Metathesis of n-alkenes over a CsNO 3-Re 2O 7-Al 2O 3 catalyst

Abstract

Homometathesis and cometathesis of fourteen kinds of linear n-alkenes (R'CH = CHR, with R'< R, and R'= H, —CH 3, —C 2H 5, —C 3H 7) containing from five to nine carbon atoms were carried out over a CsNO 3-Re 2O 7-Al 2O 3 catalyst in a continuous-flow system at atmospheric pressure in liquid phase. In the case of internal alkenes, the cis isomer was primarily used as the reactant. The effects of the structures of n-alkenes on reaction behaviors, reactivity and stereo selectivity of the reaction products were investigated. The catalyst appeared to be very selective and active for each metathesis. The selectivities of the main product and byproducts in the homometathesis were >94% and <6%, respectively. The byproducts were accompanied by the cometathesis of a reactant, with the isomer being formed by a double bond shift to the interior. Relative reactivity was investigated by competitive reactions. Reactivity of a homogeneous series decreased as the size of the molecule became larger. The reactivity of n-alkenes with the same number of carbon atoms decreased in the following sequence: 2- > 3- > 4- > 1-alkene. The reaction products consisted of cis and trans isomers. The t c ratio of products changed greatly according to the degree of conversion. The ( t c ) o was greater than unity and increased with an increase in the alkyl chain length (R). When R remained constant, ( t c ) o decreased with an increase in the carbon number in R'. Reactivity and stereochemistry are discussed and explained in terms of the metal carbene mechanism.