Catalytic synthesis of poly(arylmethylgermanes) by demethanative coupling: A mild route to σ-conjugated polymers

Article abstract of DOI:10.1021/ja981806q

A variety of poly(arylmethylgermanes) have been synthesized from aryldimethylgermanes in high yield via mild catalytic demethanative coupling using tetrakis(trimethylphosphine)dimethylruthenium as a convenient catalyst precursor. Polymerizations of germanes Me₂GeArH (At = phenyl, p-tolyl, p- fluoro, p-trifluorotolyl, p-anisyl, and m-xylyl) proceed in neat monomer at room temperature. Catalyst removal can be effected by treatment of the reaction mixture with air, which gives polymer yields between 70% and 100%. Alternatively, separation of the catalyst by precipitation of the polymers from THF solution with methanol gives lower yields, but of somewhat higher molecular weight material. The new polygermanes are characterized by ¹H NMR and by gel permeation chromatography (GPC) using both polystyrene standards and light scattering methods. Molecular weights calculated by polystyrene analysis fall in the ranges of M(w) = 3 x 10³ to 7 x 10³ and M(n) = 2 x 10³ to 6 x 10³. Values obtained from light scattering are approximately 60% and 82% higher, respectively, resulting in M(w) measured by SEC/LS in the range 5 x 10³ to 1 x 10⁴, with M(w)/M(n) ~ 1.3. The absorption spectra of the polygermanes exhibit λ(max) in the range 326-338 nm. Comparison of the properties of poly(phenylmethylgermane) prepared by catalytic demethanative coupling and Wurtz coupling of MePhGeCl₂ with sodium revealed no significant differences.

Full text of DOI:10.1021/ja981806q

9844
J. Am. Chem. Soc. 1998, 120, 9844-9849
Catalytic Synthesis of Poly(arylmethylgermanes) by Demethanative
Coupling: A Mild Route to σ-Conjugated Polymers
Sandra M. Katz, Jennifer A. Reichl, and Donald H. Berry*
Contribution from the Department of Chemistry and Laboratory for the Research on the
Structure of Matter, UniVersity of PennsylVania, Philadelphia, PennsylVania 19104-6323
ReceiVed May 26, 1998
Abstract: A variety of poly(arylmethylgermanes) have been synthesized from aryldimethylgermanes in high
yield via mild catalytic demethanative coupling using tetrakis(trimethylphosphine)dimethylruthenium as a
convenient catalyst precursor. Polymerizations of germanes Me2GeArH (Ar ) phenyl, p-tolyl, p-fluoro,
p-trifluorotolyl, p-anisyl, and m-xylyl) proceed in neat monomer at room temperature. Catalyst removal can
be effected by treatment of the reaction mixture with air, which gives polymer yields between 70% and 100%.
Alternatively, separation of the catalyst by precipitation of the polymers from THF solution with methanol
gives lower yields, but of somewhat higher molecular weight material. The new polygermanes are characterized
by 1H NMR and by gel permeation chromatography (GPC) using both polystyrene standards and light scattering
methods. Molecular weights calculated by polystyrene analysis fall in the ranges of Mw ) 3 × 103 to 7 × 103
and Mn ) 2 × 103 to 6 × 103. Values obtained from light scattering are approximately 60% and 82% higher,
respectively, resulting in Mw measured by SEC/LS in the range 5 × 103 to 1 × 104, with Mw/Mn ∼ 1.3. The
absorption spectra of the polygermanes exhibit λmax in the range 326-338 nm. Comparison of the properties
of poly(phenylmethylgermane) prepared by catalytic demethanative coupling and Wurtz coupling of MePhGeCl2
with sodium revealed no significant differences.
Introduction
chain conformation.5 One main difference between the Si and
Ge backbone polymers is that the latter exhibits a smaller band
gap.6 Polysilanes fluoresce with high quantum efficiencies,1a
and although the only reports of emission from polygermanes
are found in the patent literature,7 properties similar to those of
the polysilanes can be expected. Potential industrial applications
for these polymers include photoresists,2a,3a,8 third-order non-
linear optical materials,4 charge transport polymers,9 photocon-
ductors,9b microlithographic materials,10 and photoinitiators.2a
The primary synthetic method for making polygermanes is
via Wurtz coupling of diorganodichlorogermanes by alkali
metals. Although a variety of alkyl and aryl derivatives can be
used, there are severe limitations to this method. The high
molecular weight polymers are only prepared in low yields,
usually less than 25%,3a,5,11 and the synthesis is not tolerant of
many electronically active functional groups due to the harsh
reaction conditions.11 Other methods of preparation involve
dehydrocoupling polymerization using early transition metal
catalysts, which produces large amounts of cyclic oligomers,12
and from certain organogermylenes, which polymerize to give
Polysilanes and polygermanes are inorganic polymers with
interesting electronic and optical properties not normally as-
sociated with saturated polymers, arising from the delocalization
of σ-electrons along the polymer backbone.1,2 Although not as
extensively studied as polysilanes, polygermanes also exhibit a
red shift of λmax with increasing chain length,3 semiconductive
behavior upon oxidative doping,2c and significant nonlinear
optical behavior.4 As in the case of polysilanes, polygermanes
are thermochromic, exhibiting an abrupt increase in λmax below
a discrete temperature associated with changes in the polymer
(1) For reviews, see: (a) Miller, R. D.; Michl, J. Chem. ReV. 1989, 89,
1359-1410. (b) West, R. J. Organomet. Chem. 1986, 300, 327-346.
