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

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Abstract
The metathetical reaction of 2-(dimethylamino)benzyllithium (BzNLi) with GaCl3 afforded the salt [BzN2Ga][GaCl4] (4), the X-ray crystal structure of which revealed a four-coordinate cationic gallium center featuring two Ga−C σ-bonds and two N→Ga dative bonds. (Crystal data for 4: monoclinic, space group P21/n, a = 11.519(2) Å, b = 18.254(4) Å, c = 12.506(3) Å, β = 117.40(3)°, V = 2334.6(9) Å3, 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 GaCl3 afforded [(DAB)GaCl2][GaCl4] (7), which, by means of X-ray analysis, was shown to possess a cation (7 +) with localized CN bonds and N→Ga dative interactions with a [GaCl2]+ moiety. (Crystal data for 7: orthorhombic, space group Pbca, a = 11.882(2) Å, b = 17.289(3) Å, c = 20.424(4) Å, V = 4195.5(11) Å3, 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 [Me4C4GaCl2]- (9 -). The structure of the [NEt4]+ salt of the latter (9) has been determined by X-ray diffraction. (Crystal data for 9: monoclinic, space group P21/n, a = 9.967(1) Å, b = 13.073(2) Å, c = 15.345(2) Å, β = 96.76(1)°, V = 1985.5(4) Å3, Z = 4, R = 0.721).