Photochemical reactions of Group 6 metal carbonyls catalytic transformation of alkenes and alkynes

Abstract

This review considers some results that illustrate one of the different categories of photocatalysis where light is used to generate a thermally active catalytic species C from catalytically inactive precursor, the nominal catalyst N. In photocatalytic reactions presented here the nominal catalyst N can be a Group 6 metal carbonyl, M(CO) 6, and substrates are alkenes or or ynes. This paper summarizes the most interesting approaches in each of three photocatalytic reactions: polymerization of alkynes; isomerization of alkenes; metathesis of alkenes. Special attention is given to catalytically active intermediate species formed in photocatalytic systems and to the reaction mechanism. With the application of the low-temperature method formation of alkyne complexes of the type [( η 2-RCCH)M(CO) 5], [R(H)CCM(CO) 5] and [( η 2-RCCH)M(CO) 4], intermediate compounds proposed for the photocatalytical polymerization of terminal alkynes have been shown. The bis(alkene)tetracarbonyl complexes of tungsten are good prototypical catalysts for isomerization and metathesis of olefin. The rearrangement of these compounds to π-allyl hydrides was monitored by 1H NMR. The [(CO) 4W(μ-Cl) 3W(SnCl 3)(CO) 3] formed in the photochemical reaction of W(CO) 6 and SnCl 4 can be regarded as a prototypical catalyst for the metathesis of alkenes.