Coordination chemistry of Ga(C5Me4Ph): Novel homoleptic d10 cluster complexes of palladium

Article abstract of DOI:10.1021/ic051658m

The synthesis and characterization of the novel sterically encumbered Ga(I) ligand GaCp*^Ph (1b) (Cp*^Ph = C ₅Me₄Ph) is presented. GaCp*^Ph reacts with the Pd(0) source Pd₂(dvds)₃ (dvds = tetramethyldivinyldisiloxane) to give the trinuclear cluster [Pd ₃(GaCp*^Ph)(μ²-GaCp *^Ph)(μ³-GaCp*^Ph)₂(dvds)] (2a). 2a is the first example of a Ga(I)-containing cluster with a potentially labile olefinic ligand. It was found that 2a is an intermediate in the formation of the dinuclear cluster [Pd₂(GaCp*^Ph) ₂(μ²-GaCp*^Ph)₃] (2b), which is formed on reaction of 2a with GaCp*^Ph. Both clusters were found to be labile toward GaCp*, AlCp*, or phosphines, giving substitution products in all cases.

Full text of DOI:10.1021/ic051658m

Inorg. Chem. 2006, 45, 1789−1794
Coordination Chemistry of Ga(C5Me4Ph): Novel Homoleptic d10 Cluster
Complexes of Palladium†
Beatrice Buchin, Christian Gemel, Thomas Cadenbach, and Roland A. Fischer*
Anorganische Chemie II, Organometallics & Materials,
Ruhr-UniVersita¨t Bochum, D-44780 Bochum, Germany
Received September 27, 2005
The synthesis and characterization of the novel sterically encumbered Ga(I) ligand GaCp*Ph (1b) (Cp*Ph
) C5Me4Ph)
is presented. GaCp*Ph reacts with the Pd(0) source Pd2(dvds)3 (dvds
)
tetramethyldivinyldisiloxane) to give the
3-GaCp*Ph)2(dvds)] (2a). 2a is the first example of a Ga(I)-containing
cluster with a potentially labile olefinic ligand. It was found that 2a is an intermediate in the formation of the
dinuclear cluster [Pd2(GaCp*Ph)2( 2-GaCp*Ph)3] (2b), which is formed on reaction of 2a with GaCp*Ph. Both clusters
were found to be labile toward GaCp*, AlCp*, or phosphines, giving substitution products in all cases.
trinuclear cluster [Pd3(GaCp*Ph)( 2-GaCp*Ph)(
µ µ
µ
Introduction
of sp3 C-H activation of the methyl groups of Cp* at the
electrophilic aluminum centers of the intermediate [M(AlCp*)n]
(n < 5) to yield stable isomers of the parent [M(AlCp*)5]
with two and even three activated CH3 groups and H-bridged
M-Al bonds.11 Last but not least, we should mention the
most unusual rearrangement of [Cp(CH3)2RhGaCp*] into the
zwitterionic complex [CpRh{η5-C5H4(Ga(CH3)3)}], which
involves C-C bond cleavage at the electrophilic Ga cen-
ter.12,13 These findings point to the unique potential of the
electrophilic main-group metal ligands ECp* in typical
organometallic reactions, e.g., bond activation of small
molecules. Depending on a delicate choice of precursors and
reaction conditions, one can form not only monomeric
systems such as [M(ECp*)n] but also oligonuclear homoleptic
cluster compounds [Ma(ECp*)b] (M ) Ni, Pd, Pt) showing
fluxional behavior and an increased reactivity toward ligand
substitution as compared to their mononuclear congeners.14,15
Key questions of the chemistry of those oligonuclear
compounds include: What ranges of M, E, a, and b of such
compounds are accessible in preparative yields? Will it be
possible to derive even giant clusters [Ma(ECp*)b] with a >
b . 1, e.g., a core cluster of Ma stabilized by a shell of
Since the discovery of the low-valent group 13 element
compounds AlCp*1 and GaCp*2,3 and the development of
convenient laboratory syntheses,4,5 their coordination chem-
istry has been studied in some detail.6 Especially the d10 metal
centers Ni, Pd, and Pt have been studied intensively, with
the main focus being the mononuclear complexes of the type
[M(ECp*)4].7-10 Beyond the investigation of the structural
and bonding situation involving the M-ECp* moiety, we have
demonstrated more recently that coordinatively unsaturated
fragmenents such as [Ni(AlCp*)3] exhibit interesting reactiv-
ity and are able to activate the sp2 C-H bonds of benzene
and Si-H bonds of organosilanes. The instability of [M(Al-
Cp*)5] (M ) Fe, Ru) has been discussed as a consequence
* To whom correspondence should be addressed. Fax: (+49)234 321
4174. E-mail: roland.fischer@ruhr-uni-bochum.de.
† Organo group 13 complexes of transition metals XL; communication
XXXIX, see ref 13.
