Catalytically Active N-Acylamidine-Zirconium Complexes: Synthesis, Structures, and Application in Ethylene Polymerization

Article abstract of DOI:10.1021/acs.organomet.6b00240

Three novel N-acylamidines 1a-c with varying steric bulk and substitution patterns were synthesized and thoroughly characterized by X-ray diffraction. Compounds 1a and 1b, which contain two additional binding sites located at two pyridine substituents, were treated with equimolar amounts of cyclopentadienylzirconium(IV) trichloride at room temperature. The X-ray data of the resulting coordination compounds 7a and 7b indicate the formation of five-membered metallacycles with one of the pyridine nitrogen atoms and the carbonyl oxygen atom acting as binding sites. For the complexation of ligand 1c, a different route was chosen: 1c was first deprotonated to yield the polymeric potassium compound 8 with a very complex substitution pattern based on O, N, and aromatic interactions with the potassium ions. Transmetalation of 8 with cyclopentadienylzirconium(IV) trichloride gave amidinate complex 9, which is dimeric in the solid state but exists in solution in equilibrium with monomeric species. After addition of methylaluminoxane (MAO), the three novel cyclopentadienylzirconium complexes 7a, 7b, and 9 gave active homogeneous single-site catalysts for the polymerization of ethylene. Of these three systems, 9/MAO turned out to be the most efficient one, showing activities 3-5 times higher than 7a/MAO and 7b/MAO, respectively, and producing polymers with a well-defined "monomodal" molecular weight distribution. An important feature of these materials is their broader distribution in molecular weight (PDI > 3), which is best seen in the products of reactions at 53 °C, with a "monomodal" main fraction at higher molecular weight and only small fractions of low molecular weight.

Full text of DOI:10.1021/acs.organomet.6b00240

Article
pubs.acs.org/Organometallics
Catalytically Active N‑Acylamidine−Zirconium Complexes: Synthesis,
Structures, and Application in Ethylene Polymerization
Thorsten Holtrichter-Roßmann,†,‡ Ina Hager,† Constantin-Gabriel Daniliuc,† Roland Frohlich,†
̈
̈
̈
Klaus Bergander,† Carsten Troll,∥ Bernhard Rieger,∥ Rene S. Rojas,*,§ and Ernst-Ulrich Wurthwein*,†
́
̈
†Organisch-Chemisches Institut der Universitat Munster, Corrensstrasse 40, D-48149 Munster, Germany
̈
̈
̈
‡Chemtura Organometallics GmbH, Ernst Schering Straße 14, D-59192 Bergkamen, Germany
§Departamento de Química Inorgan
́ ́
ica, Facultad de Química, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago-22, Chile
∥WACKER-Lehrstuhl fur Makromolekulare Chemie, Technische Universitat Munchen, Lichtenbergstraße 4, D-85747 Garching,
̈
̈
̈
Germany
S
* Supporting Information
ABSTRACT: Three novel N-acylamidines 1a−c with varying
steric bulk and substitution patterns were synthesized and
thoroughly characterized by X-ray diffraction. Compounds 1a
and 1b, which contain two additional binding sites located at
two pyridine substituents, were treated with equimolar
amounts of cyclopentadienylzirconium(IV) trichloride at
room temperature. The X-ray data of the resulting
coordination compounds 7a and 7b indicate the formation
of five-membered metallacycles with one of the pyridine
nitrogen atoms and the carbonyl oxygen atom acting as
binding sites. For the complexation of ligand 1c, a different
route was chosen: 1c was first deprotonated to yield the
polymeric potassium compound 8 with a very complex substitution pattern based on O , N, and aromatic interactions with the
potassium ions. Transmetalation of 8 with cyclopentadienylzirconium(IV) trichloride gave amidinate complex 9, which is dimeric
in the solid state but exists in solution in equilibrium with monomeric species. After addition of methylaluminoxane (MAO), the
three novel cyclopentadienylzirconium complexes 7a, 7b, and 9 gave active homogeneous single-site catalysts for the
polymerization of ethylene. Of these three systems, 9/MAO turned out to be the most efficient one, showing activities 3−5 times
higher than 7a/MAO and 7b/MAO, respectively, and producing polymers with a well-defined “monomodal” molecular weight
distribution. An important feature of these materials is their broader distribution in molecular weight (PDI > 3), which is best
seen in the products of reactions at 53 °C, with a “monomodal” main fraction at higher molecular weight and only small fractions
of low molecular weight.
and Kempe,12 and Jin13 describe the work in this challenging
field and deserve special attention.
INTRODUCTION
■
After more than 30 years, the development of new single-site
catalysts for olefin polymerization based on early transition
metals continues to be one the fields of highest interest for
industry and academia. In recent years, research has been
centered on robust and efficient precatalysts that can be
synthesized in few steps from common (not exotic) materials
with the purpose of making them commercially more attractive.
Precatalysts based on bi-, tri-, and tetradentate ligands in
which carbon, nitrogen, or oxygen atoms efficiently stabilize an
early transition metal are worth mentioning (Scheme 1). The
advantage of such ligands is the easy access and great control of
the steric and electronic environment of the atoms that
coordinate the metal, characteristics that are essential for having
access to thermally more stable and efficient catalysts in olefin
homo- and copolymerization reactions. Among others, re-
views1−4 and articles from the groups of Edelmann,5 Sita,6
Hagadorn,7 Eisen,8 Rausch,9 Green,10 Lappert,11 Kretschmer
A second strategy to achieve greater competitiveness of the
systems based on early transition metals has focused on
reducing or eliminating the dependence of these systems on the
use of methylaluminoxane (MAO) as an alkylating agent
responsible for the formation of the active species. For example,
the use of alkylated precursors and alkylation of halogenated
complexes prior to the addition of MAO have been high-impact
strategies for understanding the activation of the metal.
