Polymerization of ethylene by the electrophilic mixed cyclopentadienylpyridylalkoxide complexes [CpM{NC5H4(CR2O)-2}Cl2] (M = Ti, Zr, R = Ph, Pri)

Article abstract of DOI:10.1021/om980222u

The group 4 mixed-ligand compounds [CpM-{NC₅H₄(CR₂O)-2}Cl₂] (M = Ti; R = Prⁱ (1a), Ph (1b); M = Zr, R= Prⁱ (2a), Ph (2b)) have been prepared and characterized. Single-crystal X-ray analyses

Full text of DOI:10.1021/om980222u

3408
Organometallics 1998, 17, 3408-3410
P olym er iza tion of Eth ylen e by th e Electr op h ilic Mixed
Cyclop en ta d ien ylp yr id yla lk oxid e Com p lexes
[Cp M{NC5H4(CR2O)-2}Cl2] (M ) Ti, Zr , R ) P h , P r i)
Simon Doherty,*,† R. J ohn Errington,*,† Adam P. J arvis,‡ Scott Collins,‡
William Clegg,† and Mark R. J . Elsegood†
Department of Chemistry, Bedson Building, The University of Newcastle upon Tyne,
Newcastle upon Tyne NE1 7RU, U.K., and Department of Chemistry, University of Waterloo,
Waterloo, Ontario N2L 3G1, Canada
Received March 24, 1998
Summary: The group 4 mixed-ligand compounds [CpM-
{NC5H4(CR2O)-2}Cl2] (M ) Ti; R ) Pri (1a ), Ph (1b);
M ) Zr, R ) Pri (2a ), Ph (2b)) have been prepared and
characterized. Single-crystal X-ray analyses reveal that
1a and 2b adopt four-legged piano-stool structures in
which the cyclopentadienyl ligand is asymmetrically
bonded and the pyridylalkoxide is bidentate. Toluene
solutions of [CpM{NC5H4(CR2O)-2}Cl2] and methylalu-
minoxane catalyze the polymerization of ethylene, gen-
erating high molecular weight polymers with narrow
molecular weight distributions. The activity of the
titanium- and zirconium-based catalysts are compa-
rable.
of ethylene and R-olefins.6 The most recent strategy in
catalyst design and modification has been the develop-
ment of noncyclopentadienyl-based derivatives of the
early transition metals, with the focus of attention on
nitrogen- and/or oxygen-containing ligands. In this
regard, the electronic relationship between the σ-2π
cyclopentadienide fragment and single-faced π-donor
ligands such as NR2, NR, and OR has been discussed.7
A number of chelating diamide8 and dialkoxide9 com-
plexes of the group 4 metals, mixed organoimido-
cyclopentadienyl derivatives10 of group 5, and bisimido11
complexes of group 6 have now been prepared, many of
which can be activated to yield catalysts for the polym-
erization of R-olefins. Notably, some of these complexes
show high olefin polymerization activities while others
can be activated for the living polymerization of 1-hex-
ene.8
Since the discovery of homogeneous Ziegler-Natta
catalysis by group 4 metallocenes1 considerable effort
has been devoted to catalyst modification in order to
improve polymerization activity and control polymer
properties such as stereoregularity, co-monomer incor-
poration, and microstructure.2 As a result, metallocene-
based chemistry has undergone significant develop-
ments, including the synthesis of single-site cationic
catalysts with high olefin polymerization activities,3 the
stereospecific polymerization of propylene by C2-sym-
metric ansa-metallocenes,4 and the synthesis of ther-
moplastic elastomeric polypropylene using a nonbridged
metallocene catalyst.5 Researchers at Dow and Exxon
have recently shown that constrained-geometry cata-
lysts that contain one cyclopentadienyl ligand and one
amido group, such as {SiMe2(C5H4)NR}MCl2 (M ) Ti,
Zr, Hf), are active and selective for the copolymerization
Given the impact of ligand design on catalyst perfor-
mance, we have recently begun to explore the potential
of mixed-ligand complexes of the type CpM(L)X2, where
L represents a monoanionic mono- or multidentate
ligand, as R-olefin polymerization precatalysts. In
comparison to conventional metallocene initiators
Cp2MX2, monocyclopentadienyl complexes CpM(L)X2
offer the advantage of catalyst modification by changing
the nature of the spectator ligand, L. Herein, we report
preliminary ethylene polymerization activities for the
electrophilic mixed-ligand complexes [CpM{NC5H4-
(6) (a) Canich, J . A. M. (Exxon) U.S. Patent 5,026,798, 1991. (b)
Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.; Nickias,
P. N.; Rosen, R. K.; Knight, G. A.; Lai, S.-Y. (Dow Chemical Company)
Eur. Pat. Appl. 0416 815 A2, 1990.
