Platinum-catalyzed bis-germylation of alkynes with organodigermanes and cyclic oligogermanes

Article abstract of DOI:10.1246/bcsj.74.123

Hexamethyldigermane, Me₃GeGeMe₃, reacted with various alkynes in the presence of platinum complexes at 120 °C to afford Z-1,2-bis(germyl)ethenes in moderate to good yields. Terminal alkynes exhibit higher reactivities than internal ones. [Pt(acac)₂] and [Pt(dba)₂] serve as efficient catalysts, while [Pt(PPh₃)₄], [PtCl₂(PPh₃)₂], and [Pt(dba)₂]-phosphite were found to be inactive. Four- and six-membered cyclic oligogermanes, such as dodecamethylcyclohexagermane, (Me₂Ge)₆, reacted with alkynes in the presence of platinum catalysts to yield 1,4-digermacyclohexa-2,5-dienes in ca. 30% yield. The reactions of phenylacetylene with 1,2-digermacyclohexa-3,5-dienes afforded the corresponding 1,4-digermacycloocta-2,5,7-trienes in 93% yield. Bis(germyl)platinum complexes having various tertiary phosphine ligands have been prepared as models of a key intermediate in the above mentioned catalytic bis-germylation of alkynes, and their structures have been established by spectroscopic methods and X-ray crystallography. Bis(germyl)platinum complexes reacted with phenylacetylene to give the corresponding insertion products, germyl(germylvinyl)platinum species, whose structures have been determined by spectroscopic and X-ray analysis. Germyl(germylvinyl)platinum complexes were found to liberate a bis-germylation product of the alkyne upon heating. The result supports a mechanism involving the oxidative addition of a digermane to a Pt(0) complex, the insertion of an alkyne into one of the two Pt-Ge bonds to give a germyl(germylvinyl)platinum species, and the reductive elimination of the bis-germylation product of the alkyne. Evidence suggesting the extrusion of a germylene unit from the bis-germylplatinum species has been obtained, accounting for the generation courses of other by-products.

Full text of DOI:10.1246/bcsj.74.123

© 2001 The Chemical Society of Japan
123
Bull. Chem. Soc. Jpn., 74, 123–137 (2001)
Platinum-Catalyzed Bis-Germylation of Alkynes with
Organodigermanes and Cyclic Oligogermanes
Kunio Mochida,* Tohru Wada, Kaoru Suzuki, Wakako Hatanaka, Yuriko Nishiyama ,
Masato Nanjo, Akiko Sekine,† Yuji Ohashi,† Masato Sakamoto,†† and Akio Yamamoto*,
††
Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
†Department of Chemistry, Faculty of Science, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8551
††Advanced Research Institute for Science and Engineering, Waseda University,
3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555
(Received July 21, 2000)
Hexamethyldigermane, Me3GeGeMe3, reacted with various alkynes in the presence of platinum complexes at 120
°C to afford Z-1,2-bis(germyl)ethenes in moderate to good yields. Terminal alkynes exhibit higher reactivities than in-
ternal ones. [Pt(acac)2] and [Pt(dba)2] serve as efficient catalysts, while [Pt(PPh3)4], [PtCl2(PPh3)2], and [Pt(dba)2]-phos-
phite were found to be inactive. Four- and six-membered cyclic oligogermanes, such as dodecamethylcyclohexager-
mane, (Me2Ge)6, reacted with alkynes in the presence of platinum catalysts to yield 1,4-digermacyclohexa-2,5-dienes in
ca. 30% yield. The reactions of phenylacetylene with 1,2-digermacyclohexa-3,5-dienes afforded the corresponding 1,4-
digermacycloocta-2,5,7-trienes in 93% yield. Bis(germyl)platinum complexes having various tertiary phosphine ligands
have been prepared as models of a key intermediate in the above mentioned catalytic bis-germylation of alkynes, and
their structures have been established by spectroscopic methods and X-ray crystallography. Bis(germyl)platinum com-
plexes reacted with phenylacetylene to give the corresponding insertion products, germyl(germylvinyl)platinum species,
whose structures have been determined by spectroscopic and X-ray analysis. Germyl(germylvinyl)platinum complexes
were found to liberate a bis-germylation product of the alkyne upon heating. The result supports a mechanism involving
the oxidative addition of a digermane to a Pt(0) complex, the insertion of an alkyne into one of the two Pt−Ge bonds to
give a germyl(germylvinyl)platinum species, and the reductive elimination of the bis-germylation product of the alkyne.
Evidence suggesting the extrusion of a germylene unit from the bis-germylplatinum species has been obtained, account-
ing for the generation courses of other by-products.
A transition metal-catalyzed addition of group-14 element
compounds to unsaturated organic substrates is a useful funda-
mental process in group-14 element chemistry. The addition
of Si−Si bonds to C−C triple and double bonds, i.e., bis-silyla-
tion, has attracted considerable current interest in the synthesis
of functional molecules and in applications to selective organic
synthesis.1–8 For the bis-silylation of C−C triple bonds, palladi-
um complexes have often been used as catalysts. In contrast to
the extensive use of the bis-silylation method and of consider-
able studies on reaction mechanisms, there have been few re-
ports on bis-germylation reactions, except for the reaction of
strained digermiranes,9 chlorine-substituted digermanes,10 and
ocatamethyltrigermanes.11 We report herein on the digermyla-
tion of alkynes using various substituted digermanes,
(Me2RGe)2 (R = Me, Cl, Ph), cyclic oligogermanes, (R2Ge)n (R
= Me, n = 6; iPr, n = 4), and 1,2-digermacyclohexa-3,5-dienes
in the presence of platinum complexes. We also report on the
characterization and reactivites of bis(germyl)platinum com-
plexes and germyl(germylvinyl)platinum complexes that are
assumed as key intermediates in these platinum-catalyzed pro-
cesses.
Results
Platinum-Catalyzed Reactions of Substituted Diger-
manes, Me2RGeGeMe2R (R = Me, Cl, Ph) with Alkynes.
When a degassed toluene solution of 1 mol equiv of hexameth-
yldigermane, Me3GeGeMe3 (1a) containing 5 mol equiv of
phenylacetylene (2a), and [Pt(acac)2] (acac = acetylacetonate)
(0.05 mol equiv based on 1a) was heated at 120 °C for 16 h,
Z-1-phenyl-1,2-bis(trimethylgermyl)ethene (3a) was obtained
as a sole product in moderate yield (59% GC yield based on
1a) (Eq. 1). The rest of the digermane remained unreacted.
The concentration of the reaction mixture by the evaporation of
toluene followed by preparative TLC with silica gel gave pure
3a, which showed satisfactory NMR, IR, and MS data.
(1)

124 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
The geometry was confirmed to be Z on the basis of their spec-
troscopic data12 and by a comparison with those of the authen-
tic E isomer prepared separately by a reaction of chloro-
trimethylgermane Me3GeCl, and phenylacetylene, with Mg
metal in HMPA.13 In contrast to the fairly good catalytic activi-
ty shown by [Pt(acac)2], a similar reaction of 1a with pheny-
lacetylene in the presence of a palladium complex has been re-
ported to give only 1.3% yield of 3a.10
Besides [Pt(acac)2], a zero-valent platinum complex,
[Pt(dba)2] (dba = dibenzylideneacetone), also catalyzed the
bis-germylation of 2a to give 3a in moderate yields. Under
similar conditions, the use of [PtCl2(cod)] (cod = 1,5-cyclo-
octadiene) resulted in low yields of 3a, and conventional Pt cat-
alysts such as [Pt(PPh3)4] and [PtCl2(PPh3)2], and [Pt(dba)2]-
phosphite systems (phosphite = P(OMe)3 and P(OCH2)3CEt)
proved to be inactive. The effects of various platinum catalysts
on the addition of Ge–Ge bonds of 1a to 2a are summarized in
Table 1. The effect of other experimental conditions on the
yield of 3 in the present process was examined using the
[Pt(acac)2] catalyst. Lowering the reaction temperature from
120 to 80 °C resulted in lower yields of 3a (56 to 10%), while
raising the temperature to 140 °C had a deteriorating effect,
yielding 3a in only 10%. Formation of several unidentified by-
products in minor amounts was noted in the process carried out
at 140 °C. Extending the reaction time scarcely improved the
Table 2. Reactions of Digermanes (1) with Alkynes (2) in
the Presence of [Pt(acac)2]a)
Run Digermane Alkyne Conversion of 1/% Product 3,yield/% b)
1
2
3
4
5
6
7
8
9
1a
1a
1a
1a
1a
1a
1a
1b
1c
2a
2b
2c
2d
2e
2f
2g
2a
2a
60
17
58
10
0
0
0
100
0
59 (Z/E = 100/0)
8
55
8
0
0
0
19
0
a) 1 (0.10 mmol), 2 (0.50 mmol),[Pt(acac) 2] (0.005 mmol),toluene
(1 ml),120 ◦C ,16 h. b) GC yield based on 1.
3b–3d was obtained as a single stereoisomer, probably the Z-
isomer. Internal alkynes, such as diphenylacetylene (2e), 1-
phenyl-2-(trimethylsilyl)acetylene (2f), and dimethyl acety-
lenedicarboxylate (2g), proved to be unreactive toward 1a un-
der similar conditions.
In contrast to the platinum-catalyzed reactions of alkyl-
digermane 1a with alkynes, the reaction of its chlorinated
analog, 1,2-dichloro-1,1,2,2-tetramethyldigermane, ClMe2-
GeGeMe2Cl (1b) with phenylacetylene (2a) in the presence of
[Pt(acac)2] under the same conditions as those for 1a gave a
complex mixture of germylation products. The starting diger-
mane 1b was completely consumed and converted into 1,2-
bis(chlorodimethylgermyl)-1-phenylethene (3h, 19%), 1- or 2-
(chlorodimethylgermyl)styrene (4 or 4′, 17%), germole (5,
5%), 1,4-digermacyclohexa-2,5-diene (6, 5%), and some uni-
dentified products (Eq. 2).
yield of 3a. Decreasing the ratio of 2a/1a from 5:1 to 1:1
caused a lowering of the yield of 3a (59 to 26%). An increase
in the concentration of [Pt(acac)2] relative to the digermane 1a
(from 1.0 to 10 mol%) did not influence the yields of 3a.
The reactivities of other terminal and internal alkynes,
2a–2g, with the digermane 1a and with the dichloro- and
diphenyl-substituted digermanes 1b and 1c (Eq. 2) were also
examined with [Pt(acac)2] as catalyst, as summarized in Table
2. (Trimethylsilyl)acetylene (2c) reacted with 1a under the
same reaction conditions as those for 2a to give 1,2-
bis(trimethylgermyl)-1-trimethylsilylethene (3c) in 55% yield.
Other terminal alkynes, such as 1-hexyne (2b) and methyl pro-
piolate (2d), gave the corresponding 1,2-bis(trimethylger-
myl)ethenes (3b, d) in low yields. The reaction of 2d resulted
in the formation of a complex mixture. Each compound of
Table 1. Effects of Platinum Catalysts on the Reaction of
Hexamethyldigermane (1a) with Phenylacetylene (2a)a)
The bis-germylstyrene 3h produced by alkyne-insertion into
the Ge–Ge bond in 1b was found to be a mixture of two stereo-
isomers (E/Z = 50/50). The bis-germylstryene 3h was easily
hydrolyzed with moisture. Therefore, the yield and stereo-
isomer ratio of 3h were estimated by a comparison with the au-
thentic E isomer by means of GC and NMR analysis of the cor-
responding methylated compound after treating the reaction
mixture with MeMgI. Compounds 4–6 were obtained as regio-
isomeric mixtures, and their configurations have not been un-
ambiguously established. Similar results were obtained when
[Pt(dba)2] was employed. The reaction carried out in the pres-
ence of the [Pt(dba)2]-P(OCH2)3CEt system under similar reac-
tion conditions gave 3h (9%) as the major product with a lower
conversion (36%).
Run
Catalyst
Conversion of 1a Product 3a,yield/% b)
1
2
3
4
5
6
7f)
8
[Pt(PPh3)4]
[PtCl2(PPh3)2]
[Pt(dba)2]c)
0
0
40
0
0
36
[Pt(dba)2] + ETPBd)
[Pt(dba)2] + 2P(OMe)3
[Pt(acac)2]e)
trace
trace
60
trace
trace
59
[Pt(acac)2]
[PtCl2(cod)]g)
30
10
26
10
a) 1 (0.10 mmol), 2 (0.50 mmol),[Pt(acac) 2] (0.005 mmol),toluene
(1 ml),120 ◦C,16 h. b) GC yields were calculated on the basis of
the amounts of 1a used. c) dba = dibenzylideneacetone. d) ETBP =
P(OCH2)3CEt. e) acac = acetylacetonato. f) 1a (0.5 mmol), 2a (0.5
mmol),[Pt(acac) 2] (0.005 mmol). g) cod = 1,5-cyclooctadiene.

