Palladium-catalyzed addition of tetragermetanes to alkynes

Article abstract of DOI:10.1246/bcsj.76.1023

1,1,2,2,3,3,4,4-Octaisopropyltetragermetane (ⁱPr₂Ge)₄ reacted with various alkynes in the presence of palladium complexes at 120 °C to afford 1,2,3,4-tetrahydro-1,2,3,4-tetragermins, Δ⁴-1,2,3-trigemolene, and 1H

Full text of DOI:10.1246/bcsj.76.1023

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1023–1028 (2003) 1023
Palladium-Catalyzed Addition of Tetragermetanes to Alkynes
ꢀ
Kunio Mochida, Katsuhiko Hirakue, and Kaoru Suzuki
Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
(Received October 21, 2002)
1,1,2,2,3,3,4,4-Octaisopropyltetragermetane (iPr2Ge)4 reacted with various alkynes in the presence of palladium
complexes at 120 ꢁC to afford 1,2,3,4-tetrahydro-1,2,3,4-tetragermins, ꢀ4-1,2,3-trigemolene, and 1H-germoles, depend-
ing on the kind of alkyne and the palladium complex employed. Terminal alkynes are more reactive than internal ones.
Pd(dba)2-ETBP and Pd(acac)2-ETBP systems were found to serve as efficient catalysts. The mechanism of alkyne in-
sertion reactions into the germanium–germanium bonds of (iPr2Ge)4 is discussed.
A transition-metal complex-catalyzed addition of a group-
14 element (Si, Ge, and Sn) catenates to unsaturated organic
compounds is a useful fundamental process in group-14 ele-
ment chemistry and organometallic chemistry.1{8 The addition
of group-14 element catenates to C–C triple and double bonds,
i.e., bis-metallation, has attracted considerable interest in the
synthesis of functional molecules and in applications to selec-
tive organic synthesis and new materials. For the bis-metalla-
tion of C–C triple bonds, palladium complexes have often been
used as catalysts. In contrast to the extensive use of their bis-
silylation method and considerable studies on reaction me-
chanisms, there have been few reports on bis-germylation re-
actions, except for the reaction of strained digermiranes,9
chlorine-substituted digermanes,10 and octamethyltriger-
manes.11 Recently, we have reported on the bis-germylation
of various alkynes with organodigermanes and cyclic oligoger-
manes in the presence of platinum complexes.12 In these stu-
dies we characterized bis(germyl)platinum complexes and ger-
myl(germylvinyl)platinum complexes that are assumed to be
key intermediates in these platinum-catalyzed processes, and
examined their reactivities. However, in the bis-germylation
of alkynes with 1,1,2,2,3,3,4,4-octaisopropyltetragermetane
(iPr2Ge)4 (1) the strained, germanium–germanium bonds did
not proceed with such platinum complexes. Instead we found
that the insertion reaction of alkynes into the germanium–ger-
manium bonds in 1 proceeded readily in the presence of palla-
dium complexes. We report herein on the palladium-catalyzed
reaction of the alkynes with 1 and attempt to provide insight
into the reaction mechanism.
(Eq. 1). The rest of 1 remained unreacted. Concentration of
the reaction mixture, followed by recycling preparative HPLC
(ODS column), gave pure 3a and 4a, which showed satisfac-
tory NMR, IR, and GC-MS data. Tetrahydrotetragermin 3a
contained only a single isomer, assigned to the cis configura-
tion. An examination of the molecular models showed that
the alternative trans form should be highly strained.
ð1Þ
The germoles 5a contained three isomers, assigned to 1,1-di-
isopropyl-2,4-dibutyl-1H-germole (5a-1), 1,1-diisopropy1-3,4-
dibutyl-1H-germole (5a-2), and 1,1-diisopropyl-2,3-dibutyl-
1H-germole (5a-3), in roughly a 5:1:1 ratio. The structures
of 5a-1–5a-3 were identified based on their NMR and GC-
MS spectra, and by comparing the IR and NMR data of similar
previously reported compounds (Chart 1).13;14
Although the 2,4-disubstituted 1H-germole has been pre-
viously identified, the remaining two products, 3,4- and 2,3-
disubstituted 1H-germoles, derived from germylenes, have
not been reported.13;14
1
The H NMR spectrum of 5a-1 showed two vinylic protons
Results
at 5.28 (t, 1H, J ¼ 1:19 Hz) and 5.63 ppm (t, J ¼ 1:28 Hz,
1H).13 The 1H NMR spectrum of 5a-2 showed a single vinylic
proton at 5.72 ppm (t, J ¼ 0:92 Hz, 2H). Compound 5a-3
When a degassed benzene solution of 1 molar amount of
1,1,2,2,3,3,4,4-octaisopropyltetragermetane (iPr2Ge)4 (1) con-
taining 5 molar amounts of 1-hexyne (2a), and a catalytic
amount (0.05 molar amount) of Pd(dba)2 containing 0.2 molar
amount of ETBP (dba = dibenzylideneacetone, ETBP = 4-
ethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane) was heated
at 120 ꢁC for 16 h, 5-butyl-1,1,2,2,3,3,4,4-octaisopropyl-
1,2,3,4-tetrahydro-1,2,3,4-tetragermin (3a, 18%), 4-butyl-1,1,
2,2,3,3-hexaisopropyl-ꢀ4-1,2,3-trigermolene (4a, 58%), and
1,1-diisopropy1-1H-germoles (5a, 39%) were obtained
Chart 1.