* To whom correspondence should be addressed. E-mail:
simon.doherty@newcastle.ac.uk, john.errington@newcastle.ac.uk.
† University of Newcastle upon Tyne.
(7) Gibson, V. C. J . Chem. Soc., Dalton Trans. 1994, 1477.
(8) (a) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics
1998, 17, 308. (b) Tinkler, S.; Deeth, R. J .; Duncalf, D. J .; McCamley,
A. Chem. Commun. 1996, 2623. (c) Scollard, J . D.; McConville, D. H.;
Vittal, J . J . Organometallics 1997, 16, 4415. (d) Scollard, J . D.;
McConville, D. H.; Payne, N. C.; Vittal, J . J . Macromolecules 1996,
29, 5241. (e) Scollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996,
118, 10008. (f) Gibson, V. C.; Kimberely, B. S.; White, A. J . R.; Williams,
D. J .; Houd, P. Chem. Commun. 1998, 313. (g) Schrock, R. R.;
Schattenmann, F.; Aizenberg, M.; Davis, W. M. Chem. Commun. 1998,
199.
‡ University of Waterloo.
(1) (a) Ziegler, K.; Holozkamp, H.; Briel, H.; Martin, H. Angew.
Chem. 1955, 67, 541. (b) Natta, G. J . Polym. Sci. 1959, 34, 531.
(2) (a) Brintzinger, H. H.; Fischer, D.; Mullhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b)
Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.
(3) J ordan, R. F.; Bajgur, C. S.; Willet, R.; Scott, B. J . Am. Chem.
Soc. 1986, 108, 7410.
(4) (a) Schutenhaus, H.; Brintzinger, H. H. Angew. Chem., Int. Ed.
Engl. 1979, 18, 777. (b) Wild, F. R. W. P.; Zsolnai, L.; Huttner, G.;
Brintzinger, H. H. J . Organomet. Chem. 1982, 23, 233. (c) Kaminsky,
W.; Kulper, K.; Brintzinger, H. H.; Wild, F. R. W. P. Angew. Chem.,
Int. Ed. Engl. 1985, 24, 507.
(5) (a) Hauptman, E.; Waymouth, R. M. J . Am. Chem. Soc. 1995,
17, 11586. (b) Waymouth, R. M.; Coates, G. W.; Hauptman, E. M.
(Stanford University) U.S. Patent 5,594,080, 1997. (c) Gauthier, W.
J .; Corrigan, J . F.; Taylor, N. J .; Collins, S. Macromolecules 1995, 28,
3771.
(9) (a) Fokken, S.; Spaniol, T. P.; Okuda, J .; Serentz, F. G.;
Mullhaupt, R. Organometallics 1997, 16, 4240. (b) Sarsfiled, M. J .;
Ewart, S. W.; Tremblay, T. L.; Roszak, A. W.; Baird, M. C. J . Chem.
Soc., Dalton Trans. 1997, 3097.
(10) (a) Antonelli, D. M.; Leins, A.; Stryker, J . M. Organometallics
1997, 16, 2500. (b) Chan, M. C. W.; Cole, J . M.; Gibson, V. C.; Howard,
J . A. K. Chem. Commun. 1997, 2345. (c) Coles, M. P.; Gibson, V. C.