(1) Dohmeier, C.; Robl, C.; Tacke, M.; Schno¨ckel, H. Angew. Chem. 1991,
103, 594.
(2) Loos, D.; Schno¨ckel, H. J. Organomet. Chem. 1993, 463, 37.
(3) Haaland, A.; Martinsen, K.-G.; Volden, H. V.; Loos, D.; Schno¨ckel,
H. Acta Chem. Scand. 1994, 48, 172.
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Kuhn, A. Angew. Chem. 1993, 105, 1828.
(5) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H. G. Organome-
tallics 1998, 17, 1305.
(6) Gemel, C.; Steinke, T.; Cokoja, M.; Kempter, A.; Fischer, R. A. Eur.
J. Inorg. Chem. 2004, 4161.
(11) Steinke, T.; Cokoja, M.; Gemel, C.; Kempter, A.; Krapp, A.; Frenking,
G.; Zenneck, U.; Fischer, R. A. Angew. Chem. 2005, 117, 3003.
(12) Cadenbach, T.; Gemel, C.; Schmid, R.; Block, S.; Fischer, R. A. J.
Chem. Soc., Dalton Trans. 2004, 3171.
(7) Gemel, C.; Steinke, T.; Weiss, D.; Cokoja, M.; Winter, M.; Fischer,
R. A. Organometallics 2003, 22, 2705.
(8) Jutzi, P.; Neumann, B.; Schebaum, L. O.; Stammler, A.; Stammler,
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Soc. 2005, 127, 17068-17078.
(14) Steinke, T.; Gemel, C.; Winter, M.; Fischer, R. A. Angew. Chem. 2002,
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2005, 11, 1636.
10.1021/ic051658m CCC: $33.50
Published on Web 01/21/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 4, 2006 1789

Buchin et al.
surface-bound ECp* ligands, similar to Schno¨ckel’s metalloid
aluminum cluster [Al50Cp*12]16 but with a core of transition-
metal atoms? Will it be possible to tune the oligonuclear
clusters [Ma(ECp*)b] toward interesting bond activation and
coupling reactions?
In fact, GaCp*Ph shows a rich cluster chemistry as demon-
strated by the first isolated and structurally characterized
cluster [M3(ECp*Ph)4(dvds)] (dvds ) tetramethyldivinyl-
disiloxane) with potentially labile olefinic co-ligands.
Results and Discussion
A general concept to systematically address the above
questions is based on a variation of the cone angle of the
low-valent group 13 ligands ER (R ) organic moiety).
Sterically demanding ligands ER should be able to stabilize
low-coordinated transition-metal fragments and thus allow
the study of their reactivity toward small molecules in more
detail. Furthermore, the M/E ratio of cluster compounds
[Ma(ER)b] is likely to change in favor of the transition metal
M and, thus, is thought to allow the formation of compounds
with larger cluster cores Ma. Consequently, we have recently
started to study the coordination chemistry of the bulky
gallium(I) bisimidinate Ga(DDP) {DDP ) 2-(2,6-diisopro-
pylphenyl)amino-4-[(2,6-diisopropylphenyl)imino]-2-pen-
tene}17 in comparison to that of GaCp*.18 It has been shown
that Ga(DDP) is a suitable ligand for a variety of transition
metals, e.g., we communicated some novel Au-Ga com-
plexes in this journal. Low-coordinated transition-metal
centers (Ni, Pd, Pt, Rh) and mononuclear sructures are a
common feature of all complexes of Ga(DDP) that we have
isolated and studied so far and on which subject we will
report in detail elsewhere soon.19 However, the reactivity and
coordination properties of Ga(DDP) are rather different from
those of GaCp*. The electronic properties of the sp2-
hybridized Ga(DDP) are determined by the weak Ga-N
π-bonding and charge donation to the Ga center. Thus, one
remarkable difference is the reactivity of the oxidized species
Ga(DDP)Cl2, which is much less Lewis acidic than its
counterpart GaCp*Cl2, having a large effect on the insertion
chemistry of the ligands in transition-metal halogenides.
Fine-tuning the steric situation at the group 13 ligand ER
without changing the electronic situation of the M-E bond
too much appears to be crucial for the goal of the synthesis
of clusters [Ma(ER)b]. We were thus led to introduce
substituted Cp* groups: C5Me4R′ (R′ ) Ph, t-Bu, SiMe3,
etc.), in particular C5Me4R′ ) Cp*Ph (R′ ) Ph). Recently,
we reported on the synthesis and characterization of the novel
Al(I) compound AlCp*Ph (Cp*Ph ) C5Me4Ph), which has
been shown to react with d10 M(0) sources such as M(COD)2
(M ) Ni, Pt; COD ) 1,5-cyclooctadiene).20 Indeed, mono-
mers of the type [M(AlCp*Ph)4] could be neither spectro-
scopically observed nor isolated. Herein, we now present
our studies on the coordination chemistry of GaCp*Ph as a
sterically slightly more demanding derivative of the GaCp*
ligand family. In particular, the formation of mononuclear
compounds [M(ER)4] was found to be suppressed by the
introduction of a phenyl group in the place of a methyl group.
