Exploration of Homogeneous Ethylene Dimerization Mediated by Tungsten Mono(imido) Complexes

In combination with EtAlCl2, complexes {[WCl3(μ-Cl)­(N-2,6-iPr2C6H3)]2}, [WCl4(NR)­(thf)] (R = Et, iPr, cHx, Ph, 2,6-iPr2C6H3, 4-F-C6H4, and 2,4,6-F3-C6H2), and [WCl2(NR′)­(PMe3)3] (R′ = Ph, 2,6-iPr2C6H3) were all productive ethylene dimerization pre-catalysts, giving turnover numbers (TONs) in the range of 400–144 000 (mol C2H4)­(mol W)−1 and moderate selectivities toward 1-butene (>66%) depending on the nature of the imido substituent. The formation of C6 side-products resulted from the incorporation of 1-butene rather than direct trimerization, something that is independent of butene concentration. Stoichiometric reactions between the tungsten mono­(imido) complexes and alkylaluminum reagents are described, which are consistent with the reduction of the tungsten centre playing an important part in the initiation process. Testing discrete WV and WIV mono­(imido) complexes for olefin dimerization revealed the former to be significantly more active, which offers insight into the mode of action of the commercially relevant tungsten mono­(imido)-selective dimerization initiators described herein.