A unique chlorine-methyl exchange reaction upon treatment of dichloroorganogallium compounds, RGaCl2, with the bulky alkyllithium derivative LiC(SiMe3)3

Article abstract of DOI:10.1021/om200176y

Reaction of the organogallium chlorides C₆H_6-n[C(H) dC(GaCl₂)-SiR₃]n (1 to 4; R = Me, Ph) with the bulky alkyllithium derivative Li(THF)₂C(SiMe₃)₃ did not afford the expected alkylgallium chlorides by salt elimination. Instead, compounds (5 to 7) were isolated that had methyl groups attached to gallium, while chlorine atoms moved to silicon to yield Ga(Me)-C(SiMe₃) ₂(SiMe₂Cl) moieties. On the basis of quantum chemical calculations the formation of these unprecedented structural motifs is caused by kinetic control involving cyclic transition states as initiating steps. The anticipated, but experimentally not observed products having the intact Ga(Cl)-C(SiMe₃)₃ subunits (8) were calculated to be thermodynamically favored.

Full text of DOI:10.1021/om200176y

ARTICLE
pubs.acs.org/Organometallics
A Unique ChlorineꢀMethyl Exchange Reaction upon Treatment of
Dichloroorganogallium Compounds, RGaCl2, with the Bulky
Alkyllithium Derivative LiC(SiMe3)3
Werner Uhl,*,† Michael Claesener,† Dirk Kovert,† Alexander Hepp,† Ernst-Ulrich W€urthwein,‡ and
Nugzar Ghavtadze‡
†Institut f€ur Anorganische und Analytische Chemie der Universit€at M€unster, Corrensstrasse 30, D-48149 M€unster, Germany
‡Organisch-Chemisches Institut der Universit€at M€unster, Corrensstrasse 40, D-48149 M€unster, Germany
S Supporting Information
b
ABSTRACT: Reaction of the organogallium chlorides
C6H6ꢀn[C(H)dC(GaCl2)-SiR3]n (1 to 4; R = Me, Ph) with
the bulky alkyllithium derivative Li(THF)2C(SiMe3)3 did not
afford the expected alkylgallium chlorides by salt elimination.
Instead, compounds (5 to 7) were isolated that had methyl
groups attached to gallium, while chlorine atoms moved to
silicon to yield Ga(Me)-C(SiMe3)2(SiMe2Cl) moieties. On the
basis of quantum chemical calculations the formation of these
unprecedented structural motifs is caused by kinetic control involving cyclic transition states as initiating steps. The anticipated, but
experimentally not observed products having the intact Ga(Cl)-C(SiMe3)3 subunits (8) were calculated to be thermodynamically
favored.
’ INTRODUCTION
reported by our group in two previous publications.3,4 Two of
these compounds, H5C6-C(H)dC(SiMe3)-GaCl2 (1) and
1,4-[Cl2Ga-C(SiMe3)dC(H)]2C6H4 (2), were applied in the
studies described in this article. In order to allow more systematic
investigations we synthesized two further compounds (3 and 4,
eq 1). 3 was obtained by treatment of a suspension of the hydride
H-GaCl2 in n-hexane with solid 1,3-(Me3Si-CtC)2C6H4 and
crystallized from the concentrated reaction mixture in 66% yield.
Once crystallized, the solubility of 3 in hydrocarbons consider-
ably decreased. Therefore NMR spectra were recorded in THF,
which clearly resulted in adduct formation by coordination of the
gallium atoms. In contrast to 1 to 3, compound 4 contains a
triphenylsilyl instead of a trimethylsilyl substituent attached to its
CdC double bond. It is insoluble in n-hexane and was isolated as
a colorless, amorphous solid by filtration of the reaction
Bulky substituents have often been applied in main-group
chemistry for the kinetic stabilization of unusual structural motifs
such as EꢀE single or multiple bonds or oligonuclear En
clusters.1 Although pentasubstituted cyclopentadienyl or steri-
cally encumbered aryl or silyl groups were employed in most
cases, the tris(trimethylsilyl)methyl substituent was alterna-
tively used as a protecting group for, for example, the generation
of cluster compounds such as Ga4[C(SiMe3)3]4.2 In some
recent investigations we found an easy access to various
functional dichlorogallium compounds, C6H6ꢀn[C(H)d
C(GaCl2)-SiMe3]n,3,4 via hydrogallation of oligoalkynes5 by
dichlorogallane, H-GaCl2.6 These vinylgallium dichlorides are
valuable starting compounds for the generation of the corre-
sponding dialkylgallium derivatives by treatment with alkyl-
lithium and salt elimination.7,8 We hoped to generate sterically
shielded alkylgallium chlorides by the reaction with the bulky
alkyllithium compound Li(THF)2C(SiMe3)3. The second
chlorine atom of each GaCl2 group should subsequently be
used for further functionalization, for instance by reduction
with alkali metals. However, an unexpected reaction course was
observed.
3
mixture. In both cases the JSiꢀCdCꢀH coupling constant of
about 10.5 Hz indicated the cis-arrangement of hydrogen and
silicon atoms at the CdC double bonds5,8,9 and the formal
trans-addition of the H-Ga groups. The mechanism of the cis/
trans-rearrangement with products of hydroalumination and
hydrogallation has been discussed previously.8 Crystal structure
determinations (Figures 1 and 2) verified this particular con-
figuration. They revealed the formation of dimeric compounds
via GaꢀClꢀGa bridges similar to the structures of compounds
1 and 2, which have been reported previously.3 A relatively
’ RESULTS AND DISCUSSION
Synthesis of Dichlorogallium Compounds by Hydrogalla-
tion of Alkynes. The reaction of H-GaCl2 with some trimethyl-
silylalkynes to yield alkenylgallium compounds has been
Received: February 25, 2011
Published: May 13, 2011
r
2011 American Chemical Society
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interesting tricyclic structure resulted for compound 3 that
possesses two Ga2Cl2 heterocycles in the bridging positions.
