[Ga2Cl4(dioxane)2](x): Molecular structure and reactivity of a polymeric gallium(II) halide containing two five-coordinate gallium atoms about a Ga-Ga bond

Article abstract of DOI:10.1039/a903166i

A polymeric 1,4-dioxane adduct of gallium(II) chloride, [Ga₂Cl₄(dioxane)₂](x), containing two five-coordinate gallium atoms about a Ga-Ga bond [Ga-Ga 2.3825(9) A], reacts with 1,4-dilithiotetraphenylbutadiene affording an unusual Ga(II)-tetraphenylbutadiene complex.

Full text of DOI:10.1039/a903166i

[Ga2Cl4(dioxane)2]x: molecular structure and reactivity of a polymeric
gallium(ii) halide containing two five-coordinate gallium atoms about a Ga–Ga
bond
Pingrong Wei, Xiao-Wang Li and Gregory H. Robinson*
Department of Chemistry, The University of Georgia, Athens, GA 30602-2556, USA.
E-mail: robinson@SUNCHEM.uga.edu
Received (in Columbia, MO, USA) 20th April 1999, Accepted 21st May 1999
A polymeric 1,4-dioxane adduct of gallium(ii) chloride,
[Ga2Cl4(dioxane)2]x, containing two five-coordinate gallium
atoms about a Ga–Ga bond [Ga–Ga 2.3825(9) Å], reacts
with 1,4-dilithiotetraphenylbutadiene affording an unusual
Ga(ii)–tetraphenylbutadiene complex.
took place at 0 °C. While I has a number of similarities with
Ga2Cl4(dioxane)2 and Ga2Br4(dioxane)2 (i.e. the dioxane
adducts are in the chair form), the differences are quite
remarkable. Most striking about I is the five-coordinate, almost
idealized trigonal bipyramidal coordination about both gallium
atoms [O–Ga–O 179.10(10)°] while maintaining a Ga–Ga
bond. It is particularly noteworthy that I is a rare example of a
dimeric gallane consisting of two five-coordinate gallium atoms
about a Ga–Ga bond. The trigonal bipyramidal coordination
notwithstanding, it is also surprising that the Ga–Ga bond
distance of 2.3825(9) Å in I is shorter than the values reported
for both Ga2Br4(dioxane)2 [2.395(6) Å] and Ga2Cl4(dioxane)2
[2.406(1) Å]. Indeed, the Ga–Ga bond in I is considerably
shorter than the cyclogallene Ga–Ga bond distances of 2.441(1)
and 2.4187(5) Å reported for Na2[(Mes2C6H3)Ga]3 and
K2[(Mes2C6H3)Ga]3, respectively, involving trigonal planar
coordinated gallium atoms. The independent Ga–O bond
distance of 2.4087(19) Å in I is considerably longer than the
mean values of 2.03(2) and 2.027(2) Å reported for Ga2Br4-
(dioxane)2 and Ga2Cl4(dioxane)2, respectively. However, the
Ga–O bond length of I compares well with the Ga–O(axial)
The first organometallic compound unambiguously shown to
contain a Ga–Ga bond, [(Me3Si)2HC]2Ga–Ga[CH(SiMe3)2]2
[Ga–Ga 2.541(1) Å], isolated from reaction of LiCH(SiMe3)2
with gallium(ii) bromide bis(dioxane), Ga2Br4(dioxane)2, was
reported only a decade ago.1 In the solid state, Ga2Br4(diox-
ane)2 resides in a trans geometry about a Ga–Ga bond of
2.395(6) Å.2 The solid state structure of the corresponding
bis(dioxane) adduct of gallium(ii) chloride, Ga2Cl4(dioxane)2,
assumes a similar trans geometry about a comparable Ga–Ga
bond of 2.406(1) Å.3 In both Ga2Br4(dioxane)2 and Ga2Cl4-
(dioxane)2, the gallium atoms are four-coordinate tetrahedral—
each bonding to two halide atoms, one dioxane adduct, and the
remaining gallium atom. Herein, we report a polymeric
1,4-dioxane adduct of gallium(ii) chloride, [Ga2Cl4(dioxane)2]x
I,4 wherein both gallium atoms reside in five-coordinate
trigonal bipyramidal environments about a Ga–Ga bond. The
polymeric structure of I is interesting as it is notably different
from previously reported Ga(ii) halides. Moreover, I is shown
to react with 1,4-dilithiotetraphenylbutadiene affording
[(PhCNCPhPhCNCPh)]Ga[(Cl)Li(OEt2)2]25 II (Scheme 1).
Compound I is significant as it represents a rare example of
two five-coordinate gallium atoms about a Ga–Ga bond.
Compound II involves cleavage of the Ga–Ga bond affording a
Ga(ii)–tetraphenylbutadiene complex.
From the discovery of cyclogallenes,6–8 metalloaromatic
22
22
Ga3
ring systems, to reports of a gallyne,9,10 a Ga2
organometallic analog of acetylene, this laboratory has been
interested in the dynamics of the Ga–Ga bond. These discov-
eries notwithstanding, this laboratory remained intrigued by the
chemistry of the simple bis(dioxane) adducts of gallium halides,
Ga2X4(dioxane)2 (X = Cl, Br) and their well documented
ability to stabilize both the Ga(ii) oxidation state and the Ga–Ga
bond. To this end, we sought to isolate triclinic crystals of
Ga2Cl4(dioxane)2 and explore its reactivity. To our great
surprise, we obtained orthorhombic crystals of [Ga2Cl4(diox-
ane)2]x I (Fig. 1).11 It is possibly noteworthy that I was
crystallized in our laboratory at room temperature while
crystallization in the original preparation by Small and Worrall2
Fig. 1 Molecular structure of [Ga2Cl4(dioxane)2]x I. Bond distances (Å) and
angles (°): Ga(1)–Ga(1a) 2.3825(9), Ga(1)–Cl(1) 2.1721(7), Ga(1)–O(1)
2.4087(19), O(1)–C(2) 1.439(3), Cl(1b)–Ga(1)–Cl(1) 112.75(5), Cl(1b)–
Ga(1)–Ga(1a) 123.62(2), Cl(1)–Ga(1)–Ga(1a) 123.62(2), Cl(1b)–Ga(1)–
O(1) 89.46(5), Cl(1)–Ga(1)–O(1) 90.05(5), Ga(1a)–Ga(1)–O(1) 90.45(5),
Cl(1b)–Ga(1)–O(1b) 90.05(5), Cl(1)–Ga(1)–O(1b) 89.46(5), Ga(1a)–
Ga(1)–O(1b) 90.45(5), O(1)–Ga(1)–O(1b) 179.10(10). (Symmetry codes:
a: 2x + 1/2, 2y + 1/2, z; b: x, 2y + 1/2, 2z + 1/2; c: 2x, 2y + 1, 2z + 1;
d: 2x, y 2 1.2, z 2 1/2; e: x + 1/2, 2y + 1, z 2 1/2; g: x + 1/2, y 2 1/2, 2
z + 1).
Scheme 1
Chem. Commun., 1999, 1287–1288
1287

