New molybdenum catalysts for alkyl olefin epoxidation. Their implications for the mechanism of oxygen atom transfer

We report here the design, synthesis, and characterization of new (dioxo)Mo (VI) epoxidation catalysts based on monoanionic tridentate ligands. Two imp ortant features distinguish these catalysts from those previously reported. First, their coordination environment remains well-defined during the epox idation reaction. Second, the ligand design does not permit simultaneous co ordination of olefin and alkyl hydroperoxide. Based on the study of these n ew catalysts, we conclude that direct oxygen atom transfer from coordinated alkyl peroxide to olefin remains the simplest mechanism consistent with th e available data. We discuss literature discrepancies in this regard.