Redox-tagged carbon monoxide-releasing molecules (CORMs): Ferrocene-containing [Mn(C^N)(CO)4] complexes as a promising new CORM class

This study describes the synthesis and characterization of a new class of ferrocene-containing carbon monoxide-releasing molecules (CORMs, 1-3). The ferrocenyl group is both a recognized therapeutically viable co-ligand and a handle for informative infrared spectroelectrochemistry. Deoxy-myoglobin CO-release assays and in situ infrared spectroscopy confirm compounds 2 and 3 as photoCORMs and 1 as a thermal CORM, attributed to the increased sensitivity of the Mn-ferrocenyl bond to protonation in 1. Electrochemical and infrared spectroelectrochemical experiments confirm a single reversible redox couple associated with the ferrocenyl moiety with the Mn tetracarbonyl center showing no redox activity up to +590 mV vs Fc/Fc+, though no concomitant CO release was observed in association with the redox activity. The effects of linker length on communication between the Fe and Mn centers suggest the incorporation of redox-active ligands into CORMs focus on the first coordination sphere of the CORM. Redox-tagged CORMs could prove to be a useful mechanistic probe; our findings could be developed to use redox changes to trigger CO-release.