Photochemistry of ansa-zirconocenes: ethylene-bis(1-indenyl)- and ethylene-bis(4,7-dimethyl-1-indenyl) zirconium dichlorides

This paper reports the full details of photochemical experiments on ansa ethylene-bis(indenyl) zirconium dichlorides derivatives. Photolysis of the 50 : 50 meso  :  racemic isomeric mixtures of ethylene-bis(1-indenyl) zirconium dichloride [EBIZrCl 2 ] and ethylene-bis(4,7-dimethyl-1-indenyl) zirconium dichlorides [EBDMIZrCl 2 ] produces a photostationary state made up of racemic (60%) and meso (40%) isomers. ESR spin trapping experiments showed the photogeneration of ligand- and zirconium-centered radicals. It is proposed that the meso -to- racemic photoconversion mechanism first involves the cleavage of one of the two metal-indenyl bonds. This generates a biradical species that quickly converts to the more stable products such as the racemic isomers of EBIZrCl 2 and EBDMIZrCl 2 . The study of the electronic spectra of EBIZrCl 2 , EBDMIZrCl 2 and comparison with those of Cp 2 ZrCl 2 , Cp 2 * ZrCl 2 and Ind 2 ZrCl 2 showed that the reactive excited states of ansa -zirconocenes are associated with LMCT transitions.