Bis[(amidomethyl)pyridine] zirconium(IV) complexes: Synthesis, characterization, and activity as olefin polymerization catalysts

Article abstract of DOI:10.1021/om800736w

This contribution describes the synthesis, characterization, and olefin polymerization reactivity of bis(chelate)zirconium complexes bearing (amidomethyl)pyridine ligands [(6-X-C₅H₃N)CH ₂NC₆F₅, X = CH

Full text of DOI:10.1021/om800736w

688
Organometallics 2009, 28, 688–697
Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes: Synthesis,
Characterization, and Activity as Olefin Polymerization Catalysts†
Liana Annunziata,‡ Daniela Pappalardo,§ Consiglia Tedesco,‡ and Claudio Pellecchia*,‡
Dipartimento di Chimica, UniVersita` di Salerno, Via Ponte don Melillo, I-84084 Fisciano (SA), Italy, and
Dipartimento di Studi Geologici ed Ambientali, UniVersita` del Sannio, Via dei Mulini 59/A,
I-82100, BeneVento, Italy
ReceiVed July 31, 2008
This contribution describes the synthesis, characterization, and olefin polymerization reactivity of
bis(chelate)zirconium complexes bearing (amidomethyl)pyridine ligands [(6-X-C5H3N)CH2NC6F5, X )
CH3 (Lig1H), Br (Lig2H), H (Lig3H)]. Metathesis reaction, alkane elimination, and amine elimination
provided routes to compounds (Lig1)2ZrCl2 (1), (Lig1)2ZrBz2 (4; Bz ) CH2C6H5), and (Lig2)2Zr(NMe2)2
(5). Attempts to prepare (Lig1)2Zr(NMe2)2 in a reaction between Zr(NMe2)4 and Lig1H led instead to
compound (Lig1)(Lig1*)ZrF(NMe2) (2), in which one dimethylamino group had been exchanged with
one ortho fluoride on the perfluorophenyl ring of the ligand via an aromatic nucleophilic substitution
reaction. Halide displacement reaction performed on compound 2 afforded the dichloride compound
(Lig1)(Lig1*)ZrCl2 (3). Reaction between Zr(NMe2)4 and Lig3H provided a mixture of (Lig3)2Zr(NMe2)2
and (Lig3)(Lig3*)ZrF(NMe2), the latter being analogous to 2. X-ray crystallographic analysis showed for
compound 1 a distorted octahedral geometry with C1 symmetry and for compound 2 a 7-coordinate
species. Variable-temperature NMR studies established for compound 1 an inversion of metal configuration
through dynamic interchange of the all-cis enantiomers. Fluxional behaviors in solution were also observed
for compounds 2, 3, and 4. Treatment of complexes with AliBu2H and methylalumoxane (MAO) yields
active, multisite ethylene and propylene polymerization catalysts.
In this regard, the simple aminopyridinato ligand derived from
deprotonated 2-aminopyridines was also largely studied (model
I in Chart 1). As a consequence of the relatively simple and
Introduction
The search for noncyclopentadienyl ancillary ligands for
homogeneous olefin polymerization catalysts has significantly
grown in the past decade, and a new generation of polymeri-
zation catalyst precursors with excellent performance, with
respect to activity, selectivity, living behavior, and stability has
been developed.1 The family of octahedral bis(chelate) group
4 metal complexes based on monoanionic ligands emerged as
an important and versatile class of olefin polymerization
catalysts, after the remarkable results obtained with phenoxy-
imine ligands.2-5
(2) For a recent review, see: (a) Matsugi, T.; Fujita, T. Chem. Soc. ReV.
2008, 37, 1264. (b) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.;
Tanaka, H.; Fujita, T. Chem. Lett. 1999, 1263. (c) Matsui, S.; Tohi, Y.;
Mitani, M.; Saito, J.; Makio, H.; Tanaka, H.; Nitabaru, M.; Nakano, T.;
Fujita, T. Chem. Lett. 1999, 1065. (d) Matsui, S.; Mitani, M.; Saito, J.;
Matsukawa, N.; Tanaka, H.; Nakano, T.; Fujita, T. Chem. Lett. 2000, 554.
(e) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Matsukawa, N.;
Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka, H.; Kashiwa, N.;
Fujita, T. J. Am. Chem. Soc. 2001, 123, 6847. (f) Kojoh, S.; Matsugi, T.;
Saito, J.; Mitani, M.; Fujita, T.; Kashiwa, N. Chem. Lett. 2001, 822. (g)
Saito, J.; Mitani, M.; Mohri, J.; Yoshida, Y.; Matsui, S.; Ishii, S.; Kojoh,
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Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui,
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N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 3327. (i) Saito, J.; Mitani, M.;
Mohri, J.; Ishii, S.; Yoshida, Y.; Matsugi, T.; Kojoh, S.; Kashiwa, N.; Fujita,
T. Chem. Lett. 2001, 576. (j) Mitani, M.; Furuyama, R.; Mohri, J.; Saito,
J.; Ishii, S.; Terao, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002,
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Kashiwa, N.; Fujita, T. Chem. Lett. 2002, 31, 740. (l) Tohi, Y.; Makio, H.;
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The rapid expansion of this area, stimulated by the promising
catalytic activity of the complexes, resulted also in considerable
contributions to coordination chemistry. Nitrogen-based poly-
dentate ligands (for instance, amidinates,6 pyrrolide-imine,7 2,6-
bis(N-aryliminomethyl)pyridine,8 R-diimine9) have attracted
particular interest for their advantageous feasibility and flex-
ibility in design to introduce sterically and electronically
demanding features. Recently a new family of high-performance
pyridylamidohafnium(IV) complexes was discovered by Dow
and Symyx, adopting a high-throughput parallel screening
approach. A most notable feature of these catalysts is the ortho-
metalation of the aryl substituent on the pyridine ring, resulting
in tridentate ligation of the pyridyl-amido moiety and a slightly
distorted trigonal bipyramidal Hf coordination.10-12
(3) (a) Tian, J.; Coates, G. W. Angew. Chem., Int. Ed. 2000, 39, 3626.
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1969. (b) Jones, D. J.; Gibson, V. C.; Green, S.; Maddox, P. J. Chem.
Commun. 2002, 1927.
* Author to whom correspondence should be addressed (fax +39 089
969603; telephone +39 089 969576; e-mail cpellecchia@unisa.it).
† Dedicated to Professor Attilio Immirzi on the occasion of his 70th
birthday.
(5) (a) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.;
Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149. (b)
Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs,
R. H.; Babsleben, D. A. Science 2000, 287, 460.
(6) (a) Volkis, V.; Schmulinson, M.; Averbuj, C.; Livovskii, A.;
Edelmann, F. T.; Eisen, M. S. Organometallics 1998, 17, 3155. (b) Averbuj,
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‡ Universita` di Salerno.
§ Universita` del Sannio.
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10.1021/om800736w CCC: $40.75
2009 American Chemical Society
Publication on Web 01/15/2009

Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes
Organometallics, Vol. 28, No. 3, 2009 689
Chart 1
Chart 2
high-yield synthesis, combined with easy modification of steric
and electronic properties of the precursor aminopyridines, these
compounds have led to a wide variety of mono-, bis-, tris-, and
tetrakisaminopyridinato derivatives.13,14 For the synthesis of
bis(amidopyridine) zirconium complexes, the control of the
ligand number about each metal center to two, avoiding
formation of complexes bearing one or three ligands, is
challenging. To address this problem, Scott emphasized the
importance of the choice of the amido N-substituents and
described bis(N-adamantyl-2-aminopyridinato) zirconium dichlo-
ride as a moderately active catalyst for ethylene polymeriza-
tion.15 Following this result, highly active bis(chelate) zirconium
complexes stabilized by bulky aminopyridinato ligands were
reported.14d
In this context, we pursued an alternative approach to the
synthesis of bis(aminopyridinato) zirconium complexes featuring
an increased size of the chelating ring by the introduction of
one more carbon atoms. Herein we report the synthesis of new
pentafluoro-N-((pyridin-2-yl)methyl)aniline ligands (model II in
Chart 1), the synthesis of bis(chelate) zirconium complexes
obtained thereof, and preliminary results on their olefin polym-
erization catalysis.16
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G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 1651. (d)
Gibson, V. C.; Newton, C.; Redshaw, C.; Solan, G. A.; White, A. J. P.;
Williams, D. J. J. Chem. Soc., Dalton Trans. 2002, 4017. (e) Yoshida, Y.;
Matsui, S.; Takagi, Y.; Mitani, M.; Nitabaru, M.; Nakano, T.; Tanaka, H.;
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Results and Discussion
Synthesis and Characterization of the Complexes. The
ligands [(6-X-C5H3N)CH2NC6F5, X ) CH3 (Lig1H), Br (Lig2H),
H (Lig3H)] were prepared by condensation reactions between
the pentafluoroaniline and the appropriate pyridinecarboxalde-
hyde, followed by reduction of the imine functionality by
NaBH3CN (Chart 2). The preparation of bis-chelate zirconium
complexes was achieved by different synthetic approaches,
producing in some cases unexpected ligand structure rearrange-
ments. The obtained zirconium complexes were characterized
by NMR spectroscopy, elemental analysis, and, in some cases,
also single-crystal X-ray diffraction analysis.
