Pyridyl 'ring-flipping' in the dimers [Me2E(2-py)]2 (E=B, Al, Ga; 2-py=2-pyridyl)

The boron and aluminium dimers Me2E(micro-py)]2 E=B (1); Al (2)] are formed as mixtures of two isomers in which the group 13 centres are coordinated by the bridging 2-py ligands in a cis or trans manner, however, in contrast to previous studies, we find that simply heating the mixtures of these isomers of and gives the more thermodynamically stable (synthetically useful) trans isomers exclusively (the trans isomer being the only product in the case of the gallium analogue ).