C1-symmetric pentacoordinate anilidopyridylpyrrolide zirconium(IV) complexes as highly isospecific olefin polymerization catalysts

Article abstract of DOI:10.1021/ma101789w

Two new anilinepyridinepyrrole ligand precursors bearing bulky substituents on the carbon bridging the pyridine and the aniline moieties were synthesized and used to prepare the corresponding zirconium complexes with general formula [^-NNN^-

Full text of DOI:10.1021/ma101789w

Macromolecules 2010, 43, 8887–8891 8887
DOI: 10.1021/ma101789w
C1-Symmetric Pentacoordinate Anilidopyridylpyrrolide Zirconium(IV)
Complexes as Highly Isospecific Olefin Polymerization Catalysts
Gang Li, Marina Lamberti, Sebastiano D’Amora, and Claudio Pellecchia*
ꢀ
Dipartimento di Chimica, Universita di Salerno, Via Ponte don Melillo, I-84084 Fisciano (SA), Italy
Received August 5, 2010; Revised Manuscript Received September 14, 2010
ABSTRACT: Two new anilinepyridinepyrrole ligand precursors bearing bulky substituents on the carbon
bridging the pyridine and the aniline moieties were synthesized and used to prepare the corresponding
zirconium complexes with general formula [-NNN-]Zr(NMe2)2. NMR spectra analysis of the obtained
complexes indicated a C1-symmetry in solution. Both complexes were tested as precatalysts for ethylene and
R-olefins polymerization upon activation with AliBu2H as alkylating agent and MAO as ionizing activator.
Linear polyethylene and highly isotactic polypropylene and poly(1-hexene) were obtained with good
productivities. In particular, the features of the obtained polypropylene samples, in terms of isotacticity
([mmmm] up to 95%), molecular weight (Mw up to 950 kg/mol) and melting point (Tm up to 150 °C), were
remarkable. The activity and the isospecificity of this class of catalysts were found to depend strongly on the
steric bulk of the substituents on the carbon bridging the pyridine and aniline moieties.
Scheme 1
Introduction
The design of nonmetallocene catalysts for olefin polymerization
with high activities and stereoselectivities remains a topic of wide
interest in both academic and industrial research.1,2 In particular, a
large variety of ligands with nitrogen and/or oxygen donors has
been explored, leading to several highly isospecific catalysts, e.g.,
diaminebis(phenolate) group 4 metal3 and bis(phenolate)diether
Zr or Hf catalysts,4 although in only a few cases their performance
is competitive with the metallocene systems.5
steric control were produced. A similar finding had been previously
reported by Coates et al.10 for a Cs-symmetric pyridylamido
[-NNC-] Hf(IV) complex, and in that case in situ ligand modifica-
tion due to insertion of one propene molecule into the Hf-aryl bond
was suggested to justify the unexpected isoselectivity. Since in the
case of complex 1 insertion of one monomer unit into a Zr-pyrrolyl
bond is unlikely, the origin of its isospecificity remains elusive, being
attributable, e.g., to other ligand modifications or to a change of
hapticity in the pyrrole moiety or even to a preferred square
pyramidal geometry of the cationic active species resulting in two
inequivalent coordination sites for the olefin and the growing chain.
Seeking to expand the scope of this class of ligands for the
design of stereospecific catalysts and to achieve some insight in
the factors affecting their performance, we have now synthesized
two new anilinepyridinepyrrole ligands bearing bulky substitu-
ents on the carbon bridging the pyridine and the aniline moieties,
and two C1-symmetric Zr(IV) complexes derived thereof, and
tested them as olefin polymerization catalysts.
