Kinetics and mechanism of the displacement of CO from Co4(CO)12 by phosphite ligands

Abstract

Detailed kinetic data are reported for the monosubstitutions of Co4(CO)12 with phosphite ligands: P(OMe)2Ph, P(OMe)Ph2, P(OPr-i)3 and P(OPh)3, studied by conventional methods in CHCl3 as solvent. The reaction rates suggest parallel pathways of dissociation (k1) and association (k2) and show predominantly an association pathway, the low values of ΔH‡ and negative ΔS‡ adding further support to the proposed mechanism. It is also confirmed that the reaction rates are retarded due to hydrogen-bonding between the H atom of CHC13 and the O atoms of the ligands [J. Wang et al., J. Coord. Chem., 23, 345 (1991)]. The results of the reactions of Co4(CO)12 with P(OMe)3, P(OMe)2Ph and P(OMe)Ph2 in this paper suggest that no quantitative relation exists between the O atoms in the ligand and the reaction rate.