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Article

Solution XAS Analysis for Reactions of Phenoxide-Modified (Arylimido)vanadium(V) Dichloride and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization

by
Kotohiro Nomura
*,
Itsuki Izawa
,
Mahaharu Kuboki
,
Kensuke Inoue
,
Hirotaka Aoki
and
Ken Tsutsumi
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji 192-0397, Tokyo, Japan
*
Author to whom correspondence should be addressed.
Catalysts 2022, 12(2), 198; https://doi.org/10.3390/catal12020198
Submission received: 31 December 2021 / Revised: 30 January 2022 / Accepted: 1 February 2022 / Published: 6 February 2022
(This article belongs to the Special Issue 10th Anniversary of Catalysts: Molecular Catalysis)
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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.

1. Introduction

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 thus performed with addition of large excess of ETA [5,11,18,19,20,21]. Presence of the active vanadium(III) species have been postulated based on the titration analysis as well as the ESR (electron spin resonance) spectra [22,23,24,25,26,27,28]. The approach by ESR spectroscopy (generally employed for analysis of paramagnetic compounds) [24,25,26,27,28,29,30,31,32] however faces difficulties such as observation of so called “ESR silent” species [V(III) with a 3d2 configuration through an interaction of the two unpaired electrons (spin–spin coupling), or an antiferromagnetically coupled V(IV) dimer (spin–orbit coupling), poor structural information in addition to difficulty of the quantitative analysis.
We reported that the phenoxide-modified vanadium(V) dichloride complexes containing arylimido ligand, in particular V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) [33,34,35], exhibited high activities for ethylene polymerization and the copolymerization with norbornene (NBE) in the presence of Al cocatalysts (MAO or Me2AlCl, Et2AlCl) (Scheme 1). As summarized in Table 1, the activities, the Mn values in the resultant (co)polymers, and the NBE contents in the copolymers were affected by the Al cocatalyst (and solvent) [34,35]; the activity was decreased by adding ETA [35]. The complex with anionic NHC ligand containing borate moiety (WCA-NHC, 2) showed the high activities for ethylene polymerization upon the addition of AliBu3 [36,37]; the activity by complex 2–AliBu3 showed higher (TOF 653 s−1, 66,000 kg-PE/mol-V·h) than those reported previously [37]. Moreover, 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].
As shown in Figure 1, formations of certain vanadium(III) species (observed as low energy edge shift) by reduction with halogenated Al alkyls (1,3) or AliBu3 (2) accompanying their structural changes (observed as changes in their pre-edge intensities) were suggested by the V K-edge XANES (X-ray Absorption Near Edge Structure) analyses in toluene (on the basis of reference samples including metal oxides), whereas the oxidation state and the basic coordination geometry were preserved when 1–3 were treated with MAO [37]. The observed facts (structural changes in the XANES spectra) were also supported (assigned each absorptions) by TD-DFT calculation [39,40]. The EXAFS (Extended X-ray Absorption Fine Structure) analysis revealed that the formed species contain the arylimido ligand in all cases. The results also revealed that the species contain one neutral V–Cl bond (2.34 ± 0.04 Å) when 2 was treated with AliBu3, and that two neutral V–Cl bonds were present when the phenoxide analogue (1) was treated with Me2AlCl (Table 2). Moreover, the formed species contain three neutral V–Cl bonds when 3 was treated with Me2AlCl and the edge intensity increased upon addition of ETA accompanied with decreasing the pre-edge intensity (suggesting the structural change) [37]. The results thus suggest formations of three different V(III) species which possess a different number of coordinating neutral donor (Cl) ligands for the stabilization.
As demonstrated in Figure 1, synchrotron X-ray absorption spectroscopy (XAS) provides important information of the oxidation state and the basic geometry (through XANES analysis) and the atoms coordinated to the metal center (through FT-EXAFS analysis) [41,42,43,44,45,46,47,48,49,50]. The method has been popular in the study of heterogeneous catalysis [41,42,43,44,45,46]. We recently demonstrated that the method is also useful for analysis of homogeneous catalysis, especially vanadium and titanium catalysts [40,46,47]. In this paper, we conducted XANES spectral studies for reactions of phenoxide-modified (arylimido)vanadium(V) dichloride (1) with different halogenated alkyls (effects of Al cocatalyst, solvent). As, as described above, (oxo)vanadium(V) trichloride, VOCl3, has been used as the catalyst component in the classical Ziegler-type olefin polymerization catalyst, we also studied the solution XANES analysis of VOCl3 and VO(OiPr)3 treated with Me2AlCl [51]. We thus herein demonstrate a formation of vanadium(III) species by treating the (oxo)vanadium complexes with Me2AlCl through the XANES spectra. It was revealed that their photon energies at the edge absorptions were relatively close to those observed in the solutions of complex 1 and 3 treated with Me2AlCl, but their pre-edge intensities were apparently different. The fact strongly suggests a formation of different vanadium(III) species with different coordination geometry.

