid was added, and the
solution was concentrated further. The addition of acid and boiling
down was repeated several times until the vapors from the solution no
longer turned potassium iodide-starch test paper blue. This was done
to insure the removal of all nitrogen oxides from the solution. The

solution was concentrated until crystals of Hal’tClGOBH O began to appear.

2
At that point the solution was slowly evaporated to dryness on an
electric hot plate set at approximately 80°C, which resulted in the

removal of most of the water of hydration.

Platinum Tetrachloride
This substance was prepared according to the method of Kharesch
and Ashford (10). and consisted of heating hexachlorOplatinic(IV) acid
in a tube furnace in a stream of chlorine. (See FIGUlu‘. 6.) The red—
brown partially dehydrated acid was placed in combustion boats inside
a Pyrex tube in the furnace w:.ose temperature was slowly raised from

0’.
100 L9 to 275°C over a period of two hours while a stream of chlorine

“

Ali

12

gas flowed through the tube. The chlorine was first passed through a
dry tower filled with glass wool, then a bubble tower filled with 98%
sulfuric acid. and finally an empty trap before being led into the
furnace tube. This was done in order to remove ferric chloride which is
often a contaminant in chlorine cylinders and which can be carried
along in the chlorine stream.

After the furnace tube reached 275°C, it was kept at that temper-
ature for 30 minutes and then slowly cooled to 150°C. The combustion
boats were removed and the lumps of the platinum tetrachloride were
ground to a fine powder in an agate mortar before returning the
substance to the boats for more heating. The powdered material was
then quickly heated to 275°C, kept there for 30 minutes in a chlorine
stream, and cooled to 150°C before being quickly transferred to a glass
steppered bottle for storage. The platinum tetrachloride was a sandy
brown and extremely hygroscOpic powder which had to be stored over

concentrated sulfuric acid.

*/

“012‘ 7‘ 7T173

*/ 1

A: Tube Furnace to hood

 

 

B: Pyrex Tube

C: Combustion Boats
FIGURE 5

13

Trimethylplatinum Iodide
This compound was the source of all the trimethylplatinum halides
and complexes used in this work, and was prepared using the method of
Pope and.Peachy (2) with the modifications of Lichtenwalter (1). The
reaction was carried out in a 500 ml, three necked, round bottom flask
equipped with a stirrer, a 400 mm reflux condenser, and a combination
dropping funnel and inlet for dry nitrogen. (See FIGURE 7.) Approxp
imately 2.5 gm (0.105 mol) of magnesium turnings was placed in the
flask and covered with 25 ml of dry ether. Then 15 gm (0.105 mol) of
methyl iodide. was mixed with 50 ml of ether and placed in the dropping
funnel. Methylmagnesium iodide solution was prepared by drOpwise
addition of the methyl iodide solution to the well stirred magnesium
so that gentle refluxing was maintained. All of this was carried out
under cover of dry nitrogen. When the methyl grignard reagent was
formed it was siphoned through glass wool into a second :00 m1 flask
equipped with a stirrer and condenser, diluted with 100 ml of dry ben-
zene, and cooled to ~10°C by a combination ice—salt bath. Then under
stirring and nitrogen cover, a total of 5.5 gm (0.025 mol} of platinum
tetrachloride was added in amounts of approximately.) gm. The resulting
Inixture was stirred for four hours.
Hydrolysis was accomplished by the slow dropwise addition of water
While the mixture was cooled in an ice bath. The phases were separated,
”10 aqueous portion was shaken with two 100 ml portions of bensene, and

C
Eastman C. P. grade was used as obtained.

14

these were added to the original benzene phase. The benzene extracts
were dried over anhydrous sodium sulfate for several hours, filtered,
and evaporated to dryness on the hot plate at 80°C. The resulting red
powder was extracted with 50 ml of boiling benzene, filtered, and the
resulting solution was allowed to stand 12 hours. A small quantity of
an unidentified red powder separated out and was collected on a filter.
The filtrate was evaporated to dryness and the residue was taken up in
a 50 - 50 chloroform-ethanol solution for final crystallisation. The
product consisted of light orange colored, needle shaped crystals.
Analysis of the product showed that is was trimethylplatinum iodide.
Analysis, Calculated for (033)3Pt1 x: 0, 9,52}; a, 2.4571»; Pt, 53.16%.

Iowa: 0, lOeOlfi; H. 2.46%; Pt, 53e55fie

15

4—“?

 

Et20

  

O,

 

 

 

 

 

 

   

'0‘ .
’

 

" Ooo'

 
 

FIGURE 7

16

rimethylplatinum Hydroxide
This compound was prepared according to the method of Pope and

Peachy (2) by the reaction of trimethylplatinum iodide with moist silver
oxide. The reaction was carried out in a 300 ml, three necked flask,
equipped with a stirrer and 100 mm reflux condenser, and supported in a
heating mantle. About 0.50 gm (1.36 X 10-3 mol) of orange trimethyl—
platinum iodide was dissolved in 100 ml of benzene and placed in the
flask. Then a mixture of 50 ml of acetone and 20 ml of water was added
followed by approximately 0.01 mol of freshly precipitated hydrous
silver oxide. The latter was made by mixing a solution of 1.7 gm of
silver nitrate with a solution of 0.40 gm of sodium hydroxide followed
by filtration and washing with water. The mixture was stirred under
reflux for an hour, cooled, and the phases were separated. The benzene
phase was dried for an hour over anhydrous sodium sulfate, filtered, and
evaporated to dryness. The resulting white powder was recrystallized
from a 50 - 50 mixture of chloroform and ethanol.
Analysis, Calculated for (033)3PtOH: C, 18.96%; H, 4.19%; .Pt, 75.65%.

Found: C, 14.17p; H, 4.56;; Pt, 7J.37p. (conlound explodes on analysis.)

Trimethylplatinum Chloride
This preparation was carried out according to the method outlined
b3’1P0pe and Peachy (2) in which trimethylplatinum hydroxide reacted
w1thconcentrated.hydrochloric acid. About 0.25 gm of the hydroxide
was dissolved in 50 ml of benzene and placed in a 125 m1 separatory

fundiel. A mixture of 20 m1 of acetone and 20 ml of 37% hydrochloric

1?

acid was added, and the whole mixture was shaken for five minutes
before the phases were separated. The benzene phase was dried for an
hour over anhydrous sodium sulfate before being filtered and evaporated
to dryness. The white product was recrystallized from a 50 - 50
chloroform-ethanol solution.

Analysis, Calculated for (G13)3Pt01: C, 13.0870; 3, 3.29:5; Pt, 70.7375;

Cl, 12.90%. Found: 9,. 1.5.1.5;9; H, 3.17%; ft, 71.5615; Cl, 15.01».

Trimethylplatinum Bromide
This substance was prepared by the reaction of methylmagnesium

bromide with platinum tetrachloride. he preparation can also be
carried out in the same manner as for trimethylplatinum chloride. file
apparatus used for the methylmagnesium bromide reaction was the same as
that used for the preparation of methylmagnesium iodide except that the
drapping funnel was replaced by a capillary tube whose exit was placed
below the level of the ether covering the magnesium. The grignard
reagent was prepared by passing a slow and steady stream of methyl
bromide gas into the well stirred 100 m1 of ether covering 3.0 gm of
magnesium turnings for one hour until the solution had the familiar
color of methyl grignard. From then on the reaction and recovery of
the product were carried out in the same manner as for trimethylplatinum
iodide. The white product was recrystallized from chloroform.
Analysis, Calculated for (CH3)3PtBr: 0, 11.257}; 3. 2.537.; Pt, 61.0075.

Foundr C, ~11.0Bp;-h, «.3. 64;; 1"t,_60.c$4;b.

18

Unsuccessful Attempt to Prepare
Trimethylplatinum Fluoride

.About 0.20 gm of trimethylplatinum hydroxide was dissolved in 25 ml
of chloroform and stirred for 5 minutes with about 25 ml of 48% hydro—
fluoric acid. The phases were separated, and a grayish precipitate was
filtered from the chloroform. This substance could not be dried with»
out decomposing into metallic platinum. The wet product gave an infra—
red spectrum which was distinctly different from that of the starting
material; however, the substance was converted into trimethylplatinum
hydroxide upon standing for a week over concentrated sulfuric acid.

The reason for the apparent instability of the trimethylplatinum
fluoride may lie in the fact that the fluoride ion is very small and
holds its electrons tenaciously. Under these conditions the ha10gen
bridging which is in the other trimethylplatinum halides becomes
impossible with the fluoride. Therefore several molecules of water are
necessary to hexacoordinate the platinum. This would explain the ease
of decomposition when the waters were removed.

