Mono- and dinuclear germapalladacycles obtained via the Ge-Ge bond forming reactions promoted by palladium complexes

Article abstract of DOI:10.1021/om8004349

Heating a toluene solution of bis(germyl)palladium complex [Pd(GeHPh ₂)₂(dmpe)] (2) (dmpe = 1,2-bis(dimethylphosphino)ethane) at 70 °C produced a mixture of dipalladium complexes, one with bridging digermene and germylene ligands, [{Pd(dmpe)}₂(μ-GePh ₂)(μ-Ge₂Ph₄)] (3), and also a mononuclear tetragermapalladacyclopentane, [Pd(GePh₂GePh₂GePh ₂GePh₂)(dmpe)] (4), in 92:8 molar ratio, respectively. The reaction of H₂GePh₂ with 2 in 10:1 molar ratio formed complex 4 as the main product (3:4 = 4:96). Complexes 3 and 4 were isolated from the above reactions and characterized by X-ray crystallography and NMR spectroscopy. Complex 3 reacted with H₂GePh₂ (Pd:Ge = 1:10) at 80 °C to yield 4 quantitatively, whereas simple heating of 3 at the same temperature did not form 4 at all. Reaction pathways for the Ge-Ge bond formation are discussed.

Full text of DOI:10.1021/om8004349

5
152
Organometallics 2008, 27, 5152–5158
Mono- and Dinuclear Germapalladacycles Obtained via the Ge-Ge
Bond Forming Reactions Promoted by Palladium Complexes
Makoto Tanabe, Naoko Ishikawa, Masaya Hanzawa, and Kohtaro Osakada*
Chemical Resources Laboratory (R1-3), Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
ReceiVed May 13, 2008
Heating a toluene solution of bis(germyl)palladium complex [Pd(GeHPh
bis(dimethylphosphino)ethane) at 70 °C produced a mixture of dipalladium complexes, one with bridging
digermene and germylene ligands, [{Pd(dmpe)} (µ-GePh )(µ-Ge Ph )] (3), and also a mononuclear
2 2
) (dmpe)] (2) (dmpe ) 1,2-
2
2
2
4
tetragermapalladacyclopentane, [Pd(GePh GePh GePh GePh )(dmpe)] (4), in 92:8 molar ratio, respectively.
The reaction of H GePh with 2 in 10:1 molar ratio formed complex 4 as the main product (3:4 ) 4:96).
Complexes 3 and 4 were isolated from the above reactions and characterized by X-ray crystallography
and NMR spectroscopy. Complex 3 reacted with H GePh (Pd:Ge ) 1:10) at 80 °C to yield 4 quantitatively,
2
2
2
2
2
2
2
2
whereas simple heating of 3 at the same temperature did not form 4 at all. Reaction pathways for the
Ge-Ge bond formation are discussed.
7
,8
Introduction
Si-Si bond forming reactions promoted by transition metal
to Pd(0) and Pt(0) complexes, are also well known. Alternative
important Si-Si bond formation in chemistry of late transition
metal complexes takes place via migration of a silyl group
9
complexes are of great importance and are relevant to the
bonded to the metal center to silylene ligands. Kumada and
co-workers found that Pt complex-catalyzed redistribution of
disilanes formed a mixture of the oligosilanes with Si -Si units.
They proposed the mechanism involving formation of the
intermediate Pt complexes with the silyl and silylene ligands
and migration of the silyl ligand to the electrophilic silylene
ligands. This type of Si-Si bond-forming reactions promoted
by late transition metal complexes have been investigated over
preparation of organic compounds containing Si-Si bonds and
1
the polysilanes. Catalysis using early transition metal complexes
2
6
(
Ti, Zr, and Hf) is useful for dehydrocoupling of organosilanes,
which forms new Si-Si bonds, and the mechanism for the
2
reactions has been accepted as σ-bond metathesis. Late
10
3
4
5
transition metal complexes (Rh, Ni, Pt ) promote different
kinds of the Si-Si bond-forming reactions. A commonly
proposed route involves reductive elimination of disilanes (or
oligosilanes) from the complexes with two silyl ligands at cis
11
a wide range of transition metal complexes by Tobita,
12
13
Pannell, Tilley, and their respective co-workers. Thus,
silylene complexes of transition metals have attracted significant
attention as the important intermediate of transformation of
6
positions. The reverse reactions, oxidative addition of disilanes
*
To whom correspondence should be addressed. E-mail: kosakada@
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(
1
0.1021/om8004349 CCC: $40.75  2008 American Chemical Society
Publication on Web 09/11/2008

Mono- and Dinuclear Germapalladacycles
Organometallics, Vol. 27, No. 19, 2008 5153
organosilicon complexes, although such complexes are too
unstable to be isolated in most cases.
Scheme 1
Ge-Ge bond formation promoted by transition metal com-
plexes has received limited attention partly because of the lower
reactivity of M-Ge bonds than the corresponding M-Si bonds
1
4
in late transition metal complexes. Cp2TiMe2 catalyzes de-
hydrocoupling of PhGeH3 and Ph2GeH2 to produce the polyger-
1
5
manes having Ph substituents. Tertiary germanes such as
HGeMe3 and HGeMe2Ar (Ar ) C6H5, C6H4F-p, C6H4Me-p,
C6H4OMe-p, etc.) are polymerized to form the polygermanes
1
6
via demethanation in the presence of Ru(II)-PMe3 catalysts.