1024 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Alkyne Insertion into Ge–Ge Bonds
Table 1. Reactions of 1,1,2,2,3,3,4,4-Octaisopropyltetrager-
metane (1) with 1-Hexyne (2a) in the Presence of Palla-
dium Complexesa)
Table 2. Reactions of 1,1,2,2,3,3,4,4-Octaisopropyltetrager-
metane (1) with Acetylenes (2) in the Presence of
Pd(dba)2-4 ETBPa)
Products, Yields/%b)
Products, Yield/%b)
Pd complex
Conv./%
Acetylene (2)
Conv./%
3
4
5
3
4
5
Pd(PPh3)4
PdCl2(PPh3)2
Pd(dba)2
Pd(dba)2 - 2 P(OMe)
Pd(dba)2 - 2 P(OPh)3
Pd(dba)2 - 2 ETBP
Pd(dba)2 - 4 ETBP
Pd(acac)2
0
0
0
5
5
18
70
0
78
82
0
0
0
trace
trace
0
18
0
0
0
0
0
0
1
69
0
70
67
0
0
0
0
0
15
39
0
52
50
nBuCꢂCH (2a)
70
70
—
97
19
50
42
0
18
18
26
46
6
2
0
0
0
69
69
—
100
0
6
0
0
0
39
49
9
61
0
4
0
0
0
Me(CH2)4CꢂCH (2b)
PhCꢂCH (2c)
c)
c)
p-MeC6H4CꢂCH (2d)
tBuCꢂCH (2e)
EtOCꢂCH (2f)
MeO2CCꢂCCO2Me (2g)
PhCꢂCPh (2h)
Pd(acac)2 - 2 ETBP
Pd(acac)2 - 4 ETBP
17
15
nBuCꢂCnBu (2i)
5
a) 1 (0.01 mmol), 2 (0.05 mmol), Pd(dba)2ꢁ-4 ETBP (0.05 mol.
amt. based on 1), benzene (1 mL) at 120 C for 16 h. b) GC
yields. c) Not determined by GLC.
a) 1 (0.01 mol), 2a (0.05 mmol), Pd complex (0.05 mol. amt.
ꢁ
based on 1), benzene (1 mL), 120 C for 16 h. b) GC yields.
gave two vinylic proton signals at 5.58 (dt, J ¼ 1:52, 18.13
Hz) and 6.16 ppm (dt, J ¼ 6:41, 18.13 Hz) in its 1H NMR
spectrum. The assignment of 5a-3 was established further
by a spin-spin decoupling experiment. Decoupling the meth-
ylene signal in the 3-butyl group (CH2CH2CH2CH3) at 2.26
ppm caused a collapse of both doublets of triplets for the
vinylic protons to a pair of doublets (J ¼ 18:13 Hz at 5.58
and 6.16 ppm) for 5a-3. Decoupling the two vinylic protons
at 5.58 and 6.16 ppm as two doublets of triplets causes them
to collapse into two triplets (J ¼ 1:52 and 6.41 Hz).
Palladium(0) and palladium(b) complexes without contain-
ing a phosphite ligand showed no catalytic activity to have
the tetragermetane 1 react with 1-hexyne (2a), as shown in
Table 1. The addition of P(OMe)3 and P(OPh)3 showed a sign
of promoting the reaction. A striking enhancement effect of
the catalytic reaction was observed upon the addition of ETBP
to catalyst systems containing the Pd(0) and Pd(b) complexes.
Particularly, when 4 molar amounts of ETBP were used per
Pd(dba)2, a considerable increase in the conversion as well
as in the yields of the products were observed in comparison
with the case where 2 molar amounts of ETBP was employed.
The results suggest that a Pd(0) species having the ETBP li-
gand serves as the catalytic species. The fact that the Pd(b)
complex, Pd(acac), also served as a good catalyst in the pre-
sence of added ETBP may be understood as an indication of
the occurrence of some type of reduction of the Pd(b) precur-
sor into the Pd(0) catalyst in the catalytic system (vide infra).
