Structures of binary carbonyls and related compounds. Part 1. A new approach to fluxional behaviour

Abstract

The different types of carbonyl scrambling observed in [M₄(CO)₁₂](M = Co, Rh, or Ir) compounds and substituted derivatives may be explained in terms of a single type of process. The initial icosahedral arrangement of ligands rearranges along a well defined reaction co-ordinate via a cubo-octahedral transition state; the existence of different patterns of carbonyl scrambling then arises as a consequence of the geometrical disposition of the metal-atom tetrahedron within the ligand polyhedron. Rather than using a different ad hoc mechanism to rationalise each observed fluxional process, this is a single type of carbonyl-scrambling path involving the concerted motion of all the atoms in the molecule in ways that are well defined in terms of molecular geometry.