2. Results and Discussion

2.1. Solution V K-Edge XANES Spectra of (Oxo)vanadium(V) and (Arylimido)vanadium(V) Complexes

Figure 2 shows V K-edge XANES spectra for VOCl3, VO(OiPr)3 (in toluene at 25 °C; 5.46 keV, 50 μmol-V/mL; measured in the SPring-8 facility of the Japan Synchrotron Radiation Research Institute (JASRI), the BL01B1 beam line); the spectra for V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3), V(NAr)(OAr)3, reported previously [37], are also placed for comparison.
The XANES spectra of 1 and V(NAr)(OAr)3 show sharp pre-edge absorption, generally observed in the four coordinates vanadium(V) complexes with tetrahedral geometry, at 5467.6 eV and 5468.1 eV, respectively. The pre-edge absorption is known to be due to a transition from 1s to 3d + 4p [39,40,46,47,48,49,50]. An absorption band (called a shoulder-edge absorption), which corresponds to an absorption of the V–Cl bond in 1 [39,40,46,47,50], was also observed at 5478.5 eV. Similarly, VOCl3 shows the strong pre-edge peak(s) at 5468.1 eV (and 5466.2 eV) and the similar absorption ascribed to the V–Cl bond at 5478.5 eV, whereas VO(OiPr)3 shows only the pre-edge absorption at 5468.4 eV. A weak absorption was also observed in VO(OiPr)3 at 5473.3 eV, but the reason is not currently clear.