A promising class of catalysts based on C1-symmetric pyridy-
lamido Hf(IV) complexes (Scheme 1) was recently developed using
high throughput screening technologies.6 These catalysts are able
to produce high molecular weight, highly isotactic propylene
homo- and copolymers at high temperatures, as well as olefin
block copolymers with good elastomeric properties.7 A funda-
mental aspect for the achievement of these performance was the
serendipitous modification of the ligand structure via metalation
of an aromatic substituent in the pyridine ortho position, changing
a [NN-] monoanionic bidentate ligand in a [-NNC-] dianionic
tridentate one (Scheme 1). Moreover, an increasing amount of
experimental and theoretical evidence suggested that further in situ
modification of the precatalyst via a first monomer 1,2-insertion
into Hf-Caryl bond is involved in the generation of highly active
and stereospecific catalytic species.8 It was also mentioned that
bulkier substituents on the carbon bridging the amide and the
pyridine fragment gave catalysts with better performance.6i
Recently, we reported the synthesis of Zr(IV) complex 1
(Scheme 1), bearing an anilidomethylpyridylpyrrolide [-NNN-]
tridentate ligand, which, after activation with AliBu2H/MAO,
produced isotactic polypropylene ([mmmm] = 73%) as well as
isotactic poly(1-hexene) with good activities.9 Complex 1 showed
a slightly distorted square-pyramidal geometry in the solid state
and “time averaged” Cs-symmetric structure in solution: however,
despite the precatalyst structure, isotactic polyolefins with a micro-
structure consistent with an “enantiomorphic sites” mechanism of
Results and Discussion
The anilinepyridinepyrrole ligands (H2L1,H2L2) were synthesized
by alkylation of anilinemethylenepyridinepyrrole A9 (Scheme 2)
with an excess of alkylating agents (PhLi or 2-iPrC6H4Li) in good
yields, and fully characterized by NMR spectroscopy. Complexes
2 and 3 were prepared in benzene by reaction of the correspond-
ing ligand with equimolar amount of tetrakis(dimethylamido)-
zirconium(IV) and isolated as light-yellow solids (yields: 2: 93%;
3: 76%). (Scheme 2) The complexes were also fully characterized
by NMR spectroscopy. In the 1H NMR spectrum of each
*Corresponding author. Telephone: þ39 089 969576. Fax: þ39 089
969603. E-mail: cpellecchia@unisa.it.
r 2010 American Chemical Society
Published on Web 10/05/2010
pubs.acs.org/Macromolecules

8888 Macromolecules, Vol. 43, No. 21, 2010
Li et al.
Scheme 2. Synthesis of the Zr Complexes
Table 1. Ethylene Polymerization Resultsa
Table 2. Propylene Polymerization Resultsa
run
precat.
activityb
Tm (°C)
Mw (kg/mol)
PDI
[mmmm]
(%)
regioinverted Tm
units
Mw
(°C) (kg/mol) PDI
run precat activityb
19
2
1
2
3
1841
1035
905
136.5
135.1
136.0
185
49
2.1
3.8
19
2
1
2
3
3
3
3
3
4
39
98
14
27
49
99
73
3.0
2.1
1.4
2.4
1.9
1.6
1.5
39
166
950
16
1.4
5.6
3.5
2.2
3
n.d.c
n.d.c
87.2
94.6
93.1
94.1
95.0
95.3
131
150
140
150
151
151
a General conditions: precatalyst, 2.5 μmol; toluene, 100 mL; cocatalyst,
AliBu2H/Zr = 30, Al(MAO)/Zr = 1000; aging time, 10 min; ethylene pres-
sure, 1 atm; polymerization time, 7 min; polymerization temperature, 25 °C;
dried MAO obtained by distilling off the solvent from the commercial
solution. b Activity: kgPE/mol Zr h atm. c n.d. = not determined.12
3
4c
5d
6e
7f
404 12.4
1012
195
1.9
4.6
a General condition: precatalyst, 10 μmol; toluene, 100 mL; cocata-
lyst, AliBu2H/Zr = 30, Al(MAO)/Zr = 1000; dried MAO obtained by dis-
tilling off the solvent from the commercial solution; aging time, 10 min;
polymerization temperature, 25 °C; polymerization time, 60 min; pro-
pylene pressure, 6 atm. b Activity: kgPP/mol Zr h atm. c Polymerization
temperature: 75 °C. d Propylene pressure: 2 atm. e AliBu2H/Zr = 10.
f Polymerization time: 10 min.
complex (Figure S5 and S7 in the Supporting Information),
different signals were present for each proton, indicating a
C1-symmetry in solution. In particular, two singlets for the
Zr-NMe2, and four doublets and two septets for the isopropyl
groups of the aniline moiety were detected. 13C NMR spectra
analysis led us to the same conclusion. (Figure S6 and S8 in the
Supporting Information).
