Bis(3,5-dimethylpyrazol-1-ato) zirconium complexes as precursors for ethylene polymerisation upon activation with MAO: Syntheses, characterisation and X-ray molecular structure of [Zr(η2-3,5-Me2Pz)2Cl2 (η1<

Article abstract of DOI:10.1016/j.poly.2007.08.001

Full title: Bis(3,5-dimethylpyrazol-1-ato) zirconium complexes as precursors for ethylene polymerisation upon activation with MAO: Syntheses, characterisation and X-ray molecular structure of [Zr(η²-3,5-Me₂Pz)₂Cl₂

Full text of DOI:10.1016/j.poly.2007.08.001

Available online at www.sciencedirect.com
Polyhedron 26 (2007) 5339–5348
www.elsevier.com/locate/poly
Bis(3,5-dimethylpyrazol-1-ato) zirconium complexes as precursors
for ethylene polymerisation upon activation with MAO:
Syntheses, characterisation and X-ray molecular structure
of [Zr(g2-3,5-Me2Pz)2Cl2(g1-3,5-Me2PzH)2] Æ (3,5-Me2PzH) and
[Zr(g2-3,5-Me2Pz)2(CH2Ph)2] (3,5-Me2Pz = 3,5-dimethylpyrazol-1-ato)
a
a
a,
b
*
´
´
Martial Sanz , Marta E.G. Mosquera , Tomas Cuenca , Carmen Ramırez de Arellano ,
c
c
Mark Schormann , Manfred Bochmann
a
Departamento de Quı´mica Inorga´nica, Universidad de Alcala´, Facultad de Farmacia, Campus Universitario, 28871- Alcala´ de Henares, Spain
b
Departamento de Quı´mica Orga´nica, Facultad de Farmacia, Universidad de Valencia, 46100 Valencia, Spain
Wolfson Materials Centre, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
c
Received 3 July 2007; accepted 1 August 2007
Available online 29 September 2007
Abstract
The bis(3,5-dimethylpyrazol-1-ato) zirconium complex [Zr(g2-3,5-Me2Pz)2(NMe2)2(NHMe2)2] (2) is obtained by treatment of
[Zr(NMe2)4] with 2 equiv. of 3,5-dimethylpyrazole 1. The reaction of the [ZrCl4(THF)2] adduct with 2 equiv. of the potassium salt of
1 affords the dichloro derivative [Zr(g2-3,5-Me2Pz)2Cl2]n (3), while reaction with 4.1 equiv. of 1 in the presence of 2.1 equiv. of NEt3
affords the dichloro pyrazole adduct [Zr(g2-3,5-Me2Pz)2Cl2(g1-3,5-Me2PzH)2] (4). Treatment of [Zr(CH2Ph)4] with 2 equiv. of 1 gives
the dibenzyl complex [Zr(g2-3,5-Me2Pz)2(CH2Ph)2] (5) via alkane elimination. Compound 4 presents fluxional behaviour in CDCl3 solu-
tion, which was studied and quantified by variable-temperature proton NMR experiments. All compounds were characterised by routine
analyses and the molecular structures of 4 and 5 were established by single-crystal X-ray diffraction studies. The performance of precur-
sors 3 and 5 was evaluated in ethylene polymerisation upon activation with MAO.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Zirconium; 3,5-Dimethylpyrazole; 3,5-Dimethylpyrazolato; Ethylene polymerisation
1. Introduction
Within the family of heteroatom-base ligands seen in the
literature, essentially for group 4 polyolefin precursors
[12–14], it is not surprising that preparation of nitrogen-,
oxygen-, sulfur-, and phosphorus-based molecules encom-
passes a large proportion of preligand synthesis. Particularly
interesting are ligands with nitrogen and oxygen as donor
atoms, due to their mode of complexation to an acidic metal
centre. Thus, Schiff-base-derived ligands [15–26] have had a
leading role over the last two decades. Their ability to
strongly or weakly bond to group 4 metals resides in sharing
their lone pair of electrons with the metal–heteroatom
r-bond by retro-donation or, in some cases, forming a weak
p-dative bond. In our continuing research we have exploited
Over the last two decades, investigation and applications
in olefin catalysis of new group 4 metal complexes contain-
ing heteroatom-base ligands have progressed steadily with
a view to obtaining new high-value-added materials com-
pared to those obtained using the legendary Ziegler–Natta-
or [MCp2X2] (X = halo, alkyl, aryl) metallocene precursors
[1–11].
*
Corresponding author. Tel.: +34 918854655; fax: +34 918854683.
E-mail address: tomas.cuenca@uah.es (T. Cuenca).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.08.001

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M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
such versatility as well as the steric properties of the precur-
sors, by using the ligand framework to strategically affect the
structure of the corresponding group 4 metal complex, and
therefore, its reactivity in alkene polymerisation.
lar structures of [Zr(g2-3,5-Me2Pz)2Cl2(g1-3,5-Me2PzH)2] Æ
(3,5-Me2PzH) and [Zr(g2-3,5-Me2Pz)2(CH2Ph)2] (3,5-
Me2Pz = 3,5-dimethylpyrazol-1-ato) and their performance
in ethylene and propylene polymerisation upon activation
with MAO.
Our first deliberate choice was to use nitrogen precur-
sors. Among the huge list of potential nitrogen candidates
with an appropriate binding mode and the ability to be
linked to a metal, 3,5-disubstituted-pyrazolato derivatives
are attracting attention for a number of applied reasons.
