Synthesis and structures of mono- and bis(amidinate) complexes of aluminum

The synthesis and structures of mono-and bis(amidinate) aluminum complexes are described. The reaction of AlMe3 and 1 equiv of carbodiimide, R'N=C=NR', affords {MeC(NR')(2)}AlMe2 (la, R' = Pr-i; Ib, R' = Cy = cyclohexyl). The reaction of R'N=C=NR' with MeLi or (BuLi)-Bu-t generates Li[RC(NR')(2)] (2a, R = Me, R' = Pr-i; 3a, R = Bu-f, R' = Pr-i; 3b, R = Bu-f, R' = Cy; 3c, R = Bu-t, R' = SiMe3). 2a, 3a, and 3b may be isolated or reacted in situ, while attempted isolation of 3c gave [Li((BuCN)-Bu-t){mu-N(SiMe3)(2)}](2) (3d). The reaction of 1 equiv of AlCl3 with 2a or 3a-c affords {RC(NR')(2))AlCl2 (4a, R = Me; 5a-c, R = Bu-t), and the reaction of AlMe2Cl with 3a-c affords {(BuC)-Bu-t(NR')(2))AlMe2 (6a-c). Alkylation of 5a,b with 2 equiv of PhCH2MgCl or Me3CCH2Li yields {(BuC)-Bu-t(NR')(2))Al(CH2Ph)(2) (7a,b) or {(BuC)-Bu-t(NR')(2))Al(CH2CMe3)(2) (8a,b). The reaction of 0.5 equiv of AlCl3 with 2a or 3a,b yields {RC(NR')(2)}(2)AlCl (9a, R = Me; 10a,b, R = Bu-t). Complexes Ib, 3d, 4a, 5a,b, 6b, 8b, 9a, and 10a,b have been characterized by X-ray crystallography. The crystallographic results establish that steric interactions between the IR and R' groups influence the R'-N-Al angle and, hence, the steric environment at aluminum.