Synthesis and structural analysis of niobium(V) complexes containing amine triphenolate ligands of the type, [NbCl(X)(O-2,4-R2C6H2-6-CH2)3N] (R = Me, Bu; X = Cl, CF3SO3), and their use in catalysis for ethylene polymerization

Synthesis and Structural Analysis of Four Coordinate (Arylimido)niobium(V) Dimethyl Complexes Containing Phenoxide Ligand: MAO-Free Ethylene Polymerization by the Cationic Nb(V)–Methyl Complex

“…The activities by 2a – c in n -octane further increased at 80 °C, and the activity was affected by the Al/Nb molar ratio employed (runs 4–6, S5–9 by 2a ; runs 9, 10, S16–18 by 2b ; runs 12–14, S20, 21 by 2c ). The observed facts are similar to those in the ethylene polymerization by NbCl 2 [(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 3 N]–MAO catalyst, and the reason for the low activity in toluene was speculated as coordination of toluene toward the catalytically active (cationic alkyl) species as observed in some titanium catalysts . However, the activity by 2a decreased at 100 °C, and the activities by 2a in the presence of modified MAO (MMAO, methyl isuobutyl aluminoxane) in place of MAO were apparently low (2–10 kg-PE/mol-Nb·h, runs S11–14, SI).…”

“…Table summarizes the results in ethylene polymerization by Nb­(NAr)­X 2 (O-2,6- t Bu 2 C 6 H 3 ) [X = NMe 2 ( 2 ), Me ( 5 ); Ar = 2,6- i Pr 2 C 6 H 3 ( a ), 2,6-Me 2 C 6 H 3 ( b ), 2-MeC 6 H 4 ( c )]–MAO catalysts, and additional results are shown in the Supporting Information (SI) . AlMe 3 free MAO white solid (d-MAO), prepared from the commercially available MAO toluene solution [TMAO-212, 8.9 wt % (Al) toluene solution; Tosoh Finechem Co.], ,,, was used as the Al cocatalyst.…”

“…The study should be helpful not only for better understanding of the organometallic chemistry but also for design of efficient and unique molecular catalysts, because of their potentials as promising reactivity demonstrated in classical Ziegler type vanadium catalyst systems for olefin polymerization , and as reports in polymerization of disubstituted acetylenes mostly demonstrated by niobium and tantalum catalyst systems or niobium–, tantalum–alkylidene complex catalysts. − Although the metal–alkyl complex plays an important role in olefin coordination polymerization that has been known as the key reaction in production of polyolefins [linear low density (or high density) polyethylene, isotactic polypropylene], ,,, however, the reported examples by the niobium complex catalysts (exemplified in Chart A–K) − have been less compared to those by the vanadium complex catalysts , as well as the group 4 transition metal complex catalysts. , On the basis of reported results, niobium complexes should have certain potentials, because Cp*NbCl 2 (η 4 -diene) (A) and Cp*Nb­(η 4 -diene) 2 enable living ethylene polymerization in the presence of methylaluminoxane (MAO) to proceed . Moreover, the complexes containing chelate imino ligands (G, H) exhibited high catalytic activities for ethylene polymerization upon addition of halogenated Al alkyls and chlorinated reoxidant (ethyl trichloroacetate); the dichloride complex containing amine triphenolate ligand, NbCl 2 [(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 3 N] (K), exhibited high activities in the presence of MAO at 100, 120 °C . More recently, (arylimido)­niobium­(V) complexes containing chelate (2-anilidomethyl)­pyridine ligand, Nb­(N-2,6- i Pr 2 C 6 H 3 )­Me 2 [2-(2,6-Me 2 C 6 H 3 )­NCH 2 -(C 5 H 4 N)] (L), exhibited high activity for selective dimerization of ethylene (MAO cocatalyst), and NbCl 3 (NPh)­(dme) (dme = 1,2-dimethoxyethane)–Et 2 AlCl catalyst afforded 1-butene accompanied by byproduction of polyethylene …”

Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols

“…The Nb–N bond distances in the ketimide (N=C t Bu 2 ) ligand [1.9399(16)–1.9670(17) Å] in 8 , 9 , and 11 are within the range of 4a and 4b [1.946(8)–1.957(3) Å], but apparently shorter than the Nb–N(H)=C t Bu 2 bond distances [2.440(2)–2.5448(17) Å];d the Nb–N(4)–C or Nb–N(3)–C bond angles in Nb–(H)N=C t Bu 2 [157.30(12)–160.7(3)°] are apparently small compared to the Nb–N(2)–C bond angle in the ketimide ligand [174.01(12)–178.8(3)°]. The Nb–O bond distances in 8 , 9 , and 11 [1.9879(14)–2.066(3) Å] are longer than those in 1a and 1d [1.8878(12) and 1.9231(9) Å, respectively],b 4a and 4b [1.939(3) and 1.965(7) Å, respectively], and NbCl 2 [( O -2,4-Me 2 C 6 H 2 -6-CH 2 ) 3 N] [1.8838(19)–1.925(2) Å], 59 but close to those in CpNbCl[(O-C 6 H 4 -6-CH 2 ) 3 N] [1.970(5)–2.009(6) Å]. 61…”

(Arylimido)niobium(V) Complexes Containing 2-Pyridylmethylanilido Ligand as Catalyst Precursors for Ethylene Dimerization That Proceeds via Cationic Nb(V) Species

“…This might be the similar observation in the ethylene polymerization using [NbCl 2 (O-2,4-R′ 2 C 6 H 2 -6-CH 2 ) 3 N] (R′ = Me, t Bu) that the activity in n -octane was much higher than those conducted in toluene . The probable reason would be assumed as due to coordination of toluene in the formed active (cationic alkyl) species. , …”