The dichloro bis(Lig1) zirconium(IV) compound (1) was
prepared via metathesis reaction of the lithium salt of Lig1 and
zirconium tetrachloride in tetrahydrofurane solvent (Scheme 1).
Reaction proceeded cleanly with good yield (89%), producing
1 as a pale yellow solid, which was characterized by X-ray
diffraction analysis. Suitable crystals were grown from dichlo-
romethane/hexane at room temperature. Selected bond lengths
and angles for compound 1 are listed in Table 1.
(14) For recent articles on aminopyridinato ligands, see: (a) Scott, N. M.;
Schareina, T.; Tok, O.; Kempe, R. Eur. J. Inorg. Chem. 2004, 3297. (b)
Kretschmer, W. P.; Meetsma, A.; Hessen, B.; Schmalz, T.; Qayyum, S.;
Kempe, R. Chem. Eur. J. 2006, 12, 8969. (c) Kretschmer, W. P.; Meetsma,
A.; Hessen, B.; Schmalz, T.; Qayyum, S.; Kempe, R. Chem. Eur. J. 2006,
12, 8969. (d) Kretschmer, W. P.; Hessen, B.; Noor, A.; Scott, N. M.; Kempe,
R. J. Organomet. Chem. 2007, 692, 4569. (e) Skvortsov, G. G.; Fukin,
G. K.; Trifonov, A. A.; Noor, A.; Doring, C.; Kempe, R. Organometallics
2007, 26, 5770. (f) Qayyum, S.; Haberland, K.; Forsyth, C. M.; Junk, P. C.;
Deacon, G. B.; Kempe, R. Eur. J. Inorg. Chem. 2008, 557.
(15) Morton, C.; O’Shaughnessy, P.; Scott, P. Chem. Comm. 2000, 2099–
2100.
(16) During the course of our studies different (amidomethyl)pyridine
ligands and their use in the preparation of mono(chelate)MX3 zirconium
and hafnium complexes were reported. See: (a) Nienkemper, K.; Keher,
G.; Keher, S.; Fro¨hlich, R.; Erker, G. J. Organomet. Chem. 2008, 693, 1572.
(12) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.;
Wenzel, T. T. Science 2006, 312, 714.
(13) For review articles on aminopyridinato ligands, see: (a) Kempe,
R. Angew. Chem., Int. Ed. 2000, 39, 468–493. (b) Kempe, R. Eur. J. Inorg.
Chem. 2003, 791–803.

690 Organometallics, Vol. 28, No. 3, 2009
Annunziata et al.
Scheme 1
Table 1. Selected Bond Lengths (Ångstroms) and Angles (Degrees)
for Compounds 1 and 2
noxyimine) zirconium complexes, where the two chelating
ligands are related by a crystallographic C2 symmetry, the trans
positions are occupied by the O atoms, and the cis positions
are occupied by N atoms (both at 2.355(2) Å from the Zr
atom).2e For compound 1, on the contrary, a C2 coordination
geometry would imply steric repulsion between the two ortho
methyl groups. Moreover, a closer inspection of the structure
showed that the five-atom rings Zr-N1-N2-C7-C8 and
Zr-N3-N4-C19-C20 are planar within rmsd values of 0.079
and 0.038 Å, respectively, with an angle between planes of
64.6(2)°; in this way the two aforementioned rings result in the
two planes being almost perpendicular to each other. Both
pyridine moieties lie in the previously defined 5-atom ring
planes, whereas the fluorinated aromatic rings are tilted with
respect to the coordination planes with angles of 67.5(3)° and
79.5(2)°, respectively.
With the aim of exploring the feasibility of a largely pursued
synthetic route for the preparation of zirconium bisamide
derivatives, two equivalents of Lig1H were allowed to react with
tetrakis(dimethylamido) zirconium(IV) in dry hexane, giving
the new compound 2 as a light yellow solid. Elemental analysis
of 2 was in good agreement with the expected (Lig1)2Zr(NMe2)2
formulation. The 1H NMR spectrum at room temperature
showed broad signals, an indication of a fluxional equilibrium
compound 1
compound 2
Cl1-Zr 2.433(2)
Cl2-Zr 2.440(2)
Zr-N1 2.096(6)
Zr-N3 2.114(6)
Zr-N4 2.375(6)
Zr-N2 2.460(6)
Zr-F1 1.972(3)
Zr-N1 2.449(4)
Zr-N2 2.205(4)
Zr-N3 2.177(4)
Zr-N4 2.605(4)
Zr-N5 2.085(4)
Zr-N6 2.629(4)
N1-Zr-N3 102.5(3)
N1-Zr-N4 83.5(2)
F1-Zr-N5 112.95(15)
F1-Zr-N3 123.05(14)
N5-Zr-N3 103.93(17)
F1-Zr-N2 126.37(14)
N5-Zr-N2 101.48(15)
N3-Zr-N2 83.76(15)
F1-Zr-N1 74.36(12)
N5-Zr-N1 83.75(15)
N3-Zr-N1 153.55(14)
N2-Zr-N1 69.85(14)
F1-Zr-N4 78.96(13)
N5-Zr-N4 79.61(15)
N3-Zr-N4 66.55(14)
N2-Zr-N4 149.36(14)
N1-Zr-N4 139.82(13)
F1-Zr-N6 71.73(12)
N5-Zr-N6 171.26(15)
N3-Zr-N6 67.63(14)
N2-Zr-N6 80.33(13)
N1-Zr-N6 104.83(13)
N4-Zr-N6 94.46(13)
N3-Zr-N4 72.5(2)
N1-Zr-Cl1 107.46(19)
N3-Zr-Cl1 86.31(19)
N4-Zr-Cl1 157.99(16)
N1-Zr-Cl2 141.44(19)
N3-Zr-Cl2 105.3(2)
N4-Zr-Cl2 80.07(17)
Cl1-Zr-Cl2 100.44(8)
N1-Zr-N2 70.4(2)
N3-Zr-N2 166.3(3)
N4-Zr-N2 117.1(2)
Cl1-Zr-N2 84.85(15)
Cl2-Zr-N2 86.55(16)
Compound 1 displayed a distorted octahedral geometry with
two chlorine atoms located in cis position (Cl1-Zr-Cl2
100.44(8)°), and both the N-pyridine (N2-Zr-N4 117.1(2)°)
and the N-aniline atoms (N1-Zr-N3 102.5(3)°) in a cis
relationship to each other (Figure 1). The distances between
the Zr atom and the N aniline atoms are, respectively, Zr-N1
2.096(6) Å and Zr-N3 2.114(6) Å, whereas the distances
between the Zr atom and the N pyridine atoms are, respectively,
Zr-N2 2.460(6) Å and Zr-N4 2.375(6) Å. Zr-N distance
values reflect those observed in the analogous zirconium
(amidomethyl)pyridine monochelate complexes.16
Of the five possible octahedral structures for (Lig1)2ZrCl2
complexes, compound 1 reflects the coordination geometry
depicted by model C in Chart 3 for the related dimethylamido
complex. This C1 symmetry with all-cis configuration differs
from the geometry usually observed for octahedral bis(phe-
Figure 1. ORTEP drawing for compound 1. Ellipsoids are drawn
at 30% probability level.

Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes
Organometallics, Vol. 28, No. 3, 2009 691
Chart 3
in solution and, at lower temperature, the presence of two sets
of signals in a 1:1 ratio, attributable to the ligand hydrogen atoms
(see below). More information came from the 19F NMR
spectrum at room temperature: seven broad signals were
observed in the region from -180 to -145 ppm, accounting
for nine aryl fluorine atoms, and one singlet at +52.21 ppm
accounting for one fluorine atom. The last signal was attributed
to a fluorine atom directly bonded to zirconium, on the basis of
the literature data,17 suggesting a possible structural modification
of the ligands. Hydrolysis of compound 2 followed by NMR
analysis of the organic fraction of the hydrolyzed product
resulted in identification of a pristine pyridyl-amino ligand Lig1H
in a 1:1 ratio with a modified form of the ligand (Lig1*H) (see
the Supporting Information). The structure of compound 2 was
definitively elucidated by single-crystal X-ray diffraction analy-
sis (Figure 2), disclosing a 7-coordinate zirconium bearing the
modified ligand (Lig1*), in which one fluorine atom of the aryl
group was replaced by a dimethylamino group, the pristine Lig1
ligand, one fluorine atom, and one NMe2 group. The substitution
of an ortho aryl fluoride of the ligand by a dimethylamino group
bound to a metal center has precedent in the literature and can
be justified by aromatic nucleophilic substitution reaction (SNAr)
occurring during the formation of complexes (Scheme 1).18 Deck
et al. described the partial defluorination of pentafluorophenyl-
substituted cyclopentadienyl or indenyl ligands by titanium
amide.19 Schrock et al. reported a structurally characterized
7-coordinate pyridyldiamine hafnium complex in which two
aromatic fluorines were substituted with two dimethylamino
groups,20a and documented also this type of exchange in a
molybdenum system.20b Cyclopentadienyl-iminophosphinamide
zirconium(IV) complexes in which two fluorine atoms of the
N-aryl group were replaced by dimethylamino groups have been
also reported by Scott.20c Among main group elements, Boch-
mann reported a structurally characterized zwitterionic ami-
noborane formed via nucleophilic substitution attack on an ortho
F.20d
2.629(4) Å and a sigma-bonded N3 atom at 2.177(4) Å. The
fluorine atom is at a distance of 1.972(3) Å. These values agree
with those observed for analogous 7-coordinate Hf and Mo
compounds; notably the two dative bonds show considerably
longer distances with respect to the literature compounds
(Hf-Ndonor distances are 2.355(14) Å and 2.459(11) Å;
Mo-Ndonor distances are 2.330(5), 2.482(5), and 2.440(5) Å).18
In addition, the N3 atom deviates considerably from the plane
defined by the Zr atom and the pyridine moiety (rmsd ) 0.048
Å), being displaced by -0.680(6) Å. The plane formed by the
fluorinated aromatic ring and N3 and N6 atoms (rmsd ) 0.018
Å) forms an angle of 62.5(1)° with the previously defined plane.
As for the other ligand, the N1 and N2 nitrogen atoms deviate
from the 5-atom plane Zr-N1-N2-C7-C8 (rmsd ) 0.096
Å) by, respectively, 0.11 and 0.13 Å. The fluorinated aromatic
rings are tilted with respect to this plane by 52.28(15)°.
The reaction of compound 2 with an excess of Me3SiCl
afforded in good yield compound 3 where both the Zr-F and
Zr-NMe2 groups were replaced by chlorides (Scheme 1). The
absence in the 19F NMR spectrum of the signal relative to the
Zr-F bond indicated that the reaction was complete.
With the aim of preparing a bis(Lig1)zirconium dialkyl
derivative, the reaction of tetrabenzylzirconium with 2 equiv
of Lig1H in benzene was performed. The zirconium dibenzyl
compound (4) was obtained straightforwardly (Scheme 1). The
product was stable as a solid but easily underwent degradation
reaction in solution with formation of the “free” ligand.
The sterically and electronically different (amidomethyl)py-
ridine ligands Lig2H and Lig3H were also used for the synthesis
of bis(chelate) zirconium(IV) complexes. The reaction of 2 equiv
of N-[(6-bromopyridin-2-yl)methyl]-2,3,4,5,6-pentafluoroaniline
(Lig2H) with tetrakis(dimethylamido) zirconium(IV) resulted in
the formation of the octahedral (Lig2)2Zr(NMe2)2 compound 5
1
(Scheme 2). This species showed at room temperature a H
NMR spectrum with very sharp signals and a pattern compatible
with the presence of a symmetric structure in solution. Hy-
drolysis experiments were also performed and resulted in the
isolation of the intact amino-pyridine ligand (Lig2H). The SNAr
reaction, observed for compound 2 (see above), did not occur
in this case. A previous paper highlighted that the SNAr reaction
preferentially occurs on CF bonds positioned in close proximity
to the inner coordination sphere of early transition metal amides,
suggesting an intermediate species in which both the fluorine
atom and the dimethylamino group are coordinated to the
metal.19 In the case of compound 5 the presence of a bromine
atom in the ortho position of the pyridine ring may play a
competitive role, electronically stabilizing the observed structure.
The reaction of 2 equiv of the simplest ligand Lig3H and
tetrakis(dimethylamido) zirconium(IV) was also attempted.
NMR analysis of the obtained solid displayed at room temper-
ature broad signals. A detailed NMR investigation, based on
1H, 13C, and 19F NMR analysis, also performed at lower
temperatures (see the Supporting Information), disclosed that
the solid was a mixture of two bis(chelate) zirconium com-
Selected bond lengths and angles for compound 2 are listed
in Table 1. The geometry of 2 can be roughly described as a
distorted octahedron with an extra atom at the center of a face.
More in detail, the Lig1 ligand displays the pyridine nitrogen
atom at 2.205(4) Å and the aniline nitrogen atom at 2.449(4)
Å, the Lig1* behaves as a tridentate ligand with two nitrogen
atoms (N4 and N6), providing a dative bond at 2.605(4) Å and
(17) (a) O’Connor, P. E.; Berg, D. J.; Barclay, T. Organometallics 2002,
21, 3947–3954. (b) Jager-Fiedler, U.; Arndt, P.; Baumann, W.; Spannenberg,
A.; Burlakov, V.; Rosenthal, U. Eur. J. Inorg. Chem. 2005, 2842–2849.
(c) Il’in, E. G.; Kovalev, V. V.; Aleksandrov, G. G.; Grenthe, I. Dokl. Chem.
2005, 401, 42–46 (part 1).
(18) Monitoring the reaction between two equivalents of Lig1H and
tetrakis(dimethylamido) zirconium(IV) by variable-delay 19F NMR experi-
ments in C6D6 minor signals were observed around-50 ppm, in the
characteristic region for bridging fluoride of the type Zr-F-Zr. Cfr.:(a)
O’Connor, P. E.; Berg, D. J.; Barclay, T. Organometallics 2002, 21, 3947–
3954, and references therein.
(19) Deck, P. A.; Konate`, M. M.; Kelly, B. V.; Slebodnick, C.
Organometallics 2004, 23, 1089–1097.

692 Organometallics, Vol. 28, No. 3, 2009
Annunziata et al.
zirconium compound, of formula (Lig3*)(Lig3)ZrF(NMe2) analo-
gous to compound 2, bearing one intact Lig3 ligand and one
modified ligand (Lig3*) by the substitution of an ortho aryl
fluoride with a dimethylamino group. To support this hypothesis,
the 19F NMR spectrum displayed two signal sets in about a 3:1
ratio; the main set was constituted by five signals attributable
to the intact C6F5 ring of Lig3, and the minor set was constituted
by four signals in the region of perfluorinated aryl group and
one singlet at +42.17 ppm, attributable to the fluorine atom
directly bound to zirconium. In nice agreement with this result,
the 1H NMR analysis of the organic fraction of the hydrolyzed
product displayed the presence of the pristine pyridyl-amino
ligand (Lig3H) in a 3:1 ratio with a modified pyridyl-amino
ligand (Lig3*H), where one fluorine atom of the aryl group was
replaced by a dimethylamino group. The exchange reaction of
one ortho fluoride on the pentafluorophenyl ring of the ligand
with a dimethylamino group can be also operating in this system
through SNAr. Although several attempts of crystallization were
performed, we were unable to separate the two species.
