Synthesis and characterization of [Me(2)M-mu-N(H)NMe(2)](2) (M = Al, Ga). Crystal structure of trans [Me(2)Al-mu-N(H)NMe(2)](2)

Abstract

Reactions of MMe3 (M = Al, Ga) with 1 equivalent of NH2NMe2 afford respective dimeric [Me2M-mu-N(H)NMe2](2) (M = Al (1), M = Ga (2)) complex as a mixture of trans and cis isomers. Purifications of 1 by sublimation and 2 by recrystallization give only trans isomers 1a and 2a, respectively. Variable-temperature H-1 NMR studies reveal that both 1 and 2 undergo fast cis-trans isomerization with free energy of activation (Delta G(c) double dagger), 9.3 kcal/mol for 1 and 15.6 kcal/mol for 2. The trans isomer 1a has been determined by a single-crystal X-ray diffraction study. The molecular geometry of 1a consists of a centrosymmetric and dimeric unit with two bridging hydrazido groups and two terminal methyl groups bound to each aluminum atom. The two N-NMe2 groups are trans to each other with respect to the (Al-N)(2) ring. The coordination geometry of both the aluminum and nitrogen atoms is distorted tetrahedral. (C) 1997 Elsevier Science S.A.