Understanding the CO Dissociation in [Fe(CN)₂(CO)₂(dithiolate)]^2- Complexes with Quantum Chemical Topology Tools

The active site of the [NiFe]-hydrogenase contains a pentacoordinated iron atom; therefore, a vacant coordination site is available for substrate binding. Nonetheless, most organometallic models of the [NiFe]-hydrogenase failed to reproduce this key feature of the active site. In order to rationalize such behavior, quantum chemical calculations were carried out on a series of [Fe(CN)₂(CO)_n(dithiolate)]^2- n = 1,2 complexes, where dithiolate denotes the ligands (CF₃)₂C₂S₂^2-, (CO₂Me)₂C₂S₂^2-, Ph₂C₂S₂^2-, C₆Cl₂H₂S₂^2-, C₆H₄S₂^2-, C₂H₄S₂^2-, and C₃H₆S₂^2-. Structural and energetic features are discussed, and a topological analysis based on two scalar fields, the one-electron density and the electron localization function (ELF), has been attempted to describe the nature of the metal-ligand bonds. The present approach contributes to better understand the ability of noninnocent dithiolene to strongly labilize one CO whereas innocent dithiolate cannot. The methodology developed throughout the paper could be useful in the field of the CO-releasing molecules.