Ethylene and r-Olefin Polymerization. All complexes were
used as precatalysts in combination with AliBu2H as alkylating
agent (in view of the well-known difficult alkylation of dimethyl-
amido group 4 complexes by MAO alone)11 and MAO as
ionizing activator for ethylene and R-olefins polymerization.
Ethylene polymerization data are listed in Table 1. After acti-
vation with AliBu2H/MAO, 2 and 3 promote polymerization
of ethylene to highly linear polyethylene with good productiv-
ities. In comparison with the unsubstituted complex 1, intro-
duction of bulky substituents on the bridging methylene atom
resulted in slight decreases of productivities and polymer
melting points (Tm), and in a significant decrease of molecular
weights (Mw =49 kg/mol for 2). A rather broad molecular
weight distribution (PDI: 3.8 for 2) (Table 1, run 2) was also
observed.12 Broad molecular weight distributions were also
reported for ethylene polymerization by pyridylamido Hf
catalysts.8a,13
Figure 1. 13C NMR spectrum (1,1,2,2-tetrachloroethane-d2,100 °C) of
i-PP produced in run 4 in Table 2. δ in parts per million from hexa-
methyldisiloxane.
Polymerization of propene was also investigated: the main
polymerization data and results are listed in Table 2. After
activation with AliBu2H/MAO under 6 atm monomer pres-
sure at 25 °C, the precatalyst 2 yielded highly isotactic poly-
propylene ([mmmm]=87.2%) having a melting point Tm=
131 °C with good activity (activity: 38.8 kgPP/molZr h atm)
(run 2, Table 2). GPC analysis of the obtained polypropylene
sample exhibited a broad molecular weight distribution
(PDI=5.6). Compared with precatalyst 1 under the same con-
ditions, precatalyst 2, bearing a phenyl substituent on the
bridging methylene, displayed a 10-fold increase of produc-
tivity, a 4-fold increase of molecular weight, and higher
stereoselectivity ([mmmm] = 87.2 vs 73%). A further increase
of the steric bulk of the substituent of the bridging methylene
led to a better performing catalyst: under the same conditions,
precatalyst 3 exhibited higher productivity (activity: 97.6
kgPP/molZr h atm) (run 3, Table 2), and higher stereoselectivity
([mmmm] = 94.5%), affording a polypropylene with a melting
point Tm = 150 °C. GPC analysis of the obtained polypropyl-
ene sample displayed ultrahigh molecular weight (950 kg/
mol) with a rather broad molecular weight distribution
(PDI = 3.5). Thus, the performance of 3/AliBu2H/MAO
catalyst for propene polymerization, in terms of isotacticity
and Tm, competes with that of the best nonmetallocene
catalysts reported in the literature, although the hafnium
pyridyl-amido-based catalysts are more active and afford
higher MW’s at high temperature.14
13C NMR analysis of the stereosequence distribution of
the obtained polypropylene samples produced by both 2 and
3 showed a 2:2:1 ratio of the [mmmr]/[mmrr]/[mrrm] pentads
in the methyl region, in agreement with an “enantiomorphic
sites” mechanism of the stereospecific propagation.2,5,15
Minor resonances (12.4, 13.5, 28.8, 30.4, 32.3, 33.2, 34.6,
and 41.2 ppm) (Figure 1) are attributed to isolated regiode-
fects, deriving from head-to-head or tail-to-tail misinser-
tions.6i,16 The exclusive presence of regioinverted units with
vicinal methyls in threo configuration in the Fischer projec-
tion17 indicates that primary (1,2) and secondary (2,1) monomer
insertions occur with the same enantioface selectivity, as pre-
viously observed for 1 and other nonmetallocene catalysts,6i,16b

Article
Macromolecules, Vol. 43, No. 21, 2010 8889
Table 3. 1-Hexene Polymerization Resultsa
run precat T (°C) yield (mg) [mmmm] (%) Mw (kg/mol) PDI
1
2
3
2
2
3
25
50
25
230
138
457
99
93
>99
13
5
37
2.1
2.1
2.0
a General conditions: precatalyst = 5 μmol; toluene, 5 mL, 1-hexene,
5 mL; cocatalyst, AliBu2H/Zr= 30, MAO/Zr = 1000;agingtime, 10 min;
polymerization time, 60 min.
