A carbon-bridged digallium compound as a chelating Lewis acid: Complexation of thiophenolate and benzoate anions by H5C6 - CH 2 - C(SiMe3)[Ga(CH2tBu)2] 2

Article abstract of DOI:10.1021/om800068s

The digallium compound H₅C₆ - CH ₂C(SiMe₃)(GaCl₂)₂ (6) is easily available by the 2-fold hydrogallation of phenyl(trimethylsilyl)ethyne with H - GaCl₂. Its treatment with neopentyllithium gave the corresponding tetraneopentyl compound 7 by the replacement of all four chlorine atoms. Compound 7 has two coordinatively unsaturated gallium atoms attached to one carbon atom and, hence, is suitable to act as a chelating Lewis acid. Accordingly, tetrabutylammonium thiophenolate dissolved in 1,2-difluorobenzene reacted readily with 7 to afford the adduct 8, in which the sulfur atom of the thiophenolato group is coordinated by both gallium atoms to form a four-membered CGa₂S heterocycle. A similar compound (9) was formed upon treatment of 7 with the benzoate anion. A slightly different structural motif compared to 8 resulted because each oxygen atom of the benzoate ligand is coordinated to one gallium atom to give a six-membered Ga₂C₂O₂ heterocycle.

Full text of DOI:10.1021/om800068s

2118
Organometallics 2008, 27, 2118–2122
A Carbon-Bridged Digallium Compound as a Chelating Lewis Acid:
Complexation of Thiophenolate and Benzoate Anions by
H5C6-CH2-C(SiMe3)[Ga(CH2tBu)2]2
Werner Uhl,* Michael Claesener, and Alexander Hepp
Institut für Anorganizche and Analytische Chemie der UniVersität Münster, Corrensstrasse 30,
D-48149 Münster, Germany
ReceiVed January 25, 2008
The digallium compound H5C6-CH2C(SiMe3)(GaCl2)2 (6) is easily available by the 2-fold hydrogallation
of phenyl(trimethylsilyl)ethyne with H-GaCl2. Its treatment with neopentyllithium gave the corresponding
tetraneopentyl compound 7 by the replacement of all four chlorine atoms. Compound 7 has two
coordinatively unsaturated gallium atoms attached to one carbon atom and, hence, is suitable to act as a
chelating Lewis acid. Accordingly, tetrabutylammonium thiophenolate dissolved in 1,2-difluorobenzene
reacted readily with 7 to afford the adduct 8, in which the sulfur atom of the thiophenolato group is
coordinated by both gallium atoms to form a four-membered CGa2S heterocycle. A similar compound
(9) was formed upon treatment of 7 with the benzoate anion. A slightly different structural motif compared
to 8 resulted because each oxygen atom of the benzoate ligand is coordinated to one gallium atom to
give a six-membered Ga2C2O2 heterocycle.
Scheme 1
Introduction
Compounds containing more than one coordinatively unsatur-
ated atom of a group 13 element in a single molecule are
potentially useful as effective chelating Lewis acids. They found
increasing interest in recent literature because they may be
applicable in phase transfer processes, in anion recognition, or
in catalysis.1,2 However, the true capability of these compounds
to act as polyacceptors was tested in only a few cases.1–3 One
impressive example is a methylene-bridged dialuminium com-
pound, R2Al-CH2-AlR2 [R ) CH(SiMe3)2], which was
obtained in our group several years ago.2 Its synthesis required
very bulky bis(trimethylsilyl)methyl substituents in order to
* Corresponding Author.
(1) Selected publications: (a) Kaul, F. A. R.; Tschinkl, M.; Gabbai, F. P.
J. Organomet. Chem. 1997, 539, 187. (b) Saied, O.; Simard, M.; Wuest,
J. D. Inorg. Chem. 1998, 37, 2620. (c) Saied, O.; Simard, M.; Wuest, J. D.
Organometallics 1998, 17, 1128. (d) Thiyagarajan, B.; Jordan, R. F.; Young,
V. G. Organometallics 1998, 17, 281. (e) Piers, W. E.; Irvine, G. J.;
Williams, V. C. Eur. J. Inorg. Chem. 2000, 2131. (f) Cottone, A., III; Scott,
M. J. Organometallics 2002, 21, 3610. (g) Melaimi, M.; Gabbai, F. P. J. Am.
Chem. Soc. 2005, 127, 9680. (h) Schulte, M.; Gabbai, F. P. Can. J. Chem.
2002, 80, 1308. (i) Schulte, M.; Gabbai, F. P. Chem.-Eur. J. 2002, 8, 3802.