The use of 3,5-disubstituted-pyrazolato derivatives in coor-
dination and organometallic chemistry has become con-
spicuous in the literature [27,28], showing the versatility
of such a ligand. Excluding hydridotrispyrazolylborato
derivatives [29–31] as ligands in organometallic complexes,
the 3,5-disubstituted-pyrazol-1-ato moiety acting as princi-
pal ligand has been bonded to various metals either in a
g1-coordination fashion [32] (Fig. 1a) or in a chelating
g2-coordination mode (Fig. 1b), affording relatively greater
stability in the monometallic system. Non-substituted-pyr-
azol-1-ato ligand, acting as a pyrazolato anion, can coordi-
nate to two metals in a l2-coordination mode [32] (Fig. 2),
which usually produces a polymetallic system. In this way,
the 3,5-disubstituted-pyrazol-1-ato candidate, which
appears to be structurally and electronically attractive,
has moderate electron-donating properties according to
Fujita’s [13] recent classification, which categorised some
representative oxygen, nitrogen heteroatom ligands by esti-
mating their electron-donating properties using PM3/
MNDO calculations. Some bis(3,5-di-tert-butylpyrazol-1-
ato) dialkyl and dichloro homo- and bimetallic complexes
2. Results and discussion
2.1. Preparation of bis(3,5-dimethylpyrazol-1-ato)
zirconium derivatives
3,5-Dimethylpyrazole (3,5-Me2PzH) (1) was purchased
from a commercial source or synthesised according to the
literature procedure [41] and used after sublimation under
high vacuum. Addition of 1 to a toluene solution of
[Zr(NMe2)4] at room temperature afforded, via amine elim-
ination, the thermally robust bis(dimethylamido) bis(3,5-
dimethylpyrazol-1-ato) zirconium(IV) complex 2, stabilised
by coordination of two molecules of the NHMe2 generated.
It was isolated in 95% yield as an analytically pure white
solid after the solvent was completely removed under
reduced pressure (Scheme 1). Compound 2 was subject to
a mild chloro-solvolysis in CDCl3 or treated in C6D6 with
a slight excess of SiClMe3 (2.1 equiv.) at room temperature
in an attempt to access the corresponding dichloro deriva-
tive [Zr(g2-3,5-Me2Pz)2Cl2] (3). The 1H and 13C NMR
spectra of both resulting reaction mixtures unfortunately
provide an unresolved mixture of products. To synthesise
the desired dichloro zirconium complex 3, the
[ZrCl4(THF)2] adduct was treated at À78 ꢁC with 2 equiv.
of K(3,5-Me2Pz) [42] in a THF–toluene solution (Scheme
1). After elimination of KCl and volatiles, 3 was isolated
as an analytically pure white substance in 17% yield. When
the [ZrCl4(THF)2] adduct was reacted with 4.1 equiv. of 1
in the presence of 2.1 equiv. of NEt3 in toluene at 0 ꢁC
the zirconium complex [Zr(g2-3,5-Me2Pz)2Cl2(g1-3,5-
Me2PzH)2] Æ (3,5-Me2PzH) (4) was exclusively produced
as an analytically pure off-white solid in 46% yield after
elimination of the ammonium salt (Scheme 1).
of
titanium
[33–36]
(alkyl = benzyl,
methyl,
trimethylsilylmethyl) and neutral or cationic pyrazolato
cyclopentadienyl zirconium complexes [37–39] and (g2-
pyrazolato) zirconium compounds with bulky pyrazolato
ligands bearing tert-butyl [35] indenylmethyl or fluorenyl-
methyl [40] substituents have been described.
Herein, we report the synthesis of some new bis(3,5-dim-
ethylpyrazol-1-ato) zirconium complexes, the X-ray molecu-
Methylation of 3 with 2 equiv. of LiMe in ether at
À78 ꢁC (Scheme 1) gave an unstable, intractable and unre-
1
solved mixture of products whose H NMR spectrum was
regrettably uninformative. Due to the unexpected poor
behaviour of the methyl ligand to create a stable coordina-
tion environment at the zirconium centre, the use of volu-
minous ligands was explored to stabilise the new bis(3,5-
dimethylpyrazol-1-ato) dialkyl zirconium product. The
reaction of [Zr(CH2Ph)4] with 2 equiv. of 1 in cold toluene
gave, via alkane elimination, the compound [Zr(g2-3,5-
Me2Pz)2(CH2Ph)2] (5) as an analytically pure white solid
(98% yield) after elimination of volatiles (Scheme 1). The
synthesis of dialkyl titanium compounds [Ti(g2-3,5-
tBu2Pz)2R2] (R = Me, CH2Ph, CH2SiMe3) [34] has been
reported following treatment of the dichloro derivative
[Ti(g2-3,5-tBu2Pz)2Cl2] [33] with the appropriate alkylating
reagent.
Fig. 1. Monodentate pyrazole and chelating pyrazol-1-ato coordination
modes.
Fig. 2. Bridged pyrazol-1-ato coordination mode.

M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
5341
Scheme 1.
Compounds 2–5 are air-sensitive but thermally stable in
solution and in the solid state. They are soluble in aromatic
and chlorinated solvents but poorly soluble in aliphatic
hydrocarbons. Spectroscopic (1H, 13C NMR analyses in
C6D6 and CDCl3 solutions) and elemental analyses are in
agreement with the proposed structures. The molecular
structures of 4 and 5 have been determined by X-ray dif-
fraction methods.
pseudo-octahedral disposition for 2 with the pyrazolato
and amido ligands in the equatorial positions and the
amino groups located in a trans configuration (Scheme 1).
The CDCl3-solution NMR spectrum of 3 displays one set
of proton resonances as singlets at d 6.04 and 2.47, showing
a pattern typical for methine and methyl protons in a hetero-
cyclic moiety. Attempts to obtain X-ray quality monocrys-
tals with a view to corroborating this information were
unfruitful. The molecular structure of the analogous
1
The 300 MHz H NMR spectrum of 2 (C6D6, 20 ꢁC)
exhibits the expected pattern of resonances for the methine
and methyl-substituted pyrazol-1-ato protons as singlets at
d 6.08 and 2.35, respectively. The signal at d 3.37 is
assigned to the N-methyl-amido protons. The resonance
bulky-substituted
titanium
compound
[Ti(g2-3,5-
tBu2Pz)2Cl2] [33] indicates a mononuclear disposition show-
ing a pseudo-tetrahedral geometry around the titanium
atom where the centres of the N–N bonds of the pyrazolato
ligands are considered as unidentate coordination positions.
