Selective ethylene trimerization by titanium complexes bearing phenoxy-imine ligands: NMR and EPR Spectroscopic studies of the reaction intermediates

Soshnikov, Igor E.; Semikolenova, Nina V.; Ma, Jing; Zhao, Ke-Qing; Zakharov, Vladimir A.; Bryliakov, Konstantin P.; Redshaw, Carl; Talsi, Evgenii P.

Abstract

The catalyst systems (FI)TiCl₃/MAO (FI = phenoxyimine ligand with an additional aryl–O–CH₃ donor) display exceptionally high activity in selective ethylene trimerization. By means of NMR and EPR spectroscopy, the nature of the Ti species formed in the catalyst systems (FI)TiCl₃/MAO, (FI)TiCl₃/MMAO, and (FI)TiCl₃/AlR₃/[Ph₃C]⁺[B(C₆F₅)₄]⁻ (R = Me, Et, ⁱBu) has been studied. It was shown that outer-sphere ion pairs of the type [(FI)TiIVMe₂]⁺[A]⁻ ([A]− = [MeMAO]⁻, [MeMMAO]⁻, [B(C₆F₅)₄]⁻) are formed at the initial stage of the reaction of (FI)TiCl₃ with MAO, MMAO, and AlMe₃/[Ph₃C]⁺[B(C₆F₅)₄]⁻. These ion pairs further partially convert into TiIII and TiII species. In the systems (FI)TiCl₃/MAO and (FI)TiCl₃/AlMe₃/[Ph₃C]⁺[B(C₆F5)₄]⁻, complexes with the proposed structures (FI)TiIIIMe₂, (FI)TiIICl, and [(FI)TiII(S)]⁺[A]⁻ ([A]− = [MeMAO]⁻, [B(C₆F₅)4)]⁻, S = solvent, vacancy) were observed (concentrations of TiIII species was lower than those of the TiII congeners). In contrast, in the system (FI)TiCl₃/MMAO, the concentrations of TiIII species (ion pairs of the type [(FI)TiIII(μ-H)(μ-Cl)AlⁱBu₂]⁺[MeMMAO]⁻) were higher than those of the TiII counterparts (ion pairs [(FI)TiII(S)]⁺[MeMMAO]⁻). The system (FI)TiCl₃/MMAO displays lower activity and selectivity in 1-hexene formation, in comparison to (FI)TiCl₃/MAO, due to undesirable PE generation. Probably, TiII and TiIV ion pairs are those participating in ethylene trimerization.

Citation

Soshnikov, I. E., Semikolenova, N. V., Ma, J., Zhao, K., Zakharov, V. A., Bryliakov, K. P., …Talsi, E. P. (2014). Selective ethylene trimerization by titanium complexes bearing phenoxy-imine ligands: NMR and EPR Spectroscopic studies of the reaction intermediates. Organometallics, 33(6), 1431-1439. https://doi.org/10.1021/om500017r

• Journal Article Type: Article
• Acceptance Date: Jan 8, 2014
• Online Publication Date: Mar 12, 2014
• Publication Date: Mar 24, 2014
• Deposit Date: Jul 14, 2015
• Publicly Available Date: Jul 14, 2015
• Journal: Organometallics
• Print ISSN: 0276-7333
• Electronic ISSN: 1520-6041
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 33
• Issue: 6
• Pages: 1431-1439
• DOI: https://doi.org/10.1021/om500017r
• Keywords: Ethylene trimerization , NMR spectroscopy, EPR spectroscopy
• Public URL: https://hull-repository.worktribe.com/output/376428
• Publisher URL: http://pubs.acs.org/doi/abs/10.1021/om500017r
• Additional Information: This document is the Accepted Manuscript version of a Published Work that appeared in final form in Organometallics, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/om500017r