Mechanism of the reaction of chelated tricarbonyliron complexes of α,β-unsaturated Schiff bases with Group 5 ligands

Abstract

The complexes [Fe(CO)₃(η-PhCHCH–CHN–C₆H₄X)](X = H, or 4-NMe₂, -OMe, -Me, or -Br) react with phosphine ligands to give [Fe(CO)₂L (η-PhCHCH–CHN–C₆H₄X)]. The preparation of the phosphine derivatives is described. The kinetics of substitution by the phosphine ligands L (PPh₃ or PBuⁿ₃) are first order in the complex concentration and the pseudo-first-order rate constants vary with ligand concentration. The dependence of the rate constant on the concentration of ligand and the effects of temperature, of substituent X, and of the nature of ligand L pornt to a reaction mechanism having two paths, one associative wrth the ligand and the other dissociative involving a rapid η⁴⇌σ equilibrium of the reagent complex.