Novel olefin polymerization catalysts based on iron and cobalt

Article abstract of DOI:10.1039/a801933i

A new family of olefin polymerization catalysts, derived from iron and cobalt complexes bearing 2,6-bis(imino)pyridyl ligands, is described.

Full text of DOI:10.1039/a801933i

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Novel olefin polymerization catalysts based on iron and cobalt
George J. P. Britovsek,a Vernon C. Gibson,*a† Brian S. Kimberley,b Peter J. Maddox,b Stuart J. McTavish,a
Gregory A. Solan,a Andrew J. P. Whitea and David J. Williamsa
a Department of Chemistry, Imperial College, Exhibition Road, South Kensington, London, UK SW7 2AY
b BP Chemicals, Sunbury Research Centre, Chertsey Road, Sunbury on Thames, Middlesex, UK TW16 7LN
A new family of olefin polymerization catalysts, derived
from iron and cobalt complexes bearing 2,6-bis(imino)py-
ridyl ligands, is described.
these are the first iron based catalysts to show significant
activities for the polymerization of ethylene. The precursor
complexes are prepared by treatment of FeCl2 or CoCl2 with the
2,6-bis(imino)pyridines in excellent yields according to Scheme
1.‡ Derivatives containing a variety of bulky aryl substituents
are accessible, the iron compounds 1a–d being blue, while the
aldimine complex 1e and the cobalt compound 2 are green; all
are paramagnetic. The magnetic moment of 5.34 mB (Evans
balance) of complex 1a indicates a high spin electronic
configuration with four unpaired electrons for the d6 iron(ii)
centres in these complexes.
Crystals of 1a suitable for an X-ray structure determination§
were grown from a layered CH2Cl2–pentane (1:1) solution; the
molecular structure is shown in Fig. 1. The complex has
molecular CS symmetry about a plane containing the iron, the
two chlorides and the pyridyl nitrogen atom. The geometry at
the FeII centre can probably be best described as distorted
square pyramidal, with Cl(1) occupying the apical position. The
four basal atoms are co-planar to within 0.02 Å, the iron atom
lying 0.59 Å out of this plane. The Fe–Cl bonds are noticeably
asymmetric, with that to the apical chloride being significantly
longer [at 2.311(2) Å] than that to its basal counterpart [2.266(2)
Å]. The Fe–N(imino) distances [av. 2.244(4) Å] are noticeably
longer than the Fe–N(pyridyl) bond length [2.088(4) Å],
probably as a consequence of satisfying the tridentate chelating
constraints of the ligand. The bis(imino)pyridine unit is co-
planar to within 0.19 Å, the plane extending to include the basal
chloride Cl(2) with the 2,6-diisopropylphenyl rings each being
inclined by 79° to this plane. There is no apparent delocalisation
of the imino double bonds into the pyridyl ring system, the
C(7)–N(7) and C(9)–N(9) bond lengths being 1.285(6) and
1.280(6) Å, respectively.
Metallocene catalyst technology has made a dramatic impact on
the polyolefins industry, providing access to polyolefinic
materials with new or improved performance parameters.1–7
There is thus great interest in the discovery and development of
new families of catalysts for a-olefin polymerisation with a
view to obtaining ever greater control over the properties of the
resultant polymers and to extending the family of products to
new monomer combinations. Late transition metal catalysts are
particularly attractive because of their potential for tolerating
heteroatom functionalities, which may open up the possibility
for copolymerizations of polar comonomers. A significant
development in late transition metal polymerization technology
was reported by Brookhart and co-workers who showed that
catalysts based on nickel and palladium could be used to access
a range of linear and branched polyethylenes.8–11
Here we describe a new, strikingly active family of ethylene
polymerization catalysts based on iron and cobalt bearing
2,6-bis(imino)pyridyl ligands. To the best of our knowledge
R1
R4
O
+
2
N
R2
R3
O
NH2
R1
i
R4
R3
R3
R4
R4
R2
R1
R2
R1
N
N
N
R3
Cl(1)
ii
Cl
Cl
C(9)
N
N
M
N(1)
C(7)
N
R3
R1
R2
R1
R2
N(9)
Fe
N(7)
R4
R1 R2 R3 R4
Cl(2)
M
1a Fe Me Pri Pri
1b Fe Me Me Me
H
H
1c Fe Me Me Me Me
1d Fe Me Me
1e Fe Me Me
Co Me Pri Pri
H
Me
H
H
Fig. 1 The molecular structure of 1a. Selected bond lengths (Å) and angles
(°): Fe–Cl(1) 2.311(2), Fe–Cl(2) 2.266(2), Fe–N(1) 2.088(4), Fe–N(7)
2.238(4), Fe–N(9) 2.250(4), C(7)–N(7) 1.285(6), C(9)–N(9) 1.280(6);
N(1)–Fe–N(7) 73.2(1), N(1)–Fe–N(9) 72.9(1), N(7)–Fe–Cl(2) 98.6(1),
N(9)–Fe–Cl(2) 98.9(1), N(1)–Fe–Cl(2) 147.9(1), N(7)–Fe–N(9) 140.1(1)
2
H
Scheme 1 Reagents and conditions: i, EtOH, AcOH; ii, MCl2, BunOH, 80
°C, 10 min
Chem. Commun., 1998
849