However, usually their viability is reduced by the high instability
of these species, which hinder the purification of the precatalyst
and consequently make the synthesis more expensive. These
strategies have been more successful with late transition metals,
which have resulted in well-known single-component cata-
Received: March 24, 2016
© XXXX American Chemical Society
A
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Scheme 1. Zirconium Complexes Formed by Bidentate N,N-
and N,N,O-Ligands from the Literature
Scheme 3. N,N- and N,O-Chelating Ligands and the η5
Coordination Compounds of Their Deprotonated Forms
sites considerably. For example, π conjugation over all five
atoms is present in both the neutral and anionic forms. In the
context of this work, the investigation of the influence of the
additional binding site at the central nitrogen atom is of
predominat interest. Neutral 2:1 N-acylamidine metal com-
plexes were reported by Ley and Werner as early as 1913.28
The constitutions of such coordination compounds were
established in 1969 as trans complexes by Oehme and
Pracejus.29 Bergman and co-workers published the synthesis
of a zirconocene complex featuring a doubly deprotonated N-
acylamidine ligand19 (Scheme 4). A first platinum(II) complex
lysts.14 In these studies, the incorporation of additional
functionalities into the ligand with conjugated structures has
a great impact as a strategy for improving the activation of the
metal center. Thus, as a result of geometric or affinity
limitations of the metal cation, these functionalities will remain
free in the structure of the complex. In this kind of complex,
binding of Lewis acids to those functionalities usually increases
the metal’s electrophilicity, activating it and thereby reducing its
dependence on the cocatalyst (MAO). Scheme 2 shows
examples of exocyclic, inter-, and intramolecular activation.
Scheme 4. N-Acylamidine Ligands in Zirconium Chemistry
Scheme 2. Recent Examples of Remote Activation by
Incorporation of Lewis Basic Functionalities into the
Ligands15 (LA = Lewis Acid)
of a chelating N-acylamidine was reported by Bokach,
Kukushkin, and co-workers.30 Our group has reported several
types of metal complexes formed from primary N-acylamidines
and copper(II) or palladium(II) salts.20−22 1,3,5-Triazapenta-
dienes D, in which the terminal oxygen atom of N-acylamidines
is replaced by an imino functionality, show similar coordination
properties (Scheme 3).31−33
In this article, we report on the synthesis and structural
properties of three novel zirconcene complexes and of a
potassium compound with secondary N-acylamidines acting as
ligands. The main emphasis of this study is directed toward an
investigation of the use of the zirconium coordination
compounds in metal-catalyzed polymerization of ethylene
(Scheme 4).
Furthermore, on the basis of this principle, this strategy is
suggested as an efficient route for phase transfer of the
precatalyst to an inorganic support whose surface contains
adequate Lewis acid sites to coordinate it. This will be of great
importance for later applications in heterogeneous catalysis, a
central step for commercial applications.16−19
N-Acylamidines 1/C (Scheme 3) are easily accessible
nitrogen-rich mono, bi-, and tridentate ligands for aggregation
and metal ion coordination.20−25 They may coordinate either as
neutral ligands or in deprotonated form. In comparison with β-
imino ketones A26 and β-diimines B27 and their metal
complexes, the central nitrogen atom at the 3-position
influences the electronic properties at the respective binding
RESULTS AND DISCUSSION
■
Syntheses and Structures of Ligands 1a−c. Three
different secondary N-acylamidines 1a−c were investigated
with respect to their ability to form catalytically active
zirconium coordination compounds for ethylene polymer-
ization. Two of them (1a and 1b) contain as additional
coordination sites two 2-pyridyl subunits and vary in bulkiness
at the N5 substituent. They were prepared from the
corresponding ethyl imidate 234 and 2-picolinic acid chloride
hydrochloride 3 to give ethyl N-acylimidate 4. Subsequent
B
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treatment with either 1-adamantylamine or aniline afforded N-
acylamidines 1a and 1b in 80 and 56% yield, respectively
(Scheme 5). The third N-acylamidine, 1c, has no other
Scheme 5. Synthesis of Ligands 1a−c
coordination sites besides the N-acylamidine subunit, and it is
characterized by a very bulky group at N5. It was prepared in
50% yield from amidine 5 by benzoylation using benzoyl
chloride (6). 5 was obtained from 2,6-dimethylaniline upon
deprotonation using nBuLi and benzonitrile.
The structures of 1a, 1b, and 1c in the solid state were
elucidated by X-ray crystallography. N-Acylamidine 1a adopts a
4-amino-1-oxa-3-azabuta-1,3-diene tautomeric form with a W-
shaped configuration having the two picolinyl subunits in endo
positions and the spacious adamantylamino group in the exo
position. The NH group enables the formation of linear head-
to-tail-chains within the crystal lattice by weak hydrogen
bonding to the carbonyl group of the next molecule (NH···O
distance = 2.140 Å; O−N distance = 3.014 Å; sum of van der
Waals radii = 3.14 Å) (Figure 1, top). In contrast, 1b shows a
tautomer with the proton attached to the central nitrogen atom
and a twisted U-shaped configuration with the phenyl group
bent significantly out of the molecular plane (Figure 1,
bottom). The distances from the proton at N3 to the picolinyl
nitrogen atoms amount to 2.230 and 2.400 Å, indicating
intramolecular hydrogen bonding (Figure 1, bottom). In 1c, a
third structural possibility, namely, another type of U-shaped
configuration with an intramolecular hydrogen bond between
O1 and N5 (O−N distance = 2.62 Å; H···O distance = 1.87(2)
Å) is realized (Figure 2), indicating the various structural motifs
possible for N-acylamidines due to hydrogen bonding and
configurational flexibility in the solid state, where crystal forces
may also have a profound influence on the structural properties.
