Poly(2,5-diphenylgermole): incorporation of a germole ring into a conjugated polymer

Article abstract of DOI:10.1021/om000191e

The intramolecular zirconocene coupling of 4,4-bis(hexyloxymethyl)-1,7-bis-p-halophenyl-1,6-heptadiynes provides 2,5-bis-p-halophenylzirconocyclopentadienes (bromo and chloro derivatives), which undergo efficient transmetalation reactions with GeBr₄. Methylation of the resulting dihalogermoles with MeLi provided bis-p-halophenyl-2,5-germole monomers. These functionalized germoles were polymerized via nickel coupling to give oligo- and poly(2,5-diphenylgermole) materials (7). Investigations of optical properties reveal that the monomers and a model 2,5-bisphenylgermole are somewhat photoluminescent (Φ = 0.018-0.12), while the high molecular weight polymer (M_n ≈ 20000) exhibits very efficient photoemission (Φ = 0.79). Electrochemical studies indicate that delocalization in 7 is accompanied by a modest lowering of the LUMO level relative to that of the monomer.

Full text of DOI:10.1021/om000191e

Organometallics 2000, 19, 3469-3475
3469
Articles
P oly(2,5-d ip h en ylger m ole): In cor p or a tion of a Ger m ole
Rin g in to a Con ju ga ted P olym er
Brett L. Lucht, Mihai A. Buretea, and T. Don Tilley*
Department of Chemistry, University of California at Berkeley,
Berkeley, California 94720-1460
Received February 28, 2000
The intramolecular zirconocene coupling of 4,4-bis(hexyloxymethyl)-1,7-bis-p-halophenyl-
1,6-heptadiynes provides 2,5-bis-p-halophenylzirconocyclopentadienes (bromo and chloro
derivatives), which undergo efficient transmetalation reactions with GeBr4. Methylation of
the resulting dihalogermoles with MeLi provided bis-p-halophenyl-2,5-germole monomers.
These functionalized germoles were polymerized via nickel coupling to give oligo- and poly-
(2,5-diphenylgermole) materials (7). Investigations of optical properties reveal that the
monomers and a model 2,5-bisphenylgermole are somewhat photoluminescent (Φ ) 0.018-
0.12), while the high molecular weight polymer (Mn ≈ 20 000) exhibits very efficient
photoemission (Φ ) 0.79). Electrochemical studies indicate that delocalization in 7 is
accompanied by a modest lowering of the LUMO level relative to that of the monomer.
In tr od u ction
and pyrole-containing polymers and oligomers. How-
ever, conjugated systems containing germole groups
have received far less attention, and no germole-
containing polymers have been reported to date.3j,4
Significant efforts have been expended toward the
preparation and characterization of soluble π-conjugated
polymers with various structures, in attempts to access
interesting and useful optoelectronic properties.1 The
incorporation of siloles and germoles into conjugated
polymers is of special interest, given computational
studies that suggest that silole rings have small band
gaps and a low-lying LUMO.2 Thus, polymers incorpo-
rating these units might be expected to exhibit novel
charge-transporting properties for use in polymer-based
electronic devices. However, the preparation of macro-
molecules containing silole monomer units has proven
difficult due to limited routes to the 2,5-difunctional
siloles needed for polymerization. There have been
several recent reports of the incorporation of siloles into
conjugated polymers,3 such as silole-thiophene,3a,c silole-
acetylene,3f and silole-pyrole3d alternating polymers.
Recently, Tamao’s group has succeeded in preparing the
first poly(2,5-silole).3i These silole-containing polymers
and oligomers exhibit significantly lower energy optical
absorption maxima than related phenylene-, thiophene-,
We have been investigating use of the zirconocene
coupling of diynes5 for the preparation of a variety of
polymers and macrocycles.6 Using this method, we have
obtained a range of new conjugated polymers via reac-
tions of zirconocyclopentadiene units in the polymer
backbone. In addition, we have prepared conjugated
polymers from the regioselective zirconocene coupling
of poly(arylenediyne)s.6h,i The resulting zirconium-
containing polymers were hydrolyzed to the correspond-
ing poly(arylenediene)s, for which electronic properties
are readily varied via appropriate choice of the arylene
group. Using this modular exchange of components in
(3) (a) Tamao, K.; Yamaguchi, S.; Shiozaki, M.; Nakagawa, Y.; Ito,
Y. J . Am. Chem. Soc. 1992, 114, 5867. (b) Tamao, K.; Yamaguchi, S.;
Shiro, M. J . Am. Chem. Soc. 1994, 116, 11715. (c) Tamao, K.;
Yamaguchi, S.; Ito, Y.; Matsuzaki, Y.; Yamabe, T.; Fukushima, M.;
Mori, S. Macromolecules 1995, 28, 8668. (d) Tamao, K.; Ohno, S.;
Yamaguchi, S. Chem. Commun. 1996, 1873. (e) Tamao, K.; Uchida,
M.; Izumizawa, T.; Furukawa, K.; Yamaguchi, S. J . Am. Chem. Soc.
1996, 118, 11974. (f) Yamaguchi, S.; Iimura, K.; Tamao, K. Chem. Lett.
1998, 89. (g) Corriu, R. J . P.; Devylder, N.; Guerin, C.; Henner, B.;
J ean, A. Organometallics 1994, 13, 3194. (h) Brefort, J . L.; Corriu, R.
J . P.; Gerbier, Ph.; Guerin, C.; Henner, B. J . L.; J ean, A.; Kuhlmann,
Th. Organometallics 1992, 11, 2500. (i) Yamaguchi, S.; J in, R.-Z.; Itami,
Y.; Goto, T.; Tamao, K. J . Am. Chem. Soc. 1999, 121, 10420. (j) Dubac,
J .; Gue´rin, C.; Meunier, P. In The Chemistry of Organic Silicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998;
Vol. 2, Part 3, Chapter 34.
(4) (a) Ferman, J .; Kakareka. J . P.; Klooster, W. T.; Mullin, J . L.;
Quattrucci, J .; Ricci, J . S.; Tracy, H. J .; Vining, W. J .; Wallace, S. S.
Inorg. Chem. 1999, 38, 2464. (b) Dubac, J .; Laporterie, A.; Manuel, G.