Figure 2. ORTEP drawing for compound 2. Ellipsoids are drawn
at 30% probability level.
Solution Structure of the Complexes. The configurations
of compounds 1-5 in solution were determined by variable-
temperature NMR spectroscopy.
Scheme 2
1
The H NMR spectrum of 1 at room temperature in CD2Cl2
displayed very broad signals, suggesting a fluxional equilibrium
in solution. To verify if the C1 symmetry species observed in
the solid state was preserved in solution, variable-temperature
1H NMR experiments were performed (Figure 3). As matter of
fact, at lower temperatures the broad signals split up: at 213 K
two sets of signals in a 1:1 ratio for the inequivalent hydrogen
atoms of the ligands were observed (i.e., two singlets at 2.3
and 3.1 ppm for the methyl on the pyridine moiety, two AB
patterns for methylenic hydrogen atoms at 4.3 and 4.6 ppm,
and two sets of signals in the aromatic region). A dynamic
interchange of the all-cis enantiomers could be occurring,
probably through a mechanism involving dissociation of a
pounds in about a 1: 1 ratio (Scheme 3). The first compound
was the octahedral bis(dimethylamido) zirconium(IV) compound
bearing two intact Lig3 ligands; the second was a 7-coordinate
pyridine nitrogen. The free energy of activation associated with
21
this process was calculated to be 11.91 kcal mol-1
.
The
N-pyridinic bond cleavage and the formation of a configuration-
ally labile 5-coordinate intermediate were previously proposed
by Serpone for bis(8-quinolato) titanium alkoxide complexes22
and by Jordan for analogous bis(8-quinolato) alkyl group 4 metal
complexes.23
A fluxional behavior in solution was also observed for
compound 2 by variable-temperature 1H NMR analysis (Figure
1
4). The aromatic region of the H NMR spectrum recorded at
room temperature was per se indicative, presenting one set of
well-defined sharp signals at 7.04 (d), 7.09 (d), and 7.57 (t)
ppm, attributed to the pyridine hydrogen atoms of an apparently
more strongly coordinated ligand, and a second set of broad
(20) (a) Schrock, R. R.; Adamchuck, J.; Ruhland, K.; Lopez, L. P. H.
Organometallics 2003, 22, 5079–5091. (b) Cochran, F. V., Jr.; Schrock,
R. R. Organometallics 2000, 19, 2414–2416. (c) Vollmerhaus, R.; To-
maszewski, R.; Shao, P.; Taylor, N. J.; Wiacek, K. J.; Lewis, S. P.; Al-
Humydi, A.; Collins, S. Organometallics 2005, 24, 494–507. (d) Hannant,
M. H.; Wright, J. A.; Lancaster, S. J.; Hughes, D. L.; Horton, P. N.;
Bochmann, M. Dalton Trans. 2006, 2415–2426.
(21) The free energy of activation has been calculated using the Eyring
equation, ∆Gcq ) 4576Tc[10319 + log Tc/Kc], where Tc is the coalescence
temperature and Kc is the exchange rate constant at coalescence, which is
given by Kc ) π∆ν/ꢀ2. ∆Gq was determined from the coalescence of
1
methyl proton on the pyridine ring in the H NMR spectra (Tc ) 263 K).
See: (a) Gunther, H. NMR Spectroscopy, 2nd ed.; Wiley: New York, 1995;
pp 241245. (b) Grutowsky, H. S.; Holm, C. H. J. Chem. Phys. 1956, 25,
1228.
(22) Bickley, D. G.; Serpone, N. Inorg. Chem. 1979, 18, 2200.
(23) Bei, X.; Swenson, D. C.; Jordan, R. F. Organometallics 1997, 16,
3282–3302.
Figure 3. 1H NMR spectra of compound 1 at various temperatures
(CD2Cl2).

Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes
Organometallics, Vol. 28, No. 3, 2009 693
Scheme 3
signals at 7.15, 7.19, and 7.70 ppm attributable to a fluxional
second ligand. Lowering the temperature sharpened the second
set of broad signals, too, indicating a locked coordination of
octahedral bis(chelate)Zr(NMe2)2 complexes five isomers are
possible (Chart 3). The NMR spectroscopic data are compatible
with the higher symmetries associated with two of them (D or
E), having the NMe2 groups in trans. Alternatively, these data
could be compatible with the presence of the C2 symmetry
isomers (A or B), in the Λ-∆ fast exchange regime within the
range of the explored temperatures. It is worth noting that the
analogous bis(chelate) zirconium dichloride complex 1 bearing
the pentafluoro-N-((6-methylpyridin-2-yl)methyl)anilinato ligand
displayed a C1 symmetry with all-cis configuration.
both ligands to the zirconium. The ∆Gq associated with this
21,24
process was 13.10 kcal mol-1
.
Perusal of the Zr-N bond
distances in the solid state (cfr. Table 1) disclosed that the Zr-N
pyridinic bond was significantly longer for the tridentate ligand
Lig1* than for the bidentate ligand Lig1 (cfr. Zr-N4 2.605(4)
Å against Zr-N1 2.449(4) Å). Reasonably, the fluxional
equilibrium observed could involve the dissociation of the
Zr-pyridinic nitrogen bond of the weaker coordinated ligand
Lig1*. A similar fluxional behavior in solution was also observed
for compound 3.
The coordination chemistry of this family of ligand seems to
be variable and poorly predictable, because slight differences
in their steric and electronic features dramatically influence the
coordination environment at the central Zr atom.
The dibenzyl compound 4 showed in the 1H NMR spectrum
at room temperature very broad signals. In this case variable-
Olefin Polymerization Studies. Complexes 1-5 were tested
as catalysts for the polymerization of ethylene and higher olefins
using different cocatalysts and under variable conditions.
1
temperature H NMR experiments evidenced the presence of
1
at least two isomeric species in fluxional equilibrium. The H
1
NMR spectrum registered at 233 K evidenced a signal pattern
compatible with the presence of one C1 symmetric main species
plus other minor isomeric species.
The 1H NMR spectrum at room temperature of compound 5
showed very sharp signals and a pattern compatible with the
presence of a highly symmetric structure in solution. Variable-
temperature (from 193 to 353 K) NMR studies did not show
significant change in the spectra. As pointed out above, for
Polymers were characterized by H and 13C NMR, DSC, and
GPC analyses.
Compounds 1-5 were able to promote polymerization of
ethylene under 6 atm of monomer pressure, by using MAO or
AliBu2H/MAO as cocatalysts. Activities, melting temperatures
of the polymers, and molecular weight data are collected in
Table 2. In all cases linear polyethylenes were produced (Tm )
132-136 °C), with moderate activities. As a general trend, the
AliBu2H/MAO cocatalyst system was a more efficient activator
than MAO alone. This effect was particularly evident in the
case of the less reactive dimethylamido zirconium derivatives
2 and 5, which reasonably require the presence of AliBu2H to
generate the Zr-H or Zr-alkyl bonds where the polyinsertion
may start, as previously observed for other dimethylamido
zirconium catalysts.25 On the contrary, for the zirconium
dichloride compound 3, comparable polymerization activities
were obtained with both activation systems (cfr. runs 10 and
11 in Table 2).
A variety of cocatalyst combinations, including the ionizing
agents commonly used for homogeneous polymerization cata-
lysts, were also tested for compound 2. Use of AliBu2H in
combination with either [CPh3][B(C6F5)4] or [HNMe2Ph][B-
(C6F5)4] or B(C6F5)3 resulted in comparable polymerization
activities. AliBu3 in combination with MAO gave similar results,
whereas AliBu2H/MAO at 50 °C gave significantly higher
polymerization activity (cfr. runs 6 and 8 in Table 2). A
screening of the effect of the temperature in the presence of
the latter activator system showed that when the temperature
increased from 25 to 50 °C, the catalytic activity became 15-
fold higher; a further rise to 75 °C was instead deleterious,
suggesting a partial catalyst deactivation.
(24) ∆Gq for compound 2 was determined from the coalescence of the
1
methyl proton on the pyridine ring in the H NMR spectra (Tc ) 283 K).
