Two alternative, convenient routes to bis(diphenylacetylene)platinum(0)

Article abstract of DOI:10.1021/om020230h

Two new synthetic routes are presented that allow the convenient preparation and isolation of bis-(diphenylacetylene)platinum(0) under ambient conditions. The first procedure is based on a ligand exchange reaction between Ph-C≡C-Ph and tris(styrene)platinum(0). The second framework relies on the reduction of cis-[PtCl₂(PhCH=CH₂)₂] with triphenylsilane in the presence of diphenylacetylene.

Full text of DOI:10.1021/om020230h

Organometallics 2002, 21, 3817-3818
3817
Notes
Tw o Alter n a tive, Con ven ien t Rou tes to
Bis(d ip h en yla cetylen e)p la tin u m (0)
Christian Huber,†,‡ Akshay Kokil, Walter R. Caseri,* and Christoph Weder*
‡
,†
,‡
Department of Materials, Institute of Polymers, ETH Z u¨ rich, Universit a¨ tsstrasse 41, UNO
C15, 8092 Z u¨ rich, Switzerland, and Department of Macromolecular Science and Engineering,
Case Western Reserve University, 2100 Adelbert Road, Cleveland, Ohio 44106-7202
Received March 26, 2002
2
Summary: Two new synthetic routes are presented that
allow the convenient preparation and isolation of bis-
Sch em e 1. Syn th esis of [P t(η -P h -CtC-P h )
2
] (3)
th r ou gh (i) Liga n d Exch a n ge betw een
(
diphenylacetylene)platinum(0) under ambient condi-
[P t(P h CHdCH
Red u ction of cis-[P tCl
Tr ip h en ylsila n e in P r esen ce of P h -CtC-P h
2
)
3
] (2) a n d P h -CtC-P h , a n d (ii)
(P h CHdCH ] (1) w ith
tions. The first procedure is based on a ligand exchange
reaction between Ph-CtC-Ph and tris(styrene)plati-
num(0). The second framework relies on the reduction
of cis-[PtCl2(PhCHdCH2)2] with triphenylsilane in the
presence of diphenylacetylene.
2
2 2
)
Zerovalent platinum complexes are important for a
1
wide variety of homogeneous catalytic processes. Bis-
2
(
η -alkyne)platinum(0) complexes represent a particu-
larly interesting subgroup that is viewed as a family of
potentially) useful synthetic intermediates, since the
alkyne ligands are readily replaced by other donor
(
2
-4
ligands such as PMe3, PEt3, PPh3, and t-BuCN.
These
alkyne complexes are frequently synthesized by ligand
exchange reactions from bis(1,5-cyclooctadiene)plati-
2
,3
2
4
num(0) or tris(η -ethylene)platinum(0). However, the
synthesis of the latter compounds is laborious and
5
,6
requires rigorous exclusion of oxygen and water. The
2
preparation of bis(η -alkyne)platinum(0) complexes via
decomposition of bis(4-penten-1-yl)platinum(II) in the
7
presence of alkynes has also been reported, but the
related procedures require not only a protective atmo-
sphere but also high pressure, which renders the
preparation intricate. Another method starts from the
hydrosilylation catalyst hexachloroplatinic(IV) acid,
which is heated in the presence of an excess of sym-
tetramethyldivinylsiloxane and exposed in situ to
reduction appears to be induced by impurities, subject-
ing this reaction to some imponderables. Indeed, it is
well established that the reduction of hexachloropla-
tinic(IV) acid in hydrosilylation catalysis is accompanied
8
alkynes. Surprisingly, H2[PtCl6]‚xH2O is reduced with-
out explicite addition of a reducing agent. Thus, the
9
†
by an induction period of variable length.
ETH Z u¨ rich.
Case Western Reserve University.
‡
Here, we describe two simple, well-defined and re-
(
1) Hartley, F. R. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Ed.; Pergamon Press: Oxford, 1982; Vol. 6, p 471.
2) Boag, N. M.; Green, M.; Grove, D. M.; Howard, J . A. K.; Spencer,
J . L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1980, 2170.
3) Green, N.; Grove, D. M.; Howard, J . A.; Spencer, J . L.; Stone, F.
G. A. J . Chem. Soc., Chem. Commun. 1976, 759.
4) Young, B. In Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
995; Vol. 9, p 533.
5) Ozawa, F. In Synthesis of Organometallic Compounds; Komiya,
S., Ed.; Wiley & Sons: Chichester, 1997; p 249.
6) Crascall, L. E.; Spencer, J . L.; Doyle, R. A.; Angelici, R. J . Inorg.
Synth. 1990, 28, 126.
7) Tagge, C. D.; Simpson, R. D.; Bergman, R. G.; Hostetler, M. J .;
Girolami, G. S.; Nuzzo, R. G. J . Am. Chem. Soc. 1996, 118, 2634.
8) Chandra, G.; Lo, P. Y.; Hitchcock, P. B.; Lappert, M. F. Orga-
nometallics 1987, 6, 191.
2
producible methods for the synthesis of [Pt(η -Ph-Ct
2
,8
(
C-Ph)2] (3), which can be performed under ambient
conditions. The first procedure is based on a ligand
exchange reaction between Ph-CtC-Ph and tris-
(styrene)platinum(0) (2). The latter complex is readily
(
(
10
obtained by reduction of cis-[PtCl2(PhCHdCH2)2] (1)
1
1
1
(
with triphenylsilane in a styrene solution. The styrene
solution of 2 is stable for months even in the absence of
a protective gas. Extensive NMR investigations revealed
(
(
(9) Speier, J . L. Adv. Organomet. Chem. 1979, 17, 407.
(10) Albinati, A.; Caseri, W. R.; Pregosin, P. S. Organometallics
1987, 6, 788.
(
1
0.1021/om020230h CCC: $22.00 © 2002 American Chemical Society
Publication on Web 08/02/2002

