Mechanism of chelation of phenanthroline derivatives to Mo(CO)(5) deduced from pulsed photolysis studies in several solvents at high pressure

A laser flash-photolysis kinetic study has been carried out an the concentration, temperature and pressure dependence of chelation reactions of the type [Mo(CO)(5)(L-L)] --> [Mo(CO)(4)(L-L)] + CO, where L-L represents 1,10-phenanthroline (phen) and a series of substituted phen ligands in several solvents. The activation parameters for these thermal ring-closure reactions are sensitive to the nature of the solvent, as well as to electronic and steric effects arising from the phen ligand. All the observed kinetic effects can be accounted for by an interchange ligand-substitution mechanism during which CO is displaced by the chelate.