Pope and.Peachy (2) reported that their trimethylplstinum sulfate
and nitrate could not be prepared water free presumably for the same
reason that the fluoride could not be. Also it is well known that

lleither nitrate nor sulfate are good complexing agents; so the water

molecules were needed for coordinating the platinum.

Trimethyltriammineplstinum(I) Iodide

This substance was prepared according to the method of Gel'man and

19

Gorushkina (5). A small quantity, approximately 0.2 gm, of trimethyl—

platinum iodide was dissolved in 50 ml of dry benzene, and anhydrous
ammonia from a cylinder was passed through the solution for 5 minutes.
‘During this time a white precipitate formed and was collected on a
filter, washed with more solvent, and air dried.

Analysis, Calculated for [(033)3Pt(m13)3]l: C, 8.61%; H, 4.343;;

rt, 46.47%; N, 10.047». Found: C. 8.73%: 11.4.2774: Pt, 47.107é
N. 9.98%.

Trims thylbis(p2r’ ridine) iodOplatinum( I)
The method of Lile and Menzies (6) was used in this case in which

trimethylplatinum iodide combined directly with pyridine in benzene
About 0.25 gm of white trimetlwlplatinum iodide was dissolved

The solution was

solution.

in 25 ml of benzene and 2 ml of pyridine was added.
elowly evaporated to dryness, and a white crystalline product formed.

I t was washed with ether, and air dried without any further treatment.

The presence of pyridine was definitely shown by means of the infrared

Opectrum.
Analysis, Calculated for (053)3Pt(py)2i: C, 29.7179; H,.S.E4';b; N, 5.33%;

Pt. 37.15%; I, 24.15%. Found: C, 30.11%; H, 6.673;; N, 5.08%; Pt, 35.93%

I 0 23.89%.

The chloro complex was prepared in the same manner from triznethyl-

PIG-tinum chloride and was found to have the same infrared spectrum.

Trimethyl (2, 2' -bipyridine) chlor0platinmn{ I)

This substance was prepared in a similar manner to that of the

20

previous two compounds in which 0.37 gm (1.34 r 10"3 mol) of trimethyl—
platinum chloride was dissolved in 20 ml of chloroform and 0.21 gm
(1.34 $.10"3 mol) of 2,2'-bipyridine was added and dissolved. The
resulting solution was evaporated to 5 ml on a steam bath. Eben ether
was added until a white precipitate began to form. The product was
collected on a filter, washed with absolute ethanol, and air dried.
Again the infrared spectrum indicated that the desired compound had
formed.

Analysis, Calculated for (CH3)3Pt(bipy)Gl: C, 36.14“; B, 3.97%;

H, 6.497.; “$54975; 01.a.21,.. Found:C, 35.99%; H, 3.93%;

N, 6.62%; Pt, 45.31%; 01, 8.14%.

Cis—his(pyridine)tetrachlorOplatinum(IV)

The preparation of this compound was carried out according to the
directions of Foss and Gibson (ll). The apparatus consisted of a 250 ml,
three necked flask equipped with a short reflux condenser and a stirrer.
A solution of 0.01 mol of sodium hexachlorOplatinate(IV) was prepared
by dissolving 3.37 gm (0.01 mol) of platinum tetrachloride and 1.1? gm
(0.02 mol) of sodium chloride in 100 ml of water. This was placed in
the flask along with 1.58 gm (0.02 mol) of pyridine. The resulting
mixture was stirred for 8 hours, cooled and the yellow product was
collected on a filter. Evaporation of the filtrate gave more product
which was also collected. The combined precipitates were washed with
water, acetone, chloroform, and ether, and than air dried.

Annlysis, Calculated for (py)2Pt 014: C, 24.25%; H, 2.03%; N. 5-55?:

Pt.39.4256; 01, 28.64%. Found: c, 24.65;; 5. 1.821.; m, 5.467.; rt, $6.405:

01. 28.8813.

Dimethylmercury

This highly toxic compound was prepared according to the method of
larvel and Gould (15) and was used in the unsuccessful attempts to
prepare tetramethyl platinum. (See appendix.) The apparatus consisted
of a one liter, three necked flask supported in a heating mantle,
equipped with a stirrer, reflux condenser, and drapping funnel as shown
in FIGURE 7. This was used to prepare methyl grignard reagent for
subsequent reaction with mercuric iodide. The methyl grignard was

s
prepared by drcpwiee addition of 180 gm (1.27 mol)of methyl iodide

dissolved in 350 ml of anhydrous ether to 80 gm (1.23 mol) of well
stirred magnesium turnings under 150 m1 of ether. When the addition

was completed, the solution was siphoned through glass wool into a second
one liter, three necked flask equipped with a stirrer and reflux conden-
ser. Then 170 gm (0.875 mol) of mercuric iodide was added in portions

of approximately 2 gm at a time so that the exothermic reaction with the
grignard reagent would not cause the mixture to erupt through the reflux
condenser. When the addition of the mercuric iodide was completed, the
mixture was heated under reflux and with stirring for 12 hours. All
these operations had to be carried out in an efficient hood in order to

Quickly remove any toxic fumes which might have escaped from the appan-~

atus.

m
Eastman C. P. grade used as obtained.

22

Hydrolysis of the reaction mixture was carried out in another one
liter, three necked flask equipped with a labline high speed stirrer, a
reflux condenser, and a large dropping funnel. About 250 ml of water
was placed in the flask, and the grignard solution containing the
dimethylmercury was transferred from the reaction flask to the dropping
funnel. The stirrer was turned on to high speed, and the grignard
solution was added drapwise to the water. In this manner the exo—
thermic hydrolysis reaction was carried out without eruption of the
grignard reagent. Also the use of a high speed stirrer made finely
divided magnesiun hydroxide which passed through a separatory funnel
easily during the separation of the phases. The aqueous phase was
shaken with two 100 m1 portions of ether, and these were added to the
original ether phase. The combined ether extracts were dried over
anhydrous sodium sulfate before being distilled through an 8 inch helix
packed column equipped with a reflux head. When only 50 ml of solution
was left in the distilling flask, the solution was transferred to a
small fractionating column equipped with a "cow" arrangement for collect—
ing the product in small ampoules for storage. The dimethylmercury was
collected at 90°C and formed tiny, non-adherent globules as it condensed.
No analysis was carried out on this substance since it appeared to
behave as described in the literature, and was used soon afterward

to prepare methylsodium.

23

Deuterated Trimethylplatinum Iodide
(GDs)sPtI

The preparation of this compound was undertaken with the same
apparatus and technique as that used for normal trimethylplatinum iodide.
The deuterated methyl iodide, 0031, was prepared by Tracerlab Inc. and
used without further treatment. Of all the hydrogens present at least
95% were deuterium.

Three gm (0.020? mol) of deuterated methyl iodide was mixed with
25 ml of anhydrous ether and placed in the drapping funnel. (See FIGUhE
7.) One half gm (0.0207 mol) of magnesium turnings was placed in the
flask and covered with 25 ml of anhydrous ether. The grignard solution
was prepared in the usual manner (ref.; the preparation of trimethyl—
platinum iodide), filtered through glass wool, and diluted with 50 ml
of dry benzene. The solution was cooled in an ice bath, and 1.75 gm
of platinum tetrachloride were added in portions of about 0.3 gm to the
well stirred mixture. Stirring was maintained for 4 hours at 0°C,
followed by recovery of the product in the usual manner. A total of
0.50 gm (1.33 x 10-8 mol) of product was obtained for a 26% yield.
Unfortunately, most of the expensive grignard solution was wasted
producing platinum black; however, such a side reaction can usually not
be avoided. In addition to the main product, approximately 0.02 gm
of an unidentified red platinum alkyl iodide was recovered along with
some unstable iodinated platinum complexes which decomposed upon standing.
Analysis, Calculated for (003)3Pt1: C, 9.57%; ft‘ 51.88%. pcund;

C. 9.70fi;.Pt, 51.87fi.

24

The deuterated trimethylplatinum iodide served as the starting
material for deuterated trimethylplatinum hydroxide from which the
chloride and bromide were prepared in the same manner as for the
corresponding normal compounds. Also the bis-pyridine and triamnine
complexes were prepared from the iodine.