Zirconium Complexes 7a, 7b, and 9. Treatment of
equimolar amounts of N-acylamidines 1a and 1b with
cyclopentadienylzirconium(IV) trichloride in dry tetrahydrofur-
an under argon for 12 h at room temperature yielded the novel
1:1 coordination compounds 7a and 7b in 88 and 92% yield,
respectively, as colorless solids. These complexes of the neutral
ligands were completely characterized by spectroscopic
methods as well as by X-ray diffraction analysis (Scheme 6).
Attempts to synthesize the related ionic complexes by
deprotonation of 1a and 1b with potassium hydride and
subsequent treatment with cyclopentadienylzirconium(IV)
Figure 1. Molecular structures of compounds 1a (top) and 1b
(bottom) in the solid state (X-ray diffraction, XP-plot, 30% probability
level).
Figure 2. Molecular structure of compound 1c in the solid state (X-ray
diffraction, XP-plot, 30% probability level).
trichloride did not lead to isolable compounds (compare,
however, to the reaction of 1c described below).
According to the X-ray data, in spite of the distinct
differences between the structures of ligands 1a and 1b, the
two coordination compounds 7a and 7b show very similar
structural properties, which are characterized by coordination
to the oxygen atom of the acyl moiety and the nitrogen atom of
the adjacent pyridine ring by the zirconium(IV) ion in its
C
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involving the N-acylamidine submoiety but not the pyridine
rings (for details, see the Supporting Information).
Scheme 6. Synthesis of Zirconium Complexes 7a and 7b
For the synthesis of coordination compounds of N-
acylamidine 1c, which in this case was used as an anionic
ligand, a different synthetic route was chosen. In a first step, 1c
was deprotonated using potassium hydride in dry THF for 4 h
to give 8 in a yield of 97% (Scheme 7) as a yellow solid. We
Scheme 7. Synthesis of Zirconium Complexes 9 and
Suggestions for Possible Monomers 9′, 9″, and 9‴ in
Solution
octahedral environment. The other coordination sites of the
amidine part and of the second pyridine subunit are not
involved in the bonding. The N-acylamidine ligand adopts a
slightly twisted sickle-shaped structure (Figure 3). The
were able to obtain single crystals suitable for X-ray diffraction
of the potassium compound 8 by slow diffusion of pentane into
a dichloromethane solution at room temperature. In the solid
state, compound 8 forms a complicated three-dimensional
polymeric network in which the N-acylamidine moieties are
interconnected by O and N coordination to the potassium ions
and also by strong π interactions of the η6, η2, and η1
coordination type to the aromatic rings of the ligands (Figure
4).
Transmetalation from potassium compound 8 using
cyclopentadienylzirconium(IV) trichloride in tetrahydrofuran
at room temperature for 4 h resulted in a complete
restructuring of the polymeric metal−organic network,
producing the 2:2 coordination compound 9 in 47% yield,
which is best described as an amidinate complex. Crystals
suitable for X-ray diffraction were obtained by slow diffusion of
pentane into a trichloromethane solution of 9 (Figure 5).
Compound 9 crystallizes in the asymmetric, chiral space group
P212121 with slightly different (monomer) subunits. The N-
acylamidine ligands are present in an almost planar W-shaped
configuration with the two hexacoordinate zirconium atoms
interconnecting both ligands via both nitrogen atoms and the
oxygen atom, forming four-membered Zr−N−C−N hetero-
cycles with additional contacts to the acyl oxygen atoms. The
1H NMR data obtained in CD2Cl2 solution from −90 to 25 °C,
however, show the presence of three independent main species,
Figure 3. Molecular structures of compounds 7a (left) and 7b (right)
in the solid state (X-ray diffraction, XP-plot, 30% probability level).
formation of the five-membered metallacycle resembles results
obtained by Sengupta and co-workers (no X-ray) for picolinoyl
hydrazone derivatives.35 The preference for the η4 structure
over other coordination modes is well in line with the results of
quantum-chemical density functional theory (DFT) calcula-
tions at the TPSS/def2-TZVP level of theory including the
Grimme dispersion energy GD3.36−38 Thus, the η4 structural
mode (Figure 3) is preferred by 10.7 kcal/mol (including zero-
point energy (ZPE) corrections) over an η6-N,O structure (see
Scheme 3), by 16.9 kcal/mol over an η3-N,O chelate, and by
28.1 kcal/mol over an η3-N,N chelate, the latter two both
D
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possibly involving the dimer 9 and the monomeric 1:1
coordination compounds 9′, 9″, and 9‴, as seen predominantly
from the signals of the 2,6-dimethylphenyl groups as well as
those of the cylopentadienyl subunits (Scheme 7). Also, 13C
NMR data support this observation (see the Supporting
Information for the spectra). Because of the low solubility of 9
in toluene-d8, however, high-temperature spectra could not be
measured. At present, we have no direct evidence for the
structures of the monomeric species possibly formed in
solution nor of the existence of a possible equilibrium. DFT
calculations at the TPSS/Def2-TZVP/GD3 level predict the
lowest relative energy for species 9′ (Erel = 0.0 kcal/mol,
including ZPE), followed by species 9″ (0.6 kcal/mol) and then
species 9‴ (2.1 kcal/mol). 9‴ resembles the nitrile adducts
described by Bergman and co-workers19 and may be under-
stood as a 1,3-diazabutadiene−zirconium complex. Dimeriza-
tion of 9′ in the gas phase is calculated to be exothermic by
−42.7 kcal/mol, indicating the enormous Lewis acidity of the
ZrCl2Cp unit.