The average GaꢀCl bond lengths of 3 and 4 differ according to
the different coordination numbers of the chlorine atoms and
are 2.14 (terminal) versus 2.34 Å (bridging).3,10 Standard
values were also observed for the CdC bond lengths (1.34 Å
on average).
Figure 1. Molecular structure of 3. Thermal ellipsoids are drawn at the
40% probability level. Hydrogen atoms and methyl groups of SiMe3
substituents are omitted. Important bond lengths (Å) and angles (deg):
Ga(1)ꢀCl(1) 2.141(2), Ga(1)ꢀCl(11) 2.323(2), Ga(1)ꢀCl(21)
2.346(2), Ga(2)ꢀCl(2) 2.134(2), Ga(2)ꢀCl(21) 2.369(2), Ga(3)ꢀCl-
(3) 2.144(2), Ga(3)ꢀCl(31) 2.331(2), Ga(3)ꢀCl(41) 2.336(2), Ga-
(4)ꢀCl(4) 2.140(2), Ga(4)ꢀCl(41) 2.337(2), C(1)ꢀC(11) 1.358(7),
C(2)ꢀC(21) 1.331(7), C(3)ꢀC(31) 1.335(7), C(4)ꢀC(41) 1.323(7),
C(1)ꢀC(11)ꢀC(12) 130.5(5), C(2)ꢀC(21)ꢀC(22) 126.4(5), C-
(3)ꢀC(31)ꢀC(32) 131.2(5), C(4)ꢀC(41)ꢀC(42) 127.6(5).
Reactions of the Dichlorogallium Compounds with
Li(THF)2C(SiMe3)3. In a general procedure suspensions of the
gallium chlorides 1 to 4 in n-hexane were treated with the solid
lithium compound Li(THF)2C(SiMe3)3 (one equivalent per
GaCl2 group, eq 2). After 16 h at room temperature the mixtures
were filtrered. The colorless products (5 to 7) crystallized
upon cooling of the concentrated filtrates in 46ꢀ76% yield.
Only the monoalkenyl compound 1 gave an unclear reaction
course with the formation of an oily product, which contained
a mixture of several unknown components. We were not able
to isolate any compound by crystallization from different
noncoordinating solvents. The NMR spectra of the crystalline
products 5 to 7 were relatively complicated and did not agree
with those expected for the simple substitution products.
Crystal structure determinations (Figure 3 to 5) revealed a
surprising constitution that did not comprise intact tris-
(trimethylsilyl)methyl groups. In all cases both chlorine atoms
of the GaCl2 moieties were replaced by a methyl group and
a trisilylmethyl substituent. Only two SiMe3 groups of the
latter remained intact; the third one was transformed to an
SiMe2Cl unit with a chlorine atom attached to silicon
[C(SiMe3)2SiMe2Cl]. The formation of these compounds
may be described by rearrangement with an exchange of a
chlorine atom attached to gallium and a methyl group of an
SiMe3 substituent. However, the reaction mechanism is com-
plicated, as discussed below. The gallium atoms are coordina-
tively unsaturated and bonded to three carbon atoms of
different ligands. They have an almost ideally planar
coordination sphere with a maximum deviation from the
plane of the three adjacent carbon atoms of only 0.022 Å.
The longest GaꢀC distance is observed to the carbon atom of
the bulky trisilyl groups. The planes GaC3 are almost perpen-
dicular to the planes defined by the CdC double bond and the
adjacent atoms (angles between the normal of the planes:
77.5° (5) to 81.3° (6)). This preferred conformation is clearly
caused by a minimization of steric repulsion. Bond lengths
(CdC 134.8 pm; SiꢀCl 211.3 pm on average) correspond to
standard values and do not require a detailed discussion. The
dialkenyl compounds 5 and 6 show different orientations of
the Ga-Me groups. In 5 they point toward different directions
of the molecules (anti), while they adopt a kind of a syn-
orientation in 6. This observation may help to understand the
relatively complicated NMR spectra as discussed below. Due
to the molecular geometry, relatively short intramolecular
GaꢀCl distances of 292 to 300 pm result for compounds 5
and 6. However, we do not believe in significant GaꢀCl
bonding interactions, because we observed ideal planar co-
ordination spheres at the gallium atoms with sums of the
angles of 360° and deviations of the metal atoms from the
respective C3 plane of only 0 to 0.02 Å, the torsion angles
GaꢀCꢀSiꢀCl are relatively large (25° to 35°), and much
shorter Gaꢀhalogen distances have been reported in the
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literature for compounds that clearly had such interactions to
organohalogen groups.4
Figure 2. Molecular structure of 4. Thermal ellipsoids are drawn at the
40% probability level. Hydrogen atoms are omitted. Important bond
lengths (Å) and angles (deg): Ga(1)ꢀCl(1) 2.3350(8), Ga(1)ꢀCl(1)0
2.339(1), Ga(1)ꢀCl(2) 2.149(1), C(1)ꢀC(10) 1.337(3), C(1)ꢀ
C(10)ꢀC(101) 128.5(2), Ga(1)ꢀCl(1)ꢀGa(1)0 91.86(3), Cl(1)ꢀ
Ga(1)ꢀCl(1)0 88.14(3); Ga(1)0 and Cl(1)0 generated by ꢀxþ1, ꢀyþ1,
ꢀzþ1.
