New aspects of hydrogallation reactions with alkynes: Simple addition versus formation of cyclophanes

Article abstract of DOI:10.1021/om050776e

Treatment of 1,4-bis(3,3-dimethyl-1-butynyl)benzene C₆H ₄(C≡C-CMe₃)₂ with 2 equiv of diethylgallium hydride resulted in addition of one Ga-H bond to each triple bond of the starting compound. Whereas in that case products of secondary reactions could not be isolated, dineopentylgallium hydride afforded a [3,3]-cyclophane derivative with two bridging Ga-CH₂-CMe₃ groups, which may be derived from the simple addition product by condensation and release of trineopentylgallium. A cis-arrangement of Ga and H was observed in all cases.

Full text of DOI:10.1021/om050776e

Organometallics 2006, 25, 159-163
159
New Aspects of Hydrogallation Reactions with Alkynes: Simple
Addition versus Formation of Cyclophanes
Werner Uhl,* Sima Haddadpour, and Madhat Matar
Institut fu¨r Anorganische und Analytische Chemie der UniVersita¨t Mu¨nster, Corrensstrasse 30,
D-48149 Mu¨nster, Germany
ReceiVed September 7, 2005
Treatment of 1,4-bis(3,3-dimethyl-1-butynyl)benzene C6H4(CtC-CMe3)2 with 2 equiv of diethylgallium
hydride resulted in addition of one Ga-H bond to each triple bond of the starting compound. Whereas
in that case products of secondary reactions could not be isolated, dineopentylgallium hydride afforded
a [3,3]-cyclophane derivative with two bridging Ga-CH2-CMe3 groups, which may be derived from
the simple addition product by condensation and release of trineopentylgallium. A cis-arrangement of
Ga and H was observed in all cases.
Scheme 1
Introduction
The hydrogallation of CdC double or CtC triple bonds was
described in several reports as a facile method for the generation
of alkyl- or alkenylgallium compounds.1 Although clear struc-
tural evidence was rarely provided, the structures of the products
were often derived from the addition of Ga-H bonds to the
unsaturated organic components. Thus, compounds were pos-
tulated that have dialkylgallium groups attached to one carbon
atom of the respective C2 couples. Some recent investigations
of our group showed, however, that the course of these reactions
may be more complicated. For instance, treatment of alkynyl-
dialkylgallium derivatives with the corresponding dialkylgallium
hydrides afforded heteroadamantane type compounds (1, Scheme
1) possessing cages formed by six gallium and four carbon
atoms.2 Trialkylgallium compounds were isolated as byproducts,
which may have been formed in the decomposition of the simple
addition products [(R2Ga)2CdC(H)-R′] that had the potentially
unstable geminal dialkylgallium structures. Similar reactions
were reported by our group for aluminum compounds, which
yielded the first examples of carbaalanes.3 We observed a similar
behavior when we treated 1,3,5-tris(3,3-dimethyl-1-butynyl)-
benzene, C6H3(CtC-CMe3)3, with dineopentylgallium hy-
dride.4 A [3,3,3]-cyclophane type molecule (2, Scheme 1)
resulted by the release of trineopentylgallium. Compound 2 has
two aromatic groups bridged by three C2Ga spacers and contains
(1) (a) Nogai, S.; Schmidbaur, H. Inorg. Chem. 2002, 41, 4770. (b)
Schmidbaur, H.; Klein, H. F. Angew. Chem. 1966, 78, 306. (c) Schmidbaur,
H.; Klein, H. F. Chem. Ber. 1967, 100, 1129. (d) Ohshita, J.; Schmidbaur,
H. J. Organomet. Chem. 1993, 453, 7. (e) Schumann, H.; Hartmann, U.;
Wassermann, W. Polyhedron 1990, 9, 353. (f) Johnsen, E.; Downs, A. J.;
Goode, M. J.; Greene, T. M.; Himmel, H.-J.; Mu¨ller, M.; Parsons, S.;
Pulham, C. R. Inorg. Chem. 2001, 40, 4755. (g) Pulham, C. R.; Downs, A.
J.; Godde, M. J.; Rankin, D. W. H.; Robertson, H. E. J. Am. Chem. Soc.
1991, 113, 5149. (h) Atwood, J. L.; Bott, S. G.; Jones, C.; Raston, C. L.