A zirconium compound with an iminoquinolinol ligand,
published by Jin and co-workers13 shows N,N,O-binding sites
comparable to our structure 9 and was used successfully in
polymerization reactions of ethylene.
Figure 4. Schematic details (top) and X-ray structure (bottom) of the
asymmetric unit of compound 8, showing the arrangement around K2
in the solid state and indicating the various potassium interactions (X-
ray diffraction, XP-plot, 30% probability level; for the environment of
K1, see the Supporting Information).
Reactivity toward Ethylene. A series of ethylene
polymerization reactions were carried out using zirconium
compounds 7a, 7b, and 9 under specific reaction conditions in
the presence of MAO (10 wt % in toluene (“MAO 10T”),
Chemtura Organometallics GmbH) as a coactivator. The gel-
permeation chromatography (GPC) results are summarized in
Table 1. Reactions were performed in a 100 mL autoclave
reactor in toluene at an ethylene pressure of 178 psi and a [Al]/
[Zr−N-acylamidine] ratio of 500 or 1000 (determined in our
previous studies).15d Entry 1 corresponds to the reactivity
previously reported for [(NC-nacnac)-η5-cyclopentadienyl]
zirconium dichloride/MAO and is provided for comparison.15d
In all cases we observed the formation of high-molecular-weight
polyethylene (PE) with melting points in the range of 134−140
°C, indicating that the materials are highly linear.
Entries 2−5 show the results obtained using compound 9 at
reaction temperatures of 53 and 72 °C with Al/Zr ratios of
1000 and 500 (Figure 6). Comparison of entry 2 with entry
115d shows that the activity of the new systems is more than
twice as high as that of the reference under the same reaction
conditions, but the molecular weight of the resulting polymers
is lower and the polydispersity index (PDI) is broader (Mw/Mn
Figure 5. Molecular structure of compound 9 in the solid state (X-ray
diffraction, XP-plot, 30% probability level).
a
Table 1. Results of Selected Polymerization Experiments Using Catalysts 7a, 7b, and 9
b
c
d
e
f
f
g
entry
compd
amount of catalyst
Al/Zr ratio
temp
activity
Mn
Mw
PDI
Tm
1
2
ref 15d
6.8
6.8
6.8
6.0
6.0
7.5
7.5
7.5
6.5
6.5
1000
1000
500
75
72
71
53
53
72
53
53
55
54
845
1853
1235
1600
800
65
13
21
34
25
5
138
44
2.1
3.3
3.4
4.6
8.1
3.1
7.7
5.4
8.4
8.6
137
134
133
133
138
136
134
134
134
134
9
3
9
74
4
9
1000
500
154
200
16
5
9
6
7a
7a
7a
7b
7b
1000
1000
500
400
7
520
20
29
19
30
158
157
164
260
8
240
9
1000
500
323
10
258
a
Polymerizations were carried out in 30 mL of toluene at an ethylene pressure of 178 psi (12.3 bar). The cocatalyst was MAO. The reaction time was
b
c
10 min. Precatalysts were dissolved in 2 mL of dichloromethane prior to the addition of toluene. Zr content in μmol. [Al]/[Zr−N-acylamidine]
d
e
f
g
ratio. Reaction temperature in °C. Activity in kg of polymer (mol of Zr)−1 h−1. In units of 103 g/mol. Melting temperature in °C.
E
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Figure 6. GPC results for entries 2−5 in Table 1.
ratio = 3.3). Reduction of the Al/Zr ratio to 500 at 70 °C leads
to decreased activity and, as expected, to the polymer having a
higher molecular weight without a change in the PDI (entry 3).
It is important to remark that the activity is still greater than
that of the reference. Entries 4 and 5 indicate that at a lower
temperature (53 °C) compound 9 shows lower activity than at
70 °C (entries 2 and 3) and also results in products with broad
PDIs, especially at an Al/Zr ratio of 500.
Monomodal molecular weight distributions (MWDs) were
seen for all of the polymers collected (entries 2−5), but a small
shoulder corresponding to a low-molecular-weight fraction was
present when the temperature was decreased to ∼50 °C. At
present we assume that a second species may be produced in
low concentrations. The species responsible for the predom-
inant molecular weight fraction may involve alkylation by MAO
with coordination of the oxygen by zirconium in a monomeric
fashion in form of the six-membered ring B or the dimeric
structure C (Scheme 8). This coordination mode could
increase the steric bulk around the metal center, resulting in
PE with increased molecular weight. Another possible species
may involve the less crowded, monomeric four-membered ring
species A encountering coordination at oxygen by the
aluminum Lewis acid (Scheme 8), possibly leading to low-
molecular-weight polymers
On the other hand, as expected, the average molecular weight
decreased with increasing polymerization temperature. The
accepted explanation for this widely acknowledged phenomen-
on is that the activation energy for chain transfer is greater than
that for propagation.39 Concerning the effect of the cocatalyst
concentration (Al/Zr) on the MWD of PE obtained using
catalyst 9/MAO, it appears that the molecular weight of the
polymer decreases in the presence of higher amounts of
cocatalyst, possibly because the rate of the termination reaction
via transfer to the cocatalyst increases with increasing cocatalyst
concentration.