Stoichiometric coupling reactions of halogermanes with one-
electron reducing reagent SmI2 also form a new Ge-Ge bond
1
7
under mild conditions. Germanium amide and germanium
hydride serve as precursors of linear and branched oligoger-
There have been much fewer reports of the reverse reaction,
reductive elimination of digermane from the Pt(II) or Pd(II)
complexes having two germyl ligands. Mochida and co-workers
found that thermolysis of cis-[Pt(GePh2Me)2(PMe2Ph)2] in the
presence of PPh3 gave MePh2Ge-GePh2Me in quantitative yield
18
manes. Heating of [Pt(GeMe2Cl)2(PPh3)2] at 120 °C produces
1
9
ClMe2Ge-GeMe2Cl as one of the products. The digermane is
formally the product of reductive elimination, but another
mechanism involving platinum-germylene species is also pro-
posed, based on the occurrence of scrambling of Me and Cl
substituents attached to Ge during the reaction and on the report
2
3
via reductive elimination. Wells and Banaszak Holl reported
that a bis(germyl)platinum complex with electron-withdrawing
groups, trans-[Pt(GeAr2H)2(PEt3)2] (Ar ) C6H3(CF3)2-3,5),
underwent thermal rearrangement to yield a digermyl(hydrido)-
20
on R-chloro elimination of [Pt(GeMe2Cl)2(PEt3)2]. 3,4-Benzo-
1
,2-germacyclobut-3-ene dimerizes via cleavage and formation
2
4
2
1
platinum complex, trans-[Pt(H)(GeAr2GeAr2H)(PEt3)2].
A
of the Ge-Ge bond promoted by Pd(PPh3)4 catalyst. The
pathway to form the Ge-Ge bond in the complexes is suggested
to involve platinum-germylene intermediates that were formed
complexes having a Pd-Ge-C-C-Ge five-membered ring are
observed in the reaction mixture, and they react further with
the digermane to form the cyclic dimer. Heating the complex
at high temperature (175 °C) yields the product having new
Ge-Ge bonds.
through R-migration of the substituent attached to Ge, as shown
20,24,25
in Scheme 1(i).
Another pathway via reductive elimination
of digermane and reoxidative addition of H-Ge bond cleavage
may also account for the products (Scheme 1(ii)).
Oxidative addition of digermanes to Pt(0) or Pd(0) complexes,
Bis(germyl)palladium complexes were expected to promote
similar reactions, producing a Ge-Ge bond, more easily than
the corresponding Pt-Ge complexes. Early studies by Glockling
and co-workers revealed that bis(germyl)palladium complexes
with monodentate phosphine ligands were thermally unstable
accompanied by Ge-Ge bond activation, was studied by many
1
9-22
research groups in relation to bisgermylation of alkynes.
(
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26
and decomposed in solution. In this paper, we present the
preparation and structure of mono- and dinuclear germapalla-
dacycles via Ge-Ge bond forming reactions starting from a
bis(germyl)palladium complex with a chelating phosphine
ligand.
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Results and Discussion
Treatment of the bis(silyl)palladium complex [Pd(SiHPh2)2-
7
19.
27
(
dmpe)] (1) with an excess amount of H2GePh2 at room
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1
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(
28
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9
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1
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(
1

5
154 Organometallics, Vol. 27, No. 19, 2008
Tanabe et al.
Figure 1 shows the molecular structure of 2 determined by
X-ray crystallography. The Pd-Ge bonds of 2 (2.4259(2),
2
.4266(3) Å) are longer than the Pd-Si bonds of analogous
silyl complex 1 (2.3548(9), 2.3550(7) Å) by virtue of the larger
covalent radius of Ge relative to that of Si, while the Pd-P
bond distances of 2 (2.3066(6), 2.3147(7) Å) are shorter than
those of 1 (2.3395(9), 2.3356(7) Å) due to smaller degree of
trans influence of Ge than Si atoms. The Ge-Pd-Ge bond
angle (81.27(1)°) is slightly larger than the Si-Pd-Si bond
angle of 1 (79.74(3)°). Although NMR signals of the E-H
hydrogens (E ) Si, Ge) of complexes 1 and 2 display close
chemical shifts to each other (1, E ) Si; δ 5.69; 2, E ) Ge; δ
Figure 1. ORTEP drawing of 2 with thermal ellipsoids shown at
the 50% probability level. Selected bond distances (Å) and angles
(
deg): Pd-Ge1 2.4259(2), Pd-Ge2 2.4266(3), Pd-P1 2.3066(6),
5.63), the coupling constant of 2 attributed to the two phosphorus
Pd-P2 2.3147(7), Ge1-H1 1.61(2), Ge2-H2 1.76(2), Ge1-Pd-Ge2
8
8
nuclei (14.3 Hz) is larger than the corresponding J value of 1
1.27(1), Ge1-Pd-P2 95.82(2), Ge2-Pd-P1 96.99(2), P1-Pd-P2
5.93(2).
