3 research outputs found

    Synthesis of (Adamantylimido)vanadium(V) Dimethyl Complex Containing (2-Anilidomethyl)pyridine Ligand and Selected Reactions: Exploring the Oxidation State of the Catalytically Active Species in Ethylene Dimerization

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    V­(NAd)­Me<sub>2</sub>(L) [<b>2a</b>, L = 2-ArNCH<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>N), Ar = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>], prepared from V­(NAd)­Cl<sub>2</sub>(L) (<b>1</b>) by reaction with LiMe (2.0 equiv), exhibited remarkable catalytic activities for ethylene dimerization in the presence of MAO affording 1-butene with high selectivity [TOF = 1 120 000–1 530 000 h<sup>–1</sup> (311–425 s<sup>–1</sup>), <i>C</i><sub>4</sub>′ = 97.1–98.4%], and the catalyst performances (activity, selectivity) were similar to those by the dichloride analogue (<b>1</b>) under the same conditions. The dimethyl complex (<b>2a</b>) reacted with 1.0 equiv of R′OH to yield the mono alkoxide complexes, V­(NAd)­Me­(OR′)­(L) [R′ = OC­(CF<sub>3</sub>)<sub>3</sub> (<b>3a</b>), OC­(CH<sub>3</sub>)­(CF<sub>3</sub>)<sub>2</sub> (<b>3b</b>), OC­(CH<sub>3</sub>)<sub>3</sub> (<b>3c</b>)], and structures of these complexes (<b>3a</b>–<b>c</b>) and <b>2a</b> were determined by X-ray crystallography. Reactions of <b>2a</b> with [Ph<sub>3</sub>C]­[B­(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] in Et<sub>2</sub>O and <b>3c</b> with B­(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> in THF afforded the corresponding cationic complexes confirmed by NMR spectra. Both NMR and V K-edge XANES analysis of the toluene or toluene-<i>d</i><sub>8</sub> solution of <b>1</b> and <b>2a</b> did not show any significant changes in the oxidation state upon addition of MAO, Me<sub>2</sub>AlCl, or Et<sub>2</sub>AlCl (10 equiv). Resonances ascribed to formation of the other vanadium­(V) species were observed in the <sup>51</sup>V NMR spectra, and no significant differences in the XANES spectra (V–K pre-edge peaks and edge) were observed from <b>1</b> or <b>2a</b> upon addition of Al cocatalyst. Taking into account these results and others, it is thus suggested that cationic vanadium­(V) alkyl/hydride species play a role in this catalysis

    Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2‑(2′-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization

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    (Imido)­vanadium­(V) dichloride complexes containing 2-(2′-benzimidazolyl)-6-methylpyridine ligand (L) of type V­(NR)­Cl<sub>2</sub>(L) [R = 1-adamantyl (Ad, <b>1</b>), C<sub>6</sub>H<sub>5</sub> (<b>2</b>), and 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>3</b>)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using <b>1–3</b> in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, <b>1–3</b> exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me<sub>2</sub>AlCl; the phenylimido complex (<b>2</b>) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h<sup>–1</sup>, 792 s<sup>–1</sup>)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., <i>M</i><sub>n</sub> = 1.71–2.66 × 10<sup>6</sup>, <i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 2.27–2.53]. On the basis of V nuclear magnetic resonance (<sup>51</sup>V NMR), electron spin resonance, and V K-edge X-ray absorption near-edge structure (XANES) spectra of the catalyst solution, the observed difference in the catalyst performance in the presence of (between) MAO and Me<sub>2</sub>AlCl cocatalyst should be due to the formation of different catalytically active species with different oxidation states. Apparent changes in the oxidation state were observed in the (especially in the NMR and XANES) spectra upon addition of Me<sub>2</sub>AlCl, whereas no significant changes in the spectra were observed in presence of MAO

    Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2‑(2′-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization

    No full text
    (Imido)­vanadium­(V) dichloride complexes containing 2-(2′-benzimidazolyl)-6-methylpyridine ligand (L) of type V­(NR)­Cl<sub>2</sub>(L) [R = 1-adamantyl (Ad, <b>1</b>), C<sub>6</sub>H<sub>5</sub> (<b>2</b>), and 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>3</b>)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using <b>1–3</b> in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, <b>1–3</b> exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me<sub>2</sub>AlCl; the phenylimido complex (<b>2</b>) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h<sup>–1</sup>, 792 s<sup>–1</sup>)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., <i>M</i><sub>n</sub> = 1.71–2.66 × 10<sup>6</sup>, <i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 2.27–2.53]. On the basis of V nuclear magnetic resonance (<sup>51</sup>V NMR), electron spin resonance, and V K-edge X-ray absorption near-edge structure (XANES) spectra of the catalyst solution, the observed difference in the catalyst performance in the presence of (between) MAO and Me<sub>2</sub>AlCl cocatalyst should be due to the formation of different catalytically active species with different oxidation states. Apparent changes in the oxidation state were observed in the (especially in the NMR and XANES) spectra upon addition of Me<sub>2</sub>AlCl, whereas no significant changes in the spectra were observed in presence of MAO
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