Phosphine Substitution in (η5-Cyclopentadienyl)bis(triphenylphosphine)cobalt(I): Evidence for a Dissociative Mechanism

Article abstract of DOI:10.1021/ja00396a036

The substitution of trimethylphosphine for triphenylphosphine in (η⁵-cyclopentadienyl)bis(triphenylphosphine)cobalt(I) (1) to form (η⁵-cyclopentadienyl)(trimethylphosphine)(triphenylphosphine)cobalt(I) was studied at -60 deg C by NMR spectrometry.Kinetic measurements show the process to be first order in 1 and zero order in PMe3; added PPh3 strongly inhibits the reaction rate.This information indicates the reaction proceeds by rapid reversible phosphine dissociation through the unsaturated CpCo(PPh3) intermediate.The rate for generation of that intermediate, k₁, is 1.15*10^-3 s^-1 while the ratio of rate constant k₂ (for conversion of intermediate to products) to k_-1 (return to starting materials) is 4 at -60 deg C.Possible structures for CpCo(L) are discussed in light of recent indications that the linear structure has a triplet ground state.