Structural and chemical similarities have been established
between pyrazolato and cyclopentadienyl early transition
metal complexes and comparison between [Ti(g2-3,5-
tBu2Pz)2Cl2] and [TiCp2Cl2] yields similar structural proper-
ties with the pyrazolato group, being a poorer donor ligand
than the cyclopentadienyl ring [35]. Nevertheless, the size of
the zirconium atom is larger and the zirconium complex is
unsaturated. The ESI+-TOF mass spectrum on a sample
of 3 dissolved in a chloroform solution has showed the pres-
ence of ion peaks m/z (exact mass m/z: 964.78) superior to
that expected for the mononuclear derivative 3 (exact mass
3
at d 1.78 with a coupling constant JHH of 6.3 Hz and
the multiplet signal at d 0.31 with a 6:1 proton ratio were
assigned to the methyl- and proton-amino ligand, respec-
tively, through a 1H–1H-homo decoupling experiment, sug-
gesting the evident coordination of the amino sp3-nitrogen-
donor to zirconium [43,44]. In the absence of a reliable
crystal diffraction study, these spectroscopic behaviours
allow us to formulate complex 2 as [Zr(g2-3,5-Me2Pz)2(N-
Me2)2(NHMe2)2], which was also confirmed by elemental
analysis. According to these data and on the basis of the
crystal structure analysis obtained by X-ray diffraction
for the analogous dichloro compound 4, we propose a

5342
M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
m/z: 349.96), although the corresponding peak for a dinucle-
ar species was not observed. Thus, it seems very reasonable
that 3 would form oligomeric species with either bridging
chloro or pyrazolato ligands.
1
At 25 ꢁC, the H NMR spectrum (CDCl3, 500 MHz) of
4 shows relatively uninformative broad signals. Neverthe-
less, it enables us to distinguish three regions of resonances.
The first region has a broad signal at d 10.77 representative
of the proton N–H corresponding to coordinated 3,5-dim-
ethylpyrazole. The second region features a broad signal at
d 6.08 and a singlet at d 5.90 assigned to the methine pro-
tons of the coordinated 3,5-dimethylpyrazole and the 3,5-
dimethylpyrazol-1-ato ligands, respectively. The third
region at d 2.33–2.17 contains broad signals for the methyl
protons of the 3,5-dimethylpyrazol-1-ato and the coordi-
nated 3,5-dimethylpyrazole ligands. On cooling at
À40 ꢁC, some of the signals became more defined and coa-
lescence of the two methyl resonances of the coordinated
pyrazole ligands was observed. Compared to 25 ꢁC spectra,
the amino N–H proton resonance appears downfield
shifted at d 11.26. Cooling at À60 ꢁC caused a considerable
sharpening and splitting of the signals and the resonance
for the N–H proton of the coordinated 3,5-dimethylpyraz-
ole ligand was observed at d 11.26. The spectrum shows
two singlets at d 6.02 and 5.80 assigned to the methine pro-
tons of the coordinated 3,5-dimethylpyrazole and the 3,5-
dimethylpyrazol-1-ato ligands, respectively. Two signals
for the methyl protons of the coordinated pyrazole corre-
sponding to two non-equivalent groups and a singlet for
the equivalent methyl protons of the pyrazol-1-ato ligand
are observed. Fluxional behaviour of 4 in CDCl3 solution,
corresponding to a sigmatropic displacement [45,46] of the
two consecutive nitrogen of the coordinated pyrazole mol-
ecules, was apparent from this variable-temperature 1H
NMR study. A Gibbs activation energy DG#(233 K) of
47.71 kJ molÀ1 (11.4 kcal molÀ1) in the coalescence temper-
ature was obtained for this process.
Fig. 3. X-ray ellipsoid plot of one of the independent molecules found for
4 showing the atomic numbering scheme.
to ligands coordinated by their nitrogen atoms. The centres
of the N–N bonds are considered as unique coordination
positions. The two dimethylpyrazole groups are placed in
the apical positions in a trans configuration. Both nitrogen
atoms of the symmetrically coordinated g2-fashion pyrazo-
lato ligand are nearly equidistant from the zirconium with
˚
the average Zr–N distances of 2.207 A. The Zr–N bond dis-
tances are longer for the coordinated pyrazole groups
˚
[Zr(1)–N(2) 2.377(2) A] than for the pyrazolato ligands
˚
˚
[Zr(1)–N(3) 2.188(2) A, Zr(1)–N(4) 2.226(2) A] which show
a degree of multiple bonding. All the Zr–N distances are
within the range observed in similar previously reported
1
The 500 MHz H NMR (C6D6, 25 ꢁC) spectrum of 5
˚
exhibits the expected pattern of resonances; two singlets
at d 6.20 and 2.14 for the methine and methyl protons of
the pyrazolato ligands, respectively, and four signals,
which are composed of two triplets at d 7.06 (meta-CH),
6.88 (para-CH), a doublet at d 6.65 (ortho-CH) with cou-
pling constants of 7.6 Hz, 7.4 Hz, and 7.4 Hz, respectively,
and a singlet at d 2.01 (CH2), assigned to the aromatic ring
and methylene protons of the benzyl ligand, for which the
pyrazolato/benzyl proton ratio is 1:1. Similar results were
also observed in the 13C NMR spectrum in the same
conditions.
