Dioxomolybdenum(VI) Complexes with Acylpyrazolonate Ligands: Synthesis, Structures, and Catalytic Properties

The complexes [Mo(O)2(QR)2] [R = cyclohexyl (1), ethylcyclopentyl (2), hexyl (3), and neopentyl (4)] have been obtained in good yields by treatment of [Mo(O)2(acac)2] with 2 equivalents of acylpyrazolone compounds HQR [HQR = 3‐methyl‐1‐phenyl‐4‐alkylcarbonyl‐5‐pyrazolone; R = cyclohexyl (HQCy), ethylcyclopentyl (HQEtCp), hexyl (HQHe), neopentyl (HQnPe)]. They were isolated as yellow crystalline solids and characterized spectroscopically [IR, 1H and 13C(1H) NMR] and structurally (X‐ray for 2 and 3). The deoxygenation of selected epoxide substrates to alkenes by employing compounds 1 and 3 as catalysts and PPh3 as the oxygen acceptor showed good activities in toluene. The use of the ionic liquid [C4mim]PF6 as solvent gave lower yields, but the resulting catalytic system could be conveniently recycled. The [Mo(O)2(QR)2] derivatives 1 and 3 were also found to be moderately active catalysts for the deoxydehydration of vicinal diols.