Analysis of (03$)3Pt0ii, Calculated: C, 13.5373; Pt, 73.30%. Found:
C, 13.94%: Pt, 72.7lp.
Analysis of (003)3PtCl, Calculated: C, 18.65%; Pt, 58.55%.
Found: C, 13.24%; Pt, (insufficient sample available)
Analysis of (0113,)aPtBr, Calculated: C, 10.94%; Pt, 59.3036. Found:
C, 11.24%; Pt, (insuffient sample available)
Analysis of (CD3)3Pt(py)21, Calculated: 0, 29.217»; 3:, 35.21.51»; N, 5.247..
ibund: C, 29.06%; Pt, 36.?0p; N, 5.74%.
Analysis of KCfismPflNEgflgll, Calculated: C, 8.43%; Pt, 45.68%;
N, 9.83w. Found: 8.10%; Pt, 45.02%; N, 10.02%.
HydrOgen determinations were not listed because of uncertainties in

the deuterium content of the deutero-trimethylplatinum compounds.

Trimethylplatinum Deutero-hydroxide, (CHg)3PtQD
The apparatus and method used were the same as those for the normal
hydroxide except that the silver oxide was rinsed with absolute ethanol
and ether in order to remove most of the water present. Approximately
0.20 gm of trimethylplatinum iodide was dissolved in 100 ml of dry
benzene, mixed with 20 ml of dry acetone and 5 ml of 020, and reacted as
previously outlined for normal trimethylplatinum hydroxide.

The product was a mixture of both the normal trimethylplatinum

 

 

m
tn

hydroxide and of the deutero—hydroxide with the latter predominating
according to the infrared spectrum. Several other attempts were made
to prepare the pure deutero—hydroxide; however, these resulted in

failure.

Beuterated Trimethylplatinum Deutero—hydroxide, (003)3Pt0D

An attempt was made to prepare this compound in the same manner
as that of the previous compound, but this produced only normal
deuterated trimethylplatinum hydroxide, (CD3)3PtOH.

A partially successful method involved.preparation of the hydrous
silver oxide in 230 to minimize the presence of normal hydroxide. This
was done by cutting approximately 0.2 gm of metallic sodium into pieces
about 1 mm on an edge, and storing them under pentane to minimize
hydroxide formation. Eben the pieces of sodium were allowed to react
one at a time with 5 ml of 030 in a 50 ml beaker inside a dry box.

The use of the very small pieces minimized the chances for a violent
reaction. The sodium deutero-hydroxide thus formed was mixed with a
solution of 0.5 gm of silver nitrate in 2 ml of 220. The resulting
precipitate was washed with 2 ml of heavy water and then very quickly
transferred to the reaction flask. The reaction and recovery of the
product was carried out in the usual manner. In spite of all the
precautions used the product was mostly the normal hydroxide, but
enough deuter0~hydroxide was present to be detected in the infrared

spectrum.

03
0)

Preparation of Samples for Infrared Spectra

All the trimethylplatinum halides used in this work were soluble
in chloroform and in carbon tetrachloride but not enough to give
sufficiently intense spectra. for this reason solution spectra were
seldom run. Instead mulls of each substance were prepared using both
mineral oil and hexachlorohutadiene. In this manner sharp and intense
spectra were obtained.

The best spectra, though, were obtained by using the potassium
bromide pellet technique once a suitable hydraulic press became avail-
able. The quality and resolution of the spectra far surpassed those of
either the mull or the solution method. The only noticeable difference
between the spectra of a given compound in a mull or in a pellet was a
weak and poorly defined peak which appeared at 13.511with the pellet.
This appeared to be a spurious peak caused by some interaction of the
potassium bromide with the sample material. Also the pellets usually
showed weak bands at 2.&~ and 6.1;:which were caused by small amounts
moisture in the pellet.

The pellets were prepared in a dry box using a specially purified
and finely divided infrared grade potassium bromide which was obtained
from the Harshaw Chemical Co. The preparation of satisfactory pellets
depended entirely on thorough mixing which was carried out in an agate
mortar inside the dry box. Between 8 and 5 milligrams of sample, about
200 to 400 milligrams of potassium bromide, and 5 m1 of methylene
chloride were mixed together until the last of the methylene chloride

evaporated. Then the powder was ground for another minute after which

‘1

it was put into a.glass steppered bottle and then into a drying oven for
15 minutes at 110°C.

The powder, while still warm, was very quickly poured into the
Perkin-dimer pellet die. and the entire assembly was placed on the bed
of the hydraulic press. The plunger was pushed in only part way so
that evacuation of the sample space would not cause the powder to be
sucked into the vacuum pump. Evacuation was carried on for two minutes
before full pressure of 23,000 pounds per square inch (gage) was applied
to the powder. Full pressure was maintained for at least two minutes
before it was released. The 13 mm diameter pellet was removed, placed
in a small envelope. and stored in a dessicator over indicating
"Drierite“ before use.

Since the thickness of the pellet was only 1 to 1.5 mm. a reference
pellet of pure potassium bremide was not necessary. However. one diff-
iculty in the use of this technique is that Tyndall scattering was often
a nuisance in the 2 to 5 micron region of the spectrum. This was
caused by the necessity of using considerably more platinum alkyl
compound for good intensity of spectra than would be required of a
completely organic substance. As a result the pellets became somewhat
Opaque in the short wavelength region of the spectrum. Fortunately

though, this was not too serious a problem.

Obtaining the Infrared Spectra
The spectra of all the samples were run on a Perkin—Elmer Model 21.

double-beam instrument using sodium chloride optics for the 2 to 14.6

micron region and cesium bromide optics for the 25 to 37.5 micron region.
For the region between 14.5 and 25 microns the Perkianlmer anracord
in the rhysics Department was used with potassium bromide Optics.

The most satisfactory spectra were obtained with the Model 21
instrument and sodium chloride Optics. The spectra obtained with the
same instrument and the cesium bromide optics were of very low intensity,
and the peaks were poorly defined. Very few of the compounds studied
absorbed in the 14.5 to 25 micron region.

The calibration of the Model 21 instrument in the 2 to 14.5 micron
region was accomplished by means of the spectrum of polystyrene. The

following corrections were required at the wavelength given in Ihble l.

 

@able 1
Wavelength inafi- Correction 0“)
3.20 +0.10
3.41 +0.10
5.07 +0.07
6.17 +0.07
6.63 +0.06
8.62 +0.04
9.70 +0.02

11.02 +0.01

Correction in Hicrons

40.104

00.09 4

+0e08 1

+0e0? 1

+0e06 “

+0.05 .

+0.04 ‘

+0.034

+0002 "

+Oe01 J

 

0.00

29

 

 

2.

4.0 ' 530 ' sfo 1 10.0 12.0 1430

Wavelength in Hicrons

Calibration Curve for Perkin—Elmer Model 21 Spectrograph

FIGURE 8

30

RflSULTS

The infrared spectra of the trisethylplatinum halides were ebserved
to be very simple in spite of the fact that a total of 174 vibrations
are possible according to the selection rules listed by Herzbsrg (8}.
The absorption peaks of all the trimethylplatinum halides and their
deuterated counterparts are given in the following tables using the

corrected values for the wavelengths and frequencies.

 

Table 2
(origami (CD3)3PtI

A (42 V cm'1 _1: A. San} I/(cm’lz 1“1

3.39 2950 m 8.45 2899 vw

3.48 2874 m 4.54 2203 m
3.63 2755 w 4.70 2128
7.11 1406 m 4.77 2096
7.98 1253 s 4.90 2041
8.21 1218 s 6.67 1499
7.97 1255

8.71 1148 w

9.74 1027 m

9.98 1002 m

10.40 962 e

10.52 950 m

10.69 986 s

Q
Intensity; vs = very strong. a = strong, m E medium, w a weak
vw'= very weak, (sh) a shoulder

% Transmission

p Transmission

1001'

80'

70q

50-»

504
40-
30«
201
10*

V

‘

 

100 .

80"
70‘
sol
50«
404

20‘

1

V

f

 

10

1b

U‘Ieb

5 6 ’7 (To 10

Spectrum of (053)3Pt1

A A A A
V V ' v

Wavelength in microns

Spectrum of (003)3Pt1

A A
V v

Wavelength in microns

FIGURE 9

578 910

‘P

15

Table 3

(083)3Pt8r (003)3Pt8r
M42 floor“ _I_ M8 mam-1)
3.40 2941 s 3.44 2
3.48 2874 s 4.53 2208
3.61 2770 m 4.70 2128
7.11 1407 s 4.76 2101
.7.94 1259 s 4.89 2045
8.18 1222 vs 6.89 1451
7.96 1256
8.69 1151
9.71 1030
9.82 1018
10.33 968
10.46 956
10.62 942

..a:....:k

‘8‘
A
m
D"
V

m

Spectrum of (083)3Pt8r

$1 Transmission
.5
5’

30-1!