zirconium compounds (2.306–2.369 A for Zr–pyrazole
[37] and 2.146–2.263 A for Zr–pyrazolato [38–40]). It
˚
should be noted that only a few examples of group 4 com-
plexes with pyrazolato and/or pyrazole ligands have been
described. An intramolecular hydrogen bond with a dis-
˚
tance of 3.142 A for Cl(1)Á Á ÁN(1) and an angle of 122ꢁ
for Cl(1)–H(1)–N(1) occurs in Cl(1)Á Á ÁH(1)–N(1) and
seems to have some impact on the relative disposition of
the coordinated pyrazole ligands. In contrast, the related
compound [TiCl4(g1-3,5-Me2PzH)2] shows no such H-
bond interaction [33]. Analysis of the intermolecular inter-
actions demonstrates the presence of a weak hydrogen
bond (WHB) [47] (Cl(1)Á Á ÁH(14)–C(14) (Cl(1)Á Á ÁC(14) dis-
White single crystals of 4 suitable for X-ray diffraction
studies grown in a saturated toluene solution at À40 ꢁC
were used to unequivocally establish the spatial arrange-
ment of atoms in this complex (Fig. 3). Selected bond dis-
tances and angles for the structure are listed in Table 1.
The Zr atom shows a distorted octahedral geometry
where the chloro ligands are mutually cis. The two other
equatorial positions are occupied by two dimethylpyrazola-
˚
tance of 3.687 A and Cl(1)–H(14)–C(14) angle of 140.85ꢁ)
between molecules, forming a chain arrangement in the
crystal.
Further characterisation by X-ray diffraction analysis of
a suitable single crystal grown from a toluene–pentane
solution at À40 ꢁC definitively revealed the structure of 5

M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
5343
Table 1
Selected bond distances (A) and angles (ꢁ) for 4 and 5
a
˚
Compound
4
5
Zr(1)–N(1)
Zr(1)–N(2)
Zr(1)–N(3)
Zr(1)–N(4)
Zr(1)–N(2)#1
Zr(1)–N(3)#1
Zr(1)–N(4)#1
Cl(1)–Zr(1)
N(1)–N(2)
N(3)–N(4)
N(1)–C(1)
N(2)–C(3)
N(3)–C(6)
N(4)–C(8)
Zr(1)–C(11)
Zr(1)–C(12)
Zr(1)–C(21)
Zr(1)–C(22)
N(1)–H(1)
2.1469(18)
2.1974(17)
2.2037(17)
2.1288(16)
2.377(2)
2.188(2)
2.226(2)
2.377(2)
2.188(2)
2.226(2)
2.5434(8)
1.367(3)
1.385(3)
1.391(3)
1.390(3)
1.345(4)
1.335(3)
1.345(3)
1.341(3)
2.286(2)
2.8708(18)
2.280(2)
2.598(2)
0.75(4)
N(1)–Zr(1)–N(2)
N(1)–Zr(1)–N(3)
N(2)–Zr(1)–N(3)
N(3)–Zr(1)–N(4)
N(4)–Zr(1)–N(1)
N(4)–Zr(1)–N(2)
N(3)#1–Zr(1)–N(4)#1
N(2)–Zr(1)–N(2)#1
N(3)–Zr(1)–N(3)#1
N(4)–Zr(1)–N(4)#1
C(11)–Zr(1)–C(22)
C(21)–Zr(1)–C(11)
C(21)–Zr(1)–C(22)
N(2)–Zr(1)–Cl(1)
N(3)–Zr(1)–Cl(1)
N(4)–Zr(1)–Cl(1)
N(1)–N(2)–Zr(1)
N(2)–N(1)–Zr(1)
N(3)–N(4)–Zr(1)
C(12)–C(11)–Zr(1)
C(21)–C(22)–Zr(1)
C(22)–C(21)–Zr(1)
N(4)–N(3)–Zr(1)
Cl(1)#1–Zr(1)–Cl(1)
N(2)–N(1)–H(1)
37.33(6)
131.19(6)
167.74(6)
37.36(7)
116.68(8)
36.55(8)
Fig. 4. X-ray ellipsoid plot of the independent molecule found for 5
showing the atomic numbering scheme.
94.04(10)
80.31(8)
36.55(8)
155.73(12)
86.67(13)
103.64(12)
˚
˚
C(12) of 2.286(2) A and 2.8708(18) A, respectively] as well
as between Zr and g2-benzyl [Zr(1)–C(21) and Zr(1)–C(22)
92.61(7)
126.51(8)
34.07(7)
˚
˚
of 2.280(2) A and 2.598(2) A, respectively] are similar in the
solid state in other analogues [48,49,51,53–57]. The benzyl
ligands form Zr(1)–C(11)–C(12) and Zr(1)–C(21)–C(22)
angles of 97.13(12)ꢁ and 84.96(12)ꢁ, respectively [58,59].
The two benzyl ligands are reciprocally located adopting
a chair-type conformation.
80.95(6)
94.87(7)
85.75(6)
69.36(10)
73.31(10)
73.5(2)
97.13(12)
60.97(11)
84.96(12)
Each pyrazol-1-ato ligand is bonded to the zirconium
centre by both nitrogen atoms in a chelating g2-coordina-
tion mode. The N(1)–N(2)-Zr(1)–N(3)–N(4) atoms lie in
the same plane (mean deviation 0.026). The N(1)–N(2)–
C(1)–C(2)–C(3) and N(3)–N(4)–C(6)–C(7)–C(8) rings are
both bent towards the C(11)–C(17) benzyl ligand forming
dihedral angles of 10.0ꢁ and 14.3ꢁ, respectively, with the
N(1)–N(2)-Zr(1)–N(3)–N(4) mean plane. The pyrazolyl
moieties are bonded to the Zr centre with distances
70.25(13)
73.20(14)
89.57(4)
121(3)
Symmetric code #1 = Àx + 2, y, Àz + 1/2.
a
E.s.d’s are given in parentheses.