The effect of other experimental conditions on the yields of
3a–5a in the present process was examined using the Pd(dba)2-
4 ETBP system. Lowering the reaction temperature from 120
to 60 ꢁC resulted in no reaction of 1 with alkynes, while raising
Fig. 1. Time dependence of insertion products, 3a–5a.
ing 5-pentyl-1,2,3,4-tetrahydro-1,2,3,4-tetragermin (3b, 18%),
4-pentyl-ꢀ4-1,2,3-trigermolene (4b, 69%), and 1H-germoles
(5b, 49%). Arylacetylenes, such as phenylacetylene (2c) and
p-tolylacetylene (2d), reacted with 1 to give the corresponding
5-aryl-1,2,3,4-tetrahydro-1,2,3,4-tetragermins (3c, 26% and
3d, 46%), 4-p-tolyl-ꢀ4-1,2,3-trigermolene (4d, 100%), and
1H-germoles (5c, 9% and 5d, 61%), respectively, under simi-
lar reaction conditions. The formation of 4-phenyl-ꢀ4-1,2,3-
trigermolene (4c) was detected by means of GC, NMR, and
GC-MS, but 4c could not be isolated in these reaction
mixtures. Other terminal alkynes, such as 3,3-dimethyl-1-bu-
tyne (2e) and ethoxylacetylene (2f), gave the corresponding in-
sertion products in low yields. Internal alkynes, such as di-
methyl acetylenedicarboxylate (2g), diphenylacetylene (2h),
and 4-octyne (2i), proved to be unreactive toward 1 under si-
milar reaction conditions.
ꢁ
the temperature to 150 C gave lower yields of products 3a–
5a, owing to the preferential dimerization of alkynes. Extend-
ing the reaction time scarecely improved the yields of products
3a–5a. Increasing in the concentration of Pd(dba)2-4 ETBP
relative to 1 did not affect the yields of products 3a–5a.
The reactivities of other terminal and internal alkynes with 1
were also examined with Pd(dba)2-4 ETBP as catalyst, as sum-
marized in Table 2. 1-Heptyne (2b) reacted with 1 under simi-
lar reaction conditions as those for 2a to give the correspond-
The time course of the reaction of 1 with 2a in the presence
of the Pd(dba)2-4 ETBP system, followed by GC, is shown in
Fig. 1. The yield of product 3a increased with the reaction
time, but was smaller than those of other compounds, 4a and
5a. On the other hand, the yields of products 4a and 5a pro-
gressively increased at the same time. The formation of 4a

K. Mochida et al.
Bull. Chem. Soc. Jpn., 76, No. 5 (2003) 1025
and 5a may be accounted for by the palladium-catalyzed bis-
germylation of the 1,2,3,4-tetrahydro-1,2,3,4-tetragermin 3
and the palladium–germylene complex mechanism.
A similar Pd(PPh3)4-catalyzed addition of dimethylgermy-
lene to alkynes has been reported by Neumann and co-
workers.14 Thermal reactions of 11,11-dimethyl-11-germatri-
cyclo[6.2.1.02;7]undeca-2,4,6,9-tetraene with alkynes in the
presence of the Pd(PPh3)4 complex gave 1,1-dimethyl-1H-ger-
mols and 1,1,4,4-tetramethyl-1,4-dihydro-1,2,3,4-tetragermins
in good yields.
West and co-workers have reported that octaethyltetrasilane
(Et2Si)4 reacts with alkynes in the presence of Pd(PPh3)4 to
give tetrasilacyclohex-1-enes as main products together with
small amounts of 1,4-disilacyclohexa-2,5-dienes and trisil-
acyclopentenes.15
In fact, it was confirmed that ꢀ4-1,2,3-trigermolene 4a
(47%) and 1H-germoles 5a (5%) were produced upon the ther-
molysis of 3a at 120 ꢁC for 48 h in the presence of a catalytic
amount of Pd(dba)2-4 ETBP and 5 molar amounts of 2a. The
unreacted 3a was recovered (55%). In the absence of the
Pd(dba)2-4 ETBP system, the reaction of 3a with 2a did not
give 4a and 5a under similar reaction conditions.
Discussion
ð2Þ
A mechanism for the Pd-catalyzed insertion reactions of the
alkynes into the Ge–Ge bonds of tetragermetane 1 can be pro-
posed in analogy with that suggested by us for the Pt-catalyzed
bis-germylation of alkynes with organodigermanes and cyclic
oligogermanes.12 Thus, the catalytic cycle is composed of (a)
the oxidative addition of 1 to the palladium species to form a
tetragermapalladacyclopentane intermediate (A), (b) the coor-
dination of an alkyne to A to form an alkyne-coordinated tet-
ragermapalladacyclopentane complex (B), (c) the insertion of
a coordinated alkyne into one of the Pt–Ge bonds of 1 to form
an insertion product (C), and (d) the reductive elimination of
the 1,2,3,4-tetrahydro-1,2,3,4-tetragermin from the insertion
product (C) along with the regeneration of the active palla-
dium species, that further carries the catalytic cycle.