Preparation and Characterization of GaCp*Ph (1b). The
preparation of GaCp*Ph (1b) was carried out analogously to
the published procedure for GaCp*.21 GaI (“Green’s GaI”)
is synthesized in situ from gallium and iodine in benzene
by ultrasonic sonification, giving “GaI” as a pale green
solid.22 Subsequent addition of the potassium salt of tetra-
methylphenyl cyclopentadiene (1a) gives a slightly yellow
solution and a light gray precipitate. After filtration and
removal of the solvent in vacuo, 1b is obtained as a pure
orange liquid by vacuum distillation of the oily crude residue
(10-2 Torr, 120 °C) in reproducible yields of around 60%
based on gallium.
The 1H NMR spectrum of 1b in C6D6 at room temperature
exhibits two singlet resonances at 1.93 and 2.00 ppm for
the chemically inequivalent CH3 groups, as well as a
multiplet for the aromatic C6H5 protons. The 13C NMR
spectrum measured under the same conditions expectedly
gives rise to two sets of signals for the C5Me4 moiety (10.0
and 10.7 and 126.3, 114.1, and 114.4 ppm) and four signals
for the C6H5 group (128.1, 128.5, 131.4, and 136.7 ppm).
Reaction of [Pd2(dvds)3] with GaCp*Ph. As previously
reported, the reaction of [Pd2(dvds)3] with excess of GaCp*
(dvds ) 1,3-divinyl-1,1,3,3-tetramethyldisiloxane) is very
sensitive to the reaction conditions. At low temperatures of
-30 °C in hexane, the dinuclear compound [Pd2(GaCp*)2-
(µ2-GaCp*)3] is quantitatively obtained, whereas reaction at
room temperature in toluene leads to the trinuclear cluster
[Pd3(GaCp*)8] in high yields.15 In contrast, the reaction of
[Pd2(dvds)3] with an excess of the phenyl derivative GaCp*Ph
in hexane at -30 °C gives a mixture of the Pd2Ga5 complex
[Pd2(GaCp*Ph)2(µ2-GaCp*Ph)3] (2b) and the novel trinuclear
Pd3Ga4 complex [Pd3(GaCp*Ph)(µ2-GaCp*Ph)(µ3-GaCp*Ph)2-
(dvds)] (2a). The two compounds crystallize from the
reaction mixture (hexane) as yellow (2b) and orange (2a)
single crystals. Interestingly, changing the stoichiometry of
the reactants did not alter the composition of the product
mixture. However, variation of the reaction time led to a
variation of the product ratio, with 2a being more abundant
at shorter reaction times of typically a few minutes. In
addition, as 2a and 2b exhibit different ratios M/E (3:4 for
2a and 2:5 for 2b), it is reasonable to assume that 2a
represents an intermediate on the path to the formation of
2b. Indeed, it is possible to synthesize 2a quantitatively from
[Pd2(dvds)3] and the exact stoichiometric amount of GaCp*Ph
in the presence of an excess of dvds in hexane at room
temperature according to Scheme 1. The dinuclear complex
2b can then be prepared quantitatively upon reaction of 2a
with excess of GaCp*Ph. It should be pointed out here that
(16) Vollet, J.; Hartig, J. R.; Schno¨ckel, H. Angew. Chem. 2004, 116, 3248.
(17) Hardman, N. J.; Eichler, B. E.; Power, P. P. J. Chem. Soc., Chem.
Commun. 2000, 1991.
(18) Kempter, A.; Gemel, C.; Fischer, R. A. Inorg. Chem. 2005, 44, 163.
(19) Kempter, A. Diploma Thesis, Ruhr University Bochum. Bochum,
Germany, 2004.
(21) Jutzi, P.; Schebaum, L. O. J. Organomet. Chem. 2002, 654, 176.
(22) Green, M. L. H.; Mountford, P.; Smout, G. J.; Speel, S. R. Polyhedron
1990, 9, 2763.
(20) Buchin, B.; Gemel, C.; Cadenbach, T.; Fischer, R. A. Z. Anorg. Allg.
Chem. 2005, 631, 2756.
