The reaction of permanganyl chloride with olefins: Intermediates and mechanism as derived from matrix-isolation studies and density functional theorycalculations

Density functional theory (DFT) calculations predict that the [2+3] additio n of tetramethylethylene (TME) to the MnO2 moiety of MnO3Cl is thermodynami cally favoured over [2+1] addition (epoxidation), while the kinetic barrier s for both reactions are of comparable height. However, in an experimental investigation of the TME/MnO3Cl system by means of matrix-isolation techniq ues, selective formation of the epoxidation product [ClO2Mn(O[C(CH3)(2)](2) )] (1) was observed. Compound 1 was characterised by IR spectroscopy with t he aid of isotopic-enrichment experiments in combination with DFT frequency calculations. This result, at first sight surprising, is supported by stud ies in solution, and, even with the numerically equal energy barriers sugge sted by the calculations, it can be rationalised in terms of the much broad er reaction channel leading to epoxidation as opposed to the much more narr ow approach path for formation of the glycolate.