(j) Melaimi, M.; Gabbai, F. P. AdV. Organomet. Chem. 2005, 53, 61. (k)
Ooi, T.; Takahshi, M.; Maruoka, K. J. Am. Chem. Soc. 1996, 118, 11307.
(l) Dam, M. A.; Nijbacker, T.; de Kanter, F. J. J.; Akkerman, O. S.;
Bickelhaupt, F.; Spek, A. L. Organometallics 1999, 18, 1706. (m) Dam,
M. A.; Nijbacker, T.; de Pater, B. C.; de Kanter, F. J. J.; Akkerman, O. S.;
Bickelhaupt, F.; Smeets, W. J. J.; Spek, A. L. Organometallics 1997, 16,
511. (n) Althoff, A.; Jutzi, P.; Lenze, N.; Neumann, B.; Stammler, A.;
Stammler, H.-G. Organometallics 2003, 22, 2766. (o) Uhl, W.; Hahn, I.;
Jantschak, A.; Spies, T. J. Organomet. Chem. 2001, 637–639, 300. (p) Jutzi,
P.; Lenze, N.; Neumann, B.; Stammler, H.-G. Angew. Chem. 2001, 113,
1470.; Angew. Chem., Int. Ed. 2001, 40, 1424. (q) Althoff, A.; Jutzi, P.;
Lenze, N.; Neumann, B.; Stammler, A.; Stammler, H.-G. Organometallics
2002, 21, 3018.
prevent decomposition by dismutation. It formed persistent
adducts by the chelating coordination of anions such as hydride,
azide, nitrite, or nitrate (1 to 4; Scheme 1).3 Sodium nitrate, for
instance, dissolved readily in ethereal solutions by the addition
of that particular dialuminum compound.3 Further, the impor-
tance and efficiency of chelating anion coordination by dialu-
minum compounds was shown with the syntheses of stable
carbocationic species in which the formation of the Al-H-Al
(2) (a) Layh, M.; Uhl, W. Polyhedron 1990, 9, 277. (b) Uhl, W.; Layh,
M. J. Organomet. Chem. 1991, 415, 181.
(3) (a) Uhl, W.; Layh, M. Z. Anorg. Allg. Chem. 1994, 620, 856. (b)
Uhl, W.; Koch, M.; Heckel, M.; Hiller, W.; Karsch, H. H. Z. Anorg. Allg.
Chem. 1994, 620, 1427. (c) Uhl, W.; Hannemann, F.; Saak, W.; Wartchow,
R. Eur. J. Inorg. Chem. 1998, 921. (d) Uhl, W.; Hannemann, F. J.
Organomet. Chem. 1999, 579, 18.
10.1021/om800068s CCC: $40.75
2008 American Chemical Society
Publication on Web 04/03/2008

Carbon-Bridged Digallium Compound as a Chelating Lewis Acid
Organometallics, Vol. 27, No. 9, 2008 2119
bridge is favored over the formation of a C-H bond (5).4 In
order to synthesize a broader variety of chelating Lewis acids
possessing more than two aluminum or gallium atoms, we tried
to apply the hydroalumination or hydrogallation of oligoalkynes
with dialkylelement hydrides. But these reactions proved to be
much more complicated and interesting than may be derived
from textbook knowledge. Instead of the expected simple
addition products, we isolated fascinating novel compounds such
as carbaalane clusters5,6 or cyclophane-type molecules7,8 by
condensation processes. With few exceptions8 only trimethylsilyl
alkynes yielded the expected alkenylaluminum or -gallium
compounds, H6-xC6[-C(H)dC(SiMe3)(ER2)]x, upon treatment
with aluminum or gallium hydrides.9 While the corresponding
trialkylelement compounds were not released in these cases,
cis/trans isomerization at the CdC double bonds occurred. The
course of the rearrangement depended on the bulkiness of the
element hydrides, and a persistent cis arrangement of the ER2
groups (E ) Al, Ga) and the hydrogen atoms resulted only for
the sterically most shielded di(tert-butyl) compounds. This
observation may indicate that the isomerization is initiated by
some intermolecular activation. For steric reasons only the trans
forms are potentially applicable as chelating Lewis acids, but
we did not succeed in isolating any pure adduct derived from
dialkylaluminum or -gallium derivatives.
