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
VÂ(NAd)ÂMe<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 VÂ(NAd)ÂCl<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, VÂ(NAd)ÂMeÂ(OR′)Â(L) [R′
= OCÂ(CF<sub>3</sub>)<sub>3</sub> (<b>3a</b>), OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub> (<b>3b</b>), OCÂ(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]Â[BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] in Et<sub>2</sub>O and <b>3c</b> with BÂ(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 vanadiumÂ(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 vanadiumÂ(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
(Imido)ÂvanadiumÂ(V) dichloride complexes
containing 2-(2′-benzimidazolyl)-6-methylpyridine
ligand (L) of type VÂ(NR)ÂCl<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
(Imido)ÂvanadiumÂ(V) dichloride complexes
containing 2-(2′-benzimidazolyl)-6-methylpyridine
ligand (L) of type VÂ(NR)ÂCl<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