Monomeric, Mononuclear Enediolate Complexes of Zirconium: Molecular Geometry and Electronic Structure of the Products of Reductive CO Coupling on the Metal

A transition from σ2, π to σ2 coordination occurs in going from R  Me to R  tBu in the zirconium complexes 1, Cp* = C5Me5. The chelate ring is folded in the first case and planar, for steric reasons, in the second. This observation is in accord with the predictions of MO theory.