(25) (a) Kim, I.; Nishihara, Y.; Jordan, R. F.; Rogers, R. D.; Rheingold,
A. L.; Yap, G. P. A. Organometallics 1997, 16, 3314–3323. (b) Kim, I.;
Choi, C. S. J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 1523–1539.
Figure 4. 1H NMR spectra of compound 2 at various temperatures
(CD2Cl2).

694 Organometallics, Vol. 28, No. 3, 2009
Annunziata et al.
Table 2. Ethylene Polymerization Results for Complexes 1-5
runa
precatalyst
cocatalyst
T (°C)
activityb
Tm (°C)
Mw ( × 103)
Mw/Mn
1
2
3
4
5
6
1
1
1
2
2
2
2
2
3
3
3
4
4
5
MAO
MAO
25
50
50
50
25
50
75
50
25
50
50
50
50
50
6.8
34.3
22.6
0.3
135.3
136.0
135.8
133.6
133.0
134.3
133.0
134.8
133.9
132.6
133.9
134.9
134.8
133.5
ndc
nd
208.6
2485.8
1065.3
244.7
549.6
345.3
360.0
189.9
1444.6
nd
60.8
128.9
22.8
70.1
69.7
110.3
60.0
62.0
14.6
nd
AliBu2H/MAO
MAO
AliBu2H/MAO
AliBu2H/MAO
AliBu2H/MAO
AliBu2H/[CPh3][B(C6F5)4]
MAO
5.8
83.2
32.9
5.5
7
8d
9
3.7
10
11
12
13
14
MAO
65.5
72.7
18.6
3.8
AliBu2H/MAO
AliBu2H/MAO
MAO
172.4
288.0
267.6
78.2
70.7
53.3
AliBu2H/MAO
20.0
a Conditions: precatalyst ) 20 µmol; AliBu2H/Zr ) 30; Al(MAO)/Zr )1000; ethylene pressure ) 6 atm; toluene ) 90 mL; time ) 60 min. MAO dried
b
obtained by distilling off the solvent from the commercial solution. Activity ) kg of polymer × (mol of Zr × h × atm)-1
.
c nd ) not determined.
d Compound 2 ) 40 µmol; time ) 90 min.
Table 3. Propylene Polymerization Results
runa
complex
cocatalyst
T (°C)
time (h)
activityb
[mm] %
[mr] %
[rr] %
Mw (× 103)
Mw/Mn
1
2
3
4
5
6
1
1
1
2
2
5
AliBu2H/MAO
AliBu2H/MAO
MAO
0
50
50
0
50
50
5
1
1
4
1
1
436
1016
1666
520
2083
333
38
34
41
18
24
56
33
38
30
45
47
25
29
28
29
36
29
19
1623.9
394.1
318
106.1
58.4
17.2
24.7
84.2
1639.1
62.0
107.25
301.50
AliBu2H/MAO
AliBu2H/MAO
AliBu2H/MAO
a Conditions: precatalyst ) 20 µmol; AliBu2H/Zr ) 30; Al(MAO)/ Zr )1000; propylene pressure ) 6 atm; toluene ) 90 mL; time ) 60 min. MAO
b
dried obtained by distilling off the solvent from the commercial solution. Activity ) g of polymer × (mol of Zr × h × atm)-1
.
Table 4. Crystal Data and Structure Refinement Details for
Compounds 1 and 2
Analysis of the polymer samples by GPC revealed in any
case high molecular weights with bi- or trimodal molecular
weight distributions, an indication of a non-single-center catalyst
nature. Although the mechanism causing multimodality is still
elusive and care must be taken in extrapolating the solution
structures of the precatalysts to the real active species, we
propose that the multimodal MWDs of polymers could be
connected to the highly fluxional character of the precatalysts.
A similar behavior was previously observed for an analogous
bis(phenoxy-imine) zirconium complex, which, as a conse-
quence of the unusual C1 symmetric geometry was highly
fluxional in solution and produced bi- and trimodal
polyethylenes.2j However, it is worth mentioning that ligand
redistribution could also occur during the formation of the
catalytic species and/or during the polymerization process,
giving rise to additional polymerization species that could cause
the multimodality of molecular weight distribution as previously
observed by Kempe for bis(aminopyridinato) zirconium(IV)
complexes14d and by Scott for iminophosphonamide zirconium
complexes.26 To avoid the ligand redistribution reaction, fol-
lowing the suggestion of a reviewer, an ethylene polymerization
run was performed according to previous literature data26 by
adding the dialkyl catalyst precursor 4, preactivated with [Ph3C]
[B(C6F5)4], to a toluene solution containing triisobutylaluminum
as a scavenger and saturated with the monomer.27 GPC analysis
disclosed a monomodal, although still broad, molecular weight
distribution of the polymer.
compound 1
compound 2
formula
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
C26H16Cl2F10N4ZrCH2Cl2
821.47
monoclinic
P 21/n
10.752(3)
13.018(3)
C30H28F10N6Zr
753.80
triclinic
P -1
9.463(2)
12.446(3)
12.821(3)
90.499(6)
93.571(7)
96.789(6)
1496.3(6)
2
22.022(5)
90.512(7)
3082.3(13)
4
1.770
0.791
1624
Z
Dc (g cm-3
)
1.673
0.463
760
µ (mm-1
F(000)
)
independent reflections
measured
6912
5033
param/restraints
R1 [Fo > 4σ(Fo)]
wR2 (all refl)
GooF
417
430
0.101
0.2922
1.021
-0.839
2.065
0.070
0.2182
1.133
1.512
1.410
∆Fmin (eÅ-3
)
∆Fmax (e Å-3
)
polymerization runs. Catalyst 1 produced at 50 °C a stereoir-
regular, slightly isotactic-enriched polypropylene ([mm] ) 34%).
The polymer was prevailingly regioregular, having 3.2% of
regioirregularly arranged monomers units, indicated in the 13C
NMR spectrum by the methyl resonances of the tail-to-tail units
observed between 12.6 and 15.0 ppm.28 At lower temperature
(0 °C), the activity decreased, but a slight increase in the fraction
of mm triads was observed by 13C NMR, and an ultrahigh
molecular weight was disclosed by GPC analysis (cfr. Table 3,
run 1).
Propylene polymerizations were also carried out at a monomer
pressure of 6 atm, by using AliBu2H/MAO as the activator. In
Table 3 are collected the main results of the propylene
(26) Tomaszewski, R.; Vollmerhaus, R.; Al-Humydi, A.; Wang, Q.;
Taylor, N. J.; Scott, C. Can. J. Chem. 2006, 84, 214.
In the 13C NMR spectrum of the polypropylene sample
obtained at 50 °C, the exclusive presence of isobutyl end groups
(27) Polymerization conditions: compound
4
)
20 µmol;
[CPh3][B(C6F5)4] ) 20 µmol; AliBu3H ) 600 µmol; ethylene pressure ) 1
atm; toluene ) 35 mL; temperature ) 50 °C; time ) 120 min. Activity )
2.5 kg of polymer × (mol of Zr × h × atm)-1. Tm ) 135.3 °C. GPC analysis
Mn ) 398.466, Mw ) 1.610.409, Mw/Mn ) 4.04.
(28) (a) Zambelli, A.; Gatti, G. Macromolecules 1978, 1, 1–1485. (b)
Zambelli, A.; Bajo, G.; Rigamonti, E. Makromol. Chem. 1978, 179, 1249.

Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes
Organometallics, Vol. 28, No. 3, 2009 695
was observed. The isobutyl end groups were selectively
observed also in a polymer sample obtained at 50 °C in the
presence of MAO alone, thus suggesting a primary propene
insertion operating both in the initiation and in the termination
steps. The reasonable polymerization mechanism should involve
primary insertion into Zr-CH3 bonds, followed by prevailingly
primary insertion during the propagation and termination via
chain transfer of the primary growing chain to MAO, generating
a new Zr-CH3 bond for reinsertion.
Catalyst 2 at 50 °C showed the highest activity toward
propylene polymerization and produced stereoirregular polypro-
pylene having 5.2% of regioirregularly arranged monomer units.
At 0 °C the same catalyst produced a stereoirregular, slightly
sindiotactic, regioregular polymer. In the 13C NMR spectrum
of the sample obtained at 50 °C, resonances attributable to
isobutyl end-groups were observed and, in very low amount
(1:15 ratio to isobutyl group), also resonances due to vinylidene
end-groups. Thus, chain termination by ꢀ-hydrogen transfer is
of only marginal significance.