K. Mochida et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001) 125
Bis-germylation of phenylacetylene with 1,2-dichloro-
1,1,2,2-tetramethyldigermane (1b) has been reported to pro-
ceed in the presence of the [Pd(dba)2]-P(OCH2)3CEt system in
moderate to good yields.10
°
C
. At the same time, 1,1-dimethyl-2,3,4,5-tetraphenyl-1-germa-
cyclopenta-2,4-diene (tetraphenylgermole) (11) and diphenyl-
acetylene were produced in 20 and 19% yields, respectively
.
The reaction of 1,2-diphenyl-1,1,2,2-tetramethyldigermane,
Me2PhGeGePhMe2 (1c), with 2a did not proceed, even at high-
er temperature, with longer reaction times and with higher con-
centrations of platinum complexes.
(5)
Reactions of Cyclic Oligogermanes with Phenyl-
acetylene. As an extension of studies on the reactions of
digermanes with alkynes, the reactions of cyclic oligo-
germanes with alkynes were examined. A degassed toluene so-
lution containing dodecamethylcyclohexagermane, (Me2Ge)6
(7) (1 mol equiv) and 30 mol eqiuv of phenylacetylene (2a)
(alkyne/Ge ratio = 5:1) in the presence of Pt(acac)2 (0.05 mol
equiv of 2a) was heated at 120 °C for 32 h to give a 1:1 mixture
It was confirmed that the tetraphenylgermole (11) and the
diphenylacetylene were produced upon the thermolysis of 10
above 100 °C in the presence of a catalytic amount of
[Pt(acac)2] without any involvment of phenylacetylene. The re-
sults indicate that the phenylacetylene-inserted product 10 is
decomposed at higher temperatures in the presence of the plat-
inum catalyst without the participation of phenylacetylene to
give the germole 11 and diphenylacetylene. The time course
of the reaction of 9 with 2a in the presence of [Pt(acac)2] is
shown in Fig. 1.
of
1,1,4,4-tetramethyl-1,4-digerma-2,6-diphenylcyclohexa-
2,5-diene (6a) and 1,1,4,4-tetramethyl-1,4-digerma-2,5-
diphenylcyclohexa-2,5-diene (6b) in a total yield of 38% (rela-
tive to 7) with the rest of 7 (67%) recovered unreacted from the
toluene solution (Eq. 3).
Fig. 1 shows that 1,2-digermacyclohexadiene 9 is decom-
posed, but that the alkyne-insertion product 10, tetraphenyl-
germole 11, and diphenylacetylene are not formed during the
early stage of the reaction.
The formation of the tetraphenylgermole 11 from 9 indicates
that a germylene unit was extruded in the platinum-catalyzed
thermolysis of the cyclic digermane 9. For trapping the ger-
mylene in the platinum-catalyzed reactions, the cyclic diger-
mane 9 was treated with a catalytic amount of [Pt(acac)2] at
120 °C for 16 h in toluene containing excess CCl4 which is
known to trap germylene.15 The reaction gave Me2GeCl2 (26%)
and Cl3CCCl3 (10%) together with the germole 11 and
diphenylacetylene in support of the liberation of the dimethyl-
germylene entity in the platinum-catalyzed thermolysis of the
digermane 9.
The reactivities of other dimetallacyclohexadienes 12 and
related compounds with 2a were examined with [Pt(acac)2] as
a catalyst in toluene (Eq. 6); the results are included in Table 3.
1, 1, 2, 2-Tetramethyl-3,4,5,6-tetraphenyl-1,2-disilacyclhexa-
3,5-diene (12a) reacted with 2a under similar reaction condi-
tions as those for 9 to give the alkyne-insertion product 13a
(19%), tetraphenylsilol (14a) (21%) together with a trace
amount of diphenylacetylene (run 3 in Table 3). Other
(3)
No acyclic alkyne-inserted products were detected by means of
GC and MS analyses. Other platinum complexes, such as
[Pt(dba)2] and [PtCl2(cod)], also catalyzed the reaction to give
6 in 31–33% yields. In contrast to the platinum complexes, the
[Pd(dba)2]-2P(OCH2)3CEt catalyst system was much less reac-
tive, and converted only 10% of 7 into 6 in 10% total yield.
The reaction of strained octaisopropylcyclotetragermane
(iPr2Ge)4 (8) with 2a did not occur under the same conditions
as those for 7. The result is in marked contrast to that in the re-
action of 8 with 2a performed in the presence of palladium
complexes. With the [Pd(dba)2]-2P(OCH2)3CEt as the catalyst
system, the cyclotetragermane 8 reacted with 2a to give the
corresponding alkyne-inserted tetragermacyclohexene in good
yields (70%).14
Reactions of 1,2-Digermacyclohexa-3,5-dienes with
Phenylacetylenes.
1, 1, 2, 2-Tetramethyl-3,4,5,6-tetraphe-
nyl-1,2-digermacyclohexa-3,5-diene (9) reacted with 1.5 equiv
of 2a in the presence of a catalytic amount of [Pt(acac)2] at 80
°C in 36 h with cleavage of the Ge–Ge bond to give the phenyl-
acetylene-inserted compound 10 in 96% yield as colorless
crystals (Eq. 4).
(4)
Fig. 1. The time-course of reaction of 1,1,2,2-tetra-
methyl-3,4,5,6-tetraphenyl-1,2-digermacyclohexa-3,5-
diene (9) with phenylacetylene (2a) in the presence of
[Pt(acac)2] at 100 ◦C.
The yield of the alkyne-insertion product 10 decreased from 96
to 26% upon raising the reaction temperature from 80 to 120

126 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
The structure of the new type of germanium-containing
eight-membered ring compound 10 was fully established by
spectroscopic and X-ray diffraction methods. The molecular
structure of 10 is shown in Fig. 2 and the crystallographic data
are summarized in Table 4. Selected bond lengths and angles
in complex 10 are tabulated in Table 5. Compound 10 has a
twisted geometry between the two planes Ge(1)−C(6)−C(5)−
Ge(2) and C(1)−C(2)−C(3)−C(4). The Ge(1)−C(6) and Ge(2)−
C(5) bond lengths (1.955–1.962 Å) are shorter than those of
Ge(1)−C(1) and Ge(2)−C(4) (1.977–1.985 Å).
Table 3. Reactions of Dimetallatetraphenylcyclohexadi-
enes (9,12) with Phenylacetylene (2a) in the Presence of
[Pt(acac)2]a)
Run
R2E-ER2
R’
Products, yield/%b)
Unit in cyclohexadiene
10 or 13 11 or 14 PhC CPh
1c) Me2Ge GeMe2 (9)
Ph
Ph
96
2
3
4
5
6
7
8
M
M
M
M
2Gee GeMe2 (9)
26
19
20
21
0
19
2Sei SiMe2 (12a) Ph
2Sei GeMe2 (12b) Ph
trace
trace
0
0
0
0
0
0
2Gee CH2 (12c)
H
0
Et2Ge GeEt2 (12d) Ph
trace
0
0
Et2Si SiEt2 (12e)
Et2Si GeEt2 (12f)
Ph
Ph
0
trace
0
a) 9 or 12 (0.5 mmol), 2a (0.5 mmol), [Pt(acac)2] (0.025 mmol),
toluene (1 ml), 120 ◦C, 16 h. b) GC yield based on 9 or 12. c) At 80
◦C for 36 h.
dimetallacyclohexadienes (12b, 12d–12f) and mono-
germacyclohexadiene 12c did not react with phenylacetylene.
The alkyne-insertion product by the reaction of 12a with
acetylenedicarboxylate (2g) in the presence of [PdCl2(PPh3)2]
was observed by Sakurai and co-workers.16
Fig. 2. Molecular structure of the 1,1,4,4-tetramethyl-
2,5,6,7,8-pentaphenyl-1,4-digermacyclohexa-2,5,7-
triene (10) (30% probability thermal ellipsoids drawn by
ORTEPII∗). Hydrogen atoms are omitted for clarity.
(6)
Table 4. Crystallographic Data for 10, cis-15, cis-16, trans-17, 18, 19, and cis-21
cis-15 cis-16 trans-17 18 19
10
cis-21
Chem formula
fw
Cryst syst
C40H38Ge2
664.00
triclinic
P1
9.160 (2)
19.221 (4)
21.234 (4)
108.25 (1)
98.75 (2)
102.5 (2)
3368 (1)
4
C32H44Ge2P2Pt C42H48Ge2P2Pt C52H52Ge2P2Pt C52H30Ge2P2Pt·C6H6 C32H42Ge2P2Pt C50H54Ge2P2Pt
830.88
monoclinic
C2/c
955.02
monoclinic
C2/c
1079.15
monoclinic
P21/c
1135.08
monoclinic
P21/n
828.89
1057.14
triclinic
P1
monoclinic
P21/n
Space group
˚
a/A
17.417 (1)
11.430 (1)
17.424 (1)
90
108.895 (5)
90
15.672 (5)
14.708 (5)
18.012 (5)
90
105.891 (5)
90
16.4320 (5)
11.2320 (2)
25.4170 (6)
90
105.918 (1)
90
15.754 (2)
19.864 (2)
17.025 (2)
90
105.401 (9)
90
10.686 (1)
18.669 (1)
17.660 (1)
90
105.581 (2)
90
11.349 (2)
11.515 (2)
20.271 (3)
98.370 (7)
98.342 (7)
115.056 (8)
2310.2 (6)
2
˚
b/A
˚
c/A
α/deg
β/deg
γ/deg
3
˚
V/A
3281.8 (5)
4
3963 (2)
4
4511.19 (19)
4
5136 (1)
4
3393.6 (2)
4
Z
Dcalc/g cm−3
T(K)
1.31
296
1.682
1.589
1.589
1.468
1.622
1.520
296
296
296
296
296
120
Cryst dimens/mm 0.50 × 0.10 0.20 × 0.15
0.30 × 0.25
0.30 × 0.30
0.30 × 0.20
0.15 × 0.10
0.25 × 0.2
× 0.05
Reflns (hkl) limits −10 ≤ h ≤ 0
−22 ≤ k ≤ 22
× 0.10
× 0.20
× 0.20
× 0.20
× 0.08
× 0.2
0 ≤ h ≤ 22 −17 ≤ h ≤ 17
0 ≤ k ≤ 14 −16 ≤ k ≤8
0 ≤ h ≤ 21 −19 ≤ h ≤ 20
0 ≤ h ≤ 14
0 ≤ h ≤ 14
0 ≤ k ≤14
0 ≤ k ≤ 25
0 ≤ k ≤ 24 −14 ≤ k ≤ 13
−24 ≤ l ≤ 25 −21 ≤ l ≤ 18 −19 ≤ l ≤ 20 −32 ≤ l ≤ 31 −22 ≤ l ≤ 0
−23 ≤ l ≤ 22 −26 ≤ l ≤ 25
Unique reflns
11827
3503
2852
9907
11766
7774
9008
No. of rflns used 5961(> 2σ(I)) 3503(> 2σ(I)) 2680(> 2σ(I)) 9227(> 2σ(I)) 7173(> 2σ(I))
6004(> 2σ(I)) 9008(> 2σ(I))
R
Rw
0.0460
0.0668
0.0601
0.1674
1.467
0.0181
0.0454
1.097
0.0367
0.1115
1.041
0.0532
0.1233
1.333
0.032
0.034
1.022
0.065
0.1753
1.296
Goodness of fit 0.39857