while the opposite enantioface selectivity occurs for primary and
secondary insertions in C2-symmetric metallocene catalysts.2,5
Polymerization at higher temperature (75 °C) results in the
production of a polypropylene sample having a significantly
lower molecular weight (16 kg/mol) and a narrower molecular
weight distribution (PDI = 2.2), while the stereoregularity
is only slightly affected, ([mmmm]=93.1%, Tm=140 °C, see
Table 2, run 4). An increase of regioinversions is also observed
(from 1.4 to 2.4%, Table 2, cf runs 3 and 4). In this low Mw
sample, additional low intensity resonances are detected at
45.4, 23.7, 21.8, 20.5 ppm: they are attributable, according to
the literature,18 to isobutyl end groups, reasonably deriving
from primary (1,2) propene insertion into Zr-Me or Zr-iBu
bonds in the initiation step or from hydrolysis of Zr- and/or
Al-bound primary growing chains in the termination step.
We also investigated the influence of other polymerization
conditions, i.e., monomer pressure, amount of AliBu2H, and
polymerization time, on the performance of 3 (Table 2, run 5, 6,
and 7, respectively). None of these parameters affects signifi-
cantly the polymer microstructure,19 while a strong influence
on the polymer Mw’s is observed. In fact, lowering the amount
of AliBu2H from 30 to 10 equiv resulted in a narrower molec-
ular weight distribution (PDI = 1.9) and similar isotacticity
(mmmm = 95.0%, Tm=151 °C), suggesting that broad MWD’s
could be due to chain transfer to aluminum having different
rates during the polymerization.20 In agreement with this
hypothesis, a shorter polymerization time (10 vs 60 min)
resulted in the production of a polymer sample exhibiting a
relatively broader molecularweight distribution (PDI = 4.6).
Finally, reducing the monomer pressure from 6 to 2 atm
resulted in the production of a polypropylene sample having
a very broad molecular weight distribution (PDI = 12.4).
In order to further investigate the origin of the broadening
of MWD’s, a polypropylene sample (run 3, Table 2) was
fractionated by sequential exhaustive Kumagawa extraction
with boiling n-hexane and n-heptane. Analysis of the differ-
ent fractions by GPC, NMR and DSC (see Supporting
Information) showed that, although fractions with different
molecular weights were recovered, the isotacticity was very
high and very similar in all cases, excepting for a small frac-
tion (<9%) soluble in n-hexane, having low isotacticity and
low molecular weight. In conclusion, while the hypothesis
that broad MWD’s are mainly due to chain transfer to Al
seems confirmed, these data also suggest the possible forma-
tion of some minor active species having different polymer-
ization performance.
Figure 2. 13C NMR spectrum (1,1,2,2-tetrachloroethane-d2,100 °C) of
Poly(1-hexene) produced in run 3 in Table 3; δ in parts per million from
hexamethyldisiloxane.
perfect isotacticity ([mmmm] > 99%): resonances attributable
to stereodefects and to end groups were not detected (Figure 2).
Conclusions
Two new tridentate anilinepyridinepyrrole ligands H2L, bear-
ing bulky substituents on the carbon bridging the pyridine and the
aniline moieties, and their C1-symmetric LZr(IV) bis(dimethyl-
amido) complexes have been synthesized and tested as precata-
lysts for olefin polymerization, after activation with AliBu2H/
MAO. Linear polyethylene and highly isotactic polypropylene
and poly(1-hexene) were obtained with good productivities. Inter-
estingly, in comparison with the previously reported unsubsti-
tuted anilidomethylpyridinepyrrolide Zr(IV) complex,9 intro-
duction of bulky substituents on the bridging methylene in the
ligand framework lead to propylene polymerization catalysts
performing much better in terms of activity, polymer isotacticity
and molecular weight. E.g., the complex bearing a 2-isopropyl-
phenyl substituent afforded a polymer having Mw close to
1 million Da, [mmmm] > 95% and melting temperature as high
as 151 °C, which are remarkable values for polypropylenes
produced by homogeneous catalysts.
