Understanding catalytic olefin dimerisation

Selective metal-catalysed olefin oligomerisation is used widely for enhancing low carbon number product streams and for the manufacture of important industrial commodity chemical feedstocks.1 Indeed, such methodologies represent a core technology for the production of linear, terminal, short-chain olefins (C4–C20) that are used widely as plasticiser co-monomers in polyethylene manufacture and as components of synthetic lubricant base oils and detergents.2 In this arena, tungsten-based initiators have enjoyed particular success, offering good selectivity and activity.3 Historically, such systems were prepared in situ through reaction of WCl6 with ArNH2, followed by treatment with an alkylaluminium activator, something proposed to generate a catalytically-active tungsten imido-bearing moiety.3,4

As with many olefin polymerisation and oligomerisation initiators, one of the key challenges in understanding both the mechanism and the origins of the catalytic selectivity associated with these tungsten-centered systems is to establish the precise role of the alkylaluminium-based activators. Here, we report our studies around the synthesis of a series of well-defined tungsten mono- and bis-imido complexes and their subsequent reactions with a range of alkyl aluminium reagents.5 Results exemplifying both the influence of the resulting Al-containing components and the nature of the imido substituent, on subsequent reactions with olefins will be described. Careful analysis of the post-catalysis organic products is used to probe, indirectly, both the tungsten oxidation state and catalytic mechanism.

1. D. Vogt, in Applied Homogeneous Catalysis with Organometallic Compounds, 2nd Edtn., B. Cornils and W. A. Herrmann, ed., Wiley-VCH, Weinheim, Germany, 2002, Vol. 1, pp. 240–253.
 2. H. Olivier-Bourbigou and L. Saussine, ibid, Vol. 1, pp. 253–265. 3. M. Hanton, L. Daubney, T. Lebl, S. Polas, D. M. Smith and A. Willemse, Dalton Trans., 2010, 39, 7025. 4. H. Olivier and O. Laurent-Gérot, J. Mol. Catal. A: Chem., 1999, 148, 43. 5. W. R. H. Wright, A. S. Batsanov, J. A. K. Howard, R. P. Tooze, M. J. Hanton, and P. W. Dyer, Dalton Trans., 2010, 39, 7038.