Structure and bonding of d8 allyl complexes M(η3- allyl)L3 (M = Co, Rh, Ir; L = phosphine or carbonyl)

Abstract

Density functional theory calculations were used to study structure and bonding of d8 five-coordinate allyl complexes M(η3- allyl)L3 (M = Co, Rh, Ir; L = phosphine or carbonyl). In these pseudo-square-pyramidal d8 complexes, we found that only the exo structures correspond to energy minima on the potential energy surface. The exo structures are able to maximize the metal(d)-to-allyl(π*) back-bonding interaction. The calculations predicted that the endo structures for the Ir and Co complexes are transition states for interconversion of two different exo structures. Complexes such as Ir(η3-allyl)(PMe3) 3 having only phosphines as the ancillary ligands possess the strongest metal-allyl bonding interaction, while complexes such as Co(η3-allyl)(CO)3 having only carbonyls have the weakest interactions. We also studied the η3 → η3 → η3 and η3 → η1 → η3 rearrangements of the allyl ligand and found that both the rearrangement mechanisms are energetically feasible for the d8 complexes studied in this paper. Show more