Octahedral metal carbonyls: Reactions and bonding. VII. Kinetics of the substitution reactions of 2,5-dithiahexane complexes of chromium hexacarbonyl and molybdenum hexacarbonyl

Article abstract of DOI:10.1021/ic50061a040

The complexes (DTH)Cr(CO)₄ and (DTH)Mo(CO)₄ (DTH = 2,5-dithiahexane) react with phosphites with the replacement of the bidentate ligand to yield cis- and trans-(phosphite)₂M(CO)₄ complexes according to a second-order rate law. Activation parameters and previous results suggest, however, that the reactions of the two complexes occur substantially through different mechanisms, the Cr reaction proceeding through a preequilibrium step involving the dissociation of one end of the bidentate ligand followed by attack on the resulting five-coordinate species, with the Mo reaction proceeding through the formation of a seven-coordinate intermediate. Reaction rates vary according to the steric nature of the various phosphite ligands employed; the results obtained are computed to those previously obtained for similar systems and are discussed in terms of σ- and π-bonding properties of the bidentate ligands.