Entries 6−8 for 7a/MAO polymerizations and entries 9 and
10 for 7b/MAO polymerizations show that these combinations
also offer efficient ethylene polymerization sites. A general
comparison of those entries under reaction conditions similar
to those for the 9/MAO systems shows that the polymerization
activities are more than 3 times lower. The 7a/MAO systems
show a strong temperature dependence. Because of the better
performance found for precatalyst 7a at 53 °C, precatalyst 7b
was studied only by changing the Al/Zr ratio at that
temperature, at which 7a and 7b showed similar activities. In
terms of the molecular weights of the resultant PE, both
systems yield PE with a broad “monomodal” MWD with a
shoulder toward lower molecular weight. It is assumed that the
zirconium trichloride complexes (7a and 7b) could probably
provide multisite active species at this temperature, possibly
also by dehydrochlorination, which may be responsible for the
PEs with a broad distribution.
Scheme 8. Possible Activation Modes of Dimeric and
Monomeric Complexes 9 by Addition of MAO
CONCLUSION
■
We have reported the synthesis and full characterization of
three novel N-acylamidine ligands 1a−c with varying steric and
coordination properties. They were fully analytically and
spectroscopically characterized. According to the X-ray
diffraction data, these compounds adopt very different
conformations in the solid state and offer the possibility for
inter- (1a) and intramolecular (1b and 1c) hydrogen bonding.
Treatment of 1a and 1b with cyclopentadienylzirconium(IV)
trichloride provided access to the novel zirconium complexes
7a and 7b, in which the carbonyl oxygen atom and one of the
pyridine nitrogen atoms act as coordination sites. Coordination
F
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Multiple recrystallization from chloroform yielded colorless crystals.
Yield: 3.20 g (12.5 mmol, 25%), white solid. Mp: 157 °C. IR (ATR) v
(cm−1): 3300 (w), 3163 (w), 3105 (w), 3088 (m), 3059 (s, CHarom.),
3026 (m), 2976 (s, CHaliph.), 2955 (m), 2934 (m), 2897 (m), 2864
(m), 2774 (m), 2718 (m), 2600 (w), 2448 (w), 2336 (w), 2311 (w),
1960 (w), 1944 (w), 1813 (w), 1771 (w), 1622 (s), 1603 (vs, CN),
1661 (vs, CN), 1589 (vs), 1572 (vs), 1493 (s), 1481 (s), 1472 (s,
CCarom.), 1448 (vs, δ-CH2), 1391 (s), 1366 (s, δ-CH2), 1325 (s),
1310 (vs), 1279 (vs, COCether), 1223 (s), 1186 (m), 1169 (m), 1148
(vs), 1115 (s), 1061 (vs, COCether), 1024 (vs), 1001 (s), 988 (m), 970
(m), 922 (s), 891 (s), 881 (s), 847 (m), 829 (m), 795 (w), 779 (vs),
737 (vs), 712 (vs), 692 (vs), 671 (vs), 615 (m), 573 (m), 530 (s), 444
compound 9 was obtained from 1c after deprotonation using
potassium hydride as the base to give potassium salt 8 and
subsequent treatment with cyclopentadienylzirconium(IV)
trichloride. The X-ray data for 8 show interesting multiple
interactions of the potassium cation with the heteroatoms as
well as with the aromatic moieties. Complex 9 is best described
as a dimeric amidinate−zirconium coordination compound. In
solution, an equilibrium with a monomer is observed.
̃
The compounds 7a, 7b and 9 are new types of active
zirconium precursors that can be used to polymerize ethylene
to high molecular weight in the presence of low concentrations
of coactivators (Al/Zr ratios of 500 and 1000). On the basis of
the results obtained with precatalyst 9 and compared with those
previously obtained with the Cp-diimine complex with
carbonitrile functionality,14c we propose that the reactivity of
9 is also a result of coordination of a Lewis acid (MAO) to a
Lewis basic functionality, either a nitrogen atom of the
metallocycle or the oxygen atom of the carbonyl group, leading
to an η3-N,N ligand coordination mode with the zirconium
moiety. Since in this new system the position of the
functionalities (N and O) to which the Lewis acid can
coordinate (Scheme 8) is only two atoms away from the metal
center, the effect of the reduction in the electron density at the
zirconium center (by inductive effects) is greater, making the
metal center more electrophilic and consequently leading to
greater activity. On the other hand, although the activity seen at
an Al/Zr ratio of 500 at 53 or 70 °C is lower than that at a ratio
of 1000, these results are high compared with those for similar
systems reported in the literature, supporting the idea that
adduct formation plays an important role in these systems.
In the case of the precatalysts 7a and 7b activated with MAO,
the activities were much lower than that of 9. This may be
associated with the presence of three free basic functional
groups, which can be coordinated by MAO, reducing their
effectiveness per mole of cocatalyst. Furthermore, the
trihalogenated characteristic of these compounds generates
multiple species, which is probably responsible for the wide
molecular weight distributions of the polymers obtained.9,10
1
3
(m). H NMR (300 MHz, CDCl3): δ 1.50 (t, JHH = 7.1 Hz, 3H,
CH3), 4.56 (q, 3JHH = 7.1 Hz, 2H, CH2), 7.20 (ddd, 3JHH = 7.5, 4.8 Hz,
4JHH = 1.2 Hz, 1H, CHarom.), 7.30 (ddd, 3JHH = 7.5, 4.8 Hz, 4JHH = 1.2
Hz, 1H, CHarom.), 7.69−7.76 (m, 1H, CHarom.), 7.76−7.83 (m, 1H,
CHarom.), 7.92−7.97 (m, 1H, CHarom.), 8.22−8.26 (m, 1H, CHarom.),
8.27 (ddd, 3JHH = 4.7 Hz, 4JHH = 1.7, 0.9 Hz, 1H, CHarom.), 8.50 (ddd,
4
3JHH = 4.8 Hz, JHH = 1.7, 0.9 Hz, 1H, CHarom.). 13C NMR (75 MHz,
CDCl3): δ 14.2 (CH3), 64.3 (CH2), 123.5, 123.8, 125.4, 125.6, 136.7,
137.0 (CHarom.), 146.1 (i-Carom.), 148.4, 148.9 (CNarom.), 152.3 (i-
Carom.), 155.2 (CN), 176.2 (CO). MS (ESI): m/z 278 [M + Na]+,
256 [M + H]+. HRMS [M + H]+: calcd, 256.1081; found, 256.1080.
