Me 2 C 6 H 3 ], prepared from V(NAd)Cl 2 (L) (1) 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 ), C 4 ′ = 97.1−98.4%], and the catalyst performances (activity, selectivity) were similar to those by the dichloride analogue (1) under the same conditions. The dimethyl complex (2a) reacted with 1.0 equiv of R′OH to yield the mono alkoxide complexes, V(NAd)Me(OR′)(L) [R′ = OC(CF 3 ) 3 (3a), OC(CH 3 )(CF 3 ) 2 (3b), OC(CH 3 ) 3 (3c)], and structures of these complexes (3a−c) and 2a were determined by Xray crystallography. Reactions of 2a with [Ph 3 C][B(C 6 F 5 ) 4 ] in Et 2 O and 3c with B(C 6 F 5 ) 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-d 8 solution of 1 and 2a did not show any significant changes in the oxidation state upon addition of MAO, Me 2 AlCl, or Et 2 AlCl (10 equiv). Resonances ascribed to formation of the other vanadium(V) species were observed in the 51 V NMR spectra, and no significant differences in the XANES spectra (V−K pre-edge peaks and edge) were observed from 1 or 2a 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(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate [B(C 6 F 5 ) 3 ] moiety (WCA-NHC) of the type [V(NR)-Cl 2 (WCA-NHC)] [R = 1-adamantyl, C 6 H 5 , 2,6-Me 2 C 6 H 3 ; NHC = 1,3-bis(2,6dimethylphenyl)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-Me 2 C 6 H 3 )Cl 2 (WCA-NHC)] exhibited remarkable catalytic activity (e.g., 11000 kg-PE/mol-V•h) for ethylene polymerization in the presence of Al i Bu 3 , and the activity was much higher than those in the presence of MAO and Et 2 AlCl.

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 (1a-c,e) or 1,3-R2(CH2N)2C═N (2a-d), R = (t)Bu (a), 2,6-Me2C6H3 (b), 2,6-(i)Pr2C6H3 (c), C6H5 (d), 2,6-(Ph2CH)2-4-MeC6H2 (e); L = 1,3-(2,6-(i)Pr2C6H3)2(CHN)2C═N, R' = 1-adamantyl (Ad, 3c), C6H5 (4c); L = 1,3-(2,6-(i)Pr2C6H3)2(CH2N)2C═N, R' = Ad (5c)], were prepared and characterized. The molecular structures of 1a, 2a,c,d, 3c, 4c, and 5c 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)Pr; 1b,c, 2b,c) exhibited higher catalytic activities than the (t)Bu analogues (1a, 2a), which display rather unique (small) V-N-C(imido) bond angles in the solid state. A good correlation between the activity and the (51)V NMR chemical shift was found for the (arylimido)vanadium precatalysts (1a-c,e, 2a-d, and 4c). 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)Pr2C6H3 analogues (especially 2c and 4c) showed the higher activities. The complexes 2c and 4c 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).

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.

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) (2), 8-(2,6-Me2C6H3)NCH2(C9H6N) (3); L = 2-(2,6-R'2C6H3)NCH2(C5H4N), R = 2-MeC6H4, R' = Me (4a), (i)Pr (4b); L = 2-(2,6-Me2C6H3)NCH2(C5H4N), R = 4-MeC6H4 (5), 3,5-Me2C6H3 (6)], have been prepared and identified. The reactions with ethylene by 2,3 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) (1a,b), 4-6 afforded 1-butene with high selectivities (>92%), and the activities by 4a,b are at the same level as those in 1a,b. The activities by 5,6 were lower than 4a,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.