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

Detailed kinetic data are reported for the monosubstitutions of Co^sub 4^(CO)^sub 12^ with phosphite ligands: P(OMe)^sub 2^Ph, P(OMe)Ph^sub 2^, P(OPr-i)^sub 3^ and P(OPh)^sub 3^, studied by conventional methods in CHCl^sub 3^ as solvent. The reaction rates suggest parallel pathways of dissociation (k^sub 1^) and association (k^sub 2^) and show predominantly an association pathway, the low values of ΔH^sup [double dagger]^ and negative ΔS^sup [double dagger]^ 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 CHC1^sub 3^ and the O atoms of the ligands [J. Wang et al., J. Coord. Chem., 23, 345 (1991)]. The results of the reactions of Co^sub 4^(CO)^sub 12^ with P(OMe)^sub 3^, P(OMe)^sub 2^Ph and P(OMe)Ph^sub 2^ in this paper suggest that no quantitative relation exists between the O atoms in the ligand and the reaction rate.[PUBLICATION ABSTRACT]