Synthesis and Characterization of HC{C(Me)N(C6H3-2,6-i-Pr2)}2MX2 (M = Al, X = Cl, I; M = Ga, In, X = Me, Cl, I): Sterically Encumbered β-Diketiminate Group 13 Metal Derivatives

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Abstract
A series of group 13 metal complexes featuring the β-diketiminate ligand [{(C6H3-2,6-i-Pr2)NC(Me)}2CH]- (i.e., [Dipp2nacnac]-, Dipp = C6H3-2,6-i-Pr2) have been prepared and spectroscopically and structurally characterized. The chloride derivatives Dipp2nacnacMCl2 (M = Al (3 ), Ga (5 ), In (8)) were isolated in good yield by the reaction of 1 equiv of Dipp2nacnacLi·Et2O (2) and the respective metal halides. The iodide derivatives Dipp2nacnacMI2 (M = Al (4 ), Ga (6 ), In (9)), which are useful for reduction to afford M(I) species, were made by a variety of routes. Thus, 4 was obtained by treatment of the previously reported Dipp2nacnacAlMe2 with I2, whereas the gallium analogue 6 was obtained as a product of the reaction of “GaI” with Dipp2nacnacLi·Et2O, and 9 was obtained by direct reaction of InI3 and the lithium salt. The methyl derivatives Dipp2nacnacMMe2 (M = Ga (7 ), In (10)), which are analogous to the previously reported Dipp2nacnacAlMe2, were synthesized by the reaction of GaMe3 with Dipp2nacnacH (1) or by reaction of the indium chloride derivative 8 with 2 equiv of MeMgBr in diethyl ether. The compounds 3 − 10 exist as colorless, air- and moisture-sensitive crystalline solids. Their X-ray crystal structures feature nearly planar C3N2 arrays in the Dipp2nacnac ligand backbone with short C−C and C−N distances that are consistent with a delocalized structure. However, there are large dihedral angles between the C3N2 plane and the N2M metal coordination plane which have been attributed mainly to steric effects. The relatively short M−N distances are consistent with the coordination numbers of the metals and the normal/dative character of the nitrogen ligands. The compounds were also characterized by 1H and 13C NMR spectroscopy. 1H NMR data for 7 revealed equivalent methyl groups whereas the spectrum of 10 displayed two In−Me signals which indicated that ring wagging was slow on the 1H NMR time scale.

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