A highly efficient titanium-based olefin polymerisation catalyst with a monoanionic iminoimidazolidide π-donor ancillary ligand

Article abstract of DOI:10.1039/b111343g

The titanium complex Cp[1,3-(2′,6′-Me₂C₆H₃) ₂(CH₂N)₂C=N]Ti(CH₂Ph) ₂, with a monoanionic η¹-iminoimidazolidide ancillary ligand, is shown to be a highly effi

Full text of DOI:10.1039/b111343g

A highly efficient titanium-based olefin polymerisation catalyst with a
monoanionic iminoimidazolidide p-donor ancillary ligand†‡
Winfried P. Kretschmer,* Chris Dijkhuis, Auke Meetsma, Bart Hessen and Jan H. Teuben
Dutch Polymer Institute/Centre for Catalytic Olefin Polymerisation, Stratingh Institute of Chemistry and
Chemical Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
E-mail: kretschmer@chem.rug.nl
Received (in Cambridge, UK) 12th December 2001, Accepted 12th Febraury 2002
First published as an Advance Article on the web 25th February 2002
The
titanium
complex
Cp[1,3-(2A,6A-
Me2C6H3)2(CH2N)2CNN]Ti(CH2Ph)2, with a monoanionic
h1-iminoimidazolidide ancillary ligand, is shown to be a
highly efficient catalyst for olefin polymerisation when
activated with the Lewis acid B(C6F5)3.
Since the development of highly efficient group 4 metallocene
catalysts for the polymerisation of olefins in the 1980–1990s,1
recent research efforts into the design of new single-site olefin
polymerisation catalysts have increasingly turned to non-
metallocene systems.2 Cationic mono(cyclopentadienyl) tita-
nium alkyl complexes with an additional monoanionic p-donor
ancillary ligand form a group of very interesting catalysts for the
homo- and copolymerisation of olefins. Typical p-donor
ancillary ligands that have been used in these catalysts are
substituted phenoxides 2,6-R2C6H3O2,3 ketimides R2CNN2,4
and phosphinimides R3PNN2.5 The latter are especially effec-
tive, which is possibly due to an improved p-donor capability
through the availability of a zwitterionic resonance structure,
increasing the negative charge on the nitrogen atom. Another
system that, for similar reasons, may be expected to be an
efficient ancillary ligand is the monoanionic 1,1,3,3-tetra-
(2a) and Cp[Xy2(CH2N)2CNN]Ti(CH2Ph)2 (2b) were prepared
through reaction of the corresponding dichlorides with two
equiv. of benzyl Grignard, while the latter was also accessible
by reaction of CpTi(CH2Ph)3 with the neutral iminoimidazoli-
dine (Scheme 2).
A crystal structure determination of the dichloride complex
Cp[Ph2(CH2N)2CNN]TiCl2 (1bA, Fig. 1)§ reveals a monomeric,
three-legged piano-stool structure.8 The Ti–N(1) distance is
short (1.792(2) Å), suggesting substantial p-donation to the
metal centre, although the C(6)–N(1)–Ti arrangement is slightly
bent (152.9(2)°). The distances of N(2) and N(3) to the central
carbon atom C(6) are 0.1 Å shorter than those to the backbone
carbons C(7/8), and both nitrogens are essentially planar (the
sums of the angles around each N atom are 358.4 and 359.8°
respectively), indicating substantial delocalisation in the N2CN-
fragment. A similar short Ti–N distance (1.78 Å) was found in
1
substituted h -guanidinate group, (R2N)2CNN2 (Scheme 1).