2.2. Solution V K-Edge XANES Analysis for Reactions of V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization

As described in the introduction (Table 1), the complex 1 showed high catalytic activities for ethylene polymerization and the copolymerization with NBE [33,34,35] in the presence of Al cocatalyst. It was revealed that the activities and the Mn values in the resultant (co)polymers (and the NBE contents in the copolymers) were affected by the Al cocatalyst and solvent [34,35]; 1–AlMe3 catalyst system polymerized NBE with ring-opening metathesis mechanism (rather low activity) [33].
Figure 3 shows V K-edge XANES spectra (in toluene at 25 °C) for reactions of 1 with Et2AlCl, Me2AlCl, EtAlCl2, and with AlMe3 (50 equiv), and the spectrum for the reaction with Me2AlCl in n-hexane was also placed for comparison. The spectrum for V(NAd)Cl2(HNMe2)2 [52] was also placed for comparison as a reference of (imido)vanadium(IV) dichloride complex; the spectra of vanadium oxides were also used for comparison [40,46,47]. The pre-edge absorption of 1 (5467.6 eV) in toluene shifted slightly to a low energy region when 1 was treated with halogenated Al alkyls (5465.9 eV (Et2AlCl), 5465.7 eV (Me2AlCl), 5466.1 eV (EtAlCl2)); no significant solvent effect was seen when the reaction was conducted in n-hexane (5465.9 eV). These results clearly indicate a formation of vanadium(III) species irrespective of the kind of halogenated Al alkyls.
The similar low-energy shift in the pre-edge absorption was observed with increase in the intensity when 1 was treated with 50 equiv of AlMe3 (5466.2 eV). The clear low-energy shift in the edge absorption suggests that 1 was reduced by AlMe3 but the shift was not so significant compared to those in the reactions with halogenated Al alkyls (may suggest a formation of vanadium(IV) species); the details are, however, not clear at this moment.
Figure 4 shows V K-edge XANES spectra (in toluene at 25 °C, 50 μmol-V/mL) for reactions of VOCl3 and VO(OiPr)3 with 10 equiv of Me2AlCl, and the spectrum of the reaction mixture of V(NAd)Cl3 and Me2AlCl, reported previously [53], was also placed for comparison. The XANES spectrum of V(NAd)Cl3 treated with Me2AlCl appeared similar to those for 1 treated with halogenated Al alkyls (Me2AlCl, Et2AlCl, and EtAlCl2, Figure 3), suggesting a formation of the vanadium(III) species possessing similar oxidations states and the basic structures.
Note that significant low-energy shifts in the edge absorptions along with disappearance of the pre-edge absorptions were observed when VOCl3 or VO(OiPr)3 was reacted with Me2AlCl (10 equiv). The pre-edge intensity is known to be influenced by the basic structure (coordination geometry). For instance, the pre-edge intensity in a compound in Td (tetrahedral) symmetry exhibits much higher than that in the Oh (octahedral) symmetry due to a difference in the degree of a p–d orbital hybridization [39,40,48]. Therefore, the results clearly indicate that both VOCl3 and VO(OiPr)3 were reduced by Me2AlCl accompanies with structural changes (probably compounds with Oh geometry). The significant shifts in the edge absorptions may suggest a possibility of formation of vanadium(II) species partially, although we do not have the clear evidence at this moment. The formed species in the reaction of VO(OiPr)3 with Me2AlCl seemed to be unstable (due to observed green slurry after the measurement), a clear spectrum as in the reaction of VOCl3 could not be obtained. The observed difference between VOCl3 and VO(OiPr)3 may be speculated as due to a difference of number of neutral Cl donor ligands (observed the presence through the EXAFS analysis of 1 and 3 in the presence of Me2AlCl, Table 2) [37,38].
The XANES spectra for toluene solutions of VOCl3, V(NAd)Cl3, the phenoxide complex 1 [37], and V(NAd)Cl2[2-(2′-benzimidazolyl)-6-methylpyridine] (3) [38] after treatment with Me2AlCl are summarized in Figure 5. The spectra (edge peak positions and the λmax values) were similar when these (imido)vanadium(V) complexes (1, 3, and V(NAd)Cl3) were treated with Me2AlCl, suggesting a formation of the vanadium(III) species. It was revealed that the addition of Cl3CCO2Et (ETA, 50 equiv) into a toluene solution containing 1, Me2AlCl, and NBE (50 equiv) led to a decrease in the intensity of the absorption maxima (λmax, at 5475.7 eV), whereas, as reported previously [37], no significant differences in both the peak position and the intensity were observed when 1 was further added NBE (into a toluene solution containing 1, 50 equiv of Me2AlCl). No significant spectral changes were seen (in the complex and the solution with the addition of Me2AlCl) when the diisopropylphenyl analogue, V(NAr’)Cl2(OAr’) (Ar’ = 2,6-iPr2C6H3), was used instead of the dimethylphenyl analogue (1) [37]. In contrast, as reported previously, an intensity of the edge absorption increased with decreasing the pre-edge intensity when 3 was treated with Me2AlCl and ETA [38]. The fact may explain the fact concerning effect of ETA in the ethylene polymerization; the activity by 3 increased upon the addition of ETA [38] whereas a decrease in activity was seen in 1 with the addition [35]. Different catalytically active vanadium(III) species (with different number of neutral Cl ligands) would thus play roles, as also suggested by the EXAFS analysis (Table 2).
As described above (Figure 4), a significant shift in the edge absorptions with disappearance in the pre-edge absorption was observed when VOCl3 was treated with Me2AlCl. The fact clearly suggests that VOCl3 was reduced, accompanied with certain structural change (probably from tetrahedral to octahedral). The observed fact is apparently different from those observed in the (imido)vanadium species, in which a V-N bond was preserved even after treatment with Me2AlCl (Table 2, V-N bond distances: 1.64 Å). The fact also suggests that a different catalytically active (vanadium(III)) species play a role in this catalysis.