The formation of the ꢀ4-1,2,3-trigermolene 4a from 3a indi-
cates that a diisopropylgermylene (iPr2Ge:) unit is extruded
in the platinum-catalyzed thermolysis of the 1,2,3,4-tetrahy-
dro-1,2,3,4-tetragermin 3a. The extruded germylene is readily
trapped with the 1-hexyne 2a to give 5a.
The ꢀ4-1,2,3-trigermolene 4 is a stable compound, and did
not further decompose to release germylenes in the presence of
a catalytic amount of Pd(dba)2-4 ETBP when treated with 5
molar amounts of 2a under similar reaction conditions.
In order to obtain further information on the course of for-
mation of 1H-germole 5, the reactions of free germylenes with
alkynes were examined. A benzene solution containing 10
molar amounts of 2c as alkyne and 11,11-diisopropyl-11-ger-
matricyclo[6.2.1.02;7]undeca-2,4,6,9-tetraene, which is known
to generate free germylene on mild heating, was heated at
The reason for the particular effectiveness of adding ETBP
is not clear, but it may arise from steric and electronic effects
of the phosphine ligand. A greater activity enhancement effect
of the ETBP ligand than those of the P(OMe)3 and P(OPh)3 li-
gands may be ascrible to the smaller cone angle of the ETBP
ligand,17 which allows a space to perform the elementary pro-
cess, as shown in Scheme 1.
ꢁ
80 C for 3 h. 3-Phenyl-1,1,2,2-tetraisopropyl-ꢀ3-1,2-diger-
metine was formed in 25% yield. Tetraphenylnaphthalene
and oligomers containing a diisopropylgermylene unit formed
by untrapped germylenes were also detected by GC, HPLC,
and NMR analysis. However, when we added a catalytic
amount (0.05 molar amount based on the 11-germatricy-
clo[6.2.1.02;7]undeca-2,4,6,9-tetraene) of Pd(dba)2-4 ETBP to
this benzene solution, 1,1-diisopropyl-3,4-diphenyl-1H-ger-
mole (5c) was exclusively produced under similar reaction
conditions in 15% yield (Eq. 3). No ꢀ2-1,2-digermetine
was detected by means of GC and NMR. The results suggest
that germole 5 is the trapping product of germylene liberated
in the presence of Pd complexes.
Although attempts to identify possible intermediates in the
catalytic cycle with NMR were unsuccessful under various
conditions, the cycle shown in Scheme 1 involving the
Pd(0)–Pd(b) intermediates is compatible with the mechanism
proposed for the bis-germylation of alkynes with
ð3Þ
Scheme 1.

1026 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Alkyne Insertion into Ge–Ge Bonds
digermanes.12 A puzzling result is that Pd(acac)2 catalyst in
combination with ETBP is as effective as the combination of
Pd(dba)2 and ETBP. If Pd(acac)2 serves as a catalyst precursor
for generating the Pd(0) species, a process for reducing the
Pd(acac)2 into Pd(0) species should be involved. A possible
course for the development of a catalytically active species
is a known conversion of the unusual O-bonded palladium
acetylacetonate in which a chelated enol form is changed into
a C-bonded acetylacetonato form 6 upon the addition of a base
to Pd(acac)2 (Eq. 4). Complex 6, having C-bonded and O-
bonded acetylacetonato ligands, were separately prepared,
and its effect was examined. Treatments of 1 with 2a in the
presence of 6 gave a trace amount of 3a as the alkyne insertion
product into 1. Thus, the real role of the Pd(acac)2 used in
combination of ETBP remains to be established.
Scheme 3.
to give the ꢀ3-1,2,3-germapalladetene F, followed by alkyne
insertion and reductive elimination, may give the germole 5.
The experimental result shown in Eq. 3, employing the 11-ger-
matricyclo[6.2.1.02;7]undeca-2,4,6,9-tetraene as the germylene
source, provided supporting evidence for the involvement of
germylene. The mechanism for the formation of the germole
5 was analyzed and substantiated in previous studies dealing
with platinum-catalyzed bis-germylation of alkynes with orga-
nodigermanes and with cyclic oligogermanes.12;13
The formation of 4 and 5 may be rationalized by another
mechanism, depicted in Scheme 3. The trigermapalladetane-
germylene complex (G) via ꢀ-germylene group migration
from the insertion product (C) is formed.18{20 The intermedi-
ate G may decompose to give ꢀ4-1,2,3-germolene 4 together
with the liberation of a palladium–germylene complex (H).
Complex H liberated from G may be trapped by an alkyne
to form a germacyclopentadiene 5.