We have used a 1,1,3,3-bis(pentamethylene) guanidinate
anion (A) and a sterically protected guanidinate-type ligand, the
1,3-diaryliminoimidazolidide anion (B), as ancillary ligands in
mono(cyclopentadienyl) titanium olefin polymerisation cata-
lysts. A comparison with catalysts supported by the related bis-
But-ketimide (C) and tris-But-phosphinimide ligands (D) shows
that especially the 1,3-diaryliminoimidazolidide complex is a
highly efficient catalyst for olefin homo- and copolymerisation,
with good thermal stability and good resistance towards
alkylaluminium scavengers.
a
complex of another strong p-donating ligand,
Cp(Ph3PNN)TiCl2, whereas the ketimide complex Cp(Bun-
ButCNN)TiCl2 has a longer Ti–N distance of 1.872 Å.9 While
The lithium[1,1,3,3-bis(pentamethylene)guanidinate] Li[A]
was prepared in situ by reaction6 of piperidyl lithium with
1-piperidinecarbonitrile, while the 1,3-diaryliminoimidazoli-
2
3
structures of h /h -bonded guanidinate complexes are well
documented,10 1bA represents a rare example of a structurally
1
characterised transition metal complex with a non-bridging h -
dines 1,3-Ar2(CH2N)2CNNH, with Ar
=
Xy (Xy
=
bonded guanidinate ligand.11
2,6-Me2C6H3; H[B]), Ph (H[BA]) were prepared from 1,2-diani-
linoethanes and cyanogen bromide in toluene according to
literature procedures.7 The corresponding cyclopentadienyl
titanium dichloride complexes Cp{[(CH2)5N]2CNN}TiCl2 (1a)
and Cp[Ar2(CH2N)2CNN]TiCl2 (1b, 1bA) were prepared by
reaction of CpTiCl3 with the Li-salts of the ligands. The
titanium dibenzyl complexes Cp{[(CH2)5N]2CNN}Ti(CH2Ph)2
Reaction of the dibenzyl complex 2b with the Lewis acidic
borane B(C6F5)3 leads to smooth abstraction of one benzyl
Scheme 1 Resonance structures in 1,1,3,3-tetrasubstituted guanidinate
anions.
† Electronic supplementary information (ESI) available: experimental,
spectroscopic and polymerisation details. See http://www.rsc.org/suppdata/
cc/b1/b111343g/
‡ Netherlands Institute for Catalysis Research (NIOK) publication no. RUG
01-4-05.
Scheme 2 Reagents and conditions: i, 280 to 25 °C, thf, 2 h; ii, 2 equiv.
PhCH2MgBr, 220 to 25 °C, Et2O, 12 h; iii, 50 °C, toluene, 2 h.
608
CHEM. COMMUN., 2002, 608–609
This journal is © The Royal Society of Chemistry 2002

catalyst Cp[Xy2(CH2N)2CNN]Ti(CH2Ph)2/B(C6F5)3 is also ef-
fective in ethene/1-alkene copolymerisation and propene homo-
polymerisation. Copolymerisation runs at 80 °C in 210 ml of
toluene at 5 bar ethene pressure, with 20 ml of 1-hexene or
styrene added, yielded the copolymers ethene/1-hexene (3960
kg mol21 h21, Mw = 181 3 103, Mw/Mn = 2.0, 18 wt%
1-hexene incorporation) and ethene/styrene (1960 kg mol21
h21, Mw = 179 3 103, Mw/Mn = 2.1, 10 wt% styrene
incorporation). Propene homopolymerisation (50 °C, 3 bar
propene, 210 ml toluene solvent) yielded polypropene (14360
kg mol21 h21, Mw = 81 3 103, Mw/Mn 1.9) that shows a
significant enrichment in syndiotactic triads (60% rr, 23%
mm).
In conclusion, we have established that the 1,3-bis(xylyl)imi-
noimidazolidide anion is an excellent monoanionic ancillary
ligand for monocyclopentadienyl titanium olefin polymer-
isation catalysts. The comparative ethene homopolymerisation
experiments performed thus far suggest that, under the applied
conditions, the catalyst is even more efficient than the
corresponding catalyst with the successful tris(tert-butyl)phos-
phinimide ancillary ligand.
