Synthesis and molecular structure of [Li(THF) · 12-crown- 4][PhC=CPhPhC=CPh)2Ga]: The first spirogallane [20]

Full text of DOI:10.1021/ja983547a

12994
J. Am. Chem. Soc. 1998, 120, 12994-12995
Scheme 1
Synthesis and Molecular Structure of
[Li(THF)‚12-crown-4][(PhCdCPhPhCdCPh)2Ga]:
The First Spirogallane
Jianrui Su, Sonya D. Goodwin, Xiao-Wang Li, and
Gregory H. Robinson*
Department of Chemistry, The UniVersity of Georgia
Athens, Georgia 30602-2556
ReceiVed October 8, 1998
The utilization of sterically demanding ligands such as m-
terphenyls has recently afforded a number of interesting organo-
metallic compounds of gallium ranging from 2π-electron metal-
loaromatic cyclogallenes1-4 to reports of a gallyne5,6 and a
ferrogallyne.7 The unique, if unprecedented, metal-metal bonding
in these unusual compounds has fueled a rather spirited debate
in the chemistry community.8,9 Common features in these orga-
nogallium compounds include sub-valency, low-coordination
numbers, and a striking resemblance to iconic compounds of
carbon. The third tenet is particularly germane to this contribution.
Along with bridged and fused ring systems, spirocyclic com-
pounds (below) constitute the ubiquitous class of bicyclic organic
molecules.
report the synthesis11 and molecular structure12 of [Li(THF)‚12-
crown-4][(PhCdCPhPhCdCPh)2Ga], isolated from reaction of
1,4-dilithiotetraphenylbutadienesprepared from the action of
metallic lithium on diphenylacetyleneswith gallium chloride in
the presence of 12-crown-4/THF (Scheme 1). The title compound,
characterized by 1H NMR, elemental analyses, and single-crystal
X-ray diffraction, is significant as the anion is the first example
of a spirogallanesa bicyclic organometallic compound possessing
a tetrahedral gallium atom common to both rings (Figure 1).
While synthetic reports of 1,4-dilithiotetraphenylbutadiene date
back decades,13 it is interesting that X-ray structural data (of the
1,2-dimethoxyethane adduct) of this moiety were only reported
recently.14 Although the greatest organometallic utility of tet-
raphenylbutadiene is found in transition metal chemistry, the main
group chemistry of this ligand is also noteworthy. Tetraphenyl-
butadiene has been particularly beneficial in the stabilization of
The tetrahedral carbon atom common to both rings, evident in
the simplest spirocycle, spiropentane, is distinctive. Spirocycles
beyond carbon, such as silicon-based spirocycles,10 are encoun-
tered considerably less often. Although small ring compounds
are commonplace in group 13 organometallic chemistry, the
literature reveals few examples of spirocyclic compounds wherein
the shared tetrahedral atom is one of these metals. Herein we
(1) Li, X.-W.; Pennington, W. T.; Robinson, G. H. J. Am. Chem. Soc. 1995,
117, 7578.
(12) A number of crystals of the title compound were mounted in glass
capillaries under an atmosphere of nitrogen inside the drybox. X-ray intensity
data on an appropriate sample were collected on a Siemens P4 single-crystal
diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.710
73 Å). Cell parameters and an orientation matrix for data collection, from a
least-squares analysis of the setting angles of 25 carefully centered reflections
in the range 10.0 < 2θ < 25.0°, were obtained. The monoclinic space group
is P21/n (No. 14) with unit cell parameters a ) 13.241(3) Å, b ) 26.440(6)
Å, c ) 17.260(4) Å, â ) 94.140(10)°, Dcalcd ) 1.144 g cm-3, and V ) 6027-
(2) Å3 for Z ) 4. Full-matrix F2 refinement, based upon 4843 observed
reflections, I > 2σ(I ), using the SHELXTL 5.0 system of computer programs,
converged at R1 ) 0.067, wR2 ) 0.23.
(2) Li, X.-W.; Xie, Y.; Schreiner, P. R.; Gripper, K. D.; Crittendon, R. C.;
Campana, C. F.; Schaefer, H. F., III; Robinson, G. H. Organometallics 1996,
15, 3798.
(3) Xie, Y.; Schreiner, P. R.; Schaefer, H. F., III; Li, X.-W.; Robinson, G.
H. J. Am. Chem. Soc. 1996, 118, 10635.
(4) Xie, Y.; Schreiner, P. R.; Schaefer, H. F., III; Li, X.-W.; Robinson, G.
H. Organometallics 1998, 17, 114.
(5) Su, J.; Li, X.-W.; Crittendon, R. C.; Robinson, G. H. J. Am. Chem.
