Unexpected formation of Ga4C2H4 heteroadamantane cages by the reaction of carbon-bridged bis(dichlorogallium) compounds with tert -butyllithium

Article abstract of DOI:10.1021/om200573g

Reactions of the carbon-bridged bis(dichlorogallium) compounds (Cl ₂Ga)₂C(SiR₂R′)-CH₂-Ph (1a, R = R′ = Me; 1b, R = Ph, R′ = Me; 1c, R = Me, R′ = CMe ₃) with four equivalents of tert-butyllithium yielded bis[tert-butyl(hydrido)digallium] compounds {[(Me₃C)(H)Ga] ₂C(SiR₂R′)-CH₂-Ph}₂ (3a to 3c), via β-elimination and release of isobutene. 3a to 3c are dimeric in solution and the solid state and contain unprecedented Ga₄C ₂H₄ heteroadamantane structures in which four metal atoms are bridged by four hydrogen and two carbon atoms. In contrast, n-propyllithium gave the monomeric tetra(n-propyl)digallium compound (ⁿPr ₂Ga)₂C(SiMe₃)-CH₂-Ph (2) under similar conditions, which has two coordinatively unsaturated gallium atoms and may be applicable as a chelating Lewis acid.

Full text of DOI:10.1021/om200573g

ARTICLE
pubs.acs.org/Organometallics
Unexpected Formation of Ga4C2H4 Heteroadamantane Cages by the
Reaction of Carbon-Bridged Bis(dichlorogallium) Compounds with
tert-Butyllithium
Werner Uhl,* Dirk Kovert, Sarina Zemke, and Alexander Hepp
Institut f€ur Anorganische und Analytische Chemie der Universit€at M€unster, Corrensstrasse 30, D-48149 M€unster, Germany
S Supporting Information
b
ABSTRACT:
Reactions of the carbon-bridged bis(dichlorogallium) compounds (Cl2Ga)2C(SiR2R0)-CH2-Ph (1a, R = R0 = Me; 1b, R = Ph,
R0 = Me; 1c, R = Me, R0 = CMe3) with four equivalents of tert-butyllithium yielded bis[tert-butyl(hydrido)digallium] compounds
{[(Me3C)(H)Ga]2C(SiR2R0)-CH2-Ph}2 (3a to 3c), via β-elimination and release of isobutene. 3a to 3c are dimeric in solution and
the solid state and contain unprecedented Ga4C2H4 heteroadamantane structures in which four metal atoms are bridged by four
hydrogen and two carbon atoms. In contrast, n-propyllithium gave the monomeric tetra(n-propyl)digallium compound
(nPr2Ga)2C(SiMe3)-CH2-Ph (2) under similar conditions, which has two coordinatively unsaturated gallium atoms and may be
applicable as a chelating Lewis acid.
’ INTRODUCTION
atom.10 Sterically crowded tris(trimethylsilyl)methyllithium gave
strange chlorineꢀmethyl exchange reactions,7 which have been
elucidated in detail only recently. The unexpected reactions of
the bis(dichlorogallium) compounds with tert-butyllithium are
reported in this article.
The addition of dialkylgallium hydrides to oligoalkynes
(hydrogallation)1 is a facile method for the reduction of un-
saturated organic substrates and the generation of oligogallium
compounds that are suitable to act as chelating Lewis acids2 for
the effective coordination of donor ions or molecules.3ꢀ5 Vinylic
compounds are usually generated by the addition of a single
GaꢀH bond. Dual hydrogallation was observed in rare cases only
and required relatively drastic reaction conditions.6 Dichlorogal-
lium hydride, (H-GaCl2)2,7 proved to be more reactive than
the corresponding alkyl derivatives and gave the complete
reduction of alkynes to aliphatic compounds already at room
temperature.4,8,9 Highly functional carbon-bridged digallium
compounds are formed that have a geminal arrangement of
two GaCl2 groups and are dimeric in the solid state via
GaꢀClꢀGa bridges. Their two Lewis-acidic metal atoms are
active for the chelating coordination of halide ions,4 and their
GaꢀCl bonds allow alkylation by treatment with alkyllithium
reagents and salt elimination.5,10 Neopentyllithium was a versa-
tile reagent for these experiments,5 while tert-butyllithium af-
forded the corresponding di(tert-butyl)gallium compounds only
upon application of the vinylic dichlorogallium compounds
having only a single gallium atom attached to the respective carbon
’ RESULTS AND DISCUSSION
Synthesis of Bis(dichlorogallium) Compounds by Dual
Hydrogallation of Alkynes. The dual hydrogallation of silylalk-
ynes H5C6-CtC-SiR2R0 (R = R0 = Me; R = Ph, R0 = Me; R = Me,
R0 = CMe3) follows a standard procedure.3 Suspensions of two
equivalents of (H-GaCl2)2 in n-hexane were treated with the
corresponding alkynes. The mixtures were stirred at room
temperature for 15 h, and the products (Cl2Ga)2C(SiR2R0)-
CH2-Ph (1a to 1c, eq 1) precipitated as colorless, amorphous
solids in high purity. They are insoluble in noncoordinating
solvents. Therefore, the NMR spectra were recorded in THF
solutions, which clearly gives rise to the formation of THF
adducts with an ether molecule attached to each gallium atom.
Received: June 30, 2011
Published: August 18, 2011
r
2011 American Chemical Society
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Synthesis and characterization of the trimethylsilyl derivative 1a
have been reported previously.4 The NMR data of 1b and 1c are
quite similar and do not require a detailed discussion. Most
characteristic is a singlet in the 1H NMR spectra at about δ = 3.7
for the methylene hydrogen atoms. Crystal structure determina-
tions revealed dimeric formula units via GaꢀClꢀGa bridges for
similar compounds.4,8
revealed unexpected constitutions with a Ga4C2H4 heteroada-
mantane skeleton in the molecular core. Four gallium atoms are
terminally bonded to a tert-butyl group and bridged by two
carbon and four hydrogen atoms. The hydrogen atoms are part of
3c-2e GaꢀHꢀGa bonds. The carbon atoms of the cages are
bonded to terminal benzyl (ꢀCH2C6H5) and trialkylsilyl groups.
