Ethylene Dimerization/Polymerization Catalyzed by (Adamantylimido)vanadium(V) Complexes Containing (2-Anilidomethyl)pyridine Ligands: Factors Affecting the Ethylene Reactivity

V­(N-1-adamantyl)­Cl₂[2-(2,6-Me₂C₆H₃)­NCH₂(C₅H₄N)] showed both remarkable activity and selectivity (from 92 through >99.5% selectivity) in ethylene dimerization in the presence of MAO or MMAO, and the activity increased linearly upon increasing the ethylene pressure. The same reaction in the presence of Et₂AlCl or Me₂AlCl afforded ultrahigh molecular weight polyethylene. Both the ESR spectra and the ⁵¹V NMR spectra suggest that the chelate anionic donor ligand plays an important role in stabilization of the oxidation state in the catalyst solution even containing Al alkyls

Synthesis of (Imido)vanadium(V) Alkyl and Alkylidene Complexes Containing Imidazolidin-2-iminato Ligands: Effect of Imido Ligand on ROMP and 1,2-C–H Bond Activation of Benzene

A series of (imido)­vanadium­(V) alkylidene complexes containing an imidazolidin-2-iminato ligand of the type V­(CHSiMe₃)­(NR)­(X)­(PMe₃) (R = 2,6-Me₂C₆H₃ (Ar, <b>3a</b>), 1-adamantyl (Ad, <b>3b</b>), C₆H₅ (<b>3c</b>); X = 1,3-Ar′₂(CH₂N)₂CN; Ar′ = 2,6-^<i>i</i>Pr₂C₆H₃) have been prepared in <i>n</i>-hexane in the presence of PMe₃ from the corresponding dialkyl complexes V­(NR)­(CH₂SiMe₃)₂(X) (<b>2a</b>–<b>c</b>). These alkylidene complexes (<b>3a</b>–<b>c</b>) exhibit catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene: the phenylimido analogue (<b>3c</b>) exhibits remarkable activity at 80 °C (e.g. a TOF value of 84800 h^–1 (7070 turnovers after 5 min)), affording high-molecular-weight polymers with uniform molecular weight distributions. The reaction of the (arylimido)­vanadium­(V) dialkyl complex <b>2a</b> with C₆H₆ afforded the phenyl complex V­(NAr)­(CH₂SiMe₃)­(C₆H₅)­(X) (<b>4a</b>) by 1,2-C–H activation via an alkylidene intermediate and the diphenyl complex V­(NAr)­(C₆H₅)₂(X) as the final product. The activity by <b>3a</b>–<b>c</b> for ROMP, the reactivity of <b>2a</b>–<b>c</b> for formation of these alkylidenes by α-hydrogen elimination, and the reactivity of <b>2a</b>–<b>c</b> toward benzene were highly affected by the nature of the imido ligand

Synthesis of (Imido)Vanadium(V) Dichloride Complexes Containing Anionic N‑Heterocyclic Carbenes That Contain a Weakly Coordinating Borate Moiety: New MAO-Free Ethylene Polymerization Catalysts

Synthesis and structural analysis of (imido)­vanadium­(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate [B­(C₆F₅)₃] moiety (WCA-NHC) of the type [V­(NR)­Cl₂(WCA-NHC)] [R = 1-adamantyl, C₆H₅, 2,6-Me₂C₆H₃; NHC = 1,3-bis­(2,6-dimethylphenyl)­imidazolin-2-ylidene] have been explored; the WCA-NHC forms a σ-bond with vanadium as alkyl ligand (without strong π-donation) on the basis of crystallographic analysis [V–C_NHC = 2.039(3)–2.049(2) Å]. [V­(N-2,6-Me₂C₆H₃)­Cl₂­(WCA-NHC)] exhibited remarkable catalytic activity (e.g., 11000 kg-PE/mol-V·h) for ethylene polymerization in the presence of Al^<i>i</i>Bu₃, and the activity was much higher than those in the presence of MAO and Et₂AlCl

Synthesis of (Imido)Vanadium(V) Dichloride Complexes Containing Anionic N‑Heterocyclic Carbenes That Contain a Weakly Coordinating Borate Moiety: New MAO-Free Ethylene Polymerization Catalysts

Synthesis and structural analysis of (imido)­vanadium­(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate [B­(C₆F₅)₃] moiety (WCA-NHC) of the type [V­(NR)­Cl₂(WCA-NHC)] [R = 1-adamantyl, C₆H₅, 2,6-Me₂C₆H₃; NHC = 1,3-bis­(2,6-dimethylphenyl)­imidazolin-2-ylidene] have been explored; the WCA-NHC forms a σ-bond with vanadium as alkyl ligand (without strong π-donation) on the basis of crystallographic analysis [V–C_NHC = 2.039(3)–2.049(2) Å]. [V­(N-2,6-Me₂C₆H₃)­Cl₂­(WCA-NHC)] exhibited remarkable catalytic activity (e.g., 11000 kg-PE/mol-V·h) for ethylene polymerization in the presence of Al^<i>i</i>Bu₃, and the activity was much higher than those in the presence of MAO and Et₂AlCl