ð4Þ
The course of forming the ꢀ4-1,2,3-germolene 4 and 1H-
germole 5 may be accounted for by the palladium-catalyzed
bis-germylation of the 1,2,3,4-tetrahydro-1,2,3,4-tetragermin
3, followed by reductive elimination, or alternatively, by the
elimination of a germylene unit from the putative intermediate
A in Scheme 1 to form trigermapalladetane D, as shown in
Scheme 2. The intermediate complex D may further undergo
alkyne insertion and reductive elimination to give the ꢀ4-
1,2,3-germolene 4. The germylene liberated from A may be
immediately trapped by an alkyne to form a germirene E.
The oxidative addition of E to a Pd(0) species in the system
Experimental
General Methods. The NMR spectra were obtained on a Var-
ian Unity lnova 400 MHz NMR spectrometer. The GC-MS spec-
tra were measured on a JEOL JMS-DX 303 mass spectrometer.
The IR spectra were recorded with a Shimadzu FT IR 4200
spectrometer. Gas chromatography was performed on a Shimadzu
GC 8A with a 1 m 20% SE30 column. Liquid chromatography
was performed on a Shimadzu SPD 10A and on a JAI recycling
preparative HPLC (ODS column). All solvents were purified
and dried, as reported in the literature.
Materials. 1,1,2,2,3,3,4,4-Octaisopropyltetragermetane,21 Pd-
(dba)2,22 and Pd(acac)2,23 were prepared as reported in the
literature. Alkynes and other palladium complexes were commer-
cially available.
Palladium-Catalyzed Reactions of 1,1,2,2,3,3,4,4-Octaiso-
propyltetragermetane (1) with Alkynes (2). As a representative
example, the reaction of 1 with 1-hexyne (2a) is described.
A
mixture of 1 (0.1 mmol), 2a (0.5 mmol) with Pd(dba)2 (0.005
mmol)-4 ETBP (0.020 mmol), and benzene (1 mL) was prepared
in a Pyrex tube (ꢁ ¼ 8 mm). The solution was degassed in a va-
ꢁ
cuum and heated under argon in a sealed tube for 16 h at 120 C.
GC and GC-MS analyses of the reaction mixture showed a 78%
conversion of 1 along with the formation of 5-butyl-1,1,-
2,2,3,3,4,4-octaisopropyl-1,2,3,4-tetrahydro-1,2,3,4-tetragermin
(3a, 18%), 4-butyl-1,1,2,2,3,3-hexaisopropyl-ꢀ4-1,2,3-trigermo-
lene (4a, 58%), and 1,1-diisopropyl-1H-germole (5a, 39%).
The concentration of the reaction mixture, followed by preparative
LC (ODS column), gave pure 3a, 4a and isomers 5a. 3a: 1H NMR
(ꢂ in CDCl3) 0.92 (t, J ¼ 7:2 Hz, 3H), 1.16 (d, J ¼ 7:5 Hz, 6H),
1.24–1.35 (m, 42H), 1.42–1.62 (m, 8H), 1.76–1.87 (m, 4H), 2.32
(t, J ¼ 7:9 Hz, 2H), 6.60 (s, 1H); GC–MS m=z (relative intensity)
718 (1.0, Mþ), 675 (100), 589 (4), 429 (11), 207 (32); mp 175–
Scheme 2.

K. Mochida et al.
Bull. Chem. Soc. Jpn., 76, No. 5 (2003) 1027
176 ꢁC. Found: C, 50.10; H, 9.32%. Calcd for C30H64Ge4: C,
(5, Mþ), 552 (100), 506 (20), 464 (10), 422 (5), 379 (2), 347
(10), 305 (50), 259 (70), 219 (30), 181 (40). 5d-2: 1H NMR (ꢂ
in CDC13) 1.20 (d, J ¼ 7:32 Hz, 12H), 1.62 (sept, J ¼ 7:32 Hz,
2H), 2.29 (s, 6H), 6.25 (s, 2H), 6.92–6.98 (m, 8H); GC–MS m=z
392 (Mþ). 3e: 1H NMR (ꢂ in CDCl3) 1.15 (s, 9H), 1.22–1.90
(m, 56H), 6.63 (s, 1H); GC–MS m=z (relative intensity) 718
(0.6, Mþ), 675 (100), 515 (13), 429 (21), 263 (30), 161 (23);
mp 224 ꢁC. Found: C, 48.26; H, 9.12%. Calcd for C29H64Ge4:
C, 48.52, H, 8.99%. 3f: GC–MS m=z (relative intensity) 706
(0.6, Mþ), 663 (65), 617 (100), 533 (22), 415 (11), 263 (26),
191 (27), 119 (25). 4f: GC–MS m=z (relative intensity) 546
(0.6, Mþ), 507 (100), 461 (48), 257 (29), 161 (35), 119 (75).
