Periodic Trends and Fluxionality Effects on Transition Metal Catalyzed Sulfoxidation

Despite the extended interest in d⁰ metal complexes as catalysts for peroxide activation and eventual oxygen transfer processes, there are still gaps in the understanding of how they proceed at the microscopic level. Herein, we have considered sulfide oxidation with cumyl hydroperoxide as a test system, performing the reaction with a series of eight different aminotriphenolate d⁰ metal complexes: Ti(IV), Zr(IV), Hf(IV), V(V), Nb(V), Ta(V), Mo(VI), and W(VI). The reactivity and selectivity of the catalytic systems, as well as the effect of a strong Lewis base (dimethylhexyl-N-oxide), have been determined experimentally, correlating kinetic values with Sanderson electronegativity values. Theoretical calculations of the catalytic cycles have been performed to have a clearer description of the role of the reactive peroxo species. Combining experimental results and DFT predictions, we propose suitable mechanisms for all eight metal aminotriphenolates, rationalizing the expected periodic trends, while also unveiling the unique reaction pathways available to highly flexible vanadium complexes.