Figure 1. Molecular structure of 7. The thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted. Important
bond lengths (Å) and angles (deg): Ga(1)-C(11) 1.991(2),
Ga(1)-C(12) 1.999(2), Ga(1)-C(01) 2.017(2), Ga(2)-C(21)
2.005(2), Ga(2)-C(22) 1.992(2), Ga(2)-C(01) 1.986(2), C(01)-
Si(01) 1.880(2), Ga(1)-C(01)-Ga(2) 103.58(9), C(11)-Ga(1)-C(12)
125.8(1), C(21)-Ga(2)-C(22) 121.8(1), C(01)-C(02)-C(03)
117.4(2).
In recent investigations we showed that H-GaCl210 is a very
interesting alternative reagent for the hydrogallation of silylal-
kynes.11 It afforded selectively the expected monoaddition
products that had the gallium atoms in geminal positions to the
trimethylsilyl groups. Gallium and hydrogen atoms adopted a
trans arrangement across the CdC double bonds.11 The 2-fold
hydrogallation of an alkyne did not succeed even on employing
large excesses of dialkylaluminum or dialkylgallium hydrides.
However, the complete reduction of the triple bonds with the
formation of alkane derivatives was easily achieved with the
dichloro compound.12 The products obtained by these reactions
formed interesting dimeric structures (6, Scheme 1) and were
able to coordinate chloride anions in a chelating manner.12
Furthermore, they may be suitable starting compounds for the
generation of alkyl derivatives by reactions with alkyllithium
derivatives and salt elimination. First results are reported here.
Results and Discussion
Generation of the Tetraneopentyldigallium Compound
7. The tetrachlorodigallium starting compound 6 is available
on a facile route by the treatment of phenyl(trimethylsilyl)ethyne
with 2 equiv of H-GaCl2 in boiling n-hexane.12 Reaction of 6
with 4 equiv of neopentyllithium afforded colorless crystals of
the tetraneopentyl compound 7 in an excellent yield of 86%
(eq 1). The 1H NMR spectroscopic characterization verified the
formation of 7 by the correct integration ratio of its signal
intensities. Singlets resulted for the trimethylsilyl and tert-butyl
groups and for that methylene group that bridges the gallium
atoms and the phenyl ring. The methylene protons of the
neopentyl groups become diastereotopic and gave two doublets
at δ ) 1.25 and 1.40 with a coupling constant of 13.2 Hz. In
the 13C NMR spectrum the resonance of the inner carbon atom
attached to one silicon and two gallium atoms occurs at a
relatively low field (δ ) 49.4). These values correlate to the
number of gallium atoms attached to a single carbon atom, and
even stronger shifts to δ ) 95 were detected for trigallium
compounds.6
(4) (a) Uhl, W.; Grunenberg, J.; Hepp, A.; Matar, M.; Vinogradov, A.
Angew. Chem. 2006, 118, 4465.; Angew. Chem., Int. Ed. 2006, 45, 4358.
(b) Uhl, W.; Vinogradov, A.; Grimme, S. J. Am. Chem. Soc. 2007, 129,
11259.
(5) (a) Uhl, W.; Breher, F. Angew. Chem. 1999, 111, 1578.; Angew.
Chem., Int. Ed. 1999, 38, 1477. (b) Uhl, W.; Breher, F.; Lützen, A.; Saak,
W. Angew. Chem. 2000, 112, 414.; Angew. Chem., Int. Ed. 2000, 39, 406.
(c) Uhl, W.; Breher, F.; Grunenberg, J.; Lützen, A.; Saak, W. Organome-
tallics 2000, 19, 4536. (d) Uhl, W.; Breher, F.; Mbonimana, A.; Gauss, J.;
Haase, D.; Lützen, A.; Saak, W. Eur. J. Inorg. Chem. 2001, 12, 3059. (e)
Stasch, A.; Ferbinteanu, M.; Prust, J.; Zheng, W.; Cimpoesu, F.; Roesky,
H. W.; Magull, J.; Schmidt, H.-G.; Noltemeyer, M. J. Am. Chem. Soc. 2002,
124, 5441.
(6) Uhl, W.; Cuypers, L.; Neumüller, B.; Weller, F. Organometallics
2002, 21, 2365.
(7) (a) Uhl, W.; Hepp, A.; Matar, M.; Vinogradov, A. Eur. J. Inorg.
Chem. 2007, 4133. (b) Uhl, W.; Matar, M. Z. Anorg. Allg. Chem. 2005,
631, 1177.
(1)
(8) (a) Uhl, W.; Claesener, M.; Haddadpour, S.; Jasper, B.; Hepp, A.
Dalton Trans. 2007, 4, 417. (b) Uhl, W.; Breher, F.; Haddadpour, S.