(2) (a) Mochida, K.; Nagano, S.; Kawata, H.; Wakasa, M.; Hayashi, H.
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23, 2099-2107. (b) Okano, M.; Mochida, K. Chem. Lett. 1990, 701-704.
(c) Mochida, K.; Hata, R.; Shimoda, M.; Matsumoto, F.; Kurosu, H.;
Kojima, A.; Yoshikawa, M.; Masuda, S.; Harada, Y. Polyhedron 1996, 15,
3027-3032.
(4) (a) Mochida, K.; Nagano, S.; Maeyama, S.; Kodaira, T.; Watanabe,
A.; Ito, O.; Matsuda. M. Bull. Chem. Soc. Jpn. 1997, 70, 713-716. (b)
Kodaira, T.; Watanabe, A.; Ito, O.; Matsuda, M.; Tokura, S.; Kira, M.;
Nagano, S.; Mochida, K. AdV. Mater. 1995, 7, 917-919. (c) Miller, R. D.;
Baumert, J. C.; Bjorklund, G. C; Jundt, J. H.; Jurich, M. C.; Looser, H.;
Rabolt, J. F.; Sooriyakumaran, R.; Swalen, J. D.; Twieg, R. J.; Cotts, P.
M.; Shulka, P.; Torruellas, W. E.; Schellenberg, F. M.; Byer, R. L. Polym.
Prepr., Am. Chem. Soc. DiV. Polym. Chem. 1990, 31, 304-305. (d) Miller,
R. D.; Schellenberg, F. M.; Baumert, J.-C.; Looser, H.; Shukla, P.;
Torruellas, W.; Bjorklund, G. C.; Kano, S.; Takahashi, Y. In Materials for
Nonlinear Optics: Chemical PerspectiVes; Marder, S. R., Sohn, J. E.,
Stucky, G. D., Eds.; ACS Symposium Series 455; American Chemical
Society: Washington, DC, 1991; pp 636-660. (e) Baumert, J.-C.; Bjork-
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J.; Sooriyakumaran R; Swalen, J. D.; Twieg, R. J. Appl. Phys. Lett. 1988,
53, 1147-1149.
(5) Miller, R. D.; Sooriyakumaran, R. J. Polym. Sci., Polym. Chem. Ed.
1987, 25, 111-125.
(6) Matsumoto, N. In Inorganic and Organometallic Oligomers and
Polymers; Harrod, J. F., Laine, R. M., Eds.; Kluwer Academic: The
Netherlands, 1991; pp 97-113.
(7) (a) Majima, Y.; Hiraoka, T.; Hayase, S. Japanese Patent 97241628,
09241628, 1997. (b) Majima, Y.; Nishizawa, H.; Hayase, S. Japanese Patent
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S0002-7863(98)01806-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/15/1998

Catalytic Synthesis of Poly(arylmethylgermanes)
J. Am. Chem. Soc., Vol. 120, No. 38, 1998 9845
moderate molecular weight products in yields up to 60%.11 In
addition, polygermanes have been synthesized in low yield by
electrochemical reduction of chlorogermanes.13
Table 1. Effect of Polymer Isolation Method on Molecular
Weight
methanol precipitationa
air workupa
We recently described a highly efficient ruthenium-catalyzed
process, which gives high molecular weight polydimethylger-
mane under mild conditions (25 °C) in essentially quantitative
yield.14 In this demethanative coupling reaction, germanium-
germanium bonds are produced with concurrent irreversible loss
of methane. We now report that this synthetic method can be
extended to produce a variety of poly(arylmethylgermanes) con-
taining both electron-donating and electron-withdrawing func-
tional groups on the phenyl ring. The polymerizations occur
in high yield under mild reaction conditions.
yield
yield
Ar-Ge
C6H5
p-C6H4F
p-C6H4CH3 54
(%)
Mw
Mn DPb (%)
Mw
Mn DPb
52
7900 6500 40
68 6200 4300 25
82 5700 5000 27
100 4600 3200 18
51 10100 8800 48
5500 4700 26
a Molecular weights determined by SEC/LS; values rounded to
nearest 100 Da. b DP ) Mn/(MW of repeat unit).
shown that this ruthenium compound is a convenient and readily
available precursor to the active catalytic species.14 This pre-
cursor is easily prepared by the reaction of MeMgBr reagent
with (PMe3)4RuCl2, and although it is air- and water-sensitive,
it is quite thermally stable. As shown in eq 3, the reaction
Results and Discussion.