Formula: C14H13N3O2 (M = 255.10 g/mol). Anal. Calcd: C, 65.87; H,
5.13; N, 16.46. Found: C, 65.82; H, 4.84; N, 16.53. For details of the
X-ray diffraction study, see the Supporting Information.
General Procedure for the Synthesis of Compounds 1a and
1b. A solution of 1.0 equiv of compound 4 and 1.2 equiv of amine in
dry chloroform was heated under reflux for 6 h, washed three times
with water, and dried over magnesium sulfate. After evaporation of the
solvent, the raw product was purified by recrystallization.
N-((Adamant-1-ylamino)(pyridin-2-yl)methylene)-
picolinamide (1a). According to the general procedure, compound
1a was synthesized from 1-adamantanamine (770 mg, 1.0 equiv, 5.1
mmol) and compound 4 (1.02 g, 1.0 equiv, 4.0 mmol).
Recrystallization from a mixture of dichloromethane and pentane
gave the pure product. Yield: 1.18 g (3.28 mmol, 80%), white solid.
Mp: 144 °C. IR (ATR) v (cm−1): 3346 (m, NH), 2899 (m), 2857 (w),
̃
1630 (vs, CO/CN), 1607 (vs, CO/CN), 1582 (vs), 1568
(vs), 1526 (vs), 1435 (s), 1354 (s), 1346 (s), 1296 (s), 1279 (s), 1225
(s), 1128 (s), 1099 (s), 1070 (s), 1038 (s), 993 (s), 943 (s), 880 (s),
800 (s), 762 (s), 748 (vs), 718 (s), 675 (s), 658 (s), 619 (s), 598 (s),
567 (s), 554 (s), 546 (s), 540 (s), 530 (s). 1H NMR (600 MHz, C6D6,
299 K): δ 1.48 (m, J = 39.5, 11.8 Hz, 6H, CH2,adam.), 1.87 (s, 3H,
CHadam.), 2.27 (d, J = 2.4 Hz, 6H, CH2,adam.), 6.41 (ddd, J = 7.5, 4.7, 1.0
Hz, 1H, p-CHarom.), 6.53 (ddd, J = 7.5, 4.7, 1.2 Hz, 1H, p-CHarom.),
6.69 (td, J = 7.8, 1.8 Hz, 1H, o-CHarom.), 7.07 (td, J = 7.7, 1.8 Hz, 1H,
o-CHarom.), 7.43 (br s, 1H, NH), 7.81−7.89 (m, 1H, m-CHarom.), 8.14
(ddd, J = 4.7, 1.7, 0.9 Hz, 1H, NCHarom.), 8.33 (ddd, J = 4.7, 1.7, 0.9
Hz, 1H, NCHarom.), 8.51 (dt, J = 7.8, 1.0 Hz, 1H, m-CHarom.). 13C
NMR (150 MHz, C6D6, 299 K): δ 29.8 (3C, CHadam.), 36.6 (6C,
CH2,adam.), 41.2 (6C, CH2,adam.), 53.0 (i-Cadam.), 123.6, 124.5 (o-
CHarom.), 124.7, 124.9 (p-CHarom.), 136.4, 136.7 (m-CHarom.), 148.4,
148.8 (NCHarom.), 150.8 (i-Carom.), 154.1 (CN) 154.3 (i-Carom.),
172.1 (CO), (the CN signal could not be detected.) MS (ESI):
m/z 383 [M + Na]+, 361 [M + H]+. HRMS [M + H]+: calcd,
361.2023; found, 361.2026. Formula: C22H24N4O (M = 360.19 g/
mol). Anal. Calcd: C, 73.31; H, 6.71; N, 15.54. Found: C, 72.78; H,
6.70; N, 15.46. For details of the X-ray diffraction study, see the
Supporting Information.
EXPERIMENTAL SECTION
■
All procedures were carried out under purified argon using standard
Schlenk techniques. Compounds 7−9 were prepared in a glove box
under dry argon. All of the solvents were purified and dried by
standard methods.
Picolinoyl Chloride Hydrochloride (3). Picolinic acid (8.00 g,
65.0 mmol) was added to 80 mL (1.1 m) of thionyl chloride at 0 °C
(ice cooling). At first a green suspension was formed, which turned
into a clear red solution after 40 h of stirring at rt. The mixture was
poured into 30 mL of pentane and stirred for 30 min, and then the
solvent was separated from the violet solid by decantation. Solvent
residues were removed from the crude product in vacuo. Yield: 10.35 g
1
(58.5 mmol, 90%), violet solid. Mp: 225 °C (decomp). H NMR
(400.13 MHz, DMSO-d6): δ 8.09−8.12 (m, 1H, p-CHarom.), 8.35−8.37
3
3
(d, J = 7.7 Hz, 1H, o-CHarom.), 8.54−8.57 (t, J = 7.7 Hz, 1H, m-
3
CHarom.), 8.88−8.89 (d, J = 4.9 Hz, 1H, m-CHarom.), 11.54 (br, 1H,
NH). 13C NMR (75.47 MHz, DMSO-d6): δ 126.7 (Carom.), 129.6
(Carom.), 142.9 (i-Carom.), 144.8, 145.2 (Carom.), 162.1 (CO).