K. Mochida et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001) 127
5:1 mixture of hexane and benzene at room temperature for
3–5 days.
˚
Table 5. Selected Bond Distances (A) and Angles (deg)
for 10
Complex cis-[PtCl2(PMe2Ph)2] reacted with two equiv of
Ph3GeLi in THF under similar conditions to give yellow crys-
tals of only one species [(Ph3Ge)2Pt(PMe2Ph)2] (17) having a
Ge(1) C(1)
Ge(1) C(37)
Ge(2) C(4)
Ge(2) C(39)
C(1) C(2)
1.977 (7) Ge(1) C(6)
1.929 (8) Ge(1) C(38)
1.985 (7) Ge(2) C(5)
1.931 (8) Ge(2) C(40)
1.332 (10) C(2) C(3)
1.343 (10) C(5) C(6)
1.955 (8)
1.949 (9)
1.963 (8)
1.963 (8)
1.527 (9)
1.321 (11)
1
2
trans geometry: H NMR (C6D6) δ 1.24 (vt, JH–P = 29.3 Hz,
1
3JH–Pt = 6.6 Hz, PCH3), 31P NM R (C6D6) δ –11.0 (s, JPt–P
=
C(3) C(4)
2616 Hz). The complex trans-17 in C6D6 was stable and did
not isomerize to the cis isomer, even at 70 °C. Thus, the stable
geometry for [(R3Ge)2Pt(PMe2Ph)2] complexes varies depen-
dent on the number of phenyl groups on the germanium atom.
The structures of cis-15, cis-16, and trans-17 were established
by NMR, IR, and MS spectra and by X-ray analysis. Although
crystallized 16 has a cis geometry, the dissolution of cis-16 in
benzene caused a gradual isomerization to give a cis/trans
equilibrium mixture.
C(1) Ge(1) C(6) 112.3 (3)
C(1) Ge(1) C(38) 108.8 (4)
C(6) Ge(1) C(38) 104.7 (4)
C(4) Ge(2) C(5) 109.7 (3)
C(5) Ge(2) C(40) 109.2 (4)
C(1) Ge(1) C(37) 114.3 (4)
C(6) Ge(1) C(37) 109.4 (4)
C(37) Ge(1) C(38) 106.7 (4)
C(4) Ge(2) C(39) 114.7 (4)
C(5) Ge(2) C(39) 109.9 (4)
Synthesis and Reaction of Bis(germyl)platinum Com-
plex.
In the platinum-catalyzed reaction of digermane 1
with alkynes 2, a bis(germyl)platinum complex is a possible in-
termediate to undergo further insertion of alkynes to give the
bis-germylated product of alkynes. Thus, information concern-
ing the behavior of bis(germyl)platinum type complexes is crit-
ical in understanding the reaction mechanism of the bis-germy-
lation of alkynes. We set out to prepare model compounds of
the intermediate bis(germyl)platinum complex stabilized by
tertiary phosphine ligands. Using dimethylphenylphosphine as
supporting ligands, we have been able to prepare bis(ger-
myl)platinum complexes, [(Me2PhGe)2Pt(PMe2Ph)2] (15),
[(MePh2Ge)2Pt(PMe2Ph)2] (16), and [(Ph3Ge)2Pt(PMe2Ph)2]
(17). The treatment of cis-[PtCl2(PMe2Ph)2] with two equiv of
Me2PhGeLi in THF at room temperature for 12 h afforded yel-
low crystals with a composition of [(Me2PhGe)2Pt(PMe2Ph)2]
(15). NMR examination of a C6D6 solution of the yellow crys-
(7)
The isomerization of cis-16 to trans-16 in C6D6 at various
temperatures was followed by observing the change in the two
1
methyl siganls of the PMe2Ph ligands by means of H NM R
spectroscopy. Figure 3 shows the decay of cis-16 and the
building up of trans-16 at 45–60 °C. From the concentrations
of the cis and trans isomers after equilibria were reached, the
following thermodynamic parameters were obtained: ∆H0, 6.0
kJ mol–1 and ∆S0, 13.0 J mol–1 K–1.
The assumption of the equilibration reaction (Eq. 7) follow-
ing the first-order rate law leads to a kinetic expression, Eq. 8,
where K is equal to k/k–1.17
1
tals showed a single cis-isomer: H NMR (C6D6) δ 0.73 (d,
3
3
2JH–P = 8.1 Hz, JH–Pt = 29.9 Hz, PCH3),1.05 (s, JH–Pt = 17.6
Hz), 31P NM R(C6D6) δ –10.1 (s, JPt–P = 2007 Hz). Complex
1
cis-15 in C6D6 was stable and did not isomerize to the trans iso-
mer, even at 70 °C. The complex cis-[PtCl2(PMe2Ph)2] react-
ed with two equiv of MePh2GeLi in THF at room temperature
for 12 h. The concentration of the reaction mixture by evapo-
ration of THF followed by crystallization from a 4:1 mixture
of hexane and benzene gave yellow crystals with a composition
of [(MePh2Ge)2Pt(PMe2Ph)2] (16). A NMR examination of
the C6D6 solution of the yellow crystals 16 showed the pres-
ence of cis and trans isomers of bis-germylbis(tertiary phos-
(8)
The isomerization of cis-16 exhibited first-order kinetics, as
shown in Fig. 4. From the plots shown in Fig. 4, the following
isomerization rate constants were estimated by using Eq. 8 at
phine)platinum in an approximately 60:40 ratio.
The
1H NMR of complex cis-16 displayed the two methyl signals
of the PMe2Ph ligands at 0.70 ppm (deformed q, 2JH–P = 8.2 Hz,
3JH–Pt = 20.8 Hz) and the platinum bound methyldiphenylger-
3
myl groups at 1.05 ppm (s, JH–Pt = 18.6 Hz). The 31P NM R
showed a singlet signal with satellites at –10.99 ppm (1JPt–P
=
2049 Hz). The trans-16 isomer exhibited 1H NMR spectrum
of the germanium-bound methyl groups at 1.20 (vt, 2JH–P = 6.0
3
Hz, JH–Pt = 30.8 Hz) and the 31P NM R showed a singlet at
– 10.63 ppm with satellites (1JPt–P = 2731 Hz). The smaller
1JPt–P value in cis-16 is consistent with the larger trans in-
flunece of the germanium ligand situated at the position trans
to the phophine ligand. From the cis and trans mixture, cis-16
could be isolated as yellow crystals by recrystallization from a
Fig. 3. The progress with time of isomerization of cis-
bis(methyldiphenylgermyl)bis(dimethylphenylphosphine)
platinum (16) to trans-16 at 45−60 ◦C.

128 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
A similar behavior in the isomerization of cis-
[Pt(GeClMe2)2(PEt3)2] to a cis/trans mixture in hydrocarbon
solvents was observed by Tanaka and co-workers.18
The structures of bis(germyl)platinum(II) complexes, cis-
15, cis-16, and trans-17 were confirmed by X-ray diffraction
analysis, as shown in Fig. 5–7. The crystallographic data are
included in Table 4, and Tables 6 to 8 summarize selected bond
lengths and angles in these complexes.
Both cis-15 and cis-16 have distorted square-planar cis ge-
ometries, with the dihedral angles between the planes com-
posed of P(1)−Pt(1)−P(2) and Ge(1)−Pt(1)−Ge(2) being 21.6
and 37.8°, respectively. The deformation from planarity is con-
Fig. 4. The kinetics of isomerization of cis-bis-
(methyldiphenylgermyl)bis(dimethylphenylphophine)
platinum (16).
the early stage of the reaction. The following first-order
isomerization rate constants (k) at 45–60 °C were obtained
from Fig. 4: 105 k/s = 1.89 (45 °C), 4.89 (50 °C), 7.46 (55 °C),
11.4 (60 °C). From Arrhenius plots, the energy of activation in
the isomerization of cis-16 to trans-16 was estimated to be 103
kJ mol–1.
The addition of 0.3 equiv of PPhMe2 per mol of cis-16
caused a very rapid isomerization to give a cis/trans equilibri-
um mixture within a few minutes. These results suggest that
the isomerization of cis-16 to trans-16 proceeds through an
associative pathway involving a five-coordinate intermediate
formed upon the association of the phosphine to cis-16.
Fig. 6. Molecular structure of the cis-bis(methyl-
diphenylgermyl)bis(dimethylphenylphophine)platinum
(16) (30% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity.
Fig. 5. Molecular structure of the cis-bis(dimethyl-
phenylgermyl)bis(dimethylphenylphophine)platinum
(15) (30% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity.
Fig. 7. Molecular structure of the trans-bis(triphenyl-
germyl)bis(dimethylphenylphophine)platinum
(17)
(30% probability thermal ellipsoids). Hydrogen atoms
are omitted for clarity.

