Oligomerisation of ethylene to linear α-olefins by new Cs- and C1-symmetric [2,6-bis(imino)pyridyl]iron and -cobalt dichloride complexes

A new family of C-s- and C-1-symmetric 2,6-bis(imino)pyridyl ligands has been synthesised. These ligands, which differ from their known counterparts in the contemporaneous presence of alkyl and aryl substituent at the ketimine nitrogen atoms, form stable, five-coordinate complexes with FeCl2 and CoCl2. All ligands and catalysts have been fully characterised both in the solid state and in solution. A single-crystal X-ray analysis of [CoCl2(2-[CMe=N-(2,6-dimethylphenyl)]-6-(CMe=N-C6H11)C5H3N)](H2O)-H-. shows the metal centre to adopt a highly distorted square-pyramidal geometry, In combination with methylaluminoxane (MAO), both iron and cobalt compounds act as effective and selective (> 99%) catalysts for the oligomerisation of ethylene to a Schulz-Flory distribution of alpha-olefins, with the a factor ranging from 0.61 to 0.91. The iron catalysts exhibit TOFs as high as 7(.)10(5) mol C2H4 (mol of cat x h)(-1) and are much more active than their cobalt analogues. Experiments at different ethylene pressures with the iron catalysts showed that both the propagation rate and the chain transfer rate are first order in ethylene pressure. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003).