Monoalkyl, chiral-at-metal 'constrained geometry' complexes as efficient α-olefin and methyl methacrylate polymerisation catalysts

Article abstract of DOI:10.1039/b201346k

A new class of monoalkyl or monochloro constrained geometry group 4 complexes has been synthesized; upon activation with aluminium activators they serve as efficient catalysts for olefin polymerisation and for polymerisation of methyl methacrylate.

Full text of DOI:10.1039/b201346k

Monoalkyl, chiral-at-metal ‘constrained geometry’ complexes as efficient
a-olefin and methyl methacrylate polymerisation catalysts
Jizhu Jin,a David R. Wilsonb and Eugene Y.-X. Chen*a
a Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, USA.
E-mail: eychen@lamar.colostate.edu
b The Dow Chemical Company, Chemical Sciences Capability, Midland, MI 48674, USA
Received (in Cambridge, UK) 4th February 2002, Accepted 19th February 2002
First published as an Advance Article on the web 5th March 2002
A new class of monoalkyl or monochloro constrained
geometry group 4 complexes has been synthesized; upon
activation with aluminium activators they serve as efficient
catalysts for olefin polymerisation and for polymerisation of
methyl methacrylate.
formation of 7, the dimethyl Zr complex was not observed, even
upon addition of a one-fold excess of MeLi.
While the dimethyl CGC titanium complex 7 is active for
MMA polymerization upon activation with both B(C6F5)39 and
Al(C6F5)3,10 producing syndiotactic PMMA of 80.7 and 66.0%
syndiotacticity at 25 °C, respectively, the MMA polymerization
by the monomethyl complex 5 strongly depends on the choice
of activator: the borane-activated complex is inactive but the
alane-activated complex is as active as 7. Furthermore, when
activated with a large excess of MAO, the monochloro Zr
complex 2 is highly active for copolymerization of ethylene and
1-octene with activity reaching 1.8 3 108 g polymer (mol Zr)21
h21 (conditions: 2.0 mmol 2, MAO/Zr = 500, Tp = 120 °C, 740
g Isopar E, 118 g C8, 450 psi C2, 5 mmol H2, tp = 15 min, yield
= 89.4 g). In contrast, the analogous Ti complex 1 is practically
inactive yielding only 2.0 g of the copolymer even with 10 mmol
catalyst loading. This trend holds true for propylene polymer-
isation: the monochloro Zr complex 4 is more active than the
monomethyl Ti complex 5, with both complexes producing
essentially atactic polypropylene.
Constrained geometry complexes such as Me2Si(C5Me4)(t-
BuN)–MX2 (CGC–MX2, M = Ti, Zr; X = Cl, alkyl) are
currently of great scientific and technological interest as highly
active Ziegler–Natta-type coordination catalysts for copoly-
merization of ethylene and a-olefins.1 It has been reported that
the pre-activated form of group 4 metallocene and related
complexes must have two or more alkyl (or halide or other
suitable) groups so that there is a remaining metal–alkyl bond
for monomer to insert into after one of the metal–alkyl groups
is abstracted to form the activated species.2
We have previously reported that a doubly activated
constrained geometry Ti complex, which does not contain a free
alkyl ligand in its activated form, is also a highly active olefin
polymerisation catalyst.3 Most recently, Royo et al.4 reported
that, when activated with methylaluminoxane (MAO),5
a
To seek for possible answers for the sharp difference in
polymerisation activity between the Ti and Zr catalysts, 5 was
reacted with B(C6F5)3 yielding CGC–Ti+(Cp)[MeB(C6F5)3]2
(8). The non-coordinating nature of the borate anion is
suggested by the small d (dm 2 dp) = 2.59 ppm in the 19F NMR
of the anion.11 On the other hand, the reaction of the Zr complex
doubly silylamido-bridged cyclopentadienyl zirconium benzyl
complex is active for ethylene polymerisation. These reports
prompted us to disclose here a new class of monoalkyl or
monochloro, chiral-at-metal6 constrained geometry complexes
(1–6) and their use as precursors to efficient catalysts, upon
activation with aluminium activators, for olefin polymerisation
and for polymerisation of methyl methacrylate (MMA).
6 with Al(C6F5)3 produces CGC–Zr+(Cp)MeAl(C6F5)3 (9) in
2
which the aluminate anion is weakly coordinated to the Zr
cation, as evidenced by the chemical shifts3,12 of the CH3 group
of the anion in the 1H NMR and of the C6F5 groups in the 19
F
NMR (Fig. 2). An excess of the alane does not effect the
abstraction of the Cp ligand.