Chem. Rev. 1990, 90, 215. (c) Yamaguchi, S.; J in, R. Z.; Tamao, K. J .
Am. Chem. Soc. 1999, 121, 2937. (d) Sohn, H. L.; Huddleston, R. R.;
Powell, D. R.; West, R. J . Am. Chem. Soc. 1999, 121, 2935. (e)
Yamaguchi, S.; Itami, Y.; Tamao, K. Organometallics 1998, 17, 4910.
(1) (a) Feast, W. J .; Friend, R. H. J . Mater. Sci. 1990, 25, 3796. (b)
MacDiarmid, A. G.; Epstein, A. J . Faraday Discuss. Chem. Soc. 1989,
317. (c) Patil, A. O.; Heeger, A. J .; Wudl, F. Chem. Rev. 1988, 88, 183.
(d) Handbook of Conducting Polymers; Skotheim, T. A., Elsenbaumer,
R. L., Reynolds, J . R., Eds.; Marcel Dekker: New York, 1998. (e)
Conjugated Polymers: The Novel Science of Technology and Highly
Conducting and Nonlinear Optically Active Materials; Bredas, J . L.,
Silbey, R., Eds.; Kluwer Academic Publishers: Dordecht, 1991. (f)
Gibson, H. W. Polymer 1984, 25, 3. (g) Tour, J . M. Chem. Rev. 1996,
96, 537. (h) Bradley, D. D. C. Synth. Met. 1993, 54, 410. (i) Roncali, J .
Chem. Rev. 1997, 97, 173.
(2) (a) Yamaguchi, S.; Tamao, K. J . Chem. Soc., Dalton Trans. 1998,
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2327.
10.1021/om000191e CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/04/2000

3470 Organometallics, Vol. 19, No. 18, 2000
Lucht et al.
Sch em e 1
the polymer backbone, we have obtained polymers with
tunable optical absorption and emission maxima.6h
We report here the synthesis of poly(2,5-diphenylger-
mole) and an investigation of its optoelectronic proper-
ties. Our synthetic approach takes advantage of the
metallacycle transfer from zirconium to germanium,
initially reported by Fagan and Nugent (eq 1).7
A
modification of this reaction has allowed synthesis of
2,5-bis-p-halophenylgermoles, which can be polymerized
via nickel-mediated couplings.8
Resu lts a n d Discu ssion
Mon om er Syn th esis. Diynes 1a and 1b were ob-
tained in high yield by the palladium-catalyzed cross-
couplings of 4,4-bis(hexyloxymethyl)-1,6-heptadiyne with
1-bromo-4-chlorobenzene and 1-bromo-4-iodobenzene,
respectively.9
IR spectroscopy and by high-resolution mass spectrom-
etry. Freshly prepared monomer 2 was found to give
better results in the polymerization reactions described
below.
The synthesis of 5 is outlined in Scheme 1. The
intramolecular coupling of 1b employed the zirconocene
reagent Cp2Zr(pyr)(Me3SiCtCSiMe3)10,11 and was car-
ried out in benzene at room temperature to give a red
solution from which the zirconocyclopentadiene 3 was
isolated as a red oil in 83% yield. This coupling
procedure is tolerant of the bromophenyl functional
groups in 1b, and no appreciable side products could
be detected in the crude product (by NMR spectroscopy).
Treatment of 3 in THF at -78 °C with GeBr4 afforded
the dibromogermole compound 4, which was subse-
quently converted to 5 by treatment with MeLi at -78
°C in Et2O. Pure monomer 5 was obtained by washing
the crude, vacuum-dried reaction mixture with cold
pentane and then extraction of the product into benzene
to remove it from LiBr. The benzene was removed under
reduced pressure to afford 5 as a bright yellow oil.
P olym er Mod el Com p ou n d Syn th esis. The poly-
mer model compound 6 was synthesized by a procedure
similar to that used for monomers 2 and 5. Intramo-
lecular zirconocene coupling of 1,7-diphenyl-1,6-hep-
tadiyne followed by transmetalation with GeBr4 and
alkylation with MeLi yielded 6 (31%) as a bright yellow
powder after purification by column chromatography (eq
4).
The 2,5-bis-p-halophenylgermole monomers 2 and 5
were synthesized via the three-step procedures outlined
in eq 3 and Scheme 1. For 2, a one-pot reaction was
employed. The intramolecular zirconocene coupling of
1a in THF proceeded with no apparent complications
resulting from the presence of chlorophenyl function-
alities, to afford a deep red solution of the zirconocy-
clopentadiene. This solution was treated with GeBr4, to
produce the germole dibromide as a synthetic interme-
diate, and then MeLi to give 2 in 61% yield as a bright
yellow oil after purification by column chromatography.
Alternative procedures employing the transmetalation
reagents GeCl4 and Me2GeBr2 gave lower overall yields.
The chemical structure of 2 was confirmed by NMR and
(5) (a) Nugent, W. A.; Thorn, D. L.; Harlow, R. L. J . Am. Chem. Soc.
1987, 109, 2788. (b) Negishi, E.; Cederbaum, F. E.; Takahashi, T.
Tetrahedron Lett. 1986, 27, 2829. (c) Negishi, E.; Takahashi, T. Acc.
Chem. Res. 1994, 27, 124. (d) Broene, R. D.; Buchwald, S. L. Science
1993, 261, 1696.
(6) (a) Mao, S. S. H.; Tilley, T. D. J . Am. Chem. Soc. 1995, 117, 5365.
(b) Mao, S. S. H.; Tilley, T. D. J . Am. Chem. Soc. 1995, 117, 7031. (c)
Mao, S. S. H.; Tilley, T. D. Macromolecules 1996, 29, 6362. (d) Mao, S.
S. H.; Tilley, T. D. J . Organomet. Chem. 1996, 521, 425. (e) Mao, S. S.
H.; Tilley, T. D. Macromolecules 1997, 30, 5566. (f) Tilley, T. D.; Mao,
S. S. H. Modular Chemistry; Michl, J ., Ed., Kluwer Academic Publish-
ers: Dordrecht, 1997; p 623. (g) Mao, S. S. H.; Liu, F. Q.; Tilley, T. D.
