Synthesis of a [(π-Cyano-nacnac)Cp]zirconium complex and its remote activation for ethylene polymerization

Article abstract of DOI:10.1021/om100866t

The NC-nacnacH ligand (2) was prepared by the deprotonation of the unsymmetrically N5-phenyl, N1-2,6-diisopropylphenyl substituted bis(imino) acetylacetonate nacnacH system (1) with n-butyllithium followed by cyanation with tosyl cyanide. Subsequent depro

Full text of DOI:10.1021/om100866t

6104 Organometallics 2010, 29, 6104–6110
DOI: 10.1021/om100866t
Synthesis of a [(π-Cyano-nacnac)Cp]zirconium Complex and Its Remote
Activation for Ethylene Polymerization
†
‡
†
§
€
Alan R. Cabrera, Yanika Schneider, Mauricio Valderrama, Roland Frohlich,
Gerald Kehr,§ Gerhard Erker,*,§ and Rene S. Rojas*,†
†
´
ꢀ
´
ꢀ
Departamento de Quımica Inorganica, Facultad de Quımica, Pontificia Universidad Catolica de Chile,
Casilla 306, Santiago-22, Chile, Departments of Chemistry and Biochemistry, University of
‡
§
California, Santa Barbara, California 93106, and Organisch-Chemisches Institut, Universita€t Mu€nster,
Corrensstrasse 40, 48149 Mu€nster, Germany
Received September 7, 2010
The NC-nacnacH ligand (2) was prepared by the deprotonation of the unsymmetrically N5-phenyl,
N1-2,6-diisopropylphenyl substituted bis(imino) acetylacetonate nacnacH system (1) withn-butyllithium
followed by cyanation with tosyl cyanide. Subsequent deprotonation (KH) gave the [NC-nacnac]K
salt (3), which was transmetalated by reacting it with CpZrCl3(dme), to yield the complex (NC-nacnac)-
CpZrCl2 (5). Addition of one molar equivalent of B(C6F5)3 gave [(C6F5)3B-NC-nacnac]CpZrCl2 (6). The
compounds 2, 5, and 6 were characterized by X-ray diffraction. Activation of 5 with MAO gave an active
homogeneous Ziegler-Natta catalyst for ethylene polymerization. The (NC-nacnac)CpZrCl2/MAO
system is ca. 7 times more active than the CN-free reference system (nacnac)CpZrCl2 (4)/MAO. The
B(C6F5)3-containing system 6/MAO has an activity similar to 5/MAO but allows for much lower MAO
concentration before the catalytic activity ceases.
Introduction
expensive cocatalysts such as MAO,4 there has been increased
interest in developing systems that require less, or ideally no,
cocatalyst in order to make the processes more profitable.
Remarkable examples in late transition metal systems include
the DuPont Versipol system,5 which has shown that the proper
design and synthesis of organometallic complexes can lead to
enhancements in catalytic activity, even with reduced cocatalyst
concentrations. In addition, it has been possible to develop
compounds that do not require cocatalysts (single component).6
These catalysts are often better suited for the preparation of
specialty oligomers and polymers incorporating polar func-
tionalities. Some ligand frameworks (e.g., the salicylimine
derivatives) have been utilized in the preparation of catalyst
systems based on zirconium and provide extremely high activity
for ethylene polymerization.7 The catalysts can also produce
novel polypropylene structures.8
After the development of the very successful metallocene
catalysts, several efficient catalyst systems, based on early
and late transition metals,1 supported mainly by multi-
dentate NO, NN, and NNN ligands have been investigated.2
One of the main reasons is the facile access to a large variety
of bi-, tri-, and even tetradentate ligands, which can coordi-
nate and effectively stabilize transition metals, providing
access to complexes that in the presence of cocatalysts
generate very active catalytic species for olefin polymerization.2,3
As metallocene systems are highly dependent on the use of
*Corresponding author. E-mail: rrojasg@uc.cl; erker@uni-muenster.de.
(1) (a) Gladysz, J. A. Chem. Rev. 2000, 100, 1167–1682. (b) Kaminsky,
W.; Funck, A.; Hahnsen, H. Dalton Trans. 2009, 41, 8803–8810.
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Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–315. (c) Boussie, T. R.;
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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.
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r
pubs.acs.org/Organometallics
Published on Web 10/20/2010
2010 American Chemical Society

Article
Interesting new “concepts” have been applied to catalytic
Organometallics, Vol. 29, No. 22, 2010 6105
constrained geometry complexes that combine aromatic rings
and mono- or bidentate ligands to a transition metal.13
Particularly interesting cases are the early transition metal
complexes (Ti, Zr, and Cr) derived from the combination of a
β-diketiminate ligand containing a Cp ring, which has been
used as an initiator of olefin polymerization and moderator
for the polymerization of vinyl acetate, respectively.14
Herein, we report on the synthesis, characterization, and
reactivity of a catalytic zirconium system that was designed
to produce a cationic active site and also to benefit from
removal of electron density from the metal center by the
action of a Lewis acid on the ligand framework. We decided
to use a specially funtionalized bis(imino) acetylacetone ligand
(NC-nacnac), which is a derivative of an interesting class of
ligands that has found increasing use in coordination chemistry
of late transition metals including some unusual coordination
chemistry of coinage metals.15
systems to improve and better control the reactivity, reduce
the cocatalyst concentration, and have a better control over
polymer properties. This concept involves the synthesis of
ligands with an additional functionality, for example Lewis
bases such as CO and CN groups, in the ligand backbone.9
This functionality allows for the complexation of a Lewis
acid and the generation of a zwitterionic species, which alters
the electronic properties of the metal center. The strong
Lewis acid tris(pentafluorophenyl)borane, B(C6F5)3, is par-
ticularly capable of strongly coordinating and polarizing these
kinds of functionalities in late transition metal complexes.10
To our knowledge the activation or additional activation
through an exocyclic functionality has not been reported
for early transition metal olefin polymerization complexes.