N-((Pyridin-2-yl)(phenylimino)methyl)-picolinamide (1b).
According to the general procedure, ethyl N-picolinoylpicolinimidate
(4) (1.62 g, 6.30 mmol) was dissolved in dichloromethane (70 mL).
After addition of a solution of aniline (0.59 g, 6.30 mmol) in
dichloromethane (20 mL), the reaction mixture was stirred at room
temperature for 20 h. The solvent was removed, and the product was
purified by column chromatography. Yield: 1.07 g (3.5 mmol, 56%),
yellow crystals. Rf: 0.13 (silica gel, 2:1 pentane/ethyl acetate + 3%
Ethyl N-Picolinoylpicolinimidate (4). To a stirred solution of
picolinoyl chloride hydrochloride (3) (8.90 g, 1 equiv, 50 mmol) and
17 mL of TEA (2.4 equiv, 120 mmol) in 100 mL of chloroform was
added ethyl 2-picolinimidate (2)34 (7.55 g, 1 equiv, 50 mmol) at 0 °C.
The reaction mixture was warmed to room temperature and stirred for
an additional 20 h. After removal of the ammonium salt by filtration,
the organic layer was washed two times with water and dried over
magnesium sulfate. Then the solvent was evaporated to dryness.
triethylamine). Mp: 128 °C. IR (KBr) v (cm−1): 3368 (s, NH), 3082
̃
(w), 3051 (m), 3015 (w), 2004 (w), 1977 (w), 1956 (w), 1879 (w),
G
DOI: 10.1021/acs.organomet.6b00240
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1701 (vs), 1638 (s, CCarom.), 1591 (s, CO/CN), 1566 (s, C
O/CN), 1543 (m), 1487 (vs), 1460 (vs), 1437 (vs), 1423 (vs),
1313 (m), 1296 (s), 1269 (s), 1231 (s), 1219(s), 1177 (s), 1146 (s),
1128 (s), 1092 (s), 1072 (m), 1061 (m), 1043 (s), 997 (s), 978 (m),
945 (m), 908 (m), 841 (s), 816 (m), 799 (s), 764 (s), 744 (s), 700
(vs), 631 (m), 615 (s), 581 (m), 546 (s), 532 (s), 503 (m), 476 (m).
1H NMR (300.13 MHz, CDCl3): δ 7.12 (br, 3H, CHarom.), 7.35−7.46
(m, 4H, CHarom.), 7.77−7.87 (m, 2H, CHarom.), 8.04−8.06 (m, 1H,
CHarom.), 8.28−8.33 (m, 1H, CHarom.), 8.59−8.61 (m, 1H, CHarom.),
8.66−8.69 (m, 1H, CHarom.), 11.36 (br, 1H, NH). 13C NMR (100.62
MHz/ CDCl3): δ 120.4 (2C, Carom.), 122.7, 122.9, 123.9, 125.0, 126.7
(Carom.), 128.8 (2C, Carom.), 136.9, 137.4 (Carom.), 146.7 (i-Carom.),
148.3 (2C, Carom.), 148.9, 152.7 (i-Carom.), 161.3 (CN), (the CN
signal could not be detected.). MS (ESI, methanol): m/z (%) 627
(100) [2M + Na]+, 325 (96) [M + Na]+, 303 (38) [M + H]+.
Formula: C18H14N4O (M = 302.33 g/mol). Anal. Calcd: C, 71.51; H,
4.67; N, 18.53. Found: C, 71.43; H, 4.69; N, 18.45. For details of the
X-ray diffraction study, see the Supporting Information.
(2,6-Dimethylphenyl)benzimidamide (5). To a solution of 2,6-
dimethylaniline (7.27 g, 1 equiv, 60 mmol) in dry THF (50 mL) was
added n-butyllithium (60 mmol, 1 equiv, 37.5 mL of 1.6 M solution in
n-hexane) at −78 °C. The reaction mixture was stirred for 1 h at room
temperature and cooled again to −78 °C. Then benzonitrile (6.19 g, 1
equiv, 60 mmol) was added slowly. After 20 h at room temperature,
the reaction was quenched with 50 mL of a 1:1 methanol/water
mixture, and 50 mL of chloroform was added. The layers were
separated, and the organic one was washed three times with water,
dried with magnesium sulfate, and evaporated to dryness. Compound
5 was purified by crystallization from diethyl ether and pentane. Yield:
the solvent was evaporated. A light-yellow solid was collected. For
purification the solid was suspended in diethyl ether, separated by
decantation, and freed from the solvent by evaporation. Then the solid
was washed two times with 3 mL of pentane, and a light-yellow solid
was isolated with minor impurities of diethyl ether and THF. Single
crystals of compound 8 suitable for X-ray diffraction analysis were
grown by slow diffusion of pentane into dichloromethane at room
temperature. Yield: 220 mg (0.61 mmol, 97%), yellow solid. 1H NMR
(600 MHz, THF-d8, 298 K): δ 2.18 (s, 6H, CH3), 6.53 (t, J = 7.4 Hz,
1H, p-CHanil.), 6.77 (d, J = 7.4 Hz, 1H, m-CHanil.), 7.11−7.19 (m, 3H,
CHarom.), 7.20−7.32 (m, 3H, CHarom.), 7.88 (d, J = 5.8 Hz, 1H, m-
CHarom.), 8.13 (d, J = 4.9 Hz, 1H, m-CHarom.). 13C NMR (151 MHz,
THF-d8, 298 K): δ 19.3 (2C, CH3), 120.4 (p-CHanil.), 127.4 (CHarom.),
127.6 (2C, m-CHanil.), 128.0 (CHarom.), 128.5 (2C, CHarom.), 128.6,
128.7 (CHarom.), 129.2 (2C, CHarom.), 129.3 (2C, CHarom.), 142.1 (2C,
i-C(CH3)), 143.1, 152.7 (i-Carom.), 163.1 (CN), 165.9 (CO).