5f: GC–MS m=z (relative intensity) 300 (5.1, Mþ), 273 (6.2),
257 (28), 209 (81), 153 (72), 126 (95), 69 (100).
1
50.23, H, 9.28%. 4a: H NMR (ꢂ in CDCl3) 0.90 (t, J ¼ 7:2 Hz,
3H), 1.12–1.20 (m, 36H), 1.40–1.61 (m, 8H), 1.70–1.81 (m,
2H), 2.32 (t, J ¼ 7:9 Hz, 2H), 6.80 (s, 1H); GC-MS m=z (relative
intensity) 558 (3.5, Mþ), 515 (100), 473 (34), 431 (19), 305 (16).
5a-1: 1H NMR (ꢂ in CDCl3) 0.86–0.92 (m, 6H), 1.09 (d, J ¼ 7:14
Hz, 6H), 1.14 (d, J ¼ 7:32 Hz, 6H), 1.22–1.62 (m, 10H), 2.19 (t,
J ¼ 7:51 Hz, 2H), 2.26 (m, 2H), 5.28 (t, 1H, J ¼ 1:19 Hz), 5.63 (t,
1
1H, J ¼ 1:28 Hz); GC–MS m=z 324 (Mþ). 5a-2: H NMR (ꢂ in
CDCl3) 0.93 (t, J ¼ 7:23 Hz, 6H), 1.08 (d, J ¼ 7:32 Hz, 12H),
1.16–1.64 (m, 10H), 2.32 (t, J ¼ 7:51 Hz, 4H), 5.72 (t, J ¼ 0:92
Hz, 2H); GC-MS m=z (relative intensity) 324 (Mþ, 1.3), 281
1
(100), 239 (39), 191 (14), 163 (17), 113 (12). 5a-3: H NMR (ꢂ
in CDCl3) 0.87–0.94 (m, 6H), 1.08 (d, J ¼ 7:32 Hz, 6H), 1.12
(d, J ¼ 7:32 Hz, 6H), 1.22–1.62 (m, 10H), 2.15 (t, J ¼ 6:59 Hz,
2H), 2.27 (t, J ¼ 6:96 Hz, 2H), 5.58 (dt, J ¼ 18:13, 1.64 Hz,
1H), 6.16 (dt, J ¼ 18:13, 6.36 Hz, 1H); GC–MS m=z 324 (Mþ).
3b: 1H NMR (ꢂ in CDC13) 0.90 (t, J ¼ 6:96 Hz, 3H), 1.16 (d, J ¼
7:51 Hz, 6H), 1.23–1.38 (m, 44H), 1.45–1.63 (m, 8H), 1.76–1.88
(m, 4H), 2.32 (td, J ¼ 7:88, 1.34 Hz, 2H), 6.60 (t, J ¼ 1:28 Hz,
1H); GC–MS m=z (relative intensity) 732 (1.0, Mþ), 688 (100),
644 (30), 602 (25), 531 (25),446 (30), 304 (15). 4b: 1H NMR
(ꢂ in CDC13) 0.91 (t, J ¼ 6:87 Hz, 3H), 1.18 (d, J ¼ 7:32 Hz,
12H), 1.20 (d, J ¼ 7:51 Hz, 6H), 1.21 (d, J ¼ 7:32 Hz, 6H),
1.29–1.38 (m, 14H), 1.46–2.37 (m, 8H), 1.79 (q, J ¼ 7:42 Hz,
2H), 2.35 (dt, J ¼ 7:69, 1.28 Hz, 2H), 6.83 (t, J ¼ 1:37 Hz,
1H); GC–MS m=z (relative intensity) 572 (1.0, Mþ), 535 (100),
486 (40), 445 (20), 403 (5), 347 (40), 307 (40), 264 (80). 5b-1:
1H NMR (ꢂ in CDCl3) 0.89 (t, J ¼ 6:96 Hz, 6H), 0.90 (t,
J ¼ 7:14 Hz, 3H), 1.09 (d, J ¼ 7:14 Hz, 6H), 1.14 (d, J ¼ 7:32
Hz, 6H), 1.24–1.60 (m, 14H), 2.14–2.22 (m, 2H), 2.25 (t,
J ¼ 7:05 Hz, 2H), 5.28 (t, J ¼ 1:19 Hz, 1H), 5.63 (t, J ¼ 1:28
Pd(acac)2ETBP-Catalyzed Reactions of Tetragermetane (1)
with 1-Hexyne (2a). A mixture of 1 (0.1 mmo1), 2a (0.5 mmol)
with Pd(acac)2 (0.005 mmol)-4 ETBP (0.020 mmol), and benzene
(1 mL) was prepared in a Pyrex tube (ꢁ ¼ 8 mm). The solution
was degassed in a vacuum and heated under argon in a sealed tube
for 16 h at 120 ꢁC. The reaction mixture was analyzed by GC and
GC–MS.