They are in opposite positions of the cage with a perpendicular
arrangement of the (R3)SiꢀCꢀC(benzyl) triangles. These
molecules are chiral, similar to allenes RR0CdCdCRR0, and
possess a noncrystallographic 2-fold rotational axis through the
opposite hydrogen atoms H(1) and H(4).11 These compounds
may formally be formed by the replacement of one chlorine atom
of each gallium atom by a tert-butyl group as originally expected.
The second chlorine atom is replaced by a hydride ion that
originates from tert-butyllithium via β-elimination and release of
isobutene. Cages are formed by dimerization of the monomeric
formula units [(Me3C)(H)Ga]2C(SiMe3)-CH2-Ph. The gallium
atoms are coordinatively saturated with a coordination number
of four in a distorted tetrahedral coordination sphere. GaꢀC
(2.009 Å on average) and GaꢀH distances (1.71 Å) in the cages
correspond to standard values.12 The angles in the cage differ
considerably. HꢀGaꢀH angles are relatively acute (89°), while
the largest angles are observed at the hydrogen atoms
(GaꢀHꢀGa 139°). The GaꢀCꢀGa angles (102.6°) are almost
unaffected compared to those of the tetrachloro- or tetraalk-
yldigallium compounds (see above).4,5,8 Steric interactions may
cause large CꢀGaꢀC angles between the quaternary carbon
atoms of the tert-butyl groups attached to gallium and the
bridging carbon atoms (136.3° on average).
Reactions of the Bis(dichlorogallium) Compounds 1a
to 1c with n-Propyl- and tert-Butyllithium. Treatment of
the tetrachlorodigallium compound 1a with four equivalents of
n-propyllithium afforded the corresponding tetra(n-propyl)-
digallium compound (nPr2Ga)2C(SiMe3)-CH2-Ph (2), in a
moderate yield of 55% (eq 2). Its methylene protons showed a
singlet at δ = 3.66 in the 1H NMR spectrum, and a resonance at a
relatively low field of the 13C NMR spectrum (δ = 43.3) was
observed for the carbon atom of the CGa2 group. Both shifts are
in the characteristic ranges of these carbon-bridged digallium
compounds (see above).5 Crystal structure determination ver-
ified the constitution of 2 (Figure 1). The central carbon atom
C(1) is bonded to two di(n-propyl)gallium groups, a benzyl,
and a trimethylsilyl substituent. GaꢀC(1) (1.989 Å on average)
and Si(1)ꢀC(1) bond lengths (1.862(3) Å) are in the expected
ranges. The angle Ga(1)ꢀC(1)ꢀGa(2) is relatively small
(103.8(1)°), and the largest angle at C(1) was observed between
Ga(1) and Si(1) (114.8(1)°). The corresponding tetraneopentyl
derivative has been obtained previously in a similar route.5 Ethyl-
and isopropyllithium gave the same reactions; however, the
products could not be purified by recrystallization and were
isolated only as highly viscous substances. NMR data were quite
similar to those of 2, but we abstain from a detailed discussion
due to the presence of unknown impurities.
The unexpected and unprecedented constitution of com-
pounds 3a to 3c is in accordance with their NMR data. Three
1
resonances of relatively low intensity were observed in the H
NMR spectra at about δ = 4 in an intensity ratio of 1:1:2. They
were assigned to the hydrogen atoms attached to gallium. Their
splitting pattern results from the particular molecular symmetry
and verifies the existence of dimeric formula units also in
solution. The molecules of 3a to 3c have a 2-fold rotational axis
through two opposite bridging hydrogen atoms (H(1) and H(4)
in Figure 2) as described above. These two hydrogen atoms are
chemically nonequivalent and give the resonances with the lower
A different result was obtained upon treatment of the starting
compounds 1a to 1c with four equivalents of tert-butyllithium
under similar reaction conditions (eq 3). Crystal structure
determinations with the colorless products 3a to 3c (Figure 2)
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ARTICLE
intensities. H(2) and H(3) are transferred with each other by the
C2 axis of the molecules; they show a single resonance with the
highest intensity. The molecular symmetry causes also a splitting
of the resonances of the Ga-CMe3 groups, of both phenyl groups
in 3b (SiPh2Me), and of both methyl groups attached to silicon
in 3c (SiMe2CMe3). The carbon atoms of the CGa2 moieties
have resonances at about δ = 40 in the 13C NMR spectra. We
are not able to assign unambiguously a stretching vibration for
the GaꢀH bonds in the IR spectra. Oligomeric dialkylgallium
hydrides usually show strong and broad absorption bands at
about 1650 cmꢀ1 12,13
.
However, only very weak and broad
absorptions were detected in this area for compounds 3a to 3c;
their assignment to the GaꢀH stretching vibrations is question-
able. Dimeric Ga2H6 exhibits bands for the GaꢀHꢀGa bridges
with lower wave numbers at about 1200 cm .
ꢀ1 14 Strong absorp-
tions or emissions have been observed in a similar range of the
IR and Raman spectra for the heteroadamantane cages 3a to 3c
(1160 and 1167 cmꢀ1, respectively), but they probably originate
from CꢀC stretching vibrations.
An interesting byproduct (4) was isolated in only a few crystals
from the reaction of 1c (SiMe2CMe3) with tert-butyllithium.
