Molybdenum(VI)-catalysed olefin epoxidation: Structure and reactivity study

Dioxo and oxoperoxo molybdenum(VI) complexes, I–III, containing the non-labile bidentated oxazolinyl-pyridine ligand 1, were used as catalytic precursors in the epoxidation of cyclooctene and (R)-limonene, to explore the nature of the catalytic species. The high diastereoselectivity showed by I and II towards limonene epoxide formation (trans/cis-8 = 4/1) could be justified by the kinetic resolution observed to give the double epoxide (9), but also by the olefin coordination to the metal centre due to the presence of a labile ligand (isothiocyanate).95Mo NMR monitoring experiments of complex II in the presence of (R)-limonene, together with conductivity measurements, showed the formation of an ionic metallic species (1:1 electrolyte). These results point to a bimetallic species where one of the metal atoms is coordinated to the olefin by the dissociation of the isothiocyanate group, remaining coordinated the spectator chiral ligand, which is the responsible of the selectivity observed.

Graphical abstractOxo molybdenum(VI) complexes containing non-labile bidentated oxazolinyl-pyridine ligand, were used as catalytic precursors in epoxidation processes. Studies in solution of the Mo species involved in catalysis point to the olefin coordination, remaining coordinated the spectator chiral ligand, responsible of the selectivity observed.Figure optionsDownload full-size imageDownload as PowerPoint slide