3
1
1
(
9.9 Hz). The P{ H} NMR signal of 2 (δ 19.9) was slightly
shifted to lower field compared with the chemical shift of 1 (δ
2.6).
Heating a toluene solution of 2 at 80 °C for 13 h produced
3
1
1
2.473(3) Å) and cyclohexagermane (Ph Ge) (2.456(2)-245.8(2)
2
6
32 31 1
Å). The P{ H} NMR spectrum of 3 contains two signals at
δ 15.2 and 14.2, whose coupling pattern indicates an AA′BB′
spin system (JP-P ) 7.8, 11.2 Hz). Two phosphorus atoms of
the dmpe ligands are magnetically inequivalent with different
environments, germylene and digermene ligands at the trans
a mixture of a dipalladium complex with bridging digermene
and germylene ligands, [{Pd(dmpe)}2(µ-GePh2)(µ-Ge2Ph4)] (3),
and a tetragermapalladacyclopentane, [Pd(GePh2GePh2GePh2Ge-
Ph2)(dmpe)] (4). The former complex was isolated in 36% yield
from the reaction mixture, while isolation of complex 4 was
not feasible due to a low yield in this reaction. Isolation and
characterization of 4 are presented shown below.
1
position. In the H NMR spectrum of 3, two aromatic hydrogen
peaks at δ 7.93 and 7.40 in 2:1 ratio are assigned as the ortho
hydrogens of µ-Ge2Ph4 and µ-GePh2 ligands. There have been
a limited number of transition metal complexes with bridging
disilene or digermene ligands. A diiron complex with µ-Ge2Me4
and µ-GeMe2 ligands, [{Fe(CO)4}2(µ-Ge2Me4)(µ-GeMe2)], was
obtained from the interaction of [Na2Fe(CO)4] with the dichlo-
3
3
rogermane ClMe2GeGeMe2Cl. A diplatinum complex with
bridging disilene and silylene ligands, [{Pt(H)(dmpe)}2(µ-
SiHPh)2{µ-(SiHPh)2}], was prepared via a Si-Si bond forming
reaction of the mononuclear trisilyl(hydrido)platinum(IV) com-
3
4
plex fac-[Pt(H)(SiH2Ph)3(dmpe)].
Complex 3 was characterized by X-ray crystallography, as
shown in Figure 2a. A molecule of 3 contains a twisted five-
membered ring including two Pd atoms, which have square-
planar coordination with two Ge atoms and a chelating dmpe
ligand. The long distances between two Pd atoms (4.4669(4)
Å) and of diagonal Pd · · · Ge lines (3.7736(4), 3.8178(4) Å)
indicate the absence of a Pd-Pd bond and no significant
interaction inside the five-membered ring. The two bond
distances between Ge1 and Pd1 or Pd2 atoms (Pd1-Ge1
Reaction of excess H2GePh2 with 2 at 90 °C for 30 h afforded
, which was isolated as yellow crystals in 41% yield (eq 3).
Mochida et al. proposed tetragermapalladacyclopentane as the
4
crucial intermediates in Pd-catalyzed ring-opening addition of
i
tetragermetane, (Ge Pr2)4, to alkynes to give the five- and six-
3
5
membered cyclic organogermanium compounds. Isolation of
the PdGe4 intermediates was not reported probably due to the
labile nature of the intermediates under the reaction conditions.
The crystal of 4 involves three independent molecules due to
2
.5024(4) Å, Pd2-Ge1 2.4875(4) Å) are elongated compared
with Pd-Ge bond distances of the digermene ligand (Pd1-Ge2
.4399(4) Å, Pd2-Ge3 2.4324(4) Å) and of bis(germyl)palla-
2
(
(
31) Ross, L.; Dr a¨ ger, M. Z. Anorg. Allg. Chem. 1984, 519, 225–232.
32) Dr a¨ ger, M.; Ross, L.; Simon, D. Z. Anorg. Allg. Chem. 1980, 466,
dium complex 2 (2.4259(2), 2.4266(3) Å). The Ge2-Ge3 bond
distance (2.4296(4) Å) is slightly shorter than the Ge-Ge bonds
1
45–156.
3
0
of digermane Ph3Ge-GePh3 (2.437(2) Å) and cyclic Ge
(33) Triplett, K.; Curtis, M. D. Inorg. Chem. 1975, 14, 2284–2285.
(
34) Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114, 1917–
compounds such as cyclopentagermane (Ph2Ge)5 (2.438(3)-
1
919.
35) Mochida, K.; Hirakue, K.; Suzuki, K. Bull. Chem. Soc. Jpn. 2003,
76, 1023–1028.
(
(
30) Dr a¨ ger, M.; Ross, L. Z. Anorg. Allg. Chem. 1980, 460, 207–216.