Compound 5 produced highly regioregular polypropylene
with a prevailingly isotactic microstructure ([mm] ) 56%),
although with low activity. In the 13C NMR spectrum no signals
of regioirregular monomer units or end-groups were detected.
Full pentad analysis disclosed that the relative intensities of the
mmmr, mmrr, and mrrm stereochemical pentads are roughly 2:2:
1, as expected from the statistical model of the “enantiomorphic
sites” of the stereospecific propagation.29
Compounds 1-5 were also tested in the polymerization of
1-hexene. All of the compounds were inactive, at least under
the explored conditions (i.e., AliBu2H/MAO as activator, 50 °C,
toluene solvent), apart from compound 2. Albeit with low
activity, compound 2 produced a prevailingly isotactic poly-1-
hexene, having a higher degree of isotacticity than the polypro-
pylene obtained with the same catalyst under analogous
conditions. It is worth noting that the increase in the isospec-
ificity in the polymerization of higher R-olefins with respect to
propylene has been previously observed for a binaphthyl bridged
salen zirconium catalyst.30
crystallographic analysis was also performed on compound 1
and disclosed a distorted octahedral geometry, with a C1
symmetry deriving from all-cis configuration. Variable-temper-
ature NMR studies established for compound 1 an inversion of
metal configuration through dynamic interchange of the all-cis
enantiomers. Fluxional behaviors in solution were also observed
for compounds 2, 3, and 4. Treatment of complexes with
AliBu2H and methylalumoxane (MAO) yields active, multisite
ethylene and propylene polymerization catalysts. In the screening
of their olefin polymerization reactivity several promising
aspects emerged (i.e., the ultrahigh molecular weight polypro-
pylene obtained with compound 1, the highly regioregular,
prevailingly isotactic polypropylene obtained with 5, or the
prevailingly isotactic poly-1-hexene obtained with compound
2). In conclusion, the preliminary polymerization results ob-
tained with this new class of bis(chelate) zirconium compounds
encourage the search in this field; future work will extend the
study to other group 4 transition metals and/or to different
(amidomethyl)pyridine ligands, in order to study the effects on
their structures and catalytic behavior.
Experimental Section
General Procedure. Manipulation of sensitive materials was
carried out under nitrogen using Schlenk or glovebox techniques.
Hexane, tetrahydrofurane, benzene, and toluene were refluxed over
sodium/benzophenone, methylene chloride over calcium hydride,
then distilled under nitrogen prior to use. CDCl3, CD2Cl2, and C6D6
were dried over calcium hydride, distilled prior to use, and stored
on molecular sevies. 1,1,2,2-Tetrachloroethane-d2 was used as
received for polymer sample analysis. Methylaluminoxane (MAO)
10% wt in toluene solution was purchased from Sigma-Aldrich;
the residual AlMe3 contained in it was removed by distilling the
volatile under reduced pressure, washing the resulting solid with
dry hexane, and drying the obtained white powder in vacuo.
Ethylene and propene were purchased from SON and used without
further purification; 1-hexene was distilled over calcium hydride
prior to use. NMR spectra were recorded on a Bruker Advanced
400 MHz spectrometer (1H, 400 MHz; 13C, 100 MHz; 19F 376
MHz). 13C NMR polymer spectra were recorded on an AM Bruker
62.5 MHz spectrometrer in 1,1,2,2-tetrachloroethane-d2 (C2D2Cl4)
at 100 °C and reported relative to hexamethyldisiloxane (HDMS).
Elemental analyses were recorded on a Thermo Finnigan Flash EA
1112 series C,H,N,S Analyzer.
As far as the polymerization activities are concerned, the
synthesized bischelate zirconium(IV) complexes bearing (ami-
domethyl)pyridine ligands were less active than the analogous
bis(aminopyridinato) zirconium complexes in ethylene polym-
erization. On the contrary, they exhibited some activity in the
polymerization of propylene and higher R-olefins, where these
latter were inactive.14d
Conclusions
Molecular weights (Mn and Mw) and polydispersities (Mw/Mn)
of polyethylene and polypropylene were determined by high-
temperature gel permeation chromatography (GPC) using PL-
GPC210 with PL-Gel Mixed A columns, a RALLS detector
(Precison Detector, PD2040 at 800 nm), an H502 viscometer
(Viscotek,), a refractive detectorn and a DM400 data manager. The
measurements were recorded at 150 °C using 1,2,4-trichlorobenzene
as solvent and narrow molecular weight distribution polystyrene
standards as reference. Some GPC measurements were performed
on a Waters GPC-V200 RI detector at 135 °C using 1,2-
dichlorobenzenea solvent and Styragel columns (range of 107-103).
The molecular weight and the molar mass distribution of the poly-
1-hexene sample was measured by GPC at 30 °C, using CHCl3 as
solvent, flow rate of eluant of 1 mL/min, and narrow polystyrene
standards as reference. The measurements were performed on a
Waters 1525 binary system equipped with a Waters 2414 RI
detector using four Styragel columns (range of 1 000-1 000 000
Å). Every value was the average of two independent measurements.
The new pentafluoro-N-((pyridin-2-yl)methyl)aniline ligands
described in this paper were suitable for the preparation of
bis(chelate) zirconium(IV) complexes. In fact, the dichloride
(1), the dibenzyl (4), and the diamide (5) zirconium derivatives
were prepared via traditional routes, straightforwardly and in
high yields. Quite surprisingly, attempts to prepare
(Lig1)2Zr(NMe2)2 in a reaction between Zr(NMe2)4 and Lig1H
led to the 7-coordinate compound (Lig1)(Lig1*)ZrF(NMe2) (2),
where the modified tridentate Lig1* ligand was generated by
exchange reaction of one ortho fluoride on the pentafluorophenyl
ring of the ligand with a dimethylamino group. Compound 2
was fully characterized by X-ray diffraction analysis. X-ray
(29) (a) Shelden, R. A.; Fueno, T.; Tsunetsugu, T.; Furokawa, J. J.
Polym. Sci. Part B 1965, 3, 23. (b) Wolfsgruber, C.; Zannoni, G.; Rigamonti,
E.; Zambelli, A. Makromol. Chem. 1975, 176, 2765.
(30) Lamberti, M.; Consolmagno, M.; Mazzeo, M.; Pellecchia, C.
Macromol. Rapid Commun. 2005, 26, 1866.

696 Organometallics, Vol. 28, No. 3, 2009
Annunziata et al.
Polymer melting points (Tm) were measured by differential
(CH3), 63.40 (CH2), 118.70, 124.70, 136.08, 139.13, 142.04, 145.26,
160.68 (Ar-C); 19F NMR (CD2Cl2, 293 K) δ -174.0 (1F, br t),
-166.3 (2F, br t), -160.7 (2F, br d). Anal. Calcd for
C26H16Cl2F10N4Zr (736.54): C, 42.40; H, 2.19; N, 7.61. Found: C,
41.81 H, 2.22; N, 6.94.
scanning calorimetry (DSC) using a DSC 2920 TA instrument in
nitrogen flow with a heating and cooling rate of 10 °C min-1
.
Melting temperatures were reported for the second heating cycle.
