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.-Q., Zakharov, V. A., Bryliakov, K. P., Redshaw, C., & 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
• 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
• Contract Date: Jul 14, 2015