Ligand-Tuned Mn(I) Complexes with Oxazole, Thiazole, and Selenazole Scaffolds: Synthesis and Mechanistic Insights into Light-Driven CO Release

Photoactivated carbon monoxide-releasing molecules (photo-CORMs) enable spatiotemporal control of CO delivery with therapeutic potential. We report a series of ten Mn(I) tricarbonyl complexes ( 1 – 10 ) incorporating oxazole-, thiazole-, and selenazole-based ligands, including π-extended quinoline derivatives. All complexes adopt a fac -{Mn(CO) 3 } geometry, and photophysical studies revealed MLCT absorption bands at 416–470 nm, tunable by heteroatom identity and ligand conjugation. Kinetic analyses showed first-order CO release, with thiazole-containing complexes releasing the fastest, oxazole analogs the slowest, and selenazole species intermediate. The pyridine-oxazole complex ( 1 ) displayed the slowest and more equivalent of CO release ( t 1/2 = 8.17 ± 0.02 s). While pH and temperature exerted minimal influence, solvent polarity and excitation wavelength strongly modulated the CO release rates. Mechanistic investigations combining spectroscopy and TD-DFT confirmed that MLCT excitation weakens Mn–CO backbonding, promoting CO dissociation. In biological studies, all complexes in the dark, after light trigger, and their iCORMs were nontoxic up to 40 μM. The complexes capable of light-triggered CO release have been studied using the CODP-106 probe in HeLa cells. These findings define clear structure–reactivity relationships and identify sulfur- and selenium-containing ligands (such as the ones in 2 and 3 ) as promising scaffolds for efficient Mn(I) photo-CORMs in biomedical contexts.