Vanadium( v ) tetra-phenolate complexes: synthesis, structural studies and ethylene homo-(co-)polymerization capability

• Published in: RSC advances Vol. 5; no. 109; pp. 89783 - 89796
• Main Authors: Redshaw, Carl, Walton, Mark J., Elsegood, Mark R. J., Prior, Timothy J., Michiue, Kenji
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Benchmarking; Catalysts; Chlorides; Copolymerization; Ethylene; Molecular weight; Propylene; Toluene
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/C5RA20177B

Reaction of α,α,α′,α′-tetrakis(3,5-di- tert -butyl-2-hydroxyphenyl)- p -xylene ( p - L1 H 4 ) with two equivalents of [VO(OR) 3 ] (R = n Pr, t Bu) in refluxing toluene afforded, after work-up, the complexes {[VO(O n Pr)(THF)] 2 (μ- p - L1 )}·2(THF) ( 1 ·2(THF)) or {[VO(O t Bu)] 2 (μ- p - L1 )}·2MeCN ( 2 ·2MeCN), respectively in moderate to good yield. A similar reaction using the meta pro-ligand, namely α,α,α′,α′-tetrakis(3,5-di- tert -butyl-2-hydroxyphenyl)- m -xylene ( m - L2 H 4 ) afforded the complex {[VO(O n Pr)(THF)] 2 (μ- p - L2 )} ( 3 ). Use of [V(N p -R 1 C 6 H 4 )( t BuO) 3 ] (R 1 = Me, CF 3 ) with p - L1 H 4 led to the isolation of the oxo–imido complexes {[VO( t BuO)][V(N p -R 1 C 6 H 4 ) ( t BuO)](μ- p - L1 )} (R 1 = Me, 4 ·CH 2 Cl 2 ; CF 3 , 5 ·CH 2 Cl 2 ), whereas use of [V(N p -R 1 C 6 H 4 )Cl 3 ] (R 1 = Me, CF 3 ) in combination with Et 3 N/ p - L1 H 4 or p - L1 Na 4 afforded the diimido complexes {[V(N p -MeC 6 H 4 )(THF)Cl] 2 (μ- p - L1 )}·4toluene ( 6 ·4toluene) or {[V(N p -CF 3 C 6 H 4 )(THF)Cl] 2 (μ- p - L1 )} ( 7 ). For comparative studies, the complex [(VO)(μ-O n Pr)L 3 ] 2 ( 8 ) has also been prepared via the interaction of [VO( n PrO) 3 ] and 2-(α-(2-hydroxy-3,5-di- tert -butylphenyl)benzyl)-4,6-di- tert -butylphenol ( L3H2 ). The crystal structures of 1 ·2THF, 2 ·2MeCN, 3 , 4 ·CH 2 Cl 2 , 5 ·CH 2 Cl 2 , 6 ·4toluene·THF, 7 and 8 have been determined. Complexes 1–3 and 5–8 have been screened as pre-catalysts for the polymerization of ethylene in the presence of a variety of co-catalysts (with and without a re-activator), including DMAC (dimethylaluminium chloride), DEAC (diethylaluminium chloride), EADC (ethylaluminium dichloride) and EASC (ethylaluminium sesquichloride) at various temperatures and for the co-polymerization of ethylene with propylene; results are compared versus the benchmark catalyst [ VO(OEt)Cl2 ]. In some cases, activities as high as 243 400 g mmol −1 V −1 h −1 (30.43 kgPE mmol V −1 h −1 bar −1 ) were achievable, whilst it also proved possible to obtain higher molecular weight polymers (in comparable yields to the use of [ VO(OEt)Cl2 ]). In all cases with dimethylaluminium chloride (DMAC)/ethyltrichloroacetate (ETA) activation, the activities achieved surpassed those of the benchmark catalyst. In the case of the co-polymerization of ethylene with propylene, complexes 1–3 and 5–8 showed comparable or higher molecular weight than [ VO(OEt)Cl2 ] with comparable catalytic activities or higher in the case of the imido complexes 6 and 7 .