However, the complexation of Lewis acids to metallocenes
has been demonstrated for a number of systems, including
constrained geometry complexes and coordination complexes.11
In some cases, the Lewis acid is chemically attached to the ligand
and interacts directly with the alkyl group bound to the metal
center.12 Other structures are derived from the well-known
Results and Discussion
The reaction sequence begins with deprotonation of the
previously described nacnac ligand (1)16 with n-butyllithium
followed by the reaction of the resulting anion with the reagent
tosyl cyanide (Ts-CN). This selectively introduced the cyano
functional group at the C3 position of the ligand framework to
give NC-nacnacH (2), isolated in 55% yield, Scheme 1.
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The ligand system 2 was characterized by C, H, N ele-
mental analysis, spectroscopically, and by X-ray diffraction.
It features 13C NMR resonances of a typical conjugated
enamino heterocarbonyl system (see Table 1). The 13C NMR
signal of the cyano carbon atom was found at δ 121.2 ppm.
The 2,6-diisopropylphenyl substituent at N1 features the 1H/13C
NMR signal of pairwise diasterotopic isopropyl CH3 groups
[isopropyl CH: δ 2.87 ppm (1H), 28.9 ppm (13C)]. TheIR ν~(CN)
band of compound 2 is found at 2192 cm-1
.
The X-ray crystal structure analysis shows a U-shaped
C3N2 core with alternating bond lengths. The N1-H vector
is oriented toward the inner side into the direction of N5,
with which it probably forms a hydrogen bridge. Both the
aryl substituents at N1 and N5 are substantially rotated
out of the central plane toward a perpendicular orientation
(see Table 2 and Figure 1). The CtN bond is short and the
C3-C7-N8 fragment is nearly linear.
Deprotonation of 2 was achieved by treatment with potassium
hydride in THF at room temperature (12 h). The reaction
proceeded cleanly with evolution of dihydrogen to give the
salt [NC-nacnac]K (3) in 90% yield as a dark yellow solid (see
Table 1 for characteristic spectroscopic features).
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Treatment of 3 with one molar equivalent of CpZrCl3-
(dme) (THF, rt, 12 h) gave the (NC-nacnac)CpZrCl2 com-
plex 5. It was isolated as an orange solid in 84% yield.
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6106 Organometallics, Vol. 29, No. 22, 2010
Cabrera et al.
Table 1. Selected Spectroscopic Parameters of the NC-nacnac
Systems 2, 3, 5, and 6
2a
3a
5b
6a
δ 13C NMR
CdNph
CCN
166.2
82.1
166.9
121.2
164.3
76.4
171.6
136.1
168.3
73.0
171.3
119.9
170.8
64.7
171.4
n.o
CdNAr
CtN
δ 1H NMR
Cp
HCiPr
6.34
5.95
2.87
2.00, 1.92
1.05, 0.99
3.15
2.36, 1.95
1,27, 1.21
3.33, 2.76
2.27, 2.31
1.33, 1.21,
1.19, 0.92
3.22, 2.54
1.86, 1.79
1.18, 1.14,
0.90, 0.57
MePh, MeAr
MeiPr
IR [cm-1
2134
]
ν~(CN)
2192
2210
2278
Figure 2. Molecular structure of complex 5.
a NMR spectra in C6D6 solution. b NMR spectra in CD2Cl2 solution.
Table 2. Selected Structural Parameters of the NC-nacnac
Systems 2, 5, and 6a
2
5
6
Zr-N1
2.305(3)
2.658(3)
2.227(3)
2.863(3)
2.703(3)
2.4695(9)
2.4546(10)
1.301(4)
1.463(4)
1.425(5)
1.324(4)
1.437(4)
1.140(4)
116.8(3)
122.4(3)
118.1(3)
179.0(4)
97.9(4)
2.313(3)
2.583(3)
2.261(3)
2.849(3)
2.716(3)
2.4701(10)
2.4395(10)
1.296(4)
1.479(4)
1.448(4)
1.310(4)
1.409(4)
1.135(4)
115.5(3)
121.6(3)
115.5(3)
174.6(4)
90.4(4)
Zr-C3
Zr-N5
Zr-C2
Zr-C4
Zr-Cl1
Zr-Cl2
C2-N1
1.330(2)
1.400(2)
1.450(2)
1.300(2)
1.429(2)
1.151(2)
120.0(2)
124.8(2)
118.9(2)
179.2(2)
101.8(2)
113.9(2)
C2-C3
C3-C4
C4-N5
C3-C7
C7-N8
N1-C2-C3
C2-C3-C4
C3-C4-N5
C3-C7-N8
C2-N1-C11-C12
C4-N5-C31-C32
Figure 3. Side view of the slightly boat-shaped central core of
complex 5.
13
-68.2(5)
108.2(4)
(
C: δ 23.6/21.7). The isopropyl groups of the dipp sub-
stituent at N1 are different, giving rise to a pair of CHMe2
a
ꢀ
˚
Bond lengths in A, angles and dihedral angles in deg.
methine proton NMR resonances and a total of four corre-
1
sponding H NMR CH3 doublets. For further details see
Table 1 and the Supporting Information.