K. Mochida et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001) 129
the planes composed of P(1)−Pt−Ge(1) and P(2)−Pt−Ge(2).
The four bond angles of Ge−Pt−P are close to 90°, as shown in
Table 9. The bond lengths of Pt−Ge (2.5207(3) and 2.5239(4)
Å) of trans-17 are longer than those of cis-15 and cis-16
(2.4455(9) and 2.4410(7) Å, respectively). On the contrary,
the Pt−P lengths of trans-17 (2.3011(9) and 2.3120(9) Å) are
shorter than those of cis-15 and cis-16 (2.334(2) and 2.324(1)
Å, respectively). These results indicate the greater trans influ-
ence of the germyl ligand than the phophine ligand in support
of the NMR observation.
˚
Table 6. Selected Bond Distances (A) and Angles (deg)
for cis-15
Pt(1) P(1)
Pt(1) Ge(1)
Ge(1) C(3)
Ge(1) C(2)
P(1) C(10)
2.334 (2) Pt(1) P(2)
2.4455 (9) Pt(1) Ge(2)
1.973 (9) Ge(1) C(1)
1.993 (8) P(1) C(11)
1.812 (9) P(1) C(9)
2.334 (2)
2.43455 (9)
1.987 (9)
1.811 (8)
1.835 (8)
P(1) Pt(1) P(2)
P(1) Pt(1) Ge(1)
P(1) Pt(1) Ge(2) 164.15 (6)
94.29 (10) P(2) Pt(1) Ge(1) 164.14 (6)
92.27 (6) P(2) Pt(1) Ge(2) 92.28 (6)
Ge(1) Pt(1) Ge(2) 85.15 (4)
C(3) Ge(1) C(2) 106.1 (3)
C(3) Ge(1) C(1) 96.4 (3)
A distorted square-planar structure with a dihedral angle of
28.5° has been reported for the cis-bis(chlorodimethylger-
myl)platinum complex prepared by the oxidative addition of
ClMe2GeGeMe2Cl (1b) to [Pt(PEt3)3].18 The structures of cis-
bis(stannyl)bis(phosphine)platinum with the dihedral angle be-
tween the PtP2 and PtSn2 planes being 16.8° and cis-
bis(silyl)bis(phosphine)platinum (dihedral angle 38.1°) are
also distinctly distorted from planarity.19 The distorsion from
planarity has been ascribed to steric congestion.
C(1) Ge(1) C(2) 104.4 (4)
C(1) Ge(1) Pt(1) 117.6 (3)
C(11) P(1) C(10) 104.7 (4)
C(10) P(1) C(9) 101.6 (4)
C(10) P(1) Pt(1) 122.7 (3)
C(3) Ge(1) Pt(1) 111.8 (2)
C(2) Ge(1) Pt(1) 118.0 (2)
C(11) P(1) C(9)
C(11) P(1) Pt(1) 108.7 (3)
C(9) P(1) Pt(1) 117.3 (3)
98.8 (4)
˚
Table 7. Selected Bond Distances (A) and Angles (deg)
for cis-16
For a comparison of the reactivities and structures of the
bis(germyl)platinum complexes, bis(methyldiphenylgermyl)-
platinum complexes 18 and 19 having chelate diphosphines,
dppe (dppe = 1,2-bis(diphenylphosphino)ethane), and dmpe
(dmpe = 1,2-bis(dimethylphosphino)ethane), were prepared in
a way similar to the synthesis of 15–17 by a treatment of
[PtCl2(dppe)] and [PtCl2(dmpe)], respectively, with methyl-
diphenylgermyllithium. The molecular structures of these
bis(germyl)platinum complexes with the chelate ligands are
shown in Figs. 8 and 9. The crystallographic data are included
in Table 4, and Tables 9 and 10 summarize selected bond
lengths and angles of the chelated complexes, 18 and 19.
Complex 18 has a slightly distorted square-planar geometry
with the dihedral angle between the P(1)−Pt−P(2) and Ge(1)−
Pt−Ge(2) being 7.58°, whereas 19 showed an undistorted
square planar geometry.
Pt(1) P(1)
2.318 (2) Pt(1) P(2)
2.4387 (9) Pt(1) Ge(2)
1.956 (8) Ge(1) C(1)
2.004 (8) P(1) C(15)
1.822 (9) P(1) C(14)
2.318 (2)
2.4387 (9)
1.977 (7)
1.795 (10)
1.821 (9)
Pt(1) Ge(1)
Ge(1) C(13)
Ge(1) C(7)
P(1) C(16)
P(1) Pt(1) P(2)
P(1) Pt(1) Ge(1)
97.02 (11) P(2) Pt(1) Ge(1)
153.99 (6)
92.86 (6)
92.86 (6)
P(2) Pt(1) Ge(2)
P(1) Pt(1) Ge(2) 153.98 (6)
C(13) Ge(1) C(1) 105.0 (4)
C(1) Ge(1) C(7) 100.9 (3)
C(1) Ge(1) Pt(1) 113.0 (2)
C(15) P(1) C(16) 100.4 (5)
C(16) P(1) C(14) 103.9 (4)
C(16) P(1) Pt(1) 109.0 (3)
C(2) C(1) Ge(1) 123.6 (6)
Ge(1) Pt(1) Ge(2) 88.56 (4)
C(13) Ge(1) C(7) 105.5 (4)
C(13) Ge(1) Pt(1) 124.7 (3)
C(7) Ge(1) Pt(1) 104.8 (2)
C(15) P(1) C(14) 100.3 (5)
C(15) P(1) Pt(1)
C(14) P(1) Pt(1)
C(6) C(1) Ge(1)
115.9 (4)
124.3 (3)
120.0 (6)
˚
Table 8. Selected Bond Distances (A) and Angles (deg)
for trans-17
The thermolysis behavior of these bis(germyl)platinum
complexes having two monodentate ligands (16) and chelating
ligands (18 and 19) have been examined in sealed NMR tubes.
The thermolysis of 16 in the absence of added triphenylphos-
Pt(1) P(1)
2.3011 (9) Pt(1) P(2)
2.5207 (3) Pt(1) Ge(2)
1.985 (4) Ge(1) C(1)
1.999 (3) Ge(2) C(31)
1.991 (4) P(1) C(37)
1.813 (4) P(2) C(45)
1.831 (4)
2.3120 (9)
2.5239 (4)
1.985 (3)
1.990 (4)
1.817 (4)
1.823 (4)
Pt(1) Ge(1)
Ge(1) C(13)
Ge(1) C(7)
Ge(2) C(25)
P(1) C(39)
P(2) C(47)
˚
Table 9. Selected Bond Distances (A) and Angles (deg)
for 18
P(1) Pt(1) P(2)
P(2) Pt(1) Ge(1)
P(2) Pt(1) Ge(2)
173.17 (3)
89.39 (2)
91.44 (2)
P(1) Pt(1) Ge(1)
P(1) Pt(1) Ge(2)
92.24 (2)
87.51 (2)
Pt(1) P(1)
2.294 (3)
2.4616 (12) Pt(1) Ge(2)
1.994 (10) Ge(1) C(7)
2.009 (6)
1.989 (7)
1.826 (6)
1.843 (6)
1.813 (6)
Pt(1) P(2)
2.320 (3)
2.4729 (12)
2.000 (6)
1.954 (12)
1.994 (6)
1.839 (11)
1.809 (6)
1.818 (14)
Pt(1) Ge(1)
Ge(1) C(13)
Ge(1) C(1)
Ge(2) C(20)
P(1) C(33)
P(1) C(27)
P(2) C(41)
Ge(1) Pt(1) Ge(2) 175.075 (12)
98.91 (14)
C(1) Ge(1) C(7) 103.51 (15) C(13) Ge(1) Pt(1) 112.13 (10)
C(13) Ge(1) C(1) 103.39 (15) C(13) Ge(1) C(7)
Ge(2) C(26)
Ge(2) C(14)
P(1) C(39)
P(2) C(47)
P(2) C(40)
C(1) Ge(1) Pt(1) 108.3 (2)
C(39) P(1) C(37) 100.4 (5)
C(37) P(1) C(38)
C(37) P(1) Pt(1) 109.96 (15) C(38) P(1) Pt(1)
C(7) Ge(1) Pt(1) 120.49 (9)
C(39) P(1) C(38)
C(39) P(1) Pt(1)
97.83 (19)
116.71 (12)
123.14 (13)
98.7 (2)
P(1) Pt(1) P(2)
P(2) Pt(2) Ge(1)
P(2) Pt(1) Ge(2)
C(13) Ge(1) C(7) 106.7 (4)
C(7) Ge(1) C(1) 102.1 (4)
C(7) Ge(1) Pt(1) 111.1 (2)
C(26) Ge(2) C(20) 97.2 (5)
C(26) Ge(2) C(14) 105.4 (4)
C(20) Ge(2) Pt(1) 120.1 (3)
85.20 (10)
94.78 (8)
173.60 (8)
P(1) Pt(1) Ge(1)
P(1) Pt(1) Ge(2)
Ge(1) Pt(1) Ge(2) 85.18 (4)
176.46 (8)
95.24 (7)
sidered to be caused by a steric repulsion between the bulky
ligands. The two germyl groups are bound to the platinum cen-
ter in positions cis to each other, with the bite angle, Ge(1)−
Pt(1)−Ge(2), being 88.6° for cis-15 and 85.2° for cis-16. On
the other hand, the complex trans-17 has a somewhat distorted
square-planar geometry with a dihedral angle of 8.1° between
C(13) Ge(1) C(1) 99.1 (4)
C(13) Ge(1) Pt(1) 117.0 (4)
C(1) Ge(1) Pt(1) 119.1 (2)
C(26) Ge(2) C(14) 108.2 (5)
C(26) Ge(2) Pt(1) 117.9 (4)
C(14) Ge(2) Pt(1) 106.9 (2)