Organometallics 2005, 24, 2210. (c) Uhl, W.; Haddadpour, S.; Matar, M.
Organometallics 2006, 25, 159.
The molecular structure of compound 7 is depicted in Figure
1. It has two dialkylgallium groups attached to that carbon atom
that also bears the trimethylsilyl group. Formally it may be
described as the product of a 2-fold hydrogallation of phenyl-
(trimethylsilyl)ethyne with dineopentylgallium hydride. How-
ever, as mentioned before, such a reaction does not succeed on
a direct route. To the best of our knowledge, compounds similar
to 7 having two coordinatively unsaturated dialkylgallium groups
bonded to one central carbon atom are not known in the
(9) (a) Uhl, W.; Breher, F. J. Organomet. Chem. 2000, 608, 54. (b)
Uhl, W.; Matar, M. J. Organomet. Chem. 2002, 664, 110. (c) Uhl, W.;
Bock, H. R.; Breher, F.; Claesener, M.; Haddadpour, S.; Jasper, B.; Hepp,
A. Organometallics 2007, 26, 2363.
(10) (a) Nogai, S.; Schmidbaur, H. Inorg. Chem. 2002, 41, 4770. (b)
Ohshita, J.; Schmidbaur, H. J. Organomet. Chem. 1993, 453, 7.
(11) Uhl, W.; Claesener, M. Inorg. Chem. 2008, 47, . in press.
(12) Uhl, W.; Claesener, M. Inorg. Chem. 2008, 47, 729.

2120 Organometallics, Vol. 27, No. 9, 2008
Uhl et al.
literature. Heteroadamantane cages of the type (GaR)6(CR′)4
were described that had carbon atoms coordinated to three
unsaturated gallium atoms.6 The distance (bite) between both
gallium atoms in 7 is 3.14 Å. The Ga-C-Ga angle (103.6°)
deviates slightly from the ideal tetrahedral angle. The Ga-C
bond lengths are quite similar (1.998 Å on average) and
correspond well to standard values.
Application of the Digallium Compound 7 as a Chelat-
ing Lewis Acid. The digallium compound 7 has two coordi-
natively unsaturated gallium atoms in a distance of 3.14 Å. This
particular arrangement should allow for an efficient chelating
coordination of single atoms or small molecules and anions. In
preliminary experiments we treated 7 with thiophenolate and
benzoate anions (eq 2), which had tetrabutylammonium coun-
terions in order to enhance their solubility in common organic
solvents. The corresponding adducts 8 and 9 were isolated in
72% and 50% yields after recrystallization. The synthesis of
compound 9 succeeded in toluene, from which the product
separated upon cooling as a highly viscous liquid. Interestingly,
1,2-difluorobenzene, which is relatively polar, but does not have
donor properties, proved to be the best solvent for the generation
of 8. In both cases purification was achieved by recrystallization
from 1,2-difluorobenzene. The molecular symmetry and the
shape of the NMR spectra changed dramatically by the chelating
coordination of the anions. However, complete NMR spectro-
scopic characterization succeeded only with compound 9, while
independently of the solvent too many and in part relatively
broad resonances resulted in the spectra of the thiophenolato
derivative 8. Only the signals of the butyl groups of the cation
were clearly resolved in that case. Temperature-dependent NMR
(2)
1
nolato ligand in 8 is coordinated in a chelating manner by both
gallium atoms to afford a folded four-membered Ga2CS
heterocycle. The Ga-S distances (2.534 Å on average) are
considerably longer than generally observed for thiolato-bridged
digallium compounds.14 This may be caused by the chelating
coordination of the sulfur atom and the insufficient coincidence
of the relatively rigid bite of the ligand and the covalence radius
of the sulfur atom. Further, the sulfur atom has a pyramidal
coordination sphere, and there may be a repulsive interaction
between the hydrogen atoms of the phenyl and neopentyl groups.