1790 Inorganic Chemistry, Vol. 45, No. 4, 2006

Coordination Chemistry of Ga(C5Me4Ph)
Scheme 1. Reaction of [Pd2(dvds)3] with GaCp*Ph
2a or a related structure with a Pd3 triangle bridged by GaCp*
units, e.g., [Pd3(GaCp*)n] (n ) 5, 6, etc.), has never been
observed in such reactions. However, in the case of AlCp*,
we isolated the related cluster [Pd3(AlCp*)6].15 Compound
2b proved to be stable in the presence of excess GaCp*Ph
under all conditions with respect to the formation of
[Pd(GaCp*Ph)4].
environments: Pd(1) is coordinated by one terminal, one µ2-,
and two µ3-bridging Cp*PhGa ligands, and Pd(2) is coordi-
nated by one µ2- and two µ3-bridging Cp*PhGa ligands, and
additionally by one alkene double bond of the dvds moiety,
whereas Pd(3) is coordinated by only two µ3-bridging
Cp*PhGa ligands and the second double bond of the dvds
ligand. The Pd(1)-Pd(2) bond (2.591(1) Å) is the shortest,
obviously because of the presence of an edge-bridging
GaCp*Ph ligand. In contrast, the Pd(2)-Pd(3) bond, at
2.841(1) Å, is rather long but still considerably shorter than
that in the related triangular cluster [Pd3(AlCp*)6],15 which
is presumably a result of the bridging dvds ligand. However,
the distance of 2.841(1) Å is close to the Pd-Pd separation
in the linear trinuclear complex [Pd3(GaCp*)8] [2.843(5) Å],
which is regarded as bonding, whereas the longest Pd-Pd
distance in [Pd3(AlCp*)6] (3.619(2) Å) must be regarded as
nonbonding.15 The rather symmetric triangular structure of
the cluster core is also reflected by the bond angles for the
Pd3 core in 2a, which are all very similar and lie between
54.94(2)° and 63.85(2)°. As expected, the Pd-Ga distance
for the terminal ligand is the shortest (2.367(1) Å), while all
other Pd-Ga distances vary between 2.490(1) and 2.657(1)
Å. No obvious correlation between the bridging modes and
the Pd-Ga distances is observed.
Both title complexes 2a and 2b are weakly soluble in
n-hexane but dissolve well in aromatic hydrocarbons such
as benzene or toluene. They are highly air-sensitive, but
stable at room temperature in the solid state when stored
1
under an inert gas atmosphere. The H NMR spectrum of
2a at room temperature in C6D6 shows six singlets [δ (ppm)
) 2.12 (s, 6H), 2.09 (s, 12H), 2.06 (s, 6H), 1.95, (s, 6H),
1.94 (s, 12H), 1.90 (s, 6H)], i.e., two resonances for the
methyl ligands of each chemically inequivalent GaCp*Ph
ligand, which points to three different Cp*PhGa ligands in a
ratio of 1:1:2. Furthermore, a complex multiplet at 4.60-
4.10 ppm (6H) reveals the presence of one coordinated dvds
1
ligand. The H NMR spectrum of 2b at room temperature
in C6D6 exhibits only two signals for the methyl groups of
the GaCp*Ph at 1.98 ppm (30H) and 1.90 ppm (30H) and a
multiplet for the phenyl group at 7.50-7.19 ppm (25H).
Thus, in contrast to 2a, complex 2b is fluxional in solution,
as has also been described for the parent cluster [Pd2(GaCp*)5].
The fluxional process of this latter complex involves the
exchange of the terminal and bridging ligands and has been
recently studied in more detail.15 We suggest that the situation
is quite similar for 2b. As monitored by 1H NMR spectros-
copy, heating a solution of the Pd3Ga4 cluster 2a in benzene
leads to decomposition, giving the spectroscopically clean
Pd2Ga5 cluster 2b. Precipitation of a black solid indicates
the formation of palladium metal in the course of this
remarkably selective thermolysis reaction. Because of this
thermal decomposition reaction, no assignable 13C NMR
spectrum of 2a could be obtained. Despite several attempts,
also no correct elemental analysis of 2a could be obtained.
1
However, the X-ray crystal structure together with the H
NMR spectrum is certainly sufficient to confirm the molec-
ular structure of 2a in the solid state and in solution.
The molecular structures of 2a and 2b were finally
elucidated by X-ray crystallography. Complex 2a crystallizes
in the triclinic space group P1h. The molecular structure of
2a is depicted in Figure 1 and consists of a triangular Pd3
core coordinated by two axial µ3-bridging and two equatorial
Cp*PhGa ligands (one terminal and one µ2-bridging). Ad-
ditionally, one dvds ligand occupies the vacant equatorial
coordination sites of two palladium centers.