Complex 5 was characterized by X-ray diffraction. It fea-
tures a η5-Cp ligand at zirconium with Zr-C(Cp) bond
ꢀ
˚
lengths in a range between 2.471(4) and 2.487(4) A. The
NC-nacnac ligand is bound in a U-shaped form. While it
appears that the Zr atom has interactions with all five
members of the ligating ring, making it metallocene-like,
the Zr-C/N bond lengths are systematically alternating,
producing the strongest interaction of the N1/C3/N5 atoms
with the Zr center. The Zr-N1 and Zr-N5 bond lengths are
short (see Table 2 and Figure 2). The Zr-C3 bond length of
ꢀ
˚
2.658(3) A indicates a strong metal carbon interaction,
whereas the adjacent Zr-C2/Zr-C4 bond lengths are mark-
edly longer (see Table 2), and consequently, these interac-
tions must be considered weaker. This pattern of metal-C/N
bond lengths results in a typical deviation of the NC-nacnac
ligand in complex 5 from planarity into the direction of a
boat-shaped arrangement (see Figure 3). Overall the core of
complex 5 remotely resembles a bent metallocene structure
(see Figures 2 and 3) with the open N1/N5 side pointing
toward the narrow backside of the wedge-like structure.
Figure 1. View of the molecular structure of the NC-nacnacH
ligand system 2.
1
It features a H NMR Cp singlet of 5H intensity at δ 6.34
(13C: δ 118.8) and a pair of C2/C4-CH3 resonances of the
unsymmetrically substituted NC-nacnac core at δ 2.31/2.27

Article
Organometallics, Vol. 29, No. 22, 2010 6107
Scheme 1
Table 3. Selected Ethylene Polymerization Reactionsa
entry catalyst Al/Zrb Tc yieldd
Ae
f
Mn Mw PDI Tm
f
g
1
2
3
4
5
6
7
8
5
5
5
5
5
5
6
6
6
6
5*
6*
4
1000 45 0.28
1000 60 0.38
1000 75 0.96
1000 90 1.13
500 75 0.72
250 75 0.48
500 75 0.75
250 75 0.72
125 75 0.10
50 75 0.01
500 75 0.95
244 163 338 2.1 135
334 128 264 2.1 137
845
993
635
424
654
630
88
65 138 2.1 137
22 64 2.7 134
60 113 1.9 135
55 109 2.0 136
64 155 2.4 139
65 141 2.2 139
9
35
60 1.7 136
10
11
12
13
10
830
49
86 1.8 137
500 75 1.17 1029
500 75 0.10 90
71 141 2.0 136
38 85 2.2 136
a Polymerizations were carried out in 100 mL autoclave reactors with
6.8 μmol of Zr in 30 mL of toluene and 50 psi of ethylene pressure. The
cocatalyst was MAO (MAO was added with an addition funnel when
indicated with an asterisk (*)). Duration of reaction was 10 min. b Al/Zr
ratio used. c Temperature of reaction (in °C). d Polymer obtained (in g).
e Activity in kg polymer/(mol Zr h). f ꢀ103 g/mol. g In °C.
Figure 4. Molecular structure of the B(C6F5)3(NC-nacnac)CpZr-
Cl2 adduct 6.
decreasing electrostatic electron repulsion by adding a Lewis
acid to the nitrile lone pair.17 The strengthening of the CtN
bond upon B(C6F5)3 addition even shows up in the X-ray
crystal structure analysis of 6 (see Figure 4). In the adduct 6
The C3-C7-N8 (C-CtN) vector is oriented toward the
open front side of the (lig)CpZrCl2 geometry. In the projec-
tion it is unsymmetrically located between the Zr-Cl1/Zr-
Cl2 vectors, but closer to Cl2.
ꢀ
˚
we find a CtN bond length (C7-N8) of 1.135(4) A, which is
not significantly different from that found in the direct pre-
ꢀ
˚
cursor 5 (C7-N8: 1.140(4) A).
B(C6F5)3 coordinates in a linear fashion to the NC-nacnac
For comparison for the polymerization experiments (see
below) we have also prepared the related CN-free system
(nacnac)CpZrCl2 (4). This was obtained by deprotonation of
the nacnacH derivative (1) with potassium hydride followed by
the reaction of the resulting ligand salt with CpZrCl3(dme) (see
Scheme 1). The complex (nacnac)CpZrCl2 (4) was isolated as a
pale yellow solid in 80% yield (see the Experimental Section
and the Supporting Information for its characterization).
The strong boron Lewis acid B(C6F5)3 added cleanly to the
nitrile functionality of complex (NC-nacnac)CpZrCl2 (5) to
yield the new complex 6. We purified it by crystallization
from pentane/toluene and isolated it as a light yellow solid in
80% yield. The IR ν~(CN) band is shifted very characteris-
tically upon Lewis acid adduct formation from 2210 cm-1 in
5 to 2278 cm-1 in 6. The shifting of the CtN stretching band
by 68 cm-1 to higher wavenumbers indicates a strengthening
of the CtN triple bond, which is typically caused by
ꢀ
˚
ligand in 6 (C7-N8-B1: 167.4(4)°, N8-B1: 1.586(4) A). The
C7-N8-B1(C6F5)3 unit is oriented toward the open side of
the pseudometallocene wedge in 6. In the projection the C3-
C7 vector almost bisects the Cl1-Zr-Cl2 angle (see Figure 4).
