Ring Systems Containing Anionic and Cationic Gallium Centers: Structural and Bonding Considerations

The metathetical reaction of 2-(dimethylamino)benzyllithium (Bz(N)Li) with GaCl(3) afforded the salt [Bz(N)(2)Ga][GaCl(4)] (4), the X-ray crystal structure of which revealed a four-coordinate cationic gallium center featuring two Ga-C sigma-bonds and two N-->Ga dative bonds. (Crystal data for 4: monoclinic, space group P2(1)/n, a = 11.519(2) ?, b = 18.254(4) ?, c = 12.506(3) ?, beta = 117.40(3) degrees, V = 2334.6(9) ?(3), Z = 4, R = 0.545). Two Ga.Cl interionic contacts, while somewhat long, are sufficiently strong to render the geometry of 4(+)() roughly midway between tetrahedral and octahedral. Treatment of 1,4-di-tert-butyl-1,4-diazabutadiene (DAB) with 2 equiv of GaCl(3) afforded [(DAB)GaCl(2)][GaCl(4)] (7), which, by means of X-ray analysis, was shown to possess a cation (7(+)()) with localized C=N bonds and N-->Ga dative interactions with a [GaCl(2)](+) moiety. (Crystal data for 7: orthorhombic, space group Pbca, a = 11.882(2) ?, b = 17.289(3) ?, c = 20.424(4) ?, V = 4195.5(11) ?(3), Z = 8, R = 0.460). The structure of 7(+)() is relevant to discussions of the bonding in both neutral DAB complexes of the group 13 elements and the skeletally isoelectronic anion [Me(4)C(4)GaCl(2)](-) (9(-)()). The structure of the [NEt(4)](+) salt of the latter (9) has been determined by X-ray diffraction. (Crystal data for 9: monoclinic, space group P2(1)/n, a = 9.967(1) ?, b = 13.073(2) ?, c = 15.345(2) ?, beta = 96.76(1) degrees, V = 1985.5(4) ?(3), Z = 4, R = 0.721).