PHOTO-REVERSIBLE ISOMERIZATION OF TRANS-[W(CO)(4)(ETA(2)-ALKENE)(2)] TO CIS-[W(CO)(4)(ETA(2)-ALKENE)(2)] COMPLEXES IN LOW-TEMPERATURE MATRICES

Reversible isomerisation of trans- to cis-[W(CO)(4)(eta(2)-alkene)(2)] complexes has been induced in argon matrices at low temperatures unde r the action of selective irradiation. W photolysis ( lambda approxima te to 313 nm) of trans-[W(CO)(4)(eta 2-alkene)(2)] (alkene = cyclopent ene or I-pentene) in an argon matrix at 16K results in formation of th e cis isomer as the primary photoprocess. The isomerisation is reverse d under the action of visible light (lambda approximate to 445nm). Spe cies such as [W(CO)(4)(alkene)(Ar)] are also formed in small concentra tions. Experiments involving annealing, selective photolysis and the u se of CO- or alkene-doped matrices have been performed to investigate the mechanism of the photo-isomerisation process. These studies sugges t a dissociative mechanism via expulsion of the alkene ligand.