It was characterized only by crystal structure determination and
contains a Ga4C2H4 heteroadamantane skeleton analogous to
compounds 3a to 3c (Figure 3). However, in contrast to these
compounds one gallium atom of 4 is bonded to a terminal
hydrogen atom (Ga(1)ꢀH(1), 1.48(4) Å) instead of a tert-butyl
group, which results in the composition (GaCMe3)3(GaH)-
(μ-H)4[μ-C(SiMe2CMe3)(CH2C6H5)]2. Further structural
parameters are almost unaffected in comparison to the regular
structures of 3a to 3c and do not need a detailed discussion.
Reactions of alkyllithium derivatives with the carbon-
bridged tetrachlorodigallium compounds (Cl2Ga)2C(SiR2R0)-
CH2-Ph (1a to 1c) afforded different kinds of products.
Neopentyllithium5 and—despite the presence of β-hydrogen
atoms—n-propyllithium (as well as ethyl- and isopropyllithium)
gave the expected tetraalkyldigallium compounds, (R2Ga)2C-
(SiR2R0)-CH2ꢀPh (2), via simple replacement reactions. In
contrast, tert-butyllithium gave partial β-elimination with the
formation of mixed tert-butyl-hydrido species, {[(Me3C)(H)-
Ga]2C(SiR2R0)-CH2-Ph}2 (3a to 3c). These compounds are
dimeric in solution and the solid state and form nice Ga4C2H4
heteroadamantane structures with all hydrido ligands in bridging
positions between two metal atoms. The different reactivity
pattern of the alkyllithium derivatives may depend on the steric
Figure 1. Molecular structure of 2. Thermal ellipsoids are drawn at the
40% probability level. Hydrogen atoms are omitted. Important bond
lengths (Å) and angles (deg): Ga(1)ꢀC(1) 2.004(2), Ga(2)ꢀC(1)
1.974(2), Si(1)ꢀC(1) 1.862(3), Ga(1)ꢀC(1)ꢀGa(2) 103.8(1), Ga-
(1)ꢀC(1)ꢀC(2) 108.7(2), Ga(1)ꢀC(1)ꢀSi(1) 114.8(1), Ga(2)ꢀ
C(1)ꢀSi(1) 109.2(1), Si(1)ꢀC(1)ꢀC(2) 109.9(2).
Figure 2. Molecular structure of 3a. Thermal ellipsoids are drawn at the 40% probability level. Hydrogen atoms with the exception of GaꢀH and methyl
groups of tert-butyl substituents are omitted. Important bond lengths (Å) and angles (deg): Ga(1)ꢀC(1) 1.998(2), Ga(2)ꢀC(1) 2.004(2),
Ga(3)ꢀC(2) 1.999(2), Ga(4)ꢀC(2) 2.002(2), GaꢀH 168(2) ꢀ 179(2), C(1)ꢀGa(1)ꢀC(01) 138.1(1), C(1)ꢀGa(2)ꢀC(02) 130.72(9),
C(2)ꢀGa(3)ꢀC(03) 138.9(1), C(2)ꢀGa(4)ꢀC(04) 130.73(9). Data for 3b: Ga(1)ꢀC(1) 2.011(2), Ga(2)ꢀC(1) 2.017(2), Ga(3)ꢀC(2)
2.020(2), Ga(4)ꢀC(2) 2.012(2), GaꢀH 167(2) ꢀ 176(2), C(1)ꢀGa(1)ꢀC(11) 141.93(9), C(1)ꢀGa(2)ꢀC(21) 129.24(8), C(2)ꢀGa(3)ꢀC(31)
129.90(8), C(2)ꢀGa(4)ꢀC(41) 144.09(8). Data for 3c: Ga(1)ꢀC(1) 2.001(1), Ga(2)ꢀC(1) 1.994(2), Ga(3)ꢀC(2) 2.023(4), Ga(4)ꢀC(2)
2.024(4), GaꢀH 161(4)ꢀ181(4), C(1)ꢀGa(1)ꢀC(14) 143.0(5), C(1)ꢀGa(2)ꢀC(24) 132.0(4), C(2)ꢀGa(3)ꢀC(31) 143.1(2), C(2)ꢀGa(4)ꢀC-
(41) 134.4(2).
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Figure 3. Molecular structure of 4. The thermal ellipsoids are drawn at the 40% probability level. Hydrogen atoms with the exception of GaꢀH and
methyl groups of tert-butyl substituents are omitted. Important bond lengths (Å) and angles (deg): Ga(1)ꢀC(1) 1.979(3), Ga(2)ꢀC(1) 2.015(3),
Ga(3)ꢀC(2) 1.997(3), Ga(4)ꢀC(2) 2.016(3), GaꢀH(bridge) 166(3) ꢀ 183(4), Ga(1)ꢀH(1)(terminal) 148(4), H(1)ꢀGa(1)ꢀC(1) 140(1),
C(1)ꢀGa(2)ꢀC(21) 131.7(1), C(2)ꢀGa(3)ꢀC(31) 139.6(1), C(2)ꢀGa(4)ꢀC(41) 133.7(1).
demand of the alkyl groups, and steric repulsion between the
relatively bulky tert-butyl groups may favor β-elimination.15 The
heteroadamantane structure influences the reactivity of the
GaꢀH bonds of compounds 3a to 3c. They did not show typical
reactions of likewise oligomeric dialkylgallium hydrides such as
deprotonation of terminal alkynes or hydrogallation of CtC
triple bonds. Nevertheless, thorough investigations in the reac-
tivity of these interesting tetranuclear compounds are a challen-
ging task for future experiments.