130 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
˚
Table 10. Selected Bond Distances (A) and Angles (deg)
for 19
Pt(1) P(1)
2.302 (2) Pt(1) P(2)
2.454 (1) Pt(1) Ge(2)
1.978 (7) Ge(1) C(2)
1.985 (6) Ge(2) C(14)
1.980 (6) Ge(2) C(21)
1.82 (2) P(1) C(28)
1.843 (8) P(2) C(30)
1.82 (2) P(2) C(32)
2.299 (2)
2.455 (1)
1.970 (7)
1.975 (8)
1.952 (7)
1.81 (2)
Pt(1) Ge(1)
Ge(1) C(1)
Ge(1) C(8)
Ge(2) C(15)
P(1) C(27)
P(1) C(29)
P(2) C(31)
1.807 (8)
1.84 (1)
Ge(1) Pt(1) Ge(2)
Ge(1) Pt(1) P(2)
Ge(2) Pt(1) P(2)
Pt(1) Ge(1) C(1)
Pt(1) Ge(1) C(8)
C(1) Ge(1) C(8)
86.7 (1)
173.4 (1)
93.7 (1)
117.6 (2)
114.6 (2)
99.0 (3)
Ge(1) Pt(1) P(1)
95.1 (1)
174.3 (1)
85.1 (1)
113.6 (2)
107.6 (3)
102.6 (3)
Ge(2) Pt(1) P(1)
P(1) Pt(1) P(2)
Pt(1) Ge(1) C(2)
C(1) Ge(1) C(2)
C(2) Ge(1) C(8)
Pt(1) Ge(2) C(14) 120.0 (3)
Pt(1) Ge(2) C(21) 112.3 (2)
C(14) Ge(2) C(21) 105.6 (3)
Pt(1) Ge(2) C(15) 112.8 (2)
C(14) Ge(2) C(15) 99.3 (3)
C(15) Ge(2) C(21) 105.2 (3)
Fig. 8. Molecular structure of the bis(methyldiphenyl-
germyl)[1,2-bis(diphenylphophino)ethane]platinum•C6H6
(18) (30% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity.
Pt(1) P(1) C(27)
Pt(1) P(1) C(29)
C(27) P(1) C(29)
Pt(1) P(2) C(30)
Pt(1) P(2) C(32)
116.5 (5)
106.9 (3)
103.4 (5)
121.1 (3)
106.4 (3)
Pt(1) P(1) C(28)
C(27) P(1) C(28)
C(28) P(1) C(29)
Pt(1) P(2) C(31)
C(30) P(3) C(31)
121.0 (4)
105.9 (6)
100.6 (5)
118.2 (4)
104.3 (5)
under similar conditions (Eq. 9).
On the other hand, the dppe- and dmpe-coordinated
bis(methyldiphenylgermyl)platinum complexes (18 and 19)
proved to be thermally quite stable, and showed no sign of de-
composition upon heating at 150 °C for 10 h. The chelated
platinum complexes, 18 and 19, did not decompose under the
same reaction conditions in the presence of 5 equiv of PPhMe2
per the complexes.
For examining the reactivity of the bis(germyl)platinum
complexes that are assumed to be involved in the platinum-cat-
alyzed bis-germylation of alkynes, we treated cis-16 with 5.0
equiv. of phenylacetylene (2a) at 65 °C for 24 h. The reaction
gave Z-1-phenyl-1,2-bis(diphenylmethylgermyl)ethene 20 in
31% yield (Eq. 10).
Fig. 9. Molecular structure of the bis(methyldiphenyl-
germyl)[1,2-bis(dimethylphophino)ethane]platinum
(19) (30% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity.
(10)
Synthesis and Reaction of Germyl(germylvinyl)plati-
num Complex. Vinyl-germyl type platinum complex is a
possible intermediate species in the reactions of bis(ger-
myl)platinum complexes 15−17 with phenylacetylene 2a in the
process to liberate a bis-germylation product of the alkyne.
Complex 16 reacted with 2a (2 equiv) at 65 °C for 1.5 h in C6D6
to give regioselectively the corresponding insertion complex
21 in quantitative yields, as confirmed by NMR spectroscopy
(Eq. 11).
phine (PPh3) ligand at 120 °C for 5 h led to a complete decom-
position of cis-16 with the formation of 60% of 1,2-dimethyl-
1,1,2,2-tetraphenyldigermane as the major coupling product of
the two germyl ligands. Dimethyldiphenylgermane (12%),
triphenylmethylgermane (6%), and other unidentified germani-
um-containing oligomers have been produced as by-products.
(9)
(11)
Interestingly, the addition of 5 equiv of PPh3 per 16 completely
suppressed the formation of the monogermanes and germani-
um oligomers, and the digermane (97%) was cleanly formed
Complex 21 was isolated as a pale-yellow solid in 88%
yield and characterized by NMR spectroscopy and X-ray dif-

K. Mochida et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001) 131
fraction analysis. The 31P NMR of complex 21 exhibited two
sets of doublets (2JP–P = 18 Hz) at δ –15.0 and –18.7 with 1JPt–P
values of 1811 and 1819 Hz, respectively.
The addition of 0.5–5.0 equiv of PMe2Ph hindered the
alkyne insertion and caused a lowering in the yield of cis-21
from 100% down to 30% in the reaction of 16 with phenylacet-
ylene performed at 65 °C and for 1.5 h. A similar inhibition
effect of PMe2Ph in the reaction of bis(silyl)bis(phos-
phine)platinum complex with phenylacetylene 2a was ob-
served by Ozawa and co-workers.20–23
Figure 10 shows the molecular structure of cis-21. The
crystallographic data are included in Table 4 and Table 11. The
platinum atom in cis-21 has a square-planar geometry, the sum
of the four angles about platinum being 360.2°. The C(1)–C(2)
distance (1.351 (13) Å) is in the typical range of a carbon-car-
bon double bond. The Z arrangement of the platinum and ger-
manium atoms bound to the C=C double bond clearly shows
the occurrence of the cis insertion of phenyacetylene 2a into
one of the two Pt−Ge bonds.
˚
Table 11. Selected Bond Distances (A) and Angles (deg) for 21
Pt(1) C(1)
Pt(1) P(1)
Ge(1) C(2)
Ge(1) C(9)
P(1) C(44)
2.108 (9) Pt(1) P(2)
2.353 (3) Pt(1) Ge(2)
1.927 (10) Ge(1) C(10)
1.976 (12) C(1) C(2)
1.815 (12) P(1) C(45)
2.315 (3)
2.4682 (11)
1.968 (12)
1.351 (13)
1.829 (10)
C(1) Pt(1) P(2)
P(2) Pt(1) P(1)
P(2) Pt(1) Ge(2)
175.8 (3)
C(1) Pt(1) P(1)
94.99 (10) C(1) Pt(1) Ge(2)
88.3 (3)
84.2 (3)
171.04 (7)
92.69 (7)
P(1) Pt(1) Ge(2)
C(2) Ge(1) C(10) 110.3 (5)
C(2) Ge(1) C(9) 116.4 (5)
C(2) Ge(1) C(16) 107.3 (4)
C(10) Ge(1) C(16) 108.2 (5)
C(16) Ge(1) C(9) 106.0 (5)
C(22) Ge(2) C(23) 101.3 (6)
C(22) Ge(2) Pt(1) 116.7 (4)
C(23) Ge(2) Pt(1) 117.7 (3)
C(44) P(1) C(43) 102.2 (6)
C(44) P(1) Pt(1)
C(43) P(1) Pt(1)
C(2) C(1) Pt(1)
C(1) C(2) Ge(1)
C(10) Ge(1) C(9) 108.3 (6)
C(22) Ge(2) C(29) 106.3 (5)
C(29) Ge(2) C(23) 103.6 (4)
C(29) Ge(2) Pt(1) 109.9 (3)
C(44) P(1) C(45) 100.9 (5)
C(45) P(1) C(43) 103.9 (6)
115.7 (4)
117.0 (4)
123.5 (8)
132.4 (8)
C(45) P(1) Pt(1)
C(2) C(1) C(3)
C(3) C(1) Pt(1)
114.9 (4)
119.9 (9)
116.6 (7)
The thermolysis of cis-21 was carried out to confirm the in-
termediacy of the cis-germy(germylvinyl)platinum complex
21 in the reactions of bis(germyl)platinum complex 16 with
phenylacetylene 2a. Heating of cis-21 in C6D6 at 80 °C for 8 h
led to the decomposition of cis-21 (45%) with the formation of
Z-1,2-bis(diphenylmethylgermyl)-1-phenylethene 20 in 40%
yield. Interestingly, the addition of 5 equiv of PMe2Ph per 21
completely suppressed the thermolysis of 21 under the same
conditions (80 °C and 8 h) with 21 recovered.
(12)
On the other hand, the addition of 5 equiv of diphenylacetylene
2e per 21 under similar conditions, accelerated the reaction to
have 21 cleanly liberate bis(dimethylphenylphosphine)(diphe-
nylacetylene)platinum, [Pt(PhC≡CPh)(PMe2Ph)2] (22) and 20
in quantitative yields (Eq. 12).
Discussion
Mechanism of the Platinum-catalyzed Bis-germylation
of Alkynes.
As a mechanism for the bis-germylation of
alkynes with a digermane, we propose a catalytic cycle
(Scheme 1) driven by a Pt(0) species generated from a catalyst
precursor. The catalytic cycle is composed of (a) the oxidative
addition of digermane to the platinum species to form a
bis(germyl)platinum intermediate (A), (b) the coordination of
an alkyne to A to form an alkyne-coordinated bis-germylation
complex (B), (c) the insertion of the coordinated alkyne into
one of the Pt−Ge bonds to form the insertion product (C) hav-
ing the germyl and vinyl ligands, (d) the reductive elimination
of the bis-germylation product of the alkyne with the regenera-
tion of the active platinum species that further carries the cata-
lytic cycle.
Since the zero-valent complex [Pt(dba)2] was found to be ef-
fective in the bis-germylation of the hexamethyldigermane 1a,
a zero-valent platinum complex may be playing the main role
in the catalysis. The fact that the PPh3-coordinated zero-valent
complex [Pt(PPh3)4] proved to be ineffective may be due to an
unfavorbale effect of the coordinated tertiary phosphine
ligands. Why [Pt(acac)2] serves as the best catalyst among the
platinum complexes examined remains to be clarified. How-
Fig. 10. Molecular structure of the methyldiphenyl-
germyl(1-phenyl-2-methyldiphenylgermylethylenyl)-
bis(dimethylphenylphophine)platinum (21) (30% prob-
ability thermal ellipsoids). Hydrogen atoms are omitted
for clarity.

