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

摘要

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')Cl_2(L) [R' = 2,6-Me_2C_6H_3, L = 1,3-R_2(CHN)_2C＝N (1a?c,e) or 1,3-R_2(CH_2N)_2C＝N (2a?d), R = ~tBu (a), 2,6-Me_2C_6H_3 (b), 2,6-~iPr_2C_6H_3 (c), C_6H_5 (d), 2,6-(Ph_2CH)_2-4-MeC_6H_2 (e); L = 1,3- (2,6-~iPr_2C_6H_3)_2(CHN)_2C＝N, R' = 1-adamantyl (Ad, 3c), C_6H_5 (4c); L = 1,3-(2,6-~iPr_2C_6H_3)_2(CH_2N)_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 Et_2AlCl cocatalyst; the 2,6- R_2C_6H_3 analogues (R = Me, ~iPr; 1b,c, 2b,c) exhibited higher catalytic activities than the ~tBu 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-~iPr_2C_6H_3 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 Et_2AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB).