XAS Analysis of Reactions of (Arylimido)vanadium(V) Dichloride Complexes Containing Anionic NHC That Contains a Weakly Coordinating B(C6F5)3 Moiety (WCA-NHC) or Phenoxide Ligands with Al Alkyls: A Potential Ethylene Polymerization Catalyst with WCA-NHC Ligands

Kotohiro Nomura; Go Nagai; Itsuki Izawa; Takato Mitsudome; Matthias Tamm; Seiji Yamazoe

doi:10.1021/acsomega.9b02828

XAS Analysis of Reactions of (Arylimido)vanadium(V) Dichloride Complexes Containing Anionic NHC That Contains a Weakly Coordinating B(C₆F₅)₃ Moiety (WCA-NHC) or Phenoxide Ligands with Al Alkyls: A Potential Ethylene Polymerization Catalyst with WCA-NHC Ligands

ACS Omega. 2019 Oct 31;4(20):18833-18845. doi: 10.1021/acsomega.9b02828. eCollection 2019 Nov 12.

Authors

Kotohiro Nomura¹, Go Nagai¹, Itsuki Izawa¹, Takato Mitsudome², Matthias Tamm³, Seiji Yamazoe¹

Affiliations

¹ Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan.
² Department of Materials Engineering Science, Osaka University, 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
³ Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.

Abstract

(Arylimido)vanadium(V) dichloride complexes containing anionic N-heterocyclic carbene (NHC) ligands that contain weakly coordinating B(C₆F₅)₃ moieties (WCA-NHC) of the type [V(NAr)Cl₂(WCA-NHC-Ar')] (5, Ar = 2,6-Me₂C₆H₃, Ar' = 2,6- ⁱ Pr₂C₆H₃) showed significant catalytic activity for ethylene polymerization in the presence of Al cocatalysts (MAO and Al ⁱ Bu₃); the activity by the 5-MAO catalyst (19 500 kg-PE/mol-V·h; TOF 11 600 min^-1) is the highest among those reported using the other (imido)vanadium(V) complexes in the presence of MAO, and the 5-Al ⁱ Bu₃ catalyst showed higher activity (66 000 kg-PE/mol-V·h; TOF 39 200 min^-1). The V K-edge X-ray absorption near-edge structure (XANES) analyses (in toluene) strongly suggest the formation of certain vanadium(III) species by reduction with Al ⁱ Bu₃ accompanying structural changes; the EXAFS analysis suggests the presence of the arylimido ligand and one V-Cl bond (2.34 ± 0.04 Å), which is longer than those [2.1901(8)-2.2462(8) Å] in the reported (imido)vanadium(V) complexes. The XANES analysis of [V(NAr)Cl₂(OAr)] strongly suggests the formation of the other vanadium(III) species by reduction with Me₂AlCl or Et₂AlCl, and the EXAFS analysis suggests the presence of the arylimido ligand and two V-Cl bonds (2.45 ± 0.03 Å). The XANES spectra showed no significant changes in both the pre-edge peak(s) and the edge peak when these complexes were treated with MAO, suggesting that the basic geometry and the high oxidation state were preserved under these conditions.