 

20
10

is
d
d
a

56' 7 8 9101112

”1
bee

Wavelength in microns

‘

1007 Spectrum of (003)3Pt8r

90 d

V

80 ‘F
70 u

60 «-

40 u

f Transmission
8

30 0
20 ..

 

10

O
~1-
1F
0
0’ j»
1.
db
db
1.

8 9 10 11 12

Wavelength in microns

FIGURE 10

0
D

13 14

13 14

15

Table 4

10.58

(083)3Pt01 (093) 39101
i“ -12 _L Kat is 23-12
2950 m 3.45 2899
2874 m 4.53 2208
2770 w 4.70 2128
1406 m 4.76 2101
1259 m 4.89 2045
1225 s 7.96 1256
8.68 1152
9.69 1032
9.94 1006
10.29 972
10.44 958

945

uitaid:EOQE:IH

Spectrum of (083)32t01

at
0

Transmission
88

 

a!»
.888

4b

l l
v

8 9 10 11122 13131

‘D

N
.p.
0qu
0}
fish

Wavelength in microns

Spectrum of (093)3Pt01

CD
0
#

83
.;

fi Transmission
68

 

3‘9“

...s
O

Wavelength in microns

FIGURE 11

35

T5

36

The spectrum of trimethylplatinum hydroxide had a few more peaks
than did the trimethylplatinum halides; however. the total number of
peaks was far below that expected on the basis of symmetry and the

number of atoms. The spectra are listed in Table 5.

E
a s 0 d
323588588

«JQQQNGAUN

(033)3Pt03
I" cm’ll

3559
2941
2865
2778
1410
1399
1368
1271
1238

873

858

719

4
BuBBBBmmoulH

4

DE
A
a
:3‘
V

Table 5

Agut
2.80
3.46
4.56
4.71
4.76
4.90
7.13
7.51
7.96
8.64
9.63
9.72

10.31
10.45
13.85
15.10
15.41
18.59

(0D5)3Pt08

140111-12

3571
2890
2193
2123
2101
2041
1403
1332
1256
1157
1038
1029
970
956
722
663
648
538

I...

:Iigoiflizjfldan‘o‘oll

(sh)

37

’8

fl Transmission

0|
0

 

 

3

bid.

4

$1-

5.

5

38

. 1 . .
Spectrum of ‘083)3Pt08

 

 

L

6* 7 8 9 10 11 12 13 14 15

A

Wavelength in microns

Spectrum of (CD3)3PtQH

 

 

6 7 8 '9 10 11 12 13 i4 15

lavelength in microns

FIGURE 12

...
HGQQQQQNUNU
O (EMF-40m b

11.74
14.05
16.89
18.04

(033)3Pt01)

'Vgcm'lz

2933
2865
2778
2625
1414
1397
1374
1269
1259
1236
872
852
712
592
554

EBDIOIIH

‘18
hrs.
I C
D’ 5’
VV

4
Bo

m(sh)

VI

Table 6

E

0100!“)

WQWGD—‘CD

u>u>a«q-d-d~a#s¢»éqbcsoa
s: asu:¢»N:hum
5.2: 'q-qcn~o::

10.31
10.45
14.05
15.15
15.31
18.20
18.79

(c113) anon
is cm'lz

2907
2639
2198
2128
2105
2045
1406
1374
1337
1255
1159
1037
1027
970
957
712
660
653
549
532

I...

4
2580:8053

BB‘Imm

39

100*?

80«-
70-»
60..

50"

p Transmission

30‘

f

20<

f

10‘

 

100 ‘7
90¢

80'

I

701

V

O
0

Transmission
2

M
0

db

“1’

Spectrum of (083)3Pt08«+ -OD

 

 

d.

I A a
v

A I A

Iavelength in microns

Spectrum of (CD3)3PtOH «n- 70D

 

 

 

67 891011121314

40

-i-

15

 

 

mal-

h‘.

Wavelengflh in microns

FIGURE 13

p
oft

41

The trimethyltriammineplatinum(I) ion, with its 25 atoms, should
have a total of 69 vibrations; however, only 11 absorption peaks were

observed. These are listed in Table 7.

B
A
D
:3‘
v

[(083)32t(.~183)3]1
AM 11282). ..L
3.04 3289 s
3.10 3226 m
3.16 3165 I
3.41 2933 m
3.49 2865 s
3.60 2778 w
6.23 1590 m
7.09 1410 w
7.93 1261 m
8.15 1227
8.27 1209 vs

Table 7

L‘s.)

3.03
3.10
3.17
3.45
4.56
4.77
4.89
5.92
6.30
7.16
8.25
9.70

10.43
10.60
10.70

3300
3226
3155
2899
2193
2096
2045
1689
1587
1397
1212
1031

959

944

935

[(023)3Pt(1183)3] 1
Zuni). .L.

aBanBIBEu

V8

m(sh)

42

% Transmission

fi Transmission

 

 

 

43
Spectrum of [cayaptmask] I

 

 

A l A A A... A A L A .
T V V V V V v v 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15

Iayclength in microns

Spectrum of E®3)3Pt(N33)3]I

 

 

 

 

20 fi

10 d!-
0 : 3; t : : 3 : : :7 : :7 4:
2 3 4 5 6 7 9 10 11 12 13 14 15

6
Wavelength in microns

FIGURE 14

44

The Spectrum of cis~bis(pyridine)tetrachlor0platinnmélv) would
be expected to have a total of 15 vibrations in addition to those of
the pyridine itself, of which there are many. Only a few extra
vibrations were observed, and some of these were believed to be
overtone or combination vibrations. The others were in the skeletal
region beyond 15 microns. The epectra of pyridine and of

cis-bieryridine)tetrachlor0p1atinum(IV) are shown in Table 8.

Table 8

pyridine (liquid) ci s-(py)2Pt014

Am I" and] i 19“} VS on?”
2.52 3966 I 3.22 3106
3.29 3040 m 3.27 3056
3.34 2994 m 3.47 2662
5.09 1965 I 5 . 00 2000
5.26 1901 I 5.32 1660
5.42 1645 W 5. 59 1769
6.16 1623 W 5.97 1675
6.30 1567 m 6 .25 1600
6.36 1572 8 6 .40 1563
6.54 1529 W 6.76 1475
6. 79 1473 m 6.61 1466
7 .00 1429 8 6 . 91 1447
6 .26 1211 m 7 .20 1369
6.78 1139 m 7.46 1340
9 .40 1064 m 6.06 1241
9. 75 1026 m 6 .33 1200
10. 13 967 m 6.67 1153
13.41 746 B 6.73 1145
14 .26 700 V8 9. 15 1093
14 . 90 672 8( 8h) 9 . 37 1067
16.66 600 8 9.64 1016
24.60 404 8 10. 69 936
11.81 647
13.01 766
13. 22 756
14.53 666
14.76 676
15.26 656
16 .02 555
21.33 466

#1501110516m359033912flalH

46

Spectrum of pyridine
100

30 -
! ~ A
‘1
2: F

so ..

 

 

40'?

% Transmission

m4)

 

 

 

A
V

10

ID

1'4 Ts

CC"
to
H...
H
Edi
...-I
(A?

6' 7

(L

01”
#5..
UHF

Wavelength in microns

Spectrum of cis-(py)2Ptcl4
100 ..
90 W

so 1, n

70 0

 

 

 

 

% Transmission
3‘

 

 

 

 

‘ A I ‘ I I I ‘ .
I I v I V I w w r

53 1 56 7 8 9101115131415

Wavelength in microns

FIGURE 15

47

A similar situation to that of the previous compound was found in
the spectra of trimethylbis(pyridine)iod0platinum(l) and the correspond—
ing deutero-trimethyl compound. Only a very small number of extra
peaks were observed besides those of the methyl groups and of pyridine
itself, even though a total of 42 vibrations are possible. The

spectra of both compounds are listed in Table 9.

 

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FIGURE 16

50

D ISCU SSION

A comparison of the spectre of the trimethylplatinum halides and
the corresponding deuterium substituted compounds shows without any
question that the few vibrations observed are only the carbon—hydrogen
stretching and deformation frequencies of the methyl grows. No
platinum-carbon or platinum-halogen vibrations of any kind were
observed. In addition, the spectra of the trimethylplatinum halides
show some very close similarities to those of the methyl halides (8).

The peaks at 3.39 and at 3.48 microns are quite obviously those
of the carbon-hydrogen stretching vibrations, while those at 7.1, 8.0.
and 8.2 microns are all carbon-hydrogen deformation vibrations. The
peak at 3.63 microns is an overtone of the of the unsymmetrical C - H
deformation at 7.11 microns. There are no appreciable shifts in any
of the C - H stretching frequencies or in the unsymetric c - H
deformation mode with the change from chloride to bromide to iodide.
However. there are slight shifts in the other two C .. 8 deformation
Peaks upon changing the halogen. file assignments of the various peaks

are given in Table 10.

51

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52

The agreement between the observed and calculated stretching
frequencies for the trimethylplatinum halides and their deuterated
equivalents was of the order of 175. (See appendix.) The same was true
for the unsymmetric C - H deformation frequency; however, the agree-
ment for the latter two 0 - H deformations was in the range of 4%.

These agreements are of the same order of magnitude as those for the
.nonlal and deuterated methyl halides. The assignment of the first four
vibrations is based upon the comparisons with those of the methyl halides
in which the agreement is very close. The assiment of the symmetric
C — H deformation is based on the fact that the intensity of this peak
remains the same regardless of which halogen is present. It is, in
addition. a rather intense peak in most methyl compounds as pointed out
by Bellamy (9) who also reports that the position of the peak can vary
considerably depending on the substituents attached to the methyls. For
example the peak for tetramethyltin is at 8.41 microns. methylsilane
compounds at 8.00 microns. methyl chloride at 7.38 microns. and methyl-
amine at 7.05 microns.

The other C - H deformation peak at approximately 8.00 microns is
a degenerate deformation since there are three such modes possible with
a methyl group attached to a heavy atom with resulting 03v symmetry.
However, the location of the peak does not agree with the third degener-
ate mode, or the methyl rocking frequency of the methyl halides which
varies with the halogen; 8.38 microns for fluoride, 9.85 microns for
chloride, 10.50 microns for bromide, and 11.86 microns for the iodide.

In the case of the trimethylplatinum halides. the change in frequency of

58

this degenerate C — H deformation is very slight with the change in
halogen; however, the intensity of this peak shows a marked decrease
upon changing from iodide to bromide and then to chloride. This peak
may very well be the methyl rocking frequency since the methyls at all
times are attached to platinum which of course has a constant mass and
electronegativity rather than to atoms whose masses and electronegativi-
ties can vary as with the halogens.

The only vibration not accounted for is the methyl-platinum stretch-
ing mode which does not seem to occur in the region studied. The
reason for this is not known, but may possibly be the result of having
three halogens around each platinum as well as the three methyls. 0n
the other hand. the methylsilanes (9). dimethylmercury. dimethylsinc.
and dimethylcadmium have a metal—carbon stretching frequency (12)(13).
Such a vibration would certainly be expected and would appear in the
region of 20 microns according to an expression formulated by Linnett
(14) for the stretching force constant of a chemical bond. From this
the frequency or wavelength can be calculated. 1n the spectra of the
trimethylplatinum halides there was not the slightest hint of any
carbonpplatinum stretch vibration.

In the spectrum of the deuterated trimethylplatinum halides,
several very”veak bands were noted. These are most likely caused by
the vibrations of the residual normal hydrogens which are present to
the extent of 5% of all hydrogens in the molecule. Also interaction
between the normal hydrogens and the deuteriums may cause some of the

Peaks to appear.

54

The spectrum of trimethylplatinum hydroxide is similar in several
respects to the spectra of the trimethylplatinum halides; namely. the
same assignments for all the c — H stretch and deformations apply to the
Trimethylplatinum hydroxide. In addition there is a strong 0 — H
stretching vibration and what is believed to be a Pt - 0 stretching
vibration as well as two unidentified C - H deformation vibrations.
Deuteration of the hydroxy group caused the expected shift in the O — H
stretch and in the Pt - 0 stretch as well. There was no indication of
any 0 - H deformation vibration whatsoever. The assignments of the

spectral peaks of trimethylplatinum hydroxide are listed in Thble 11.

 

 

Table 11
(033)3th (magma Assignment
2.81 3.79 0 — H stretch
3.40 4.55 Unsymmetric (degerate) c — H stretch
3.49 4.75 Symmetric G.— H stretch
3.60 4.89 Overtone from unsymmetric C - 8 deformation
7.09 7.07 Overtone from Pt - O stretch
7.15 9.74 ‘Unsymmetric (degenerate) C — H deformation
7.31 7.48 Unidentified
7.87 10.31 Degenerate C — H deformation (methyl rocking)
8.08 10.45 Symmetric C - H deformation
11.45 15.15 Unidentified C - H deformation
11.65 15.31 Unidentified G - H deformation

13.91 14.05 Pt - 0 stretch

55

The assignment of the 0 - H stretch is quite easy to make since the
peak is very intense and is well known to occur in the 2.7 to 2.9 micron
region of the spectrum (9). The lack of an 0 — 8 deformation vibration
seems unusual especially since this type of vibratien occurs in alchols
and phenols although there is often some uncertainty concerning its
locatien (9). .At first it was thought that the peak at 7.28 microns
was an 0 - H deformatien; however. this peak did not shift appreciably
upon deuteration of the hydroxide. A.shift to the 9.5 - 9.7 micron
region was expected, but none was observed. This peak at 7.28 microns
was then thought to be an overtone or combination peak, but all attempts
to find a correct cembinatien failed. The peak shifted to 7.48 microns
in both the (GD3)3Pt08 and (CD3)3PtQD, and could not be accounted fer on
the basis sf deuteration of either the methyl groups or the hydroxide:
so this peak remains unidentified.

The peak at 11.46 microns with the shoulder at 11.74 microns is
definitely a C - H vibration because deuteratien ef the methyl groups
causes the peak to shift to 15.15 microns and 15.31 microns which is in
the range expected for such a change in mass of the vibrating atoms.
However, it is not knewn just what kind of c - H vibration this is since
only two symmetrical and three degenerate G — H modes are pessible for a
methyl group attached te a heavy atom, and all of these are accounted for.
Apparently there is some kind of interaction between the nethyls, the
Platinum, and the hydrexides, to produce this particular vibration as
"11..perhape, as that at 7.25 microns.

The assignment of the peak at 13.91 microns to a Pt - 0 stretch is

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based on the fact that no shift occurred in this band upon deuteration
ef the methyls, but a slight shift to 14.05 microns took place with
deuteration ef the hydrexide. The observed shift agreed to within 2%
of that expected for a Pt — 0 vibration in which the OH or 0D group is
considered as a peint mass. Such approximations have been found to be
very good (8).

in addition, the peaks at 16.89 microns and 18.04 microns in
(083)3Pt00 and at 18.20 microns and 18.79 microns in (CD3)3PtOD are all
unidentified because their locations appear to be random. Also these
peaks appear only with the deuterated hydroxide which is mixed in
substantial quantity with the normal hydroxide. This might possibly
result in interactions which cause these random peaks.

The weak peaks in the (GD3)3PtGH are the residual normal carbon—
hydrogen and carbon-hydrogen—deuterium interaction vibrations which
appear in the same positions as the deuterated trimethylplatinum halides.

The spectra of the trimethyltriamminoplatinum(I)iodide and its
deuterated trimethyl counterpart are essentially those of the methyl

groups and of ammonia itself. The assignments are given in Tnble 12.

57

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58

The assignments for the C - H vibrations are exactly the same as
those of the trimsthylplatinum halides. The N - H stretch and deform—
ation vibrations were essentially those of free ammonia because, with its
03v symmetry, two symmetric and two doubly degenerate modes are possible,
and were observed in this case. The assignments for the N — H stretch
modes are easily made since these vibrations have been characterized in
many compounds containing N83 itself amine groups (8)(9). The degener-
ate 3 - 8 deformation appears to vary somewhat depending on the symmetry
of the molecule and also upon the atom to which the ammonia is attached.
Quagliano (7g) reported degenerate N - H deformations in the 6 to 6.5
micron region for cis— and trans—d1chlorodiamminoplatinum(II). The
degenerate node for gaseous ammonia appears at 6.15 microns; so it
would seem that the assignment of the degenerate mode is quite certain.