δ 132.3 (ortho-C of CtC-Ph), 128.6 (para-C of CtC-Ph), 128.5
(meta-C of CtC-Ph), 123.8 (ipso-C of CtC-Ph), 106.7 (Ph-CtC),
92.6 (CtC-Si), 26.4 (SiꢀCMe3), 16.9 (Si-CMe3), ꢀ4.4 (Si-CH3). 29Si
NMR (C6D6, 79 MHz): δ ꢀ8.0. IR (KBr plates, paraffin, cmꢀ1): 2158 vs
ν(CtC); 1960 w, 1942 m, 1892 w, 1875 m, 1820 w, 1800 w, 1749 w,
1668 w, 1595 s, 1576 m phenyl; 1487 s, 1462 vs (paraffin); 1408 w
δ(CH3); 1377 s (paraffin); 1361 s, 1248 vs δ(CH3); 1219 s, 1175 w,
1155 w, 1096 w, 1069 m, 1028 m, 1007 s ν(CC); 939 m, 912 m, 846 vs,
835 vs, 804 s, 775 s, 756 vs F(CH3Si); 721 w (paraffin); 689 vs, 615 s,
565 vw, 536 s ν(SiC). MS (EI, 20 eV, 25 °C): m/z (%) 217 (3.6), 216
t
(8.9) [M]+; 160 (16), 159 (100) [M ꢀ Bu]+.
Syntheses of (Cl2Ga)2C(SiR2R0)-CH2-Ph (1b and 1c): Gen-
eral Procedure. Two equivalents of H-GaCl2 (based on the mono-
meric formula unit, ca. 2 g) was suspended in n-hexane (100 mL)
and treated with one equivalent of the corresponding ethynylsilane
(H5C6-CtC-Si(C6H5)2Me or H5C6-CtC-SiMe2CMe3) at room tem-
perature. The mixture was stirred for 15 h. A colorless solid precipitated,
which was filtered off and washed two times with 5 mL of toluene. Both
products 1b and 1c were directly obtained in high purity.
Characterization of 1b (R = C6H5, R0 = Me). Yield: 78%. Mp
(argon, sealed capillary): 148 °C. Anal. Calcd for C21H20Cl4Ga2Si
(581.7; based on the monomeric formula unit): C, 43.4; H, 3.5. Found:
C, 43.3; H, 3.5. 1H NMR (THF-d8, 400 MHz): δ 7.80 (4 H, m, ortho-H
of Si-Ph), 7.45 (2 H, m, ortho-H of CH2ꢀPh), 7.27 (2 H, m, para-H of
Si-Ph), 7.26 (4 H, m, meta-H of Si-Ph), 7.09 (2 H, m, meta-H of CH2-Ph),
7.08 (1 H, m, para-H of CH2-Ph), 3.75 (2 H, s, CH2), 0.93 (3 H, s,
Si-CH3). 13C NMR (THF-d8, 100 MHz): δ 143.7 (ipso-C of CH2ꢀPh),
138.7 (ipso-C of Si-Ph), 137.2 (ortho-C of Si-Ph), 131.4 (ortho-C of
CH2ꢀPh), 129.9 (para-C of Si-Ph), 128.7 (meta-C of CH2ꢀPh), 128.0
(meta-C of Si-Ph), 127.2 (para-C of CH2-Ph), 37.6 (CH2), 31.0
(CGa2Si), 1.3 (Si-CH3). 29Si NMR (THF-d8, 79 MHz): δ ꢀ8.9. IR
(KBr plates, paraffin, cmꢀ1): 1946 w, 1881 vw, 1815 w, 1584 m, 1549 m,
1489 m phenyl; 1462 vs (paraffin); 1427 m, 1408 w δ(CH3); 1377 s
(paraffin); 1348 w, 1302 w, 1260 s δ(CH3); 1194 w, 1157 m, 1105 vs,
1078 m, 1028 w ν(CC); 999 m, 970 w, 934 m, 908 s, 891 s, 839 s, 787 vs,
754 s, 737 vs F(CH3Si); 727 vs (paraffin); 698 vs, 673 m, 654 w, 619 vw
ν(SiꢀC); 588 w, 554 m, 525 m, 488 vs, 471 vs, 434 s ν(GaCl), ν(GaC).
’ EXPERIMENTAL SECTION
All procedures were carried out under purified argon. Diethyl
ether and toluene were dried over Na/benzophenone; n-pentane and
n-hexane, over LiAlH4. The starting compounds (H-GaCl2)2,6 H5C6-
CtC-Si(C6H5)2Me,16 [H5C6-C(H)dC(SiMe3)-GaCl2]2 (1a),17 and
18
LiCH2CH2CH3 were obtained according to literature procedures.
Solutions of tert-butyllithium in pentane or hexane were applied as
purchased. The assignment of the NMR spectra is based on HMBC,
HSQC, ROESY, and DEPT135 data. Only the most intensive masses of
the mass spectra are given; the complete isotopic patterns are in
accordance with the calculated ones.
Synthesis of H5C6-C;C-SiMe2CMe3. A solution of phenyl-
ethyne (4.02 g, 39.4 mmol) in diethyl ether (150 mL) was treated with
equimolar quantities of n-butyllithium (1.6 M in n-pentane, 24.6 mL,
39.4 mmol) at ꢀ78 °C. The solution was warmed to room temperature
and stirred for 2 h. One equivalent of Cl-SiMe2CMe3 was added, and the
mixture was heated under reflux for 3 d. After cooling to room
temperature the mixture was treated with dilute HCl (6%, 100 mL).
The organic phase was separated, washed with a saturated solution of
sodium bicarbonate, and dried with anhydrous MgSO4. The solvent was
removed in vacuo, and the remaining yellow oil was distilled (50 °C, 0.15
mbar) to obtain the silylethyne as a colorless liquid. Yield: 4.43 g (52%).