Fig. 1 Molecular structure of Cp[Ph2(CH2N)2CNN]TiCl2 1bA (hydrogen
atoms omitted for clarity). Selected interatomic distances (Å) and angles (°):
Ti–Cl(1) 2.3045(7), Ti–Cl(2) 2.2902(7), Ti–N(1) 1.792(2), N(1)–C(6)
1.305(3), N(2)–C(6) 1.359(3), N(2)–C(7) 1.465(3), N(3)–C(6) 1.362(3),
N(3)–C(8) 1.467(4); Ti–N(1)–C(6) 152.9(2), Cl(1)–Ti–Cl(2) 100.90(2),
Cl(1)–Ti–N(1) 104.92(6), Cl(2)–Ti–N(1) 105.55(6).
2
Notes and references
group to yield the ionic complex {Cp[Xy2(CH2N)2CNN]Ti(h -
CH2Ph)2}+[PhCH2B(C6F5)3]2. As seen by NMR spectroscopy
(C6D5Br solvent),12 the anion is non-coordinating and the
§ Crystallographic data for Cp[1,3-Ph2(CH2N)2CNN]TiCl2 (1bA):
C20H19Cl2N3Ti, M = 420.15, orthorhombic, space group P212121, a =
9.868(1), b = 10.320(1), c = 18.840(1) Å, U = 1918.6(3) Å3, T = 180 K,
Z = 4, Dc = 1.455 g cm23, m = 7.33 cm21, Enraf-Nonius CAD-4F
diffractometer, l(Mo-Ka) = 0.71073 Å, 4401 unique reflections, final
residuals wR(F2) = 0.0764, R(F) = 0.0316 for 4018 reflections with Fo !
4s(Fo) and 311 parameters. CCDC reference number 176621. See http://
www.rsc.org/suppdata/cc/b1/b111343g/ for crystallographic data in CIF or
other electronic format.
2
cationic metal centre is stabilised by an h -bonding of the
remaining metal-bound benzyl group.13
In order to compare their efficiency in olefin polymerisation
catalysis, all the complexes Cp(L)Ti(CH2Ph)2 (2a–2b), with L
= [(CH2)5N]2CNN2 (A), Xy2(CH2N)2CNN2 (B), But2CNN2
(C) and But3PNN2 (D) were synthesised, and tested for ethene
homopolymerisation with B(C6F5)3 activator, both in the ab-
sence and presence of partially hydrolysed tris(isobutyl)alumin-
ium (TIBAO)14 as impurity scavenger. The results of these
experiments are listed in Tables 1 and 2 respectively.
From these data it can be seen that the catalyst with the
iminoimidazolidide ligand B is highly efficient, both with and
without TIBAO scavenger. Under the applied conditions this
catalyst performs even better than the catalyst with the
phosphinimide ligand D. The catalysts with the ketimide C and
guanidinate A ancillary ligands are less efficient, with the
guanidinate being especially susceptible to deactivation by
TIBAO scavenger. The steric protection imparted by the xylyl
substituents in the iminoimidazolidide catalyst apparently
makes the system much more robust, while retaining the
favourable electronic properties of the N2CNN ligand core. The
1 W. Kaminsky, Macromol. Chem. Phys., 1996, 197, 3907; M. Boch-
mann, J. Chem. Soc., Dalton Trans., 1996, 255; H. G. Alt and A. Köppl,
Chem. Rev., 2000, 100, 1205.
2 G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., 1999,
111, 448; G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew.
Chem., Int. Ed., 1999, 38, 428.
3 K. Nomura, N. Naga, M. Miki, K. Yanagi and A. Imai, Organome-
tallics, 1998, 17, 2152; K. Nomura, N. Naga, M. Miki and K. Yanagi,
Macromolecules, 1998, 31, 7588.
4 S. Zhang, W. E. Piers, X. Gao and M. Parvez, J. Am. Chem. Soc., 2000,
122, 5499; J. McMeeking, X. Gao, R. P. v. H. Spence, S. J. Brown and
D. D. Jeremic, World Pat., WO 9914250, 1999(Nova Chemicals).
5 D. W. Stephan, J. C. Stewart, F. Guérin, R. E. v. H. Spence, W. Xu and
D. G. Harrison, Organometallics, 1999, 18, 1116; D. W. Stephan, J. C.
Stewart, S. J. Brown, J. W. Swabey and Q. Wang, Eur. Pat., EU
0881233, 1998 (Nova Chemicals).
