Steric and electronic modulation of iron catalysts as a route to remarkably high molecular weight linear polyethylenes
Five structurally related bis(arylimino)pyridine-iron( ii ) chloride complexes, [2-[CMeN{2,6-{(4-FC 6 H 4 ) 2 CH} 2 -4-NO 2 }]-6-(CMeNAr)C 5 H 3 N]FeCl 2 (Ar = 2,6-Me 2 C 6 H 3 Fe1 , 2,6-Et 2 C 6 H 3 Fe2 , 2,6-i-Pr 2 C 6 H 3 Fe3 , 2,4,6-Me 3 C 6 H 2 Fe4 , and 2,6-Et 2 -4-MeC 6 H 2 Fe5 ), incorporati...
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Veröffentlicht in: | Dalton transactions : an international journal of inorganic chemistry 2019-12, Vol.48 (47), p.17488-17498 |
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Sprache: | eng |
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Zusammenfassung: | Five structurally related bis(arylimino)pyridine-iron(
ii
) chloride complexes, [2-[CMeN{2,6-{(4-FC
6
H
4
)
2
CH}
2
-4-NO
2
}]-6-(CMeNAr)C
5
H
3
N]FeCl
2
(Ar = 2,6-Me
2
C
6
H
3
Fe1
, 2,6-Et
2
C
6
H
3
Fe2
, 2,6-i-Pr
2
C
6
H
3
Fe3
, 2,4,6-Me
3
C
6
H
2
Fe4
, and 2,6-Et
2
-4-MeC
6
H
2
Fe5
), incorporating one
N
-2,6-bis{di(4-fluorophenyl)methyl}-4-nitrophenyl group and one distinct
N
-aryl group, have been prepared in good yield through the interaction of the corresponding free ligands (
L1-L5
) with FeCl
2
·4H
2
O. All ferrous complexes were paramagnetic which was manifested by broad and highly shifted peaks in their
1
H NMR spectra. The marked steric imbalance imposed by the two inequivalent
N
-aryl groups was a key feature highlighted in the molecular structures of representative complexes
Fe1
and
Fe2
. Upon activation with either MAO or MMAO,
Fe1-Fe5
all exhibited high activities for ethylene polymerization with good thermal stability [activities as high as 1.58 × 10
7
g (PE) mol
−1
(Fe) h
−1
at 60 °C], affording especially high molecular weight linear polyethylenes (3.92 × 10
5
g mol
−1
at 70 °C;
T
m
> 130 °C). To the best of our knowledge, the molecular weights of the polyethylenes produced by the current class of iron catalysts exceed the highest values reported for related bis(imino)pyridine-iron catalysts to date; changes in the
ortho
-R
1
substitution pattern offered some additional fine control of the molecular weight. Moreover, the nature of the aluminoxane co-catalyst employed had a noticeable effect on the polymer end group composition. When using MAO, unsaturated polymers containing both vinyl and
n
-propyl end groups were evident, whereas with MMAO, fully saturated polymers were generated containing both isobutyl and
n
-propyl end groups.
The depicted
N
,
N
,
N
-iron(
ii
) chloride precatalysts, upon activation with either MAO or MMAO, not only display excellent thermal stability but are also capable of generating exceptionally high molecular weight linear polyethylenes. |
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ISSN: | 1477-9226 1477-9234 |
DOI: | 10.1039/c9dt03880a |