Photochemical reactions of fac-[Mn(CO)3(phen)imidazole]+: evidence for long-lived radical species intermediates.

The electronic absorption spectrum of fac-[Mn(CO)3(phen)imH]+, fac-1 in CH2Cl2 is characterized by a strong absorption band at 378 nm (emax = 3200 mol−1 L cm−1). On the basis of quantum mechanical calculations, the visible absorption band has been assigned to ligand-to-ligand charge-transfer (LLCT, im→phen) and metal-to-ligand charge-transfer (MLCT, Mn→phen) charge transfer transition. When fac-1 in CH2Cl2 is irradiated with 350 nm continuous light, the absorption features are gradually shifted to represent those of the meridional complex mer-[Mn(CO)3(phen)imH]+, mer-1 (λmax = 556 nm). The net photoreaction under these conditions is a photoisomerization, although, the presence of the long-lived radical species was also detected by 1H NMR and FTIR spectroscopy. 355 nm continuous photolysis of fac-1 in CH3CN solution also gives the long-lived intermediate which is readly trapped by metylviologen (MV2+) giving rise to the formation of the one-electron reduced methyl viologen (MV•+). The UV−vis spectra monito...