Two complete sets of resonances of two different species were
detected in the NMR spectra of compounds 5 and 6. Each set
reflects the pattern expected from the molecular structures in the
solid state. Methyl groups bonded to gallium and the vinylic
1
80 °C. The intact SiMe3 groups gave two narrow resonances
only upon cooling to 0 °C (1H NMR, 0 °C: δ 0.65 (GaMe), 0.35
and 0.27 (SiMe2Cl), 0.055 and 0.050 (SiMe3)). The activation
barrier was estimated to be 17 kcal/mol.
trimethylsilyl groups gave singlets in the H NMR spectra at
about δ = 0.7 and 0.4, respectively. Interestingly, two resonances
were observed for both intact trimethylsilyl groups of each CSi3
substituent and also for the methyl groups of each SiMe2Cl
moiety. This splitting is caused by the particular molecular
conformation with the GaꢀMe bonds perpendicular to the
alkenyl plane and a hindered rotation about the GaꢀC(vinyl)
bond. Hence, these molecules do not possess mirror planes that
would transfer the respective groups in each other. The two
different molecular species may result from the different orienta-
tion of both GaꢀMe groups (syn or anti) in accordance with
the different molecular structures observed in the solid state.
Hindered rotation is important in these cases, as was shown by a
high-temperature NMR experiment with compound 6. Upon
warming to 100 °C in toluene, the different sets of resonances in
the 1H NMR spectrum coincided and gave the expected singlets
of a single molecule for the GaMe (δ = 0.56), SiMe2Cl (δ = 0.50,
broad), vinylic SiMe3 (δ = 0.30), and C(SiMe3)2 groups
(δ = 0.16, broad). The rotational barrier was estimated from
the coalescence temperature of different groups of resonances to
be about 19 kcal/mol. The NMR spectra of compound 7 are
simpler. Nevertheless hindered rotation about the GaꢀC(vinyl)
bond resulted in a splitting of the 1H and 13C NMR resonances of
the SiMe2Cl groups into two singlets at room temperature. In the
1H NMR spectrum these resonances coincided upon warming,
and the coalescence temperature was determined to be about
Quantum Chemical Calculations and Reaction Mecha-
nism. In order to gain deeper insight into the mechanism of this
series of transformations, high-level gas phase quantum chemical
calculations have been carried out. We were particularly inter-
ested in elucidating the reaction pathways that starting from 9
and 10 lead to the actually isolated compound 7 or to the originally
expected product of the replacement of a chlorine atom by a bulky
alkyl group (8). These calculations should help to understand the
kinetic and thermodynamic factors governing these competing
reactions. Compound 8 (Scheme 1) was calculated to be thermo-
dynamically favored over the experimentally obtained product 7
by 8.6 kcal/mol. For the exploration of the relevant parts of the
energy hypersurface, the sum of the energies of (Z)-[2-phenyl-
1-(trimethylsilyl)vinyl]gallium dichloride (9) and the adduct of
dimethyl ether (as a model for experimentally used tetra-
hydrofuran) with tris(trimethylsilyl)methyllithium 10 was taken
as a reference (Erel = 0.0 kcal/mol, Scheme 2). These two species
are able to form two different types of complexes (11 and 14). 11
(Erel = ꢀ14.5 kcal/mol) is an essential intermediate for the
formation of compound 7 (Scheme 2, left side). Its main structural
features are a relatively short distance of the migrating methyl
group to the gallium atom of 254.5 pm, a substantial LiꢀCl
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Figure 4. Molecular structure of 6. Thermal ellipsoids are drawn at the
40% probability level. Hydrogen atoms are omitted. Important bond lengths
(Å) and angles (deg): Ga(1)ꢀC(1) 1.990(2), Ga(1)ꢀC(2) 1.985(2),
Ga(1)ꢀC(3) 2.041(2), C(1)ꢀC(10) 1.345(3), Si(31)ꢀCl(31) 2.124(1),
Ga(2)ꢀC(4) 1.994(2), Ga(2)ꢀC(5) 1.985(2), Ga(2)ꢀC(6) 2.039(2),
C(4)ꢀC(40) 1.351(3), Si(61)ꢀCl(61) 2.1341(9), C(1)ꢀGa(1)ꢀC(2)
114.5(1), C(1)ꢀGa(1)ꢀC(3) 125.26(9), C(2)ꢀGa(1)ꢀC(3) 120.2(1),
C(4)ꢀGa(2)ꢀC(5) 114.9(1), C(4)ꢀGa(2)ꢀC(6) 125.25(9), C(5)ꢀ
Ga(2)ꢀC(6) 119.8(1).