The increase of the coordination numbers of the gallium atoms
from three in 7 to four in 8 results in the expected lengthening
of the Ga-C bonds by up to 0.04 Å. The strongest effect occurs
for the bridging carbon atom in the ring. Caused by the chelating
coordination of the anion, the angle Ga-C-Ga decreased from
103.6° in 7 to 97.0° in the adduct 8. The most acute angle of
the heterocycle appeared at the sulfur atom (74.5°). Each oxygen
atom of the carboxylato group in compound 9 (Figure 3) is
coordinated to one gallium atom of the dipodal chelating Lewis
acid 7. Thus, in this case a six-membered Ga2C2O2 heterocycle
resulted by adduct formation. The ring is not planar with the
carbon atom C1 0.69 Å above the average plane spanned by
the remaining five atoms. Due to the higher coordination
numbers at the gallium atoms, the Ga-C bonds are lengthened
by up to 0.04 Å compared to the starting compound 7. The
Ga-O bond lengths (2.037 Å) are a little longer than in
carboxylato-bridged digallium compounds possessing Ga-Ga
bonds and correspond to distances observed for the terminal
coordination of a single gallium atom by a chelating carboxylato
spectra did not help for a better understanding. The best H
NMR spectrum was recorded in CD2Cl2, the results of which
are given in the Experimental Section. These difficulties may
be caused by the slow decomposition observed in solution at
room temperature and by some dynamic effects, which both
may be influenced by the insufficient correspondence of the bite
between both gallium atoms and the covalence radius of the
sulfur atom (see below). Hence, characterization of 8 is restricted
to elemental analysis and crystal structure determination. 8 is
stable in the solid state over months.
In contrast, clearly resolved spectra were determined for
compound 9. Caused by the fixed conformation in the resulting
heterocycle, the neopentyl groups attached to one gallium atom
became chemically different and show two independent sets of
resonances. Two neopentyl groups are neighboring the trim-
ethylsilyl residue, while the two remaining ones are on the same
side of the heterocycle as the benzyl group. The lack of mirror
planes in the molecules and the prochiral character of the carbon
atoms in the heterocycles cause the splitting of the methylene
hydrogen atoms of the neopentyl groups, which show two pairs
1
of doublets in the H NMR spectra. Compared to the neutral
starting compound 7, the most dramatic alteration of a chemical
shift was observed for the carbon atom attached to both gallium
atoms (δ ) 49.4 for 7 to 19.0 for 9). This shift to a higher field
is in accordance with former observations and indicates an
enhancement of the coordination numbers of the gallium atoms
from three to four.13
Both adducts were characterized by crystal structure deter-
minations (Figures 2 and 3). The sulfur atom of the thiophe-
(14) (a) Maelia, L. E.; Koch, S. E. Inorg. Chem. 1986, 25, 1896. (b)
Hoffmann, G. G.; Burschka, C. Angew. Chem. 1985, 97, 965.; Angew.
Chem., Int. Ed. Engl. 1985, 24, 970. (c) Hoffmann, G. G.; Burschka, C. J.
Organomet. Chem. 1984, 267, 229. (d) Uhl, W.; Gerding, R.; Hahn, I.;
Pohl, S.; Saak, W.; Reuter, H. Polyhedron 1996, 15, 3987. and references
therein.
(13) (a) Uhl, W.; Prött, M. Z. Anorg. Allg. Chem. 2002, 628, 2259. (b)
Uhl, W.; Prött, M.; Geiseler, G.; Harms, K. Z. Naturforsch. 2002, 57b,
141. (c) Uhl, W.; Spies, T. Z. Anorg. Allg. Chem. 2000, 626, 1059. (d)
Uhl, W.; Hannemann, F.; Saak, W.; Wartchow, R. Eur. J. Inorg. Chem.
1999, 771.

Carbon-Bridged Digallium Compound as a Chelating Lewis Acid
Organometallics, Vol. 27, No. 9, 2008 2121
Figure 3. Molecular structure of 9. The thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted. Important
bond lengths (Å) and angles (deg): Ga(1)-C(1) 2.041(3), Ga(1)-C(3)
2.018(3), Ga(1)-C(4) 2.020(3), Ga(1)-O(1) 2.035(2), Ga(2)-C(1)
2.0483(3), Ga(2)-C(5) 2.026(3), Ga(2)-C(6) 2.019(3), Ga(2)-O(2)
2.039(2), C(1)-Si(1) 1.853(3), Ga(1)-C(1)-Ga(2) 105.4(2), C(1)-
Ga(1)-O(1) 105.60(9), C(1)-Ga(2)-O(2) 105.7(1), Ga(1)-O(1)-
C(2) 126.0(2), Ga(2)-O(2)-C(2) 133.3(2).
