Photochemical isomerization of platinum(II) complexes containing phosphine and carbonyl ligands: Pt(CO)(PR3)X2 (X=Cl, Br, I)

Abstract

The photo-induced cis-trans isomerization of Pt(CO)(PR3)X2, where X=Cl, Br and I; PR3=PEt3, PMePh2 and PPh3, has been studied in chloro-hydrocarbon solvents, with emphasis on the chloro-triethyl complexes. Photo-induced dimerization was a concurrent reaction to varying degrees for the complexes. In chloroform and carbon tetrachloride, an induction period was observed for isomerization. Addition of carbon monoxide enhanced isomerization but suppressed dimerization, while continuous purging with nitrogen produced the opposite effects. For cis-Pt(CO)(PEt3)Cl2, the quantum yield of cis-trans conversion was about 0.6 at different wavelengths of incident light; it was invariable towards the presence of oxygen or 1,3-pentadiene, but increased to about 0.8 in the presence of carbon monoxide introduced at different pressures. These results indicate that isomerization takes place from a singlet state of relatively long lifetime, with metal-carbonyl bond breaking as the first step, followed by catalysis of the reaction by the free ligand. © 1990.