Trans–cis isomerization and structure of dimeric [Me2M-μ-N(H)NPh2]2 (M=Al, Ga)

Reaction of MMe3 (M=Al, Ga) with one equivalent of NH2NPh2 affords a dimeric complex [Me2M-μ-N(H)NPh2]2 [M=Al (1), M=Ga (2)] as a mixture of trans and cis isomers. Purification of 1 and 2 by recrystallization gives only trans isomers 1a and 2a, respectively. Variable-temperature 1H-NMR studies reveal that both 1 and 2 in solution undergo trans→cis isomerization with free energy of activation (ΔGc‡) values of 15.9 for 1 and 18.3 kcal mol−1 for 2. The solid state structures of trans isomers 1a and 2a have been determined by single-crystal X-ray diffraction studies. The molecular geometries of 1a and 2a consist of a centrosymmetric and dimeric unit (MN)2 with two bridging hydrazido groups and two terminal methyl groups bound to each metal atom. The two NNPh2 groups are trans to each other with respect to the (MN)2 core plane. The coordination geometry of both metal and nitrogen atoms are distorted tetrahedral.