3. Materials and Methods

All experiments were performed under a nitrogen atmosphere in a Vacuum Atmospheres drybox. Anhydrous grade toluene and n-hexane (Kanto Kagaku Co., Ltd., Tokyo, Japan) were transferred into a bottle containing molecular sieves (a mixture of 3A 1/16, 4A 1/8, and 13X 1/16) in the drybox, and Al reagents (Me2AlCl, Et2AlCl, EtAlCl2, and AlMe3 (Kanto Kagaku Co., Ltd.)) were used as received. VOCl3, VO(OiPr)3 (Sigma-Aldrich, St. Louis, MO, USA), and Cl3CCO2Et (Tokyo Chemical Industry, Co., Ltd., Tokyo, Japan) were used as received. V(NAd)Cl3 (Ad = 1-adamantyl) [54], V(N-2,6-Me2C6H3)Cl2(O-2,6-Me2C6H3) (1) [33] were prepared according to a published method.
V K-Edge X-ray absorption near edge structure (XANES) was carried out at the BL01B1 beam line at the SPring-8 facility of the Japan Synchrotron Radiation Research Institute (JASRI, proposal nos. 2016B1509, 2017A1512, 2018A1245, 2018B1335, 2019A1233, and 2020A1473). V K-Edge XAFS spectra of V complex samples (toluene solution, 50 μmol/mL, at 25 °C, a Si (111) two-crystal monochromator was used for the incident beam) were recorded in the fluorescence mode using an ionization chamber as the I0 detector and 19 solid state detectors as the I detector. The X-ray energy was calibrated using V2O5, and the data analysis was performed with the REX2000 Ver. 2.5.9 software package (Rigaku Co., Tokyo, Japan). The XANES data was analyzed using a cubic spline from the χ spectra with removal of the atomic absorption background and normalization of them to the edge height.

4. Conclusions

We herein present that the solution V K-edge XANES studies in reactions of (oxo)vanadium(V) and (imido)vanadium(V) complexes with various halogenated Al alkyls (Me2AlCl, Et2AlCl, and EtAlCl2), which exhibit remarkable catalytic activities for ethylene polymerization. The formation of certain vanadium(III) species has been demonstrated through the spectral changes by treatment of these vanadium(V) complexes with Al alkyls, whereas, as reported previously [37], no significant changes in either the oxidation state or the basic geometry were observed when these (imido)vanadium(V) complexes were treated with methylaluminoxane (MAO). No significant differences in the spectra were observed in the reaction of V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) with halogenated Al alkyls, except AlMe3, suggesting a formation of similar catalytically active vanadium(III) species: no significant differences in the spectra were observed when 1 was treated with Me2AlCl in n-hexane.
In contrast, significant low-energy shift with the disappearance of the pre-edge absorption was observed when VOCl3 was treated with Me2AlCl. The fact clearly suggests a formation of different vanadium(III) species (and may form the species with lower oxidation state partially) in situ. As far as we know, this is the first clear observation of formation of low oxidation state vanadium species in the reaction of VOCl3 with Me2AlCl in solution through XANES analysis. In addition to the EXAFS analysis, reported previously for 1 and the others [37,38], the information here should be helpful to better understand the catalysis mechanism for olefin polymerization using homogeneous vanadium catalysts. We believe that the solution XAS analysis should be a powerful tool for the study of the catalytically active species, which are very difficult to monitor by NMR and ESR spectra.

Author Contributions

Conceptualization, supervision, project administration, methodology, funding acquisition, writing—original draft, and review and editing, K.N.; formal analysis and investigation, I.I., M.K., K.I., H.A., K.T. and K.N.; and data curation, I.I. and K.N. All authors have read and agreed to the published version of the manuscript.

Funding

This project was partly supported by Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS, Grant Nos. 18H01982, 21H01942), and Fund for the Promotion of Joint International Research (Fostering Joint International Research (B), 99KK0139).

Data Availability Statement

Not applicable.

Acknowledgments

Authors express their thanks to T. Mitsudome (Osaka University) and S. Yamazoe (Tokyo Metropolitan Univ., TMU) for their kind support for analysis of the XANES spectra and the discussion. The authors also express their thanks to G. Nagai, T. Omiya, T. Yamada, and H. Harakawa (TMU) for their technical assistance for the XAS analysis at the BL01B1 beam line at the SPring-8 facility of Japan Synchrotron Radiation Research Institute (JASRI, proposal nos. 2016B1509, 2017A1512, 2018A1245, 2018B1335, 2019A1233, 2020A1473).

