TIME-RESOLVED INFRARED SPECTRAL STUDIES OF INTERMEDIATES FORMED IN THE LASER FLASH-PHOTOLYSIS OF MN(CO)(5)CH3

Laser flash photolysis (308 nm) of Mn(CO)(5)CH3 (I) in different solvents leads predominantly to CO photodissociation and the formation of reactive intermediates formulated as the solvento 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 approximate to H2O approximate to THF > P(OMe)(3) approximate to PPh(3) > CO approximate to N-2. 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 eta(2)-acyl-coordinated intermediate rather than to a solvento complex.