Monomer Syntheses. Unlike their silicon analogues, ger-
mane monomers of the form Me2GeArH used in these poly-
merizations are not readily available. The obvious synthetic
approach would be to selectively displace one chloride from
dimethyldichlorogermane with an aryl group, using either the
corresponding lithium or Grignard reagent. However, this
approach does not give the desired selectivity and results in a
mixture of mono- and disubstituted aryl products. Thus, the
less direct, but high yield, route shown in eqs 1 and 2 was
utilized.
proceeds with concurrent evolution of methane. Although the
synthesis of poly(phenylmethylgermane) has been described in
the literature,2a,c,3c,4a,b,11,16 the substituted poly(arylmethylger-
manes) reported herein have not been previously prepared.
Preparations of polysilane analogues for all but the m-xylyl
derivative are described in the literature, albeit in much lower
yields.17
The polymers have been isolated from the catalyst by two
different methods. During all manipulations, the polygermane
products must be protected from room light to prevent photo-
decomposition because these materials are very light-sensitive,
especially in the presence of oxygen. In the first separation
method, the reaction mixture is dissolved in tetrahydrofuran,
then stirred in air (protected from room light) for ca. 30 min,
during which the ruthenium catalyst decomposes to a fine black
precipitate. The solution is filtered through a column of Celite,
and removal of the solvent leaves a gummy solid in nearly
quantitative yield. The second method involves dissolving the
reaction mixture in tetrahydrofuran, then precipitating the
polymer with a large excess of methanol. Interestingly, the
ruthenium species remains soluble, even after the polymer is
precipitated in air. Polygermanes obtained by this method are
white powdery materials that are not tacky. Yields from
methanol precipitation are generally in the 50%-60% range
and tend to have higher molecular weights, reflecting the partial
fractionation of the polymer based on solubility. For purposes
of comparison, three monomers were polymerized, then split
into equal portions for isolation by the two methods. The data
from these experiments are illustrated in Table 1.
The diaryldimethylgermanes are prepared in >95% yield from
dimethyldichlorogermane with excess Grignard reagent. These
products are air- and water-stable and are easily isolated and
purified. Selective cleavage of one aryl group with exactly 1
equiv of triflic acid15 yields the aryldimethylgermyltriflate,
which is not isolated but is reacted directly with LAH to provide
the desired Me2GeArH compound. The combined yield for
these two steps is typically 70%-93%. The only monomer
synthesis for which high yields were not obtained was the meta-
xylyl derivative. Even when the mixture of Grignard reagent
and dimethyldichlorogermane was refluxed for several hours,
the yield of diaryldimethylgermane was only 62% and the
combined yield for the triflic acid and reduction steps was only
56%. Mass spectrometry confirmed that a significant byproduct
of the Grignard reaction was the coupling product, 3,3′,5,5′-
tetramethylbiphenyl.
Demethanative Coupling of Me2GeArH. Polymerization
of the dimethylarylgermanes is accomplished by stirring ∼1 mol
% of (PMe3)4RuMe2 in neat germane monomer at room
temperature under a nitrogen atmosphere. We have previously
The GPC chromatograms for air and methanol treatments of
the phenyl polygermane are shown in Figure 1, revealing the
(12) (a) Aitken, C.; Harrod, J. F.; Malek, A.; Samuel, E. J. Organomet.
Chem. 1988, 349, 285-291. (b) Harrod, J. F. In Inorganic and Organo-
metallic Polymers; Zeldin, M., Wynne, K. J., Allcock, H. R., Eds.; ACS
Symposium Series 360; American Chemical Society: Washington, DC,
1988; pp 89-100.
(16) (a) Mochida, K.; Shimoda, M.; Kurosu, H.; Kojima, A. Polyhedron
1994, 13, 3039-3040. (b) Mochida, K.; Kimijima, K.; Chiba, H.; Wakasa,
M.; Hayashi, H. Organometallics 1994, 13, 404-406.
(17) (a) Harrah, L. A.; Zeigler, J. M. Macromolecules 1987, 20, 601-
608. (b) Trefonas, P.; Djurovich, P. I.; Zhang, X-H.; West, R.; Miller, R.
D.; Hofer, D. J. Polym. Sci., Polym. Lett. Ed. 1983, 21, 819-822. (c)
Kakimoto, M.; Ueno, H.; Kojima, H.; Yamaguchi, Y.; Nishimura, A. J.