Anal. Calcd for C14H20Si (216.4): C, 77.7; H, 9.3. Found: C, 76.7; H, 9.3.
1H NMR (C6D6, 400 MHz): δ 7.40 (2 H, m, ortho-H of CtC-Ph), 6.91
(1 H, m, para-H of CtC-Ph), 6.90 (2 H, m, meta-H of CtC-Ph), 1.03
(9 H, s, Si-CMe3), 0.17 (6 H, s, Si-CH3). 13C NMR (C6D6, 100 MHz):
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MS (EI, 20 eV, 120 °C): m/z (%) 547 (6.1), 545 (8.9), 543 (4.4)
[M (monomer) ꢀ Cl]+.
Characterization of 3a (R = R0 = Me). Yield: 30%. Mp (argon,
sealed capillary): 174 °C (dec). Anal. Calcd for C38H72Ga4Si2 (864.0):
C, 52.8; H, 8.4. Found: C, 52.8; H, 8.5. 1H NMR (C6D6, 400 MHz): δ
7.41 (4 H, d, 3JHꢀH = 7.3 Hz, ortho-CH), 7.16 (4 H, m, meta-CH), 7.03
(2 H, t, 3JHH = 7.3 Hz, para-CH), 4.28 (1 H, br, t, 2JHꢀH = 4.9 Hz, Ga-H),
Characterization of 1c (R = Me, R0 = CMe3). Yield: 57%. Mp
(argon, sealed capillary): 168 °C. Anal. Calcd for C14H22Cl4Ga2Si
(499.7; based on the monomeric formula unit): C, 33.7; H, 4.4. Found:
4.17 (2 H, br, pseudo-t, 2JHꢀH = 4.7 Hz, Ga-H), 3.98 (1 H, br, t, 2JHꢀH
=
C, 33.4; H, 4.4. 1H NMR (THF-d8, 400 MHz): δ 7.63 (2 H, d, 3JHꢀH
=
4.6 Hz, Ga-H), 3.62 (4 H, s, CH2), 1.33 and 1.22 (each 18 H, s, CMe3),
0.32 (18 H, s, SiMe3). 13C NMR (C6D6, 100 MHz): δ 146.2 (ipso-C),
129.3 (ortho-C), 129.2 (meta-C), 126.7 (para-C), 42.4 (CGa2), 38.8
(Ph-CH2), 32.2 and 32.1 (CMe3), 29.9 and 29.0 (CMe3), 4.9 (SiMe3).
29Si NMR (C6D6, 79 MHz): δ ꢀ0.4. IR (CsI plates, paraffin, cmꢀ1):
1678 w, 1580 w ν(GaH, ?), phenyl; 1454 vs, 1377 vs (paraffin); 1304 w,
1244 m δ(CH3); 1167 m, 1030 w, 1009 w ν(CC); 962 w, 935 m,
907 w, 841 s, 831 s, 808 m, 754 m, 743 m F(CH3Si); 721 w (paraffin);
700 m νas(SiC); 656 w, 644 vw νs(SiC); 554 w, 461 w, 417 w ν(GaC),
δ(CC). MS (EI, 70 eV, 150 °C): m/z (%) 807 (100), 805 (92) [M ꢀ
CMe3]+; 431 (30), 429 (23) [1/2 M ꢀ H]+; 375 (3.8), 373 (4.0)
[1/2 M ꢀ CMe3]+.
7.3 Hz, ortho-H of Ph), 7.21 (2 H, pseudo-t, meta-H of Ph), 7.13 (1H, t,
3JHꢀH = 7.3 Hz, para-H of Ph), 3.67 (2 H, s, CH2), 1.08 (9 H, s,
Si-CMe3), 0.11 (6 H, s, Si-CH3). 13C NMR (THF-d8, 100 MHz):
δ 143.8 (ipso-C of Ph), 131.6 (ortho-C of Ph), 128.7 (meta-C of Ph),
127.3 (para-C of Ph), 37.5 (CH2), 32.3 (CGa2), 29.7 (SiCMe3), 22.4
(SiCMe3), ꢀ0.5 (SiCH3). 29Si NMR (THF-d8, 79 MHz): δ 8.0. IR (KBr
plates, paraffin, cmꢀ1): 1956 w, 1938 w, 1819 vw, 1703 w, 1601 m, 1582
m, 1491 m phenyl; 1464 vs (paraffin); 1413 w δ(CH3); 1377 s
(paraffin); 1302 w, 1263 m, 1252 m δ(CH3); 1206 w, 1180 vw, 1152
vw, 1078 m, 1007 m ν(CC); 941 w, 912 m, 837 s, 812 s, 770 s, 746 m
F(SiCH3); 727 s (paraffin); 706 m, 699 m, 656 w ν(SiC); 583 w, 556 w,
428 m ν(GaC), ν(GaCl). MS (EI, 20 eV, 130 °C): m/z (%) 485 (1.5),
483 (1.3) [M (monomer) ꢀ CH3]+; 463 (11), 461 (5) [M ꢀ Cl]+; 443
Characterization of 3b (R = C6H5; R0 = Me). Yield: 62%. Mp
(argon, sealed capillary): 187 °C. Anal. Calcd for C58H80Ga4Si2
t
(100), 441 (91) [M ꢀ Bu]+; 344 (18), 342 (13) [M ꢀ CH3 ꢀ GaCl2]+.