Figure 2. Molecular structure of 8. The thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted. Important
bond lengths (Å) and angles (deg): Ga(1)-C(1) 2.057(3), Ga(1)-C(4)
2.023(4), Ga(1)-C(5) 2.027(4), Ga(2)-C(1) 2.036(3), Ga(2)-C(2)
2.028(4), Ga(2)-C(3) 2.014(4), C(1)-Si(1) 1.856(3), Ga(1)-C(1)-
Ga(2) 97.0(1), C(1)-Ga(1)-S(1) 88.20(9), C(1)-Ga(2)-S(1)
88.1(1), Ga(1)-S(1)-Ga(2) 74.46(3).
ligand.15,16 The angle O-C-O (126.6°) is relatively inflexible
and similar to those observed for other gallium compounds.16
The Ga-C-Ga angle increased by about 2° compared to 7
(105.4°).
(CMe3), 32.9 (CMe3), 4.5 (SiMe3). 29Si NMR (C6D6, 79 MHz): δ
–4.9. IR (CsBr plates, paraffin, cm-1): 1954 w, 1937 w, 1856 w,
1790 w, 1728 vs, 1601 s, 1582 m, 1493 s (phenyl); 1465 vs
(paraffin); 1385 s δ(CH3); 1360 vs (paraffin); 1332 w, 1287 s, 1258
vs, 1244 vs, 1226 vs δ(CH3); 1132 vs, 1103 s, 1076 m, 1051 w,
1015 s, 1001 s, 974 s, 949 s, 932 m ν(CC), ν(CN); 908 w, 899 m,
841 vs, 746 vs, 730 vs F(CH3(Si)); 720 vs (paraffin); 698 vs, 667 s
νas(SiC); 646 s, 608 s νs(SiC); 581 w, 544 s, 513 m, 460 s, 436 s
ν(GaC), δ(CC). MS (EI, 70 eV) (%): 583 (1), 585 (2), 587 (1) M+
- Me; 527 (70), 529 (100), 531 (39) M+ - SiMe3.
Experimental Section
All procedures were carried out under purified argon. Toluene
was dried over Na/benzophenone; 1,2-difluorobenzene, over mo-
12
lecular
sieves.
H5C6-CH2-C(SiMe3)(GaCl2)2
and
neopentyllithium17were obtained according to literature procedures.
The commercially available compounds tetrabutylammonium thiophe-
nolate and benzoate were thoroughly evacuated prior to use. Only
the most intensive peaks of the mass spectrum of 7 are given; the
complete isotopic patterns are in accordance with the calculated
ones. The assignment of the NMR spectra is based on HMBC,
HSQC, ROESY, and DEPT135 data.
Synthesis of the Thiophenolato Adduct 8. Tetrabutylammo-
nium thiophenolate (0.281 g, 0.80 mmol) was dissolved in 10 mL
of 1,2-difluorbenzene. The mixture was added dropwise to a solution
of the digallium compound 7 (0.480 g, 0.80 mmol) in 20 mL of
the same solvent at room temperature. After stirring for 3 h the
solution was concentrated to a few milliliters and cooled to 4 °C
to yield colorless crystals of 8. Yield: 0.55 g (72%). 8 decomposes
slowly in solution, but is stable in the solid state. Mp (argon, sealed
capillary): 126 °C. Anal. Calcd [C53H101NSiSGa2] (950.4): C, 66.87;
H, 10.69; Ga, 14.65; S, 3.37. Found: C, 66.5; H, 10.5; Ga, 13.7; S,
Synthesis of 7. Compound 6 (1.58 g, 3.46 mmol) was dissolved
in 200 mL of warm toluene (50 to 60 °C). After cooling to –80 °C
neopentyllithium (1.08 g, 13.8 mmol) dissolved in 25 mL of toluene
was added dropwise. The reaction mixture was warmed to room
temperature and stirred for 24 h. About 150 mL of the solvent were
removed under vacuum, and the remaining suspension was filtered.
Further concentration of the filtrate to a few milliliters and cooling
to -45 °C yielded colorless crystals of compound 6. Yield: 1.78 g
(86%). Mp (argon, sealed capillary): 82 °C. Anal. Calcd [C31H60-
SiGa2] (599.4): C, 62.02; H, 10.07; Ga, 23.23. Found: C, 61.7; H,
10.1; Ga, 23.1. 1H NMR (C6D6, 400 MHz): δ 7.19 (2 H, m, meta-H
of phenyl), 7.15 (2 H, m, ortho-H of phenyl), 7.05 (1 H, m, para-H
of phenyl), 4.12 (2 H, s, CH2-Ph), 1.40 and 1.25 (each 4 H, d, 2JHH
) 13.2 Hz, GaCH2tBu), 1.22 (36 H, s, tBu), 0.23 (9 H, s, SiMe3).