Figure 3. Molecular structure of 5. Thermal ellipsoids are drawn at the
40% probability level. Hydrogen atoms are omitted. Important bond lengths
(Å) and angles (deg): Ga(1)ꢀC(1) 1.985(2), Ga(1)ꢀC(2) 1.984(2),
Ga(1)ꢀC(3) 2.037(2), C(1)ꢀC(10) 1.349(3), Si(31)ꢀCl(31) 2.123(4),
C(1)ꢀGa(1)ꢀC(2) 112.75(9), C(1)ꢀGa(1)ꢀC(3) 126.76(9), C(2)ꢀ
Ga(1)ꢀC(3) 120.5(1); symmetry operation: ꢀxþ1, ꢀyþ1, ꢀz.
interaction with a LiꢀCl distance of 253.3 pm, and a short
LiꢀOMe2 distance of 194.4 pm. Starting from this complex the
transfer of the methyl group from the silicon atom of compound
10 to the gallium atom of compound 9 was calculated. This
process is predicted to proceed through a six-membered-ring
transition structure, TS-12, of the ZimmermanꢀTraxler type,11
which is 10.0 kcal higher in energy than complex 11. The MeꢀSi
distance in TS-12 is calculated to be 212.3 pm, and the MeꢀGa
distance, 231.7 pm (LiꢀCl distances 250.4 and 263.8 pm;
LiꢀOMe2 197.6 pm). From IRC calculations starting from TS-
12 structure 13 is obtained (Erel = ꢀ22.5 kcal/mol), in which the
Me group is attached to the gallium atom and the Li atom is
connected to both chlorine atoms. The LiꢀCl separations are
238.4 and 239.3 pm (LiꢀOMe2 196.9 pm). The bond between
the central carbon atom and the silicon atom, which has lost
the Me group, is shortened to 174.1 pm and may have some
π-character.
A reasonable pathway for the formation of the experimentally
not observed compound 8comprises the formation of an alternative
complex, 14, in which both starting compounds are connected by
an interaction between the lithium and a chlorine atom (LiꢀCl
260.2 pm; LiꢀOMe2 194.2 pm; Scheme 2 on the right). The
resulting transition state TS-15 (Erel = ꢀ3.8 kcal/mol), which
represents the first step for GaꢀC bond formation (GaꢀC distance
345.1 pm), is sterically more crowded compared to TS-12. Con-
sequently, the LiꢀOMe2 distance is relatively long (200.1 pm)
despite the lower coordination number of the lithium atom. This
transition state gives intermediate 16 (Erel = ꢀ48.2 kcal/mol),
which already contains all features of the not observed product
8, e.g., a short Gaꢀcarbon bond (206.2 pm). Finally, formal
elimination of LiCl, coordinated by Me2O, results in the formation
of 8. Its relative energy of ꢀ21.9 kcal/mol indicates its thermo-
dynamic preference over product 7 (ꢀ13.3 kcal/mol).
In conclusion both competitive pathways differ only slightly in
their energetic profiles with small thermodynamic and kinetic
advantages in the initial steps for the formation of compound 7
(11 versus 14 and TS-12 versus TS-15), but a significant thermo-
dynamic preference for product 8. Since the calculations are
carried out for the species in the gas phase, the structures following
the transition states TS-12 and TS-15 might be artificial. Ifformed,
one would expect that in solution both transition structures will
collapse into the products 7 and 8 by elimination of LiCl. The
formation of the crystalline, ionic LiCl certainly will be the main
driving force of this transformation. It should be pointed out that
consideration of one molecule of dimethyl ether as model solvent
was crucial in these calculations. Without the Lewis base, the
reaction pathway to the experimentally not observed product 8 is
kinetically and thermodynamically favored.
Interestingly, the transfer of a methyl group instead of the
replacement of a chlorine atom by the complete C(SiMe3)3
substituent has been observed previously when particular ele-
ment chlorides were treated with LiC(SiMe3)3 (many other
reactions, e.g., observed by our group, have not been published at
all).12 Hence, the applicability of this important protecting group
proved to be relatively limited. A reasonable mechanism for these
unexpected reactions has not been discussed before; however,
the heterocyclic compound [Me2Si-C(SiMe3)2]2 has been
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Scheme 1. Calculated Relative Energies of the Actually Iso-
lated and the Originally Expected Products 7 and 8
Scheme 2. Alternative Calculated Pathways for the Forma-
tion of Compound 7 or 8
Figure 5. Molecular structure of 7. Thermal ellipsoids are drawn at the
40% probability level. Hydrogen atoms are omitted. Important bond
lengths (Å) and angles (deg): Ga(1)ꢀC(1) 2.010(3), Ga(1)ꢀC(2)
1.985(3), Ga(1)ꢀC(3) 1.988(3), C(2)ꢀC(20) 1.345(4), Si(12)ꢀ
Cl(1) 2.059(1), C(1)ꢀGa(1)ꢀC(2) 127.2(1), C(1)ꢀGa(1)ꢀC(3)
121.5(1), C(2)ꢀGa(1)ꢀC(3) 111.2(1).
identified as a byproduct in several cases. It was probably formed
via an intermediate compound containing a SidC double bond.