1
Synthesis of (nPr2Ga)2C(SiMe3)-CH2-Ph (2). A solution of the
bis(dichlorogallium) compound 1a (0.470 g, 1.03 mmol, based on the
monomeric formula unit) in 150 mL of toluene was cooled to ꢀ78 °C
and treated with a solution of n-propyllithium in n-hexane (2.1 mL, 1.95
M, 4.11 mmol). The mixture was slowly warmed to room temperature,
stirred for 24 h, concentrated, and filtered. The residue was washed with
n-hexane. All volatiles of the filtrate were removed in vacuo, and the red-
brown residue was dissolved in n-pentane. Colorless crystals of com-
pound 2 were obtained upon cooling of the solution to ꢀ78 °C. Yield:
0.276 g (55%). Mp (argon, sealed capillary): 99 °C. Anal. Calcd for
C23H44Ga2Si (488.1): C, 56.6; H, 9.1. Found: C, 57.1; H, 9.0. 1H NMR
(1112.3): C, 62.6; H, 7.2. Found: C, 62.7, H, 7.3. H NMR (C6D6,
400 MHz): δ 7.73 (8 H, m, ortho-H of Si-Ph; both resonances coincide),
7.53 (4 H, d, 3JHꢀH = 7.2 Hz, ortho-H of CH2-Ph), 7.18 (8 H, m, meta-H
of Si-Ph; both resonances coincide), 7.14 (4 H, m, meta-H of CH2-Ph),
7.13 (4 H, m, para-H of Si-Ph; both resonances coincide), 7.03 (2 H, t,
3JHꢀH =7.5Hz, para-H of CH2-Ph), 4.95 (1 H, br, t, 2JHꢀH = 5.0 Hz, Ga-H),
2
4.45 (2 H, br, pseudo-t, JHꢀH = 4.5 Hz, Ga-H), 4.11 and 4.03 (each
2 H, d, 2JHꢀH = 15.3 Hz, CH2), 3.96 (1 H, br, t, 2JHꢀH = 4.2 Hz, Ga-H),
1.18 and 1.02 (each 18 H, s, Ga-CMe3), 0.96 (6 H, s, Si-CH3). 13C NMR
(C6D6, 100 MHz): δ 145.4 (ipso-C of CH2Ph), 141.6 and 140.7 (ipso-C
of Si-Ph), 136.0 and 135.9 (ortho-C of Si-Ph), 129.5 (ortho-C of CH2-
Ph), 129.31 and 129.28 (para-C of Si-Ph), 129.0 (meta-C of CH2-Ph),
128.23 and 128.20 (meta-C of Si-Ph), 126.8 (para-C of CH2-Ph), 39.1
(CGa2), 38.6 (CH2), 32.3 and 32.0 (CMe3), 31.1 and 30.2 (CMe3). 29Si
NMR (C6D6, 79 MHz): δ ꢀ9.7. IR (KBr plates, paraffin, cmꢀ1): 1954
w, 1883 w, 1813 vw, 1663 vw, 1601 w, 1578 w, 1558 vw ν(GaH, ?),
phenyl; 1460 vs, 1377 vs (paraffin); 1302 w, 1248 w δ(CH3); 1159 m,
1099 s, 1074 w, 1009 w ν(CC); 961 w, 935 m, 893 m, 849 w, 806 m,
779 m F(SiꢀC); 723 s (paraffin); 696 m, 664 w, 627 m ν(SiC); 552 m,
517 w, 482 s, 455 w ν(GaC), δ(CC). Raman (neat, 1064 nm, cmꢀ1):
3052 s, 2959 m, br, 2843 s, 2769 w, 2705 w ν(CH3); 1605 w, 1587 m,
1567 w phenyl; 1462 w, 1439 w δ(CH3); 1167 s, 1101 vw, 1031 m, 1001
s ν(CC); 809 m F(SiMe3); 661 vw, 621 w, 518 s ν(SiC), ν(GaC). MS
(EI, 20 eV, 160 °C): m/z (%) 555 (2.7), 553 (5.0), 551 (3.1) [1/2 M ꢀ
3
(C6D6, 400 MHz): δ 7.08 (2 H, d, JHꢀH = 7.3 Hz, ortho-CH), 7.07
(2 H, m, meta-CH), 6.92 (1 H, m, 3JHH = 7.3 Hz, para-CH), 3.66 (2 H, s,
CH2); the hydrogen atoms of the n-propyl groups gave an ABC2D3 spin
system with A and B as the diastereotopic hydrogen atoms of the CH2
3
groups attached to gallium: 1.59 (8 H, m, JHꢀH = 7.2 Hz (to CH3),
3JHꢀH = 7.55 and 8.55 Hz (to the diasterotopic hydrogen atoms of
3
GaCH2), CH2CH3), 1.03 (12 H, t, JHꢀH = 7.2 Hz, CH2CH3), 0.79
(4 H, m, 3JHꢀH = 7.55 Hz, 2JHꢀH = ꢀ13.6 Hz, GaCH2), 0.76 (4 H, m,
3JHꢀH = 8.55 Hz, 2JHꢀH = ꢀ13.6 Hz, GaCH2), 0.17 (9 H, s, SiMe3). 13
C
NMR (C6D6, 100 MHz): δ 147.9 (ipso-C), 130.1 (meta-C), 1296.8
(ortho-C), 126.7 (para-C), 43.3 (CGa2), 37.5 (Ph-CH2), 23.8 (GaCH2),
20.3 (CH2CH3), 20.0 (CH2CH3), 2.4 (SiMe3). 29Si NMR (C6D6, 79
MHz): δ ꢀ5.1. IR (CsI plates, paraffin, cmꢀ1): 1960 vw, 1942 w, 1919
vw, 1869 w, 1805 vw, 1599 vs, 1580 m, 1491 vs phenyl; 1452 vs
(paraffin); 1406 m δ(CH3); 1371 vs (paraffin); 1323 vs, 1290 w, 1258
vs, 1246 vs δ(CH3); 1207 w, 1173 m, 1155 sh, 1057 vs ν(CC); 982 vs,
949 s, 907 m, 849 vs, 829 vs, 752 vs F(CH3Si); 725 s (paraffin);
704 s, 675 s νas(SiC); 637 vs, 615 vs νs(SiC); 548 s, 525 s, 509 s,
457 w ν(GaC), δ(CC). MS (EI, 70 eV, 25 °C): m/z (%) 445 (29.6), 443
(22.0) [M ꢀ CH2CH2CH3]+; 403 (4.9), 401 (3.6) [M ꢀ 2CH2-
CH2CH3]+; 333 (7), 331 (11) [M ꢀ GanPr2]+; 291 (64), 289 (100)
[M ꢀ GanPr2 ꢀ propene]+.
t
3H]+; 499 (98), 497 (100), 495 (38) [1/2 M ꢀ Bu ꢀ 2H]+.