Polym. Bull. 1994, 33, 529.
(11) Poole, A.; Gibson, V. C. J . Chem. Soc., Chem. Commun. 1995,
2261.
S0276-7333(98)00222-2 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/07/1998

Communications
Organometallics, Vol. 17, No. 16, 1998 3409
described as square-based pyramidal with the centroid
of the C5H5 ring occupying the apical site and the
pyridyl alkoxide and chlorides occupying the basal
positions. Interestingly, the Ti-C bond lengths differ
significantly, ranging from 2.3482(14) to 2.4154(14) Å
(∆Ti-C ) 0.0672 Å), with one short, two medium, and
two long bonds. Notably, the shortest Ti-C bond length
(Ti(1)-C(1) ) 2.3482(4) Å) is trans to Ti(1)-Cl(1),
suggesting that the difference in Ti-C bond lengths may
reflect the different trans influence of the donor atoms
in the basal plane. A similar bond length pattern has
recently been suggested to reflect a tendency toward
three-electron η3-coordination.17 Surprisingly, the Ti-
Cl bond trans to the pyridyl nitrogen is considerably
longer (Ti(1)-Cl(2) ) 2.3482(4) Å) than that trans to
the alkoxide (Ti(1)-Cl(1) ) 2.3396(4) Å, ∆Ti-Cl )
0.0389 Å), contrary to what is expected based solely on
trans influence trends. For comparison, we have pre-
pared and structurally characterized CpTi(tmhd)Cl2,
which contains a symmetrically chelating 2,2,6,6-tet-
ramethylheptanedionate ligand.18 The Ti-C bond length
differences in CpTi(tmhd)Cl2 (∆Ti-C ) 0.033(3) Å) are
less pronounced than those in 1a as are the differences
in the Ti-Cl bond lengths (∆Ti-Cl ) 0.0041(6) Å). The
Ti-O bond length in 1a (Ti(1)-O(1) ) 1.8267(9) Å) is
slightly shorter than that recently reported by Marks
and co-workers19 for the phenolate constrained geometry
catalyst [{C5Me4-2-Me-C6H3O}Ti(CH2Ph)2] (1.851(7) Å),
which may reflect O(pπ)-Ti(dπ) donation to the metal.
Complex 2b crystallizes in the noncentrosymmetric
space group P212121 as a single enantiomer.16 The
molecular structure, shown in Figure 2, revealed that
the zirconium center has a pseudosquare-based pyra-
midal geometry. While the gross structural features of
2b are similar to those of 1a , there are several note-
worthy differences, the most striking of which is the
smaller variation in M-C bond lengths, which lie
between 2.486(3) and 2.525(3) Å (∆Zr-C ) 0.039 Å).
As in 1a , the M-Cl bond trans to the pyridine (Zr(1)-
Cl(2) ) 2.4528(8) Å) is longer than that trans to the
alkoxide (Zr(1)-Cl(1) ) 2.4439(8) Å), although these
differences are somewhat smaller than those in 1a
(∆Zr-Cl ) 0.0089 Å). The chelate O(1)-Zr(1)-N(1)
F igu r e 1. Molecular structure of [CpTi{NC5H4(CPri O)-
2}Cl2], 1a . H-atoms omitted for clarity.
2
(CR2O)-2}Cl2] that contain one cyclopentadienyl and one
chelating pyridylalkoxide ligand.