Polym. Sci., Part A: Polym. Chem. 1996, 34, 2753-2758. (d) Yi, S. H.;
Maeda, N.; Suzuki, T.; Sato, H. Polym. J. 1992, 24, 865-870. (e) Miller,
R. D.; Thompson, D.; Sooriyakumaran, R.; Fickes, G. N. J. Polym. Sci.,
Part A: Polym. Chem. 1991, 29, 813-824. (f) Kim, H. K.; Hove, C. R.;
Ober, C. K. J. Macromol. Sci., Pure Appl. Chem. 1992, A29, 787-800.
(13) (a) Aeiyach, S.; Lacaze, P.-C.; Satge´, J.; Rima, G. Synth. Met. 1993,
58, 267-270. (b) Shono, T.; Kashimura, S.; Murase, H. J. Chem. Soc., Chem.
Commun. 1992, 896-897.
(14) Reichl, J. A.; Popoff, C. M.; Gallagher, L. A.; Remsen, E. E.; Berry,
D. H. J. Am. Chem. Soc. 1996, 118, 9431-9432.
(15) Bassindale, A. R.; Stout, T. J. Organomet. Chem. 1984, 271, C1-
C3.

9846 J. Am. Chem. Soc., Vol. 120, No. 38, 1998
Katz et al.
Figure 1. Influence of polymer isolation method on molecular weight
distribution. Chromatograms of (PhMeGe)x purified by air workup (solid
line) and polymer precipitated from THF/MeOH (dashed line).
Figure 2. Comparison of GPC peaks determined by polystyrene and
light scattering analyses. Solid line denotes molecular weight determined
relative to polystyrene; dots indicate molecular weight measured by
light scattering.
Table 2. Effect of Time on MW and λMax for
Poly(phenylmethylgermane) Polymerization
a
a
time
1 h
1 day
Mw
Mn
DPb
λmax
with methanol, and a larger, lower molecular fraction remained
in solution (Mn < 1000). It thus appears that either the coupling
of these monomers is particularly sluggish or the catalyst lifetime
is unusually short in these cases. Attempts to optimize the
polymerization of these monomers is continuing.
5300
6400
6900
4000
4900
5100
24
30
31
326
328
330
1 week
a Air workup, molecular weights by SEC/LS; values rounded to
nearest 100 Da. b DP ) Mn/(MW of repeat unit).
Molecular Weights Determined by Polystyrene and Light
Scattering Methods. It has been reported that molecular
weights for polysilanes as determined relative to polystyrene
standards can differ by as much as a factor of 2-3 from more
absolute values obtained with techniques such as light scat-
tering1a,18 and viscometry.14 It is therefore useful to compare
the molecular weights obtained relative to polystyrene with those
measured using a multiangle light scattering detector. Static
light scattering is an absolute characterization method allowing
one to determine the molecular weight and size (root mean
square radius) of a macromolecule without reference to an
external standard.19 The only property which must be known
for each type of polymer to be studied is the refractive index
increment with concentration, dn/dc. This value was measured
for poly(phenylmethylgermane) in tetrahydrofuran to be 0.190
( 3% mL/g20 using standard procedures21 and taken as constant
for the other aryl derivatives. The degree of anisotropy of a
macromolecule can also affect light scattering, but the polyger-
manes under consideration are sufficiently small (Mw < 10 000)
that isotropic scattering can be safely assumed.
Table 3. Details of Polymerization Reactions
mmol of
monomer
mol %
catalyst
reaction
timea
Ar-Ge
C6H5
p-C6H4F
p-C6H4CF3
p-C6H4CH3
m-C6H3(CH3)2
p-C6H4OCH3
yieldb (%)
5.53
1.49
1.18
0.83
1.54
0.90
0.7
0.9
1.0
1.9
1.0
1.0
5 weeks
2 weeks
1 week
1 week
1 week
2 weeks
52
51
7c
54
61
19d
a Reactions performed at varied times showed similar results; see
text. b Precipitated from tetrahydrofuran with methanol c Yield of air
workup 44%. d Yield of air workup 95%.
decrease in the lower molecular weight fractions in material
precipitated from methanol.
The influence of reaction time on polymer molecular weight
and λmax was investigated in the polymerization of dimeth-
ylphenylgermane. Aliquots were removed from the reaction
mixture (1 mol % catalyst, 25 °C) after 1 h, 1 day, and 1 week.
After 1 h, the aliquot was a viscous liquid with Mw ∼ 5300,
but after 1 day, the reaction mixture was a tacky solid exhibiting
a 25% increase in Mw. Finally, only a modest gain of ∼10%
in Mw was observed in the material which was allowed to react
for 1 week. Molecular weights (SEC/LS) and λmax values
(measured in THF solution) are shown in Table 2.
