Kinetics and mechanism of halide promoted migratory CO insertion of fac-[FeMe{o-C6H4(AsMe2)2}(CO)3]ClO4

Abstract

The kinetics for the iodide and bromide promoted carbonyl insertion of fac-[FeMe{o-C₆H₄(AsMe₂)₂}(CO)₃]ClO₄ have been examined at +10 °C in methylene chloride, acetone, and mixed aqueous–acetone solvents. In the presence of excess halide the insertion rate is first order in Fe substrate. The pseudo-first-order rate constants, K_obs. show a complicated dependence both on halide concentration and on solvent, which is analysed in terms of a mechanism involving a pre-equilibrium ion-pair formation between the cationic substrate complex and the promoting halide. The proposed mechanism is used to account for the known solvent-dependent regiospecificity of the insertion.