Synthesis of 2,3,4,5,6-Pentafluoro-N-((6-methylpyridin-2-yl)-
methyl)aniline (Lig1H). To a solution of 6-methyl-2-pyridinecar-
boxaldehyde (1.50 g, 12 mmol) and 2,3,4,5,6-pentaluoroaniline
(2.61 g, 14.0 mmol) in THF (100 mL), containing 3 Å molecular
sieves was added p-toluenesulfonic acid (200 mg) at room tem-
perature. The resulting solution was refluxed for 18 h. After
filtration, the solvent was distilled off by rotary evaporation. The
crude product was purified from dichlorometane/hexane, obtaining
a pale yellow solid (yield ) 65%). Reduction of the imine function
of ligand was carried out by using NaBH3CN in methanol, following
a previously reported procedure,31 obtaining Lig1H as a light yellow
Synthesis of Complex 2. Lig1H (0.800 g, 2.77 mmol) and
tetrakis(dimethylamido)zirconium (0.370 g, 1.38 mmol) were
dissolved in 30 mL of hexane. The solution was stirred for 5 h at
room temperature. The solvent was then distilled off in vacuo and
the resulting powder washed twice with hexane. The complex was
crystallized from dichloromethane/hexane. Suitable crystals for
X-ray analysis were grown from dichloromehane/pentane at room
temperature (0.870 g, 84%): 1H NMR (CD2Cl2; 293 K) δ 2.60 (18H,
br s, -CH3), 4.75 (2H, br s, -CH2), 5.12 (2H, br s, -CH2), 6.9-7.3
(4H, br m, ArH), 7.5-7.8 (2H, br t, p-ArH); 13C NMR (CD2Cl2;
293 K) δ 23.44, 24.65 (CH3), 42.43, 45.91 (N(CH3)2), 58.2, 61.1
(CH2), 117.9, 123.3, 137.5 (Ar-C); 19F NMR (CDCl3, 293 K) δ
-177.1 (1F, br s), -168.88 (1F, br s), -167.39 (2F, br s), -162.94
(1F, br s), -157.35 (1F, br s), -151.70 (1F, br s), - 148.15 (2F,
br s), 52.21 (1F, s, Zr-F). Anal. Calcd for C30H28F10N6Zr (753.79):
C, 47.80; H, 3.74; N, 11.15. Found: C, 47.50; H, 3.62; N, 10.98.
Hydrolysis of Complex 2. To a solution of 30 mg of complex
2 in dichloromethane (2 mL) was added 5 mL of water. The organic
product was extracted with diethyl ether and dried over Na2SO4,
and the solvent was removed by rotary evaporation. Product was
characterized by NMR spectroscopy, disclosing Lig1H and Lig1*H
1
powder (yield ) 95%): H NMR (CDCl3; 293 K) δ 2.55 (3H, s,
-CH3), 4.55 (2H, br d, -CH2), 5.14 (1H, br s, NH), 7.05 (2H, m,
ArH), 7.54 (1H, t, p-ArH); 13C NMR (CDCl3; 293 K) δ 24.62 (CH3),
50.66 (CH2), 118.85, 122.22, 124.25, 132.52, 134.89, 137.15,
139.57, 156.19, 158.39 (Ar-C); 19F NMR (CDCl3, 293 K) δ
-172.4 (t, 1F, p-F), -165.14 (t, 2F, m-F), -159.96 (d, 2F, o-F).
Anal. Calcd for C13H9F5N2 (288.21): C, 54.17; H, 3.15; N, 9.72.
Found: C, 53.75; H, 3.17; N, 9.48.
Synthesis of N-((6-Bromopyridin-2-yl)methyl)-2,3,4,5,6-pen-
tafluoroaniline (Lig2H). The imine ligand was obtained as above
by reacting 6-bromo-2-pyridine-carboxaldehyde (1.0 g, 5.3 mmol)
and 2,3,4,5,6-pentaluoroaniline (1.10 g, 6.0 mmol). The crude
product was purified by column chromatography on neutral alumina,
using hexane/diethyl ether (yield ) 64%). The subsequent reduction
reaction with NaBH3CN gave amino ligand in good yield (75%):
1H NMR (CDCl3; 293 K) δ 4.55 (2H, br d, -CH2), 4.76 (1H, br s,
NH), 7.22-7.56 (3H, m, ArH); 13C NMR (CDCl3; 293 K) δ 50.44
(CH2), 120.64, 127.22, 139.30, 142.20, 159.13 (Ar-C); 19F NMR
(CDCl3, 293 K) δ -171.2 (t, 1F, p-F), -164.6 (t, 2F, m-F), -159.45
(d, 2F, o-F). Anal. Calcd for C12H6BrF5N2 (353.08): C, 40.82; H,
1.71; N, 7.93. Found: C, 39.99; H, 1.81; N, 6.98.
1
in a 1:1 ratio. Lig1*H: H NMR (CDCl3; 293 K) δ 2.53 (3H, s,
-CH3), 2.70 (6H, s, Ar-N(CH3)2), 4.51 (2H, br d, -CH2), 5.90
(1H, br s, NH), 7.00 (2H, m, ArH), 7.50 (1H, t, p-ArH); 13C NMR
(CDCl3; 293 K) δ 29.91 (CH3), 43.73 (Ar-N(CH3)2), 51.27 (CH2),
118.91, 121.96, 124.38, 137.04, 139.57, 156.16, 158.29 (Ar-C);
19F NMR (CDCl3, 293 K) δ -173.93 (t, 1F, p-F), -162.19 (t, 1F,
m-F), -160.16 (d, 1F, o-F), -150.80 (d, 1F, o-F).
Synthesis of Complex 3. Complex 2 (200 g, 0.3 mmol) and
Me3SiCl (0.195 g, 1.8 mmol) were dissolved in 20 mL of dry
toluene, and the solution was stirred at room temperature for 24 h.
The light yellow precipitate was filtered off, washed with dry
hexane, and dried in vacuo (yield 90%): 1H NMR (CDCl3; 298 K)
δ 2.68 (6H, br s, -CH3), 2.72 (6H, br s, -CH3), 4.56 (2H, br s,
-CH2), 4.59(2H, br s, -CH2), 7.04-7.7 (6H, br m, ArH); 13C NMR
(CD2Cl2; 293 K) δ 24.69, 25.13 (CH3), 43.88 (Ar-N(CH3)2), 50.77,
51.27 (CH2), 119.08-138.91 (Ar-C); 19F NMR (CD2Cl2, 293 K)
δ -168.48 (2F, br s), -167.11 (1F, br s), -163.78 (1F, br s),
-159.00 (1F, br s), -151.68 (1F, br s), -149.04 (2F, br s), -
147.83 (1F, br s). Anal. Calcd for C28H22Cl2F9N5Zr (761.62): C,
44.16; H, 2.91; N, 9.20. Found: C, 43.98; H, 2.86; N, 9.15.
Synthesis of Complex 4. To a solution of Lig1H (0.500 g, 1.76
mmol) in benzene (20 mL) was slowly added a solution of
tetrabenzylzirconium (0.400 g, 0.88 mmol) in benzene (10 mL).
The solution was stirred for 3 h at room temperature, the solvent
was distilled off in vacuo, and the resulting crude product was
washed with hexane and crystallized from toluene (yield ) 68%):
1H NMR (C6D6; 293 K) δ 2.60 (6H, br s, -CH3), 2.34 (4H, br m,
CH2Ph), 4.75 (4H, br m, -CH2), 6.05-6.99 (16H, br m, ArH);
13C NMR (C6D6; 293 K) selected resonances δ 25.35, 26.24 (CH3),
45.67 (CH2), 58.69 (CH2Ph), 118.65-160.10 (Ar-C); 19F NMR
(C6D6, 293 K) δ main resonances δ -166.4 (1F, br s), -166.0
(2F, br t), -147.0 (2F, br d), minor resonances -179.5 (br s),
-167.2 (br s), -159.4 (br s), -155.0 (br s). Anal. Calcd for
C40H30F10N4Zr (847.90): C, 56.66; H, 3.57; N, 6.61. Found: C,
56.50; H, 3.42; N, 6.60.
Synthesis of 2,3,4,5,6-Pentafluoro-N-((pyridin-2-yl)methyl)a-
niline (Lig3H). The imine ligand was obtained as above by reacting
2-pyridinecarboxaldehyde (1.5 mL, 15.7 mmol) and 2,3,4,5,6-
pentafluoroaniline (2.9 g, 16 mmol) (yield ) 80%). The subsequent
reduction reaction with NaBH3CN gave the amino ligand as a light
1
brown powder in good yield (98%): H NMR (C6D6; 293 K) δ
4.21 (2H, br d, -CH2), 5.31 (1H, br s, NH), 6.48-6.94 (3H, m,
ArH), 8.29 (1H, br d, o-ArH); 13C NMR (C6D6; 293 K) δ 49.97
(CH2), 121.44, 122.22, 136.16, 149.15, 156.76 (Ar-C); 19F NMR
(C6D6, 293 K) δ -173.5 (t, 1F, p-F), -165.6 (t, 2F, m-F), -161.2
(d, 2F, o-F). Anal. Calcd for C12H7F5N2 (274.18): C, 52.57; H, 2.57;
N, 10.22. Found: C, 52.34; H, 2.42; N, 9.89.
