Abstract
V K-edge XANES (XANES = X-ray Absorption Near Edge Structure) spectra of the reaction solution of V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) with halogenated Al alkyls (Me2AlCl, Et2AlCl, EtAlCl2, 50 equiv) in toluene showed low energy shifts (2.6–3.6 eV on the basis of inflection point in the photon energy) in the edge absorption accompanying slight shift to low photon energy in the pre-edge peak (λmax values); a similar spectrum was observed when the reaction of 1 with Me2AlCl was conducted in n-hexane. These results strongly suggest a formation of similar vanadium(III) species irrespective of kind of Al alkyls and solvent (toluene or n-hexane). Significant low-energy shifts in the edge absorption accompanied with diminishing the strong pre-edge absorption were also observed when VOCl3 or VO(OiPr)3 was treated with Me2AlCl (10 equiv) in toluene, clearly indicating a formation of low oxidation state vanadium species accompanied with certain structural changes (from tetrahedral to octahedral) in solution.
Highlights
Transition metal catalyzed olefin polymerization plays a key role in commercial production of polyolefin [1,2,3,4,5,6,7,8,9,10,11]
As described above,vanadium(V) trichloride, VOCl3, has been used as the catalyst component in the classical Ziegler-type olefin polymerization catalyst, we studied the solution X-ray absorption near edge structure (XANES) analysis of VOCl3 and VO(OiPr)3 treated with Me2AlCl [51]
We present that the solution V K-edge XANES studies in reactions ofvanadium(V) andvanadium(V) complexes with various halogenated Al alkyls (Me2AlCl, Et2AlCl, and EtAlCl2), which exhibit remarkable catalytic activities for ethylene polymerization
Summary
Transition metal catalyzed olefin polymerization plays a key role in commercial production of polyolefin [1,2,3,4,5,6,7,8,9,10,11]. The classical Ziegler-type vanadium catalyst systems (consisting of VOCl3 and halogenated Al alkyls, etc.) displays notable reactivity toward olefins [12,13,14,15,16,17,18], and the catalyst system has been used for commercial production of synthetic (ethylene propylene diene monomer, EPDM) rubber [5,11,19,20,21] In this catalyst system, large excess of Cl3CCO2Et (ETA, called re-oxidant) was required to improve a severe concern of the rapid catalyst decomposition, assumed as due to conversion to the inactive species by reduction; ethylene polymerizations by most of the catalyst systems were performed with addition of large excess of ETA [5,11,18,19,20,21]. The related (adamantylimido)vanadium(V) complex containing 2-(2 -benzimidazolyl)pyridine ligand (3) exhibited significant activities for ethylene polymerization in the presence of Me2AlCl, and the activity further increased with addition of ETA [38]
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