˚
˚
Zr(1)–N(1) 2.1469(18) A, Zr(1)–N(2) 2.1974(17) A, Zr(1)–
˚
˚
(Fig. 4). Selected bond distances and angles are listed in
Table 1.
N(3) 2.2037(17) A and Zr(1)–N(4) 2.1288(16) A. The Zr–
N distances are comparable with other g2-(pyrazol-1-ato)
zirconium analogues [37,40]. The distance between two
consecutive nitrogens of the same pyrazol-1-ato moiety
coordinated to zirconium, of about 1.391(2) A for N(1)–
N(2) and 1.390(3) A for N(3)–N(4), is much longer than
In the molecular structure, the zirconium atom is
bonded to two pyrazol-1-ato and two benzyl ligands in a
distorted tetrahedral geometry, considering that the two
nitrogens of each pyrazol-1-ato moiety and each benzyl
ligand occupy only one coordination position.
The C(11)–C(12) benzyl ligand is coordinated in a termi-
nal g1-mode while the C(21)–C(22) benzyl ligand coordi-
nates in a g2-mode with both C(21) and C(22) bonded to
the Zr atom. These features in the solid state are well
known and well documented elsewhere [48–57]. The dis-
tance between Zr and g1-benzyl [Zr(1)–C(11) and Zr(1)–
˚
˚
that of a simple Nsp2–Nsp3 single bond type of an indepen-
˚
dent preligand 1 whose value is 1.334 A [60].
2.2. Polymerisation studies
The strategy of searching for new olefin polymerisation
catalysts [61] by making new early metal cations and new

5344
M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
generation of ‘‘non-metallocene’’ catalysts for the polymer-
isation of a-olefins has been recently developed based on
group 4 metal complexes containing diamido ligands.
These compounds exhibit a close relationship to the half-
sandwich metal amido ‘‘constrained-geometry’’ catalyst
system and to metallocene derivatives. g2-Pyrazolato
ligands act formally as three-electron donors (covalent cri-
terion) with similar behaviour to amidinato and amido
ligands. In this way, the study of the synthesised pyrazolato
complexes as precatalysts in a-olefin polymerisation seems
to be pertinant [38]. The zirconium complexes 3 and 5 have
been preliminary examined as catalyst precursors for ethyl-
ene and propylene polymerisations upon activation with
methylaluminoxane (MAO). Olefin polymerisations were
investigated in toluene at 25 ꢁC and 50 ꢁC with 1 atm and
4 atm of olefin pressure (Al/Zr ratio ꢀ 1000:1). The results
are summarised in Table 2. No polymerisation of propyl-
ene using either precursor 3 or 5, at whichever operating
temperature or olefin pressure, occurred. Precursor 3
remained inactive in the polymerisation of ethylene what-
ever the polymerisation conditions applied. This lack of
activity is attributed to the non-generation of catalytically
active species in solution, probably resulting from the pre-
mature decomposition of the dimethyl zirconium interme-
diate when the dialkylation of the corresponding dichloro
derivative occurs with MAO before abstraction of the
methyl ligand. This hypothesis is supported by the results
of the dialkylation of 3 with 2 equiv. of LiMe already
described. This is a common problem with precursors that
contain N-based ligands. Polyethylene was exclusively iso-
lated using precursor 5 (Table 2). At 1 atm of monomer
pressure low activity was observed before 30 min, indepen-
dent of temperature. Activity increased with time from
30 min, but was ca. twofold greater at 60 than 30 min,
regardless of temperature (entries 1–4). At 4 atm and
25 ꢁC or 50 ꢁC, the catalytic activity of precursor 5 depends
on the polymerisation time. At 25 ꢁC, the highest activity
of 5 was reached after 15 min (entry 6), which was ca. two-
fold greater than at 5 min. After 15 min, a continuous
activity rate decrease occurred, probably due to the
destruction of active sites. At 50 ꢁC, the highest activity
of 5 occurred up to 5 min (entry 9), followed by a rate
decrease to roughly constant value of 4 kg of polymer/
(mol Zr h atm ethylene) (entries 10–12). This decrease of
activity can be explained by a thermal deactivation or by
a further reduction of the group 4 transition metal by the
MAO co-activator where diffusion control of the propaga-
tion reaction can also be postulated [62]. The GPC data
indicate great differences in the molecular weight of the
resulting polymers with Mw values in the range of
222000–690000 and the polydispersity values larger than
57, indicating the presence of different types of catalytically
active species in the reaction mixture. For 1 atm at 25 ꢁC
the Mw values increased with polymerisation time,
whereas, for 4 atm at 50 ꢁC, the Mw values tend to be con-
stant with polymerisation time. The polymers produced by
this precatalyst exhibit single DSC endotherms, with melt-
ing point Tf ꢁ 133 ꢁC. These results suggest the utility of
these compounds under the used conditions in alkene poly-
merisation is not very promising.
3. Conclusions
In this report, we have provided a contribution to the
synthesis and characterisation of new and somewhat unu-
sual bis(3,5-dimethylpyrazol-1-ato) zirconium complexes
supported by dimethylamido (2), dichloro- (3 and 4) and
dibenzyl (5) ligands. We have demonstrated that 4 pre-
sented a highly fluxional behaviour in CDCl3 solution,
which was quantified by variable-temperature proton
NMR experiments. The new complexes are interesting
from basic coordination chemistry perspectives because
only a few derivatives of this type are known. Initial studies
of their ethylene polymerisation performance under MAO-
activation conditions have been developed. Long apparent
activation times, low activities, and broad molecular weight
distribution are observed.