J . Am. Chem. Soc. 1998, 120, 1193. (h) Lucht, B. L.; Mao, S. S. H.;
Tilley, T. D. J . Am. Chem. Soc. 1998, 120, 4354. (i) Lucht, B. L.; Tilley,
T. D. Chem. Commun. 1998, 1645.
The molecular structure of 6, as determined by X-ray
crystallography (Figure 1), is similar to that of other
crystalline germole derivatives.4a,12 The germole ring is
almost planar, and no unusual distortions of the diene
(7) (a) Fagan, P. J .; Nugent, W. A. J . Am. Chem. Soc. 1988, 110,
2310. (b) Dufour, P.; Dartiguenave, M.; Dartiguenave, Y.; Dubac, J . J .
Organomet. Chem. 1990, 384, 61. (c) Fagan, P. J .; Nugent, W. A.;
Calabrese, J . C. J . Am. Chem. Soc. 1994, 116, 1880.
(8) (a) Semmelhack, M. F.; Helquist, P. M.; J ones, L. D. J . Am.
Chem. Soc. 1971, 93 5903. (b) Zembayashi, M.; Tamao, K.; Yoshida,
J .; Kumada, M. Tetrahedron Lett. 1977, 47, 4089. (c) Colon, I.; Kelsey,
D. R. J . Org. Chem. 1986, 51, 2627. (d) Colon, I.; Kwiatkowski, G. T.
J . Polym. Sci., Part A: Polym. Chem. 1990, 28, 367. (e) Qibing, P.;
Yang, Y. J . Am. Chem. Soc. 1996, 118, 7416.
(9) (a) Heck, R. F.; Nolley, J . P. J . Org. Chem. 1972, 37, 2320. (b)
Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467.
(c) Sonogashira, K.; Takahashi, S. J . Synth. Org. Chem. J pn. 1993,
51, 1053. (d) Trumdo, D. L.; Marvel, C. S. J . Polym. Sci., Part A: Polym.
Chem. 1987, 25, 839.

Poly(2,5-diphenylgermole)
Organometallics, Vol. 19, No. 18, 2000 3471
(COD)2 and bipyridine in DMF/toluene solution.13 Ad-
dition of monomer 5 to this reagent at 60 °C resulted
in a red solution, from which the polymer was isolated
as a bright yellow solid (7c, 88%) after precipitation with
methanol (Scheme 2). This material is visually similar
to 7b but has a much higher molecular weight (Mn
)
20 000, PDI ) 2.9) and correspondingly different optical
properties.
Op tica l P r op er ties. The photophysical properties of
2, 5, 6, and 7a -c were investigated in dilute deoxygen-
ated chloroform solution. Absorption and emission data
are summarized in Table 1, and Figure 2 presents
absorption and emission spectra for 7b, which are
representative for the series of polymer samples de-
scribed here. All samples of polymer 7 exhibit λmax
values in their absorption spectra that are significantly
red-shifted with respect to values for poly(p-phe-
nylene),14 indicating a greater degree of delocalization
in 7. The optical absorption for 7 is also red-shifted with
respect to that for poly(diphenyl-1,4-cis-dienylene) (λmax
) 396).6i This is presumably due to either a decrease in
steric interactions along the polymer chain allowing
better orbital overlap and a longer conjugation length
or a lowering of the LUMO level in the π-system by
incorporation of the germole ring. Emission spectra of
all compounds investigated are independent of the
excitation wavelength (over a range of 350-450 nm),
and the excitation spectra reproduce the corresponding
absorption spectra. There is a substantial shift in the
absorption maxima of 7 relative to that of 6 (40 nm for
7a , 66 nm for 7b, and 78 nm for 7c), suggesting that
the conjugation length of the polymer extends well
beyond seven repeat units. In addition, the photolumi-
nescence quantum yields were found to be dependent
on the polymer molecular weight, with higher molecular
weight corresponding to a greater quantum yield.
For 7a -c, the wide range in absorption λmax values
precludes the use of a single standard for the quantum
yield determination. A solution of quinine in sulfuric
acid (λmax ) 350 nm) was used as a fluorescence
standard in most cases, as its absorption overlaps
significantly with those of 2, 5, 6, and 7a . For 7b and
7c, [Ru(bipy)3][PF6]2 in MeCN (λmax ) 450 nm) was also
used. When irradiated at 440 nm, the observed quantum
yields for 7b and 7c were much higher and in proportion
to the lower values obtained with the quinine standard
(Table 1). Clearly, in these cases, use of the [Ru(bipy)3]-
[PF6]2 standard is most appropriate.
F igu r e 1. X-r a y cr ysta llogr a p h ic str u ctu r e of m od el
com p ou n d 6.
moiety or phenyl groups are evident. The dihedral
angles between the least-squares plane of the germole
ring and the two phenyl rings are 12° and 24°. This
suggests that conjugation along the backbone of phe-
nylene-germole polymers is not optimal, as expected.
P olym er Syn th esis. A diphenylgermole polymer was
first prepared via the zerovalent nickel-mediated ho-
mocoupling of 2 (Scheme 2). This synthesis is based on
the method of Colon and co-workers for the preparation
of biaryls and polyaryls utilizing a mixture of NiCl2, Zn,
triphenylphosphine, and bipyridine in dimethylaceta-
mide (DMAc).8c,d We observed that higher molecular
weights were obtained with activated zinc, rigorously
anhydrous conditions, and high monomer purity. The
reaction mixture was heated to 70 °C for 20 min,
resulting in a deep red solution, indicating the formation
of the active nickel coupling reagent, to which was added
a DMAc solution of 2. The resulting mixture was
allowed to stir for 3 days at 70 °C and was then poured
into methanol. Filtration and removal of solvent from
the supernatant gave a small amount of oligomers (7a ;
Mn ) 1900; PDI ) 1.2) as a yellow oil. The remaining
precipitate was dissolved in THF and reprecipitated
with methanol to give polymer sample 7b as a yellow
solid (25% yield). The molecular weight of polymer 7b,
determined by gel permeation chromatography (GPC;
polystyrene standards; Mn ) 4700; PDI ) 1.9), is similar
to that determined by end group analysis (Mn ) 3800;
Electr och em istr y. Further insight into the elec-
tronic structure of 7 was obtained by comparing its
electrochemical behavior with that of model compound
6. The cyclic voltammogram of 6 in THF solution
exhibits an irreversible reduction at -3.02 V vs Fc/Fc+,
while polymer 7c undergoes quasi-reversible reduction
at -2.66 V. This shift in redox behavior between model
compound (monomer) and polymer parallels trends
observed for silole-containing polymers2a,3 and poly-
thiophene15 and is consistent with the expected drop in
the HOMO-LUMO gap accompanying increased con-
1
DP ≈ 7, by H NMR integration). Attempts to increase
the molecular weight of 7b via this synthetic procedure
were unsuccessful, so an alternative method was de-
veloped.