On the basis of this study, the inactivity of the MMA
polymerization by complex 5 when activated with B(C6F5)3 can
be attributed to the formation of the separated ion pair 8 in
which there is no metal–alkyl group to initiate MMA polymer-
Complexes 1 and 2 were prepared from the reaction of
sodium cyclopentadienide in THF with the corresponding
dichloride precursors in greater than 80% yield.7 Complexes 3
and 4 were synthesized in the same manner, however, the
products are a mixture of two isomers in ~ 1+1 ratio as a result
of dissymmetric silyl bridging. These two isomers can be
separated by fractional recrystallization from a solvent mixture
of toluene and hexanes. Both 1H and 13C NMR data indicate the
5
Cp ligand is h -bonded to the metal for complexes 1–6, all of
which have been characterized spectroscopically and analyt-
ically, and complex 6 has also been characterized crystallogra-
pically (Fig. 1).†
Reaction of 1 with MeLi in diethyl ether produced a 6+1 ratio
of the monomethyl derivative (5) and the unexpected dimethyl
derivative CGC–TiMe2 (7).8 Formation of 7 can be avoided by
replacing MeLi with MeMgBr, and thus a clean formation of 5
was observed which was isolated in 84% yield.‡ The analogous
reaction of 2 with MeLi in diethyl ether cleanly produced the Zr
derivative 6 which was isolated in 91% yield. In contrast to the
Fig. 1 The molecular structure of 6. Selected bond lengths and angles (Å, °):
Zr–N 2.129(2), Zr–C(21) 2.283(8), Zr–Me4Cp 2.225, Zr–Cp 2.281, N–Zr–
Me4Cp 101.2, N–Zr–Cp 111.4.
708
CHEM. COMMUN., 2002, 708–709
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C
20H32NClSiZr, found (calc.): C, 54.25 (54.44); H, 7.18 (7.31); N, 2.97
(3.17%).
1
Ph(Me)Si(Me4C5)(tBuN)Ti(Cp)Cl (3, isomer A): NMR: H (300 MHz,
C6D6): d 7.61 (m, 2H, Ph), 7.24 (m, 3H, Ph), 5.95 (s, 5H, Cp), 2.59, 1.83,
1.46, 1.24 (s, 3H, Me4C5), 1.47 (s, 9H, tBu), 0.94 (s, 3H, MePhSi). 13C{1H}
(75 MHz, C6D6): d 142.88, 138.07, 137.39, 135.52, 130.02, 129.70, 128.32,
127.16, 115.43 (Cp), 110.56, 64.46, 34.32, 17.13, 14.65, 13.45, 13.30, 8.35.
3, isomer B: NMR: 1H (300 MHz, C6D6): d 7.98 (m, 2H, Ph), 7.05 (m, 3H,
Ph), 5.97 (s, 5H, Cp), 2.02, 1.72, 1.65, 1.52 (s, 3H, Me4C5), 1.47 (s, 9H,
tBu), 0.70 (s, 3H, MePhSi). Anal. C25H34ClNSiTi, found (calc.): C, 65.17
(65.28); H, 7.39 (7.45); N, 2.88 (3.05%).
1
Ph(Me)Si(Me4C5)(tBuN)Zr(Cp)Cl (4, isomer A): NMR: H (300 MHz,
C6D6): d 7.96, (dd, 2H, Ph), 7.27 (m, 3H, Ph), 6.06 (s, 5H, Cp), 1.84, 1.83,
1.71, 1.55 (s, 3H, Me4C5), 1.38 (s, 9H, tBu), 0.83 (s, 3H, MePhSi). 13C
(C6D6): d 143.76, 137.27, 136.29, 130.50, 129.72, 128.90, 128.24, 125.20,
113.31 (Cp), 104.64, 58.58, 36.09, 15.64, 14.62, 13.12, 11.68, 6.66. 4,
1
isomer B: NMR: H (300 MHz, C6D6): d 7.72 (dd, 2H, Ph), 7.27 (m, 3H,
Ph), 6.06 (s, 5H, Cp), 2.46, 1.86, 1.55, 1.30 (s, 3H, Me4C5), 1.39 (s, 9H,
tBu), 0.94 (s, 3H, MePhSi). 13C (C6D6): d 143.51, 135.51, 133.18, 132.23,
129.68, 126.22, 125.34, 121.28, 113.80 (Cp), 106.86, 58.47, 35.45, 16.02,
14.27, 12.79, 12.65, 8.33. Anal. C25H34ClNSiZr, found (calc.): C, 59.49
(59.66); H, 7.05 (6.81); N, 2.60 (2.78%).