Typical polymerization data for all poly(arylmethylgermanes)
are shown in Table 3. These experiments involve approximately
1 mol % of the ruthenium catalyst precursor and are allowed to
proceed for 1-2 weeks before the polymers are precipitated
with methanol. Note that the reaction times are unnecessarily
long, as explained above, and similar results would be expected
Sample GPC traces are shown in Figure 2, incorporating
molecular weights determined by light scattering and relative
to polystyrene calibrant.
Molecular weights as determined by the two methods are
tabulated in Table 4. For comparison, a sample of poly-
(phenylmethylgermane) prepared by Wurtz coupling is included.
For all but the trifluorotolyl polymer, the conjugation lengths
as determined by light scattering are significantly higher than
those calculated relative to polystyrene. This may reflect a
deviation in dn/dc for the fluorinated material. Ignoring the
trifluorotolyl derivative, the average ratio PS/LS for Mw is 0.63
and 0.55 for Mn.
1
after only 1 day. The polymers exhibited H NMR spectra
Electronic Properties. The absorption spectrum for each
of the polymers was measured in dilute solution (1-2 mg/50
consistent with the expected structures; methyl and aryl protons
on the main chain showed broad resonances in the ranges δ
0.9 to -0.2 ppm and δ 7.8 to 6.3 ppm, respectively. A few
very small sharper peaks rise slightly above the broad reso-
nances. Tolyl protons exhibited a broad peak at δ 2.08, m-xylyl
protons at δ 2.06, and anisyl protons at δ 3.32.
(18) Cotts, P. M.; Miller, R. D.; Trefonas, P. T.; West, R.; Fickes, G. N.
Macromolecules 1987, 20, 1046-1052.
(19) Wyatt, P. J. Anal. Chim. Acta 1993, 272, 1-40.
(20) Determined at λ ) 690 nm and T ) 22 °C.
(21) (a) Polymer Handbook, 3rd ed.; Brandup, J., Immergut, E. H., Eds.;
Wiley: New York, 1989; pp VII/409-411. (b) Light Scattering From
Polymer Solutions; Huglin, M. B., Ed.; Academic: London/New York,
1972; Chapter 6.
Polymers containing p-trifluorotolyl and p-anisyl substituents
were obtained in significantly lower yield following precipitation

Catalytic Synthesis of Poly(arylmethylgermanes)
J. Am. Chem. Soc., Vol. 120, No. 38, 1998 9847
Table 4. Molecular Weights of Poly(arylmethylgermanes) as Determined by GPC/LS and against Polystyrene Calibrant
DPb
Mw PS/Mw LS
Mn PS/Mn LS
a
b
a
Ar-Ge
Mw PS
Mn PS
DPPS
Mw LS
Mn LS
LS
C6H5-Wurtzc
6000
5400
6500
7000
3400
4200
3000
4300
3600
4900
6100
2700
3000
2500
26
22
27
26
15
15
13
8500
7900
10100
6900
5500
6000
6000
7100
6500
8800
6100
4700
4900
5500
43
40
48
26
26
25
28
0.70
0.69
0.65
1.01
0.62
0.70
0.50
0.61
0.54
0.56
0.99
0.58
0.61
0.46
C6H5
p-C6H4F
p- C6H4CF3
p-C6H4CH3
m-C6H3(CH3)2
p-C6H4OCH3
a “PS” denotes calibration against polystyrene; “LS” indicates determination of molecular weight by GPC/light scattering. b DP ) Mn/(MW of
repeat unit). c (PhMeGe)x prepared by reduction of PhMeGeCl2 with sodium.
Table 5. Absorption Data for Substituted
Poly(arylmethylgermanes)
analogue, as well as low intrinsic viscosity and small hydro-
dynamic diameter.14 More recently, the degree of branching was
quantitatively determined by digesting the polygermane with
bromine, which cleaves all Ge-Ge bonds while leaving
Ge-Me bonds intact. Analysis of the resulting monogermane
fragments revealed that ∼60% of the backbone is made up of
the expected -GeMe2- units. The remaining 40% is equally
distributed between -GeMe- and -GeMe3- groups, the latter
arising from redistribution or branching.22 Unfortunately, it was
not possible to utilize a similar method to digest the aryl
polygermanes because bromine cleaves germanium-aryl bonds
as well as Ge-Ge bonds. Iodine was found to be similarly
unselective. In addition, the radii of the polymers are not large
enough to permit accurate determination of branching by light
scattering methods.
