CO-photorelease studies: effect of different thioether moieties on tricarbonyl manganese(I) compounds

Abstract

Manganese(I) tricarbonyl complexes bearing different thioether moieties were synthesized and evaluated to elucidate the electronic factors governing CO photorelease. Although variations in sulfur coordination (pendant vs. bound) and trans-ligand identity influence Mn-CO interactions, combined spectroscopic, photochemical, and computational analyses reveal that ligand π-conjugation is the dominant parameter controlling photoreactivity. The imine-containing complex displays a quantum yield (ΦCO = 49.5 × 10−3) nearly fivefold higher than its reduced amine analogue (ΦCO = 8.98 × 10−3), consistent with enhanced MLCT character and more efficient weakening of Mn → CO π-backbonding upon excitation. In contrast, substitution of Br by coordinated sulfur (ΦCO = 4.20 × 10−3) or variation in sulfur coordination mode (ΦCO = 2.35 × 10−3) results in comparatively modest changes in CO-release efficiency. These findings establish a clear hierarchy of design parameters in this series, where ligand conjugation outweighs trans-ligand identity and sulfur coordination mode in determining photochemical performance.