Fig. 2 NMR spectra of 9 in toluene-d8, 23 °C. Top: 19F NMR spectrum;
bottom: 1H NMR spectrum. Resonances at 2.10 (s) and 2.09 (m) are from
toluene in the alane (used as a toluene adduct) and the NMR solvent,
repectively.
Me2Si(Me4C5)(tBuN)Ti(Cp)Me (5): NMR: 1H (300 MHz, C6D6): d 5.67
(s, 5H, Cp), 2.22, 1.83, 1.56, 1.42 (s, 3H, Me4C5), 1.27 (s, 9H, tBu), 0.59,
0.47 (s, 3H, Me2Si), 0.20 (s, 3H, MeTi). 13C{1H} (75 MHz, C6D6): d
131.25, 129.96, 124.18, 119.92, 111.41 (Cp), 104.84, 61.31, 35.56, 33.82,
15.93, 16.36, 12.85, 11.44, 8.84, 8.38. Anal. C21H35NSiTi, found (calc.) C,
66.59 (66.82); H, 9.10 (9.34); N, 3.58 (3.71%).
isation.13 The efficient MMA polymerization with the same
complex, but activated with the alane, can be explained with a
different mechanism via enolaluminates.14 For olefin polymer-
isation by the Zr catalysts, the observations that excess of the
alane does not effect the abstraction of the Cp ligand from 9 and
that the olefinic region of a low molecular weight poly-
propylene sample by 4 shows only vinylidene (b-H elimination,
80%) and allyl (b-Me elimination, 20%) end groups argue that
the olefin monomer is unlikely to be inserted into the Zr–Cp
bond. The initiation step presumably involves nucleophilic
attack on the polarized olefin (10) and formation of
Zr…CH2(R)…Al bonds (11) [eqn. (1)], a bimetallic mechanism
resembling that originally proposed by Natta and Mazzanti.15
Me2Si(Me4C5)(tBuN)Zr(Cp)Me (6): NMR: 1H (300 MHz, C6D6): d 5.80
(s, 5H, Cp), 2.25, 1.93, 1.61, 1.60 (s, 3H, Me4C5), 1.20 (s, 9H, tBu), 0.60,
0.48 (s, 3H, Me2Si), 20.07 (s, 3H, MeZr). 13C{1H} (75 MHz, C6D6): d
128.81, 124.20, 123.69, 120.42, 110.64 (Cp), 103.18, 56.55, 35.96, 22.82,
15.84, 14.66, 12.52, 11.62, 10.35, 7.69. Anal. C21H35NSiZr, found (calc.):
C, 59.65 (59.94); H, 8.12 (8.38); N, 2.77 (3.33%).
2
Me2Si(Me4C5)(tBuN)Ti+(Cp)MeB(C6F5)3 (8): NMR: 1H (300 MHz,
C7D8): d 5.75 (s, 5H, Cp), 1.78, 1.47, 1.21, 1.10 (s, 3H, Me4C5), 1.23 (s, 9H,
tBu), 0.54, 0.12 (s, 3H, Me2Si), 0.47 (s, 3H, MeB). 19F (282 MHz, C7D8):
d 2131.78 (d, 6F, o-F), 2164.25 (t, 3F, p-F), 2166.84 (m, 6F, m-F).
2
1
Me2Si(Me4C5)(tBuN)Zr+(Cp)MeAl(C6F5)3 (9): NMR: H (300 MHz,
C7D8): d 5.76 (s, 5H, Cp), 1.79, 1.52, 1.45, 1.39 (s, 3H, Me4C5), 0.91 (s, 9H,
tBu), 0.43, 0.20 (s, 3H, Me2Si), 20.15 (s, 3H, MeAl). 19F (282 MHz, C7D8):
d –122.35 (d, 6F, o-F), 2154.58 (t, 3F, p-F), 2162.07 (m, 6F, m-F).
1 For reviews, see: P. S. Chum, W. J. Kruper and M. J. Guest, Adv.
Mater., 2000, 12, 1759; A. L. McKnight and R. M. Waymouth, Chem.
Rev., 1998, 98, 2587.
(1)
2 For recent reviews, see: Chem. Rev., ed. J. A. Gladysz, 2000, 100, 1167;
Top. Catal., ed. T. J. Marks and J. C. Stevens, 1999, 7, 1; J. Mol. Catal.,
ed. R. F. Jordan, 1998, 128, 1; M. Bochmann, J. Chem. Soc., Dalton
Trans., 1996, 255.
3 E. Y.-X. Chen, W. J. Kruper, G. R. Roof and D. R. Wilson, J. Am. Chem.
Soc., 2001, 123, 745.
