Synthesis and Structures of Mono- and Bis(amidinate) Complexes of Aluminum

Abstract

The synthesis and structures of mono- and bis(amidinate) aluminum complexes are described. The reaction of AlMe 3 and 1 equiv of carbodiimide, R‘N C NR‘, affords {MeC(NR‘) 2 }AlMe 2 ( 1a, R‘ = i Pr; 1b, R‘ = Cy = cyclohexyl). The reaction of R‘N C NR‘ with MeLi or t BuLi generates Li[RC(NR‘) 2 ] ( 2a, R = Me, R‘ = i Pr; 3a, R = t Bu, R‘ = i Pr; 3b, R = t Bu, R‘ = Cy; 3c, R = t Bu, R‘ = SiMe 3 ). 2a, 3a, and 3b may be isolated or reacted in situ, while attempted isolation of 3c gave [Li( t BuCN){μ-N(SiMe 3 ) 2 }] 2 ( 3d ). The reaction of 1 equiv of AlCl 3 with 2a or 3a − c affords {RC(NR‘) 2 }AlCl 2 ( 4a, R = Me; 5a − c, R = t Bu), and the reaction of AlMe 2 Cl with 3a − c affords { t BuC(NR‘) 2 }AlMe 2 ( 6a − c ). Alkylation of 5a, b with 2 equiv of PhCH 2 MgCl or Me 3 CCH 2 Li yields { t BuC(NR‘) 2 }Al(CH 2 Ph) 2 ( 7a, b ) or { t BuC(NR‘) 2 }Al(CH 2 CMe 3 ) 2 ( 8a, b ). The reaction of 0.5 equiv of AlCl 3 with 2a or 3a, b yields {RC(NR‘) 2 } 2 AlCl ( 9a, R = Me; 10a, b, R = t Bu). Complexes 1b, 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 R and R‘ groups influence the R‘−N−Al angle and, hence, the steric environment at aluminum.