Kinetics and Mechanism of Phosphine Substitution for CO in (-)

Article abstract of DOI:10.1021/ja00191a021

Rate laws and activation parameters were determined for CO substitution of by phosphine ligands.These results along with the dependence of the reaction on the nature of the incoming ligand support an associative mechanism.Previous NMR data indicate that the phosphines selectively attack the Co metal center.Activation parameters are ΔH(excit.) = +7.2 to +10.3 kcal/mol and ΔS(excit.) = -34.0 to -45.5 cal/mol K.The activated complex is proposed to attain an open structure by breaking either a metal-metal or metal-carbon bond.An increase insolvent polarity increases the rate of ligand substitution, whereas a change in the cation from PPN(+) to Me4N(+) has a negligible effect.The rates of reaction were influenced by both the basicity and steric properties of the phosphines.