Table 2
Ethylene polymerisation catalysed with 5/MAO systema
Entry
P
T
t
Activityb Mcw
Mcn Mw/Mn Tdf Tdc
(atm) (ꢁC) (min)
1e
2e
3e
4e
5f
1
1
1
1
4
4
4
4
4
4
4
4
25
25
50
50
25
25
25
25
50
50
50
30
60
30
60
5
15
45
88
5
0.363
0.727
0.363
0.818
4.23
9.51
5.65
1.228
7.91
4.06
405000 2454 165
556000 3706 150
134 115
132 119
132 116
131 120
131 117
134 116
136 116
133 120
132 115
132 117
132 117
132 117
690000 4928 140
222000 3894 57
383000 5039 76
296000 4933 60
302000 2745 110
425000 3863 110
405000 2454 165
556000 3706 150
690000 4928 140
222000 3894 57
4. Experimental
6f
4.1. General considerations
7f
8f
All manipulations and reactions were carried out under
argon (Air Liquide N45, O2: 1 ppm; H2O: 3 ppm) using
Schlenk and high-vacuum line techniques or in a dry argon
atmosphere MBraun glovebox model MB150B-G. The sol-
vents (Baker and SDS) were of reagent grade and were
purified by distillation under argon before use by employ-
ing the appropriate drying agent. Deuterated solvents
(SDS) were firstly degassed by several freeze–thaw cycles
and then stored at room temperature over freshly activated
9f
10f
11f
12f
a
22
50
5.23
3.35
50 105
Conditions: 10 lmol of precatalyst, 50 mL of toluene, Al/Zr
ratio ꢀ 1000:1.
b
Expressed in kg polymer/(mol Zr h atm ethylene).
Determined by GPC.
Melting point (Tf) and crystallisation point (Tc) determined by DSC.
MAO used as a 10% toluenic solution.
c
d
e
f
˚
MAO used as a AlMe3-free solid dissolved in toluene.
4 A molecular sieves (10% w/v). Commercial 3,5-di-

M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
5345
methylpyrazole 1 (Aldrich) was used as received, otherwise
prepared [41] and freshly sublimed. SiClMe3, LiMe (a
1.6 M solution in Et2O) (Aldrich) were used as received.
NEt3 (Aldrich) was treated with KOH pellets and fraction-
ally distilled under argon over CaH2. KH, as a 30 wt% dis-
persion in mineral oil (Aldrich), was washed and filtered
three times with n-hexane, and dried until complete remov-
ing of the volatiles. K(3,5-Me2Pz) [42], [Zr(NMe2)4] [63],
[ZrCl4(THF)2] [64], [Zr(CH2Ph)4] [65] were prepared by a
known procedure. C, H, and N microanalyses were per-
formed on a Perkin–Elmer 240B microanalyser. NMR
spectra were recorded on Varian Mercury VX–300 and
UnityPlus 500 spectrometers at room temperature, other-
wise as indicated. The chemical shifts d and coupling con-
stant J are quoted in ppm and in hertz (Hz), respectively,
and are referenced with respect to residual proton and car-
HN(CH3)3). NMR 13C{1H} (75 MHz, C6D6): d = 145.1
(C-ipso), 110.7 (CH), 46.0 (N-CH3), 38.7 (HN(CH3)3),
13.1 (CH3-pyrazol-1-ato). Anal. Calc. for C18H40N8Zr
(459.79): C, 47.02; H, 8.76; N, 24.37. Found: C, 47.10; H,
8.69; N, 24.44%.
4.3. Synthesis of [Zr(g2-3,5-Me2Pz)2Cl2]n (3)
Compound 1 (1.17 g, 12.2 mmol) in a one portion was
added to a stirred suspension of KH (490 mg, 12.22 mmol)
in THF (55 mL) at room temperature, with instantaneous
gas evolution. The resulting mixture was stirred for a fur-
ther 1 h as soon as gas ceased to evolve. The room-temper-
ature mixture was then slowly transferred by cannula to a
solution of [ZrCl4(THF)2] (2.3 g, 6.1 mmol) in toluene
(50 mL) at À78 ꢁC. The turbid pale yellow solution was
warmed gradually with stirring overnight when volatiles
were completely removed under reduced pressure and the
residue was extracted into toluene (60 mL) for 2 days.
The resulting precipitate was allowed to settle at 0 ꢁC over-
night, and the solution was filtered. The volatiles were com-
pletely removed under reduced pressure, yielding the
desired compound as an analytically pure white solid iden-
tified as 3 (370 mg, 17% yield based on [ZrCl4(THF)2]).
1
bon resonances of the solvent (CDCl3: H: 7.25 ppm, 13C:
1
77.1 ppm; C6D6: H: 7.15 ppm, 13C: 128.0 ppm), which is
also referenced with respect to SiMe4. Variable-tempera-
ture (VT) 1H NMR experiments were recorded on the
Varian UnityPlus 500 spectrometer. Polymerisation grade
ethylene and propylene (Air Liquide N35) were purified
by passage through two columns packed with activated
˚
4 A molecular sieves. Methylaluminoxane (MAO)
1
(10 wt% solution in toluene) was purchased from CROMP-
TON GmbH. Solid AlMe3-free methylaluminoxane was
obtained by drying MAO under reduced pressure at
50 ꢁC to remove the uncoordinated AlMe3 and used after
washing with hexanes and dryness. Polymer melt endo-
therms were determined using a Perkin–Elmer DSC-4 dif-
ferential scanning calorimeter at a heating rate of
10 ꢁC minÀ1. The GPC measurements were performed on
a Polymer Laboratories PL-220 instrument, equipped with
a refractive index detector. The samples were analysed in
trichlorobenzene (TCB) stabilised with 0.0125% BHT on
two columns of PLgelMIXED B (length 600 mm) at
160 ꢁC with a flow rate of 1.0 mL minÀ1. The ESI+-TOF
LC/MS experiment was carried out on an Agilent appara-
tus model 6210 using a mixture of MeOH/water (75/25, v/
v) with an aqueous solution of ammonium formate (5 mM)
as a mobile phase.