3
818 Organometallics, Vol. 21, No. 18, 2002
Notes
that 2 readily converts in situ into a variety of Pt(0)
derivatives by ligand exchange, in particular with 1,2-
bis(diphenylphosphino)ethane (diphos), P(OEt)3, and
1
2
fyingly, 3 could indeed be isolated with this method in
1
4
high purity. Preliminary experiments have shown that
2
also [Pt(η -HOMe2C-CtC-CMe2OH)2] can be synthe-
,5-cyclooctadiene (cod).11 Regrettably, however, neither
nor derivatives prepared via the latter could be
sized by this framework, while attempts to prepare [Pt-
(cod)2] using the same procedure have hitherto been
unsuccessful.
isolated in the past from the styrene solution. We now
have found that treating a styrene solution of 2 with
Thus, in summary, we have demonstrated two new
2
2
Ph-CtC-Ph leads to the formation of [Pt(η -Ph-Ct
and convenient routes for the synthesis of bis(η -alkyne)-
C-Ph)2] (3) (Scheme 1). In situ 1 Pt NMR experiments
95
platinum(0). Both methods depart from readily acces-
sible, chemically stable intermediates, are based on
straightforward and undemanding reaction conditions,
and afford the desired product in high purity.
revealed that the signals related to 2 at -5874.8 and
-5893.2 ppm are fully suppressed upon addition of 2
equiv of Ph-CtC-Ph per Pt atom, and the only
detectable resonance is that of 3 at -3548 ppm. Thus,
even in the presence of a large excess of styrene, the
styrene ligands coordinated to Pt(0) are very efficiently
replaced by Ph-CtC-Ph. In contrast to the in-situ-
prepared complexes mentioned above, we were able to
Ack n ow led gm en t. We are indebted to Prof. Paul
Smith of ETH Z u¨ rich for his support of this work. We
also cordially thank Mr. F. Bangerter of ETH Z u¨ rich
for crucial assistance with the NMR experiments. We
also acknowledge partial funding for this study from the
Case School of Engineering.
1
2,13
isolate 3 by precipitation upon addition of pentane.
We subsequently explored the possibility of preparing
directly through the reduction of cis-[PtCl2(PhCHd
3
OM020230H
CH2)2] with triphenylsilane in the presence of Ph-Ct
C-Ph (Scheme 1) and under ambient conditions. Grati-
(
14) Triphenylsilane (439 mg, 1.68 mmol) was added to a mixture
of [PtCl (PhCHdCH ] (400 mg, 0.844 mmol) and Ph-CtC-Ph (1.50
g, 8.46 mmol) in CH Cl (16 mL), and the reaction mixture was stirred
2
2 2
)
2
(
(
11) Caseri, W.; Pregosin, P. S. Organometallics 1988, 7, 1373.
12) Ph-CtC-Ph (3.00 g, 16.9 mmol) was added to a solution of
2
for 30 min. Aqueous ammonia (37 mL, 3%) was added, and the mixture
was vigorously stirred for 90 min. The organic phase was separated
off, extracted with water (33 mL), and filtered through a 3 cm plug of
Pt(PhCHdCH
2
)
3
(∼0.37 mmol) in styrene (20 mL), and styrene was
distilled off (10 mbar, 50 °C) to reduce the volume of the mixture to 5
mL. Pentane (15 mL) was added, and the mixture was cooled to 0 °C.
The resulting solid was filtered off, washed with pentane, dried in
Alox (basic, activity I), which was subsequently rinsed with CH
2 2
Cl
(16 mL), and the organic layers were combined. CH Cl was distilled
2
2
vacuo, and reprecipitated from CH
to afford a pale yellow solid (117 mg, ∼57%). Pt NMR (64 MHz, CD
Cl , 263 K): δ -3553 ppm. Anal. Calcd for C28 20Pt: C, 60.98; H, 3.65.
Found: C, 60.81; H, 4.06.
13) Note that the reactions reported here have not yet been
optimized for yield.
2
Cl
2
/pentane (5/30 mL) at -78 °C
off to reduce the volume of the mixture to 5 mL, pentane (20 mL) was
added, and the mixture was cooled to 0 °C. The resulting solid was
filtered off, washed with pentane, and dried in vacuo to afford a pale
1
95
2
-
2
H
1
95
yellow solid (121 mg, 26%).
-3553 ppm. Anal. Calcd for C28H
Pt NMR (64 MHz, CD
2 2
Cl , 263 K): δ
(
20Pt: C, 60.98; H, 3.65. Found: C,
61.14; H, 4.13.