Increasing the CO-Release Photosensitivity of Mn(I) Carbonyl Complexes Towards Longer Wavelengths by Electronically Tuning Their Schiff Base Ligands

Abstract

Five novel manganese (I) tricarbonyl complexes were synthesized by the reaction of Mn (CO)₅Br with quinoline-2-carboxaldehyde and different anilines. The IR, UV, and myoglobin results indicate that these complexes can be used as photoCORMs (photo photoinduced carbon monoxide releasing molecules) activated by red light. The visible range spectra display strong charge transfer (CT) bands, the maxima of which are sensitive to the ligand substituents. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations show that these CT transitions are admixtures of metal-to-ligand and aniline-to-quinoline charge transfers and that increasing the electron-donating ability on the aniline functionality can lead to shifts in the absorption bands of the corresponding compounds to longer wavelengths and to enhanced band intensities, thus enhancing their photoactivity. Photolysis of these complexes in aerobic solution leads to CO photodissociation followed by oxidation of the Mn(I) center to Mn(II).