Inorg. Chem. 1991, 30, 4868. (i) Henderson, M. J.; Kennard, C. H. L.;
Raston, C. L.; Smith, G. J. Chem. Soc., Chem. Commun. 1990, 1203. (j)
Uhl, W.; Molter, J.; Neumu¨ller, B. J. Organomet. Chem. 2001, 634, 193.
(k) Jennings, J. R.; Wade, K. J. Chem. Soc. A 1967, 1222.
three coordinatively unsaturated gallium atoms. To obtain better
insight into the course of these hydrogallation reactions, we have
systematically changed the alkyne starting compounds and the
steric demand of the substituents attached to the gallium atoms
of the hydrides. Here we report some reactions with the
bisalkyne 1,4-bis(3,3-dimethyl-1-butynyl)benzene, C6H4(CtC-
CMe3)2.
Results and Discussion
(2) Uhl, W.; Cuypers, L.; Neumu¨ller, B.; Weller, F. Organometallics
2002, 21, 2365.
(3) (a) Uhl, W.; Breher, F. Angew. Chem. 1999, 111, 1578; Angew.
Chem., Int. Ed. 1999, 38, 1477. (b) Uhl, W.; Breher, F.; Lu¨tzen, A.; Saak,
W. Angew. Chem. 2000, 112, 414; Angew. Chem., Int. Ed. 2000, 39, 406.
(c) Uhl, W. Inorganic Chemistry Highlights; Meyer, G., Naumann, D.,
Wesemann, L., Eds.; Wiley-VCH: Weinheim, 2002; p 229.
Reactions of Diethylgallium and Dineopentylgallium Hy-
dride with the Bisalkynylbenzene 1,4-(Me3C-CtC-)2C6H4.
While hydroalumination usually proceeds under relatively mild
conditions below room temperature,5 hydrogallation reactions
are slower and require refluxing n-hexane as solvent in order
to complete the reactions in a reasonable time. Accordingly,
(4) Uhl, W.; Breher, F.; Haddadpour, S. Organometallics 2005, 24, 2210.
10.1021/om050776e CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/15/2005

160 Organometallics, Vol. 25, No. 1, 2006
Uhl et al.
we treated the bisalkyne 1,4-(Me3C-CtC-)2C6H4 with 2 equiv
of diethylgallium hydride in n-hexane at reflux for 24 h until
the starting alkyne was completely consumed. The NMR
spectrum of the crude product of the reaction showed a
complicated pattern of many unassigned resonances. The
corresponding trialkylgallium compound could not be detected
unambiguously, which is in contrast to the reaction of the
trisalkynylbenzene with di(neopentyl)gallium hydride cited
above.4 Despite the confusing NMR spectrum, repeated recrys-
tallization yielded the pure product 3 as a colorless solid in
moderate yield. Strong evacuation of solid 3 in order to
completely remove the solvent should be avoided, because
decomposition seems to occur under these conditions with an
alteration of the consistency of the residue and the formation
of small drops of a yellow oil. This decomposition reaction
proceeds slowly, and its mechanism remains unknown. The
characterization of 3 was accomplished using samples that
contained different amounts of the solvent n-hexane. NMR data,
in particular the very characteristic integration ratios, clearly
verified that the hydrogallation reaction in this case did not
afford a cyclophane type molecule similar to 2 (Scheme 1) by
condensation. Instead, the simple addition product with one
diethylgallium unit attached to each of the CdC double bonds
was isolated (eq 1). Similar addition products were obtained in
hydroalumination reactions only in those cases where at least
one trimethylsilyl group was attached to the carbon atoms of
the CtC triple bonds.5 These compounds contain coordinatively
unsaturated aluminum and gallium atoms and may be suitable
to act as chelating Lewis acids. In view of the relative instability
of 3 we did not find the molecular mass of compound 3 in the
mass spectrum (EI). Instead, a peak was detected in addition to
those of unknown products, which could be assigned to a
cyclophane type molecule minus one ethyl group. Triethylgal-
lium-derived peaks were found in only very low intensity. Thus,
it seems that decomposition of 3 yielded at least partially a
cyclophane type molecule. After isolation of 3 and evaporation
of the mother liquor a dark yellow highly viscous liquid
remained, which showed a multitude of NMR resonances due
to unknown products.