Synthesis and Structural Analysis of (Imido)Vanadium(V) Complexes Containing Chelate (Anilido)Methyl-imine Ligands: Ligand Effect in Ethylene Dimerization

A series of (imido)vanadium dichlorido complexes containing chelate anionic donor ligands of the type, VCl₂(L)­(NR) [R = 1-adamantyl (Ad), L = 2-(2,6-Me₂C₆H₃)­NCH₂(C₉H₆N) (<b>2</b>), 8-(2,6-Me₂C₆H₃)­NCH₂(C₉H₆N) (<b>3</b>); L = 2-(2,6-R′₂C₆H₃)­NCH₂(C₅H₄N), R = 2-MeC₆H₄, R′ = Me (<b>4a</b>), ^<i>i</i>Pr (<b>4b</b>); L = 2-(2,6-Me₂C₆H₃)­NCH₂(C₅H₄N), R = 4-MeC₆H₄ (<b>5</b>), 3,5-Me₂C₆H₃ (<b>6</b>)], have been prepared and identified. The reactions with ethylene by <b>2</b>,<b>3</b> in the presence of methylaluminoxane (MAO) afforded a mixture of high molecular weight polyethylene and oligomers. Reactions with ethylene by VCl₂[2-(2,6-R′₂C₆H₃)­NCH₂(C₅H₄N)]­(NAd) (<b>1a,b</b>), <b>4</b>–<b>6</b> afforded 1-butene with high selectivities (>92%), and the activities by <b>4a</b>,<b>b</b> are at the same level as those in <b>1a</b>,<b>b</b>. The activities by <b>5</b>,<b>6</b> were lower than <b>4a</b>,<b>b</b> and were at the same level of that by VCl₂[2-(2,6-Me₂C₆H₃)­NCH₂(C₅H₄N)]­(NPh). These results thus suggest that both the chelate anionic donor and the imido ligands play a role for both the activity and the selectivity

Synthesis and Structural Analysis of (Imido)Vanadium(V) Complexes Containing Chelate (Anilido)Methyl-imine Ligands: Ligand Effect in Ethylene Dimerization

A series of (imido)vanadium dichlorido complexes containing chelate anionic donor ligands of the type, VCl₂(L)­(NR) [R = 1-adamantyl (Ad), L = 2-(2,6-Me₂C₆H₃)­NCH₂(C₉H₆N) (<b>2</b>), 8-(2,6-Me₂C₆H₃)­NCH₂(C₉H₆N) (<b>3</b>); L = 2-(2,6-R′₂C₆H₃)­NCH₂(C₅H₄N), R = 2-MeC₆H₄, R′ = Me (<b>4a</b>), ^<i>i</i>Pr (<b>4b</b>); L = 2-(2,6-Me₂C₆H₃)­NCH₂(C₅H₄N), R = 4-MeC₆H₄ (<b>5</b>), 3,5-Me₂C₆H₃ (<b>6</b>)], have been prepared and identified. The reactions with ethylene by <b>2</b>,<b>3</b> in the presence of methylaluminoxane (MAO) afforded a mixture of high molecular weight polyethylene and oligomers. Reactions with ethylene by VCl₂[2-(2,6-R′₂C₆H₃)­NCH₂(C₅H₄N)]­(NAd) (<b>1a,b</b>), <b>4</b>–<b>6</b> afforded 1-butene with high selectivities (>92%), and the activities by <b>4a</b>,<b>b</b> are at the same level as those in <b>1a</b>,<b>b</b>. The activities by <b>5</b>,<b>6</b> were lower than <b>4a</b>,<b>b</b> and were at the same level of that by VCl₂[2-(2,6-Me₂C₆H₃)­NCH₂(C₅H₄N)]­(NPh). These results thus suggest that both the chelate anionic donor and the imido ligands play a role for both the activity and the selectivity

Synthesis and Structural Analysis of (Imido)vanadium(V) Dichloride Complexes Containing Imidazolin-2-iminato- and Imidazolidin-2-iminato Ligands, and their Use as Catalyst Precursors for Ethylene (Co)polymerization