132 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
and methyldiphenylgermyl groups, respectively, and the com-
mon dimethylphenylphosphine ligands, have considerably dis-
torted cis square planar configurations with the dihedral angles
between the P(1)−Pt−P(2) and Ge(1)−Pt−Ge(2) planes of 21.6°
and 37.8°, respectively. They also have P−Pt−P bite angles
94.2° for cis-15 and 97.2° for cis-16, both larger than 90°. On
the other hand, complex 17, having sterically more demanding
triphenylgermyl groups, has a trans square-planar geometry
with some distorsion, as reflceted by the dihedral angle of 8.1°
between the P(1)−Pt−Ge(1) and P(2)−Pt−Ge(2) planes. The ex-
pulsion between the two bulky triphenylgermyl groups in the
cis configuration is considered to be released by taking the
trans configuration in 17.
The cis to trans isomerization observed for the cis-16 dis-
solved in benzene along with an entropy increase may be due
to the effect of releasing the repulsion in the cis form by
isomerization into the trans form. In the dppe-coordinated
methyldiphenylgermylplatinum complex 18, a dihedral angle
of 7.58° between the P(1)−Pt−P(2) and Ge(1)−Pt−Ge(2)
planes, reflecting the distortion from planarity, is smaller than
in the monophosphine-coordinated complexes, whereas in the
dmpe-coordinated complex 19 no distortion is observed.
Complexes having diphosphine ligands, 18 and 19, show
smaller bite angles of P(1)–Pt–P(2) of 85.12° and 85.1°, re-
spectively, causing a release in the steric repulsion in the che-
lated complexes. The less bulky dmpe ligand may exert less
strain on the complex, giving the undistorted square-planar ge-
ometry for 19.
Scheme 1.
ever, it is known that the O-bonded acetylacetonato ligand in
[Pt(acac)2] can be converted into a C-bonded acetylacetonato
complex.24–28 This conversion may further lead to Pt–C bond
fission to yield a catalytically active Pt(0) species.
For obtaining further information we attempted the detec-
tion of an intermediate species involved in the process by a
NMR examination of the reaction system, but without success.
However, since dichlorotetramethyldigermane is known to
readily oxidatively add to Pt(0) complexes to give a bis-germy-
lation product,18,29 it is probable that the hexamethyldigermane
also oxidatively adds, although less readily, to a Pt(0) species
to give a bis(germyl)platinum complex.
It is noted that the thermolysis of cis-16 liberated 1,2-
dimethyl-1,1,2,2-tetraphenyldigermane as the main thermo-
lysis product together with minor amounts of monogermanes
and germanium oligomers (Eq. 9), and the addition of
triphenylphosphine to the system cleanly gave the digermane.
This result suggests the involvement of a coordinatively unsat-
urated species in the thermolysis of 16 in extrusion of the ger-
mylene unit. Possible processes to liberate the germylene unit
are given in Scheme 2.
The thermolysis of cis-16 in the absence of the added
triphenylphosphine may proceed with the liberation of one of
the two dimethylphenylphosphine ligands in solution to give a
coordinatively unsaturated, three coordinate bis-germyl inter-
mediate. The α-elimination of the phenyl or methyl group at-
tached to the germanium by platinum may yield a phenyl- or
methylplatinum complex having a germylene-platinum bond-
ing. The reductive elimination of the methyl or phenyl group
with the remaining GeMePh2 ligand produces monogermane,
The formation of the bis-germylation product 20 of phenyl-
acetylene upon a treatment of cis-16 with phenylacetylene at
65 °C (Eq. 10) lends support to the involvement of the
bis(germyl)platinum complex in the catalytic bis-germylation
of alkynes, as proposed in Scheme 1. For examining whether
the isolated bis(germyl)platinum complex 16 in fact acts as a
catalyst for the bis-germylation of phenylacetylene,
hexamethyldigemane 1a was treated with phenylacetylene 2a
in the presence of 16 at 65 °C for 24 h. The bis-germylation
product of phenylacetylene 2a was obtained in 2% yield. The
low yield may be partly due to an interference effect of the
phosphine ligand, which was used to stabilize the
bis(germyl)platinum complex in the oxidative addition of the
digermane to a Pt(0) species.
The structures of the bis(germyl)platinum complexes (cis-
15 and cis-16) having two dimethylphenylphophine ligands
and chelating diphosphine ligands (18 and 19) deserve com-
ments. Complexes 15 and 16, having dimethylphenylgermyl
Scheme 2.

K. Mochida et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001) 133
MePh3Ge or Me2Ph2Ge, and the rest of the germylene unit may
be converted into oligomers. A similar mechanism involving
the α-elimination of the chlorine atom in the chlorodimethyl-
germanium complex has been proposed by Tanaka and co-
workers.18
lated products, 4 and 4′, as well as the germole 5 and 1,4-diger-
macyclohexa-2,5-diene 6, the elimination of a germylene unit
from the bis(germyl)platinum species is required. Scheme 4
provides possible courses to account for the formation of the
by-products in Eq. 2.
The regioselective formation of the germyl(germyl-
vinyl)platinum complex 21 upon the treatment of cis-16 with
phenylacetylene supports on involvement of possible interme-
diates corresponding to B and C in Scheme 1. The addition of
dimethyphenylphoshine to the system retarded the insertion of
phenylacetylene into one of the two Ge−Pt bonds in cis-16.
As an alternative route to give C, a process involving a prior
coordination of the alkyne to a Pt(0) species followed by the
oxidative addition of digermane is conceivable. However, a
phenylacetylene-coordinated triphenylphosphine complex 23
did not react with MePh2GeGePh2Me or Me3GeGeMe3 upon
heating at 60–120 °C for 16 h, and no bis-germylation product
of phenylacetylene was produced.
In this Scheme the expulsion of a germylene unit from a
bis(germyl)platinum intermediate is assumed along with the
liberation of a monogermane by the reductive elimination of
trialkylgermyl and alkyl groups, as proposed in Scheme 2.
The liberated germylene unit may be trapped by free alkyne to
form a germacyclopropene, which may interact with a Pt(0)
species and further with alkyne to give the germole 5, while the
1,4-digermacyclohexadiene 6 may be produced by dimeriza-
tion of the germacyclopropene.15
A similar oxidative-addition process involving the Ge–Ge
bond cleavage followed by germylene unit expulsion may be
also be invoked to account for the formation of 6a and 6b in the
platinum-catalyzed reaction of cylcohexagermane 7 with
phenylacetylene 2a (Eq. 3).
(13)
Conclusion
Platinum complexes were found to act as catalysts for the di-
germylation of alkynes with digermanes as well as with cyclo-
germane oligomers. Bis(germyl)platinum (II) complexes with
tertiary phophine ligands assumed as the intermediate in the
catalytic cycle were prepared as models of the reaction inter-
mediates and unequivocally characterized by spectroscopic
means and X-ray crystallography. Thermolysis studies of the
bis(germyl)platinum complexs revealed the simple reductive
elimination course of the digermanes as well as the α-elimina-
tion course with the extrusion of a germylene unit. The bis(ger-
myl)platinum complexes reacted with phenylacetylene under
mild conditions to give the corresponding insertion complexes,
Presumably, the coordination of phenylacetylene to the Pt(0)
complex through a π bond makes the platinum complex less
electron-rich by back-donation, and renders it less susceptible
to an oxidative addition reaction with the digermane.
The platinum-catalyzed formation of the eight-membered
cyclodigermaoctatriene 13 in the reaction of 12 and pheny-
lacetylene 2a (Eq. 6) can be also accounted for by assuming the
oxidative addition of 12 to a Pt(0) species with the Ge–Ge bond
cleavage, followed by the alkyne insertion and reductive elimi-
nation, as shown in Scheme 3.
The platinum-catalyzed formation of 3h, the bis-germyla-
tion product of phenylacetylene 2a in the reaction of 1,2-
dichloro-1,2-tetramethyldigermane 1b with 2a, as shown in
Eq. 2, can also be accounted for by a mechanism similar to
Scheme 1 involving the formation of a bis(germyl)platinum in-
termediate. For explaining the formation of the m onogermy-
Scheme 3.
Scheme 4.

