Mono-, di- and tri-metallic complexes of trimethylenemethane: an EHMO study of the TMM rotational barrier

The rotational barrier of a trimethylenemethane ligand relative to an Fe(CO)2L unit, where L  CO or a phosphine, is analyzed by molecular orbital calculations at the extended Hückel level. It is shown that the original Hoffmann-Albright model fits well for carbonyl complexes, but yields barriers for phosphine complexes that are too high. A rationale is presented to account for the different behavior of the bimetallic complexes …