(eq 2). It was isolated from the crude product by distillation
under vacuum in 34% yield. However, it could not be removed
completely from the remaining solid. The product (4) was
isolated in pure form by recrystallization of the residue from
toluene. NMR spectroscopic characterization verified a reaction
course similar to that described in the Introduction for the
trisalkynylbenzene 1,3,5-(Me3C-CtC)3C6H3. A [3,3]-cyclo-
phane type compound was formed by condensation and release
of trineopentylgallium, which possesses two bridging neopen-
tylgallium groups. Thus, interestingly the simple addition
product seems to be unstable in this case and may occur only
as an intermediate. From steric shielding we would expect just
the reverse behavior, and the bulkier substituents should prevent
the facile approach of the molecules to initiate the exchange
process. Indeed, stable addition products of the type R2Al-
(H5C6)CdC(H)-CMe3 were obtained by employing the very
bulky bis(trimethylsilyl)methyl groups attached to aluminum.8
The most characteristic spectroscopic findings of compounds 3
and 4 are the chemical shifts of the hydrogen atoms attached to
the CdC bonds (δ ) 6.11 and 6.20), which, however, do not
allow a clear distinction between both types of molecules. There
is a small difference in the 13C NMR resonances of the ipso-
carbon atoms of the aromatic groups (δ ) 142.5 and 155.2,
respectively) and of the R-carbon atoms of the CdC double
bond attached to gallium (δ ) 153.9 and 142.2). However, it is
not yet clear whether these differences are indicative for the
respective structures.
An intermediate was detected by NMR spectroscopy in the
course of the dineopentylgallium hydride reaction (eq 2). It
showed two doublets of equal intensity in the phenyl range (δ
) 7.46 and 6.86; J ) 8 Hz). These resonances disappeared with
the complete consumption of the starting bisalkyne. A tert-butyl
resonance could not be assigned. The observation of doublets
for the phenyl protons is indicative of a nonsymmetric product
with, for example, the addition of Ga-H to only one ethynyl
group, but it is not clear whether the condensation already
occurred at that stage. To isolate this intermediate, we conducted
the reaction according to eq 2 with a 1:1 ratio of the starting
compounds. The intermediate was formed once again. However,
decomposition occurred with the formation of unknown products
before the bisalkyne was consumed. A further byproduct was
detected, which showed a chemical shift of δ ) 6.98. It could
be enriched in the mother liquor after isolation of compound 4
together with trineopentylgallium and some unknown impurities,
but we could not isolate it in pure form. We are not able to
make a reasonable suggestion for its constitution.
The reactions of dineopentylgallium hydride usually are faster,
and the starting compounds were completely consumed on
heating at reflux overnight. The slightly different reactivity may
depend on the bulkiness of the substituents and the degree of
oligomerization (R ) Et: trimeric; R ) CH2CMe3: dimeric).6,7
Trineopentylgallium was formed in the course of the reaction
(5) (a) Uhl, W.; Matar, M. J. Organomet. Chem. 2002, 664, 110. (b)
Uhl, W.; Breher, F. J. Organomet. Chem. 2000, 608, 54.
(6) Uhl, W.; Cuypers, L.; Geiseler, G.; Harms, K.; Massa, W. Z. Anorg.
Allg. Chem. 2002, 628, 1001.
(7) (a) Uhl, W.; Cuypers, L.; Graupner, R.; Molter, J.; Vester, A.;
Neumu¨ller, B. Z. Anorg. Allg. Chem. 2001, 627, 607. (b) Baxter, P. L.;
Downs, A. J.; Goode, M. J.; Rankin, D. W. H.; Robertson, H. E. J. Chem.
Soc., Dalton Trans. 1990, 2873.
Whether compound 3 is a singular case is not clear yet. All
attempts to conduct such reactions starting with sterically less
(8) Uhl, W.; Matar, M. Z. Anorg. Allg. Chem. 2005, 631, 1177.