Recent reports on improved aryl-aryl coupling meth-
ods prompted us to employ a reagent consisting of Ni-
(10) (a) Rosenthal, U.; Ohff, A.; Baumann, W.; Tillack, A. Z. Anorg.
Allg. Chem. 1995, 621, 77. (b) Rosenthal, U.; Ohff, A.; Baumann, W.;
Tillack, A.; Burlakov, V. V. Angew. Chem., Int. Ed. Engl. 1994, 33,
1605.
(11) Nitschke, J .; Zu¨rcher, S.; Tilley, T. D. Submitted for publication.
(12) Lindeman, S. V.; Shklover, V. E.; Struchkov, Y. T.; Vasnyova,
N. A.; Sladkov, A. M. Cryst. Struct. Commun. 1981, 10, 827.
(13) Yamamoto, T. Bull. Chem. Soc. J pn. 1999, 72, 621.
(14) Froyer, G.; Pelous, Y.; Ollivier, G. Springer Ser. Solid State Sci.
1987, 76, 303.
(15) (a) Tourillon, G.; Garnier, F. J . Electroanal. Chem., 1982, 135,
173. (b) Yassar, A.; Roncali, J .; Garnier, F. Macromolecules 1989, 22,
804. (c) Schlick, U.; Teichert, F.; Hanack, M. Synth. Met. 1998, 92, 75.

3472 Organometallics, Vol. 19, No. 18, 2000
Lucht et al.
Sch em e 2
Ta ble 1. Op tica l P r op er ties of Ger m ole-Con ta in in g
Ma ter ia ls
Con clu d in g Rem a r k s
In this contribution we have described the first route
to germole-containing polymers, via zirconocene-cou-
pling chemistry. As we have recently reported else-
where,16 the zirconocene-coupling reaction is tolerant
of chloro- and bromophenyl groups, allowing the syn-
thesis of 2,5-bis-p-halophenylzirconocyclopentadienes,
which are readily converted to functionalized monomers.
In the chemistry described here, functionalized germoles
were polymerized with incorporation of germole rings
into the polymer’s main chain. The optical properties
of this polymer indicate considerable delocalization and
a conjugation length that is greater than about 7
monomer units (or 21 rings). For comparison, we have
recently determined (based on studies with discrete
oligomers) that the conjugation length in phenylene-
thiophene-1-oxide and phenylene-thiophene-1,1-dioxide
chains is 15-20 rings.17 Interestingly, 7 displays pho-
toemission properties that are strongly dependent on
chain length over the molecular weights investigated.
The sample with highest molecular weight (ca. 20 000)
is strongly emissive, suggesting possible applications in
light-emitting devices. Electrochemical studies indicate
that delocalization in 7 is accompanied by a modest
lowering of the LUMO level relative to that of the
monomer. Future investigations will further probe the
electronic properties of this and related structures,
obtained via zirconocene-coupling routes to well-defined
oligomeric species.
λ
max (nm)
absorption
λmax (nm)
compound
emission
Φ350
Φ440
2
5
6
368
376
364
404
430
442
457
464
452
486
498
500
0.084
0.12
0.018
0.059
0.14
7a , Mn ) 1900
7b, Mn ) 4700
7c, Mn ) 20000
0.52
0.79
0.21
F igu r e 2. Absorption (- - -) and emission (s) spectra of
7b (Mn ) 4700).
jugation. However, the polymer and model compound
oxidize at similar potentials. The oxidation waves for
both 7c and 6 are weak in THF and appear only as
broad, ill-defined features, both centered at approxi-
mately 0.6 V. For an acetonitrile solution of 6, an
irreversible reduction wave was observed at -2.53 V,
and distinct oxidation waves appeared at 0.75 and 1.21
V. Unfortunately, polymer 7c was insufficiently soluble
in acetonitrile for analysis, but measurements on film
samples revealed a broad oxidation feature centered
around 0.8 V. No reduction behavior could be observed
for films of 7c within the potential limits of the instru-
ment. The observation that oxidation potentials are
similar while the reduction potential decreases moder-
ately from monomer to polymer suggests that a decrease
in the energy of the LUMO is the primary mechanism
by which the band gap in the polymer is decreased with
increasing conjugation. This is in keeping with recent
theoretical and experimental investigations by Tamao
on silole-containing oligomers and polymers.3
Exp er im en ta l Section
Gen er a l Com m en ts. Organometallic reagents were stored
and handled under nitrogen atmosphere in a glovebox or using
Schlenk techniques. Toluene, THF, benzene, pentane, and
diethyl ether were dried by distillation from K/benzophenone
under N2. DMAc, DMF, and acetonitrile were dried by distil-
lation from CaH2 under N2. Pd-catalyzed coupling was carried
i
out using Pr2NH that had been sparged with nitrogen for 30
min before use. All NMR spectra were obtained using Bruker
AMX-300, AMX-400, or DRX-500 spectrometers. Infrared
spectra were recorded on a Mattson Infinity FTIR spectrom-
eter, and UV-visible spectra were recorded on an HP 8452A
instrument. Elemental analyses and mass spectra were ob-
(16) J iang, B.; Tilley, T. D. J . Am. Chem. Soc. 1999, 121, 9744.
(17) Suh, M. C.; J iang, B.; Tilley, T. D. Angew. Chem., Int. Ed. Engl.,
in press.

