Mononuclear and Binuclear Cyclopentadienyl Oxo Molybdenum and Tungsten Complexes: Syntheses and Applications in Olefin Epoxidation Catalysis

International audienceNew half-sandwich molybdenum complexes [Mo(CpBz)Cl2(O)] (1), [{Mo(CpBz)(O)2}2(μ-Ο)] (5), and [Mo(CpBz)Cl2]2 (6) (CpBz = C5(CH2Ph)5), the tungsten derivative [W(CpBz)Cl(O)2] (3), and a high yield synthesis of [Mo(CpBz)Cl(O)2] (2) are described. The molecular structures and cyclic voltammetry measurements of 1 and 2 and a comparative study of various molybdenum dioxo complexes as olefin epoxidation catalyst precursors are also presented. The performance of [Mo(CpPri4)Cl(O)2] (9) as cyclooctene epoxidation catalyst using TBHP as oxidant was determined and compared with other [MoCp‘Cl(O)2] complexes (Cp‘ = C5H5 (7), C5Me5 (8), CpBz (2)) to assess the activity dependence on the ring substituents. Under the same experimental conditions, bimetallic compounds [{MoCp‘(O)2}2(μ-Ο)] (Cp‘ = CpBz (5), Cp* (10), CpBut3 (11), CpPri4 (12)) have been tested and [CpMoO2]2O was checked in aqueous solution, with H2O2 and TBHP as oxidant. Finally, [Mo(CpBz)(CO)3CH3] (4) was used as a catalyst precursor for cyclooctene epoxidation in the presence of TBHP. The analogy between the behaviors displayed by this complex and complex 2 is discussed