Ethylene Polymerization
A series of ethylene polymerizations were carried out using
compounds 4-6 under various reaction conditions, with
MAO as the coactivator (Table 3). In all cases, one observes
€
(17) (a) Jacobsen, H.; Berke, H.; Doring, S.; Kehr, G.; Erker, G.;
€
Frohlich, R.; Meyer, O. Organometallics 1999, 18, 1724–1735. See also:
€
(b) Jacobsen, H.; Berke, H.; Brackemeyer, T.; Eisenblatter, T.; Erker, G.;
€
Frohlich, R.; Meyer, O.; Bergander, K. Helv. Chim. Acta 1998, 81, 1692–
€
1709. (c) Brackemeyer, T.; Erker, G.; Frohlich, R. Organometallics 1997, 16,
531–536.

6108 Organometallics, Vol. 29, No. 22, 2010
Cabrera et al.
Scheme 2
activity is observed with the adduct (6) because the activator is
required to generate only the catalytic species, since the CN
functionality is already bound by the B(C6F5)3.
Thermal analysis of the polymer products was performed
using differential scanning calorimetry (DSC). Samples were
scanned from 25 to 200 at 10 °C/min. One sharp thermal
transition around 136 ((3) °C was observed for the PE
obtained from the three systems under study. Variation in
the reaction conditions did not change the linearity of the
products.
Conclusion
the formation of high molecular weight PE. Entries 1-4 show
the behavior of 5 over a range of temperatures. There is a
substantial increase in activity when the temperature is in-
creased from 45 °C (244 kg/mol h) to 90 °C (993 kg/mol h),
consistent with an increase in the rate of propagation. The
result in entry 4 also demonstrates that the system is stable at
high temperatures, and despite the increased polydispersity of
the product, its GPC trace remains monomodal (see the Sup-
porting Information). As was expected, the molecular weights
of the resulting polymers decrease from 338 to 62 kg/mol upon
increasing the temperature in this range. Entries 3, 5, and 6
show the results obtained at different Al/Zr ratios with 5/MAO.
Comparison of these entries shows that the ethylene consump-
tion decreases by nearly 200 units when the Al/Zr ratio is
reduced from 1000 to 500 to 250. There is also a slight decrease
in the molecular weight of the products.
It is informative at this point to compare the ethylene
polymerization activities obtained with 4 and 5. Complex 4
in the presence of MAO has an activity of ca. 90 kg PE (mol
Zr)-1 h-1 (at 75 °C and 500 Al/Zr ratio), while the system 5
under the same conditions shows an activity of 635 kg
PE (mol Zr)-1 h-1, 7 times higher. Clearly, complex 5 is a
precursor to a significantly more active catalytic species,
most likely as a result of the interaction between the Lewis
acid and the exocyclic CN functionality. This interaction
generates a reduction in the electron density at the zirconium
center by inductive effects, as shown in Scheme 2. This causes
the metal center to become more electrophillic, resulting in
increased activities.
To verify these phenomena, we decided to use the isolated
B(C6F5)3 5 adduct (6), obtained by treating the precatalyst 5
with one equivalent of B(C6F5)3 in toluene. Entry 7 demon-
strates that when 6 is activated with MAO, the resulting
activity and molecular weight are similar to those obtained
with 5 under the same conditions (entry 5). In terms of the
polymer properties, the 6/MAO system produces more linear
polyethylene with slightly higher melting points and slightly
higher polydispersities. When the ratio of Al/Zr was gradu-
ally lowered, the activity remained constant until an Al/Zr
ratio of 250. The adduct was also studied at lower Al/Zr
ratios of 125 and 50 (entries 8 and 9, respectively); however a
substantial decrease in the activity was observed, most likely
because the coactivator concentrations were below the mini-
mal content of MAO necessary to alkylate and generate the
catalytic species. However the performance of these systems
is remarkable, even at such low equivalents of MAO.
To minimize the probability of deactivation of the catalytic
species in the reaction medium, the polymerizations were initi-
ated by introducing MAO to a stirring solution of precatalysts
(5 or 6) in the presence of ethylene via a pressure addition
funnel. Under such conditions, the complexes exhibited an
increase in catalytic activity of 19% (entries 11 and 12). Higher
In short, we have reported the synthesis and full characteriza-
tion of a new type of active early transition metal catalyst pre-
cursor that can be used to polymerize olefins to high molecular
weight in the presence of low concentrations of coactivators.
Comparison with the reactivity observed with the Cp-diimine
complex 4 illustrates that the presence of the carbonitrile func-
tionality in 5leads to a substantial increase in activity for ethylene
polymerization under otherwise analogous reaction conditions.
On the basis of the considerations above, we propose that the
increase in reactivity of 5 versus 4 isa result of the attachment of
a Lewis acid to the exocyclic nitrogen site on the propagating
cationic species. This has been probed indirectly by isolating the
B(C6F5)3-5 adduct (6), which results in a similar activity in the
presence of ethylene to that of 5. Furthermore, the use of the
adduct makes it possible to reduce the MAO concentration
to 250 Al/Zr ratio without any detriment to the activity, as
observed with 5. The general concept was previously illustrated
by late transition metals.10h,i,j-l,m A straightforward explana-
tion, Scheme 2, is a reduction of the electron density at the
zirconium center by inductive effects, making the metal center
more electrophilic. Additionally, the CN base functionality
has another advantage; due to the sp hybridization, it is geo-
metrically located in an opposite direction to the metal center,
making it more probable that the Lewis acid interacts and
thus has an electronic influence on the metal center, which is
reflected in the improved performance of the catalytic system.
