Time-resolved infrared spectral studies of intermediates formed in the laser flash photolysis of Mn(CO)5CH3

Article abstract of DOI:10.1021/om00021a028

Laser flash photolysis (308 nm) of Mn(CO)₅CH₃ (I) in different solvents leads predominantly to CO photodissociation and the formation of reactive intermediates formulated as the solvente complexes cis-Mn(CO)₄(solv)CH₃. This conclusion is based upon the solvent sensitivity of the time-resolved infrared spectra and the dynamics of reactions with various ligands. For example, the reaction of cis-Mn(CO)₄(solv)CH₃ with CO displays second-order kinetics with a rate constant k_CO nearly 8 orders of magnitude larger for solv = perfluoro-(methylcyclohexane) than for solv = tetrahydrofuran. The k_L values for the second-order reaction of cis-Mn(CO)₄(solv)CH₃ in cyclohexane with various ligands L follow the approximate order 4-phenylpyridine ≈ H₂O ≈ THF > P(OMe)₃ ≈ PPh₃ ≈ CO ≈ N₂. The quantitative behaviors of intermediates seen in the flash photolysis of I are compared with those seen in similar studies of the acetyl complex Mn(CO)₅(COCH₃) (II) (Organometallics, 1993, 12, 4739-4741), and this comparison is used to substantiate the earlier conclusion that CO dissociation from II in weakly coordinating solvents leads to an η²-acyl-coordinated intermediate rather than to a solvento complex.