Hydrogallation Reactions with Alkynes
Organometallics, Vol. 25, No. 1, 2006 161
Figure 1. Molecular structure of 3. The thermal ellipsoids are
drawn at the 40% probability level. Methyl groups of the tert-butyl
substituents and hydrogen atoms of the phenyl groups are omitted
for clarity. The drawing shows both independent molecules. One
resides on a center of symmetry [Ga(2)]; the second one on a 2-fold
rotation axis [Ga(1)]. The dashed lines indicate the intermolecular
interactions. Important bond lengths (Å) and angles (deg): Ga-
(1)-C(11) 2.030(3), Ga(1)-C(31) 1.977(3), Ga(1)-C(41) 1.979-
(4), C(11)-C(12) 1.350(4), C(11)-C(111) 1.500(4), Ga(2)-C(21)
2.045(3), Ga(2)-C(51) 1.982(3), Ga(2)-C(61) 1.976(4), C(21)-
C(22) 1.345(4), C(21)-C(211) 1.496(4), Ga(1)-C(21) 2.560(4),
Ga(2)-C(11) 2.581(4), C(11)-Ga(1)-C(31) 114.9(1), C(11)-Ga-
(1)-C(41) 115.0(2), C(31)-Ga(1)-C(41) 116.7(2), C(12)-C(11)-
C(111) 123.5(3), C(21)-Ga(2)-C(51) 112.6(1), C(21)-Ga(2)-
C(61) 116.4(2), C(51)-Ga(2)-C(61) 117.9(2), C(22)-C(21)-
C(211) 122.0(3). The atoms Ga(1)′ and Ga(2)′ were generated by
-x, y, -z+0.5 and -x, -y, -z, respectively.
Figure 2. Molecular structure of 4. The thermal ellipsoids are
drawn at the 40% probability level. Methyl groups attached to C(22)
and C(32) and hydrogen atoms are omitted for clarity. Important
bond lengths (Å) and angles (deg): Ga(1)-C(1) 1.994(3), Ga(1)-
C(2) 1.975(4), Ga(1)-C(3)′ 1.975(4), C(2)-C(21) 1.345(5), C(2)-
C(41) 1.493(5), C(3)-C(31) 1.339(5), C(3)-C(44) 1.492(5), C(1)-
Ga(1)-C(2) 117.1(2), C(1)-Ga(1)-C(3)′ 119.1(2), C(2)-Ga(1)-
C(3)′ 123.7(2), C(21)-C(2)-C(41) 125.4(3), C(31)-C(3)-C(44)
125.4(4); C(3)′ was generated by -x+0.5, -y+0.5, -z+0.5.
around the C-C bonds to the central phenylene groups may
equilibrate both forms in solution so that only one set of NMR
resonances was detected. The spectra did not change upon
cooling of samples dissolved in toluene to -60 °C. The planes
of the phenylene groups are almost perpendicular to the planes
defined by each substituent including the CdC double bonds
[angles between the normals of the planes 100° with Ga(1) and
91° with Ga(2)]. Thus, a mesomeric stabilization of the
molecules by an interaction between the aromatic systems and
the CdC double bonds can clearly be excluded at least for the
solid state. The CdC double bond lengths (1.348 Å) are almost
indistinguishable for both molecules and are in the normal
range.9 Interestingly, the longer Ga-C distances (2.038 versus
1.979 Å on average) are observed for those carbon atoms [C(11)
and C(21)] that formally are sp2-hybridized and are part of the
CdC double bonds (see for comparison the structure of 4). That
particular effect is caused by an intermolecular interaction that
results in the formation of one-dimensional coordination
polymers possessing zigzag chains alternating the two types of
molecules. Relatively narrow Ga-C contacts to the R-carbon
atoms of the CdC double bonds result [Ga(1)‚‚‚C(21) 2.560
Å; Ga(2)‚‚‚C(11) 2.581 Å], which were indicated by dashed
lines in Figure 1 and give strongly faulted Ga2C2 heterocycles.
These contacts cause a considerable deviation of the gallium
atoms from the plane of the three carbon atoms C(11), C(31),
C(41) or C(21), C(51), C(61) [0.429 Å and sum of the angles
346.6° for Ga(1); 0.424 Å and sum of the angles 346.9° for
Ga(2)].
shielded dimethylgallium hydride failed. That hydride is rela-
tively unstable,6 and fast decomposition of the hydride was
observed for solutions at temperatures > 50 °C without any
attack on the alkyne. At room temperature hydrogallation
reaction did not occur even after prolonged reaction times of
several weeks.
Molecular Structures. The molecular structures of the
hydrogallation products 3 and 4 are depicted in Figures 1 and
2, respectively. The ethyl compound 3 represents the product
of a simple addition of Ga-H to both CtC triple bonds without
a secondary reaction and is thus in complete accordance with
the usual formulations of hydroalumination or hydrogallation
products found in the literature. The second compound, 4, bears
the bulkier neopentyl groups and may be described as a [3,3]-
cyclophane with two bridging GaC2 moieties in para-position
of the aromatic rings. In both compounds the gallium and
hydrogen atoms attached to the CdC double bonds adopt a cis-
arrangement, and the GaR2 or GaR groups are bonded to those
carbon atoms that are in R-position to the phenylene rings. This
particular position may be favored by a mesomeric stabilization
of the negative charge induced by the bonding of that carbon
atom to gallium.
