Catalytic sulfoxidation and epoxidation using oxomolybdenum compounds generated from tricarbonyl(1-methylimidazole)molybdenum(0)

The scope of molybdenum carbonyl precatalysts has been expanded to include [Mo(CO)₃(1-mim)₃] (1) (1-mim = 1-methylimidazole) for application in epoxidation and sulfoxidation processes, using relatively ecofriendly and industrially used oxidants. The mechanisms of conversion of 1 to active species were investigated by systematically combining catalytic and characterization studies. With tert-butylhydroperoxide (TBHP), 1 gives the functionalized polyoxomolybdate (1-Hmim)₄[Mo₈O₂₆(1-mim)₂]·2H₂O (2), which then leads to the stable salt (1-Hmim)₄[Mo₈O₂₆]·2H₂O (3) containing β-octamolybdate molecular anions. With H₂O₂, 1 gives a structurally distinct octamolybdate, (1-Hmim)₄[Mo₈O₂₆] (4), with characterization data that point to the presence of [Mo₈O₂₆]_n⁴ⁿ⁻ chains. In the reactions of cis-cyclooctene or dl-limonene with H₂O₂, 4 is a reaction-induced self-separating catalyst, i.e., in the initial stages it dissolves to give a homogeneous solution, but then self-precipitates once the oxidant is consumed. In the sulfoxidation of methyl phenyl sulfide, 4 was effective in producing the sulfoxide selectively with TBHP, and the sulfone with H₂O₂.