Mono- and Dinuclear Germapalladacycles
Organometallics, Vol. 27, No. 19, 2008 5155
(
81.27(1)°), suggesting no significant interaction between two
Ge atoms. A similar tetragermacyclopentane structure involving
the ytterbium atom, [Yb(GePh2GePh2GePh2GePh2)(THF)4], was
reported to form a slightly twisted cyclic five-membered
36
structure. The Ge-Ge-Ge bond angles of 4 (96.42(4)-97.63(5)
Å) are significantly smaller than the Pd-Ge-Ge bond angles
(
105.38(4)-116.81(4)°) and the Yb-Ge-Ge and Ge-Ge-Ge
bond angles (116.0(1)° and 107.6(1)°) of the ytterbium complex.
The Ge2-Ge3 bond distances (2.418(2)-2.432(1) Å) opposite
the Pd atoms of 4 are slightly shortened compared with the
Ge1-Ge2 (or Ge3-Ge4) bonds proximal to Pd atoms (2.433(1)-
2
.485(1) Å), while all Ge-Ge bonds of the ytterbium complex
are within the range 2.479(2)-2.489(2) Å. Thus, complex 4
and the YbGe4 complex have different conformations of the
five-membered chelate rings.
Cyclic Pd or Pt complexes with two Ge atoms coordinated
to the metal center were reported to undergo insertion of alkynes
2
1b,22
into the M-Ge bonds.
Reactions of tetragermapalladacycle
4
with a 5-fold amount of dimethyl acetylenedicarboxylate or
3
-fold amount of methyl propiolate at rt and 70 °C, however,
Figure 2. ORTEP drawings of (a) 3 and (b) 4 with thermal
ellipsoids shown at the 50% probability level. The crystal structure
of 4 contains three independent molecules in the unit cell. Selected
bond distances (Å) and angles (deg) for 3: Pd1-Ge1 2.5024(4),
Pd1-Ge2 2.4399(4), Pd1-P1 2.3166(9), Pd1-P2 2.311(1), Pd2-Ge1
did not afford a product with new C-Ge bonds (eq 4).
Figure 3a shows a change in the concentration of complexes
2-4 during the thermal reaction of 2 at 70 °C in C6D6, which
1
is monitored by H NMR spectroscopy. Decrease of 2 and
formation of 3 take place smoothly, although they are ac-
companied by much slower formation of 4. The reaction is
completed in 5 h to produce a mixture of 3 and 4 in a 92:8
molar ratio of the complexes. The time-dependent change of
the reaction of H2GePh2 with 2 (Ge:Pd ) 10:1) at 70 °C is
shown in Figure 3b. The decrease in 2 is slower than the reaction
without added H2GePh2. The major product is the mononuclear
complex 4 rather than the dinuclear complex 3, from the
beginning of the reaction. At the initial stage (0-1.5 h) of the
reaction, total amounts of 2, 3, and 4 are not balanced due to
the presence of a small amount of intermediates in the reaction
mixture, which is mentioned below. After 44 h, the NMR
spectrum exhibited signals of 4 and no signal due to 2 and 3,
indicating that complexes 2 and 3 were completely converted
into 4.
2
.4875(4), Pd2-Ge3 2.4324(4), Pd2-P3 2.3185(9), Pd2-P4
.307(1),Ge2-Ge32.4296(4),Ge1-Pd1-Ge281.23(2),Ge1-Pd2-
2
Ge3 83.95(1), Pd1-Ge1-Pd2 127.06(2), Pd1-Ge2-Ge3 101.60(2),
Pd2-Ge3-Ge2 103.48(2). Selected bond distances (Å) and angles
(
(
deg) for 4: Pd-Ge 2.459(1)-2.480(1), Pd-P 2.038(2)-2.346(2),
Pd-)Ge-Ge 2.433(1)-2.485(1), (Ge-)Ge-Ge 2.418(2)-2.432(1),
Ge-Pd-Ge 87.82(4)-88.26(4), Pd-Ge-Ge 105.38(4)-116.81(4),
Ge-Ge-Ge 96.42(4)-97.63(5).
Chart 1
The reaction of 3 with excess H2GePh2 in C6D6 at 80 °C
3
1
1
was monitored by P{ H} NMR spectroscopy, as shown in
Figure 4. Figure 4a shows the signals of 3 with an AA′BB′
spin system. Heating of the solution for 3 h (Figure 4b) leads
to the signals due to bis(germyl)palladium complex 2 (δ 19.9),
tetragermapalladacycle 4 (δ 21.8), and remaining dinuclear
complex 3 (δ 15.2 and 14.2). Small signals with an AB spin
system were observed at different positions from complexes 2-4
the different orientation of the Ph groups in the unit cell. Each
molecule of 4 involves a five-membered PdGe4 ring with an
envelope conformation (Figure 2b). The Pd atom has a square-
planar environment and is occupied by two terminal Ge atoms
of a tetragermylene fragment. Chart 1 summarizes the bond
parameters of complexes 2-4. The Pd-Ge bonds of 4
(
δ 19.3 and 18.4). After 47 h, the signals other than 4 become
negligible, indicating that complex 4 is the final product of the
reaction (Figure 4c). These results suggest that complex 3 reacts
(
2.459(1)-2.480(1) Å) are slightly longer than those of bis-
germyl)palladium complex 2 (2.4259(2), 2.4266(3) Å) and of
(
31
with H2GePh2 to form 2 and uncharacterized species ( P NMR:
dipalladium complex 3 (Pd1-Ge2: 2.4399(4) Å, Pd2-Ge3:
δ 19.3 and 18.4) as the initial products and transformation from
2
.4324(4) Å). The Ge-M-Ge bond angles of complexes with
2
and H2GePh2 into 4 takes place, as shown in reaction 3.