Two independent molecules are found in the crystal structure
of compound 3, which reside on two symmetrically different
special positions. One with the atom Ga(1) is located on a
crystallographic 2-fold rotation axis, which is perpendicular to
the aromatic ring and causes both diethylgallium fragments to
be on the same side of the phenylene group. The second
molecule possesses a center of symmetry with a trans-
arrangement of the organometallic substituents. A fast rotation
The molecules of the cyclophane type compound 4 are located
on crystallographic centers of symmetry. Its structural param-
eters are similar to those of the corresponding [3,3,3]-cyclo-
(9) March, J. AdVanced Organic Chemistry, 3rd ed.; Wiley: New York,
1985; p 19.

162 Organometallics, Vol. 25, No. 1, 2006
Uhl et al.
Table 1. Crystal Data, Data Collection Parameters, and
Structure Refinement Details for Compounds 3 and 4
phane, which has three bridging neopentylgallium groups and
was published by our group only recently.4 The Ga-C bond
lengths differ slightly. Expectedly, the shorter ones were detected
for those Ga-C bonds that include the sp2-carbon atoms of the
CdC double bonds (1.975 compared to 1.994 Å). Probably
owing to some strain in the cage, the larger C-Ga-C angles
occur in the cyclophane skeleton [C(2)-Ga(1)-C(3′) 123.7°
compared to 118.1° on average for the remaining two angles].
An almost ideally planar surrounding of the gallium atoms can
be derived from the sum of the C-Ga-C angles of 359.9°.
The CdC double bonds have the usual lengths of 1.342 Å on
average.9 As forced by the molecular arrangement, the planes
defined by the alkenyl groups are almost perpendicular to the
planes of the aromatic rings, and the angles between their
normals are 76.4° [Ga(1)] and 80.0° [Ga(1′)]. The phenylene
rings are ideally coplanar; however, owing to the particular
angles between the molecular planes as discussed before, they
are slightly shifted with respect to each other. The distances
between the carbon atoms of both aromatic rings are in a normal
range of van der Waals interactions (3.41 to 3.52 Å).10
3
4‚toluene
C52H70Ga2
monoclinic
I2/a (No. 15)14
4
formula
cryst syst
space group
Z
C26H44Ga2
monoclinic
C2/c (No. 15)14
8
temp, K
D
193(2)
1.226
193(2)
1.102
calcd, g/cm3
a, Å
b, Å
c, Å
27.869(3)
11.2663(7)
18.501(2)
90
112.30(1)
90
16.753(1)
14.144(1)
21.247(2)
90
92.495(6)
90
5029.8(7)
1.101
0.24 × 0.18 × 0.06
R, deg
â, deg
γ, deg
V, 10-30 m3
µ, mm-1
cryst dimens, mm
radiation
θ range, deg
index ranges
5374.8(8)
2.013
0.21 × 0.21 × 0.09
Mo KR; graphite monochromator
1.97-26.03
-34 e h e 34
-13 e k e 13
-22 e l e 22
3499
1.73-26.11
-20 e h e 20
-17 e k e 17
-23 e l e 26
3108
no. of obsd reflns
no. of unique reflns
no. of params
5240 [Rint ) 0.0505]
263
4982 [Rint ) 0.0658]
238
Experimental Section
R1 (reflns I > 2σ(I))
wR2 (all data)
0.0356
0.0829
0.0512
0.1253
General Procedures. All procedures were carried out under
purified argon. n-Hexane was dried over LiAlH4; toluene over Na/
benzophenone. Dineopentylgallium hydride and diethylgallium
hydride were obtained according to literature procedures.6
max./min. residual
electron density,
1030 e/m3
0.715/-0.638
0.724/-0.331
8 Hz, CH3 of ethyl), 1.08 (18 H, s, CMe3), 0.54 (8 H, q, 3JH‚‚‚H
)
Syntheses of 1,4-Bis(3,3-dimethyl-1-butynyl)benzene. The
synthesis of this bisalkyne has been reported before.11 We employed
a simpler coupling reaction, which followed a well-known general
procedure.12 3,3-Dimethyl-1-butyne (6.99 g, 0.085 mol) was added
dropwise to a solution of 1,4-dibromebenzene (10.05 g, 0.043 mol),
copper(I) iodide (25 mg, 0.13 mmol), and dichlorobis(triph-
enylphosphino)palladium(II) (0.200 g, 0.29 mmol) in 300 mL of
triethylamine. The mixture was stirred at 70 °C for 7 h. The
precipitate was filtered off and washed with n-pentane. The solvents
were removed in a vacuum. The residue was dissolved in n-pentane
and filtered through a column of alumina. The purified solution
was concentrated and cooled to -30 °C to obtain colorless crystals
of the product. Yield: 5.08 g (50%). Mp (argon, sealed capillary):
154 °C. 1H NMR (C6D6, 200 MHz): δ 7.25 (4 H, s, phenyl), 1.23
(18 H, s, CMe3). 13C NMR (C6D6, 200 MHz): δ 131.8 (C-H of
phenyl), 123.7 (ipso-C of phenyl), 99.9 and 79.8 (CtC), 31.0 (Me),
28.1 (CMe3). IR (paraffin, CsBr plates, cm-1): 2236 m ν(CtC).