Poly(2,5-diphenylgermole)
Organometallics, Vol. 19, No. 18, 2000 3473
tained at the University of California, Berkeley Microanalyti-
cal Facility and Mass Spectrometry Facility. Electrochemical
measurements were carried out using a BAS 50W potentiostat
using a standard cell consisting of a Pt disk working electrode,
a Pt wire counter electrode, and a reference electrode contain-
ing silver wire and 0.01 M AgNO3 in dry acetonitrile. The
supporting electrolyte was 0.1 M tetrabutylammonium hexaflu-
orophosphate in dry acetonitrile or dry THF. Ferrocene was
used as an internal standard (E1/2 for Fc/Fc+ ) 0) for measure-
ments involving a soluble species and as an external standard
for film measurements. Compound 6 was analyzed as a 0.1 M
solution in THF or acetonitrile, and polymer 7c was analyzed
as a saturated solution (ca. 6 mg/g of THF with 0.1 M
electrolyte). Films of 7c were cast onto the working electrode
by allowing a concentrated THF solution to evaporate in a
glovebox. The film-coated electrodes were then exposed to
vacuum for ca. 10 min. Reduction and oxidation scans were
run on separate samples of films, due to the irreversible nature
of the redox processes observed. All scans were initiated at or
near zero, and the potential was ramped at rates ranging from
200 to 500 mV/s. All measurements were carried out with the
29.6, 31.7, 42.8 (CH2), 71.7, 71.9 (OCH2), 81.5, 88.1 (CC), 122.5,
128.5, 132.5, 133.5 (C6H4). IR (neat, KBr, cm-1): 2930, 2860,
2224, 1897, 1652, 1489, 1466, 1428, 1375, 1288, 1094, 1015,
827, 524. Anal. Calcd for C33H42O2Cl2: C, 73.17; H, 7.83.
Found: C, 72.87; H, 8.00.
4,4-Bis(h exyloxym et h yl)-1,7-b is-p -b r om op h en yl-1,6-
h ep ta d iyn e (1b).16 1-Bromo-4-iodobenzene (11 g, 40 mmol),
4,4-bis(hexyloxymethyl)-1,6-heptadiyne 4 g, 20 mmol), Pd-
(PPh3)4 (0.42 g, 0.36 mmol), and CuI (0.14 g, 0.73 mmol) were
dissolved in 100 mL of THF under nitrogen. After addition of
40 mL of diisopropyamine, the resulting solution was stirred
for 2 days. The white precipitate was removed by filtration.
The filtrate was diluted with hexane and washed with 10%
NH4OH, water, and brine. After drying over MgSO4, the
solvents were removed under vacuo. The oily residue was
subjected to column chromatography on silica gel, eluting first
with hexanes followed by mixture solvents (hexane/ethyl
1
acetate ) 10:1), to obtain 1b as a colorless oil (10 g, 83%). H
NMR (500 MHz, CDCl3): δ 7.40 (d, J ) 10.5, 4H), 7.25 (d, J )
11.0, 4H), 3.46 (s, 4H), 3.43 (t, J ) 6.5, 4H), 2.60 (s, 4H), 1.55
(m, 4H), 1.53-1.26 (m, 16H), 0.87 (t, J ) 7.5, 6H). 13C{1H}
NMR (100 MHz, CDCl3): δ 133.0, 131.4, 123.1, 122.2, 88.3,
81.9, 71.8, 71.6, 42.8, 31.6, 29.5, 25.8, 23.2, 22.6, 14.0. Anal.
Calcd for C33H42Br2O2: C, 62.86; H, 6.71. Found: C, 62.53; H,
6.75.
cell in
a Vacuum Atmospheres glovebox with an argon
atmosphere. Photoluminescence measurements were per-
formed using a Spex FluoroMax fluorimeter on optically dilute
(A ≈ 0.06 in 1 cm quartz cell), degassed solutions of the sample.
Quantum efficiencies were calculated as described18 using
either quinine in degassed 1 N H2SO4 or [Ru(bipy)3][PF6]2 in
dry, degassed acetonitrile as emission standards. Cp2Zr(pyr)-
(Me3SiCCSiMe3) was synthesized according to the literature
procedure.10a
C
35H48GeO2Cl2 (2). A 250 mL Schlenk flask was charged
with Cp2ZrCl2 (3.0 g, 11.0 mmol) and 150 mL of dry THF. This
solution was cooled to - 78 °C in a dry ice acetone bath, and
nBuLi (8.6 mL, 2.45 M, 21.0 mmol) was added dropwise over
5 min. The resulting solution was allowed to stir for 15 min
at -78 °C, and then 1a (4.5 g, 10.0 mmol of diyne) in 10 mL
of dry THF was slowly added over 5 min. The reaction mixture
was allowed to stir under N2 while the cold bath slowly
warmed to room temperature over 3-4 h. Stirring was
continued for an additional 1 h at room temperature. The
zirconocyclopentadiene was not isolated but was converted
directly to the intermediate dibromogermole by addition of
GeBr4 (1.6 mL, 13 mmol) at 0 °C. The reaction mixture was
allowed to stir for 24 h at room temperature, and then the
solvent was removed under vacuum. The resulting residue was
washed with pentane (3 × 75 mL) to separate the intermediate
dibromogermole from the zirconocene dibromide. The pentane
was removed, and the intermediate dibromogermole was
redissolved in 150 mL of THF. The reaction mixture was cooled
to -78 °C, and MeLi (12.6 mL, 1.43 M mmol, 18.0 mmol) was
added dropwise over 5 min. The solution was allowed to slowly
warm to room temperature over 3 h and was then stirred for
an additional 1 h at room temperature. Diethyl ether (100 mL)
was added to the reaction mixture. The resulting mixture was
washed with dilute HCl (150 mL, 0.5 M), H2O (150 mL), dilute
NaHCO3 (150 mL, 1.0 M), and H2O (150 mL). The organic layer
was dried with Na2SO4, and the solvent was removed by
rotoevaporation. The crude product was purified by column
chromatography (25% toluene in hexane). This yielded 2 (61%,
4,4-Bis(h exyloxym eth yl)-1,6-h epta d iyn e. This compound
was prepared from 4,4-bis(hydroxymethyl)-1,6-heptadiyne via
a modified literature procedure.19 A 1 L Erlenmeyer flask was
charged with 4,4-bis(hydroxymethyl)-1,6-heptadiyne (24 g, 158
mmol), 1-bromohexane (59 g, 360 mmol), potassium hydroxide
(36 g, 640 mmol), and DMSO (500 mL). The reaction mixture
was allowed to stir for 10 h at room temperature. The reaction
mixture was then poured into 1 L of H2O and extracted with
Et2O (3 × 250 mL). The solvent was removed by rotoevapo-
ration, and the residue was purified by column chromatogra-
phy (10% EtOAc in hexanes). This yielded 4,4-bis(hexyloxy-
methyl)-1,6-heptadiyne (83%, 42 g) as a colorless oil. 1H NMR
(300 MHz, CDCl3): δ 0.88 (t, J ) 5.1, 6 H, CH3), 1.28 (m, 12
H, CH2), 1.53 (quint, 4 H, CH2), 1.95 (t, J ) 2.1, 2 H, CCH),
2.35 (d, J ) 2.1, 4 H, CCH2), 3.38 (s, 4 H, OCH2), 3.41 (t, J )
4.8, 4 H, OCH2). 13C{1H} NMR (100 MHz, CDCl3): δ 14.0
(CH3), 21.8, 22.6, 25.8, 29.5, 31.7 (CH2), 71.7 (CC4), 70.12, 71.2
(OCH2), 71.4 (CC), 80.9 (CC). IR (neat, KBr, cm-1): 3311, 2956,
2931, 2860, 2798, 2119 (CC), 1466, 1429, 1375, 1117, 636.
