Olefin Epoxidation Catalyzed by cis-Dioxdomolybdenum(VI) Complexes Containing Chiral Alkoxo-Imino Ligands Derived from (+)-α-Pinene

New chiral cis-dioxidomolybdenum compounds [MoO2(acac)(RN,O)] [R = Bn (1), pic (2)] and [{MoO2(acac)}2{mu-(O,N,N,O)}] (3) have been synthesized by treating [MoO2(acac)2] withthe corresponding enantiomerically pure alcohol-iminocompounds derived from (+)-a-pinene modification, (RN,OH) (R = Bn, pic) and (HO,N,N,OH), respectively. Compound [MoO2Cl2(O,N,N,O)] (4) has also been prepared. All the compounds were fully characterized both in solution and in the solid state, including by single-crystal X-ray diffraction analysis of enantiomerically pure 3. DFT studies support the stereoselectivity of the synthesis of compound 3. Catalytic olefin epoxidation studies were performed with cis-cyclooctene, (R)-limonene, and trans-beta-methylstyrene by using derivatives 14 as catalyst precursors and tert-butyl hydroperoxide (TBHP) or H2O2 as oxidant. All the catalytic systems showed high chemoselectivity irrespective of the terminal oxidant used. The molybdenum compounds exhibited medium to high catalytic activity at mild reaction temperatures, but no substantial optical induction was observed. This study represents the first use of chiral monoacetylacetonato-cis-dioxidomolybdenum compounds as homogeneous olefin epoxidation catalysts.