The unprecedented compounds reported here (5 to 7) and the
suggested mechanism may help to understand these reactions. In
cases where at least two chlorine atoms are bonded to the central
atom a cyclic transition state similar to TS12 may result in
formation of methyl-element species and an exchange of a SiMe3
methyl group by a chlorine atom. The intermediate compound
13 may play a key role in these reactions. Hence, the compounds
reported in this article not only are important due to their
particular functionality but also help to understand the unique
reaction behavior of the important lithium compound LiC-
(SiMe3)3 with the possible formation of three different types
of products. The isolation of the expected sterically shielded
compounds having intact C(SiMe3)3 groups may be prevented
by alternative reaction pathways that may lead to methyl-element
compounds via the elimination of silaethenes or to chlorosilane
derivatives similar to 5 to 7 (eq 2). The degradation of a bulky
ligand has also been observed in a few reactions of subvalent
gallium or germanium compounds with LiSi(SiMe3)3, which
resulted in the formation of Ga-SiMe3 or Ge-Me groups. The
mechanisms were not discussed.13
according to literature procedures. 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 1,3-[Me3Si-(Cl2Ga)CdC(H)]2C6H4 (3). H-GaCl2
(2.57 g, 18.1 mmol) was suspended in 250 mL of n-hexane and treated
with solid 1,3-bis(trimethylsilylethinyl)benzene (2.34 g, 8.65 mmol,
0.48 equiv) at room temperature. The mixture was stirred for 16 h. A
small quantity of an unknown colorless solid precipitated and was
filtered off. The product (3) crystallized from the concentrated filtrate
upon cooling to 5 °C. Yield: 3.15 g (66%). Mp (argon, sealed capillary):
’ EXPERIMENTAL SECTION
All procedures were carried out under purified argon. n-Hexane
and cyclopentane were dried over LiAlH4; 1,2-difluorobenzene was
dried over molecular sieves. The starting compounds H-GaCl2,6
(H5C6)3Si-CtC-C6H5,14 1,3-(Me3Si-CtC)2C6H4,15 1,4-[C(H)dC-
(SiMe3)-GaCl2]2C6H4 (2),3 and Li(THF)2C(SiMe3)316 were obtained
150 °C (dec). 1H NMR (THF-d8, 400 MHz): δ 7.87 (2 H, s, 3JHꢀSi
=
10.3 Hz, CdCH), 7.59 (1 H, s, br, 2-H of phenyl), 7.51 (2 H, m, 4,6-H of
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phenyl), 7.32 (1 H, t, br, 5-H of phenyl), 0.26 (18 H, s, SiMe3). 13C
NMR (THF-d8, 100 MHz): δ 155.7 (HCdCGa), 148.7 (HCdCGa),
142.6 (1,3-C of phenyl), 129.0 (2-C of phenyl), 128.7 (5-C of phenyl),
127.7 (4,6-C of phenyl), 0.1 (SiMe3). 29Si NMR (THF-d8, 79 MHz): δ
ꢀ0.1. IR (CsI plates, paraffin, cmꢀ1): 1597 m, 1584 s, 1553 vs ν(CdC),
phenyl; 1470 vs (paraffin); 1435 m, 1408 s, 1402 s δ(CH3); 1377 s
(paraffin); 1337 w, 1315 w, 1300 w, 1250 vs, 1175 w, 1161 w, 1090 s
ν(CC), δ(CH); 964 s, 928 vs, 899 vs, 827 vs, 783 vs, 745 vs F(CH3Si);
721 vs (paraffin); 698 vs, 635 vs, 611 vs, 600 vs ν(SiC); 577 vw, 542 vs,
501 s, 476 vw, 455 vs, 417 vs ν(GaCl), ν(GaC). MS (EI, 20 eV, 160 °C):
m/z (%) 517 (0.2), 519(0.2) [M(monomer)ꢀ Cl]þ, 443 (10), 445 (10)
s, 1248 s δ(CH3); 1196 w, 1107 w ν(CC), δ(CH); 984 w, 907 m, 847 vs,
773 w, 750 w F(CH3Si); 721 m (paraffin); 673 s νas(SiC); 619 m νs(SiC);
554 m, 540 w, 480 m, 469 m, 434 m ν(SiCl), ν(GaC). MS (EI, 20 eV,
170 °C): m/z (%) 931 (4.5), 929 (4.8) [M ꢀ Me]þ, 693 (1.2) [M ꢀ
C(SiMe3)2SiMe2Cl]þ, 594 (28), 592 (21) [M ꢀ Ga(Me)C(SiMe3)2-
SiMe2Cl ꢀ Me]þ; 337 (100), 335 (92) [GaMeC(SiMe3)2SiMe2Cl]þ.
Characterization of 6. Yield: 76%. Mp (argon, sealed capillary):
132 °C. Anal. Calcd for C36H78Cl2Ga2Si8 (946.0): C, 45.7; H, 8.3.