The position of the symmetric N - H deformation appears to vary
in much the same manner as the symmetric C - H deformation of the methyl
group; namely, that the frequency can shift very drastically depending
‘upon what atom or group the ammonia is attached to. Gaseous ammonia
exhibits this mode at 10.6 microns (8). Quagliano (7Q)(7u) reports that
this vibration appears in the following positions for the compounds
listed: cis-(Nfiu)2Pt012 — 7.68 microns

trans—(Rhs)aftclg — 7.75 microns
[Co(N&6)5lO] 012 -- - 7.72 microns

[Gdansk] 012m — 8.52 microns

0n the basis of the above data the assignment of the symmetrical

59

N - 8 deformation seems certain. Quagliano also reports an 8H3 rock—
ing frequency in the region of 12.5 microns for the above four com-
pounds; however, none was observed for the trimethyltriammineplatinum—
(I) iodide. This would seem to be in keeping with the fact that the
absorption peaks in the trimethylplatinum complexes are essentially
those of the methyls and the free ligands rather than those of the
molecule as a whole plus the ligands and methyls.

The spectra of the trimethylbis(pyridine)iedoplatinum(l) and the
corresponding deuterated trimethyl compound are those of the methyls
and of pyridine. In addition, several overtone bands are present
which do not appear in the spectra of either the pyridine or the
trinethylplatinum halides alone. Since pyridine has so many absorption
bands, the spectra of the complexes consist mostly of these peaks: how-
ever, the peaks of the methyl groups are easily distinguished and the
same assignments are made for them as for the uncomplexed trimethyl—
platinum halides. In addition, the spectrum of cis—bis(pyridine)tetra-
chlerOplatinum(IV) showed that the same overtone peaks and spectral
shifts were present as for the trimethyl compound. The assignments
for the principal peaks are made in Table 13 along with a comparison

spectrum of pyridine.

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The (003)3Pt(py)21 exhibits the same spectrum with respect to the
pyridine peaks as does the (083)3Pt(py)21. The symmetric and degenerate
methyl 6 - D deformations appear as oxPocted at 10.65 microns and 10.37
microns respectively; however, the unsymmetric methyl 0 — D deformation
is masked by the three strong peaks which appear between 9.4 and 9.9
microns. The same vibration in the normal methyl compound is obscured
by the C = 0 peak at 6.96 microns, but the broad base of this peak is
still noticeable. In general the complexing with pyridine does not
affect the positions of the methyl 0 — H vibrations to any great extent.

The positions of some of the pyridine vibrations, on the other
hand, are very drastically shifted while some are shifted only slightly
or not at all. The pyridine C - H stretch peaks are shifted slightly to
shorter wavelengths even though the carbon atoms do not take part in the
bonding with the platinum so that there should not be much change in the
C — H stretch frequency. The same should hold true for the c - H deform-
ations and CI- 0 single bond vibrations as well; yet, these are the ones
which are most profoundly affected. The vibrations shifted the least
are the three strong peaks between 6.2 and 7.0 microns which are listed
as C 2 C and C = N ring stretching vibrations (15)(9). It is not known
‘which one belongs to the 0 = N vibration because the shifting seems to
appear equally strong for the 6.3 micron and 6.8 micron vibrations. This
means that the effects of the pyridine bonding to the platinum are
‘transmittod throughout the entire pyridine ring presumably ‘hy means of
the conjugated double bonds present and without affecting the force

constants of these bonds very much.

63

The peaks between 8.2 and 16.0 microns consist of several modes of
C — H deformation and two of C - C single bond vibrations, the latter
two being shifted to shorter wavelengths which would indicate a shorten-
ing of the bond distances upon complexing. Most of the shifting of the
0 - E vibrations is toward the shorter wavelength and of the spectrum;
however, two of them are shifted to longer wavelengths. The expected
shifts of all the C - H deformation peaks would be toward the longer
wavelengths since complexing would tend to withdraw electrons from the
ring and cause a slight weakening of the C - H bonds with a resultant
shift of the bond vibration to longer wavelength. Just why there
should be this inconsistency is not known.

In order to make sure that the observed shifts were not caused by
having the pyridine and the complexes in differing environments, the
spectra of both pyridine and of (033)3Pt(py)21 dissolved. in carbon
tetrachloride were obtained. The resulting spectra were no different
from those of pure liquid pyridine and of the (083)3Pt(py)2I in a
potassium bromide pellet.

The fact that the preceding spectra exhibit either methyl vibrations
alone or uncoupled methyl vibrations along with essentially free ligand
Ivibrations seems strange at first. This is especially so when it is
known that the dimethyl alkyls of zinc, cadmium, and mercury, and the
‘tetramethyl alkyls of tin and lead exhibit all the vibrations which are
expected of them on the basis of their symmetry preperties (12)(13)(18).
However, the difference between the spectra of the platinum alkyls and

tiuose of the zinc group might possibly be explained on the basis of the

64

ease of exchange of ligands in the complexes formed by platinum and by
these other metals.

It is well known that most of the square planar tetracovalent and

octahedral hexacovalent complexes of platinum do not undergo ligand
exchange very readily, and some complexes do not undergo exchange

reactions at all. What few reactions do occur though, often have to be

forced by means of elevated temperatures, very concentrated reagents,

catalysts, or combinations of these. On the other hand, the complexes
of the zinc group undergo very rapid ligand exchange reactions. The
complexes of the silicon group undergo hydrolysis reactions, but rates

of reaction are not known (19).

Since the platinum complexes, including those of the trimethyl—
platinum halides, are generally inert and unreactive it stands to reason
that the bonds between platinum and carbon, halogens and nitrogen,
should be rigid. Apparently this rigidity prevents the low energy inf rs.-

red radiation from causing any kind of Pt - C, Pt - X, or Pt - N
vibrations or coupling between the methyl vibrations and ligand vibra-

tions, so that only those vibrations alone are observed. The dimethyl
alkyls of the zinc group evidently do not have such rigid bonds just as
in the case of the complexes of these metals; therefore, the expected
vibrations are observed in the spectra of the zinc group alkyls.

The lack of any Pt - 1!, Pt - 0, Pt - X bonds might be explained on
the basis of extreme rigidity of such bonds, as stated earlier. However,
the presence of a Pt - 0 vibration appears to run counter to this argue-

ment since this vibration is very strong. The explanation for this

65

apparent inconsistency cannot be found in a comparison of the force
constants for the Pt - 0, Pt — N, and Pt - C bonds using the expression
of Linnett (14) because all these figures are of the same order of
magnitude. Also, such vibrations would be expected in the 17 — 20
micron range; yet, only Pt - 0 is observed, and that is near 14 microns.
The only noticeable difference between the Pt — 0 bond and the Pt - C
and Pt - N bonds is that each oxygen contributes two pairs of electrons
to two adjoining platinum atoms so that each platinum is hexacoordinated

for stability. Whether this is of any significance or not is not known.

66

SUMMARY

The trimethylplatinum halides, hydroxide, the ammonia and pyridine
complexes, and their equivalent deutero-trimethylplatinum compounds
were all prepared for study of their infrared spectra.

It was heped that the observed spectra could be correlated with
the known structures of the compounds or possibly be used to help
determine the configurations of the complexes. Neither of these
objectives could be accomplished because the observed spectra of the
trimethylplatinum halides consisted only of the vibrations of the methyl
group alone as though it were attached to a single heavy atom as in the
case of the methyl halides. The spectra of the ammonia and pyridine
complexes showed only the uncoupled vibrations of the methyls and of the
ligands themselves. In these latter instances there were shifts in some
of the absorption peaks of the ligands upon complex formation, but there
were essentially no shifts in the methyl peaks under the same conditions.
.Llso, no peaks were observed which could be classified as vibrations of
whole molecules.

The reason for this may be the fact that the very stable hexap
coordinate platinum compounds most likely have such very rigid bonds
'between the platinum and the carbons, halogens, or nitrogens that the
relatively low energy infrared radiation can not cause these atoms to
*vibrate. The one exception to this is the Pt - 0 vibration which occurs
in trimethylplatinum hydroxide. It is not known um this one vibration

can occur while Pt - C and Pt - N vibrations can not.

