Electrochemical Deoxygenation of a TiIV-Oxo Complex to Enable Catalytic Reductive Oxygen-Atom Transfer from Organic...

Well-defined (TTP)TiII (TTP = 5,10,15,20-tetratolylporphyrin) complexes have been shown to promote stoichiometric deoxygenation of organic molecules, such as sulfoxides and epoxides, forming a stable (TTP)TiIV=O product. Here, we explore strategies to promote catalytic deoxygenation reactivity by regenerating (TTP)TiII through chemical or electrochemical reduction. A survey of Lewis acids revealed the effectiveness of B(OPh)3 in promoting activation and loss of the Ti-oxo group, enabling TiII-mediated reductive oxygen-atom transfer (OAT) of diphenyl sulfoxide. Cyclic voltammetry, coulometry, EPR spectroscopy, and X-ray crystallography have been used to probe and characterize TiIII and TiII species from the electroreductive deoxygenation of the TiIV=O complex. The data implicate a Lewis-acid-coupled electron-transfer deoxygenation pathway for TiIV=O turnover. These fundamental studies are complemented by electrochemical reactions demonstrating catalytic reductive oxygen-atom transfer from sulfoxides, pyridine N-oxides, and epoxides.