NMR H (300 MHz, CDCl3): d = 6.04 (s, 2H, CH), 2.47
(s, 12H, CH3). NMR 13C{1H} (75 MHz, CDCl3):
d = 144.7 (C-ipso), 106.1 (CH), 11.1 (CH3). Anal. Calc.
for C10H14Cl2N4Zr (as mononuclear: 352.37): C, 34.08;
H, 4.00; N, 15.98. Found: C, 33.99; H, 4.15; N, 15.88%.
ESI+-TOF, exact mass m/z: 964.78.
4.4. Synthesis of [Zr(g2-3,5-Me2Pz)2Cl2(g1-3,5-Me2
PzH)2] Æ (3,5-Me2PzH) (4)
A stirred solution of 1 (2.14 g, 22.34 mmol), and NEt3
(1.55 mL, 11.17 mmol) in toluene (45 mL) was rapidly
transferred by cannula to
a
stirred solution of
[ZrCl4(THF)2] (2.01 g, 5.32 mmol) in toluene (50 mL) at
0 ꢁC. The resulting solution was warmed gradually with stir-
ring for 21 h. The stirred mixture was cooled at 0 ꢁC, when
stirring was stopped to allow the precipitates to settle. The
undesired precipitates (1.57 g) were isolated by filtration
and the clean colorless solution was cooled at À40 ꢁC to
crystallise. White crystals of X-ray quality of 4 (1.38 g,
4.2. Synthesis of [Zr(g2-3,5-Me2Pz)2(NMe2)2(NHMe2)2]
(2)
1
46% yield) were carefully isolated by filtration. NMR H
[Zr(NMe2)4] (250 mg, 0.93 mmol) and
1
(180 mg,
(500 MHz, CDCl3, À60 ꢁC): d = 11.26 (s, 2H, NH), 6.02
(s, 2H, CH-coordinated pyrazole), 5.80 (s, 2H, CH-pyrazo-
lato), 2.55 (s, 6H, CH3-coordinated pyrazole), 2.35 (s, 6H,
CH3-coordinated pyrazole), 1.79 (s, 12H, CH3-pyrazol-1-
ato). NMR 13C{1H} (125 MHz, CDCl3, À60 ꢁC):
d = 152.0 (C-ipso-coordinated pyrazole), 145.6 (C-ipso-pyr-
azol-1-ato), 139.1 (C-ipso-coordinated pyrazole), 113.3
(CH-pyrazol-1-ato) 106.0 (CH-coordinated pyrazole), 13.8
(CH3-coordinated pyrazole), 11.2 (CH3-pyrazol-1-ato),
10.3 (CH3-coordinated pyrazole). Anal. Calc. for
C20H30Cl2N8Zr Æ 1/4C5H8N2 (544.64 + 24.03): C, 44.88;
H, 5.67; N, 20.93. Found: C, 44.68; H, 5.73; N, 20.34%.
1.87 mmol) were rapidly placed into a Teflon-valved
ampoule under dry argon and toluene (5 mL) was immedi-
ately introduced. The closed ampoule was coupled with a
mechanical stirrer using rubber and T-glass tubes. The
ampoule was then stirred slowly at room temperature for
18 h. The solution was filtered and the volatiles were
removed under reduced pressure affording 410 mg of an
analytically pure white solid identified as 2 (95% yield).
1
NMR H (300 MHz, C6D6): d = 6.08 (s, 2H, CH), 3.37
(s, 12H, N–CH3), 2.35 (s, 12H, CH3-pyrazol-1-ato), 1.78
3
(d, JHH = 6.3 Hz, 6H, HN(CH3)3), 0.31 (m, 1H,

5346
M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
4.5. Synthesis of [Zr(g2-3,5-Me2Pz)2(CH2Ph)2] (5)
was terminated by methanol injection. The polymer was
precipitated with 100 mL of a 5% solution of HCl in
MeOH, stirred, filtrated and washed successively with
50 mL of a 5% solution of HCl in MeOH, 100 mL of water,
and 100 mL of MeOH. The polymer was finally dried
under vacuum at 50 ꢁC for 24 h to constant weight.
A stirred solution of 1 (858 mg, 8.92 mmol) in toluene
(60 mL) was added by cannula to a stirred solution of
[Zr(CH2Ph)4] (2.03 g, 4.46 mmol) in toluene (60 mL) at
0 ꢁC. The mixture was slowly warmed to room temperature
with stirring and then further stirred for 19 h. The solution
was filtered through a short pad of celite and the volatiles
were removed under reduced pressure affording 2.03 g of
an analytically pure white solid (98% yield). Suitable single
crystals of 5 for X-ray diffraction analysis were collected by
filtration from a toluene–pentane solution at À40 ꢁC.
4.8. X-ray crystallographic study of [Zr(g2-3,5-
Me2Pz)2Cl2(g1-3,5-Me2PzH)2] Æ (3,5-Me2PzH) (4) and
[Zr(g2-3,5-Me2Pz)2(g2-CH2Ph)2] (5)
Suitable crystals of 4 and 5 were selected, manipulated
under perfluoropolyether, mounted on a glass fibre and
the data collected on a Nonius KappaCCD diffractometer
(4) at 200 K and a Rigaku R-Axis IIc image plate diffrac-
tometer (5) at 150 K. Data were processed using the
DENZO/SCALEPACK programs [66]. The structure was deter-
mined by direct method routines and refined by full-matrix
1
NMR H (500 MHz, C6D6): d = 7.06 (t, J = 7.6 Hz, 4H,
meta-CH of phenyl ring), 6.88 (t, J = 7.4 Hz, 2H, para-
CH of phenyl ring), 6.65 (d, J = 7.4 Hz, 4H, ortho-CH of
phenyl ring), 6.20 (s, 2H, CH-pyrazol-1-ato), 2.14 (s,
12H, CH3-pyrazol-1-ato), 2.01 (s, 4H, CH2-benzyl).
