Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

Abstract

The synthesis and the characterization of a series of phosphine adducts of (imido)vanadium(IV) dichloride complexes of the type V(NR)Cl 2 (PMe 2 Ph) 2 [R = 2,6-Cl 2 -Ph (1), 2,6-i Pr 2 -Ph (2), and t Bu (3)] and V( N t Bu)Cl 2 (PMe 3 ) 2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N−V−C bond. Complexes 1−3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et 2 AlCl (500 equiv to V) and Cl 3 CCO 2 Et (ETA, 10 equiv to V), 1−3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly(ethylene)s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo-and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron-donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V−N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand.

Copolymerization of ethylene with propylene and higher α-olefins catalyzed by (imido)vanadium(iv) dichloride complexes

“…Compounds [V(=NR)Cl 2 (PMe 2 Ph) 2 ] [R = t Bu (3a), and 2,6-i Pr 2 -C 6 H 3 (3d)] were prepared according to our published procedure. 35,37 Aniline 2,6-(Ph 2 CH) 2 -4-Cl-C 6 H 2 (Ar**NH 2 ) was prepared according to a known synthesis, 38 and carefully dried first in dichloromethane solution under MgSO 4 , and then in the solid state in a desiccator with P 2 O 5 under vacuum, and stored in the glove box before use.…”

“…In this framework, we recently reported the synthesis of a set of phosphine adducts of (imido)V(IV) complexes, and we demonstrated their successful application as catalyst precursors for the copolymerization of ethylene with cyclic olefins. 35 Herein, to expand our study on this family of complexes, we report the synthesis, and the characterization of 35 were performed as well for comparison. The (co)polymers have been characterized by NMR, DSC, TGA, and SSA, a thermal fractionation technique based on sequential application of self-nucleation and annealing steps.…”

Titanium and Vanadium Catalysts with 2-Hydroxyphenyloxazoline and Oxazine Ligands for Ethylene-Norbornene (co)Polymerization

“…One of the methods to do this is to use a designed catalyst that has a direct impact on the molecular structure of copolymer, which in turn affects its properties [1,6,7,[10][11][12][13][14][15][16]. The key factor determining tacticity and distribution of mers in the polymer chain is catalyst symmetry, which depends on the presence of various ligands in the coordination sphere of transition metal [1,[6][7][8][9][10][11][12][13][14][15][16][17][18]. Similar to the synthesis of polyethylene and ethylene copolymers with 1-olefins, in particular E-NB copolymers, the catalysts with zirconium [1,6,12,19] and titanium [8,12,20] atoms in the active center are the most often studied.…”

“…Similar to the synthesis of polyethylene and ethylene copolymers with 1-olefins, in particular E-NB copolymers, the catalysts with zirconium [1,6,12,19] and titanium [8,12,20] atoms in the active center are the most often studied. The vanadium catalysts [21,22] are less studied, but they receive interest because it is possible to obtain the E-NB copolymers with high molecular weight, narrow molecular weight distribution, and high norbornene incorporation [13,[15][16][17][18][23][24][25][26]. In contrast to the zirconium and titanium catalysts, which work best after methylaluminoxane (MAO) activation [1,[6][7][8]12,19,20], the vanadium catalysts reveal the best performance when activated by AlEt 2 Cl in the presence of reactivator, ethyl trichloroacetate (ETA), which prevents reduction of the vanadium atom to lower oxidation states and influences positively termination and re-initiation processes [13][14][15][16][17][18].…”

“…The vanadium catalysts [21,22] are less studied, but they receive interest because it is possible to obtain the E-NB copolymers with high molecular weight, narrow molecular weight distribution, and high norbornene incorporation [13,[15][16][17][18][23][24][25][26]. In contrast to the zirconium and titanium catalysts, which work best after methylaluminoxane (MAO) activation [1,[6][7][8]12,19,20], the vanadium catalysts reveal the best performance when activated by AlEt 2 Cl in the presence of reactivator, ethyl trichloroacetate (ETA), which prevents reduction of the vanadium atom to lower oxidation states and influences positively termination and re-initiation processes [13][14][15][16][17][18]. A method of stabilizing the vanadium active center, and in consequence, a prolongation of catalyst lifetime, is to apply ligands with electron-donating atoms-oxygen, nitrogen, or phosphorus [14][15][16][17][18][20][21][22][23][24][25][26][27][28].…”