Palladium-Catalyzed Reaction of 1,2,3,4-Tetrahydro-1,2,3,-
4-tetragermin 3a with 1-Hexyne (2a). A mixture of 3a (0.01
mmo1) and 2a (0.05 mmol) with Pd(dba)2 (0.0005 mmol)-4 ETBP
(0.0025 mmol) (0.05 mol. amt. based on 3a), and benzene (1 mL)
was prepared in a Pyrex tube (ꢁ ¼ 8 mm). The solution was de-
gassed in a vacuum and heated under argon in a sealed tube for 48
h at 120 ꢁC. GC and GC–MS analyses of the reaction mixture
showed a 45% conversion of 3a along with the formation of 4-bu-
tyl-1,1,2,2,3,3-hexaisopropyl-ꢀ4-1,2,3-trigermolene (4a, 47%),
and 1,1-diisopropy1-1H-germoles (5a, 5%).
Preparation of 11,11-Diisopropyl-1,8,9,10-tetraphenyl-11-
germatricyclo[6.2.1.02;7]undeca-2,4,6,9-tetraene. The 11-ger-
matricyclo[6.2.1.02;7]undeca-2,4,6,9-tetraene was prepared by a
reaction of 1,1-diisopropyl-2,3,4,5-tetrapheny1-1H-germole with
1
Hz, 1H); GC–MS m=z 352 (Mþ). 5b-2: H NMR (ꢂ in CDC13)
0.90 (t, J ¼ 7:14 Hz, 6H), 1.09 (d, J ¼ 7:32 Hz, 12H), 1.27–
1.38 (m, 8H), 1.39–1.54 (m, 6H), 2.26 (t, J ¼ 7:69 Hz, 4H),
5.72 (t, J ¼ 0:92 Hz, 2H); GC–MS m=z 352 (Mþ). 5b-3: 1H NMR
(ꢂ in CDCl3) 0.88 (t, J ¼ 6:96 Hz, 3H), 0.90 (t, J ¼ 7:23 Hz, 3H),
1.08 (d, J ¼ 7:14 Hz, 3H), 1.12 (d, J ¼ 7:32 Hz, 3H), 1.20 (d, J ¼
6:96 Hz, 3H), 1.22 (d, J ¼ 7:14 Hz, 3H), 1.24–1.45 (m, 12H),
1.48–1.58 (m, 2H), 2.10–2.18 (m, 2H), 2.25 (t, J ¼ 6:96 Hz,
2H), 5.58 (dt, J ¼ 18:3, 1.52 Hz, 1H), 6.16 (dt, J ¼ 18:13, 6.41
Hz, 1H); GC–MS m=z 352 (Mþ). 3c: 1H NMR (ꢂ in CDCl3)
1.0–2.0 (m, 56H), 6.7 (s, 1H), 7.0–7.3 (m, 5H); GC–MS m=z (re-
lative intensity) 736 (1.7, Mþ), 695 (100), 651 (86), 537 (8), 263
(27), 161 (29). Found: C, 52.38; H, 8.50%. Calcd for C32H52Ge4:
ꢁ
1
benzyne, as reported in the literature.24 mp 196 C, H NMR (ꢂ
in CDC13) 0.88 (d, J ¼ 6:9 Hz, 6H), 1.38 (d, J ¼ 6:9 Hz, 6H),
1.30–2.80 (m, 2H), 6.80–7.80 (m, 24H). Anal. Calcd for
C40H42Ge: C, 80.69; H, 7.11%. Found: C, 80.72; H, 7.25%.
Palladium-Catalyzed Reaction of 11-Germatricyclo[6.2.-
1.02;7]undeca-2,4,6,9-tetraene with Phenylacetylene (2c).
A
mixture of 11,11-diisopropyl-1,8,9,10-tetraphenyl-11-germatricy-
clo[6.2.1.02;7]undeca-2,4,6,9-tetraene (0.1 mmol), 2c (1.0 mmol)
with Pd(dba)2 (0.005 mmol)-4 ETBP (0.020 mmol) (0.05 mol.
amt. based 11-germatricyclo[6.2.1.02;7]undeca-2,4,6,9-tetraene),
and benzene (0.5 mL) was prepared in a Pyrex tube (ꢁ ¼ 8
mm). The solution was degassed in a vacuum and heated under
1
C, 52.13, H, 8.48%. 4c: H NMR (ꢂ in CDCl3) 1.5–2.3 (m, 56H),
7.6–7.8 (m, 6H); GC–MS m=z (relative intensity) 578 (10, Mþ),
1
ꢁ
535 (100), 493 (33), 263 (34), 161 (51), 78 (8). 5c-2: H NMR
(ꢂ in CDCl3) 1.5–1.9 (m, 14H), 6.8 (s, 2H), 7.3–7.7 (m, 10H);
GC–MS m=z (relative intensity) 364 (3.2, Mþ), 321 (100), 279
argon in a sealed tube for 3 h at 70 C. GC and GC–MS analyses
of the reaction mixture showed the formation of 1,1-diisopropyl-
1H-germole in 15% yield.
