STERIC AND ELECTRONIC EFFECTS IN LIGAND SUBSTITUTION OF METAL CARBONYLS. RAPID KINETICS OF LABILE CARBONYLMANGANESE COMPLEXES BY TRANSIENT ELECTROCHEMICAL TECHNIQUES.

Article abstract of DOI:10.1021/ja00325a011

The ligand substitution kinetics of a series of carbonylmanganese cations MeCpMn(CO)//2L** plus with L equals 3- and 4-substituted pyridine ligands are measured for a variety of phosphine nucleophiles N of differing steric and electronic properties. The unified free energy relationship is shown for the first time to accommodate all the extensive rate data, if the steric effect is evaluated by Tolman's cone angles for the phosphines, and the electronic effects are evluated by the acid-base dissociation constants of the pyridine ligands and the phosphine nucleophiles. The range of second-order rate constants k//1 for ligand substitution of MeCpMn(CO)//2L** plus extends over four decades from 3. 0 to 2 multiplied by 10**4 M** minus **1 s** minus **1. The mechanism of ligand substitution of metal carbonyls is central to the successful catalysis of a variety of important processes leading to the reduction of carbon monoxide.