Found: C, 46.2; H, 8.2. Two conformers, A and B, were observed in the
1
NMR spectra in a molar ratio of 0.55:0.45 at room temperature. H
NMR (C6D6, 400 MHz, 300 K): Isomer A: δ 7.78 (2 H, s, 3JHꢀSi = 11.6
Hz, CdCH), 7.15 (3 H, m, 2-H and 5-H of phenyl), 7.00 (2 H, d, 4,6-H
of phenyl), 0.67 (6 H, s, Ga-CH3), 0.57 and 0.52 (each 6 H, s, ClSiCH3),
0.38 (18 H, s, CdC-SiMe3), 0.18 and 0.16 (each 18 H, s, C(SiMe3)2);
isomer B: δ 7.83 (2 H, s, 3JHꢀSi = 11.7 Hz, CdCH), 7.25 (3 H, m, 2-H
and 5-H of phenyl), 7.00 (2 H, d, 4,6-H of phenyl), 0.65 (6 H, s,
Ga-CH3), 0.57 and 0.49 (each 6 H, s, ClSiCH3), 0.38 (18 H, s, Cd
C-SiMe3), 0.22 and0.15(each18H, s, C(SiMe3)2). 1H NMR (toluene-d8,
400 MHz, 370 K): δ 0.56 (6 H, Ga-CH3), 0.50 (broad, 12 H, s, SiMe2Cl),
0.30 (18 H, s, CdC-SiMe3), 0.16 (broad, 36 H, s, C(SiMe3)2). 13C NMR
(C6D6, 100 MHz): Isomer A: δ 167.9 (HCdCGa), 151.2 (HCdCGa),
146.4 (1,3-C of phenyl), 127.1 (2-C and 5-C of phenyl), 125.6 (4,6-C of
phenyl), 19.3 (CSi3), 10.4 (Ga-CH3), 9.1 and 8.7 (ClSiCH3), 5.5 and 5.4
(C(SiMe3)2), 1.4 (CdCꢀSiMe3); isomer B: δ 167.5 (HCdCGa), 151.1
(HCdCGa), 146.0 (1,3-C of phenyl), 127.2 (2-C and 5-C of phenyl),
125.4 (4,6-C of phenyl), 19.0 (CSi3), 9.8 (Ga-CH3), 9.0 and 8.6
(ClSiCH3), 5.6 and 5.3 (C(SiMe3)2), 1.5 (CdC-SiMe3). 29Si NMR
(C6D6, 79 MHz): Isomer A: δ 27.4 (SiCl), ꢀ3.7 and ꢀ4.4
(C(SiMe3)2), ꢀ3.8 (CdC-SiMe3); isomer B: δ 26.9 (SiCl), ꢀ3.4 (Cd
C-SiMe3), ꢀ3.6 and ꢀ4.2 (C(SiMe3)2). IR (KBr plates, paraffin, cmꢀ1):
1688 w, 1655 w, 1580 m, 1543 m ν(CdC), phenyl; 1460 s (paraffin);
1402 m δ(CH3); 1377 s (paraffin); 1304 w, 1250 s δ(CH3); 1198 m,
1080 w, 1043 w ν(CC), δ(CH); 953 w, 914 w, 864 vs, 847 vs, 783 w, 748 w
F(CH3Si); 721 m (paraffin); 673 m νas(SiC);619wνs(SiC); 592 w, 557 m,
536 w, 471 m, 446 m ν(SiCl), ν(GaC). MS (EI, 20 eV, 140 °C): m/z (%)
931 (4.9), 929 (4.6) [M ꢀ Me]þ, 693 (2.7), 695 (1.9) [M ꢀ C(SiMe3)2-
SiMe2Cl]þ, 594 (28), 592 (22) [M ꢀ Ga(Me)C(SiMe3)2SiMe2Cl ꢀ
Me]þ; 337 (100), 335 (90) [GaMeC(SiMe3)2SiMe2Cl]þ.
[M ꢀ HCl ꢀ SiMe3] þ
.
Synthesis of [(H5C6)3Si-(Cl2Ga)CdC(H)]C6H5 (4). H-GaCl2
(2.02 g, 14.3 mmol, small excess) was suspended in 100 mL of n-hexane
and treated with solid triphenylsilylethinylbenzene (4.68 g, 13.0 mmol)
at room temperature. After a few hours the product started to pre-
cipitate. Stirring was continued for 12 h. The colorless product (4) was
filtered off, washed with 10 mL of n-hexane, and evacuated to 10ꢀ3 Torr
to completely remove all volatiles. Yield: 2.60 g (40%). Mp (argon,
sealed capillary): 175 °C. 1H NMR (THF-d8, 400 MHz): δ 7.91 (1 H, s,
3JHꢀSi = 10.7 Hz, CdCH), 7.71 (6 H, m, ortho-H of Si-phenyl), 7.57
(2 H, m, ortho-H of CdC-phenyl), 7.39 (3 H, m, para-H of Si-phenyl),
7.38 (6 H, m, meta-H of Si-phenyl), 7.32 (2 H, m, meta-H of Cd
C-phenyl), 7.29 (1 H, m, para-H of CdC-phenyl). 13C NMR (THF-d8,
100 MHz): δ 163.6 (HCdCGa), 142.8 (br, HCdCGa), 142.6 (ipso-C of
CdC-phenyl), 137.3 (ortho-C of Si-phenyl), 136.1 (ipso-C of Si-phenyl),
130.3 (para-C of Si-phenyl), 129.3 (para-C of CdC-phenyl), 128.9
(meta-C of CdC-phenyl), 128.7 (ortho-C of CdC-phenyl), 128.6 (meta-
C of Si-phenyl). 29Si NMR (THF-d8, 79 MHz): δ ꢀ12.7. IR (KBr plates,
paraffin, cmꢀ1): 1962 vw, 1877 w, 1765 w, 1684 w, 1645 m, 1553 s, 1533
w, 1499 w ν(CdC), phenyl; 1466 w, 1427 w, 1375 m (paraffin); 1331 w,
1306 w, 1261 w, 1188 w, 1157 w, 1111 m, 1067 vw, 1026 w, 997 w,
964 vw, 930 m, 885 s, 839 w, 816 m, 799 s, 743 m ν(CC), δ(CH);
698 s, 677 m, 621 m ν(SiC); 586 m, 557 s, 507 s, 473 w, 453 m, 428 m
ν(GaCl), ν(GaC). MS (EI, 20 eV, 160 °C): m/z (%) 466 (3.4), 464 (3.3)
[M(monomer)ꢀ HCl]þ, 395 (100), 396 (30), 397 (37) [M(monomer) ꢀ
HGaCl]þ, 360 (26.0) [M(monomer) ꢀ HGaCl2]þ.
Synthesis of Compounds 5 to 7: General Procedure. Solid
Li(THF)2C(SiMe3)3 (about 2.6 mmol, one equivalent per GaCl2
group) was added in small portions to cooled (0 °C) suspensions of
the corresponding dichlorogallium compounds in 50 mL of n-hexane.