1
(57), 175 (42), 151 (52). 3d: H NMR (ꢂ in CDCl3) 1.11 (d, J ¼
Thermal Reaction of 11-Germatricyclo[6.2.1.02;7]undeca-
2,4,6,9-tetraene with Phenylacetylene (2c). A mixture of 11,-
11-diisopropyl-1,8,9,10-tetraphenyl-11-germatricyclo[6.2.1.02;7]-
undeca-2,4,6,9-tetraene (0.1 mmol), 2c (1.0 mmol), and benzene
(0.5 mL) was prepared in a Pyrex tube (ꢁ ¼ 8 mm). The solution
was degassed in a vacuum and heated under argon in a sealed tube
for 3 h at 70 ꢁC. GC and GC–MS analyses of the reaction mixture
showed the formation of 3,3,4,4-tetraisopropyl-2-phenyl-ꢀ3-1,2-
digermetene in 25% yield. Tetraphenylnaphthalene and oligomers
containing a diisopropylgermylene unit were also detected. The
concentration of the reaction mixture, followed by preparative
TLC (silica gel, hexane), gave pure ꢀ3-1,2-digermetene.
7:51 Hz, 6H), 1.13 (d, J ¼ 7:87 Hz, 6 H), 1.20 (d, J ¼ 7:32 Hz,
6H), 1.37 (d, J ¼ 7:69 Hz, 6H), 1.33 (d, J ¼ 7:87 Hz, 6H), 1.34
(d, J ¼ 7:32 Hz, 6H), 1.37 (d, J ¼ 7:69 Hz, 6H), 1.39 (d,
J ¼ 7:87 Hz, 6H), 1.50–1.68 (m, 4H), 1.82–1.94 (m, 4H), 2.33
(s, 3H), 6.68 (s, 1H), 6.95–7.08 (m, 4H); GC–MS m=z (relative in-
tensity) 756 (5.0, Mþ), 712 (100), 548 (55), 462 (70), 420 (60),
260 (80). 4d: 1H NMR (ꢂ in CDC13) 1.09 (d, J ¼ 7:51 Hz,
6H), 1.13 (d, J ¼ 7:32 Hz, 6H), 1.23 (d, J ¼ 7:69 Hz, 6H), 1.25
(d, J ¼ 8:24 Hz, 6H), 1.38 (d, J ¼ 6:96 Hz, 6H), 1.39 (d,
J ¼ 6:96 Hz, 6H), 1.53–1.71 (m, 4H), 1.80–1.93 (m, 2H), 2.34
(s, 3H), 7.08–7.10 (m, 5H); GC–MS m=z (relative intensity) 592

1028 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Alkyne Insertion into Ge–Ge Bonds
1H NMR (ꢂ in CDC13) 1.26 (d, J ¼ 4:7 Hz, 12H), 1.28 (d, J ¼ 4:7
Hz, 12H), 1.7 (m, 4H), 7.0–7.4 (m, 5H), 7.83 (s, 1H); GC–MS m=z
(relative intensity) 418 (9.6, Mþ), 377 (76), 249 (53), 189 (57),
149 (100), 89 (48).
Preparation of Bis(acetylacetonate)(ETBP)palladium (6).
A mixture of Pd(acac)2 (0.304 g, 0.1 mmol) and ETBP (0.162
g, 0.1 mmol) was stirred in benzene (6 mL) at room temperature
in an atmosphere of nitrogen for 1 h until the solution became
clear. Petroleum ether was then added to precipitate the product
Pd(acac)2ETBP in 70% yield. 1H NMR (ꢂ in CDCl3) ꢃ0:13 (t,
J ¼ 7:60 Hz, 3H), 0.01 (q, J ¼ 7:69 Hz, 2H), 1.82 (s, 6H), 2.58
(s, 6H), 3.52 (d, J ¼ 4:94 Hz, 6H), 4.59 (d, J ¼ 4:58 Hz, 1H),
5.12 (s, 1H).
403 (1995) and references cited therein.
M. Suginome, H. Oike, S.-S. Park, and Y. Ito, Bull. Chem.
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The authors thank Prof. Akio Yamamoto of Waseda Univer-
sity for valuable discussion. This work was supported by the
Ministry of Education, Science, Culture and Sports (Grant
No. 10640529).
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