MS (EI, 70 eV): m/z (%) 238 (M+, 92), 223 (M+ - Me, 100).
Synthesis of 3. A solution of freshly sublimed 1,4-bis(3,3-
dimethyl-1-butynyl)benzene (0.800 g, 3.36 mmol) in 30 mL of
n-hexane was treated with diethylgallium hydride (0.898 g, 6.98
mmol) at room temperature. The mixture was heated at reflux for
24 h. After cooling to room temperature the yellow solution was
concentrated and cooled to +8 °C to obtain a relatively impure
precipitate of compound 3. Repeated recrystallization from n-hexane
afforded colorless crystals of 3. Owing to the instability of 3 in a
vacuum, the solid material was evacuated to a minimum pressure
of 5 × 10-2 Torr for a short period only. Thus, solid 3 includes
n-hexane in different concentrations. The characterization was done
with this substance containing 0.5 to 2 solvent molecules per
formula unit of 3. Yield: 0.912 g (47% based on one hexane
molecule per formula unit). Mp (argon, sealed capillary): 52 °C;
owing to the easily changing concentration of n-hexane, elemental
8 Hz, CH2 of ethyl); resonances of n-hexane are ignored. 13C NMR
(C6D6, 200 MHz): δ 153.9 (both resonances of the CdC double
bond coincide), 142.5 (ipso-C of phenyl), 126.5 (C-H of phenyl),
37.1 (CMe3), 31.7 (CMe3), 10.0 (CH3 of ethyl), 8.6 (GaCH2);
resonances of n-hexane are ignored. IR (CsBr plates, paraffin,
cm-1): 1678 w, 1652 w, 1602 m, 1558 w phenyl, ν(CdC); 1463
vs, 1377 s (paraffin); 1363 s δ(CH); 1299 w, 1276 w δ(CH3); 1231
w, 1202 w, 1164 w, 1100 m, 1058 m, 1034 sh, 963 w, 939 w, 895
w, 863 w ν(CC); 722 m (paraffin); 653 m phenyl; 562 m, 506 w,
462 w ν(GaC), δ(C3C). MS (EI, 70 eV): m/z (%) 649 (cyclophane
type molecule minus ethyl, 1.6), 551 (cyclophane type molecule
minus GaEt2, 3.3), 339 and 341 (M+ - GaEt2 - ethene, 72 and
46), 127 and 129 (GaEt2, 100 and 68).