Compounds 1a ,b and 2a ,b are readily synthesized via
slow addition of a toluene solution of Li[NC5H4(CR2O)-
2] (R ) Pri, Ph) to a toluene solution of CpTiCl3 or
CpZrCl3(dme), respectively12 (eq 1). In the 13C{1H}
NMR spectrum of 1a ,13 the isopropyl methyl groups
appear as two singlets, which suggests that the pyridyl-
alkoxide is coordinated in a bidentate manner. Similar
features are apparent in the 13C{1H} NMR spectrum of
2a .14 Single-crystal X-ray analyses of 1a and 2b were
undertaken in order to provide precise structural de-
tails.15,16
(15) Crystal data for 1a . C17H23Cl2NOTi, Mr ) 376.16, monoclinic,
P21/c, a ) 7.4335(5) Å, b ) 16.8859(12) Å, c ) 13.9126(10) Å, â )
97.577(2)°, V ) 1731.1(2) Å3, Z ) 4, Dcalcd ) 1.443 g cm-3, µ ) 0.804
mm-1, (Mo KR, λ ) 0.710 73 Å), F(000) ) 784; 10 734 reflections (θmax
) 28.83°) measured on a Bruker SMART CCD area detector diffrac-
tometer at 160 K, 4023 unique data (Rint ) 0.0197) were corrected
semiempirically for absorption (transmission 0.862-0.725 for crystal
size 0.50 × 0.23 × 0.18 mm); structure solution by direct methods,
refinement on F2 with statistics-based weighting scheme, anisotropic
displacement parameters for all non-H atoms, and constrained isotropic
The molecular structure shown in Figure 1 reveals
1a to be monomeric, with a coordination geometry best
(12) P r ep a r a tion of 1a : A solution of Li[NC5H4(CPri2O)-2], pre-
pared by the addition of nBuLi (2.20 mL, 5.5 mmol) to a toluene solution
of the pyridyl alcohol (1.07 g, 5.5 mmol), was added to a rapidly stirred
suspension of CpTiCl3 (1.20 g, 5.5 mmol) in toluene. The reaction
mixture was stirred overnight and filtered, and the solvent was
removed under reduced pressure to give a yellow-orange solid residue.
The product was crystallized by slow diffusion of hexane into a
dichloromethane solution of 1a . Compounds 1b and 2a ,b were prepared
following a procedure similar to that described above.
H atoms; final wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2 ) 0.0673 for all
2
data, conventional R ) 0.0245 on F values for 3550 reflections having
Fo2 > 2σ(Fo2), S ) 1.038 on F2 for all data and 204 refined parameters;
final difference map extremes +0.420 and -0.314 e Å-3
.
(16) Crystal data for 2b. C23H19Cl2NOZr, Mr ) 487.51, orthorhombic,
P212121, a ) 9.277(2) Å, b ) 14.377(3) Å, c ) 15.795(4) Å, V ) 2106.7(8)
Å3, Z ) 4, Dcalcd ) 1.537 g cm-3, µ ) 0.789 mm-1, (Mo KR, λ ) 0.710 73
Å), F(000) ) 984; 11 663 reflections (θmax ) 28.93) at 173 K, 4876
unique data (Rint ) 0.0380), transmission 0.746-0.564 for crystal size
0.39 × 0.36 × 0.33 mm; refinement as for 1a ; final wR2 ) 0.0558 for
(13) Spectroscopic data for 1a : 13C{1H} NMR (125.65 MHz, CDCl3,
δ): 170.2 (s, C5N), 150.3 (s, C5N), 138.8 (s, C5N), 123.7 (s, C5N), 121.7
(s, C5N), 121.4 (s, C5H5), 107.1 (s, Py-C-O), 37.1 (s, CH(CH3)2), 19.5
(s, CH(CH3)2), 17.9 (s, CH(CH3)2). Anal. Calcd for C17H23Cl2NOTi: C,
54.25; H, 6.12; N, 3.72. Found: C, 54.19; H, 6.17; N, 3.71.