NMR 13C{1H} (125 MHz, C6D6): d = 147.1 (ipso-C-pyra-
zol-1-ato), 140.0 (ipso-C of phenyl ring), 129.3 (ortho-CH
of phenyl ring), 128.5 (meta-CH of phenyl ring), 122.9
(para-CH of phenyl ring), 116.1 (CH-pyrazol-1-ato), 58.7
(CH2-benzyl), 12.6 (CH3-pyrazol-1-ato). Anal. Calc. for
C24H28N4Zr (463.74): C, 62.16; H, 6.09; N, 12.08. Found:
C, 61.89; H, 6.11; N, 12.25%.
Table 3
Crystal data and structure refinement details for 4 and 5
Compound
4
5
Molecular formula
Formula weight
Temperature (K)
C
640.77
200(2)
Mo Ka
0.71073
monoclinic
C2/c
25H38Cl2N10Zr
C24H28N4Zr
463.72
150(2)
Mo Ka
0.71073
monoclinic
P21/n
4.6. Polymerisation procedure at 1 atm
˚
Radiation k (A)
˚
k(Mo Ka) (A)
Toluene (50 mL) was introduced under argon into the
Schlenk reactor equipped with a magnetic stirrer and main-
tained at the desired temperature using external thermal
control with vigorous stirring for 30 min. MAO (8 mL,
12.19 mmol) was then injected and the mixture stirred for
15 min. The argon was replaced by the olefin by degassing
the solution under vacuum and refilling with the olefin.
This procedure was repeated and the solution was finally
saturated with the olefin for 15 min. As soon as the zirco-
nium complex was injected to the mixture, polymerisation
time was counted. The polymerisation was terminated by
methanol injection. The polymer was precipitated with
100 mL of a 5% solution of HCl in MeOH, stirred, filtrated
and washed successively with 50 mL of a 5% solution of
HCl in MeOH, 100 mL of water, and 100 mL of MeOH.
The polymer was finally dried under vacuum at 50 ꢁC for
24 h to constant weight.
Crystal system
Space group
Unit cell dimensions
˚
a (A)
14.983(2)
15.631(2)
15.5485(11)
116.284(12)
3264.9(7)
4
10.7839(2)
13.0955(2)
16.0136(2)
92.568(5)
2259.18(6)
4
˚
b (A)
˚
c (A)
b (ꢁ)
Volume (A )
3
˚
Z
Dcalc (Mg mÀ3
)
1.302
1.363
Absorption coefficient 0.531
(mmÀ1
F(000)
Color
0.503
)
1324
white
960
pale yellow
0.26 · 0.26 · 0.20
3.83–27.48
Crystal size (mm)
h Range for data
collection (ꢁ)
0.55 · 0.33 · 0.33
3.03–27.56
Index ranges
À19 6 h 6 19,
À20 6 k 6 20,
À19 6 l 6 20
13685
À13 6 h 6 14,
À17 6 k 6 17,
À17 6 l 6 20
17950
Reflections collected
Independent reflections 3746
5148
0.0417
full-matrix least-
squares on F2
3959/0/266
4.7. Polymerisation procedure at 4 atm
Rint
Refinement method
0.0409
full-matrix least-
squares on F2
3746/0/188
The sealed ampoule containing precursor 5 at the
desired amount was placed into the Buchi reactor. The sys-
¨
Data/restraints/
parameters
Goodness-of-fit on F2 1.044
tem, at the desired temperature, was evacuated under vac-
uum for 1 h. Toluene (50 mL) was introduced under argon
into the reactor and MAO (8 mL, 12.19 mmol) was then
injected. The mixture was stirred for 15 min. The argon
was replaced by the olefin by degassing the solution under
vacuum and refilling with the olefin. As soon as precursor 5
was liberated into the solution by breaking the ampoule
polymerisation time was counted. The polymerisation
1.043
R1 = 0.0318
R1 [I > 2r(I)]
R1 = 0.0374,
wR2 = 0.0947
R1 = 0.0522,
wR2 (all data)
wR2 = 0.0710
wR2 = 0.1021
0.687 and À 0.653
Largest difference in
peak and hole
0.377 and À0.366
(e AÀ3
)

M. Sanz et al. / Polyhedron 26 (2007) 5339–5348
5347
least-squares methods on F2 (SHELXS and SHELXL programs)
[67]. All non-hydrogen atoms were anisotropically refined.
Compound 4: hydrogen atoms were geometrically placed
and left riding on their parent atoms except for H1, H2,
H5, and H7 which were found in the difference map and
refined isotropically. Half of a disordered molecule of free
ligand appeared in the asymmetric unit. Compound 5:
methyl hydrogen atoms were refined as rigid, others riding.
Relevant crystallographic data and details of the refine-
ments for the two structures are given in Table 3.
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Acknowledgements
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Financial support for this research by DGICYT (Project
MAT2004-02614), CAM: (Project S-0505-PPQ/0328-02)
and by European Commission (Contract No. HPRN–
CT2000-00004) is gratefully acknowledged. The authors
would like to express the thanks to Prof. Dr. Mikhail V.
Galakhov for his helpful assistance for the NMR studies
and Dr. Yann Sarazin, from the Department of Prof. Dr.
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Appendix A. Supplementary material
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[34] C. Yelamos, M.J. Heeg, C.H. Winter, Organometallics 18 (1999) 1168.
CCDC 635011 and 635579 contain the supplementary
crystallographic data for 4 and 5. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.poly.2007.08.001.
´
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