6 W. Clegg, R. Snaith, H. M. M. Shearer, K. Wade and G. Whitehead, J.
Chem. Soc., Dalton Trans., 1983, 1309.
7 L. Toldy, M. Kürti and I. Schäfer, Ger. Pat., DE 2916140, 1979 (Egyt
Gyo. Gyar.).
Table 1 Ethene homopolymerisation with Cp(L)Ti(CH2Ph)2/B(C6F5)3 ca-
talysts (10 mmol Ti, 1.1 equiv. B(C6F5)3, 210 ml toluene, 5 bar ethene, 80
°C, 15 min run time)
8 A crystal structure determination of 1a revealed a similar monomeric
structure. These data will be reported separately.
9 I. A. Latham, G. J. Leigh, G. Huttner and I. Jibril, J. Chem. Soc., Dalton
Trans., 1986, 377.
Productivity/
kg(PE) mol(Ti)21
Ligand L
PE yield/g
h21 bar21
1023 Mw
Mw/Mn
10 P. J. Bailey and S. Pace, Coord. Chem. Rev., 2001, 214, 91.
11 N. Kuhn, R. Fawzi, M. Steinmann and J. Wiethoff, Z. Anorg. Allg.
Chem., 1997, 623, 769.
A
B
C
D
4.7
11.2
4.4
376
896
353
848
406
361
543
518
1.9
1.9
1.9
2.2
12 1H NMR (C6D5Br, 293 K): d 2.23 (s, 12 H, CH3), 2.73 (s, 2 H,
C6H5CH2Ti), 3.39 (s, br, 2 H, C6H5CH2B), 3.51 (s, 4 H, NCH2), 5.21 (s,
5H, C5H5), 6.29 (d, 2 H, JHH 7.7 Hz, C6H5CH2), 6.83 (t, 2 H, JHH 7.4 Hz,
C6H5CH2), 6.90–7.25 (m, 12 H, Me2C6H3, C6H5CH2); 13C{1H} NMR
(C6D5Br, 293 K, all CF resonances were excluded): d 18.4 (CH3), 33.0
(br, BCH2), 46.6 (CH2CH2), 69.9 (TiCH2), 112.8 (C5H5), 117.4 (Ph),
122.5 (Ph), 123.4 (Ph), 127.8 (C6H3), 128.8 (Ph), 129.7 (C6H3), 130.6
(Ph), 134.3 (C6H3), 135.7 (Ph), 137.5 (C6H3), 149.6 (Ph), 152.4 (Ph),
160.6 (CN); 19F NMR (C6D5Br, 293 K): d 2131.1 (d, o-F), 2164.4 (t,
p-F), 2167.2 (t, m-F); Dd [(p-F) 2 (m-F)] 2.8 ppm.
10.6
Table 2 Ethene homopolymerisation with Cp(L)Ti(CH2Ph)2/B(C6F5)3
catalysts and TIBAO scavenger (10 mmol Ti, 1.1 equiv. B(C6F5)3, Al/Ti =
20, 260 ml toluene, 5 bar ethene, 80 °C, 15 min run time)
Productivity/
kg(PE) mol(Ti)21
13 A. D. Horton, J. de With, A. J. van der Linden and H. van de Weg,
Organometallics, 1996, 15, 2672; C. Pellecchia, A. Immirzi, A. Grassi
and A. Zambelli, Organometallics, 1993, 12, 4473; A. D. Horton and J.
de With, Chem. Commun., 1996, 1375.
14 Prepared according to: J. F. van Baar, P. A. Schut, A. D. Horton, T.
Dall’occo and G. M. M. van Kessel, World Pat., WO0035974, 2000
(Montell).
Ligand L
PE yield/g
h21 bar21
1023 Mw
Mw/Mn
A
B
C
D
0.4
20.0
5.8
32
1600
464
583
663
—
1.7
2.2
—
14.1
1128
717
2.1
CHEM. COMMUN., 2002, 608–609
609