Insertion and isomerisation of internal olefins at alkylaluminium hydride: catalysis with zirconocene dichloride

Abstract

The insertion of internal olefins (hydroalumination) and chain walking isomerisation at di-n-octylaluminium hydride [Al(Oct)₂H], promoted by zirconocene dichloride [Cp₂ZrCl₂] has been studied. The reaction between [Cp₂ZrCl₂] and [Al(Oct)₂H] in non-polar solvents leads to clusters containing bridging hydride ligands between Zr and Al. This system promotes hydroalumination of 1-octene but is largely ineffective for internal octenes (2-, 3-, 4-octene). In tetrahydrofuran the Zr–Al hydride clusters formed are more reactive and catalyse insertion and isomerisation of internal olefins to primary metal–alkyls, although this is accompanied by catalyst deactivation. Elimination and removal of 1-octene from the system post insertion/isomerisation was attempted, but it was found that the presence of the Zr catalyst leads to back-isomerisation to internal octenes, along with further decomposition with n-octane formation. Some possible pathways of catalyst decomposition, involving reduction of Zr and alkane elimination, have been studied theoretically.