Figure 1. Molecular structure of [Pd3(GaCp*Ph)(µ2-GaCp*Ph)(µ3-GaCp*Ph)2-
(dvds)] (2a) in the solid state (ORTEP drawing; 50% level of probability
for the metal atoms; carbon atoms displayed as spheres for clarity). Selected
bond lengths (Å): Pd(1)-Pd(2) 2.591(1), Pd(2)-Pd(3) 2.841(1), Pd(1)-
Pd(3) 2.774(1), Pd(1)-Ga(1) 2.566(1), Pd(1)-Ga(2) 2.367(1), Pd(1)-Ga(3)
2.530(1), Pd(1)-Ga(4) 2.464(1), Pd(2)-Ga(1) 2.591(1), Pd(2)-Ga(3)
2.657(1), Pd(2)-Ga(4) 2.549(1), Pd(3)-Ga(1) 2.490(1), Pd(3)-Ga(3)
2.456(1).
The Pd-Pd distances vary in the range between 2.591(1)
and 2.841(1) Å, because of their rather different coordination
Inorganic Chemistry, Vol. 45, No. 4, 2006 1791

Buchin et al.
[Ni(COD)2] with AlCp* in hexane leads to the formation of
[Ni(AlCp*)4], but in benzene, C-H activation of the solvent
is observed, giving [Ni(AlCp*)3{AlCp*(Ph)}(H)]. In contrast,
the reaction of [Ni(COD)2] with GaCp* yields only
[Ni(GaCp*)4] regardless of which solvent is used. Particu-
larly, in the gallium case, bond activation reactions were not
observed. A possible explanation for this result involves the
solubility of the ligands: That is, AlCp* is only poorly
soluble in organic solvents, and its concentration is very low
throughout the whole reaction. Hence, intermediates
[Ni(AlCp*)n] (n < 4) are more likely to be generated. In
contrast, GaCp* is highly soluble, and thus, reactive inter-
mediates are not formed or are very short-lived. In the hope
that the increased steric bulk of GaCp*Ph might favor the
formation of low-coordinated intermediates of the kind
[Ni(GaCp*Ph)3], we treated [Ni(COD)2] with GaCp*Ph. Reac-
tion of [Ni(COD)2] with GaCp*Ph in hexane resulted in a
brown solution, from which only [Ni(COD)2] could be re-
isolated, however. Also, in the presence of phosphines or
other co-reactants (such as benzene or organosilanes), defined
reactions to yield new products were not observed. Recently,
we reported on similar observations in the reaction of
[Ni(COD)2] with AlCp*Ph, which lead to unidentifiable
product mixtures under all conditions. The reason for the
apparent inertness of [Ni(COD)2] with respect to the phenyl-
substituted ligand GaCp*Ph in terms of isolable products
probably lies in the fact that the steric demand of GaCp*Ph
does not allow the coordination of four ligands to one metal
center, and thus, the substitution of the four olefinic ligands
in [Ni(COD)2] becomes thermodynamically unfavorable. In
other words, COD effectively competes with GaCp*Ph,
leading to the thermodynamic product upon crystallization:
[Ni(COD)]2. Investigations of the substitution chemistry of
potentially more reactive Ni(0) sources such as the labile
[Ni(CDT)] (CDT ) t,t,t-1,5,9-cyclododecatriene) and even
[Ni(C2H4)3] featuring less-competing alkene ligands is the
subject of current research.
Ligand-Exchange Reactions at 2a and 2b. As recently
shown, electronically and sterically unsaturated complexes
[Ma(GaCp*)b] react with a wide variety of ligands to yield
substitution products. Thus, substitution of coordinated
GaCp* in [M2(GaCp*)5] by AlCp*, PPh3, CO, or isonitriles
(t-BuNC) is favorable, as in all reactions, partial or full ligand
exchange was observed. It was shown that π-acceptor ligands
prefer a terminal position in the dinuclear products, whereas
remaining GaCp* ligands are found in bridging positions.
In addition, AlCp* substitutes GaCp* preferring the bridging
position, as shown by the compound [(Cp*Ga)Pd(µ2-AlCp*)3-
Pd(GaCp*)].15 Scheme 2 provides an overview of ligand-
substitution reactions of complex 2a. Treatment of 2a with
AlCp* in toluene leads to quantitative substitution of
GaCp*Ph and dvds and the formation of the trinuclear
complex [Pd3(AlCp*)6]. After gentle heating of a mixture
of the two starting materials in toluene, immediate precipita-
tion of dark red microcrystals is observed, which are
identified by NMR spectroscopic analysis as the known
cluster [Pd3(AlCp*)6]. Similarly, treatment of 2a with sto-
ichiometric GaCp* in toluene at room temperature leads to
Figure 2. Molecular structure of [Pd2(GaCp*Ph)2(µ2-GaCp*Ph)3] (2b) in
the solid state (ORTEP drawing; 50% level of probability for the metal
atoms; carbon atoms displayed as spheres for clarity). Selected bond lengths
(Å): Pd(1)-Pd(2) 2.572(10), Pd(1)-Ga(4) 2.336(13), Pd(1)-Ga(1) 2.479(1),
Pd(1)-Ga(2) 2.467(1), Pd(1)-Ga(5) 2.465(1), Pd(2)-Ga(3) 2.338(1),
Pd(2)-Ga(1) 2.468(1), Pd(2)-Ga(2) 2.493(1), Pd(2)-Ga(5) 2.491(1).
