Synthesis and characterization of [Me2M-μ-N(H)NMe2]2 (M = Al, Ga). Crystal structure of trans [Me2Al-μ-N(H)NMe2]2

Abstract Reactions of MMe 3 (M = Al, Ga) with 1 equivalent of NH 2 NMe 2 afford respective dimeric [Me 2 M- μ (H)NMe 2 ] 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 1 H NMR studies reveal that both 1 and 2 undergo fast cis-trans isomerization with free energy of activation (Δ G c ‡ ), 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−NMe 2 groups are trans to each other with respect to the (Al−H) 2 ring. The coordination geometry of both the aluminum and nitrogen atoms is distorted tetrahedral.