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67

Bibliography

Lichtenwalter, IL, Ph.D Thesis, Iowa State College, (1938)
Pepe, W. J., and Peachy, 3. J., J. Chem. Soc., _9_§, 571 (1909)
Menzies, R. C., and Overton, 5., ibid. 1290 (19%)

Bundle, 3. E., and Sturdivant, J. 11., J. Am. Chem. Soc. Q2, 1561
(1947)

Gel'man, A. D., and Gorushkina, 11., Dokledy Akad. Nauk 8.8.3.3., __7_,
48-4 (1947); C.A. $5, 9294b (1950)

Lile, I. J., and Menzies, R. C., J. Chem. Soc., lloa (123g)
Quagliano, J. V. et a1:

1, J. Am. Chem. Soc., 7, 211 (1955)
II, J. Phys. Chem., 9, 293 (1555)

111, J. Chem. Phys., :51, 1367 (1955)
IV, J. Am. Chem. Soc., 11, 5008 (1955)
v, my, _7_2, 5159 (1955)

H, m" 21, 6521 (1955)

VII, 1pm., 1:1, as? (1955)

VIII, 1119., 1:1, 839 (1955)

IX, Spectrochim. Acta, 2, 51 (1957)

x, J. Am. Chem. Soc., _7_9_, 1575 (1956)
XI, Spectrochim. Acta, .2, 199 (1957)
Jill, J. Am. Chem. Soc., 13, 3.313 (1957)
x111, 11151., .99, 525 (1958)

XIV, 151m, m, 527 (1958)

XV, Spectrochim. Acta, 1;, .339 (1958)

(p)
(q)
(r)
(s)
(t)
(n)
(V)

10.

11.
12.
13.
14.

15.

16.
17.
18.
19.
20.

21.

68

XVI, J. Am. Chem. Soc., 99, 5015' (195d)
XVII, Spectrochim. Acta, 1}, 31 (1955)
XVIII, in press.

XIX, Spectrochim. Acta, in press.

XX, J. Am. Chem. Soc., 1, 8818 (1959)
XXI, ibid., 321, 3521 (1959)

XXII, ibid., 31],, 3824 (1959)

Herzberg, 6., Infrared and figmgg Spectrg 9f Pglyatomig Molegules,
D. van Nostrand Co., New York, 1945

L. J. Bellamy, 31;; Iggrged §pectra 3f 99321;; Noleculeg, John Iiley
and Sons, New York, 1958

Kharaech, N. 8., and Ashford, T. A., J. Am. Chem. Soc., 55,, 1733
(1955)

Foss, N. 3., and Gibson, C. S., J. Chem. Soc., 301 (.1951)
Gutowsky, H. S., J. Am. Chem. Soc., 2),, 3194 (1949)
Gutowsky, H. 8., J. Chem. Phys., _11, 128-138 (1949)
Linnett, J. 11., Quarterly Revs., 1, 73—90 (1947)

Randall, H. 11., Mean, 11., Fowler, R. 6., Dangl, J. 3., M13229.

Determination 2; Mg §tmctugeg, D. Van Nostrand Co. New York,
1949

Marvel, C. S., and Gould, V. 1.., J. Am. Chem. Soc. 51, 154 (1922)
Bundle, R. E“, J. Am. Chem. Soc., 59, 1327—31 (1947)

Sheline, a. K., and Pitzer, K. 5., J. Chem. Phys. is, 595 (1950)
Tanbe, 11., Chem. Revs., 52, 69 (1952)

Doyle, J. 3., Private Communication.

Gilman, 11., and Lichtenwalter, 14., J. Am. Chem. Soc., 33,), 3085
(1938)

Lichtenwalter, 11., Iowa State Coll. J. 551., .15, 5'7 (1939)

23.

25.

26.

27.

69

Bundle, :1. 2., and Holman, A). J., J. Am. Chem. Soc., _7_1,, 3264
(1949)

Illuminati, G., and itundle, R. 11]., ibid., 11, 3575 (1949)

Gilman, 11., Lichtenwalter, IL, and Benkeser, 3.. A., ibid., 15,
2063 (1953)

Gibson, C. 3., Evens, 11. V. 9., and Foes, id. 5., Nature 1.93.. 593
(1948)

Knap, C. P.. Ph.D Thesis, Michigan State University, (1958)

APPENDI C113

70

71

APPENDIX I

COMPAhISONS 0F OBSERVED AND CALCULATED PEAKS FOR
DEUTEBO-TRIHETBYLPLATINUM HALIDES, HYDBOXIDE,
AND THE PYBIDINE AND ANHONIA COMPLEXES.

The wavelength or frequency of an infrared absorption peak depends
on both the force constant of the bond and upon the reduced mass of the
vibrating atoms, as explained in the Theoretical section. The force
constant depends on such factors as the electronegativities of the
atoms and the bond distance. For a bond between two given atoms these
factors remain constant so that changes in the isotopic masses do not
change the force constant appreciably (8). However, the reduced mass
of the two atoms can be altered very drastically by a change in the
isotopic mass of one or both of the atoms. This is especially true
of bonds between hydrogen and the lighter elements like carbon, boron,
nitrogen, and oxygen. The substitution of deuterium for normal
hydrogen can change the reduced mass by a factor almost equal to 2.
This change can produce shifts in the spectra of 1-2 microns as were
actually observed in the case of the (CD3)3PtX compounds.

The reduced masses of the C - B and C - D bonds were calculated

from the equation:

A - fl_ (1.55 x 10"24 gm)
- “‘1 “ ‘2

where ml and n12 are the masses of carbon and hydrogen, and 1.66 x 10"24

gym is the weight of a hydrogen atom in grams. For a C - H bond As:=

4 24

...2 _ , ..
1.544 X 10 go, and for a C - D bond A:2.t156 A 10 gm,

72

The agreement between the observed and calculated wavelengths for
a C — D stretch vibration is of the order of 1% as shown by the follow-

ing sample calculation for (CD3)3PtI.

Azunguo"): 19,55 1 1914 in microns

n— v:—

c = 3 K 1010 cm/sec., k = force constant in dyne/cm,

,u. :. reduced mass in grams

A

3.39 microns for the assymetric C - H stretch

k = (M)3w) .-. M 30,5... x 10-24)
A 5.39
e 47.74 x 104 dyne/cm

14
Equivalent c .. D wavelength: A = W— = 4.51 microns

$4232 g 16“-
2.555 x 10

Observed C - D wavelength = 4.54 microns

Difference — 0.07 microns

sore-smug”

4.54

The calculations for the other wavelengths were carried out in the
same manner and are listed in Table 14. Calculations based on a
deuterated hydroxide group were carried out for both (0113);;th and

(CD3)3Pt0D.

73

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APPENDIX I I

THE ATTM’TM PLUIPARA'I‘ION 0F TEWTHYLPMTINUM

Tetramethylplatinum was first reported by Lichtenwalter (1) who
prepared it by the reaction of methylsodium with trimethylplatinum
iodide. me structure was later determined by Bundle (4) who showed
that the substance was a cubic tetramer with methyl groups bridging
the four platinums. (See figure 1.) Since the methyl groups do not
have sufficient electrons for coordinate covalent sigma bonds, nor
sufficient orbitals for dative pi bonds. the tetramethylplatinum can
be called an electronically deficient compound (17). This condition
should make the substance an even better acceptor for complexing
agents than the trimethylplatinum halides. It was with this idea that
the research project of preparing tetramethylplatinum and its complexes
was undertaken.

This author spent the better part of a year in trying to prepare
tetramethylplatinum by Lichtenwalter's method, and the only products
obtained were either platinum black, white trimethylplatinum iodide,
or a mixture of trimethylplatinum hydroxide and methoxide. The reason
for the failure did not become apparent until the hydroxide-alkoxide
mixture was prepared by reaction of methyllithium with orange
trimethylplatinum iodide followed by the hydrolysis of the reaction
mixture with methanol.

Up to this time the attempts involved the use of methylsodium

which proved to be completely unsuccessful. The first few attempts

79

produced only platinum black while later and more careful work resulted
only in recovery of white trimethylplatinum iodide. At this point a
review of the method might be in order, and the following passage is
quoted directly from N. Lichtenwalter's Ph.D Thesis.

"To a solution containing 4 gm of dimethylmercury in 60
m1 of benzene-free hexanes was added 1.5 gm of sodium. This
mixture was stirred for two days. The methylsodium formed
was forced by means of nitrogen pressure through a small tube
into a dry flask. Dry mercury was added to remove any par-
ticles of metallic sodium which might be present. The suspen-
sion was then forced over into another flask.