13C NMR analysis of the obtained polypropylenes revealed a
microstructure in agreement with the “enantiomorphic sites”
mechanism of the stereospecific propagation, as well as the
occurrence of a few regioinverted units having vicinal methyls in
threo configuration,17 thus indicating that primary and secondary
monomer insertions occur with the same enantioface selectivity,
as previously observed for other nonmetallocene catalysts.6i
Finally, the detection of isobutyls as the only end groups in low
MW samples suggested that 1,2 insertion is the main regiochem-
istry of propagation.
The MWD’s of the polypropylene samples range between that
expected for a single site catalyst and broader ones, depending on
the polymerization conditions and, in particular, on the amount
of AliBu2H. The latter and other lines of evidence suggest that
broadening of MWD’s could be mainly due to chain transfer to
aluminum having different rates during the polymerization.
Work is in progress to synthesize complexes of this class bearing
mobile ligands different from NMe2, amenable to be activated
without using aluminum alkyls, in order to reduce chain transfer
and possibly achieve living polymerization.
We also studied the behavior of precatalysts 2 and 3 in
1-hexene polymerization. After activation with AliBu2H/MAO,
the precatalysts 2 - 3 yielded moderate activities and poly-
merized 1-hexene to regioregular and isotactic poly(1-hexene)
with narrow molecular weight distribution (PDI: 2.1 for 2; 2.0
for 3, respectively). The poly(1-hexene) sample produced by
2/AliBu2H/MAO at 25 °C polymerization temperature exhib-
ited a good isotacticity ([mmmm] = 99%) and a rather low
molecular weight (13 kg/mol) (Table 3, run 1). Increasing the
polymerization temperature to 50 °C resulted in decrease of
both isotacticity and molecular weight. However, the poly-
(1-hexene) sample produced by 3/AliBu2H/MAO showed almost
Experimental Section
General Procedures. All manipulations of air- and or water-
sensitive compounds were carried out under a nitrogen atmo-
sphere using standard Schlenk or glovebox techniques. All sol-
vents, purchased from Carlo Erba, were refluxed over sodium/
benzophenone or calcium hydride (CaH2) and then distilled
under nitrogen before use. 1-Bromo-2-isopropylbenzene was
purchased from Alfa Aesar without purification before use. All
other chemicals were purchased from Sigma-Aldrich and used

8890 Macromolecules, Vol. 43, No. 21, 2010
Li et al.
as received. MAO (10 wt % solution in toluene) was dried by
distilling off the volatile materials under reduced pressure and
excess of trimethylaluminium (AlMe3) was removed by washing
the resulting solid with dry hexane. The volatiles were removed
under reduced pressure to obtain a white powder. Ethylene and
propene were purchased from SON and used without further
purification. 1-Hexene was distilled over CaH2 prior to use.
using hexane/diethyl ether (20/1) as eluent. The colorless oil was
concentrated under vacuum (120 mg, yield: 88%). 1H NMR
(CD2Cl2): δ 0.95-0.98 (12H, m, CH(CH3)2), 1.01 (6H, d, J =
9.14 Hz, CH(CH3)2), 2.89 (2H, sept, CH(CH3)2), 3.04 (1H, sept,
CH(CH3)2), 4.24 (1H, br, s, NHCHPh), 5.42 (1H, s, NCHPh), 6.23
(1H, m, NC4H3), 6.67 (1H, m, NC4H3), 6.84 (1H, m, NC4H3), 6.94
(1H, m, H-Py), 7.00-7.03 (3H, m, H-Ar), 7.24 (3H, m, H-Ar),
7.37 (1H, m, H-Py), 7.54 (1H, t, H-Py), 7.66(1H, m, H-Ar), 9.26
(1H, br, s, HNC4H3). 13C NMR (CD2Cl2): δ 23.96 (CH(CH3)2),
24.23 (CH(CH3)2), 24.37 (CH(CH3)2), 28.27 (CH(CH3)2), 29.09
(CH(CH3)2), 66.53 (NHCHPh), 107.58, 110.70, 116.54, 118.88,
120.16, 123.94, 124.03, 126.00, 126.40, 127.83, 127.89, 132.02,
137.62, 140.45, 142.98, 143.36, 146.84, 150.36, 162.57.
