Coordination Chemistry of a Chelating Amidoximato Ligand

A potentially general strategy for accessing the rarely encountered coordination of amidoximates through both oximato O and amido N atoms was developed. The new amidoxime (Z)-R1C(NOH)NR2H (R1 = mesityl, R2 = 2-[{dimethylamino}methyl]phenyl), H2L, was prepared by reaction of equimolar amounts of the appropriate nitrile oxide and primary amine. Treatment of H2L with 1 equiv of AlMe3 produced the dimeric species (MeAlL)2 (1) possessing the formally dianionic ligand L2- bound to the aluminum via the oximato oxygen and the amido and amino nitrogens. The oximato oxygen atoms serve to link the two monomeric organoaluminum units together. Reaction of (ON)Cr(NiPr2)3 with H2L provided the diamagnetic complex (ON)Cr(NiPr2)(η3-L) (2). Interaction of 2 with excess methanol led, in particular, to the oxidative loss of NO and yielded the paramagnetic dimer [Cr(LH)(OMe)(μ-OMe)]2 (3) containing the η3-bound amidoximato ligand protonated at its oximato nitrogen. In addition to spectroscopic characterizations of the new substances, single-crystal X-ray structures of H2L, 1·4/3C6H6, and 3·MeOH were obtained.