The addition of MAO in the presence of ethylene shows an
improvement in the catalytic activity for 5 and 6; however the
improvement was higher in the case of the B(C6F5) adduct 6,
supporting the notion that adduct formation plays an impor-
tant role in these systems. Further optimization of reaction
conditions, types of activators, alkylation reagents, and varia-
tions in R-cyano-β-diimine frameworks will enable improve-
ments in polymerization control. Our current efforts are aimed
at delineating the behavior of these systems in R-olefin and cyclic
monomer copolymerizations, alkylation of the metal center,
and heterogenization of this type of exocyclic-functionalized
complexes.
Experimental Section
General Procedures. All manipulations were performed under
an inert atmosphere using standard glovebox and Schlenk-line
techniques. All reagents were used as received from Aldrich unless
otherwise specified. Ethylene was purchased from Matheson
Tri-Gas (research grade, 99.99% pure). Toluene, THF, ether,
and pentane were distilled from benzophenone ketyl. All poly-
merization reactions were carried out in a Parr autoclave reactor
as described below. Toluene for polymerization was distilled
from sodium benzophenone. The following instruments were
used for the physical characterization of the compounds. NMR:
Varian Inova 500 (1H: 500 MHz, 13C: 126 MHz, 19F: 470 MHz,

Article
Organometallics, Vol. 29, No. 22, 2010 6109
11B: 160 MHz), Bruker Unity Plus 600 (1H: 600 MHz, 31C: 151
MHz, 19F: 564 MHz, 11B: 64 MHz) and Bruker Advance 400.
Most NMR assignments were supported by additional 2D
experiments. IR spectra were recorded on a Bruker Vector-22
spectrophotometer using KBr pellets, and in solution using
C6D6 as solvent. X-ray crystal structure analyses: Data sets
were collected with Nonius KappaCCD diffractometers, in the
case of Mo-radiation equipped with a rotating anode generator.
Programs used: data collection COLLECT (Nonius B.V., 1998),
data reduction Denzo-SMN (Z. Otwinowski, W. Minor, Meth-
ods Enzymol. 1997, 276, 307-326), absorption correction SOR-
TAV (R. H. Blessing, Acta Crystallogr. 1995, A51, 33-37; R. H.
Blessing, J. Appl. Crystallogr. 1997, 30, 421-426) and Denzo
(Z. Otwinowski, D. Borek, W. Majewski, W. Minor, Acta Crystallogr.
2003, A59, 228-234), structure solution SHELXS-97 (G. M.
Sheldrick, Acta Crystallogr. 1990, A46, 467-473), structure refine-
mentSHELXL-97(G. M. Sheldrick, ActaCrystallogr. 2008, A64,
112-122), graphics XP (BrukerAXS, 2000). Graphics show
thermal ellipsoids at the 50% probability level. R values are given
for the observed reflections; wR2 values for all.
m-Ph), 7.08 (m, 1H, p-Ar), 6.84 (m, 1H, p-Ph), 6.49 (m, 2H,
o-Ph), 3.15 (hept, 3J = 6.9 Hz, 2H, HCiPr), 2.36 (s, 3H,
3
NdCMePh), 1.95 (s, 3H, NdCMeAr), 1.27 (d, J = 6.9 Hz, 6H,
0
3
MeiPr), 1.21 (d, J = 6.9 Hz, 6H, MeiPr ) ppm. 13C{1H} NMR
(126 MHz, C6D6, 343 K): δ 171.6 (CdNPh), 164.3 (CdNAr),
153.2 (i-Ph), 148.4 (i-Ar), 138.5 (o-Ar), 136.1 (CtN), 129.8
(m-Ph), 123.6 (m-Ar), 122.9 (p-Ar), 122.3 (o-Ph), 122.1 (p-Ph),
76.4 (CCN), 28.6 (HCiPr), 24.1 (MeiPr ), 23.5 (MeiPr), 21.5
0
(
NdCMeAr), 20.8 (NdCMePh) ppm.