In summary, mono-alkyl or -chloro CGC Zr complexes
demonstrate high olefin polymerisation activity when activated
with aluminum activators. The current finding that group 4
metal complexes containing a single insertable or abstractable
metal-alkyl bond can be activated for olefin polymerisation
significantly expands the polymerisation catalyst library by
including a class of monoalkyl and –chloro metal complexes.
4 J. Cano, P. Royo, M. Lanfranchi, M. A. Pellinghelli and A. Tiripicchio,
Angew. Chem., Int. Ed., 2001, 40, 2495.
5 H. Sinn and W. Kaminsky, Adv. Organomet. Chem., 1980, 18, 99.
6 For examples of chiral-at-metal metallocene complexes, see: N. W.
Alcock, H. J. Clase, D. J. Duncalf, S. L. Hart, A. McCamley, P. J.
McCormack and P. C. Taylor, J. Organomet. Chem., 2000, 605, 45.
7 D. R. Wilson, US Pat., 5 659 054, 1997; D. R. Wilson, US Pat.,
5 504 224, 1996.
8 J. C. Stevens, F. J. Timmers, D. R. Wilson, G. F. Schmidt, P. N. Nickias,
R. K. Rosen, G. W. Knight and S. Lai, Eur. Pat. Appl., EP 416 815-A2,
1991.
9 A. G. Massey and A. J. Park, J. Organomet. Chem., 1964, 2, 245.
10 P. Biagini, G. Lugli, L. Abis and P. Andreussi, US Pat., 5 602 269,
1997.
11 A. D. Horton, J. de With, A. J. van der Linden and H. van de Weg,
Organometallics, 1996, 15, 2672; B. Temme and G. Erker, J.
Organomet. Chem., 1995, 488, 177.
Notes and references
† Crystal data for complex 6: C21H35NSiZr, M = 420.81, orthorhombic,
space group Pna21, a = 15.8874(7) , b = 10.2802(4) , c = 13.2006(6) Å,
V = 2156.0(2) Å3, Z = 4, Dc = 1.296 Mg m23, T = 173(2) K, m(Mo-Ka)
= 0.568 mm21; 15448 reflections measured, 4674 unique (Rint = 0.0349),
F2 refinement, R1 = 0.0351 (I > 2s(I)), wR2 = 0.993 (all data). CCDC
reference number is 179845. See http:/www.rsc.org/suppdata/ccb2/
b201346k/ for crystallographic data in CIF or other electronic format.
‡
Me2Si(Me4C5)(tBuN)Ti(Cp)Cl (1): NMR: 1H (300 MHz, C6D6): d 5.86
(s, 5H, Cp), 2.48, 1.82, 1.77, 1.59 (s, 3H, Me4C5), 1.35 (s, 9H, tBu), 0.61,
0.25 (s, 3H, Me2Si). 13C{1H} (75 MHz, C6D6): d 137.7, 135.5, 129.6, 125.4,
114.3, 109.4, 63.7, 34.2, 16.8, 15.1, 12.9, 12.8, 9.7, 6.1. Anal.
C20H32NClSiTi, found (calc.): C, 60.09 (60.37); H, 7.95 (8.11); N, 3.34
(3.52%).
Me2Si(Me4C5)(tBuN)Zr(Cp)Cl (2): NMR: 1H (300 MHz, C6D6): d 5.97
(s, 5H, Cp), 2.36, 1.85, 1.81, 1.67 (s, 3H, Me4C5), 1.29 (s, 9H, tBu), 0.61,
0.38 (s, 3H, Me2Si). 13C{1H} (75 MHz, C6D6): d 132.7, 130.2, 126.1, 122.9,
112.9, 106.2, 57.7, 35.2, 15.6, 14.5, 12.3, 12.2, 10.1, 6.7. Anal.
12 J. Klosin, G. R. Roof, E. Y.-X. Chen and K. A. Abboud, Organome-
tallics, 2000, 19, 4684; A. H. Cowley, G. S. Hair, B. G. McBurnett and
R. A. Jones, Chem. Commun., 1999, 437; M. Bochmann and M. J.
Sarsfield, Organometallics, 1998, 17, 5908.
13 H. Frauenrath, H. Keul and H. Höcker, Macromolecules, 2001, 34, 14;
Y. Li, D. G. Ward, S. S. Reddy and S. Collins, Macromolecules, 1997,
30, 1875.
14 A. D. Bolig and E. Y.-X. Chen, J. Am. Chem. Soc., 2001, 123, 7943.
15 G. Natta and G. Mazzanti, Tetrahedron, 1960, 8, 86.
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