Synthesis of Complexes. Zr Complex (2). A solution of
Zr(NMe2)4 (103 mg, 0.38 mmol) in benzene (5 mL) was added
dropwise into a stirred solution of H2L1 (158 mg, 0.38 mmol)
in benzene (5 mL). The solution was stirred for 30 min at room
temperature. All volatiles were removed under vacuum. The pro-
duct was crystallized from hexane (1 mL) at -20 °C, and washed
with hexane, obtaining a light yellow solid (208 mg, yield: 93%).
1H NMR (400 MHz; CDCl3): δ 0.15 (3H, d, J = 6.84 Hz,
CH(CH3)2), 1.04 (3H, d, J = 6.84 Hz, CH(CH3)2), 1.07 (3H, d,
J = 6.84 Hz, CH(CH3)2), 1.33 (3H, d, J = 6.84 Hz, CH(CH3)2),
2.60 (6H, s, ZrN(CH3)2), 2.84 (1H, sept, CH(CH3)2), 2.95 (6H, s,
ZrN(CH3)2), 3.24 (1H, sept, CH(CH3)2), 5.58 (1H, s, NCHPh),
6.32 (1H, m, NC4H3), 6.58 (1H, d, J = 7.6 Hz, H-Py), 6.80 (1H,
m, NC4H3), 6.92-6.94 (3H, m, Ar-H), 7.05 (1H, t, Ar-H), 7.11
(1H, m, Ar-H), 7.16 (1H, m, NC4H3), 7.18-7.21(3H, m, Ar-H),
7.37 (1H, d, J = 7.92 Hz, H-Py), 7.63 (1H, t, H-Py). 13C NMR
(300 MHz; CDCl3): δ 24.15 (CH(CH3)2), 24.64 (CH(CH3)2),
25.03 (CH(CH3)2), 26.91 (CH(CH3)2), 27.64 (CH(CH3)2),
28.47 (CH(CH3)2), 40.96 (N(CH3)2), 42.42 (N(CH3)2), 80.81
(NCHPh), 109.18 (NC4H3), 111.73 (NC4H3), 114.46 (C-Py),
116.37 (C-Py), 123.61, 124.12, 124.28, 127.54, 128.64, 129.07,
133.15, 140.30, 140.40, 143.97, 145.96, 146.57, 146.98, 154.87,
167.27.
Zr Complex (3). A solution of Zr(NMe2)4 (42 mg, 0.157
mmol) in benzene (3 mL) was added dropwise into a stirred
solution of H2L2 (71 mg, 0.157 mmol) in benzene (5 mL). The
solution was stirred for 30 min at ambient temperature. All
volatiles were removed under vacuum to yield a yellow solid.
The product was crystallized from hexane (1 mL) at -20 °C and
then washed with hexane. The light yellow solid was obtained in
76% yield (75 mg, 0.119 mmol). 1H NMR (400 MHz; CDCl3):
δ 0.13 (3H, d, J = 6.84 Hz, CH(CH3)2), 0.58 (3H, d, J = 6.84 Hz
CH(CH3)2), 1.02-1.07 (9H, m, CH(CH3)2), 1.29 (3H, J =
6.72 Hz, CH(CH3)2), 2.50 ((1H, m, CH(CH3)2), 2.62 (6H, s,
N(CH3)2), 2.88 (1H, m, CH(CH3)2), 3.00 (6H, s, N(CH3)2), 3.30
(1H, m, CH(CH3)2), 5.96 (1H, s, NCHPh), 6.32 (1H, m, NC4H3),
6.46 (1H, d, J=7.64 Hz, H-Py), 6.79 (1H, m, NC4H3), 6.94 (1H,
m, Ar-H), 7.01 (1H, t, Ar-H), 7.07-7.19 (6H, m, Ar-H), 7.33
(1H, d, J = 7.92 Hz, H-Py), 7.56 (1H, t, H-Py). 13C NMR (400
MHz; CDCl3): δ 22.08 (CH(CH3)2), 23.75 (CH(CH3)2), 24.98
(CH(CH3)2), 25.55 (CH(CH3)2), 25.77 (CH(CH3)2), 26.04
(CH(CH3)2), 27.75 (CH(CH3)2), 28.32 (CH(CH3)2), 28.60
(CH(CH3)2), 41.16 (ZrN(CH3)2), 42.77 (ZrN(CH3)2), 74.95
(NCHPh), 109.11 (NC4H3), 111.75 (NC4H3), 114.15 (C-Py),
116.09 (C-Py), 123.75, 124.28, 124.51, 125.25, 126.25, 127.44,
130.17, 133.13, 140.43, 141.43, 145.80, 146.65, 147.11, 147.26,
154.81, 168.69.
