New seven-coordinate oxo(peroxo)molybdenum(VI) complexes with bidentate chiral oxazolines, anionic κ 2 -N,O (V) and neutral κ 2 -N,N (VI), have been prepared and fully characterised by NMR spectroscopy and single-crystal X-ray diffraction studies. Dimetallic dioxo(µ-oxo)molybdenum(VI) compounds containing oxazolinylpyridine ligands II−IV have also been synthesised. NMR studies showed the presence of several isomers (up to six species) due to the Mo−O−Mo bridge angle and the unsymmetrical nature of the N,N ligand. The roles of mono-(I, V and VI) and dimetallic (II) oxomolybdenum(VI) complexes in the catalytic epoxid-

Oxomolybdenum(VI) complexes containing diverse ligands from an electronic and topological point of view have been analysed by means of (95)Mo NMR in solution with the purpose of using this technique as a tool to study their coordination chemistry and reactivity. The relationship between the electronic density on the metal tuned by the electron-donor ability of the coordinated ligands and the (95)Mo chemical shift has been proved for mono- and bimetallic complexes showing a hexa- or hepta-coordination around the metal centre. The different origins of the signal broadening (associated either to the symmetry of the metallic polyhedron or to the presence of isomers or to the ligand de-coordination) have been also considered to rationalise the obtained data.

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