2
all data, R ) 0.0298 on F values for 4144 reflections having Fo > 2σ-
(Fo2), S ) 0.966 on F2 for all data and 254 refined parameters; final
(14) Spectroscopic data for 2a : 13C{1H} NMR (125.65 MHz, CDCl3,
δ): 170.0 (s, C5N), 149.8 (s, C5N), 138.7 (s, C5N), 122.9 (s, C5N), 121.5
(s, C5N), 116.6 (s, C5H5), 98.6 (s, Py-C-O), 35.6 (s, CH(CH3)2), 18.1
(s, CH(CH3)2), 17.3 (s, CH(CH3)2). Compound 2b: 13C{1H} NMR (125.65
MHz, CDCl3, δ): 169.9 (s, C5N), 149.8 (s, C6H5), 144.9 (s, C5N), 139.0
(s, C5N), 128.1 (s, C6H5), 128.0 (s, C6H5), 127.4 (s, C6H5), 125.4 (s, C5N),
123.4 (s, C5N), 116.1 (s, C5H5), 96.0 (s, Py-C-O).
difference map extremes +0.325 and -0.467 e Å-3
.
(17) Redshaw, C.; Gibson, V. C.; Clegg, W.; Edwards, A. J .; Miles,
B. J . Chem. Soc., Dalton. Trans. 1997, 3343.
(18) Doherty, S.; Errington, R. J .; Clegg, W.; Elsegood, M. R. J .
Unpublished results.
(19) Chen, Y.-X.; Fu, P. F.; Stern, C. L.; Marks, T. J . Organometallics
1997, 16, 5958.

3410 Organometallics, Vol. 17, No. 16, 1998
Communications
Ta ble 1. Su m m a r y of Eth ylen e P olym er iza tion
Resu lts Usin g Com p lexes 1a ,b a n d 2a ,b
activity/g of
temp/ PE (mol of
entry precatalyst
°C
cat)-1 h-1
Mw
Mn
Mw/Mn
1
2
3
4
5
1a
1b
2a
2a
2b
30
30
30
30
30
80 000
320 000
430 000
710 000
370 000
450 000 225 000 2.00
544 000 292 000 1.86
567 000 261 000 2.17
862 000 250 000 3.44
658 000 378 000 1.74
zation profiles with little evidence for catalyst decay
were observed in all four cases, suggesting that the
active species are stable under these conditions. Inter-
estingly, the nature of the R groups on the alkoxide
ligand has a significant effect on productivity, the Pri-
substituted systems being about twice as active as the
Ph-substituted derivatives. This could possibly repre-
sent a steric effect and/or greater π-donation to the
metal center by the oxygen atom in the more electron-
rich alkoxide complexes 1a and 2a , although the geom-
etry of the chelate ring would seem to preclude strong
π-donation analogous to that seen in cationic alkoxide
complexes of group 4.23,24 A number of monocyclopen-
tadienylmetal complexes of group 4 have been shown
to polymerize ethylene. To compare, Chien and co-
workers have reported that CpTiCl3/MAO has an eth-
ylene polymerization activity of 6.2 × 104 g of polymer
(mol of Ti)-1 h-1, substantially lower than (η5-C5H4CH2-
CH2NMe2)TiCl3/MAO mixtures which showed activities
as high as high as 5 × 106 g of polymer (mol of Ti)-1
h-1 under similar conditions. The molecular weights
(MW) of the PE produced using 1a ,b and 2a ,b also
exhibited some variation, although considerably less so
than that observed for catalyst activities; in general, the
Pri-substituted systems provided lower MW PE than the
Ph derivatives, suggesting faster rates of chain transfer
for the former. Given the uncertainty in active site
concentrations in these experiments, the evaluation of
single-component versions of these catalyst systems
should prove more informative in this regard.
In summary, mixed-ligand complexes of the group 4
transition metals containing one cyclopentadienyl ligand
and one anionic pyridylalkoxide spectator ligand have
been prepared. In the presence of MAO, these com-
pounds are active for the polymerization of ethylene,
generating high molecular weight polymers with narrow
molecular weight distributions. The influence of ligand
modification on the structure and activity of these new
precatalysts, the synthesis of single-site cationic deriva-
tives of the type [CpM(L)R]+, and their applications as
Lewis-acid catalysts are currently under investigation.
