Selective dimerisation of 1-hexene mediated by aluminium alkyl chloride-activated tungsten imido complexes

Abstract

The selective dimerisation of 1-hexene to dodecenes was accomplished using catalysts generated from a tungsten mono-[WCl₄(NR)(thf)] or bis-[WCl₂(NR)₂(dme)] imido complex following activation with EtAlCl₂. These catalytic systems achieve 1-hexene dimerisation with productivities of up to 3760 mol C₆ per mol W and selectivities towards the dimer fraction of 88–99 wt%. Tungsten pro-catalysts bearing imido ligands with electron donating groups give high productivity and good selectivity towards the desired methyl-branched dimers. Contrastingly, complexes with electron withdrawing imido motifs are inactive for oligomerisation, instead mediating 1-hexene isomerisation. The efficacy of different aluminium-containing activators is described, with EtAlCl₂ giving the best catalytic performance at a low W : Al ratio of 8–20. Addition of catalyst modifiers (e.g. Oct₄NCl and Et₃N) is found to significantly improve the catalytic performance of the alkyl aluminium-activated olefin oligomerisation systems.