4,4-Bis(h exyloxym et h yl)-1,7-b is-p -ch lor op h en yl-1,6-
h ep ta d iyn e (1a ). A 500 mL Schlenk flask was charged with
1-bromo-4-chlorobenzene (5.9 g, 31 mmol), Pd(PPh3)4 (0.20 g,
0.17 mmol), CuI (0.10 g, 0.52 mmol), iPr2NH (50 mL), and THF
(100 mL). To this solution under N2 was added 4,4-bis-
(hexyloxymethyl)-1,6-heptadiyne (4.8 g, 15 mmol). The solution
was allowed to stir at room temperature for 3 days. During
this period a substantial amount of white precipitate formed.
Pentane (100 mL) was added to the reaction mixture, which
was then washed with dilute NH4OH (75 mL, 1.0 M) and H2O
(75 mL). The organic layer was dried with Na2SO4, and the
solvent was removed by rotoevaporation. This yielded 1a (67%,
1
4.3 g) as a yellow oil. H NMR (300 MHz, CDCl3): δ 0.65 (s, 6
H, GeCH3), 0.90 (t, J ) 6.5, 6 H, CH3), 1.26 (m, 12 H, CH2),
1.52 (m, 4 H, CH2), 2.65 (s, 4 H, CH2), 3.32 (s, 4 H, OCH2),
3.39 (t, J ) 6.6, 4 H, OCH2), 7.27 (m, 8 H, C6H4). 13C{1H} NMR
(100 MHz, CDCl3): δ -0.8 (GeCH3), 14.0 (CH3), 22.6, 25.8,
29.5, 31.7, 36.3, 50.0 (CC4), 71.5, 73.6 (OCH2), 128.6, 129.1,
131.4, 134.6, 138.4, 155.2 (C6H4 and C4Ge). IR (KBr, cm-1
2955, 2930, 2858, 1661, 1588, 1487, 1465, 1243, 1109, 1013,
827. Anal. Calcd for 35H48GeO2Cl2: C, 65.24; H, 7.52.
)
1
5.5 g) as a clear oil. H NMR (300 MHz, CDCl3): δ 0.85 (t, J
) 6.6, 6 H, CH3), 1.30 (m, 12 H, CH2), 1.56 (m, 4 H, CH2), 2.61
(s, 4 H, CH2), 3.45 (t, J ) 6.5, 4 H, CH2), 3.47 (s, 4 H, OCH2),
7.28 (d, J ) 8.2, 4 H, C6H4), 7.32 (d, J ) 8.5, 4 H, C6H4). 13C-
{1H} NMR (100 MHz, CDCl3): δ 14.1 (CH3), 22.7, 23.3, 25.9,
C
Found: C, 64.33; H, 7.64. HRMS (EI): Calcd for C35H48GeO2-
Cl2: 644.2226. Found: 644.2226.
C
43H52Br 2O2Zr (3). A 150 mL Schlenk tube was charged
with Cp2Zr(py)(Me3SiC2SiMe3) (1.18 g, 3.0 mmol) and 25 mL
of benzene to give a very dark red solution. To this was slowly
added a solution of 1b (1.63 g, 3.0 mmol) in 10 mL of benzene
until the deep red color changed to light red-orange. The
solution was stirred at room temperature for 2 h and was then
(18) (a) Handbook of Organic Photochemistry; Scaiano, J . C., Ed.;
CRC Press: Boca Raton, FL, 1989; Vol. 1, Chapter 8, p 231. (b) Demas,
J . N.; Crosby, G. A. J . Phys. Chem. 1971, 75, 991.
(19) Fox, H. H.; Wolf, M. O.; O’Dell, R.; Lin, B. L.; Schrock, R. R.;
Wrighton, M. S. J . Am. Chem. Soc. 1994, 116, 2827.

3474 Organometallics, Vol. 19, No. 18, 2000
Lucht et al.
frozen and exposed to vacuum. After sublimation of the
benzene a red oil remained. This oil was dissolved in benzene,
and the resulting solution was frozen and exposed to vacuum
to sublime away the benzene and remove other volatiles. This
procedure was repeated to remove bis(trimethylsilyl)acetylene.
The resulting red oil contained only small amounts of the
alkyne and was pure enough for use in subsequent reactions.
This product can be further purified by crystallization from
pentane. Cooling of a very concentrated solution of crude 3
gave fluffy orange-red microcrystals after 2 days at -40 °C.