Preparation of Complex 4. 2-(2,6-Diisopropylphenyl)amino-
pent-2-ene-4-(phenyl)imine (1) (90 mg, 0.27 mmol) and KH
(22 mg, 0.54 mmol) were stirred in THF for 12 h. The reaction
showed rapid gas evolution. The slightly cloudy mixture was
filtered through Celite and added dropwise to CpZrCl3(dme)
(95 mg, 0.27 mmol) in THF. The reaction mixture was stirred for
6 h. The resulting yellow solution was filtered over Celite. The
solvent volume was reduced, and pentane and ether were added
separately to wash the solid. A light yellow powder correspond-
ing to compound 4 was isolated in 86% yield (C28H34Cl2N2Zr
(M = 560.71 g/mol): C 59.97, H 6.11, N 4.99; found C 59.32, H
1
5.89, N 5.21). H NMR (500 MHz, CD2Cl2, 298 K): δ 7.46
(m, 2H, m-Ph), 7.32 (m, 2H, m-, p-Ar), 7.31 (m, 1H, p-Ph), 7.23
Preparation of Compound 2. n-BuLi (3.4 mL, 1.6 M, 5.5 mmol)
was added dropwise to a stirred solution of 2-(2,6-diisopropyl-
phenyl)aminopent-2-ene-4-(phenyl)imine (1)16 in THF (40 mL)
(1.4 g, 4.2 mmol) at -78 °C. The reaction was allowed to warm
to room temperature over 2 h to afford the lithium salt. The
resulting yellow suspension was then cooled to -78 °C, and
p-toluenesulfonyl cyanide (0.9 g, 5.0 mmol) in THF (10 mL) was
added. The reaction mixture was again allowed to warm to room
temperature over 24 h. From this mixture, all volatiles were
removed under vacuum, and the residue was dissolved in
CH2Cl2 (50 mL). This was washed with brine (2 ꢀ 100 mL),
dried over Na2SO4, and filtered. The solvent was subsequently
removed under vacuum to yield a light brown oil. Precipitation
from methanol provided a light yellow solid of 3-cyano-2-(2,6-
diisopropylphenyl)aminopent-2-ene-4-(phenyl)imine (2) in 55%
yield. Single crystals suitable for X-ray diffraction studies were
obtained by evaporation of an acetone solution of compound 2 at
room temperature (C24H29N3 (M = 359.59 g/mol): C 80.16, H
8.13, N 11.69; found: C 79.85, H 8.74, N 11.02). IR (KBr): ν~ /
(br, 2H, o-Ph), 7.21 (m, 1H, m0-Ar), 6.30 (s, 5H, Cp), 5.70 (s, 1H,
CH), 3.60 (hept, 3J = 6.7 Hz, 1H, HCiPr(o)), 2.70 (hept, 3J = 6.7
0
Hz, 1H, HCiPr(o )), 2.07 (s, 3H, NdCMeAr), 2.02 (s, 3H,
3
3
NdCMePh), 1.36 (d, 0 J = 6.7 Hz, 3H, MeiPr(o)), 1.20 (d, J =
0
6.7 Hz, 3H, MeiPr(o) ), 1.18 (0d, 3J = 6.7 Hz, 3H, MeiPr(o )), 0.92
0
(d, 3J = 6.7 Hz, 3H, MeiPr(o ) ) ppm. 13C{1H} NMR (126 MHz,
CD2Cl2, 298 K): δ 168.4 (CdNAr), 161.8 (CdNPh), 150.0 (i-Ph),
144.6 (i-Ar), 143.6 (o-Ar), 141.5 (o0-Ar), 129.4 (m-Ph), 127.8
(p-Ar), 126.5 (p-Ph), 125.9 (m-Ar), 124.6 (br, o-Ph), 124.3 (m0-Ar),
0
117.6 (Cp), 90.8 (CH), 27.79 (HCiPr(o )), 27.76 (HCiPr(o)), 25.7
0
0
0
(MeiPr(o)0 ), 25.0 (MeiPr(o ) ), 24.6 (MeiPr(o) ), 24.1 (NdCMeAr), 23.2
(MeiPr(o )), 23.1 (NdCMePh) ppm.
Preparation of Complex 5. The potassium salt 3 (89 mg,
0.25 mmol) in THF (2 mL) was added to CpZrCl3(dme)18
(100 mg, 0.25 mmol) in THF. The reaction mixture was stirred
for 12 h. The resulting orange solution was filtered over Celite.
The solvent volume was reduced, and pentane and ether was
added separately to wash the solid. A light brown powder was
isolated in 84% yield. Single crystals for X-ray crystal structure
analysis were grown by evaporation of C6D6 solution of com-
pound 5 at room temperature (C29H33Cl2N3Zr ꢀ C4H8O (M =
657.83 g/mol): C 60.25, H 6.28, N 6.39; found C 59.92, H 6.41, N
5.97). IR (KBr): ν~/cm-1 2210 (ν(CtN), s). 1H NMR (500 MHz,
CD2Cl2, 298 K): δ 7.52 (m, 2H, m-Ph), 7.38 (m, 1H, p-Ph), 7.37
(m, 2H, m-, p-Ar), 7.26 (m, 1H, m0-Ar), 7.20 (br, 2H, o-Ph), 6.34
1
cm-1 2192 (ν(CtN), s). H NMR (500 MHz, C6D6, 298 K): δ
14.56 (s, 1H, NH), 7.09 (m, 1H, p-Ar), 7.02 (m, 2H, m-Ar), 7.01
(m, 2H, m-Ph), 6.86 (m, 1H, p-Ph), 6.69 (m, 2H, o-Ph), 2.87 (hept,
J = 6.9 Hz, 2H, HCiPr), 2.00 (s, 3H, NdCMePh), 1.92 (s, 3H,
NdCMeAr), 1.05 (d, J = 6.9 Hz, 6H, MeiPr), 0.99 (d, J = 6.9 Hz,
0
6H, MeiPr ) ppm. 13C{1H} NMR (126 MHz, C6D6, 298 K): δ
166.9 (CdNAr), 166.2 (CdNPh), 144.8 (i-Ph), 142.4 (o-Ar), 138.3
(i-Ar), 129.3 (m-Ph), 127.0 (p-Ar), 124.9 (p-Ph), 123.8 (m-Ar),
(s, 5H, Cp), 3.33 (hept, 3J = 6.6 Hz, 1H, HCiPr(o)), 2.76 (hept, 3J
123.0 (o-Ph), 121.2 (CtN), 82.1 (CCN), 28.9 (HCiPr), 24.3
0
= 6.7 Hz, 1H, HCiPr(o )), 2.31 (s, 3H, NdCMeAr), 2.27
0
(MeiPr ), 22.5 (MeiPr), 19.4 (NdCMePh), 19.3 (NdCMeAr) ppm.