Synthesis of 3c (R = Me, R0 = CMe3). Yield: 52%. Mp (argon,
sealed capillary): 156 °C. Anal. Calcd for C44H84Ga4Si2 (948.2): C,
55.7; H, 8.9; C, 56.7; H, 9.0. 1H NMR (C6D6, 400 MHz): δ 7.38 (4 H, d,
3JHꢀH = 8.0 Hz, ortho-H of Ph), 7.18 (4 H, pseudo-t, meta-H of Ph), 7.04
(2 H, t, 3JHꢀH = 7.4 Hz, para-H of Ph), 4.65 (1 H, br, t, 2JHꢀH = 4.3 Hz,
GaH), 4.40 (2 H, br, pseudo-t, 2JHꢀH = 4.5 Hz, GaH), 4.10 (1 H, br, t,
2JHꢀH = 4.3 Hz, GaH), 3.77 (4 H, s, CH2), 1.40 and 1.38 (each 18 H, s,
Ga-CMe3), 1.02 (18 H, s, Si-CMe3), 0.12 and 0.06 (each 6 H, s, Si-CH3).
13C NMR (C6D6, 100 MHz): δ 145.3 (ipso-C of Ph), 129.5 (ortho-C of
Ph), 128.9 (meta-C of Ph), 126.8 (para-C of Ph), 40.4 (CH2), 36.9
(CGa2), 33.2 and 33.1 (Ga-CMe3), 30.8 and 29.9 (Ga-CMe3), 28.8
(Si-CMe3), 18.8 (Si-CMe3), 0.2 and ꢀ0.1 (SiCH3). 29Si NMR (C6D6, 79
MHz): δ 12.1. IR (KBr plates, paraffin, cmꢀ1): 1938 vw, 1719 w, 1649 w,
1578 m, 1558 m ν(GaH, ?), phenyl; 1458 vs, 1377 vs (paraffin); 1364 sh,
1302 w, 1244 s δ(CH3); 1161 m, 1076 w, 1030 w, 1007 m ν(CC); 961
w, 939 s, 899 s, 826 s, 810 s, 762 m, 744 s F(SiꢀC); 723 w (paraffin); 700
m, 635 m ν(SiC); 573 w, 550 m, 507 w, 424 m ν(GaC), δ(CC). Raman
(neat, 1064 nm, cmꢀ1): 3070 w, 3051 m, 3034 w, 2924 m, br, 2844 s,
2770 w, 2708 w ν(CH3); 1602 w, 1585 vw phenyl; 1464 m, 1442 m
Syntheses of the Heteroadamantane Compounds
{[(Me3C)(H)Ga]2C(SiR2R0)-CH2-Ph}2 3a to 3c: General Proce-
dure. A suspension of the corresponding bis(dichlorogallium) com-
pound (about 1.2 g) in toluene (100 mL) was treated with four
equivalents (based on monomeric 1a to 1c) of tert-butyllithium
(1.6 M in n-pentane) at ꢀ78 °C. The mixture was warmed to room
temperature and stirred for 16 h (2 h for 3c). The solvent was removed
in vacuo, and the dark residue was suspended in 20 mL of n-pentane. LiCl
was filtered off and washed two times with 5 mL of n-pentane. The red
filtrate was concentrated and cooled to ꢀ45 °C to yield the correspond-
ing product as colorless crystals.
4740
dx.doi.org/10.1021/om200573g |Organometallics 2011, 30, 4736–4741

Organometallics
ARTICLE
δ(CH3); 1200 w, 1167 s, 1031 w, 1004 m ν(CC); 942 vw, 916 vw, 812 m
F(SiMe3); 655 vw, 634 vw, 623 vw, 577 w, 524 m, 510 m, 430 vw,
394 vw ν(SiC), ν(GaC), δ(CC). MS (EI, 20 eV, 130 °C): m/z (%) 419
(32), 417 (100), 415 (75) [1/2 M ꢀ CMe3]+; 289 (23), 287 (36)
[Ga-C(SitBuMe2)CH2Ph]+.
(8) Uhl, W.; Claesener, M.; Kovert, D.; Hepp, A.; W€urthwein, E.-U.;
Ghavtadze, N. Organometallics 2011, 30, 3075.
(9) Uhl, W.; Claesener, M.; Hepp, A.; Jasper, B.; Vinogradov, A.; van
W€ullen, L.; K€oster, T. K.-J. Dalton Trans. 2009, 10550.
(10) (a) Uhl, W.; Bock, H. R.; Claesener, M.; Layh, M.; Tiesmeyer,
I.; W€urthwein, E.-U. Chem.—Eur. J. 2008, 14, 11557. (b) Uhl, W.;
Claesener, M.; Haddadpour, S.; Jasper, B.; Tiesmeyer, I.; Zemke, S. Z.
Anorg. Allg. Chem. 2008, 634, 2889.
(11) Kalsi, P. S. StereochemistryꢀConformation and Mechanism,
6th ed.; New Age International Publishers, 2005; p 142.