1
The H and 13C NMR spectra were recorded on a Bruker
Avance spectrometer at 400 and 100.6 MHz. 13C NMR spectra
of polymers were recorded on a Bruker AM-250 spectrometer at
62.5 MHz in 1,1,2,2-tetrachloroethane-d2 (C2D2Cl4) at 100 °C
and referenced vs hexamethyldisiloxane (HMDS).
Molecular weights (Mn and Mw) and polydispersities (PDI) of
the polymers were determined by high-temperature GPC using a
Waters GPCV 2000 equipped with refractive index and vis-
cometer detectors. The measurements were recorded at 135 °C
using 1,2-dichlorobenzene as a solvent and Styragel columns
(range 107 to 103). Every value was the average of two indepen-
dent measurements.
Polymers melting points (Tm) were measured by differential
scanning calorimetry using a TA Instruments DSC 2920 in nitro-
gen flow with a heating and cooling rate of 10 °C/min. Melting
temperatures were reported for the second heating cycle.
Synthesis of Ligands. (E)-N-(6-(1H-Pyrrol-2-yl)pyridin-2-yl)-
methylene)-2,6-diisopropylbenzenamine was synthesized acc-
ording to the literature.9
N-((6-(1H-Pyrrol-2-yl)pyridine-2-yl)(phenyl)methyl)-2,6-diiso-
propylbenzenamine (H2L1). A solution of PhLi (0.58 mL, 1.08
mmol, 1.9 M in nBu2O) was added dropwise into a solution of
(E)-N-(6-(1H-pyrrol-2-yl)pyridin-2-yl)methylene)-2,6-diisopro-
pylbenzenamine (180 mg, 0.54 mmol) in diethyl ether (2 mL)
cooled to -78 °C. Then, the solution was allowed to warm to
room temperature and stirred for 20 h. The reaction was followed
byTLC and then quenched bythe addition of NH4Cl(aq) at0 °C.
The organic phase was separated and reserved. The aqueous
phase was washed by diethyl ether (3 ꢀ 30 mL). The combined
organic phases were washed using water (2 ꢀ 50 mL), and brine
(1 ꢀ 50 mL), and then dried over Na2SO4. The solvent was
distilled off by rotary evaporation. The crude product was puri-
fied by flash column chromatography on silica gel using hexane/
diethyl ether (20/1, 9/1) as eluent. The colorless oil was concen-
trated in vacuum, obtaining a white powder (158 mg, yield: 73%).
1H NMR (CD2Cl2): δ 0.97 (6H, d, J = 6.8 Hz, CH(CH3)2), 1.07
(6H, d, J = 6.8 Hz, CH(CH3)2), 3.12 (2H, sept, CH(CH3)2), 4.78
(1H, br, s, NHCHPh), 5.11 (1H, s, NCHPh), 6.28 (1H, m,
NC4H3), 6.72 (1H, m, NC4H3), 6.90-6.92 (1H, m, NC4H3),
6.94-6.99 (3H, m, H-Ar), 7.01 (1H, d, J = 3.6 Hz, H-Py),
7.19-7.31(3H, m, H-Ar), 7.39-7.42 (2H, m, H-Ar), 7.43 (1H,
d, J = 0.96 Hz, H-Py), 7.55 (1H, t, H-Py), 9.50 (1H, br, s,
HNC4H3). 13C NMR (CD2Cl2): δ 24.28 (d, J = 20.22 Hz,
CH(CH3)2), 28.18 (CH(CH3)2), 69.76 (NHCHPh), 107.85, 110.75,
116.93, 119.72, 120.29, 123.66, 123.99, 127.45, 127.82, 128.69, 131.88,
137.55, 142.60, 142.95, 143.67, 148.51, 150.66, 161.59.