13C NMR (C6D6, 100 MHz): δ 146.2 (ipso-C of phenyl), 128.9
(meta-C of phenyl), 128.2 (ortho-C of phenyl), 126.5 (para-C of
phenyl), 49.4 (GaCGa), 42.4 (GaCH2tBu), 39.7 (GaCH2Ph), 35.1
1
3.2. H NMR (CD2Cl2, 400 MHz): δ 3.53 (2 H, s, CH2-Ph), 2.99
(8 H, pseudo-t, NCH2), 1.32 (8 H, m, NCH2CH2), 1.20 (8 H, m,
NCH2CH2CH2), 1.11 (36 H, s, CMe3), 0.83 (12 H, t,
NCH2CH2CH2CH3), –0.25 (9 H, s, SiMe3); resonances of phenyl
protons and of methylene protons of the neopentyl groups are not
resolved; impurities by decomposition. IR (CsBr plates, paraffin,
cm-1): 1940 w, 1871 w, 1800 w, 1607 s, 1597 s, 1574 vs, 1492 s
(phenyl); 1470 s, 1460 s, 1454 s (paraffin); 1447 s, 1418 w δ(CH3);
1377 m (paraffin); 1354 m, 1331 vw, 1310 vw, 1226 vs δ(CH3);
1179 w, 1152 m, 1132 m, 1107 m, 1082 s, 1028 m, 1021 m,
1007 m, 991 m, 943 m ν(CC), ν(CN); 903 m, 895 m, 880 m, 853 s,
826 s F(CH3(Si)); 727 s (paraffin); 694 s, 668 s νas(SiC); 655 m,
633 w νs(SiC); 590 s, 530 m, 509 m, 480 m, 459 s, 422 m ν(GaC),
δ(CC).
Synthesis of the Benzoato Adduct 9. Tetrabutylammonium
benzoate (0.364 g, 1.00 mmol) was dissolved in 60 mL of toluene.
The mixture was added dropwise to a solution of the digallium
compound 7 (0.599 g, 1.00 mmol) in 60 mL of the same solvent.
After stirring for 4 h at room temperature the reaction mixture was
filtered. The filtrate was concentrated and cooled to –45 °C. An
oily phase separated, which was isolated. A second fraction was
(15) (a) Uhl, W.; Er, E. Organometallics 2006, 25, 5832. (b) Uhl, W.;
El-Hamdan, A.; Schindler, K. P. Eur. J. Inorg. Chem. 2006, 1817. (c) Uhl,
W.; Fick, A.-C.; Spies, T.; Geiseler, G.; Harms, K. Organometallics 2004,
23, 72.
(16) Uhl, W.; Spies, T.; Koch, R. J. Chem. Soc., Dalton Trans. 1999,
2385.
(17) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100, 3359.

2122 Organometallics, Vol. 27, No. 9, 2008
Uhl et al.
Table 1. Crystal Data, Data Collection Parameters, and Structure Refinement Details for Compounds 7, 8, and 9
7
8
9
formula
C31H60Ga2Si
monoclinic
P21/n
C
56.5H101Ga2NSSi
C54H101Ga2NO2Si
monoclinic
P21/n
cryst syst
space group
Z
monoclinic
P21/n
4
4
4
temp, K
Dcalcd, g/cm3
a, Å
b, Å
c, Å
153(2)
1.163
153(2)
1.089
14.202(2)
20.403(3)
21.021(3)
90
95.521(3)
90
153(2)
1.101
12.112(2)
18.898(3)
15.118(2)
90
97.756(3)
90
3428.7(9)
1.622
0.90 × 0.40 × 0.20
11.476(2)
21.410(3)
23.672(3)
90
90.414(3)
90
5816(1)
0.982
0.30 × 0.08 × 0.06
R, deg
ꢀ, deg
γ, deg
V, 10-30 m3
µ, mm-1
cryst dimens, mm
radiation
θ range, deg
index ranges
6063(2)
0.975
0.18 × 0.18 × 0.02
Mo KR; graphite monochromator
1.66 – 30.05
-19 e h e 19
-28 e k e 28
-29 e l e 29
17 683 [Rint ) 0.0843]
562
1.73 – 30.13
-16 e h e 17
-26 e k e 26
-21 e l e 21
10 035 [Rint ) 0.0559]
322
1.28 – 30.06
-16 e h e 15
-29 e k e 28
-32 e l e 32
16 832 [Rint ) 0.0968]
617
no. of unique reflns
no. of params
R1 (reflns I > 2σ(I))
0.0428 (7367)
0.1018
1.101/-0.449
0.0681 (10146)
0.1801
1.819/-0.548
0.0584 (9593)
0.1376
0.736/-0.372
wR2 (all data)
max./min. residual electron density, 1030 e/m3
obtained after further concentration of the solution. The oily phases
were dissolved in 1,2-difluorobenzene. Colorless crystals of 9 were
isolated upon cooling to -4 °C. Yield: 0.470 g (50%). Mp (argon,
sealed capillary): 139 °C. Anal. Calcd [C54H101NO2SiGa2] (962.4):
C, 67.29; H, 10.56; Ga, 14.47. Found: C, 67.3; H, 10.8; Ga, 14.3.
