Epoxidation of cis-cyclooctene using diamine bis(phenolate) vanadium, molybdenum and tungsten complexes as catalysts

The dioxomolybdenum and dioxotungsten complexes [MoO2L1] (1-Mo) and [WO2L1] (2-W), supported by a diamine bis(phenolate) ligand (L1 = Me2NCH2CH2N(CH2-2-O-3,5-C6H2tBu2)2) were prepared from MoO2Cl2 and WO2Cl2(dme) in good yields. The solid-state structures of both compounds obtained by single crystal X-ray diffraction reveal distorted octahedral geometries around the metals with cis terminal oxo ligands. Their performance in the catalytic epoxidation of cis-cyclooctene using H2O2 and TBHP as oxidants was evaluated. 2-W displays high activity with H2O2 as terminal oxidant, achieving 84% conversion in 6 h (TOF = 1400 molsub molcat−1 h−1), while its molybdenum counterpart 1-Mo was inactive in the same conditions. Using TBHP as oxidant the opposite trend was observed and 1-Mo attained 93% conversion in 6 h (TOF = 1550 molsub molcat−1 h−1). The Oxovanadium complexes [VOL1Cl] (3-V), [VOL2Cl] (4-V, L2 = Me2NCH2CH(CH3)N(CH2-2-O-3,5-C6H2tBu2)2) and [(VOL1)2(μ-O)] (5-V) were also tested as catalysts in the epoxidation of cis-cyclooctene. The three compounds display high activity when the epoxidation reaction is performed using TBHP as oxidant. Using H2O2, 3-V and 4-V are moderately active while 5-V is inactive.