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Table 1 Results of ethylene polymerisation runs using procatalysts 1 and 2a
Activity/
Procatalyst
(mmol)
Activator
(mmol/equiv)
Pressure
C2H4/bar
Yield
PE/g
g mmol21
h21 bar21
Run
1
T/°C
25
50
25
50
25
50
25
50
25
25
50
Solvent
toluene
Mw
1a
(10)
1a
(0.5)
1b
(20)
1b
(0.6)
1c
(10)
1c
(0.6)
1d
(20)
1d
MAO
(1.0/100)
MAO
(0.5/1000)
MAO
(8.0/400)
MAO
(0.6/1000)
MAO
(1.0/100)
MAO
(0.6/1000)
MAO
(8.0/400)
MAO
1
10
1
5.8
26.9
5.7
1170
5430
570
203000
611000
29000
242000
52000
562000
260
2
isobutane
toluene
3
4
isobutane
toluene
10
1
56.5
6.2
9340
1230
11020
120
5
6
isobutane
toluene
10
1
63.1
1.2
7
8
isobutane
toluene
10
1
7.8
1280
740
470
(0.6)
1e
(10)
2
(10)
2
(0.6/1000)
MAO
(1.0/100)
MAO
(1.0/100)
MAO
9
3.7
15000
26000
14000
10
11
toluene
1
2.3
460
isobutane
10
3.7
450
(0.5)
(0.5/1000)
a General conditions: 1 atm Schlenk tests carried out in toluene over 30 min, reaction quenched with dil. HCl and the solid PE washed with MeOH (50 cm3)
and dried in a vacuum oven at 50 °C. 10 atm tests performed in 1 l autoclave, procatalyst dissolved in toluene, isobutane solvent, triisobutylaluminium
scavenger, runs carried out over 60 min.
The results of ethylene polymerization tests are collected in
Table 1. Several features are noteworthy. In general, the
activities of the iron catalysts are exceptionally high, in many
cases comparable or even higher than those seen by metal-
locenes under analogous conditions. All of the catalysts produce
essentially linear polyethylene with molecular weights that are
dependent upon the aryl substitution pattern. Most notable is a
dramatic fall-off in molecular weight to a-olefin oligomers for
derivatives with one o-methyl substituent (runs 7,8) compared
with derivatives that contain methyl substituents in both ortho
positions. Clearly steric protection of the active site is a crucial
factor in controlling molecular weight.
There is also a marked dependence of the polymer molecular
weight on ethylene pressure for the iron catalyst system, an
effect that is not seen for the cobalt catalyst 2 (runs 10, 11); the
cobalt catalyst also displays a considerably lower activity than
its iron analogue. 13C NMR end-group analysis of the polymers
generated by 1a–c (runs 2, 4, 6) reveals isopropyl end-groups in
addition to low levels of vinyl unsaturation. This is consistent
with a termination mechanism involving alkyl group transfer
from the AlBui3 scavenger in addition to b-H transfer. The
polymers formed from 1d and the aldimine catalyst 1e contain
a larger proportion of vinyl end-groups ( > 4 per 1000 carbons)
indicating that b-H transfer plays a more dominant role in chain
termination for these catalysts.
Notes and References
† E-mail: v.gibson@ic.ac.uk
‡ Satisfactory elemental analyses have been obtained.
§Crystal data for 1a: C33H43N3Cl2Fe·0.5H2O, M = 617.5, triclinic, P1 (no.
2), a = 8.779(1), b = 9.876(1), c = 20.976(1) Å, a = 83.70(1), b =
88.18(1), g = 65.67(1)°, V = 1646.9(3) Å3, Z = 2, Dc = 1.245 g cm23
m(Cu-Ka) = 53.6 cm21, F(000) = 654. A deep blue platy needle of
dimensions 0.40 3 0.20 3 0.03 mm was used. 4878 independent reflections
were measured on a Siemens P4/PC diffractometer with Cu-Ka radiation
using w-scans. The structure was solved by direct methods and all of the
non-hydrogen atoms were refined anisotropically using full-matrix least-
squares based on F2 to give R1 = 0.061, wR2 = 0.144 for 3595 independent
observed, absorption corrected reflections [ıFoı > 4s(ıFoı), 2q @ 120°]
and 362 parameters. CCDC 182/812.
¯
,
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The new catalyst family described herein represents a
significant addition to the growing armoury of technologically
important olefin polymerization catalysts.
BP Chemicals Ltd is thanked for financial support. Dr J.
Boyle and Dr G. Audley are thanked for NMR and GPC
measurements, respectively.
Received in Liverpool, UK, 10th March 1998; 8/01933I
850
Chem. Commun., 1998