The CdC double bonds of the coordinated diene moiety
in 2a are very slightly elongated (mean ) 1.38 Å) compared
to uncoordinated CdC bonds (1.34 Å), indicating only a
weak π-back-bonding from the Pd(0) center to the alkene
ligands. Virtually the same situation was described in the
complex [Pd(PMe3)(η2,η2-C6H10O)].23 It should be mentioned
that the free ligand GaCp*Ph (1b) has not been characterized
by an X-ray crystal structure analysis so far, and a discussion
of the Ga-C bond lengths of its complexes 2a and 2b is
therefore difficult.
Complex 2b crystallizes in the triclinic space group P1h
and is almost isostructural with [Pd2(GaCp*)5], exhibiting
only small deviations in the geometrical parameters because
of the presence of the phenyl groups.15 The molecular
structure of 2b is shown in Figure 2 and consists of a central
unit of two palladium atoms with a rather short Pd-Pd bond
of 2.572(1) Å, compared to 2.609(1) Å in [Pd2(GaCp*)5].
The Pd2 unit of 2b is surrounded by two terminal and three
bridging Cp*PhGa ligands. The terminal Pd-Ga bond
distances in 2b of 2.336(1) and 2.338(1) Å are somewhat
shorter than those in [Pd2(GaCp*)5] (2.358(1) and 2.362(1)
Å). The bridging Cp*Ga units have values in the range of
2.465(1)-2.493(1) Å. The average values for the Ga-
Cp*PhCentr. distance are, at 1.998 Å for the terminal and 2.023
Å for the bridging GaCp*Ph ligands, only slightly shorter
than the average values in [Pd2(GaCp*)5] (1.999 Å for the
terminal and 2.048 Å for the bridging ligands).
Reactions of Ni(COD)2 with GaCp*Ph. Recall that
activation reactions at low-coordinated, reactive fragments
[Ni(AlCp*)n] (n < 4) are possible.24 Thus, treatment of
(23) Krause, J.; Haack, K.-J.; Cestaric, G.; Goddard, R.; Po¨rschke, K.-R.
Chem. Commun. 1998, 1291.
(24) Steinke, T.; Gemel, C.; Cokoja, M.; Winter, M.; Fischer, R. A. Angew.
Chem. 2004, 116, 2349.
1792 Inorganic Chemistry, Vol. 45, No. 4, 2006

Coordination Chemistry of Ga(C5Me4Ph)
Scheme 2. Ligand-Exchange Reactions of Pd3(dvds)(GaCp*Ph
)
4
theformationoftheknownlinearPd3Ga8 cluster[Pd3(GaCp*)8]
GaCp*Ph ligands is obviously unfavorable in the case of
Ni(0). Taking all of the results above together, it is clear
that the concept of slightly increasing the steric bulk of ECp*-
type ligands, the title ligand GaCp*Ph being an example, holds
promise for further success in line with the goal of the
synthesis of transition-metal-rich oligonuclear clusters of the
type [Ma(ER)b]. A delicate balance of ligand properties,
transition-metal precursors, and reaction conditions appears
to be important for the synthetic success. Exactly this
complex situation seems to offer rich opportunities for
unusual further discoveries in this chemistry.
1
as shown by H NMR spectroscopy.15
The reaction of 2a with excess of PPh3 in C6D6 at room
temperature leads to a mixture of GaCp*Ph and PPh3-
containing species, as indicated by 1H and 31P NMR
spectroscopy. However, isolation and identification of pure
products were not successful. Heating the solution to 80 °C
even for a short time leads to the loss of all GaCp*Ph ligands
and formation of the homoleptic phosphine complex
[Pd(PPh3)4]. Variation of the amount of PPh3 in this reaction
does also not lead to defined mixed-ligand cluster complexes.
Apparently, the choice of the phospine ligand plays an
important role. 2a does not undergo selective activation
reactions with HSiEt3 or H2. Instead, the formation of 2b
was observed in both reactions.