X-ray crystal structure analysis of 2: formula C24H29N3, M =
(s, 3H, NdCMePh), 1.33 (0d, 3J = 6.6 Hz, 3H, MeiPr(o)), 1.21 (d,
0
3J = 6.7 Hz, 3H, MeiPr(o )), 1.19 (d, 3J 0= 6.6 Hz, 3H, MeiPr(o) ),
˚
359.50, colorless crystal 0.45 ꢀ 0.25 ꢀ 0.05 mm, a = 10.3543(4) A,
0
3
0.92 (br d, J = 6.7 Hz, 3H, MeiPr(o ) ) ppm. 13C{1H} NMR
(126 MHz, CD2Cl2, 298 K): δ 171.3 (CdNAr), 168.3 (CdNPh),
148.5 (i-Ph), 143.14 (i-Ar), 143.07 (o-Ar), 140.7 (o0-Ar), 129.8
(m-Ph), 128.6 (p-Ar), 127.4 (p-Ph), 126.4 (m-Ar), 124.5
˚
˚
b = 21.0372(9) A, c = 10.4706(5) A, β = 112.054(2)°, V =
2113.88(16) A , Fcalc = 1.130 g cm-3, μ = 0.510 mm-1, empirical
3
˚
absorption correction (0.803 e T e 0.975), Z = 4, monoclinic,
˚
space group P21/n (No. 14), λ = 1.54178 A, T = 223(2) K, ω
(m0-Ar), 124.0 (br, o-Ph), 119.9 (br, CtN), 118.8 (Cp), 73.0
and j scans, 14 753 reflections collected ((h, ( k, ( l), [(sin θ)/λ] =
0
(br, CCN0 ), 28.1 (HCiPr(o )), 27.9 (HCiPr(o)), 25.9 (MeiPr(o)), 25.2
0.60 A-1, 3717 independent (Rint = 0.051) and 2996 obser-
˚
0
0
0
(MeiPr(o ) ), 24.4 (MeiPr(o) ), 23,6 (NdCMeAr), 22.7 (MeiPr(o )),
21.7 (NdCMePh) ppm.
X-ray crystal structure analysis of 5: formula C29H33-
ved reflections [I g 2σ(I)], 254 refined parameters, R =
0.051, wR2 = 0.140, max. (min.) residual electron density
0.23 (-0.17) e A-3, hydrogen atoms calculated and refined as
˚
Cl2N3Zr C4H8O, M = 657.81, colorless crystal 0.35 ꢀ 0.15 ꢀ
3
riding atoms.
˚
0.05 mm, a = 10.2577(1) A, b=13.2092(2) A, c = 13.6742(3) A,
˚
˚
Preparation of the Potassium Salt 3. Compound 2 (0.28 g,
0.8 mmol) and KH (63 mg, 1.6 mmol) were stirred in THF for
12 h. The reaction showed rapid gas evolution. The slightly
cloudy mixture was filtered through Celite, and excess THF was
removed under vacuum. A dark yellow powder corresponding
3
˚
R = 72.173(1)°, β = 87.628(1)°, γ = 68.432(2)°, V = 1635.03(5) A ,
Fcalc = 1.336 g cm-3, μ = 0.529 mm-1, empirical absorption
(18) (a) Lund, E. C.; Livinghouse, T. Organometallics. 1990, 9, 2426–
2427. See also: (b) Erker, G.; Sarter, C.; Albrecht, M.; Dehnicke, S.; Kr€uger, C.;
to compound 3 was isolated in 90% yield (C24H28N3K C4H8O
(M = 469.71 g/mol): C 71.60, H 7.72, N 8.94; found: C 72.15, H
3
ꢀ
Raabe, E.; Schlund, R.; Benn, R.; Rufinska, A.; Mynott, R. J. Organomet.
Chem. 1990, 382, 89–102. (c) Erker, G.; Sarter, C.; Werner, S.; Krueger, C.
J. Organomet. Chem. 1989, 377, C55–C58. (d) Erker, G.; Berg, K.; Treschanke,
L.; Engel, K. Inorg. Chem. 1982, 21, 1277–1278.
1
7.37, N 9.13). IR (KBr): ν~ /cm-1 2134 (ν(CtN), s). H NMR
(500 MHz, C6D6, 343 K): δ 7.19 (m, 2H, m-Ar), 7.15 (m, 2H,

6110 Organometallics, Vol. 29, No. 22, 2010
Cabrera et al.
0.66 A-1, 12 255 independent (Rint = 0.045) and 10 634 ob-
served reflections [I g 2σ(I)], 670 refined parameters, R = 0.064,
wR2 = 0.176, max. (min.) residual electron density 1.58 (-0.81)
˚
correction (0.837 e T e 0.974), Z = 2, triclinic, space group P1
˚
(No. 2), λ = 0.71073 A, T = 223(2) K, ω and j scans, 15500
reflections collected ((h, ( k, ( l), [(sin θ)/λ] = 0.66 A-1, 7414
˚
independent (Rint = 0.063) and 5757 observed reflections [I g
2σ(I)], 413 refined parameters, R = 0.052, wR2 = 0.133, max.
e A-3, solvent molecule refined with restraints, hydrogen atoms
˚
calculated and refined as riding atoms.
(min.) residual electron density 0.70 (-0.81) e A-3, solvent
Homopolymerization of Ethylene. Polymerizations were car-
ried out in a Parr autoclave reactor (100 mL), loaded inside a
glovebox with an appropriate amount (6.8 μmol) of the pre-
catalyst (4, 5, or 6) and the corresponding MAO with toluene,
such that the final volume of the toluene solution was 30 mL.
