Reactive Intermediates in Olefin Oxidations with Chromyl Chloride. IR-Spectroscopic Proof for O=CrCl(2)-Epoxide Complexes.

Abstract

After photolytic induction (411 nm) of the reaction between chromyl chloride and olefins in low-temperature matrixes, for the first time primary products of this system have been isolated and identified: the reaction of propylene yields O=CrCl(2).O=CHCH(2)CH(3) and while in the case of trans- and cis-2-butylene, OCrCl(2).O=C(CH(3))(CH(2)CH(3)) as well as OCrCl(2).(trans-2,3-butylene oxide) and OCrCl(2).(cis-2,3-butylene oxide) are obtained, respectively. Epoxide formation proceeds under complete retention of stereochemistry, and the regioselective reaction route leading to the carbonyl products can be suppressed if all hydrogen atoms at the olefinic bond are substituted: tetramethylethylene is selectively oxidized to tetramethylethylene oxide, which forms a complex with OCrCl(2). All products were characterized by IR spectroscopy, which was further supported by DFT calculations in certain cases. The mechanism leading to the formation of these products, their electronic states, and the implications of the matrix results on the thermal reactions of chromyl chloride are discussed.