Soc. 1997, 119, 5472.
(6) Xie, Y.; Grev, R. S.; Gu, J.; Schaefer, H. F., III; Schleyer, P. v. R.; Su,
J.; Li, X.-W.; Robinson, G. H. J. Am. Chem. Soc. 1998, 120, 3773.
(7) Su, J.; Li, X.-W.; Crittendon, R. C.; Campana, C. F.; Robinson, G. H.
Organometallics 1997, 16, 4511.
(13) (a) Orechoff, A. Ber. 1914, 47, 89. (b) Schlenk, W.; Bergmann, E.
Ann. 1928, 463, 71. (c) Bergmann, E.; Zwecker, O. Ann. 1931, 487, 155. (d)
Bergman, E.; Schreiber, W. Ann. 1933, 500, 118. (e) Smith, L.; Hoehn, H. H.
J. Am. Chem. Soc. 1941, 63, 1184.
(8) Dagani, R. Chem. Eng. News 1997, 75 (24), 9.
(9) Dagani, R. Chem. Eng. News 1998, 76 (11), 31.
(10) (a) Dubac, J.; Mazerolles, P.; Lesbre, M.; Joly, M. J. Organomet.
Chem. 1970, 25, 367. (b) Damrauer, R.; Davis, R. A.; Burke, M. T.; Karn, R.
A.; Goodman, G. T. J. Organomet. Chem. 1972, 43, 121. (c) Salomon, R. G.
J. Org. Chem. 1974, 39, 3602. (d) Terunma, D.; Hatta, S.; Araki, T.; Ueki,
T.; Okazaki, T.; Suzuki, Y. Bull. Chem. Soc. Jpn. 1977, 50, 1545. (e) Eckert-
Maksic, M. J. Organomet. Chem. 1979, 169, 295.
(14) Pauer, F.; Power, P. P. J. Organomet. Chem. 1994, 474, 27.
(15) Eisch, J. J.; Hota, N.; Kozima, S. J. Am. Chem. Soc. 1969, 91, 4575.
(16) (a) Parkanyi, L. J. Organomet. Chem. 1981, 216, 9. (b) Tamao, K.;
Asahara, M.; Kawachi, A. J. Organomet. Chem. 1996, 521, 325.
(17) Meier-Brocks, F.; Weiss, E. J. Organomet. Chem. 1993, 453, 33.
(18) Nakayama, J.; Matsui, T.; Sugihara, Y.; Ishii, A.; Kumakura, S. Chem.
Lett. 1996, 269.
(11) Inside the drybox (M Braun Labmaster 130) a reaction vessel was
charged with 1,4-dilithiotetraphenylbutadiene, prepared by reaction of lithium
(0.068 g, 10 mmol) and diphenylacetylene (1.78 g, 10 mmol) in diethyl ether,
gallium chloride (0.44 g, 2.5 mmol), and diethyl ether (25 mL). Upon returning
to the benchtop, the system was allowed to stir for 4 h. This solution was
filtered and immediately introduced to 12-crown-4 (0.41 mL, 2.5 mmol),
resulting in a yellow powdery precipitate. After evaporation of the solvent,
tetrahydrofuran (10 mL) was added, resulting in yellow crystals (0.63 g, 24%
yield): mp 193.2 °C. Anal. (E+R Microanalytical Laboratories, Parsipanny,
(19) Abel, E. W. J. Chem. Soc., Chem. Commun. 1973, 258.
(20) (a) Meier-Brock, F.; Weiss, E. J. Organomet. Chem. 1993, 453, 33.
(b) Lindeman, S. V.; Shklover, V. E.; Struchkov, Yu. T.; Vasnyova, N. A.;
Sladkov, A. M. Cryst. Struct. Commun. 1981, 10, 827.
(21) (a) Although no X-ray structural or spectroscopic data were given,
characterization being based solely upon elemental analyses and melting point
determinations, the literature reveals a report describing a tin- and germanium-
based tetraphenylbutadiene spirocycle: Leavitt, F. C.; Manuel, T. A.; Johnson,
F.; Matternas, L. U.; Lehman, D. S. J. Am. Chem. Soc. 1960, 82, 5099. (b) A
paramagnetic spirocyclic-like aluminum complex of 1,4-di-tert-diazabutadiene
has been reported: Geoffrey, F.; Cloke, N.; Dalby, C. I.; Henderson, M. J.;
Hitchcock, P. B.; Kennard, C. H. L.; Lamb, R. N.; Raston, C. L. Chem.
Commun. 1990, 1394.