Experimental Section
All manipulations were carried out in an atmosphere of purified
argon using standard Schlenk and glovebox techniques. Hexane,
toluene, THF, and Et2O were dried using an mBraun Solvent
Purification System; all other solvents were dried by distillation
over standard drying agents. The final H2O content in all solvents
used was checked by Karl Fischer titration and did not exceed 5
ppm. [C5Me4PhH],25 [Pd2(dvds)3],26 AlCp*,27 and GaCp*21 were
prepared according to recent literature methods. Elemental analyses
were performed by the Microanalytical Laboratory of the Ruhr-
Universita¨t Bochum. Melting or decomposition points were deter-
mined thermogravimetrically on a Seiko EXSTAR 6300S11 TG/
DTA instrument. NMR spectra were recorded on a Bruker Avance
DPX-250 spectrometer (1H, 250.1 MHz; 13C, 62.9 MHz) in C6D6
at 298 K unless otherwise stated. Chemical shifts are given relative
to TMS and were referenced to the solvent resonances as internal
standards.
As indicated by 1H NMR spectroscopy, substitution of the
GaCp*Ph ligand in 2b with AlCp* and GaCp* yields the
compound [Pd2(ECp*)5] (E ) Al, Ga).
Conclusions and Outlook
In this article, we have presented the preparation and
characterization of new d10 cluster complexes of palladium
using the novel compound GaCp*Ph as a stabilizing ligand.
The higher cone angle of GaCp*Ph compared to GaCp* does
indeed inhibit the coordination of four ligands to one
transition-metal center; thus, di- and trinuclear cluster
complexes are the preferred products. The novel trinuclear
Pd3Ga4 cluster 2a was isolated and characterized as an
intermediate in the formation of the dinuclear Pd2Ga5 cluster
2b. Compound 2a is the first example of a trinuclear Pd/Ga
cluster coordinated by a potentially substitution-labile olefinic
ligand. However, all attempts to selectively substitute only
these olefinic groups by other ligands such as ECp* (E )
Al, Ga), PPh3, H2, or HSiEt3 lead either to full substitution
of all of the GaCp*Ph ligands or to a thermal decomposition
of 2a giving 2b. Ni(COD)2 proved to be inert toward
GaCp*Ph, as the substitution of four olefinic ligands by three
The crystal structures of 2a and 2b were measured on an Oxford
Excalibur 2 diffractometer using Mo KR radiation (λ ) 0.71073
Å). The structures were solved by direct methods using SHELXS-
97 and refined against F2 on all data by full-matrix least-squares
with SHELXL-97.
(25) Bjoergvinsson, M.; Halldorsson, S.; Arnason, I.; Magull, J.; Fenske,
D. J. Organomet. Chem. 1997, 544, 207.
(26) Krause, J.; Cestaric, G.; Haak, K.-J.; Seevogel, K.; Storm, W.;
Po¨rschke, K.-R. J. Am. Chem. Soc. 1999, 121, 9807.
(27) Schormann, M.; Klimek, K. S.; Hatop, H.; Varkey, S. P.; Roesky, H.
W.; Lehmann, C.; Ro¨pken, C.; Herbst-Irmer, R.; Noltemeyer, M. J.
Solid State Chem. 2001, 162, 225.
Inorganic Chemistry, Vol. 45, No. 4, 2006 1793

Buchin et al.
Table 1. Crystallographic Data for Compounds 2a and 2b
2a
2b
empirical formula
C68H86Ga4OPd3Si2
1573.63
104(2)
0.71073
triclinic
C75H85Ga5Pd2
1547.95
105(2)
0.71073
triclinic
P1h
12.139(2)
13.509(4)
22.7429(19)
103.958(15)
92.333(12)
108.32(2)
3408.3(12)
2
Mr (g mol-1
)
temperature (K)
wavelength (Å)
crystal system
space group
a (Å)
P1h
12.546(3)
13.577(4)
20.051(5)
97.25(2)
b (Å)
c (Å)
R (deg)
â (deg)
96.51(2)
γ (deg)
101.04(2)
3292.2(15)
2
1.587
2.489
V (Å3)
Z
F
calc (g cm-3
)
1.508
2.502
1564
µ (mm-1
F(000)
)
1584
2θ range (deg)
2.88-25.05
-10 e h e 14, -16 e k e 16,
-23 e l e 23
25856
11608 (Rint ) 0.0444)
0.929
2.97-25.17
index ranges
-12 e h e 14, -16 e k e 16,
-27 e l e 23
23341
reflections, collected
reflections, unique
GOF on F2
12035 (Rint ) 0.0440)
0.962
final R indices [I > 2s(I)]
R1 ) 0.0456
wR2 ) 0.0727
R1 ) 0.0727
wR2 ) 0.1085
R1 ) 0.0549
wR2 ) 0.1459
R1 ) 0.0793
R indices (all data)
wR2 ) 0.1591
The relatively high residual electron-density peaks in the refined
crystal structure of 2a (1.726 and -0.956) are located rather far
from the metal centers and can thus not be explained by absorption
effects; yet no meaningful model for a disorder in the ligand sphere
was found. The presence of solvent molecules can also be excluded.
