Pathway bifurcations in the cage rearrangement of metallacarboranes: experimental and computational evidence.

Thirteen new metallacarborane complexes of rhodium and iridium with covalently bound cage carbon atoms were synthesized and their thermal stability was investigated. Two iridium complexes undergo a polyhedral rearrangement with the formation of more than one isomer. The structures of the new isomers were determined by a single crystal X-ray diffraction analysis and B{H}-B{H} COSY NMR. A full isomerization scheme of the less thermally stable complex was proposed based on DFT calculations. According to this mechanism sequential downhill and uphill bifurcations arise in the reaction pathway. Each bifurcation is responsible for a new product formation.