SYSTEMATIC LIGAND EFFECTS ON THE RATES OF CO SUBSTITUTION OF (ETA-5-C5H4CO2ME)CO(CO)2

The reaction of (eta-5-C5H4CO2Me)Co(CO)2 with phosphines and phosphites gives the monosubstituted products (eta-5-C5H4CO2Me)Co(CO)L. The reaction proceeds solely by a second-order process, first order in metal complex and first order in the nucleophile. The effects of phosphorus(III) ligands on the kinetics of this reaction have been studied. The electronic profile shows the division of ligands into one group that shows no steric effects and another group that shows steric effects. The former includes alkylphosphines and mixed alkylarylphosphines as well as triaryl phosphites. The intrinsic reactivity and steric properties of (eta-5-C5Me5)Co(CO)2 and (eta-5-C5H4CO2Me)Co(CO)2 are compared. The carbomethoxy complex shows higher intrinsic reactivity and greater steric threshold (theta-st) and is more flexible than the pentamethyl complex.