134 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
phenylphosphine)platinum(II) (15).
To a solution of dichlo-
germyl(germylvinyl)platinum species. The thermolysis the
germyl(germylvinyl)platinum complex gave the bis-germyla-
tion product of the alkyne. The mechanism for the catalytic di-
germylation of alkynes comprises alkyne insertion into the ger-
mylplatinum bond, followed by the reductive elimination of
the germyl and germylvinyl ligands to liberate the digermylat-
ed alkyne.
robis(dimethylphenylphosphine)platinum (1.30 g, 2.76 mmol) in
THF (10 ml) was added a THF solution (4 ml) of dimethylphe-
nylgermyllithium (5.70 mmol) at room temperature. The mixture
was stirred at room temperature for 12 h and the solution was con-
centrated to ca. 5 ml. After benzene (10 ml) was slowly added, the
organic layer was filtered through a filter-paper. When the organic
layer was allowed to stand at room temperature for 1 day, cis-
[(Me2PhGe)2Pt(PMe2Ph)2] (15) (0.15 g, 0.19 mmol, 6.7%) was
formed as yellow crystals. Recrystallization from benzene/hexane
(1/5) at room temperature afforded pure cis-15: 1H NMR (C6D6) δ
0.73 (d with two satellites, 2JH–P = 8.1 Hz, 3JH–Pt = 29.9 Hz, 6H),
Exeperimenal
General Methods.
The NMR spectra were obtained on a
Varian Unity Inova 400 MHz NMR spectrometer. The GC-MS
spectra were measured on a JEOL JMS-DX 303 mass spectrome-
ter. The UV and UV-vis spectra were recorded with a Shimadzu
UV 2200 spectrometer. The infrared spectra were recorded with a
Shimadzu FT IR 4200 spectrometer. Gas chromatography was
performed on a Shimadzu GC 8A with 1 m 20% SE30 column.
Liquid chromatography was performed on a Twincle with an Asa-
hipak GS 310 column. X-ray crystallographic data and diffraction
intensities were collected on a Rigaku AFC6/S diffractometer for
10, a Siemens SMART diffractometer for cis-16, Rigaku AFC-7R
diffractometer for 18 and 19, and a MacScience DIP2030 diffrac-
tometer for cis-15, trans-17, and cis-21 utilizing graphite-mono-
chromated Mo Kα (λ = 0.71073 Å) radiation. The structures were
solved by direct methods using the program system MULTAN 78
for 10, and SHELXL-97 for cis-15, cis-16, 18, and 19, and SIR-92
for trans-17 and cis-21. Calculations were carried out by a FA-
COM M-780 with UNICS III for 10. A refinement was performed
by full-matrix least-square using program SHELXL97 for cis-16,
18, and 19, and a SILICON Graphics O2 with maXus for cis-15,
trans-17, and cis-21. Toluene, benzene, hexane, and other sol-
vents were purified and dried as reported in the literature.
3
1.05 (s, with two satellites, JH–Pt = 17.6 Hz, 6H), 6.86–7.90 (m,
30H). 31P NMR (C6D6) δ –10.1 (1JPt–P = 2007 Hz). Found: C,
46.46; H, 5.50%. Calcd for C32H44Ge2P2Pt: C, 46.26; H, 5.34%.
Preparation of cis-Bis(methyldiphenylgermyl)bis(dimeth-
ylphenylphosphine)platinum(II) (16). To a solution of dichlo-
robis(dimethylphenylphosphine)platinum (0.33 g, 0.61 mmol) in
THF (5 ml) was added a THF solution (4 ml) of methyldiphenyl-
germyllithium (1.83 mmol) at room temperature. The mixture
was stirred at room temperature for 12 h, and the solution was con-
centrated to ca. 5 ml. After benzene (10 ml) was slowly added, the
organic layer was filtered through filter-paper. When the organic
layer was allowed to stand at room temperature for 1 day, cis- and
trans-[(MePh2Ge)2Pt(PMe2Ph)2] (16) (0.36 g, 0.38 mmol, 62.0%)
were formed as yellow crystals. Recrystallization from benzene/
1
hexane (1/5) at room temperature afforded pure cis-16: H NMR
(C6D6) δ 0.70 (d with two satellites, 2JH–P = 8.2 Hz, 3JH–Pt = 20.8
3
Hz, 12H), 1.05 (s, with two satellites, JH–Pt = 18.6 Hz, 6H),
6.91–6.95 (m, 30H). 31P NMR (C6D6) δ –10.99 (1JPt–P = 2049 Hz),
195Pt NMR (C6D6) δ 5274.48 (t, J = 1998.4 Hz). Found: C, 52.62;
H, 5.27%. Calcd for C42H48Ge2P2Pt: C, 52.82; H, 5.07%. trans-
16: 1H NMR (C6D6) δ 0.48 (d with two satellites, 3JH–Pt = 9.3 Hz, 6
H), 1.21 (vt, with two satellites, 2JH–P = 6.0 Hz, 3JH–Pt = 30.8 Hz, 12
H), 7.01–7.72 (m, 30H). 31P NMR (C6D6) δ –10.63 (1JPt–P = 2731
Hz).
Materials.
Hexamethyldigermane,30 1,2-dichloro-1,1,2,2-
tetramethyldigermane,31 1,1,2,2-tetramethyl-1,2-diphenyldiger-
mane,31 dodecamethylcyclohexagermane,32 octaisopropylcyclo-
tetragermane,33 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-diger-
macyclohexa-3,5-diene,34 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-
1,2-disilacyclohexa-3,5-diene,35 1,1,2,2-tetraethyl-3,4,5,6-tetra-
phenyl-1,2-digermacyclohexa-3,5-diene,35 1,1,2,2-tetraethyl-
3,4,5,6-tetraphenyl-1,2-disilacyclohexa-3,5-diene,35 1,1,2,2-tetra-
ethyl-3,4,5,6-tetraphenyl-1-germa-2-silacyclohexa-3,5-diene,35
Preparation of trans-Bis(triphenylgermyl)bis(dimethylphe-
nylphosphine)platinum(II) (17).
To a solution of dichloro-
bis(dimethylphenylphosphine)platinum (0.23 g, 0.42 mmol) in
THF (5 ml) was added a THF solution (4 ml) of triphenyl-
germyllithium (2.06 mmol) at room temperature. The mixture was
stirred at room temperature for 12 h, and the solution was concen-
trated to ca. 5 ml. After benzene (10 ml) was slowly added, the or-
ganic layer was filtered through filter-paper. When the organic
layer was allowed to stand at room temperatute for 2 days, trans-
[(Ph3Ge)2Pt(PMe2Ph)2] (17) (0.01 g, 0.01 mmol, 2.0%) was
formed as yellow crystals. Recrystallization from benzene/hexane
(1/5) at room temperature afforded pure trans-17: 1H NMR (C6D6)
δ 1.24 (vt with two satellites, 2JH–P = 29.3 Hz, 3JH–Pt = 6.6 Hz, 12
H), 7.04–7.63 (m, 48 H). 31P NMR (C6D6) δ –11.0 (1JPt–P = 2616
Hz). Found: C, 52.92; H, 4.90%. Calcd for C52H52Ge2P2Pt: C,
57.88; H, 4.86%.
1,1-dimethyl-2,5-diphenyl-1-germacyclohexa-2,4-diene,36
1,1-
dimethyl-2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-diene,37 1,1-
dimethyl-2,3,4,5-tetraphenyl-1-silacyclopenta-2,4-diene,38
[Pt-
(acac)2],39 [Pt(dba)2],40 bis(triphenylphosphine)(styrene)plati-
num,41 and bis(dimethylphenylphosphine)(diphenylacetylene)-
platinum22 were prepared as reported in the literature. Alkynes
and other platinum complexes were commecially available.
Preparation of E-1-phenyl-1,2-bis(trimethylgermyl)ethene.
A mixture of chlorotrimethylgermane (7.9 g, 52 mmol), Mg metal
(0.46 g, 19 mmol), and HMPA (15 ml) was heated at 120 °C. To
this solution was added phenylacetylene (2.6 g, 26 mmol). After
refluxing at 130 °C for 48 h, the reaction mixture was extracted
with hexane. After the solvent was evaporated, the residue was pu-
rified by preparative column chromatography (silica gel, hex-
ane). Pure E-1-phenyl-1,2-bis(trimethylgermyl)ethene was ob-
Preparation of cis-Bis(methyldiphenylgermyl)[1,2-bis-(di-
phenylphosphino)ethane]platinum (18).
To a solution of
dichloro[1,2-bis(diphenylphosphino)ethane]platinum (0.80 g,
1.20 mmol) in THF (10 ml) was added a THF solution (8 ml) of
methyldiphenylgermyllithium (4.0 mmol) at room temperature.
The mixture was stirred at room temperature for 12 h, and the so-
lution was concentrated to ca. 5 ml. After benzene (30 ml) was
slowly added, the organic was filtered through a filter-paper.
Upon allowing the organic layer to stand at room temperature for 1
day, [(MePh2Ge)2Pt(dppe)] (18) (0.60 g, 0.58 mmol, 48.3%) was
1
tained in 15% yield. H NMR (CDCl3) δ –0.02 (s, 3H), 0.26 (s,
3H), 6.33 (s, 1H), 6.95−7.31 (m, 5H). 13C NMR (CDCl3) δ –2.03,
–0.21, 125.58, 126.93, 127.64, 141.90, 145.36, 164.69. IR (neat)
706, 824, 1235, 2972 cm–1. GC-MS m/z (relative intensity) 338 (4,
M+), 323 (20), 221 (9), 181 (8), 119 (100), 89 (9).
Preparation of cis-Bis(dimethylphenylgermyl)bis(dimethyl-

