KINETIC STUDIES OF LEWIS BASE ADDITION TO CpFe(CO)(η³-CH₂C₆H₄-p-X); X = OMe, Me, H,F, Cl, Br

Abstract

Abstract Kinetic studies illuminate details of the reaction of photoproduced CpFe(CO)(η3-CH2C6H5) with two electron Lewis bases. Rate constants of 151(10)M−1s−1 for CO back reaction and between 440 and 3200 M−1s−1 for reaction with various phosphine nucleophiles were recorded. Linear free energy analysis quantifies the stereoelectronic effect of the nucleophile. Variation of the para-substituent on the benzyl group demonstrates that an electron rich benzyl group impedes reaction. The effect of ancillary ligands was seen by substitution of C5Me5 for C5H5. The large, electron rich C5Me5 speeds up CO substitution but slows down PPh3 substitution. Mechanistic clues were obtained from Eyring plots for reaction of CpFe(CO)(η3-CH2C6H5) with 4 different phosphines. Examination of the measured enthalpy and entropy barriers suggests a stepwise reaction mechanism.