Triosmium Cluster Bearing a Metalated Dibenzylideneacetone Ligand: Synthesis, Structure, Redox and Electronic Properties

Dibenzylideneacetone (DBA) reacts with [Os3(CO)10(NCMe)2] in boiling benzene to afford the triosmium cluster [Os3(CO)10{κ2-(C,O)-C17H13O}(µ-H)] (1) formed through activation of one of the β-C–H bond of the DBA ligand after initial coordination of the ketonic oxygen. The molecular structure of 1 has been determined unequivocally by single crystal X-ray diffraction analysis which reveals that the metalated DBA ligand formed a five-membered osmacycle by coordinating to a single osmium atom using its both donor atoms. Cluster 1 exhibits two closely spaced irreversible reduction peaks at –1.20 V and –1.30 V, respectively, together with an irreversible oxidation peak at 0.57 V. DFT calculations reveals the frontier orbitals are primarily either metal-based (HOMO) or ligand-based (LUMO) which suggests that the oxidation occurs from the metallic core while the first reduction is ligand-centered. Cluster 1 displays two absorption peaks at 337 nm and 477 nm in the UV-visible absorption spectrum. The lowest energy absorption at 477 nm can be attributed to the transition from HOMO to LUMO (MLCT) based on its frontier orbitals.