Synthesis and structures of mononuclear and dinuclear gallium complexes with α-diimine ligands: reduction of the metal or ligand?

Reduction of the dichloro gallium(III) alpha-diimine complex [(L-ipr)center dot-GaCl2] (1, L-ipr = [(2,6-iPr(2)C(6)H(3)) NC(Me)](2)) by different equivalents of sodium metal afforded the gallium complexes [(L-ipr)Ga-2-(III)(mu(2)-Cl)(2)Na(THF)(4)] (2) and [(Na(THF)(6))(+)center dot((L-ipr)Ga2--Ga(L-ipr)(2-))(center dot-)] (3). Interestingly, in complex 2 a Na+Cl- ion pair is incorporated, while compound 3 is an anionic digallium complex. Moreover, a cationic gallium complex with a tetrachlorogallium(III) counter anion, [(LGaCl2)(+)center dot(GaCl4)(-)] (4), was accessed from the reaction of GaCl3 with 0.5 equiv. of ligand L-ipr. In contrast, the reaction of GaCl3 with the doubly reduced anion (Na2L2-) of the smaller a-diimine ligands L-Me ([(2,6-Me2C6H3) NC(Me)] 2) or L-Et ([(2,6-Et2C6H3) NC(Me)](2)) yielded the Ga-Ga-bonded complexes [(L-Et)(center dot-ClGaII)-(GaCl)-Cl-II(L-Et)(center dot-)] (5) and [(L-Me)(center dot-ClGaII)-(GaCl)-Cl-II(L-Me)(center dot-)] (6). Here L is the neutral alpha-diimine ligand, L(center dot-)represents the monoanion, and L2- is the dianionic form of the ligand. The complexes were characterized by X-ray diffraction and their electronic structures were studied by DFT computations.