Implication of oxidant activation on olefin epoxidation catalysed by Molybdenum catalysts with aroylhydrazonato ligands: Experimental and theoretical studies

Abstract

• Dinuclear and mononuclear molybdenum(VI) complexes with aroylhydrazonato ligands were tested as catalysts for cyclooctene and oct-1-ene epoxidation. • TBHP in decane provided outstanding results in terms of cyclooctene epoxidation: TOF 2.5 min >9000 with 0.25 mol % [Mo] loading. • DFT calculations confirmed the relationship between the ligand nature and reactivity with TBHP and H 2 O 2 as oxidant agents. Dinuclear and mononuclear molybdenum(VI) complexes with aroylhydrazonato ligands were studied as catalysts for cyclooctene and oct-1-ene epoxidation. Different isomers of the OH and NH 2 functionalised aroylhydrazones led to four specific [MoO 2 L] units showing different catalytic activity. Three oxidants have been investigated: tert -butylhydroperoxide (TBHP) in water or in decane, and hydrogen peroxide (H 2 O 2 ). Catalytic processes with TBHP in decane provided outstanding results in the case of cyclooctene epoxidation: TOF 2.5 min > 9000 with 0.25 mol % [Mo] loading. DFT calculations confirmed the relationship between the ligand nature and reactivity with TBHP and H 2 O 2 as oxidant agents. In the case of TBHP as oxidant, calculations considered the solvent in which the oxidant is delivered to the olefin. A plausible mechanism with H 2 O 2 has been proposed after considering various pathways.