digermyl ligands might be interpreted as a criterion of Ge · · · Ge
interaction. The Ge-Pd-Ge angles of two germapalladacycles
(36) Bochkarev, L. N.; Makarov, V. M.; Zakharov, L. N.; Fukin, G. K.;
3
and 4 (3, 81.23(2)°, 83.95(1)°; 4, 87.82(4)-88.26(4)°) are
Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1995, 490, C29-
C31.
larger than that of the mononuclear palladium complex 2

5
156 Organometallics, Vol. 27, No. 19, 2008
Tanabe et al.
3
1
1
Figure 4. Monitoring of P{ H} NMR spectra during the
conversion of 3 into 4 in the presence of H GePh (a) at 0 h, (b)
after 3 h at 80 °C, and (c) after 47 h at 80 °C. The two doublets
δ 19.3 and 18.4) with an asterisk may be assigned as one of
intermediate D or F.
2
2
(
Scheme 2
Figure 3. Change in amounts of 2 (9), 3 (b), and 4 (×) during the
thermal reaction of 2 at 70 °C in benzene-d (a) with no additive
[2] ) 49 mM) and (b) with a 10-fold molar amount of H GePh
[2] ) 42 mM).
6
(
(
2
2
Although complex 3 is prepared from 2 together with elimina-
tion of H2GePh2, the reaction is reversible to regenerate 2 from
3
and added H2GePh2. In contrast, simple heating of 3 in the
1
absence of H2GePh2 at 80 °C did not change the H NMR
spectra of the reaction mixture at all for 48 h.
Mononuclear bis(silyl)palladium complex 1 was reported to
be in equilibrium with a dinuclear complex, [{Pd(dmpe)}2-
(
µ-SiPh2)2], having a four-membered Pd2Si2 core with bridging
Scheme 3
27
silylene ligands in solution. The reversible reaction ac-
companies elimination and addition of H2SiPh2 to the Pd
complex, as shown in Scheme 2. Addition of H2SiPh2 to
[
{Pd(dmpe)}2(µ-SiPh2)2] cleaves a bridging Pd-Si bond and
37
forms a new Pd-Si bond. A σ-bond metathesis type reaction
involving an intermediate (A) causes smooth cleavage of the
bridging coordination bond. Further cleavage of the bridging
Pd-Si-Pd bond by addition of H2SiPh2 generates mononuclear
complex 1. Conversion of 3 into 2 by added H2GePh2 may also
similarly involve Pd-Ge bond cleavage. It is not clear whether
the Ge-Ge bond of 3 is cleaved directly by addition of H2GePh2
or not.
(
37) (a) Koizumi, T.; Osakada, K.; Yamamoto, T. Organometallics 1998,
7, 5721–5727. (b) Maruyama, Y.; Yamamura, K.; Sagawa, T.; Katayama,
H.; Ozawa, F. Organometallics 2000, 19, 1308–1318.
Schemes 3 and 4 depict the plausible mechanisms for the
formation of 3 and 4, respectively. Rearrangement of bis(ger-
1

Mono- and Dinuclear Germapalladacycles
Organometallics, Vol. 27, No. 19, 2008 5157
Scheme 4
unsymmetrical structure. Species D and/or F may be assigned
to this intermediate. Since the H NMR spectra of the reaction
1
mixture do not contain any signals due to Pd-H hydrogen,
3
1
1
intermediates E and G do not correspond to the P{ H} NMR
signals. Other pathways, for example, involving intermediate
[
Pd(GePh2GePh2H)2(dmpe)], can also be considered.
Conclusion
We demonstrated the preparation and structure of five-
membered germacycles containing one or two palladium atoms
from simple thermolysis of a bis(germyl)palladium complex.
The chemoselectivity to produce complexes 3 and 4 depends
on the presence or absence of H2GePh2 in the reaction mixture.
Compared with the analogous silyl complexes, bis(germyl)
complexes undergo facile formation of Ge-Ge bonds promoted
by Pd complexes. The preparations of 3 and 4 might be
important to form a digermyl(hydrido)palladium complex by
rearrangement of germylene species of 2. Use of the chelating
dmpe ligand enabled the formation of the complexes with new
Ge-Ge containing ligands. Ge-Ge bond formation reported
by Mochida also employed complexes with chelating digermyl
myl)palladium complex 2 gives a digermyl(hydrido)palladium
complex (B) via migration of the germyl group to the germylene
ligand, which is generated by R-migration of hydrogen at the
Ge atoms, similarly to Scheme 1(i). The NMR study of
the reaction mixture did not provide direct evidence for the
presence of Pd-germylene species probably due to their instabil-
ity. The Pd-H bond in structure B is expected to be reactive
toward the Ge-H bond of the unreacted starting material 2 to
form the dinuclear complex with a bridging germylene ligand
21
ligands. This may facilitate Ge-Ge bond formation via germyl
group migration to the germylene ligand.