Ack n ow led gm en t. We acknowledge the Royal So-
ciety for support (S.D.), the EPSRC for funding for a
diffractometer (W.C.), and the Natural Sciences and
Engineering Research Council of Canada for financial
support of this work (S.C. and A.P.J .).
F igu r e 2. Molecular structure of [CpZr{NC5H4(CPh2O)-
2}Cl2], 2b. H-atoms omitted for clarity.
angle of 69.70(7)° is acute and similar to the previously
reported values of 69.2(1)° and 70.1(1)° in the pyridyl-
alkoxide-substituted zirconium complex [(NC5H4CMe2O)2-
Zr(CH2Ph)2].20 The Zr(1)-O(1)-C(11) angle of 130.05-
(15)° suggests that O(1) is sp2 hybridized, while the
Zr(1)-O(1) distance of 1.9544(16) Å is substantially
shorter than those in [(NC5H4CMe2O)2Zr(CH2Ph)2],
which contains a trans-O-Zr-O and cis-N-Zr-N ar-
rangement of the pyridylalkoxide ligands with Zr-O
bond lengths of 1.995(3) and 2.004(3) Å and Zr-N bond
lengths of 2.429(3) and 2.391(3) Å. This bond length
shortening may reflect greater O(pπ)-Zr(dπ) donation
trans to a chloride compared to that when trans to
another alkoxide or Coulombic stabilization by an ionic
contribution to the zirconium-oxygen bond, i.e., Zr+-
O-, as discussed recently by Parkin and co-workers in
a structural comparison within the series [(η5-C5Me5)2-
Zr(EPh)2] (E ) O, S, Se, Te).21
The results of preliminary studies on ethylene po-
lymerization activities and polymer properties are sum-
marized in Table 1.22 Toluene solutions of 1a ,b, 2a ,b,
and methylaluminoxane (MAO) are active catalysts for
the polymerization of ethylene, generating high molec-
ular weight polymers with a narrow molecular weight
distribution. Under these conditions, stable polymeri-
(20) (a) Tsukahara, T.; Swenson, D. C.; J ordan, R. F. Organome-
tallics 1997, 16, 3303. (b) Bei, X.; Swenson, D. C.; J ordan, R. F.
Organometallics 1997, 16, 3282.
(21) Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995,
34, 5900. (b) Howard, W. A.; Parkin, G. J . Am. Chem. Soc. 1994, 116,
606.
(22) P olym er iza tion p r oced u r e: Ethylene polymerizations were
conducted in a toluene slurry in a 1 L stirred autoclave at 75 psig of
Su p p or tin g In for m a tion Ava ila ble: A table giving spec-
troscopic and analytical data for 1a ,b and 2a ,b and tables
giving details of the crystal structure analyses of 1a and 1b
(12 pages). Ordering information is given on any current
masthead page.
C2H4 at 30 °C. In
a typical procedure, solid MAO (Al:M 1000:1)
dissolved in 25 mL of toluene was added via pressurized sample vessel
to 450 mL of toluene at the desired process temperature, and the
solution was then saturated with monomer, stirring at 500 rpm. The
complex, dissolved in 25 mL of toluene, was introduced using another
sample vessel, using a slight overpressure of nitrogen. Monomer uptake
was monitored by calibrated mass flow meters. Polymerizations were
quenched by venting the monomer and quenching with a small volume
of MeOH. The polymers were isolated by filtration, washed with MeOH,
de-ashed with a solution of 4 M HCl in MeOH, washed with MeOH,
and then dried in vacuo at 60 °C prior to GPC analysis (1,2,4-
trichlorobenzene at 145 °C using both narrow MWD polystyrene and
broad MWD PE standards for calibration).
OM980222U
(23) See, e.g.: Collins, S.; Koene, B. E.; Ramachandran, R.; Taylor,
N. J . Organometallics 1991, 10, 2092.
(24) Flores, J . C.; Chien, J . C. W.; Rausch, M. D. Organometallics
1994, 13, 4140.