KINETIC-STUDIES OF LEWIS BASE ADDITION TO CPFE(CO)(ETA-3-CH2C6H4-P-X)- X=OME, ME, H, F, CL, BR

Kinetic studies illuminate details of the reaction of photoproduced Cp Fe(CO)(eta3-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 fr ee energy analysis quantifies the stereoelectronic effect of the nucle ophile. Variation of the para-substituent on the benzyl group demonstr ates that an electron rich benzyl group impedes reaction. The effect o f ancillary ligands was seen by substitution of C5Me5 for C5H5. The la rge, electron rich C5Me5 speeds up CO substitution but slows down PPh3 substitution. Mechanistic clues were obtained from Eyring plots for r eaction of CpFe(CO)(eta3-CH2C6H5) with 4 different phosphines. Examina tion of the measured enthalpy and entropy barriers suggests a stepwise reaction mechanism.