This project is concerned with developing new strategies for the delivery of carbon monoxide to physiological targets. The first generation of photoCORMs (photo-activated carbon monoxide releasing molecules) typically required photo-excitation of metal carbonyl ligand field (LF) states, which labilize CO release through weakening both σ and π bonding between metal and carbonyl. However, LF transitions of such species are usually high energy and require UV or shorter visible wavelengths that have the disadvantage of poor penetration into mammalian tissue and can cause collateral damage to living cells. In this work, we synthesized four rhenium-manganese dinuclear metal carbonyl complexes: Re(CO)5Mn(CO)3(bipyridine) (1), Re(CO)5Mn(CO)3(phenanthroline) (2), Re(CO)5Mn(CO)3(biquinoline) (3), (bipyridine) (CO)3ReMn(CO)5 (4). For the complexes, the metal-metal (M-M) bond is the most labile bond, and the homolytic cleavage of this bond can occur through the photo-excitation of a σMMb to σMM* transition. However, complexes such as 1-4 having the conjugated diimine ligands (L) also display σMMb to πL* charge transfer bands at longer visible, more penetrating wavelengths. Photolysis of these metal-metal to ligand charge transfer (MMLCT) also leads to homolytic cleavage of the M-M bond to generate the mononuclear metal radicals. Although the radicals themselves are unlikely to be particularly reactive toward CO release, they have proved to be reactive with dioxygen to form metal oxides, at the same time to form species that are much more labile toward CO release. In this context, we are studying photochemistry of these dinuclear carbonyl complexes and their potential as visible light or near-IR light activated photoCORMs.

Rhenium-manganese dinuclear carbonyl complexes as long wavelength absorbing photoCORMs

251st National Meeting (2016)

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