K. Mochida et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001) 135
formed as yellow crystals. Recrystallization from benzene/hexane
magnesium iodide, the products were characterized by comparing
the NMR and GC-MS data of previously reported similar com-
pounds.
(1/5) at room temperature afforded pure 18: mp 180–181 °C.
2
1H NMR (C6D6) δ 0.89 (d with two satellites, JH–P = 1.83 Hz,
3JH–Pt = 16.8 Hz, 6H), 1.44–1.60 (m, 4H), 6.93–7.48 (m, 40H).
13C NMR (C6D6) δ 6.53, 32.34–32.61, 126.25, 127.01, 128.43,
130.41, 131.17, 133.57, 136.16, 151.03. 31P NMR (C6D6) δ 55.3
(1JPt–P = 944 Hz). Found: C, 59.32; H, 3.02%. Calcd for
C52H30Ge2P2Pt: C, 59.09; H, 2.86%.
Platinum-Catalyzed Reaction of Dodecamethylcyclohexa-
germane (7) with Phenylacetylene (2a).
The reaction of 7
with 2a was carried out in a similar manner as above for 1a. A
mixture of 7 (0.1 mmol), 2a (0.5 mmol), Pt(acac)2 (0.005 mmol),
and toluene (1.0 ml) was heated under argon in a sealed tube at 120
°C for 32 h. GC and GC-MS analyses of the reaction mixture
showed 33% conversion of 7. The concentration of the reaction
mixture followed by preparative TLC (silica gel, hexane) gave 6.
1H NM R(C6D6) δ 0.40 (s, 6H), 0.43 (s, 6H), 6.82 (s, 1H), 6.90 (s,
1H), 7.20–7.37 (m, 10H). 13C NMR (C6D6) δ –1.20, –0.26, 0.09,
126.02, 126.24, 126.43, 126.45, 128.18, 128.31, 143.34, 144.05,
145.52, 146.43, 159.95, 161.70. GC-MS m/z (relative intensity)
410 (22, M+), 395 (21), 308 (17), 293 (30), 206 (19), 191 (27), 173
(41), 119 (100), 89 (100).
Preparation of cis-Bis(methyldiphenylgermyl)[1,2-bis(dim-
ethylphosphino)ethane]platinum (19).
To
a
solution of
dichloro[1,2-bis(dimethylphosphino)ethane]platinum (0.21 g,
0.50 mmol) in THF (5 ml) was added a THF solution (4 ml) of
methyldiphenylgermyllithium (1.5 mmol) at room temperature.
The mixture was stirred at room temperature for 12 h, and the so-
lution was concentrated to ca. 5 ml. After benzene (30 ml) was
slowly added, the organic layer was filtered through filter-paper.
Upon allowing the organic layer to stand at room temperature for 1
day, [(MePh2Ge)2Pt(dmpe)] (19) (0.22 g, 0.26 mmol, 52.0%) was
formed as yellow crystals. Recrystallization from benzene/hexane
(1/5) at room temperature afforded pure 19: mp 206–207 °C.
1H NMR (C6D6) δ 0.56–0.63 (d with two satellites, 2JH–P = 9.5 Hz,
3JH–Pt = 23.1 Hz, 12H), 1.01 (d with two satellites, 2JH–P = 1.8 Hz,
3JH–P = 17.5 Hz, 6H), 6.95–7.50 (m, 40H). 13C NMR (C6D6) δ
2.58, 6.72, 24.0–24.61, 128.71, 133.08, 135.40, 139.08. 31P NM R
(C6D6) δ 12.8 (1JPt–P = 900 Hz). Found: C, 46.45; H, 5.22%. Cal-
cd for C32H42Ge2P2Pt: C, 46.37; H, 5.11%.
Platinum-Catalyzed Reactions of Dimetallacyclohexadienes
(9, 12) with Phenylacetylene (2a). As a representative exam-
ple, the reaction of 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-di-
germacyclohexa-3,5-diene (9) with 2a is described. The reaction
of 9 with 2a was carried out in a similar manner as above for 1a.
A mixture of 9 (0.1 mmol), 2a (0.5 mmol), [Pt(acac)2] (0.005
mmol), and toluene (1.0 ml) was heated under argon in a sealed
tube at 80 °C for 36 h. GC and GC-MS analyses of the reaction
mixture showed 96% conversion of 10. Concentration of the reac-
tion mixture followed by preparative TLC (silica gel, hexane) gave
Platinum-Catalyzed Reactions of Organodigermanes (1)
1
with Alkynes (2).
As a representative example, the reaction of
pure 10. H NM R(C6D6) δ –0.12 (s, 3H), 0.09 (s, 3H), 0.83 (s,
hexamethyldigermane (1a) with phenylacetylene (2a) is de-
scribed. A mixture of 1a (0.1 mmol), 2a (0.5 mmol), [Pt(acac)2]
(0.005 mmol), and toluene (1.0 ml) was prepared in a Pyrex tube
(φ = 8 mm). The solution was degassed in a vacuum and heated
under argon in a sealed tube for 16 h at 120 °C. GC and GC-MS
analyses of the reaction mixture showed 59% conversion of 1a,
along with the formation of Z-1-phenyl-1,2-bis(trimethyl-
germyl)ethene (3a). Concentration of the reaction mixture fol-
lowed by preparative TLC (silica gel, hexane) gave 3a (59%
yield). 1H NM R(CDCl3) δ 0.30 (s, 3H), 0.36 (s, 3H), 6.56 (s, 1H),
7.03–7.04 (m, 5H). 13C NMR (CDCl3) δ 0.83, 1.14, 125.73,
126.27, 127.90, 143.30, 149.76, 163.37. IR (neat) 706, 825, 1236,
2951 cm–1. GC-MS m/z (relative intensity) 338 (3, M+), 321 (18),
181 (11), 119 (100), 104 (10), 87 (15). Found: C, 50.04; H,
3H), 0.97 (s, 3H), 6.78 (s, 1H), 7.01–7.33 (m, 25H). 13C NM R
(C6D6) δ 0.41, 0.83, 2.06, 3.89, 125.37, 125.44, 125.86, 126.24,
126.55, 126.95, 127.03, 127.51, 127.75, 127.87, 128.55, 128.68,
130.14, 130.32, 139.37, 139.44, 141.75, 141.95, 143.15, 143.40,
146.80, 147.87, 151.87, 152.13, 162.05. GC-MS m/z (relative in-
tensity) 664 (12, M+), 634 (20), 619 (18), 589 (42), 443 (80), 207
(76), 105 (100). 1,1,4,4,-Tetramethyl-2,5,6,7,8-pentaphenyl-1,4-
1
disilaocta-2,5,7-triene (13a): H NM R (C6D6) δ –0.25 (s, 3H),
0.06 (s, 3H), 0.82 (s, 3H), 1.25 (s, 3H), 6.66 (s, 1H), 7.00–7.30 (m,
25H). 13C NMR (C6D6) δ 1.21, 1.54, 2.09, 2.83, 103.08, 125.36,
125.77, 126.27, 126.43, 126.55, 126.86, 126.91, 127.35, 127.60,
127.78, 129.21, 130.22, 130.45, 139.43, 139.60, 140.34, 140.74,
143.11, 143.76, 148.80, 149.59, 154. 34, 154.84, 163.58. GC-MS
m/z (relative intensity) 576 (12, M+), 546 (10), 529 (18), 500 (21),
443 (100), 207 (76), 105 (100). Found: C, 72.40; H, 5.80%. Cal-
cd for C40H38Ge2: C, 72.35; H, 5.77%.
Thermolysis of 1,1,2,2-Tetramethyl-3,4,5,6-tetraphenyl-1,2-
digermacyclohexa-3,5-diene (9) in the presence of [Pt(acac)2].
A mixture of 9 (0.1 mmol), [Pt(acac)2] (0.005 mmol), and toluene
(1.0 ml) was heated under argon in a sealed tube under various
conditions. The yields of reaction products were estimated with
GC.
7.37%.
Calcd for C14H24Ge2: C, 49.82; H, 7.17%. 1,2-
Bis(trimethylgermyl)-1-hexene (3b): 1H NM R(CDCl3) δ 0.10 (s,
9H), 0.91 (t, J = 6.0 Hz, 3H), 1.24–1.27 (m, 4H), 2.22 (t, J = 6.4
Hz, 2H), 6.29 (s, 1H). 13C NMR (CDCl3) δ 0.49, 0.62, 13.92,
22.31, 31.97, 43.85, 128.92, 141.19. GC-MS m/z (relative inten-
sity) 318 (5.6, M+), 186 (38), 171 (31), 119 (100), 89 (18). 1,2-
Bis(trimethylgermyl)-1-trimethylsilylethylene (3c): 1H NM R
(CDCl3) δ 0.10 (s, 9H), 0.16 (s, 9H), 0.19 (s, 9H), 7.34 (s, 1H).
13C NMR (CDCl3) δ –0.15, 0.68, 1.77, 161.10, 167.55. GC-MS
m/z (relative intensity) 336 (M+). Found: C, 39.35; H, 8.64%.
Calcd for C11H28Ge2Si: C, 39.60; H, 8.46%. 1-Methylcarbonyl-
Reaction of cis-Bis(methyldiphenylgermyl)bis(dimethyl-
phenylphosphine)platinum (16) with Phenylacetylene (2a) at
65 °C for 1.5 h.
A mixture of cis-16 (0.04 mmol), 2a (0.08
1
1,2-bis(trimethylgermyl)ethylene (3d): H NM R(CDCl3) δ 0.24
mmol), and C6D6 (0.5 ml) was prepared in a Pyrex NMR tube.
The tube was degassed in a vacuum and heated with stirring under
argon at 65 °C for 1.5 h. NMR analyses of the reaction mixture
showed the formation of (1-phenylethylenyl-2-phenylmethyl-
germyl)bis(dimethylphenylphosphine)platinum (21) in a quantita-
tive yield. Concentration of the reaction mixture followed by
crytallization in hexane/benzene gave pure 21 as pale yellow crys-
tals in 88% yields. 1H NM R(C6D6) δ 0.76 (d, JP–H = 8.2 Hz, JPt–H
(s, 9H), 0.25 (s, 9H), 3.62 (s, 3H), 7.16 (s, 1H). 13C NMR (CDCl3)
δ 0.31, 0.42, 60.29, 128.21, 153.31, 157.65. GC-MS m/z (relative
intensity) 306 (32, M+), 247 (5), 203 (15), 135 (15), 119 (100), 89
(18).
Platinum-Catalyzed Reactions of 1,2-Dichloro-1,1,2,2-tet-
ramethyldigermane (1b) with Alkynes (2).
The reaction of
1b with 2a was carried out in a similar manner as described above
for 1a. After the reaction mixture was treated with methyl-
= 18.4 Hz, 3H), 0.97–1.07 (m, 9 H), 1.20 (d, JP–H = 8.2 Hz, JPt–H
=

136 Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Bis-Germylation
18.8 Hz, 3H), 1.65 (s, 3 H), 6.80–8.20 (m, 36 H); 31P NMR (C6D6)
δ –18.7 (d, JP–P = 18 Hz, JPt–H = 1819 Hz), –15.0 (d, JP–P = 18 Hz,
JPt–P = 1811 Hz). Found: C, 56.92; H, 5.24%. Calcd for
C50H54Ge2P2Pt: C, 56.81; H, 5.15%.
Reaction of cis-Bis(methyldiphenylgermyl)bis(dimethyl-
phenylphosphine)platinum (16) with Phenylacetylene (2a)
(21) with Dimethylphenylphosphine. A mixture of 21 (0.08
mmol), PMe2Ph (0.40 mmol), and C6D6 (0.6 ml) was heated under
argon in a sealed NMR tube at 80 °C for 8 h. The NMR spectra
showed that the germyl(germylvinyl)platinum 21 remained com-
pletely unreacted.
Reaction of Germyl(germylvinyl)platinum Complex (21)
with Dimethylphenylphosphine at 65 °C for 1.5 h.
A
mix-
with Diphenylacetylene (2e).
A mixture of 21 (0.08 mmol),
ture of 16 (0.04 mmol), 2a (0.08 mmol), PMe2Ph (0.2 mmol), and
C6D6 (0.6 ml) was heated under argon in a sealed NMR tube at 65
°C for 1.5 h. NMR analyses showed the formation of 21 in 30%
yield.
Reaction of cis-Bis(methyldiphenylgermyl)bis(dimethyl-
phenylphosphine)platinum (16) with Phenylacetylene (2a) at
diphenylacetylene (0.40 mmol), and C6D6 (0.6 ml) was heated un-
der argon in a sealed NMR tube at 80 °C for 8 h. NMR and GC-
MS analyses showed the formation of 20 and bis(dimethylphenyl-
phophine)(diphenylacetylene)platinum (22) in quantitative yields,
respectively.
Reaction of Bis(triphenylphosphine)(phenylacetylene)plati-
65 °C for 24 h.
A mixture of cis-16 (0.1 mmol), 2a (0.3
num (23) with Hexamethyldigermane (1a).
A mixture of 23
mmol), and benzene (1.0 ml) was prepared in a 25 ml-Schlenk
tube. The tube was degassed in a vacuum and heated with stirring
under argon at 65 °C for 24 h. GC and GC-MS analyses of the re-
action mixture showed the formation of 1,2-bis(methyldiphenyl-
germyl)-1-phenylethylene (20) in 31% yield. Concentration of
the reaction mixture followed by preparative TLC (silica gel,
hexane) gave pure 20. NMR (C6D6) δ 0.30 (s, 3H), 0.48 (s, 3H),
7.1–7.3 (m, 31H), GC-MS m/z (relative intensity) 586 (1.2, M+),
345 (16), 243 (100), 151 (16).
Thermolysis of Bis-germylplatinum Complexes. As a rep-
resentative example, the thermolysis of cis-bis(methyldiphe-
nylgermyl)bis(dimethylphenylphosphine)platinum (16) is de-
scribed. A mixture of 16 (0.01 mmol), toluene (2 µl, 0.02 mmol)
as an internal standard, and C6D6 (0.6 ml) was heated under argon
in a sealed NMR tube at 120 °C for 5 h. NMR, GC-MS, and GPC
analyses showed the formation of MePh2GeGePh2Me (60%),
Ph2Me2Ge (12%), Ph3MeGe (6%), and oligomers containing ger-
manium.
(0.08 mmol), Me3GeGeMe3 1a (0.40 mmol), and C6D6 (0.6 ml)
was heated under argon in a sealed NMR tube at 60–120 °C for 12
h. The NMR spectra showed no-germylation products of phenyl-
acetylene.
We thank Misses Kazuko Yuzawa and Naoko Toyoda for
preliminary reactions of 1,2-digermacyclohexadienes with
alkynes in the presence of [Pt(acac)2]. This work was support-
ed by the Ministry of Education, Science, Culture and Sports
(Grant No. 10640529 for K. M).
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Thermolysis of Germyl(germylvinyl)platinum Complex

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