Photochemical behaviour of trans-[W(CO)4(η2-alkene)2] complexes in low temperatures IR characterization of catalytically important intermediates

Abstract

UV irradiation (313 or 367 nm) of trans-[W(CO)₄(η²-alkene)₂] [alkene=propene (1), 1-butene (2), cyclopentene (3)] complexes in an alkane solution at temperatures ranging from 123 to 263 K leads to two primary photoprocesses, alkene and CO loss. The loss of the alkene is accompanied by the formation of 16-electron coordinatively unsaturated species: trans- and cis-[W(CO)₄(η²-alkene)(s)], A (s=solvent molecule). The CO loss leads to the formation of mer- and fac-[W(CO)₃(η²-alkene)₂(s)]. In the case of propene and 1-butene, the 16-electron complex A transforms into the IR detected cis-[WH(π-allyl)(CO)₄], B. Under conditions of excess alkene, the 16-electron tetracarbonyl species A binds alkene and forms cis-[W(CO)₄(η²-alkene)₂], C, but the 16-electron tricarbonyl species transforms to fac-[W(CO)₃(η²-alkene)₃], D, and mer-[W(CO)₃(η²-alkene)₃], E. The relative amounts of the photoproducts A–E were dependent on the temperature, photolysis time, type of alkene ligand, photolysing radiation wavelength and the presence in solution of free alkene.