Synthesis of 4. A solution of dineopentylgallium hydride (0.659
g, 3.10 mmol) in 20 mL of n-hexane was added to a solution of
the bisalkyne 1,4-(Me3CCtC)2C6H4 (0.378 g, 1.59 mmol) in 20
mL of the same solvent. The mixture was heated at reflux for 14
h. After cooling to room temperature the solvent was removed in
a vacuum. The residue was evacuated (<10-2 Torr) at 50 °C for 3
h to remove the trineopentylgallium byproduct (0.15 g, 0.531 mmol,
34%) and was subsequently recrystallized from toluene (20/-15
°C) to yield colorless crystals of 4. The mother liquor remaining
after isolation of 4 still contained considerable quantities of
trineopentylgallium, which thus could not be completely removed
from the crude product by distillation. Yield: 0.38 g (4; 63%). Mp
(argon, sealed capillary): 146 °C. Anal. Calcd for 4 [C46H70Ga2]
(762.5): C, 72.46; H, 9.25; Ga, 18.29. Found: C, 72.6; H, 9.35;
1
Ga, 18.05. H NMR (C6D6, 600 MHz): δ 6.55 (8 H, s, phenyl),
6.20 (4 H, s, CdC-H), 1.27 (18 H, s, CMe3 of neopentyl), 1.15 (4
H, s, Ga-CH2), 1.05 (36 H, s, CMe3 attached to the CdC double
bond). 13C NMR (C6D6, 125.8 MHz): δ 156.1 (Ga-CdC-H),
155.2 (ipso-C of phenyl), 142.2 (Ga-CdC-H), 126.6 (C-H of
phenyl), 37.1 (CMe3 attached to CdC double bond), 35.3 (CMe3
of neopentyl), 32.3 (CMe3 of neopentyl), 31.5 (CMe3 attached to
CdC double bond), 28.1 (GaCH2). IR (CsBr plates, paraffin, cm-1):
1646 w, 1605 m, 1572 m, 1497 m phenyl, ν(CdC); 1464 vs
(paraffin); 1396 m δ(CH3); 1377 s (paraffin); 1359 s, 1251 w δ-
(CH3); 1229 m, 1201 s, 1185 m, 1163 m δ(CH); 1120 w, 1098 m,
1040 w, 1018 m, 1013 w, 947 w, 917 m, 890 w, 818 m ν(CC);
1
analysis was not conducted. H NMR (C6D6, 400 MHz): δ 6.78
3
(4 H, s, phenyl), 6.11 (2 H, s, CdC-H), 1.16 (12 H, t, JH‚‚‚H
)
(10) (a) Uhl, W.; Hannemann, F.; Wartchow, R. Organometallics 1998,
17, 3822. (b) Smith, G. D.; Jaffke, R. L. J. Phys. Chem. 1996, 100, 9624.
(11) Kamikawa, T.; Hayashi, T. J. Org. Chem. 1998, 63, 8922
(12) Brandsma, L. PreparatiVe Acetylenic Chemistry; Elsevier: Am-
sterdam, 1988.

Hydrogallation Reactions with Alkynes
Organometallics, Vol. 25, No. 1, 2006 163
759 w, 740 w, 721 s (phenyl, paraffin); 607 w, 580 w, 532 s, 453
eters, and structure refinement details are given in Table 1. The
molecules of 4 reside on crystallographic centers of symmetry.
Further details of the crystal structure determinations are available
from the Cambridge Crystallographic Data Center on quoting the
depository numbers CCDC-286806 (3) and -286807 (4).
m ν(GaC), δ(C3C). MS (EI, 70 ev) (%): 760 (1.3), 762 (2) M+;
1
689 (7), 691 (10) M+ - CH2CMe3; 381 (100), 383 (84) /2M+;
two most intensive mass peaks of each group.
Crystal Structure Determination of 3 and 4. Single crystals
of 3 and 4 were obtained by recrystallization from n-hexane (20/
+8 °C) and toluene (20/-15 °C), respectively. The crystals of 4
enclose toluene molecules, which are highly disordered over a
crystallographic 2-fold rotation axis. Only the carbon atoms of the
phenyl rings could be detected. They were refined with isotropic
displacement factors, with occupancy factors of 0.5 and with
restrictions of bond lengths and angles. Hydrogen atoms were not
considered. The crystallographic data were collected with a STOE
IPDS diffractometer. The structure was solved by direct methods
and refined with the program SHELXL-9713 by a full-matrix least-
squares method based on F2. Crystal data, data collection param-
Acknowledgment. We are grateful to the Deutsche Fors-
chungsgemeinschaft and the Fonds der Chemischen Industrie
for generous financial support.
Supporting Information Available: Tables of atomic coordi-
nates, isotropic and anisotropic displacement parameters, and all
bond lengths and angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM050776E
(13) 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; Universita¨t Go¨ttingen: Germany, 1997.
(14) Hahn, T., Ed. International Tables for Crystallography, Space-Group
Symmetry, Vol. A; Kluwer Academic Publishers: Dordrecht, 1989.