Ar-Ge
DP (LS)
λ )
max (nm) ꢀ/Ge-Ge (L mol-1 cm-1
C6H5-Wurtza
43
40
48
26
26
25
28
332
332
336
332
326
330
338
5600
8000
5100
3000
7500
7100
10100
C6H5
p-C6H4F
p-C6H4CF3
p-C6H4CH3
m-C6H3(CH3)2
p-C6H4OCH3
a (PhMeGe)x prepared by reduction of PhMeGeCl2 with sodium.
mL); λmax values and corresponding extinction coefficients are
listed in Table 5. Poly(arylmethylgermanes) as synthesized by
demethanative coupling exhibit λmax between 326 and 338 nm;
there is no convincing trend in the effect of electron-donating
To qualitatively probe the issue of branching in the aryl-
substituted polygermanes, the spectroscopic and electronic
properties of poly(phenylmethylgermane) prepared by demetha-
native coupling were compared with those of the linear analogue,
synthesized by Wurtz condensation of MePhGeCl2. The mo-
or -withdrawing ability on λmax
.
The molecular weight and λmax of poly(phenylmethylgermane)
prepared by demethanative coupling are consistent with those
of similar materials synthesized by Wurtz condensation as
described in the literature2a,c,3c,4a,11,16a and as performed in our
laboratory.
lecular weights of the two polymers are comparable, (Mw
)
1
7900 and 8500). The H NMR spectra of the two polymers
are very similar, and their absorption spectra nearly identical
(Table 5). The tentative conclusion suggested by these data is
that there is no significant branching in the aryl polygermanes
as synthesized by demethanative coupling. Branching would
be expected to broaden the absorption peak due to increased
σ-conjugation in more than one direction.23
Mechanistic Considerations. We have previously proposed
a mechanism for the demethanative coupling in which Ge-C
bond cleavage and Ge-Ge bond formation are accomplished
by sequential R-CH3 and germyl to germylene migration steps.14
This process is easily adapted for the polymerization of Me2-
GeArH monomers, as illustrated in Scheme 1. Initially, reaction
of (PMe3)4RuMe2 is believed to yield PnRu(GeMe2Ar)2 (n ) 3
or 4) and CH4. Although the active bis(germyl) complex is
not directly observed in this case, (PMe3)4Ru(GeMe3)2, isolated
from the analogous reaction with GeMe3H, has been shown to
be the active catalyst in the polymerization of Me3GeH.14
Considering this proposed mechanism, it is possible that the
aryl group, rather than the methyl group, migrates from the
germanium to the ruthenium center. This migration might
ultimately lead to the elimination of arene. However, in a study
of the polymerization of Me2GePhH, analysis by 1H NMR and
GC shows no evidence for benzene evolution during the course
of the polymerization. In addition, 1H NMR integrations
indicate that the polymer contains equal numbers of phenyl and
methyl groups. However, this observation does not rule out
the possibility of a reVersible R-aryl migration to ruthenium,
but merely indicates that aryl-H reductive elimination does not
ultimately occur. Investigation of the polymer microstructure
is needed to determine whether there is redistribution of the
aryl and methyl groups occurring along the polymer chain.
Polymer Microstructure. The mechanism of demethanative
coupling allows for the possibility of either linear or branched
chains, depending on whether the methyl group migrates from
a group containing one or more Ge groups. Analysis of poly-
(dimethylgermane) synthesized by demethanative coupling has
proven that the backbone is indeed branched. Qualitative
evidence includes greater solubility compared with the linear
Conclusions
The method of demethanative coupling has been shown to
be useful for the synthesis of a variety of substituted poly-
(arylmethylgermanes). These polymers exhibit the anticipated
absorbance spectra associated with σ-conjugation. Polymers
were characterized by GPC using both light scattering methods
and polystyrene standards. Light scattering values were shown
to be ca. 70% greater than those determined relative to
polystyrene. Comparison of poly(phenylmethylgermane) pre-
pared by demethanative coupling with a sample from a typical
Wurtz condensation reveals that the two polymers are nearly
identical in all respects.
Experimental Section
Materials and Procedures. All manipulations were carried out in
dried glassware under a N2 atmosphere in a drybox or using standard
Schlenk and high vacuum line techniques. Solvents were dried over
sodium benzophenone ketal and then refluxed and distilled under
nitrogen prior to use. Benzene-d6 was dried over Na/K alloy. Phenyl,
(22) Reichl, J. A.; Berry, D. H. Manuscript in preparation.
(23) (a) Watanabe, A.; Tsutsumi, Y.; Matsuda, M. Synth. Met. 1995,
74, 191-196. (b) Matyjaszewski, K.; Chrusciel, J.; Maxka, J.; Sasaki, M.
J. Inorg. Organomet. Polym. 1995, 5, 261-279. (c) van Walree, C. A.;
Cleij, T. J.; Jenneskens, L. W.; Vlietstra, E. J.; van der Laan, G. P.; de
Haas, M. P.; Lutz, E. T. G. Macromolecules 1996, 29, 7362-7373.

9848 J. Am. Chem. Soc., Vol. 120, No. 38, 1998
Katz et al.
