Bis(β‐enaminoketonato) vanadium (III or IV) complexes as catalysts for olefin polymerization

Abstract

Bis(b-enaminoketonato) vanadium(III) complexes (2a-c) [O(R 1 )C¼ ¼C(H) x C(R 2 )¼ ¼NC 6 H 5 ] 2 VCl(THF) and the corresponding vanadium(IV) complexeshave been synthesized from VCl 3 (THF) 3 and VOCl 2 (THF) 2 , respectively, by treating with 2.0 equivalent b-enaminoketonato ligands in tetrahydrofuran. Structures of 2b and 3a-c were further confirmed by X-ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et 2 AlCl. Complexes 2a-c and 3a-c exhibited high catalytic activities (up to 23.76 kg of PE/mmol V h bar), and afforded polymers with unimodal molecular weight distributions at 70 C indicating the good thermal stability. The cata-lytic behaviors were influenced not only by the oxidation state of the catalyst precursors but also by the ligand structures. Complexes 2a-c and 3a-c were also effective catalyst precursors for ethylene/1-hexene copolymerization. The influence of polymerization parameters such as reaction temperature, Al/V molar ratio and hexene feed concentration on the ethylene/hexene copolymerization behaviors have bee also investigated in detail. In addition, the agents such as AlMe 3 , Al i Bu 3 , MeMgBr, MgCl 2 , and ZnEt 2 were applied to control the molecular weight and molecular weight distribution modal. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: [3062][3063][3064][3065][3066][3067][3068][3069][3070][3071][3072] 2010

Well-defined vanadium complexes as the catalysts for olefin polymerization

“…2 and 3) [51]. By comparison, a small but significant lengthening of the V-O and V-N bond distances in vanadium complex 2b in contrast with those in the mono(␤-enaminoketonato) vanadium(III) complexes (1.910-1.922Å and 2.048-2.064Å) was observed because the two coordinated ligands repulsed each other.…”

“…The influence of chain transfer reagents on the molecular weights and molecular weight distributions of the resultant PEs produced by 2b/Et2AlCl[51]. (1: 50 equiv.…”

Oxovanadium(IV) complexes with [ONNO]-chelating ligands as catalysts for ethylene homo- and copolymerization

“…The chain transfer reaction was enhanced at higher temperatures and polyethylene with lower molecular weight was formed at 50°C then at 30°C (Table 1, entry 6 and 7). It is a result of higher activation energies for the chain transfer reactions then for the monomer insertions which affects the relative rate of chain transfer as compared to the rate of propagation [34]. In addition, the molecular weight distributions increase with the temperature increase.…”

Olefin Polymerization with Non-metallocene Catalysts (Early Transition Metals)

“…A series of vanadium(III) complexes containing b-enaminoketonato [99, 100], phenoxy-imine [101][102][103][104], imino-pyrrolide [105] ligands (exemplified in Scheme 3.11) were tested as olefin polymerization catalyst in the presence of Et 2 AlCl and Cl 3 CCO 2 Et. The selected results are summarized in Table 3.5 [99,100,103,105]. The observed activities by certain complexes were slightly/apparently higher than those by VCl 3 (THF) 3 , and the activities decreased at 70 8C probably due to the rapid deactivation even for short period (5 min) and in the presence of excess amount of re-oxidant (300 equivalent to V).…”

“…Although both the activities and the polymerization behavior were affected by the ligand substituents, the detailed explanation by electronic/steric factors seems difficult (factors such as ligand transfer to Al, reductions etc.). In contrast, the imino-pyrrolide analogues (28) showed remarkable activities [105], and the activities by 28 increased in the order (ethylene 1 atm, 50 8C for 5 min): 28c (R = 2,6- [99,100,103,105] (4-CF 3 C 6 H 4 ) [ 28a (cyclohexyl). The results thus suggest that both electronic and steric factors play an important role (probably for strong coordination).…”