1
NJ). Calcd (found) for C76H80O9LiGa: C, 75.20 (75.89); H, 6.64 (6.38). H
NMR (300 MHz, 298 K, C4D8O): δ 1.13 (t, 4H, -CH2 (THF)), 3.40 (t, 4H,
-CH2 (THF)), 3.60 (s, 16H, -CH2 (12-crown-4)), 6.79 (m, 40H, -CH
(aromatic)). 13C NMR (300 MHz, 298 K, C4D8O) proved largely uninformative
as several signals overlapped in the 120-135 ppm region.
10.1021/ja983547a CCC: $15.00 © 1998 American Chemical Society
Published on Web 12/01/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 49, 1998 12995
concerningstructureandbondinginthe[(PhCdCPhPhCdCPh)2Ga]-
anion. The general features of the butadiene backbone, essentially
two CdC double bonds bridged by a C-C single bond and
C-C-C bond angles of ca. 120°, are quite comparable to that
as previously reported for the 1,2-dimethoxyethane adduct of the
ligand. Four-coordinate gallium atoms with their coordination
spheres saturated by carbon atoms are reasonably rare with the
recently reported Me3Ga:carbene complex23 being a notable
example. The coordination of the gallium atom in the spirogallane
anion is severely distorted tetrahedral with bond angles ranging
from 87.4(2)° to 131.8(2)° for C(1)-Ga-C(22) and C(1)-Ga-
C(50), respectively. Indeed, this C-Ga-C bond angle range of
44.4° is the largest on record for a four-coordinate tetrahedral
gallium atom. For comparison, the corresponding range of
C-Ga-C bond angles for Me3Ga:carbene is a mere 8.3° (105.9°
to 114.2°). In addition, the Ga-C bond distances are uniformly
long, reaching a maximum value of 2.023(5) Åsa bit shorter than
the longest Ga-C bond distance reported for the Me3Ga:carbene
of 2.214(6) Å. Most significant, however, is the fact that the
gallium atom in the anion is common to both five-membered
tetraphenylbutadiene-based heterocycles. The two five-membered
rings formed by the two tetraphenylbutadiene units and the
gallium atom are perfectly planar and orthogonal to each others
thereby contributing to the distorted environment about the metal.
The title compound offers a convenient organometallic retort to
the well-known organic class of spirocyclic molecules: the
Figure 1. Molecular structure of the [(PhCdCPhPhCdCPh)2Ga]- anion
(thermal ellipsoids are shown at 35% probability levels). Selected bond
distances (Å) and angles (deg): Ga-C(1), 2.003(5); Ga-C(22), 2.023(5);
Ga-C(29), 2.019(5); Ga-C(50), 2.001(5); C(1)-C(8), 1.353(7); C(8)-
C(15), 1.504(7); C(15)-C(22), 1.346(7); C(29)-C(36), 1.361(7); C(36)-
C(43), 1.502(8); C(43)-C(50), 1.363(8); C(1)-Ga-C(50), 131.8(2);
C(29)-Ga-C(50), 87.8(2); C(1)-Ga-C(29), 121.8(2); C(22)-Ga-
C(50), 115.5(2); C(1)-Ga-C(22), 87.4(2); C(22)-Ga-C(29), 115.0(2);
C(1)-C(8)-C(15), 118.4(5); C(8)-C(15)-C(22), 118.1(5); C(29)-
C(36)-C(43), 118.0(5); C(36)-C(43)-C(50), 118.3(5).
[(PhCdCPhPhCdCPh)2Ga]- anion is the first example of a
spirogallane.
main group compounds such as boron,15 silicon,16 sulfur,17
selenium,18 arsenic,19 and germanium20 based five-membered-ring
heterocycles.21 Relative to compounds of tetraphenylbutadiene
with group 13 metals, the literature reveals only (pentaphenyl)-
aluminacyclopentadiene and its complex with 1,5-cyclooctadi-
enenickel.22
Acknowledgment. We are grateful to the National Science Foundation
(G.H.R., CHE-9520162) and to the donors of the Petroleum Research
Fund, administered by the American Chemical Society, for support of
this work.
Supporting Information Available: A textual summary of data
collection and refinement and tables of crystal data, bond distances and
angles, final fractional coordinates, and thermal parameters (13 pages,
print/PDF). See any current masthead page for ordering information and
Web access instructions.
Although the cation consists of a lithium ion complexed by
both 12-crown-4 and THF, a number of points are noteworthy
(22) Kru¨ger, C.; Sekutowski, J. C.; Hoberg, H.; Krause-Go¨ing, R. J.
Organomet. Chem. 1977, 141, 141.
(23) Li, X.-W.; Su, J.; Robinson, G. H. Chem. Commun. 1996, 2683.
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