Two recrystallizations gave analytically pure 3 (2.12 g, 2.50
nBuLi (6.6 mL, 1.6 M, 10.6 mmol) was added dropwise over 5
min. The solution was allowed to stir for 15 min at -78 °C,
and then 1,7-diphenyl-1,6-heptadiyne (1.3 g, 5.3 mmol) in 10
mL of dry THF was slowly added over 5 min. The zirconocy-
clopentadiene was not isolated, but was converted directly to
6 by addition of GeBr4 (2.3 g, 5.9 mmol) at 0 °C. The reaction
mixture was allowed to stir for 24 h at room temperature and
was then cooled to -78 °C, and MeLi (7.7 mL, 1.43 M) was
added dropwise over 5 min. The solution was allowed to slowly
warm to room temperature over 3 h and was then stirred for
1 h at room temperature. Pentane (100 mL) was added to the
reaction mixture, and the resulting mixture was washed with
dilute HCl (75 mL, 0.5 M), H2O (75 mL), dilute NaHCO3 (75
mL, 1.0 M), and H2O (75 mL). The organic layer was dried
with Na2SO4, and the solvent was removed by rotoevaporation
to yield the crude product, which was purified by column
chromatography (5% EtOAc in hexanes). This yielded 6 (31%,
0.6 g) as a yellow solid. 1H NMR (300 MHz, CDCl3): δ 0.70 (s,
6 H, GeCH3), 2.07 (quint, J ) 5.4, 2 H, CH2), 2.74 (t, J ) 5.4,
4 H, CH2), 7.19 (m, 4 H, C6H5), 7.35 (m, 6 H, C6H5). 13C{1H}
NMR (100 MHz, CDCl3): δ -0.7 (GeCH3), 27.5, 30.7 (CH2),
125.7, 128.8, 128.5, 134.5, 140.3, 156.2 (C6H5 and C4Ge). IR
(KBr, cm-1): 3045, 2957, 1592, 1487, 1439, 1079, 826, 764,
694, 599, 574. Anal. Calcd for C21H22Ge: C, 72.67; H, 6.40.
Found: C, 72.29; H, 6.56. HRMS (EI): Calcd for C21H22Ge:
348.0938. Found: 348.0939.
1
mmol, 83%). H NMR (300 MHz, C6D6): δ 0.86 (t, J ) 5.4, 6
H, CH3), 1.18-1.26 (m, 12 H, CH2), 1.45-1.53 (m, 2 H, CH2),
2.60 (s, 4 H, CH2), 3.29 (s, 4 H, OCH2), 3.33 (t, J ) 5.0, 4 H,
OCH2), 5.75 (s, 10 H, ZrCp), 6.82 (d, J ) 6.3, 4 H, C6H4), 7.43
(d, J ) 6.3, 4 H, C6H4). 13C{1H} NMR (100 MHz, C6D6): δ 14.3
(CH3), 20.3, 26.3, 30.0, 32.0, 40.5, 49.7 (CH2), 71.8, 73.7 (OCH2),
110.4 (ZrCp), 114.1, 117.8 (GeC4), 125.8, 131.7, 148.9, 183.6
(C6H4). IR (KBr, Nujol, cm-1): 1478, 1111, 1073, 1015, 1006,
876, 840, 796, 734. Anal. Calcd for C43H52Br2O2Zr: C, 60.63;
H, 6.16. Found: C, 60.42; H, 6.25.
C
33H42Br 4GeO2 (4). In a Schlenk tube, 3 (0.342 g, 0.40
mmol) was dissolved in 5 mL of dry ether. To this red solution
was added GeBr4 (0.160 g, 0.40 mmol) dissolved in 2 mL of
ether. After stirring for 14 h at room temperature, the solution
color had changed to orange and a light yellow precipitate had
formed. The ether was removed in vacuo to give yellow crystals
and an orange oil. Extraction with pentane (3 × 5 mL) gave
an orange solution containing product and a yellow crystalline
residue, which was identified as Cp2ZrBr2 by 1H NMR spec-
troscopy. The orange solution was concentrated to ca. 3 mL
and cooled to -40 °C. More Cp2ZrBr2 precipitated, and the
supernatant was filtered and cooled again to remove yet more
Cp2ZrBr2. The remaining supernatant was removed, filtered,
and dried in vacuo to give 4 (0.318 g, 92%) as an orange oil
containing a very small amount of Cp2ZrBr2. 1H NMR (300
MHz, C6D6): δ 0.849 (t, J ) 7.14, 6 H, CH3), 1.12-1.34, 1.40-
1.51 (m, 16 H, CH2), 2.63 (s, 4 H, CH2), 3.15 (s, 4 H, OCH2),
3.20 (t, J ) 6.43, 4 H, OCH2), 7.21 (d, J ) 6.62, 4 H, C6H4),
7.44 (d, J ) 6.63, 4 H, C6H4). 13C{1H} NMR (100 MHz, C6D6):
δ 14.2 (CH3), 23.0, 26.2, 29.5, 29.8, 31.9, 37.6 (CH2), 49.1
(C(CH2)4), 71.7, 73.6 (OCH2), 122.3, 126.7, 130.0, 132.2, 134.0,
152.2 (C6H4 and GeC4). IR (neat, KBr, cm-1): 2954, 2930, 2857,
1486, 1465, 1395, 1111, 1076, 1007, 822, 676. Anal. Calcd for
P olym er s 7a ,b. A 100 mL Schlenk flask was charged with
NiCl2 (0.005 g, 0.04 mmol), Zn dust (0.40 g, 6.1 mmol), Ph3P
(0.30 g, 1.1 mmol), bipyridine (0.008 g, 0.05 mmol), and 5.0
mL of DMAc (dimethylacetamide). The mixture was heated
to 70 °C in an oil bath for 20 min, resulting in the formation
of a red/brown solution indicating the formation of the active
Ni catalyst. Compound 2 (0.90 g, 1.5 mmol) in 2.5 mL of dry
DMAc was then added dropwise. The reaction mixture was
allowed to stir for 3 days at 70 °C and was then poured into
200 mL of rapidly stirring MeOH to precipitate the polymer.