N-((6-(1H-Pyrrol-2-yl)pyridine-2-yl)(2-isopropylphenyl)methyl)-
2,6-diisopropylbenzenamine (H2L2). n-Butyl lithium (0.35 mL, 0.88
mmol, 2.5 M in hexane) was added to a solution of 1-bromo-2-
isopropylbenzene (162 mg, 0.81 mmol) in dry diethyl ether (5 mL)
cooled to 0 °C. The colorless solution was warmed to room tem-
perature and stirred for 3 h. Then, the solution was added dropwise
to a dry diethyl ether (2 mL) solution of (E)-N-(6-(1H-pyrrol-2-
yl)pyridin-2-yl)methylene)-2,6-diisopropylbenzenamine (100 mg,
0.30 mmol) at -78 °C. The yellow solution was warmed to room
temperature and stirred for 30 min. The color turned to red. The
reaction was followed by TLC and then quenched with NH4Cl
(aq) at 0 °C. The organic phase was separated and reserved. The
aqueous phase was washed with diethyl ether (3 ꢀ 30 mL). The
combined organic phases were extracted with water (2 ꢀ 30 mL)
and brine (1 ꢀ 30 mL). The organic phase was dried over Na2SO4.
The solvent was distilled off by rotary evaporation. The crude
product was purified by flash column chromatography on silica gel
Polymerizations Procedure. General Procedure for Ethylene and
Propylene Polymerization. The polymerizations were carried out
€
in a magnetically stirred flask (250 mL) or in a Buchi glass auto-
clave (500 mL). Under a nitrogen atmosphere, the required equi-
valents of AliBu2H were added to a solution of the complexes in
toluene (2 mL) and then stirred for 10 min at room temperature.
The reactor vessels were charged sequentially with toluene, dried
MAO and a solution of the precatalyst in toluene. The stirred
mixture was thermostated at the required temperature, and then
the monomer gas feed was started. After the prescribed time, the

Article
Macromolecules, Vol. 43, No. 21, 2010 8891
polymerization mixture was poured into acidified ethanol. The
polymers were filtered, washed with ethanol, and dried in a
vacuum oven at 40 °C overnight.
T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc,
M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.; Rosen, R. K.;
Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.; Talarico, G. Angew.
Chem., Int. Ed 2006, 45, 3278–3283.
General Procedure for 1-Hexene Polymerization. Polymeriza-
tions were carried out in a magnetically stirred flask (50 mL).
Under a nitrogen atmosphere, AliBu2H (150 μmol) was added to
a solution of complex (5 μmol) in toluene (2 mL) and aged for
10 min. The solution of precatalyst was added to the flask. The
flask was sequentially charged with dried MAO, toluene (3 mL)
and 1-hexene (5 mL). After 1 h, the polymerization mixture was
poured into acidified ethanol. Polymers were recovered and
dried in a vacuum oven at 40 °C.
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Acknowledgment. The authors are grateful to Dr. Maria
Grazia Napoli for GPC analysis and to Dr. Patrizia Oliva for
some NMR experiments. This work was supported by the
University of Salerno (FARB Grant).
(9) Annunziata, L.; Pappalardo, D.; Tedesco, C.; Pellecchia, C.
Macromolecules 2009, 42, 5572–5578.
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(12) The PE produced by complex 3 was highly insoluble, and therefore
its molecular weight could not be determined by high-temperature
GPC.
(13) Niu, A.; Stellbrink, J.; Allgaier, J.; Richter, D.; Hartmann, R.;
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Supporting Information Available: Figures showing 1H and
13C NMR spectra of ligand H2L1 and H2L2, and complexes 2
and 3 and text describing a fractionation experiment and a table
giving characterization data of each fraction. This material is
available free of charge via the Internet at http://pubs.acs.org.
(14) As suggested by a reviewer, comparison with the data reported in
reference 6i showed that the pyridylamido-based hafnium com-
plexes have activities of two or 3 orders of magnitude larger than
that of complex 3. It must be added, however, that the polymeri-
zation protocols are completely different in terms of reactor scale
(a few milliliters in ref 6i vs 500 mL in this work) and, above all, in
terms of polymerization times (100-300 s vs 30-60 min). As a
matter of fact, pyridylamido-based complexes performing propyl-
ene polymerizations under more similar conditions (see ref 10),
showed an activity higher than, but of the same order of magnitude
as, that of catalyst 3.
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