(12) Dialkylgallium hydrides: (a) Uhl, W.; Cuypers, L.; Graupner,
R.; Molter, J.; Vester, A.; Neum€uller, B. Z. Anorg. Allg. Chem. 2001,
627, 607. (b) Uhl, W.; Cuypers, L.; Geiseler, G.; Harms, K.; Massa, W. Z.
Anorg. Allg. Chem. 2002, 628, 1001.
(13) (a) Baxter, P. L.; Downs, A. J.; Goode, M. J.; Rankin, D. W. H.;
Robertson, H. E. J. Chem. Soc., Dalton Trans. 1990, 2873. (b) Uhl, W.;
Claesener, M.; Haddadpour, S.; Jasper, B.; Hepp, A. Dalton Trans.
2007, 417.
(14) Downs, A. J.; Goode, M. J.; Pulham, C. R. J. Am. Chem. Soc.
1989, 111, 1936.
Crystal Structure Determinations. Single crystals were ob-
tained by crystallization from n-pentane (2, ꢀ80 °C; 3a to 3c,
ꢀ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-9719 by a full-matrix least-squares
method based on F2. Hydrogen atoms (except Ga-H of compounds 3
and 4, which were refined isotropically) were positioned geometrically
and allowed to ride on their respective parent atoms. Two n-propyl
groups of 2 were disordered; the atoms were refined on split positions
(C122, 0.55 to 0.45; C221, 0.61 to 0.39). Compound 3c showed a
disorder of a complete C(SiMe2CMe3)CH2Ph group; site-occupancy
factors were 0.77 and 0.23. A tert-butyl group of 4 was disordered
(split positions 0.55 to 0.45). Further details of the crystal structure
determinations are available from the Cambridge Crystallographic Data
Center on quoting the depository numbers CCDC-830856 (2), -830857
(3a), -830858 (3b), -830859 (3c), and -830860 (4).
(15) Similar reactions of tert-butyllithium have been observed with
simple aluminum halides: (a) Uhl, W Z. Anorg. Allg. Chem. 1989, 570, 37.
(b) Uhl, W.; Schnepf, J. E. O. Z. Anorg. Allg. Chem. 1991, 595, 225.
(c) Uhl, W.; Schnepf, E.; Wagner, J. Z. Anorg. Allg. Chem. 1992, 613, 67.
(d) Uhl, W.; Vester, A. Chem. Ber. 1993, 126, 941.
’ ASSOCIATED CONTENT
(16) The synthesis of H5C6-CtC-Si(C6H5)2Me follows a literature
procedure: (a) Freeburger, M. E.; Spialter, L. J. Org. Chem. 1970, 35, 652.
(b) Uhl, W.; Kovert, D.; Layh, M.; Hepp, A. Chem. Eur. J., in press.
(17) Uhl, W.; Claesener, M. Inorg. Chem. 2008, 47, 4463.
(18) Houben-Weyl. Methoden der Organischen Chemie, Vol. XIII/1,
Metallorganische Verbindungen, 4th ed.; Georg Thieme: Stuttgart,
1970, p 134.
(19) SHELXTL-Plus, Rel. 4.1; Siemens Analytical X-Ray Instru-
ments Inc.: Madison, WI, 1990. Sheldrick, G. M. SHELXL-97, Program
for the Refinement of Structures; Universit€at G€ottingen: Germany, 1997.
S
Supporting Information. CIF files giving the crystal data
b
for compounds 2, 3a to 3c, and 4. Table of crystal data and
structure refinement. This material is available free of charge via
the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: +49-251-8336660. E-mail: uhlw@uni-muenster.de.
’ ACKNOWLEDGMENT
We are grateful to the Deutsche Forschungsgemeinschaft for
generous financial support. We thank Dr. J. J. Weigand and Dipl.
Chem. M. Holthausen (University of M€unster) for recording the
Raman spectra.
’ REFERENCES
(1) Uhl, W. Coord. Chem. Rev. 2008, 252, 1540.
(2) (a) Reeske, G.; Bradtm€uller, G.; Sch€urmann, M.; Jurkschat, K.
Chem.—Eur. J. 2007, 13, 10239. (b) Reeske, G.; Sch€urmann, M.;
Jurkschat, K. Dalton Trans. 2008, 3398. (c) Tagne Kuate, A. C.; Reeske,
G.; Sch€urmann, M.; Costisella, B.; Jurkschat, K. Organometallics 2008,
27, 5577. (d) Hudnall, T. W.; Kim, Y.-M.; Bebbington, M. W. P.;
Bourissou, D.; Gabbai, F. P. J. Am. Chem. Soc. 2008, 130, 10890. (e) Solꢀe,
S.; Gabbai, F. P. Chem. Commun. 2004, 1284. (f) Hudnall, T. D.; Chiu,
C.-W.; Gabbai, F. P. Acc. Chem. Res. 2009, 42, 388. (g) Melaimi, M.;
Gabbai, F. P. Adv. Organomet. Chem. 2005, 53, 61. (h) Cottone, A., III;
Scott, M. J. Organometallics 2002, 21, 3610.
(3) Uhl, W.; Heller, D.; Rohling, M.; K€osters, J. Inorg. Chim. Acta
2011, 374, 359.
(4) Uhl, W.; Claesener, M. Inorg. Chem. 2008, 47, 729.
(5) Uhl, W.; Claesener, M.; Hepp, A. Organometallics 2008,
27, 2118.
(6) Uhl, W.; Cuypers, L.; Neum€uller, B.; Weller, F. Organometallics
2002, 21, 2365.
(7) (a) Nogai, S.; Schmidbaur, H. Inorg. Chem. 2002, 41, 4770.
Hydrogallation of an alkene with HGaCl2:(b) Ohshita, J.; Schmidbaur,
H. J. Organomet. Chem. 1993, 453, 7.
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