New monometallic dioxomolybdenum complexes, 2 and 3, containing the bis(oxazoline) B and the oxazolinyl-pyridine C respectively, have been prepared and fully characterized both in solution and solid state, including the single-crystal X-ray diffraction analysis for 2, which represents the first structure of a Mo(VI) complex coordinated to a bis(oxazoline). These complexes, together with the bimetallic system 1, were used as catalytic precursors for alkenes epoxidation (cyclooctene, (R)-limonene, trans-beta-methylstyrene) in imidazolium- and pyrrolidinium-based ionic liquids, exhibiting a high chemoselectivity towards the epoxide formation, mainly for cyclooctene and (R)-limonene epoxidation, without formation of the corresponding diols. In [BMP][NTf2] (BMP=butyl methyl pyrrolidinium: NTf2 = bis(trifluoromethanesulfonyl)amide), complex 1 exclusively gave trans(R)-limonene 1,2-epoxide, while monometallic catalytic systems led to a low diastereoselectivity. Mo-95 NMR studies helped to understand the catalytic behaviour of 1 and 2 in ionic liquid medium. (C) 2011 Elsevier B.V. All rights reserved.