Synthesis and characterization of HC{C(Me)N(C6H3-2,6-i-Pr-2)}(2)MX2 (M = Al, X = Cl, I; M = Ga, In, X = Me, Cl, I): Sterically encumbered beta-diketiminate group 13 metal derivatives

Abstract

series of group 13 metal complexes featuring the beta -diketiminate ligand [((C6H3-2,6-i-Pr-2)NC(Me))(2)CH](-) (i.e., [Dipp(2)nacnac](-), Dipp = C6H3-2,6-i-Pr-2) have been prepared and spectroscupically and structurally characterized. The chloride derivatives Dipp(2)nacnacMCl(2) (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 Dipp(2)nacnacMI(2) (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 Dipp(2)nacnacAlMe(2) with I-2, whereas the gallium analogue 6 was obtained as a product of the reaction of "GaI" with Dipp(2)nacnacLi . Et2O, and 9 was obtained by direct reaction of InI3 and the lithium salt. The methyl derivatives Dipp(2)nncnacMMe(2) (M = Ga (7), In (10)), which are analogous to the previously reported Dipp(2)nacnacAlMe(2), were synthesized by the reaction of GaMe3 with Dipp(2)nacnacH (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 Dipp(2)nacnac 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 H-1 and C-13 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 H-1 NMR time scale.