Scheme 1. Proposed Mechanism for Demethanative Coupling
p-tolyl, and p-fluorophenyl Grignard reagents were purchased from
Aldrich. Bromoaryl compounds were purchased from Aldrich, then
dried over calcium hydride before use and purity checked by NMR.
Dimethyldichlorogermane was synthesized by the direct reaction of
germanium metal with methyl chloride24 and purified by spinning band
DAWN multiangle light scattering detector with a 690-nm laser light
source. Tetrahydrofuran used as the mobile phase was dried, filtered,
and degassed in-line (Degasys DG-1210) prior to delivery to the GPC
pump. During measurements, the flow rate was 1 mL/min. Polymer
solutions were approximately 8-15 mg/mL in tetrahydrofuran; a loop
size of 100 µL was employed, making each injection size 0.8-1.5 mg.
The signals from the in-line detectors were sent to a Pentium
microcomputer and analyzed using Astra 4.5 software from Wyatt
Technology Corp. The dn/dc value (refractive index increment with
concentration) was determined for poly(phenylmethylgermane) to be
0.190 mL/g in THF at 690 nm and 22 °C using DNDC software from
Wyatt Technology Corp. and assumed to be constant for all aryl
derivative polygermanes. Upon processing the data, a zero- or first-
order line fit was chosen to best fit the data from the three light
scattering detectors. Calculated experimental errors in Mw and Mn
ranged from 2% to 10%.
Me2GeArH Monomer Syntheses. For three of the monomers
prepared (Ar ) phenyl, p-tolyl, and p-fluoro), the diaryldimethylger-
manes were synthesized from commercially available Grignard reagents
and Me2GeCl2. For the remaining three derivatives (p-trifluorotolyl,
p-anisyl, and m-xylyl), the Grignard reagents were prepared from the
corresponding para-brominated arenes. A typical monomer synthesis
is described below. Yields for the diaryldimethylgermanes ranged from
95 to 99%, except for the m-xylyl, for which the yield was 62%.
Combined yields for the triflic acid and reduction steps were in the
range of 70%-93%, except for the m-xylyl, which was 56%. Prior to
polymerization, Me2GeArH monomers were dried over sodium chips
or molecular sieves.
25
distillation. The literature procedures for preparing (PMe3)4RuMe2
from (PMe3)4RuCl2 were followed. Wurtz coupling of PhMeGeCl2 was
performed as reported in the literature.11
Spectra. 1H NMR spectra were obtained on a Bruker AC-200
spectrometer. NMR spectra were obtained at room temperature using
benzene-d6 as a solvent. Chemical shifts are reported relative to
tetramethylsilane. Mass spectra were recorded on a VG ZAB-E
spectrometer using CH4 CI. Gas chromatography was performed on a
Hewlett-Packard 5890A gas chromatograph equipped with a flame
ionization detector. The column employed was an Alltech Econo-Cap
capillary column (30 m length, 0.32 mm i.d., film 0.25 µm, packed
with cross-linked poly(dimethylsiloxane)).
Absorption and Emission Spectroscopy. All measurements were
performed in spectrophotometric-grade tetrahydrofuran in a fused quartz
cell with a path length of 1 cm. Absorption spectra were measured
using an HP8452A diode array spectrophotometer connected to a
microcomputer. Analyses were performed on fresh solutions, and
samples were protected from room light to prevent photodecom-
position.
Gel Permeation Chromatography. Molecular weights were de-
termined by gel permeation chromatography, using both polystyrene
standards and by using an in-line light scattering detector in conjunction
with an RI detector. The GPC-LS instrument consists of a Rainin
HPXL solvent delivery system connected to a Shodex GPC KF-801
column and three Waters Ultrastyragel columns of pore size 500, 103,
and 104 Å maintained at 40 °C. Three in-line detectors are connected
in series: a Rainin Dynamax UV-1 absorbance detector, a Wyatt Optilab
903 interferometric refractometer, and a Wyatt Technology Corp. mini-
Bis(4-trifluorotolyl)dimethylgermane. 4-Trifluorotolylmagnesium-
bromide was prepared from 15.338 g (68.17 mmol) of p-bromotri-
fluorotoluene (Aldrich) in 35 mL of dry ether and 2.358 g (97.02 mmol)
of Mg turnings. This solution was added using a double-tipped needle
to a 0 °C solution of 4.42 g (25.47 mmol) of dimethyldichlorogermane
in 8 mL of dry ether in a two-neck flask equipped with a gas inlet and
rubber septum. The resulting dark red solution was allowed to stir for
1 h at 0 °C, then warmed to room temperature and stirred overnight.
Methanol was added to kill the excess Grignard; the solution was then
(24) Lee, M. E.; Bobbitt, K. L.; Lei, D.; Gaspar, P. P. Synth. React.
Inorg. Met.-Org. Chem. 1990, 20, 77-81.