The polymer was redissolved in 10 mL of THF. Filtration
removed the unreacted zinc, and the polymer was reprecipi-
tated with 200 mL of MeOH. This yielded 7b (31%, 0.25 g) as
a bright yellow powder and a yellow supernatant solution from
which the oligomer fraction 7a was isolated by removal of the
solvent. 1H NMR (300 MHz, CDCl3): δ 0.71-0.77 (m, 6 H,
GeCH3), 0.87 (br, 6 H, CH3), 1.27 (br, 12 H, CH2), 1.55 (br, 4
H, CH2), 2.72-2.78 (m, 4 H, CH2), 3.35-3.42 (br m, 8 H,
OCH2), 7.45 (br, 4 H, C6H4), 7.61 (br, 4 H, C6H4). 13C{1H} NMR
(100 MHz, CDCl3): δ -0.40 (GeCH3), 14.1 (CH3), 22.7, 25.9,
29.5, 31.7, 36.7 (CH2), 71.6, 73.8 (OCH2), 126.8, 128.6 (C6H4).
IR (KBr, cm-1): 2954, 2928, 2855, 1597, 1490, 1465, 1110, 821.
Anal. Calcd for C35H48GeO2: C, 73.30; H, 8.45. Found: C,
71.49; H, 8.59.
C
33H42Br4GeO2: C, 45.93; H, 4.91. Found: C, 45.68; H, 4.73.
C
35H48Br 2GeO2 (5). In a Schlenk tube, 4 (0.35 g, 0.41 mmol)
was dissolved in 5 mL of Et2O, and the reaction mixture was
cooled to -78 °C. A fresh solution of 1.4 M MeLi in Et2O (0.59
mL, 0.82 mmol) was added to the orange solution of 4. The
color changed slowly from orange to yellow upon warming to
room temperature over 30 min. A small amount of LiBr
precipitated, and after the mixture was stirred for an ad-
ditional 30 min the solvent was removed to give a cloudy yellow
oil. This material was washed with dry pentane and dried in
vacuo to give a bright yellow powder. Extraction with benzene
produced a yellow solution, which was separated from the
white LiBr residue by filtration. The benzene was removed in
vacuo, leaving 5 (0.24 g, 63%) as a yellow oil. 1H NMR (400
MHz, CDCl3): δ 0.65 (s, 6 H, GeCH3), 0.87 (t, J ) 6.9, 6 H,
CH3), 1.25 (m, 12 H, CH2), 1.52 (m, 4 H, CH2), 2.64 (s, 4 H,
CH2), 3.32 (s, 4 H, OCH2), 3.39 (t, J ) 6.6, 4 H, OCH2), 7.19
(d, J ) 8.4, 4 H, C6H4), 7.44 (d, J ) 8.4, 4 H, C6H4). 13C{1H}
NMR (100 MHz, CDCl3): δ -0.8 (GeCH3), 14.0 (CH3), 22.6,
25.8, 29.5, 31.6, 36.2, 50.0 (C(CH2)4), 71.5, 73.6 (OCH2), 119.5,
129.4, 131.6, 134.7, 138.9, 155.4 (C6H4 and C4Ge). IR (neat,
KBr, cm-1): 2954, 2929, 2857, 1485, 1465 (sh), 1384, 1111,
1076, 1007, 823. HRMS (EI)Calcd. for C35H48Br2GeO2: 732.1239.
Found: 732.1231.
P olym er 7c. A 250 mL Schlenk tube was charged with Ni-
(COD)2 (0.14 g, 0.51 mmol) and bipyridine (0.08 g, 0.51 mmol).
DMF (10 mL) and toluene (5 mL) were added. A deep blue
solution resulted, which was shielded from light with Al foil
and heated at 60 °C for 20 min. To this mixture was added 5
(0.30 g, 0.43 mmol) all at once via a gastight syringe as a
toluene solution (10 mL). A color change to red was observed,
and the mixture was stirred under nitrogen in the dark for 3
h. At this point small, bright yellow droplets of the product
polymer formed on the walls of the reaction vessel. Wet THF
(20 mL) was promptly added to stop the reaction and dissolve
the portion of the product that had precipitated. The red-yellow
mixture was poured into a rapidly stirred solution (100 mL)
of 0.06 M HCl in MeOH. The bright yellow polymer that
precipitated was collected by centrifugation and washed with
neutral MeOH (2 × 40 mL). The polymer was dried in air and
then swelled with 2 mL of THF. After addition of 10 mL of
CHCl3 and heating at 45 °C for 2 days, the entire polymer
sample dissolved. The fluorescent yellow solution was filtered
and poured into 100 mL of MeOH to reprecipitate the polymer.
After washing with MeOH (2 × 40 mL), the bright yellow solid
C
21H22Ge (6). A 250 mL Schlenk flask was charged with
Cp2ZrCl2 (1.6 g, 5.4 mmol) and 100 mL of dry THF. The
solution was cooled to - 78 °C in a dry ice acetone bath, and

Poly(2,5-diphenylgermole)
Organometallics, Vol. 19, No. 18, 2000 3475
was dried in vacuo to give a yellow powder (0.21 g, 0.39 mmol,
90%). 1H NMR (300 MHz, CDCl3): δ 0.77 (m, 6 H, GeCH3),
0.87 (br, 6 H, CH3), 1.27 (br, 12 H, CH2), 1.55 (br, 4 H, CH2),
2.72-2.78 (br m4 H,, CH2), 3.35-3.42 (br m, 8 H, OCH2), 7.45
(br, 4 H, C6H4), 7.61 (br, 4 H, C6H4). 13C{1H} NMR (100
MHz,CDCl3): δ -0.40 (GeCH3), 14.1 (CH3), 22.6, 25.8, 29.5,
31.7, 36.7 (CH2), 50.0 (CC4), 71.5, 73.8 (OCH2), 126.8, 128.5,
135.3, 137.9, 139.0, 155.0 (GeC4 and C6H4). IR (KBr, cm-1):
3023, 2953, 2928, 2853, 1598, 1490, 1465, 1365, 1232, 1107,
1001, 819, 791, 723, 576. Anal. Calcd for C35H48GeO2: C, 73.30;
H, 8.44. Found: C, 73.06; H, 8.45.
Ack n ow led gm en t is made to the National Science
Foundation for their generous support of this work. We
thank Prof. J im McCusker for use of his Spex fluorim-
eter and BAS potentiostat.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal,
data collection, and refinement parameters, bond distances
and angles, and anisotropic displacement parameters for 6.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM000191E