Cyclogallanes and Metalloaromaticity. Synthesis and
Molecular Structure of Dipotassium
Tris((2,6-dimesitylphenyl)cyclogallene),
K2[(Mes2C6H3)Ga]3 (Mes = 2,4,6-Me3C6H2): A Structural
and Theoretical Examination
posted on 1996-09-03, 00:00authored byXiao-Wang Li, Yaoming Xie, Peter R. Schreiner, Kevin D. Gripper, R. Chad Crittendon, Charles F. Campana, Henry F. Schaefer, Gregory H. Robinson
The cyclogallane dipotassium
tris((2,6-dimesitylphenyl)cyclogallene),
K2[(Mes2C6H3)Ga]3
(Mes = 2,4,6-Me3C6H2), has been
prepared by either of two distinct synthetic routes.
Disproportionation of gallium(II) chloride,
Ga2Cl4, in the presence of
(2,6-dimesitylphenyl)lithium, (Mes2C6H3)Li, followed
by potassium metal reduction in Et2O affords the
title
compound as large ruby red crystals. Alternatively,
K2[(Mes2C6H3)Ga]3
may readily be
approached by direct alkali metal reduction of
(Mes2C6H3)GaCl2.
The title compound was
characterized by 1H and 13C NMR, elemental
analyses, IR spectroscopy, and single-crystal
X-ray diffraction. The cyclogallane resides about the planar
Ga3 triangle constituted by
extremely short Ga−Ga bonds: 2.4260(5), 2.4317(5), and
2.4187(5) Å. Theoretical examination of the Ga32- anionic core in
[GaH]32-,
Na2[GaH]3, and
K2[GaH]3 suggests a
well-defined
π-molecular orbital. Both experimental and theoretical results
strongly support the
cyclogallene dianion,
[(Mes2C6H3)Ga]32-,
as a well-defined metalloaromatic systema metallic
ring system exhibiting aromatic behavior.