Vanadium( v ) tetra-phenolate complexes: synthesis, structural studies and ethylene homo-(co-)polymerization capability
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...
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Published in | RSC advances Vol. 5; no. 109; pp. 89783 - 89796 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
01.01.2015
|
Subjects | |
Online Access | Get full text |
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Summary: | 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
. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 2046-2069 2046-2069 |
DOI: | 10.1039/C5RA20177B |