(25) Statler, J. A.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M.
B. J. Chem. Soc., Dalton Trans. 1984, 1731-1738.

Catalytic Synthesis of Poly(arylmethylgermanes)
J. Am. Chem. Soc., Vol. 120, No. 38, 1998 9849
extracted with an aqueous NaCl solution. After washing the organic
layer three times, it was dried over magnesium sulfate and filtered.
Removal of the solvent in vacuo yielded a dark red oil, yield 99.4%.
1H NMR (C6D6): δ 7.36 (d, 4H, aryl), 7.15 (d, 4H, aryl), 0.36 (s, 6H,
GeCH3).
removal of the benzene, followed by stirring the mixture in tetrahy-
drofuran in air to decompose the ruthenium catalyst. Filtration of the
solution through a column of Celite to remove the ruthenium and
removal of the solvent in vacuo left a sticky solid. 1H NMR (C6D6):
δ 7.4-6.5 (Ar), 2.06 (Ar-CH3), 0.8-0.1 (Ge-CH3).
(4-Trifluorotolyl)dimethylgermane. Triflic acid (2.0 mL, 22.60
mmol) was slowly added via a gastight syringe to 9.3769 g (23.87
mmol) of neat bis(4-trifluorotolyl)dimethylgermane in an ice bath. The
solution immediately turned purple-black. The solution was warmed
to room temperature after the addition, then stirred for 2 h. No further
color change was observed. The volatiles were removed in vacuo to
yield a dark gray solid, (4-trifluorotolyl)dimethylgermyltriflate. This
compound (8.8 g, 22.2 mmol) was slowly added to a solution of 0.90
g (23.7 mmol) of lithium aluminum hydride in dry ether. The solution
was degassed and stirred overnight, turning greenish-yellow in color.
After the reaction mixture was immersed in an ice bath, a 10% aqueous
ammonium chloride solution was added dropwise to kill the excess
lithium aluminum hydride. The solution was then filtered to remove
the salts and the filtrate was extracted with three portions of ammonium
chloride solution. The bright yellow organic layer was separated and
dried over magnesium sulfate. Filtration and removal of the volatiles
in vacuo left a bright yellow liquid in 95% yield. 1H NMR (C6D6): δ
7.37-7.33 (d, 2H, aryl), 7.19-7.15 (d, 2H, aryl), 4.53 (m, 1H, Ge-H),
0.21 (d, 6H, GeCH3).
Polymerization Reactions. NMR-Tube Scale. Poly(m-xylyl-
methylgermane) is given as a representative reaction. In a sealed tube,
32 mg (0.153 mmol) m-xylyldimethylgermane was combined with 35
µL of a stock solution made up of 5 mg of (PMe3)4RuMe2 in 200 µL
of benzene-d6 (2.0 × 10-3 mmol, 1.3 mol % catalyst). Hexamethyl-
benzene was added as an internal standard, and the reaction was
monitored by 1H NMR. After an induction period of 20 min, methane
evolution could be detected, and within 2 h, the spectrum clearly
indicated the presence of polymer peaks. After 9 h, monomer
resonances could no longer be detected. The polymer was isolated by
Bulk Polymerization Reactions. Poly(phenylmethylgermane) is
given as a representative example. Phenyldimethylgermane (1.00 g,
5.53 mmol) was reacted with 0.017 g (0.039 mmol, 0.70 mol %) of
(PMe3)4RuMe2 in a Wheaton vial under nitrogen at room temperature.
The colorless solution initially turned reddish-purple with vigorous
bubbling, then turned yellow and solid within 12 h. No further visible
change was observed. After ca. 4 weeks, the polymer was dissolved in
tetrahydrofuran and split into two equal portions. Note that subsequent
studies (vide supra) indicate that the majority of polymerization is
complete after 1 day and that almost no change in molecular weight is
observed after 7 days. One portion of the polymer solution was stirred
in air for 2 h to decompose the catalyst and filtered through Celite,
and the solvent was removed in vacuo to yield 0.309 g (68%) of a
tacky white solid (GPC/LS: Mw ) 6200, Mn ) 4300.) Note that the
yield in this specific case is lower than generally observed due to
accidental loss of material during workup. The second portion of
polymer solution was treated with methanol (ca. 40 volumes) under
nitrogen. The precipitate was collected by filtration and dried under
vacuum to yield 0.236 g (52%) of a white powder (GPC/LS: Mw
)
7900, Mn ) 6500.). 1H NMR (C6D6): δ 7.6-6.7 (Ge-C6H5), 0.7-0.2
(Ge-CH3). Additional, lower weight polymer can be obtained by
removing solvents from the filtrate in vacuo.
Acknowledgment. Financial support for this research from
the National Science Foundation (DMR-96-32598) is gratefully
acknowledged.
JA981806Q