The mixtures were warmed to room temperature and stirred for 16 h.
LiCl was filtered off. The pale yellow filtrates were concentrated and
cooled to ꢀ15 °C to obtain the crystalline products 5 to 7.
Characterization of 7. Yield: 46%. Mp (argon, sealed capillary):
152 °C. Anal. Calcd for C36H48ClGaSi4 (698.3): C, 61.9; H, 6.9. Found:
1
C, 61.3; H, 6.6. H NMR (C6D6, 400 MHz, 300 K): δ 8.14 (1 H, s,
3JHꢀSi = 12 Hz, CdCH), 7.88 (6 H, pseudo-d, ortho-H of SiPh3), 7.21
(9 H, m, meta- and para-H of SiPh3), 7.10 (2 H, m, ortho-H of CdC-Ph),
7.00 (2 H, m, meta-H of CdC-Ph), 6.99 (1 H, pseudo-t, para-H of
CdC-Ph), 0.67 (3 H, s, Ga-CH3), 0.38 and 0.32 (each 3 H, s, ClSiCH3),
0.08 (18 H, s, C(SiMe3)2). 1H NMR (toluene-d8, 400 MHz, 270 K): δ
0.65 (3 H, s, GaMe), 0.35 and 0.27 (each 3 H, s, SiMe2Cl), 0.055 and 0.050
(each 9 H, s, C(SiMe3)2). 13C NMR (C6D6, 100 MHz): δ 159.5 (HCd
CGa), 159.0 (HCdCGa), 144.6 (ipso-C of CdC-Ph), 137.3 (ortho-C of
SiPh3), 136.4 (ipso-C of SiPh3), 130.1 (meta-C of CdC-Ph), 129.9 (para-C
of SiPh3), 128.7 (para-C of CdC-Ph), 128.3 (meta-C of SiPh3), 127.2
(ortho-C of CdC-Ph), 20.4 (CSi3), 10.1 (Ga-CH3), 9.0 and 8.8 (ClSiCH3),
5.4 (C(SiMe3)2). 29Si NMR (C6D6, 79 MHz): δ 24.9 (SiCl), ꢀ4.1
(SiMe3), ꢀ14.7 (SiPh3). IR (KBr plates, paraffin, cmꢀ1): 1655 w, 1580
m, 1560 w, 1531 m ν(CdC), phenyl; 1460 vs, 1377 s (paraffin); 1306 w,
1252 s δ(CH3); 1196 w, 1159 w, 1103 s, 1028 w, 997 w ν(CC), δ(CH);
924 w, 881 s, 866 s, 845 s, 793 w, 773 w, 736 s F(CH3Si), phenyl; 723 s
(paraffin); 700 s phenyl; 671 m, 650 m νas(SiC); 619 w νs(SiC); 592 m,
547 s, 496 s, 455 m ν(SiCl), ν(GaC). MS (EI, 20 eV, 120 °C): m/z (%)
683 (4.9), 681 (3.8) [M ꢀ Me]þ, 447 (6.4), 445 (8.5) [M ꢀ
C(SiMe3)2SiMe2Cl]þ, 337 (100), 335 (88) [GaMeC(SiMe3)2SiMe2Cl]þ.
Crystal Structure Determinations. Single crystals were obtained
bycrystallizationfromn-hexane(3, 20/þ4 °C), cyclopentane (4, storing a
solution at room temperature), and cyclopentane (5ꢀ7, 20/þ5 °C). The
Characterization of 5. Yield: 58%. Mp (argon, sealed capillary):
212 °C. Anal. Calcd for C36H78Cl2Ga2Si8 (946.0): C, 45.7; H, 8.3.
Found: C, 45.6; H, 8.3. Two conformers A and B were observed in the NMR
spectra in a molar ratio of 0.67:0.33 at room temperature. 1H NMR (C6D6,
400 MHz): Isomer A: δ7.77 (2 H, s, 3JHꢀSi =12.0Hz, CdCH), 7.17 (4 H, s,
aromatic ring), 0.77 (6 H, s, Ga-CH3), 0.56 and 0.52 (each 6 H, s, ClSiCH3),
0.37 (18 H, s, CdC-SiMe3), 0.22 and 0.14 (each 18 H, s, C(SiMe3)2);
isomer B: δ 7.83 (2 H, s, 3JHꢀSi = 12.0 Hz, CdCH), 7.23 (4 H, s, aromatic
ring), 0.63 (6 H, s, Ga-CH3), 0.57 and 0.53 (each 6 H, s, ClSiCH3), 0.36
(18 H, s, CdC-SiMe3), 0.21 and 0.17 (each 18 H, s, C(SiMe3)2). 13C NMR
(C6D6, 100 MHz): Isomer A: δ 167.1 (HCdCGa), 150.3 (HCdCGa),
144.2 (1,4-C of phenyl), 128.1 (C-H of phenyl), 18.6 (CSi3), 9.7 (Ga-CH3),
9.0 and 8.6 (ClSiCH3), 5.4 and 5.2 (C(SiMe3)2), 1.4 (CdC-SiMe3); isomer
B: δ 167.8 (HCdCGa), 150.5 (HCdCGa), 144.6 (1,4-C of phenyl), 128.3
(C-H of of phenyl), 18.9 (CSi3), 9.8 (Ga-CH3), 9.2 and 8.6 (ClSiCH3), 5.4
and 5.3 (C(SiMe3)2), 1.4 (CdCꢀSiMe3). 29Si NMR (C6D6, 79 MHz):
Isomer A: δ27.7 (SiCl), ꢀ3.5 (CdC-SiMe3), ꢀ3.6 and ꢀ4.4 (C(SiMe3)2);
isomer B: δ 27.5 (SiCl), ꢀ3.6 (CdC-SiMe3), ꢀ3.6 and ꢀ4.2 (C(SiMe3)2).