View Article Online
We are grateful to the National Science Foundation (G. H. R.:
CHE-95-9520162) and to the donors of the Petroleum Research
Fund, administered by the American Chemical Society, for
support of this work.
Notes and references
1 W. Uhl, M. Layh and T. Hildenbrand, J. Organomet. Chem., 1989, 364,
289.
2 R. W. H. Small and I. J. Worrall, Acta Crystallogr., Sect. B, 1982, 38,
250.
3 J. C. Beamish, R. W. H. Small and I. J. Worrall, Inorg. Chem., 1979, 18,
220.
4 Inside the drybox (M. Braun Labmaster 130) Ga2Cl4 (Aldrich Chemical
Co.) (17.8 mmol, 5 g) was dissolved in 1,4-dioxane (25 mL). The
resulting mixture was filtered and the solution was allowed to stand at
room temperature for several days resulting in colorless cubic crystals (4
g, 62% yield). Mp 158–159 °C. Anal. (E + R Microanalytical
Laboratories, Parispanny, NY) Calc. (found) Ga2Cl4(dioxane)2: C,
21.00 (21.17); H, 3.50 (2.90%). The less than ideal hydrogen analysis
may be due to the loosely associated solvent molecules. 1H NMR (300
MHz, 298 K, THF-d8): d 3.52 (m, 2H, –OCH2); 13C NMR (300 MHz,
298 K, THF-d8): d 72.7 (–OCH2).
5 A suspension of 1,4-dilithiotetraphenylbutadiene in diethyl ether (50
mL), obtained from reaction of diphenylacetylene (Aldrich Chemical
Co.) (10 mmol, 1.78 g) and lithium (10 mmol, 0.071 g), was added to a
diethyl ether solution of I (2.5 mmol, 1.14 g) at 278 °C. After stirring
for 3 h at 278 °C, the system was allowed to slowly warm to room
temperature, stirring continued overnight. The resulting solution was
separated from the precipitate by filtration, and concentrated to about a
half of its volume, and then kept at 220 °C for several days. Yellow
crystals were obtained (1.0 g, 31%). Mp 92 °C. Anal. Calc. (found)
Ph4C4GaCl2Li2(Et2O)3: C, 65.50 (65.07); H, 6.82 (6.54%). 1H NMR
(300 MHz, 298 K, THF-d8): d 1.07 (m, 18H, –OCH2CH3), 3.35 (m,
12H, –OCH2CH3), 6.68–7.15 (br, m, 20H, Ph H); 13C NMR (300 MHz,
298 K, THF-d8): d 15.7 (–OCH2CH3), 66.3 (–OCH2CH3), 123.7, 125.1,
127.4, 127.5, 130.2, 131.5, 141.6, 143.6, 148.8, 149.6.
Fig. 2 Molecular structure of [(PhCNCPhPhCNCPh)]Ga[(Cl)Li(OEt2)2]2 II.
Bond distances (Å) and angles (°): Ga(1)–C(1a) 1.966(4), Ga(1)–C(1)
1.966(4), Ga(1)–Cl(1a) 2.2306(18), Ga(1)–Cl(1) 2.2305(18), Cl(1)–Li(1)
2.625(18), Li(1)–O(1) 2.07(2), Li(1)–O(2) 2.31(2); C(1a)–Ga(1)–C(1)
91.4(3), (1a)–Ga(1)–Cl(1a) 115.56(15), C(1)–Ga(1)–Cl(1a) 116.17(13),
C(1a)–Ga(1)–Cl(1) 116.17(13), C(1)–Ga(1)–Cl(1) 115.57(15), Cl(1a)–
Ga(1)–Cl(1) 102.68(14), (1)–Cl(1)–Li(1) 125.8(4). (Symmetry codes: a,
y + 1/3, x 2 1/3, 2z + 1.6; b: y + 1/3, x 2 1/3, 2z + 7/6).
6 X.-W. Li, W. T. Pennington and G. H. Robinson, J. Am. Chem. Soc.,
1995, 117, 7578.
7 X.-W. Li, Y. Xie, P. R. Schreiner, K. D. Gripper, R. C. Crittendon, C. F.
Campana, H. F. Schaefer, III and G. H. Robinson, Organometallics,
1996, 15, 3798.
8 Y. Xie, P. R. Schreiner, H. F. Schaefer, III, X.-W. Li and G. H.
Robinson, J. Am. Chem. Soc., 1996, 118, 10 635.
9 J. Su, X.-W. Li, R. C. Crittendon and G. H. Robinson, J. Am. Chem.
Soc., 1997, 119, 5471.
distances of 2.450(5) and 2.278(5) Å reported for the trigonal
bipyramidal coordinated gallium atom in the azacrown ether
complexation of the dimethylgallium fragment of [(Me2Ga)-
(diaza-18-crown-6)[GaMe3]2.12 Also noteworthy, a view of the
unit cell of
I reveals an extended array stabilized
by Cl…H(dioxane) interactions at contacts of 2.836 Å.
Effectively, these interactions allow the dioxane moieties to
loosely associate Ga2Cl4(dioxane)2 units in infinite chains
within the unit cell.
10 Y. Xie, R. S. Grev, J. Gu, H. F. Schaefer, III, P. v. R. Schleyer, J. Su,
X.-W. Li and G. H. Robinson, J. Am. Chem. Soc., 1998, 120, 3773.
11 X-Ray intensity data were measured at room temperature on a Bruker
SMART TM CCD-based X-ray diffractometer system with graphite-
monochromated Mo-Ka radiation (l = 0.710 73 Å). Crystallographic
data: For I: orthorhombic, space group Pnnn (no. 48) with unit cell
parameters a = 8.2481(1), b = 8.277(1), c = 11.385(1) Å, V =
The tetraphenylbutadiene ligand is potentially useful in
organogallium chemistry. Indeed, this ligand was utilized in the
stabilization of the recently reported spirogallane anion,
[(PhCNCPhPhCNCPh)2Ga]2.13 Reaction of I with 1,4-dilithio-
tetraphenylbutadiene yields the interesting gallium(ii) product
II (Fig. 2).11 II resides about a two fold mirror plane passing
through the Ga(1) atom and bisecting the C(8)–C(8a) bond. The
coordination about the gallium atom is distorted tetrahedral.
The Ga–C bonds in II are a little shorter than those reported for
the spirogallane. Although the mechanism which affords II
remains unclear, Ga–Ga bond cleavage was clearly involved.
Moreover, it is interesting that instead of the system eliminating
LiCl, the lithium atoms, stabilized by diethyl ether, remained in
the coordination sphere via bridging chlorine atoms [Li(1)–
Cl(1)–Ga(1) bond angle is 125.8(4)°]. The Ga–Cl bond distance
of 1.966(4) Å in II is considerably shorter than the values of
777.4(2) Å3, Z = 8. Refinement converged at R1 = 0.024 and wR2
=
0.059.
¯
For II: trigonal, space group R3c (no. 167) with unit cell parameters
a
=
45.008(4), c 10.413(1) Å, V 36.
=
=
18.268(3) Å3, Z
=
Refinement converged at R1 = 0.052 and wR2 = 0.131.
CCDC 182/1272.
12 B. Lee, W. T. Pennington and G. H. Robinson, Organometallics, 1990,
9, 1709.
13 J. Su, S. D. Goodwin, X.-W. Li and G. H. Robinson, J. Am. Chem. Soc.,
1998, 120, 12 994.
14 X.-W. Li, W. T. Pennington and G. H. Robinson, Organometallics,
1995, 14, 2109.
15 J. Su, X.-W. Li and G. H. Robinson, Chem. Commun., 1998, 2015.
2.177(5) and 2.201(5)
Å
for (Mes2C6H3)2GaCl14 and
[(Pri3C6H2)2C6H3GaCl2]2,15 respectively.
Communication 9/03166I
1288
Chem. Commun., 1999, 1287–1288