Experimental Section
General Procedures. All manipulations of the complexes were
carried out using standard Schlenk techniques under an argon or
nitrogen atmosphere. Hexane and toluene were purified by passing
1
13
1
through a solvent purification system (Glass Contour). H, C{ H},
(
C). Subsequent intramolecular cyclization of C via a σ-bond
3
1
1
and P{ H} NMR spectra were recorded on Varian Mercury 300
metathesis of Pd-Ge and Ge-H bonds forms the five-
membered ring structure 3, accompanied by elimination of
H2GePh2. Instead of the σ-bond metathesis pathway, a six-
coordinated Pd(IV) intermediate formed by oxidative addition
of the Ge-H bond of the germyl ligand may also be proposed
for the ligand exchange. An octahedral platinum(IV) complex
with three silyl and a hydrido ligand, fac-[Pt(H)(SiH2-
1
13
1
or JEOL EX-400 spectrometers. Chemical shifts in H and C{ H}
NMR spectra were referenced to the residual peaks of the solvents
3
1
1
used. The peak positions of the P{ H} NMR spectra were
referenced to external 85% H PO (δ 0) in C . The reagent
GePh was obtained from a reduction reaction of Cl GePh
Sigma-Aldrich) by LiAlH . The compound [Pd(SiHPh (dmpe)]
1) was prepared according to the reported procedure. IR
3
4
6 6
D
H
2
2
2
2
(
(
4
2 2
)
27
3
4
Ph)3(dmpe)], was prepared and characterized by Tilley et al.
absorption spectra were recorded on a Shimadzu FT/IR-8100
spectrometer. Elemental analysis was carried out using a LECO
CHNS-932 or Yanaco MT-5 CHN autorecorder.
Scheme 4 shows the plausible pathway for preparation of 4
starting from digermyl(hydrido)palladium complex B. The
addition of excess H2GePh2 to the solution of 2 leads to faster
σ-bond metathesis of the Pd-H bond of B with the Ge-H bonds
of H2GePh2 than those of complex 2 to form a digermyl(ger-
myl)palladium complex (D), followed by rearrangement of
digermyl(germyl) ligands to trigermyl(hydrido) groups (E).
Repeated exchange of a hydrido with GePh2H ligands (F) and
migration of the germylene moiety afford a tetragermyl(hydri-
do)palladium complex (G), propagating the GePh2 unit. Finally,
tetragermapalladacycle 4 is formed by intramolecular cyclization
of G. Mochida and co-workers reported that the intramolecular
cyclization of hydrido(germyl)platinum complexes, [PtH(GePh2-
Preparation of [Pd(GeHPh
4 mL) of complex 1 (812 mg, 1.30 mmol) was added excess
GePh (1.49 g, 6.51 mmol). The solution was stirred at room
2 2
) (dmpe)] (2). To a toluene solution
(
H
2
2
temperature for 1 h. The solvent was removed under reduced
pressure to produce a white solid, which was washed with 2 mL
of hexane three times and dried in Vacuo to yield 2 (706 mg, 76%).
Recrystallization of 2 from hexane/toluene (5:1) at room temperature
gave colorless crystals suitable for X-ray crystallography. Anal.
Calcd for C30
H
38Ge
2
P
2
Pd · 1/2C
2.96; H, 5.53. H NMR (300 MHz, C
.80 (dd, 8H, C ortho, JH-H ) 8.1, 1.2 Hz), 7.23-7.14 (m,
2H, C meta and para), 5.63 (apparent triplet, 2H, GeH, JP-H
7
H
8
: C, 53.06; H, 5.58. Found: C,
1
5
7
1
6 6
D
, room temperature): δ
6
H
5
6
H
5
(
SiMe2)nGePh2H)(PPh3)2] (n ) 1, 2), produced four- or five-
2
)
14.3 Hz), 0.72 (d, 4H, CH , JP-H ) 17.4 Hz), 0.66 (d, 12H,
3
2
membered germaplatinacycles, [Pt(GePh2(SiMe2)nGePh2)-
2 13 1
PCH
, JP-H ) 8.4 Hz). C{ H} NMR (75 MHz, C
6
D
6
, room
ipso, JP-C ) 7.2 Hz), 136.6 (C
ortho), 127.6 (C H , meta), 127.0 (C H , para), 28.8 (t, PCH , J
3
8
3
(
PPh3)2]. Complexes symmetrically coordinated by tri- and
temperature): δ 146.7 (t, C
6
H
5
6
H
5,
tetragermylene ligands such as trigermapalladacyclobutane,
6
5
6
5
2
P-C
3
1
1
)
23 Hz), 12.4 (t, PCH
3
, JP-C ) 9.5 Hz). P{ H} NMR (121
[
Pd(GePh2GePh2GePh2)(dmpe)], and pentagermapalladacyclo-
MHz, C , room temperature): δ 19.9. IR data (KBr): 1952 (νGe-H)
D
6 6
-1
hexane, [Pd(GePh2GePh2GePh2GePh2GePh2)(dmpe)], were not
detected during the reaction mixture. On the other hand, the
cm
.