Two Cp*Ph rings in the crystal structure of 2b were strongly
disordered (Ga1 and Ga3), which could not be modeled in the
refinement. Therefore, some ring carbon atoms of the Cp*Ph ligands
show rather large anistropic parameters and could only be refined
isotropically. Comparably high residual electron-density peaks
(2.407 and -1.290) are also explained by this disorder. However,
the disorders of both structures 2a and 2b are not relevant for the
structural issues discussed in this article. Supplementary crystal-
lographic data for both 2a and 2b have been deposited with the
Cambridge Crystallographic Data Centre. These data can be obtain
free of charge via the Internet at www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB21EZ, U.K.; fax
(+44)1223-336-033; e-mail: deposit@ccdc.cam.uk).
2.159 mmol) in hexane (5 mL) was cooled to -30 °C and treated
with [GaCp*Ph] (461 mg, 1.727 mmol). The resulting orange
solution was slowly warmed to room temperature, whereupon an
orange precipitate was formed. The mixture was cooled to -30
°C. The product was isolated by means of cannulation, washed twice
with small amounts of hexane, and dried in vacuo. Yield: 491 mg
(72%).
1H NMR (C6D6, 250 MHz, 25 °C): δ (ppm) ) 7.27 (m, 20H),
4.21 (m, 6H), 2.12 (s, 6H), 2.09 (s, 12H), 2.06 (s, 6H), 1.95 (s,
6H) 1.94 (s, 12H), 1.90 (s, 6H), 0.17 (s, 3H), 0.16 (s, 3H), 0.11 (s,
3H), 0.02 (s, 3H).
[Pd2(GaCp*)2(µ2-GaCp*)3] (2b). A suspension of 2a (125 mg,
0.079 mmol) in hexane (15 mL) was treated with [GaCp*Ph] (74
mg, 0.277 mmol). The mixture was stirred for 30 min until the
color of the precipitate turned from orange to yellow. The mixture
was cooled to 0 °C. The product was isolated by means of
cannulation, washed twice with small amounts of hexane, and dried
in vacuo. Yield:140 mg (76%).
1H NMR (C6D6, 250 MHz, 25 °C): δ (ppm) 7.50-7.19 (m, 25H),
1.98 (s, 30H), 1.90 (s, 30H). 13C NMR (C6D6, 62.9 MHz, 60 °C):
136.6, 131.5, 128.2, 126.4, 122.5, 114.4, 11.6, 10.8. Anal. Calcd
for C75H85Ga5Pd2: C, 58.19; H, 5.53. Found: C, 57.62, H, 6.18.
[K(C5Me4Ph)] (1a). [C5HMe4Ph] (27.54 g, 0.139 mol) was
added to a suspension of KH (5 g, 0.125 mol) in THF (200 mL).
The suspension was allowed to stir for 15 h at room temperature.
The white precipitate was collected by filtration and washed with
THF (3 × 20 mL) and dried in vacuo for 15 h. Yield: 28.3 g (96%).
[GaCp*Ph] (1b). GaI was prepared in situ from Ga (3.54 g, 0.051
mol) and I2 (6.46 g, 0.051 mol) in benzene (40 mL) by ultrasonic
irradiation according to the literature method, giving a green solid.
To the suspension was added K(C5Me4Ph) (12.0 g, 0.051 mol).
The mixture was allowed to stir for 48 h. The resulting gray solid
was removed by filtration and washed with toluene (3 × 20 mL).
The solvent was removed in vacuo. The residue was distilled under
vacuum at 125 °C, giving GaCp*Ph in 59% yield as orange liquid.
1H NMR (C6D6, 250 MHz, 25 °C): δ (ppm) ) 7.27 (m, 5H),
2.00 (s, 6H), 1.93 (s, 6H). 13C NMR (C6D6, 62.9 MHz, 25 °C):
136.7, 131.4, 128.5, 128.1, 126.3, 114, 114.1, 10.7, 10.0.
Substitution Experiments with 2a and 2b. In a typical
experiment, 2a or 2b (50 mg) was dissolved in toluene (1 mL).
After the respective reactant had been added, the reaction mixture
was stirred for several minutes at 60 °C. Small impurities were
filtered off by extraction with toluene, and the solvent was removed
in vacuo to yield the products as colored powders. All analytical
data for these products were in accordance with the published data
(Table 1).
Supporting Information Available: X-ray crystallographic data
in CIF format for compounds 2a and 2b. This material is available
free of charge via the Internet at http://pubs.acs.org.
[Pd3(dvds)(GaCp*Ph)(µ2-GaCp*Ph)(µ3-GaCp*Ph)2] (2a). A so-
lution of [Pd2(dvds)3] (500 mg, 1.295 mmol) and dvds (402 mg,
IC051658M
1794 Inorganic Chemistry, Vol. 45, No. 4, 2006