A series of (imido)­vanadium­(V) dichloride complexes containing 1,3-imidazolin-2-iminato or 1,3-imidazolidin-2-iminato ligands of the type, V­(NR′)­Cl₂(L) [R′ = 2,6-Me₂C₆H₃, L = 1,3-R₂(CHN)₂CN (<b>1a</b>–<b>c</b>,<b>e</b>) or 1,3-R₂(CH₂N)₂CN (<b>2a</b>–<b>d</b>), R = ^<i>t</i>Bu (<b>a</b>), 2,6-Me₂C₆H₃ (<b>b</b>), 2,6-^<i>i</i>Pr₂C₆H₃ (<b>c</b>), C₆H₅ (<b>d</b>), 2,6-(Ph₂CH)₂-4-MeC₆H₂ (<b>e</b>); L = 1,3-(2,6-^<i>i</i>Pr₂C₆H₃)₂(CHN)₂CN, R′ = 1-adamantyl (Ad, <b>3c</b>), C₆H₅ (<b>4c</b>); L = 1,3-(2,6-^<i>i</i>Pr₂C₆H₃)₂(CH₂N)₂CN, R′ = Ad (<b>5c</b>)], were prepared and characterized. The molecular structures of <b>1a</b>, <b>2a</b>,<b>c</b>,<b>d</b>, <b>3c</b>, <b>4c</b>, and <b>5c</b> were determined by X-ray crystallography. All complexes showed high catalytic activity for ethylene polymerization especially in the presence of Et₂AlCl cocatalyst; the 2,6-R₂C₆H₃ analogues (R = Me, ^<i>i</i>Pr; <b>1b</b>,<b>c</b>, <b>2b</b>,<b>c</b>) exhibited higher catalytic activities than the ^<i>t</i>Bu analogues (<b>1a</b>, <b>2a</b>), which display rather unique (small) VNC­(imido) bond angles in the solid state. A good correlation between the activity and the ⁵¹V NMR chemical shift was found for the (arylimido)­vanadium precatalysts (<b>1a</b>–<b>c,e</b>, <b>2a</b>–<b>d</b>, and <b>4c</b>). These complexes showed high catalytic activity for the copolymerization of ethylene with norbornene (NBE), affording ultrahigh molecular weight copolymers with uniform molecular weight distributions. The activities were affected by the imido ligand as well as by the substituents in the anionic ligand, and the 2,6-^<i>i</i>Pr₂C₆H₃ analogues (especially <b>2c</b> and <b>4c</b>) showed the higher activities. The complexes <b>2c</b> and <b>4c</b> also showed high activities with efficient comonomer incorporation for the ethylene copolymerization with 5-ethylidene-2-norbornene (ENB) in the presence of Et₂AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB)

Synthesis of (Imido)vanadium(V) Complexes Containing 8‑(2,6-Dimethylanilide)-5,6,7-trihydroquinoline Ligands: Highly Active Catalyst Precursors for Ethylene Dimerization

A series of (imido)­vanadium­(V) dichloride complexes containing 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands of the type V­(NR)­Cl₂[8-(2,6-Me₂C₆H₃)­N­(C₉H₁₀N)] (R = Ad (<b>3</b>), 2-MeC₆H₄ (<b>4</b>), 2,6-Me₂C₆H₃ (Ar, <b>5</b>)) have been prepared and identified, and their structures have been determined by X-ray crystallographic analysis. The ethylene dimerization catalyst generated from complex <b>3</b> upon treatment with an excess amount of MAO exhibited remarkable catalytic activities (e.g. TOF = 9600000 h^–1 (2670 s^–1), Al/V = 4000 (molar ratio)), affording 1-butene as the major product (95.0–99.4%). The activities of <b>3</b> and <b>4</b> were higher than those exhibited by the corresponding 2-(anilide)­methylpyridine analogues; <b>3</b> showed higher 1-butene selectivity than the others and the activity did not decrease remarkably at 50 °C. Complex <b>5</b> afforded a mixture of polymer and oligomers with low activities, suggesting that a fine tuning of both the imido and the anionic donor ligands plays an essential role in this catalysis

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

V­(NAd)­Me₂(L) [<b>2a</b>, L = 2-ArNCH₂(C₅H₄N), Ar = 2,6-Me₂C₆H₃], prepared from V­(NAd)­Cl₂(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^–1 (311–425 s^–1), <i>C</i>₄′ = 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(CF₃)₃ (<b>3a</b>), OC­(CH₃)­(CF₃)₂ (<b>3b</b>), OC­(CH₃)₃ (<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 [Ph₃C]­[B­(C₆F₅)₄] in Et₂O and <b>3c</b> with B­(C₆F₅)₃ 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>₈ solution of <b>1</b> and <b>2a</b> did not show any significant changes in the oxidation state upon addition of MAO, Me₂AlCl, or Et₂AlCl (10 equiv). Resonances ascribed to formation of the other vanadium­(V) species were observed in the ⁵¹V 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