Preparation of [{Pd(dmpe)} (µ-GePh )(µ-Ge Ph )] (3). A
2
2
2
4
3
1
1
minor P{ H} NMR signals at δ 19.3 and 18.4 in Figure 4b
toluene solution (20 mL) of 2 (706 mg, 0.99 mmol) was heated at
80 °C for 13 h, and the solution changed from colorless to yellow.
Removal of the solvent under reduced pressure gave a solid, which
was reprecipitated with toluene/hexane (3:1) twice and was washed
suggest the presence of palladium intermediates having an
(
38) Usui, Y.; Hosotani, S.; Ogawa, A.; Nanjo, M.; Mochida, K.
Organometallics 2005, 24, 4337–4339.
with Et O three times, followed drying in Vacuo to give 3 as yellow
2

5
158 Organometallics, Vol. 27, No. 19, 2008
Tanabe et al.
powder (212 mg, 36%). Anal. Calcd for C48
H
62Ge
3
P
4
Pd
H, 5.24. Found: C, 48.26; H, 5.29. H NMR (300 MHz, C
temperature): δ 7.93 (m, 8H, C ortho), 7.40 (m, 4H, C
meta and para), 0.84 (br, 4H, PCH
2
: C, 48.30;
, room
ortho),
),
P-H ) 6.9 Hz), 0.51 (d, 12H,
, JP-H ) 6.9 Hz). C{ H} NMR (75 MHz, C , room
temperature): δ 156.0 (m, C ipso), 152.3 (m, C ipso), 137.4
ortho), 136.2 (C ortho), 127.1 (C meta), 126.5 (C
meta or para), 125.9 (C meta or para), 124.6 (C para), 30.4
), 13.9 (apparent triplet, PCH
Table 1. Crystallographic Data and Details of Refinement of 2, 3,
and 4
1
6
D
6
H
6 5
6
H
5
2
3
4
7
0
PCH
.06-7.13 (m, 18H, C
6
H
5
2
formula
fw
C
30
H
38Ge
2
P
2
Pd
C
48
H
62
P
4
Pd
2
Ge
3
C
54
H
4 2
56Ge P Pd
2
.79 (m, 16H, PCH and PCH2,
3
J
712.16
1193.48
1163.79
2
13
1
D
6
cryst size/mm
0.15 × 0.20 × 0.18 × 0.22 ×
0.05 × 0.18 ×
3
6
0
.35
0.35
0.21
6
H
5
6 5
H
cryst syst
cryst color
space group
a/Å
monoclinic
colorless
monoclinic
yellow
monoclinic
yellow
(
C
6
H
5
6
H
5
6
H
5
6 5
H
H
6 5
6
H
5
P2 /n (No. 14)
P2 /c (No. 14)
P2 /a (No.14)
1
1
1
(
7
m, PCH
2
), 29.3 (m, PCH
.2 Hz), 13.0 (apparent doublet, PCH
3
, room temperature): δ 14.2 (dd, PCH , JP-P
2
3
, JP-H
)
12.063(3)
16.287(2)
22.863(4)
3
1
1
b/Å
c/Å
19.635(4)
13.470(3)
105.616(3)
3072(1)
4
16.178(2)
18.868(2)
93.813(2)
4960.6(9)
4
21.865(3)
30.131(5)
101.893(2)
14739(4)
12
3
, JP-H )13 Hz). P{ H}
2
NMR (121 MHz, C
)
3
D
6 6
ꢀ
/deg
V/Å
2
11.7, 7.8 Hz), 15.2 (dd, PCH
was prepared also by a direct method from the reaction of
(dmpe)] (529 mg, 1.85 mmol) with twice the molar amount
GePh (845 mg, 3.69 mmol) in toluene (3 mL) at room
3
, JP-P ) 11.7, 7.8 Hz). Complex
3
Z
D
calcd/g cm-
3
1.539
1.598
1.573
[PdMe
2
F(000)
µ/mm
no. of reflns measd
1432
2.6431
22 547
2392
7008
of H
2
2
-1
2.6679
35 463
11 042
0.037
2.8777
110 880
33 623
0.052
temperature for 4 days. Complex 3 was obtained as a yellow solid
in 45% yield.