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 12 00198 sch001 550
Scheme 1. Selected (imido)vanadium(V) dichloride complex catalysts for ethylene polymerization, ethylene/norbornene copolymerzation [33,34,35,36,37,38].
Scheme 1. Selected (imido)vanadium(V) dichloride complex catalysts for ethylene polymerization, ethylene/norbornene copolymerzation [33,34,35,36,37,38].
Catalysts 12 00198 sch001
Catalysts 12 00198 g001 550
Figure 1. V K-edge XANES spectra (in toluene at 25 °C) for (left) V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) [37], V(NAr)Cl2(WCA-NHC) (2) [37], and (right) V(NAd)Cl2(L) [3, Ad = 1-adamantyl, L = 2-(2′-benzimidazolyl)-6-methylpyridine] [38] in the presence of methylaluminoxane (MAO), Me2AlCl or AliBu3.
Figure 1. V K-edge XANES spectra (in toluene at 25 °C) for (left) V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) [37], V(NAr)Cl2(WCA-NHC) (2) [37], and (right) V(NAd)Cl2(L) [3, Ad = 1-adamantyl, L = 2-(2′-benzimidazolyl)-6-methylpyridine] [38] in the presence of methylaluminoxane (MAO), Me2AlCl or AliBu3.
Catalysts 12 00198 g001
Catalysts 12 00198 g002 550
Figure 2. V K-edge XANES spectra for VOCl3, VO(OiPr)3, V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3), and V(NAr)(OAr)3 (in toluene at 25 °C; 5.46 keV, 50 μmol-V/mL).
Figure 2. V K-edge XANES spectra for VOCl3, VO(OiPr)3, V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3), and V(NAr)(OAr)3 (in toluene at 25 °C; 5.46 keV, 50 μmol-V/mL).
Catalysts 12 00198 g002
Catalysts 12 00198 g003 550
Figure 3. The V K-edge XANES spectra for V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) in the presence of Et2AlCl, Me2AlCl, EtAlCl2, and AlMe3 (in toluene or n-hexane at 25 °C).
Figure 3. The V K-edge XANES spectra for V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) in the presence of Et2AlCl, Me2AlCl, EtAlCl2, and AlMe3 (in toluene or n-hexane at 25 °C).
Catalysts 12 00198 g003
Catalysts 12 00198 g004 550
Figure 4. The V K-edge XANES spectra for VOCl3, VO(OiPr)3 in the presence of Me2AlCl (in toluene at 25 °C).
Figure 4. The V K-edge XANES spectra for VOCl3, VO(OiPr)3 in the presence of Me2AlCl (in toluene at 25 °C).
Catalysts 12 00198 g004
Catalysts 12 00198 g005 550
Figure 5. The V K-edge XANES spectra (in toluene at 25 °C) for VOCl3, V(NAd)Cl3 [53], V(NAr)Cl2(OAr) (1) [37], and V(NAd)Cl2(L) [3, L = 2-(2′-benzimidazolyl)-6-methylpyridine] [38] in the presence of Me2AlCl (and addition of Cl3CCO2Et, ETA).
Figure 5. The V K-edge XANES spectra (in toluene at 25 °C) for VOCl3, V(NAd)Cl3 [53], V(NAr)Cl2(OAr) (1) [37], and V(NAd)Cl2(L) [3, L = 2-(2′-benzimidazolyl)-6-methylpyridine] [38] in the presence of Me2AlCl (and addition of Cl3CCO2Et, ETA).
Catalysts 12 00198 g005
Table
Table 1. Effect of Al cocatalyst, solvent and ETA (Cl3CCO2Et) in ethylene polymerization by V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3)—Al cocatalyst systems [35] a.
Table 1. Effect of Al cocatalyst, solvent and ETA (Cl3CCO2Et) in ethylene polymerization by V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3)—Al cocatalyst systems [35] a.
RunCat.1/μmolAl Cocat.SolventActivity b