1H NMR (C6D6/1,2-F2C6H4, 400 MHz): δ 8.52 (2 H, m, ortho-H
of benzoate), 7.72 (2 H, pseudo-d, ortho-H of benzyl), 7.19 (2 H,
m, meta-H of benzyl), 7.17 (1 H, m, para-H of benzoate), 7.16 (2
H, m, meta-H of benzoate), 7.00 (1 H, m, para-H of benzyl), 3.95
(2 H, s, CH2-Ph), 2.27 (8 H, t, NCH2), 1.55 and 1.50 (each 18 H,
Crystal Structure Determinations of Compounds 7, 8, and
9. Single crystals of 7, 8, and 9 were obtained by recrystallization
from toluene (20/-45 °C). The crystallographic data were collected
with a Bruker APEX diffractometer. The structures were solved
by direct methods and refined with the program SHELXL-9718 by
a full-matrix least-squares method based on F2. Crystal data, data
collection parameters, and structure refinement details are given in
Table 1. The crystals of 8 enclosed a toluene molecule that was
strongly disordered across a crystallographic center of symmetry.
One n-butyl group of 9 showed a disorder; the atoms were refined
on split positions. Further details of the crystal structure determina-
tions are available from the Cambridge Crystallographic Data Center
on quoting the depository numbers CCDC-675459 (7), -675460 (8),
and -675461 (9).
2
s, tBu), 1.40 and 1.30 (each 2 H, d, JHH ) 13.2 Hz, CH2-tBu),
2
1.41 and 1.15 (each 2 H, d, JHH ) 13.2 Hz, CH2tBu), 1.06 (8 H
m, NCH2CH2CH2), 0.98 (8 H, m, NCH2CH2), 0.80 (12 H, t,
NCH2CH2CH2CH3), 0.32 (9 H, s, SiMe3). 13C NMR (C6D6/1,2-
F2C6H4, 100 MHz): δ 173.4 (CO2), 150.8 (ipso-C of benzyl), 137.0
(ipso-C of benzoate), 131.0 (ortho-C of benzyl and benzoate), 130.9
(para-C of benzoate), 127.9 (meta-C of benzoate), 127.6 (meta-C
of benzyl), 124.4 (para-C of benzyl), 58.5 (NCH2), 41.7 (PhCH2),
37.2 and 35.7 (tBuCH2), 36.1 and 35.8 (CMe3), 33.6 and 33.0
(CMe3), 23.6 (NCH2CH2), 19.7 (NCH2CH2CH2), 19.0 (GaCGa),
13.4 (NCH2CH2CH2CH3), 6.4 (SiMe3). 29Si NMR (C6D6/1,2-
F2C6H4, 79 MHz): δ –1.3. IR (CsBr plates, paraffin, cm-1): 1597 s,
1562 s (phenyl); 1454 vs (paraffin); 1393 w δ(CH3); 1377 s
(paraffin); 1356 m, 1231 m δ(CH3); 1173 w, 1152 w, 1128 w,
1117 w, 1105 w, 1067 w, 1026 w, 980 w, 932 w ν(CC), ν(CN);
907 w, 883 w, 851 m, 829 w, 756 m F(CH3(Si)); 719 w (paraffin);
704 w, 677 w νas(SiC); 654 vw, 636 vw νs(SiC); 603 w, 590 w,
579 w, 540 w, 511 vw, 473 m, 447 w ν(GaC), δ(CC).
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie for generous financial support.
Supporting Information Available: CIF files giving the crystal
data for compounds 7, 8, and 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM800068S
(18) SHELXTL-Plus, REL. 4.1; Siemens Analytical X-Ray Instruments
Inc.: Madison, WI, 1990. Sheldrick, G. M. SHELXL-97, Program for the
Refinement of Structures; Universität Göttingen, Germany, 1997.
(19) Hahn, T., Ed. International Tables for Crystallography, Space-
Group Symmetry, Vol. A; Kluwer Academic Publishers: Dordrecht, 1989.