The reactor was sealed inside the glovebox (where indicated,
MAO was put into the addition funnel). The reactor was
attached to an ethylene line, and the gas was fed continuously
into the reactor to a pressure of 50 psi. The pressurized reaction
mixture was stirred at temperatures ranging from 45 to 90 °C.
After 10 min, the ethylene was vented and acetone was added to
quench the polymerization. The precipitated polymer was col-
lected by filtration and dried overnight. The obtained polymers
were characterized by gel permeation chromatography (GPC).
GPC analysis was performed on a Polymer Laboratories high-
temperature GPC system (model PL 220) equipped with a
refractive index detector. Samples were run at 150 °C in spectro-
photometric grade 1,2,4-trichlorobenzene (TCB), stabilized
with BHT (0.5 g BHT/4 L solvent). Molecular weights were
calculated by using a universal calibration from narrow poly-
styrene standards in the molecular weight range of 580 to
7.5 million g/mol. Mark-Houwink parameters of a = 0.7 and
k = 47.7 were utilized to correct for polyethylene. Polymer
melting points were measured on a TA Instruments differential
scanning calorimeter (model DSC 290 module, TA Instruments)
at a rate of 10 °C/min for two cycles in the temperature range
25-200 °C.
˚
molecule refined with split positions, hydrogen atoms calculated
and refined as riding atoms.
Preparation of Complex 6. One equivalent of tris(penta-
fluorophenyl)borane (114 mg in 1 mL of toluene, 0.22 mmol)
was added to a toluene solution of 5 (130 mg, 0.22 mmol). The
reaction mixture was stirred for 12 h and filtered through Celite,
and the volatiles were removed under vacuum. Compound 6 was
isolated as a light yellow solid in 80% yield. Single crystals for
X-ray crystallography were grown by evaporation of a C6H6
solution of compound 6 at room temperature (C47H33BCl2-
F15N3Zr C6H6 (M = 1175.80 g/mol): C 54.14, H 3.34, N 3.57;
3
found C 55.03, H 3.80, N 3.33). IR (KBr): ν~ /cm-1 (ν(CtN), s).
1H NMR (600 MHz, C6D6, 298 K): δ 7.03 (m, 2H, m-Ph), 7.00
(m, 2H, m-,p-Ar), 6.94 (m, 1H, p-Ph), 6.90 (br, 2H, o-Ph), 6.85
3
(m, 1H, m0-Ar), 5.95 (s, 5H, Cp), 3.22 (hept, J 0= 6.9 Hz, 1H,
3
HCiPr(o)), 2.54 (hept, J = 6.9 Hz, 1H, HCiPr(o )), 1.86 (s, 3H,
3
NdCMePh), 1.79 (s, 3H, NdCMeAr), 1.18 (d, J = 6.9 Hz, 3H,
0
MeiPr(o)), 1.14 (d, 3H, 3J = 6.9 Hz, MeiPr(o) ), 0.90 (d, 3J = 6.9
0
0 0
3
Hz, 3H, MeiPr(o )) 0.57 (d, J = 6.9 Hz, 3H, MeiPr(o ) ) ppm.
13C{1H} NMR (151 MHz, C6D6, 298 K): δ 171.4 (CdNAr),
170.8 (CdNPh), 148.4 (dm, 1JFC ≈ 247 Hz), 140.7 (dm, 1JFC
≈
253 Hz), 137.6 (dm, 1JFC ≈ 247 Hz) (C6F5), 147.3 (i-Ph), 142.8
(o-Ar), 141.9 (i-Ar), 139.5 (o0-Ar), 129.7 (m-Ph), 128.9 (p-Ar),
127.5 (p-Ph), 126.6 (m-Ar), 124.0 (m0-Ar), 123.1 (br, o-Ph), 118.9
0
(Cp), 64.7 (CC0 N), 27.9 (HCiPr(o )), 27.7 (HCiPr(o)), 26.1 (MeiPr(o)),
0
0
0
25.2 (MeiPr(o ) ), 23.5 (MeiPr(o) ), 23.1 (NdCMeAr), 22.1 (MeiPr(o )),
21.4 (NdCMePh), n.o. (CtN, i-C6F5) ppm. 19F NMR (564 MHz,
C6D6, 298 K): δ -133.8 (m, 2F, o-C6F5), -156.1 (t, 3JFF = 20.5
Hz, 1F, p-C6F5), -163.3 (m, 2F, m-C6F5) ppm. 11B{1H} NMR
(192 MHz, C6D6, 298 K): n.o.
Acknowledgment. Financial support from FONDECYT
project nos. 11060384 and 1100286, Alexander von Hum-
boldt Foundation auspices, through Experience Research
Program to R.S.R. is gratefully acknowledged.
X-ray crystal structure analysis of 6: formula C47H33BCl2-
F15N3Zr C6H6, M = 1175.80, colorless crystal 0.25 ꢀ 0.15 ꢀ
3
˚
0.12 mm, a = 11.5478(1) A, b = 13.8426(2) A, c = 18.8875(3) A,
˚
˚
R = 101.636(1)°, β = 105.908(1)°, γ = 106.604(1)°, V =
3
2650.95(6) A , Fcalc = 1.473 g cm-3, μ = 0.400 mm-1, empirical
Supporting Information Available: Text and figures giving
further experimental and spectroscopic details and CIF files
(2, 5, and 6) giving crystallographic data. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
˚
absorption correction (0.907 e T e 0.954), Z = 2, triclinic,
˚
space group P1 (No. 2), λ = 0.71073 A, T = 223(2) K, ω and j
scans, 20 995 reflections collected ((h, ( k, ( l), [(sin θ)/λ] =