no. of unique reflns 7000
R
int
0.023
6017
Preparation of [Pd(GePh
mixture of 2 (200 mg, 0.28 mmol) and excess H
.4 mmol) in toluene (3 mL) was heated at 90 °C for 30 h. The
2
GePh
2
GePh
2
GePh
2
)(dmpe)] (4). A
no. of obsed reflns
(I > 2.00σ(I))
no. of variables
R1 (I > 2.00σ(I))
wR2 (I > 2.00σ(I))
GOF
8732
15 678
2
GePh (322 mg,
2
360
576
1816
1
0.0309
0.0850
1.004
0.0287
0.0559
1.084
0.0562
0.1320
0.957
solvent was evaporated to give a solid, which was washed with 3
mL of hexane three times and dried in Vacuo to afford complex 4
4 2
as a yellow powder (135 mg, 41%). Anal. Calcd for C54H56Ge P Pd:
1
C, 55.72; H, 4.85. Found: C, 55.21; H, 4.87. H NMR (300 MHz,
, room temperature): δ 7.71 (m, 8H, C ortho), 7.47 (m,
H, C ortho), 7.08-6.94 (m, 24H, C meta and para), 0.72
d, 4H, PCH , JP-H ) 8.7
1
31
1
were confirmed by H and P{ H} NMR spectroscopy. Thermoly-
sis of 3 in the absence of H GePh in toluene-d at 80 °C did not
C
6
D
6
6 5
H
2
2
8
8
6
H
5
6
H
5
1
change the H NMR spectra of the reaction mixture at all for 48 h.
X-ray Crystallography. Crystals of 2, 3, and 4 suitable for an
X-ray diffraction study were mounted on a glass capillary tube.
The data were collected to a maximum 2θ value of 55.0°. A total
of 720 oscillation images were collected on a Rigaku Saturn CCD
area detector equipped with monochromated Mo KR radiation
2
2
(
2
, JP-H ) 18 Hz), 0.60 (d, 12H, PCH
Hz). C{ H} NMR (75 MHz, C , room temperature): δ 148.2
ipso, JP-C ) 6.9 Hz), 141.5 (C ipso) 137.7 (C
ortho), 137.2 (C ortho), 127.8 (C meta), 127.5 (C meta
or para), 127.3 (C meta or para), 127.0 (C para), 29.2 (t,
PCH , JP-C ) 22.5 Hz), 12.9 (m, PCH ). P{ H} NMR (121 MHz,
, room temperature): δ 21.8.
Thermal Reaction of 2. A solution of 2 (21 mg, 0.029 mmol)
and 4,4′-dimethylbiphenyl (14 mg 0.077 mmol) as an internal
standard in C (0.6 mL) was heated at 70 °C in an NMR sample
3
1
3
1
6
D
6
3
(
t, C
6
H
5
6
H
5
6 5
H
6
H
6
5
6
H
5
6 5
H
H
5
6 5
H
3
1
1
2
3
(
λ ) 0.71073 Å) at -160 °C. Hydrogen atoms, except for the GeH
6 6
C D
hydrogens of 2, were located by assuming the ideal geometry and
were included in the structure calculation without further refinement
of the parameters. Crystallographic data and details of refinement
are summarized in Table 1.
6
D
6
tube. The reaction mixture was monitored at 70 °C for 5 h. The
concentrations of 2 (δ 7.80), 3 (δ 7.93), and 4 (δ 7.71) were
Acknowledgment. This work was financially supported
by grants-in-aid for Scientific Research for Young Chemists
No. 19750043), for Scientific Research (No. 1925008), and
for Scientific Research on Priority Areas (No. 19027018),
from the Ministry of Education, Culture, Sport, Science, and
Technology, Japan. We thank Dr. N. Nakata (Saitama
University) for helpful discussions.
1
estimated from the intensity of the C
6
H
5
ortho signals in the H
NMR spectra. Heating of the solution of 2 for 5 h converted into
a mixture of 2 (2.7 mM), 3 (22.6 mM), and 4 (1.8 mM).
(
Thermal Reaction of 2 in the Presence of H
of 2 (20 mg, 0.028 mmol), H GePh (64 mg, 0.28 mmol), and
dibenzyl (7.7 mg 0.042 mmol) as an internal standard in C (0.6
2 2
GePh . A solution
2
2
6
D
6
mL) was heated at 70 °C in an NMR sample tube. After 5 h, the
1
H NMR spectrum of the solution was observed as a mixture of 2
Note Added in Proof. The Ge–Ge bond forming reaction of a
bis(germyl)platinum complex [Pt{GeH (C H Me -2,4,6)} (PPh ) ]
2 6 2 3 2 3 2
similarly to Scheme 1(i) has recently been reported: Arii, H.; Nanjo,
M.; Mochida, K. Organometallics 2008, 27, 4147–4151.
(
14.8 mM), 3 (1.1 mM), and 4 (25.5 mM). The reaction was
complete after 44 h to give complex 4 as the final product.
Reaction of 3 with Excess H GePh . To a C solution (0.6
mL) of 3 (22 mg, 0.019 mmol) in an NMR sample tube was added
2
2
6 6
D
31
1
excess H
after 3 h at 80 °C exhibited three signals assigned as 2 (δ 19.9), 3
δ 15.2, 14.2), and 4 (δ 21.8), and a small peak attributed to possible
2 2
GePh (45 mg, 0.20 mmol). The P{ H} NMR spectrum
Supporting Information Available: Crystallographic data for
, 3, and 4 as a CIF file. This material is available free of charge
via the Internet at http://pubs.acs.org.
2
(
intermediate D or F (δ 19.3, 18.4), as mentioned in Scheme 4.
After 47 h, the conversion into 4 and disappearance of 2 and 3
OM8004349