Synthesis of Complex 1. To a stirred solution of Lig1H (1.0 g,
3.47 mmol) in THF (50 mL) at -78 °C was added a butyllithium
hexane solution (1.45 mL, 2.5 M, 3.62 mmol). The mixture was
allowed to warm to room temperature and stirred for 3 h. The
resulting yellow solution was added dropwise to a stirred solution
of ZrCl4 · 2THF (0.652 g, 1.73 mmol) in 50 mL of THF at -78
°C. The mixture was allowed to warm to room temperature and
stirred overnight. Removal of the solvent in vacuo gave a dark
yellow powder. The crude product was extracted in dichlo-
romethane, and the solution was filtered, concentrated, and layered
with hexane. A pale yellow powder deposited overnight (1.14 g,
89%). Suitable crystals for X-ray crystal structure determination
were grown from dichloromethane/hexane at room temperature: 1H
NMR (CD2Cl2; 293 K) δ 2.82 (6H, br s, -CH3), 4.65 (2H, br s,
-CH2), 4.84 (2H, br s, -CH2), 7.16 (2H, br d, ArH), 7.27 (2H, br
d, ArH), 7.80 (2H, br t, p-ArH); 13C NMR (CDCl3; 293 K) δ 24.98
Synthesis of Complex 5. Lig2H (0.625 g, 1.77 mmol) and
tetrakis(dimethylamido)zirconium (0.235 g, 0.88 mmol) were
dissolved in 30 mL of dry hexane. The resulting solution was stirred
for 5 h at room temperature. The solvent was then distilled off in
vacuo, and the resulting powder was washed with hexane. The
complex was crystallized from dichloromethane (0.670 g, 86%):
(31) Domski, G. J.; Lobkovsky, E. B.; Coates, G. W. Macromolecules
2007, 40, 3510–3513.

Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes
Organometallics, Vol. 28, No. 3, 2009 697
1H NMR (CDCl3; 293 K) δ 2.79 (12H, s, -N(CH3)2), 5.09 (4H, s,
-CH2), 7.06 (2H, d, ArH), 7.31 (2H, d, ArH), 7.43 (2H, t, p-ArH);
13C NMR (CDCl3; 293 K) δ 42.55 (N(CH3)2), 58.08 (CH2), 119.65,
126.76, 139.83, 164.71 (Ar-C); 19F NMR (CDCl3, 293 K) δ
-166.3 (2F, br d), -153.3 (2F, br s), -148.3 (1F, br s). Anal.
Calcd for C28H22Br2F10N6Zr (883.53): C, 38.06; H, 2.51; N, 9.51.
Found: C, 38.62; H, 2.36; N, 8.99.
and warmed to 50 °C. Then a solution of complex 2 (20 µmol) in
toluene (2 mL), preaged for 10 min with a solution of AliBu2H in
toluene (2.15 mL, 0.28 M in), was added. After 5 h, the
polymerization mixture was poured into acidified ethanol. Polymer
was recovered and dried in a vacuum oven (yield ) 0.060 g). From
13C NMR spectrum [mmmm] ) 84%. From GPC: Mw/Mn ) 4.54;
Mn ) 46700.
Reaction between Lig3H and Zr(NMe2)4. Lig3H (0.700 g, 2.55
mmol) and tetrakis(dimethylamido)zirconium (0.330 g, 1.25 mmol)
were dissolved in 30 mL of hexane. The solution was stirred for
6 h at room temperature, the solvent was distilled off in vacuo,
and the resulting powder was washed with hexane (0.750 g, 82%):
1H NMR (C6D6; 293 K) δ 2.63 (12H, s, -N(CH3)2), 4.66 (4H, br
s, -CH2), 6.3 (4H, br m, ArH), 6.3 (2H, br t, ArH), 8.7 (2H, br d,
o-Py-H); 13C NMR (CDCl3; 293 K) δ 43.29 (N(CH3)2), 61.31 (CH2),
121.27, 121.95, 137.84, 149.17, 163.61 (Ar-C); 19F NMR (C6D6,
293 K) δ -168.8 (3F, br t), -166.8 (6F, br t), -149.77 (6F, br d);
minor resonances -169.5 (1F, br s), -162.9 (1F, br s), -158.5
(1F, br s), -151.3 (1F, br s), 42.17 (1F, s, Zr-F). Anal. Calcd for
C28H24F10N6Zr (724.09): C, 46.34; H, 3.33; N, 11.58. Found: C,
45.87; H, 3.21; N, 11.08.
X-ray Crystallography. Suitable crystals of both compounds 1
and 3 were selected and mounted on a cryoloop with paratone oil
and measured at 100 K with a Rigaku AFC7S diffractometer
equipped with a Mercury2 CCD detector using graphite monochro-
mated MoKR radiation (λ ) 0.71069 Å). Data reduction was
performed with the crystallographic package CrystalClear.32 Data
have been corrected for Lorentz, polarization, and absorption. The
structures were solved by direct methods using the program SIR9733
and refined by means of full-matrix least-squares based on F2 using
the program SHELXL97.34
For both compounds all non-hydrogen atoms were refined
anisotropically; hydrogen atoms were positioned geometrically and
included in structure factor calculations but not refined. As for
compound 1 the crystallographic asymmetric unit consists of one
molecule of 1 and one molecule of CH2Cl2. The difficulties in
modeling the disorder of the CH2Cl2 molecule could account for
the lower quality of the X-ray analysis of 1.
Hydrolysis of the Reaction Product between Lig3H and
Zr(NMe2)4. Thirty milligrams of the obtained sample was dissolved
in dichloromethane (2 mL) and treated with water (5 mL). The
organic fraction was extracted with diethyl ether and dried over
Na2SO4; volatiles were removed by rotary evaporation. The resulting
solid product was characterized by NMR spectroscopy, disclosing
Crystal data and refinement details are reported in Table 4.
Crystal structures are drawn by means of the program ORTEP32.35
1
a mixture of Lig3H and Lig3*H in a 3:1 ratio. Lig3*H: H NMR
Acknowledgment. We are grateful to Prof. Vincenzo
Busico, Prof. Roberta Cipullo, and Dr. Maria Grazia Napoli
for some GPC analysis, to Dr. Patrizia Oliva for some NMR
experiments, and to Dr. Patrizia Iannece for elemental
analysis of the complexes.
(CDCl3; 293 K) δ 2.70(6H, s, Ar-N(CH3)2), 4.56 (2H, br d, -CH2),
5.81 (1H, br s, NH), 7.20 (2H, m, ArH), 7.63 (1H, t, p-ArH), 8.55
(1H, d, o-ArpyH); 13C NMR (CDCl3; 293 K) δ 44.00 (Ar-N(CH3)2)
51.3 (CH2), 116.4, 123.3, 136.8, 149.6 (Ar-C); 19F NMR (CDCl3,
293 K) δ -173.69 (t, 1F, p-F), -162.10 (t, 1F, m-F), -160.09 (d,
1F, o-F), -150.67 (d, 1F, o-F).
Polymerizations. Ethylene and propylene polymerizations were
performed in a magnetically stirred reactor (100 cm3) or in a 500
mL Bu¨chi glass autoclave. The reactor vessels were charged
sequentially with MAO and a toluene solution of the precatalyst.
The mixture was thermostated at the required temperature, and the
monomer gas feed was started. After the required polymerization
time, the mixture was poured into acidified ethanol. The precipitated
polymer was recovered by filtration and dried at 40 °C in a vacuum
oven. Details and results of polymerization are reported in Tables
2 and 3.
Supporting Information Available: X-ray crystallographic
1
information files in CIF format for compounds 1 and 2; H, 13C,
1
and 19F NMR spectra of the ligands and of complexes 1-5, H
NMR of hydrolysis products, and 13C NMR spectra of polyhexene
and polypropylene samples. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM800736W
(32) CrystalClear, Crystal Structure Analysis Package, Rigaku-Molecular
Structure Corp.
(33) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(34) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(35) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
1-Hexene Polymerization. Polymerization was performed in a
magnetically stirred reactor (50 °C) that was charged sequentially
with dried MAO (20 mmol), 4 mL of toluene, and 8 mL of 1-hexene