To this suspension of methylsodium was added 1 gm of
trimethylplatinum iodide, The reaction was stirred for 24
hours and then hydrolyzed by the addition of 2 ml of n-amyl
alcohol followed by ethyl alchol and finally water was added.
The hexane layer was separated, dried over sodium sulfate,
filtered, and evaporated to dryness. The residue was covered
With 20 m1 of petroleum ether (B.P. = 60-6506). After stand-
ing for thirty minutes, the pet. ether was filtered off and
concentrated slowly. Large hexagonal crystals of tetramethyl-
platinum were deposited with a yield of 0.32 gm or 46%. The
compound is a colorless solid, readily soluble in the cold in
benzene, acetone, ether, and pet. ether (B.P. = 60-68°C). The
compound has no melting point and decomposes with a slight

explosion on heating in an Open flame, but does not explode

80

with anything near the violence of hexamethyldiplatinum."

Lichtenwalter also reported that tetramethylplatinum in solution
reacted with gaseous HCl to produce trimethylplatinum chloride, but
did not mention whether any methane was collected or not. Several
other things are apparent in the previous account: namely, no indication
of color or physical state of the methylsodium was given, nor was there
any description of the state of subdivision of the metallic sodium used
to prepare the methylsodium. In addition, the last step of the reaction,
the hydrolysis with n-amyl alcohol, seems to be superfluous. The
reason for this is that the methylsodium is insoluble in hydrocarbons
while the product is readily soluble. Therefore, it should be a simple
matter to siphon out the hydrocarbon containing the product, rinse the
methylsodium with more solvent and siphon this also, then hydrolyze the
methylsodium with alcohol afterwards. In this manner the product
would not be subjected to possible reduction by the action of methyl—
sodium and possibly metallic sodium and alcohol.

This latter method was used by this author repeatedly without
success. Also different methods of preparation of methylsodium were
used in which dimethylmercury was allowed to react with.pieces of
sodium approximately 1 mm on an edge or with sodium sand prepared with
a high speed stirrer under boiling ligroin (B.P. :5 100°C). Several
other slight mouifioations of tecnnique were also used, but the sole
product was white trimethylplatinum iodide.

Finally an attempt was made with methyllithium even though

81

Lichtenwalter had reported that this reagent in other solution did not
work. Since methyllithium in ether is most likely an etherated complex,
there was a possibility that steric hinderance might have prevented the
reaction with the (Cdg)3Pti. Therefore, the reagent was prepared by
reaction of methyl iodide with finely divided lithium in ether. ‘hen
the ether was stripped off by distillation and pentane was substituted
so that the methyllithium was precipitated, and the (C83)3PtI could
react at the surface of the methyllithium. When the reaction was
finished a hydrolysis with methanol was carried out because the methyl-
lithium was found to be slightly soluble in the pentane so that the
product could not be siphoned out as in the case of the methylsodium.
The product consisted of a mixture of trimethylplatinum hydroxide and
trimethylplatinum methoxide as indicated by a C - O stretch.peak at 9.8
microns in the infrared spectrum. This mixture exploded upon analysis
just as tetramethylplatinum itself did.

Shortly afterwards the methyllithium reaction was repeated only
this time the excess reagent was destroyed by the addition of both
gaseous, and powdered, solid carbon dioxide. The product this time was
white trimethylplatinum iodide.

Following this, another attempt was made to utilize methylsodium.
This was done by mixing the orange trimethylplatinum iodide with
dimethylmercury together with sodium sand all under n—pentane and
stirring for two days. The pentane was siphoned out, and the product
once again was the white form of the starting material.

The orange color of the starting material is believed to be caused

m
(U

by traces of adsorbed iodine since this substance is present in the
reaction products of the methyl grignard used to make the (053)3Pt1.
The iodine most likely comes from the decomposition of some of the
unstable iodinated platinum complexes formed during the reaction. The
color difference cannot possibly be caused by crystal or molecular
structure differences because the XPBay powder patterns and infrared
spectra of the two forms are identical. The fact that the orange
color of the starting material was removed by a combination of metallic
sodium and dimethylmercury most likely meant that methylsodium formed
and subsequently reacted with the adsorbed iodine. In order to make
sure that the metallic sodium alone was not removing the orange color,
a pentane solution of orange trimethylplatinum iodide was stirred for
two days with sodium sand. Orange starting material was recovered.

The final attempt consisted of a reaction carried out in the same
manner as the previously described attempt to make tetramethylplatinum
except that only half of the pentane solution was siphoned out at the
end of the reaction. The product from this was the white form of the
starting material as usual. The remainder of the pentane solution in
the reaction flask was hydrolyzed by the dropwise addition of methanol
with stirring. The product in this case consisted of white trimethyl-
platinum iodide, trimethylplatinum hydroxide, and the trimethylplatinum
methoxide according to the infrared spectrum.

Once this last bit of information was known, this author began to
have serious doubts about the very existence of tetramethylplatinum.

These doubts were intensified by a comparison of the X—Ray "d"

83

spacings of tetramethylplatinum as determined in a single crystal
rotation pattern by handle (4), and those from a powder pattern of a
sample of trimethylplatinum hydroxide prepared by this author. In
addition Professor Doyle of the University of Iowa reported that he
was also unable to prepare tetramethylplatinum using Lichtenwalter's
method (20). The Xpfiav data are listed in Table 21. No intensities
are given because the two samples were determined by different methods;
however, a print of a powder pattern of tetramethylplatinum was obtain-
ed from Professor Sturdivant at the California Institute of Technology.
In this case the intensities of the diffraction rings were of the

same order of magnitude as those in the powder pattern of trimethyl-
platinum hydroxide.

The data in Table 21 show without a doubt that the two substances
are isostructural and are just about identical in size; however, the
evidence is not conclusive that tetramethylplatinum in reality is a
mixture of mostly trimethylplatinum hydroxide and the trimethylplatinum
amyloxide since n-amyl alchol was used to hydrolyze the reaction
mixture. The only way to prove this latter point conclusively would
'be to obtain a sample of what is supposed to be tetramethylplatinum
tand.obtain its infrared spectrum. This would show if any hydroxide or
C - 0 linkage*were present, and if so, would readily support the above
¢=ontention. However, all attempts to obtain such a sample met with
(nmnplete failure since all the people who were asked reported that they
D13 longer had any of the substance. These persons included Drs.

3- Lichtsnwalter, H. Gilman, and J. H. Sturdivant.

Table 21

"d" spacings for (033)3Pt0H
according to this author

“d“ spacings for (CH3)4Pt
according to R. E. Kindle

 

 

 

O O
7.17 A 7.18 A
4.14 4.11
-— 3.19
2.93 2.91
—— 2.69
2.54 2.53
2.39 2.3a
2.16 2.15
2.07 —
_ 1.98
__ 1.85
1.79 1.79
1.74 1.74
1.69 —
1.65 1.64
...—... 1.56
1.53 1.53
1.49
1.46 1.46
1.43 1.43
1.38 1.38
1.27 1.29
1.25 1.25

85

To date the only persons who have reported anything on the subject-
of tetramethylplatinum have been Gilman et al., and Rundleet al. (21)
(22)(23)(24)(25). Another worker in the field has been unable to
prepare the substance (20).

Several weeks after the last attempt had been made, an alternate
approach to the problem of tetramethylplatinum was tried. This
involved two attempts to produce a derivative of the substance directly.
The first attempt involved the reaction of methyllithium in n—pentane
with (Ch5)3Pt(py)21 in an effort to substitute a methyl group for the
iodine. The presence of the pyridine was for the purpose of providing
stabilization through stronger hexacoordination than could be achieved
by methyl bridging as in tetramethylplatinum itself. The only product
was [(Ciig)3l’t(py) I] 2 which had been reported earlier by Gibson (26).
Analysis, Calculated for [(CHJ)3Pt(py)I] 2 :C, 21.5%; H, 3.1%; N, 3.17»;
Pt, 43.7% r‘ound: C, 21.879; H, 3.370; N,.8.0$; Pt, 443.6%. This
result quite obviously shows that the pyridine was not as firmly
attached to the platinum as had been thought previously.

Accordingly, trimethyl(2,2'-bipyridine)chlorOplatinum(1) was
prepared. (See p. 19.) The 2, 2'-—bipyridine is a very strong chelating
agent and is not easily dislodged from the platinum except by thermal
decomposition at temperatures above 200°C (27). The use of chloride
instead of iodide was decided upon because of crystal energy consider-
ations favoring the formation of lithium chloride rather than the
iodide. Unfortunately all these considerations went for naught

because the product was unreacted starting material which was shown by

the infrared spectrum. This was confirmed by treating some of the
product with moist silver oxide followed by recovery of silver chloride.
Once this information was known, all further work on this line of
approach was abandoned.. 'hether or not success can be achieved

through work in a similar direction remains to be seen.

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