IR (KBr plates, paraffin, cmꢀ1): 1710 w, 1580 m, 1555 m, 1495 m ν(CdC),
phenyl; 1462 vs (paraffin); 1404 w δ(CH3); 1377 s (paraffin); 1304 w, 1258
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dx.doi.org/10.1021/om200176y |Organometallics 2011, 30, 3075–3082

Organometallics
ARTICLE
crystallographic data were collected with a STOE IPDS-II (4) and a
Bruker APEX diffractometer. The structures were solved by direct
methods and refined with the program SHELXL-9717 by a full-matrix
least-squares method based on F2. The crystals of compound 3 decom-
posed rapidly after picking them up from the solvent or upon warming to
room temperature. They became amorphous and could be mounted and
measured only with difficulties. The only usable crystal was twinned with
two domains; the reflections of one domain were used for structure
refinement. The molecules of 4 and 5 reside on crystallographic centers of
symmetry. The crystals of 5 enclose two molecules of cyclopentane per
formula unit; their carbon atoms were refined with isotropic displacement
parameters. The C(SiMe3)2(SiMe2Cl) group showed a disorder; the
atoms were refinedonsplit positions (0.67:0.33). The crystalsof6 enclose
a molecule of cyclopentane per formula unit. The molecular core of 7
showed a disorder; the atoms GaCSi3Cl were refined on split positions
(0.94:0.06). Further details of the crystal structure determinations are
available from the Cambridge Crystallographic Data Center on quoting
the depository numbers CCDC-812976 (3), -812977 (4), -812978
(5 2C5H10), -812979 (6 C5H10), and -812980 (7).
Quantum Chemical Calculations. All computations have been
performed using the Gaussian 09 suite of programs.18 The Becke three-
parameter exchange functional and the correlation functional of Lee,
Yang, and Parr (B3LYP)19 with the 6-311G(d,p) basis set were used to
compute the geometries and the normal mode vibration frequencies of
the structures. For single-point energy calculations on DFT-optimized
geometries the SCS-MP2 method20 with the def2-TZVP basis set21
taken from the EMSL Basis Set Library22 was used. In order to verify the
character of the stationary points, they were subjected to frequency
analyses. The vibration related to the imaginary frequency corresponds
to the nuclear motion along the reaction coordinate under study.
Further, intrinsic reaction coordinate calculations were performed in
order to unambiguously connect the transition structures with the
reactants and the products.
Uhl, W.; Wiberg, N. Molecular Clusters of the Main Group Elementsꢀ
Extending Borders From Molecules To Materials; Driess, M.; N€oth, H.,
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J. Organomet. Chem. 2002, 646, 39. (h) Weidenbruch, M. Organometallics
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Chem. 1992, 104, 1378. Angew. Chem., Int. Ed. Engl. 1992, 31, 1364.
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Chem. 1997, 109, 64. Angew. Chem., Int. Ed. Engl. 1997, 36, 64.
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H.-G.; Noltemeyer, M. Angew. Chem. 1998, 110, 2059. Angew. Chem.,
Int. Ed. 1998, 37, 1952. (f) Uhl, W.; Jantschak, A. J. Organomet. Chem.
1998, 555, 263. (g) Uhl, W.; Jantschak, A.; Saak, W.; Kaupp, M.;
Wartchow, R. Organometallics 1998, 17, 5009. (h) Schnepf, A.;
St€osser, G.; Schn€ockel, H J. Am. Chem. Soc. 2000, 122, 9178.
(i) Uhl, W.; Melle, S.; Geiseler, G.; Harms, K. Organometallics
2001, 20, 3355. (j) Uhl, W.; Melle, S. Chem.—Eur. J. 2001,
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3
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Hydrogallation of an alkene with HGaCl2:(b) Ohshita, J.; Schmidbaur,
H. J. Organomet. Chem. 1993, 453, 7.
(7) (a) Uhl, W.; Claesener, M. Inorg. Chem. 2008, 47, 729. (b) Uhl,
W.; Claesener, M.; Hepp, A. Organometallics 2008, 27, 2118.
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W€urthwein, E.-U. Chem.—Eur. J. 2008, 14, 11557.
’ ASSOCIATED CONTENT
(9) Uhl, W.; Bock, H. R.; Breher, F.; Claesener, M.; Haddadpour, S.;
Jasper, B.; Hepp, A. Organometallics 2007, 26, 2363.
S
Supporting Information.
CIF files giving the crystal
b
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data for compounds 3 to 7. Table of crystal data and structure
refinement. Cartesian coordinates (B3LYP/6-311G(d,p)) and
SCS-MP2/def2-TZVP//B3LYP/6-311G(d,p)þZPE energies of
the calculated structures. This material is available free of charge
via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: þ49-251-8336660. E-mail: uhlw@uni-muenster.de.
’ ACKNOWLEDGMENT
We are grateful to the Deutsche Forschungsgemeinschaft for
generous financial support.
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’ DEDICATION
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Dedicated to Hansgeorg Schn€ockel on the occasion of his 70th
birthday.
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