Ring opening of monocyclic dimethyl cyclopropene via metathesis by tungsten catalyst– A computational study

Abstract

Metathesis reaction of 3,3-disubstituted cyclopropene mediated by the model catalyst tungsten alkylidene W(NH)(CH2)(OCH3)2 has been studied at the B3LYP/LANL2DZ level of theory. The stationary points on the potential energy surface for ring opening metathesis were calculated considering all stereochemically distinct approaches of the 3,3-disubstituted cyclopropene to the model tungsten catalyst. The ring opening of cyclopropene moiety proceeds in two steps i.e., cycloaddition and ring opening. Each step involves a twisted trigonal bipyramidal transition structure. The syn orientation of cyclopropene to the NH group of the tungsten alkylidene is more favourable for product formation. Cyclopropene addition to tungsten alkylidene takes place preferentially on the CNO face; which is favoured by 10.89 kcal/mol over the COO face. The energy barriers for the syn cycloaddition and syn ring opening steps are 8.47 and 10.94 kcal/mol, respectively. The ring opening step is the rate determining step for the reaction of cyclopropene with tungsten catalyst, in contrast with the case of the molybdenum catalyst.