XAS Analysis of Reactions of (Arylimido)vanadium(V) Dichloride Complexes Containing Anionic NHC That Contains a Weakly Coordinating B(C(6)F(5))(3) Moiety (WCA-NHC) or Phenoxide Ligands with Al Alkyls: A Potential Ethylene Polymerization Catalyst with WCA-NHC Ligands.

(Arylimido)vanadium(V) dichloride complexes containing anionic N-heterocyclic carbene (NHC) ligands that contain weakly coordinating B(C(6)F(5))(3) moieties (WCA-NHC) of the type [V(NAr)Cl(2)(WCA-NHC-Ar')] (5, Ar = 2,6-Me(2)C(6)H(3), Ar' = 2,6- (i) Pr(2)C(6)H(3)) showed significant catalytic activity for ethylene polymerization in the presence of Al cocatalysts (MAO and Al (i) Bu(3)); 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) Bu(3) 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) Bu(3) accompanying structural changes; the EXAFS analysis suggests the presence of the arylimido ligand and one V-Cl bond (2.34 ± 0.04 à ), which is longer than those [2.1901(8)-2.2462(8) à ] in the reported (imido)vanadium(V) complexes. The XANES analysis of [V(NAr)Cl(2)(OAr)] strongly suggests the formation of the other vanadium(III) species by reduction with Me(2)AlCl or Et(2)AlCl, and the EXAFS analysis suggests the presence of the arylimido ligand and two V-Cl bonds (2.45 ± 0.03 à ). 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.