×10−3		Mnc
×10−5		Mw/MncNBE d
/mol%
21.0MAOtoluene8803.021.7923.9
30.05Me2AlCln-hexane2400---
40.05EtAlCl2n-hexane47,3003.563.85-
50.05Me2AlCltoluene27,50089.8 e--
60.05Me2AlCltoluene23,4009.561.8315.2
70.05Et2AlCltoluene11,70025.71.42-
90.05EtAlCl2toluene37,4001.983.04-
a Conditions: catalyst 0.05 μmol, solvent + cocatalyst solution = total 30 mL, ethylene 8 atm, NBE 0 (runs 1,3–5,7–8) or 15 mmol (runs 2 and 7), 10 min, Al cocatalyst 250 μmol. b Activity in kg-polymer/mol-V·h. c GPC data in o-dichlorobenzene vs. polystyrene standards. d NBE content (mol %) estimated by 13C-NMR. e Molecular weight by viscosity. f Polymerization in the co-presence of CCl3CO2Et (ETA 10.0 equiv to V).
Table
Table 2. Summary of data for V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) [37], V(NAr)Cl2(WCA-NHC) (2) [37], and V(N-1-adamantyl)Cl2[2-(2′-benzimidazolyl)-6-methylpyridine]) (3) [38] in the presence of Me2AlCl or AliBu3 (V K-edge EXAFS oscillations and FT-EXAFS spectra in toluene at 25 °C).a.
Table 2. Summary of data for V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) [37], V(NAr)Cl2(WCA-NHC) (2) [37], and V(N-1-adamantyl)Cl2[2-(2′-benzimidazolyl)-6-methylpyridine]) (3) [38] in the presence of Me2AlCl or AliBu3 (V K-edge EXAFS oscillations and FT-EXAFS spectra in toluene at 25 °C).a.
Complex 11 + Me2AlCl
(50 Equiv)		Complex 22 + AliBu3
(100 Equiv)		Complex 33 + Me2AlCl
(10 Equiv)
AtomC.N.r (Å)C.N.r (Å)C.N.r (Å)C.N.r (Å)C.N.r (Å)C.N.r (Å)
N(O)2.4 (3)1.80 (5)1.3 (2)1.64 (4)2.1 (2)1.62 (3)0.8 (3)1.66 (17)1.7 (2)1.683 (5)0.9 (3)1.64 (2)
N 1.2 (8)2.290 (42)
Cl1.9 (2)2.18 (3)2.0 (2)2.45 (3)1.0 (2) 1.0 (2)2.16 (4) 2.34 (5)1.0 (2)2.34 (4)1.6 (2)2.293 (3)2.6 (1)2.455 (7)
a Atom: neighbor atom, C.N.: coordination number, r: bond length.
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Nomura, K.; Izawa, I.; Kuboki, M.; Inoue, K.; Aoki, H.; Tsutsumi, K. Solution XAS Analysis for Reactions of Phenoxide-Modified (Arylimido)vanadium(V) Dichloride and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization. Catalysts 2022, 12, 198. https://doi.org/10.3390/catal12020198

AMA Style

Nomura K, Izawa I, Kuboki M, Inoue K, Aoki H, Tsutsumi K. Solution XAS Analysis for Reactions of Phenoxide-Modified (Arylimido)vanadium(V) Dichloride and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization. Catalysts. 2022; 12(2):198. https://doi.org/10.3390/catal12020198

Chicago/Turabian Style

Nomura, Kotohiro, Itsuki Izawa, Mahaharu Kuboki, Kensuke Inoue, Hirotaka Aoki, and Ken Tsutsumi. 2022. "Solution XAS Analysis for Reactions of Phenoxide-Modified (Arylimido)vanadium(V) Dichloride and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization" Catalysts 12, no. 2: 198. https://doi.org/10.3390/catal12020198

APA Style

Nomura, K., Izawa, I., Kuboki, M., Inoue, K., Aoki, H., & Tsutsumi, K. (2022). Solution XAS Analysis for Reactions of Phenoxide-Modified (Arylimido)vanadium(V) Dichloride and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization. Catalysts, 12(2), 198. https://doi.org/10.3390/catal12020198

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