Formula: C22H19N2OK (M = 366.11 g/mol). Anal. Calcd: C, 72.10; H,
5.23; N, 7.64. Found: C, 72.07; H, 5.25; N, 7.69. For details of the X-
ray diffraction study, see the Supporting Information.
Zirconium(IV) Coordination Compounds 7a, 7b, and 9. (N-
((Adamant-1-ylamino)(pyridin-2-yl)methylene)picolinamide)-
(cyclopentadienyl)zirconium(IV) Trichloride (7a). A solution of
compound 1a (155 mg, 1 equiv, 0.513 mmol) in THF (5 mL) was
added to CpZrCl3 (129 mg, 0.95 equiv, 0.491 mmol) dissolved in
THF (5 mL). The reaction mixture was stirred for 12 h, and the
resulting mixture was filtered, washed three times with 5 mL of ether,
and dried under vacuum. Single crystals of compound 1a suitable for
X-ray crystal structure analysis were grown by diffusion of cyclo-
pentane into dichloromethane at room temperature. Yield: 250 mg
1
40
1
(0.44 mmol, 88%), colorless powder. H NMR (600 MHz, CD2Cl2,
6.17 g (27.5 mmol, 46%; lit. 80% ), white solid. Mp: 104 °C. H
298 K): δ 1.75 (m, 6H, CH2,adam.), 2.21 (br s, 3H, CHadam.), 2.29 (t, J =
12.9 Hz, 6H, CH2,adam.), 6.31 (s, 5H, CHCp), 7.67 (ddd, J = 7.3, 4.7, 1.4
Hz, 1H, CHarom.), 7.72 (ddd, J = 7.6, 5.4, 1.4 Hz, 1H, CHarom.), 8.00
(m, 2H, CHarom.), 8.09 (td, J = 7.7, 1.6 Hz, 1H, CHarom.), 8.30 (ddd, J =
7.8, 1.3, 0.8 Hz, 1H, CHarom.), 9.70 (ddd, J = 5.4, 1.6, 0.8 Hz, 1H,
CHarom.), (the NH signal could not be detected). 13C NMR (151
MHz, C6D6, 298 K): δ 29.3 (3C, CHadam), 35.6 (3C, CH2,adam.), 40.5
(3C, CH2,adam.), 57.4 (i-Cadam.), 118.4 (5C, CCp), 125.8, 125.9, 128.2,
128.4 (CHarom.), 136.8 (i-Carom.), 139.1, 138.4 (CHarom.), 143.0 (i-
Carom.), 149.3 (NCHarom.), 149.4 (NCHarom.), 166.1 (CN), 167.6
(CO). Formula: C27H29Cl3N4OZr (M = 620.05 g/mol). Anal.
Calcd: C, 52.04; H, 4.69; N, 8.99. Found: C, 51.91; H, 4.78; N, 8.78.
For details of the X-ray diffraction study, see the Supporting
Information.
NMR (300 MHz, CDCl3): δ 2.16 (s, 9H, CH3), 4.61 (br s, 2H, NH2),
6.90−6.95 (m, 1H, CHarom.), 7.08 (d, JHH = 7.5 Hz, 2H, CHarom.),
3
3
4
7.41−7.52 (m, 3H, CHarom.), 7.91 (dd, JHH = 7.8 Hz, JHH = 1.4 Hz,
2H, CHarom.). 13C NMR (75 MHz, CDCl3): δ 17.8 (3C, CH3), 122.8
(CHarom.), 126.7 (2C, CHarom.), 128.2 (2C, CHarom.), 128.6 (2C,
CHarom.), 128.9 (2C, i-C−CH3), 130.5 (CHarom.), 135.6 (i-C−CN),
146.3 (i-C−NC), 153.2 (CN). Formula: C15H16N2 (M = 224.13
g/mol).
N-(((2,6-Dimethylphenyl)amino)(phenyl)methylene)-
benzamide (1c). To a solution of compound 5 (2.58 g, 1 equiv,
11.52 mmol) in THF (40 mL) was added a solution of benzoyl
chloride (6) (1.34 mL, 1 equiv, 11.52 mmol) in 15 mL of THF slowly
over a period of 1 h at 0 °C. The reaction solution was stirred for 40 h.
After filtration of the ammonium salt, 2.0 mL of chloroform was
added, and the mixture was washed three times with water. The
organic layer was dried over magnesium sulfate and evaporated to
dryness. Multiple recrystallizations from a mixture of THF and
pentane gave the pure product. Yield: 1.97 g (6.0 mmol, 50%), white
(N-((Phenylamino)(pyridin-2-yl)methylene)picolinamide)-
(cyclopentadienyl)zirconium(IV) Trichloride (7b). Compound 7b was
synthesized according to the procedure for compound 7a from
compound 1b (100 mg, 1 equiv, 0.332 mmol) and CpZrCl3 (86 mg,
0.98 equiv, 0.327 mmol). Single crystals of compound 7b suitable for
X-ray crystal structure analysis were grown by diffusion of cyclo-
pentane into dichloromethane at room temperature. Yield: 172 mg
solid. Mp: 117 °C. IR (ATR) v (cm−1): 2361 (w), 2340 (w), 1593 (s,
̃
CO/CN), 1549 (vs, CO/CN), 1472 (w), 1447 (m), 1418
(m), 1412 (m), 1406 (m), 1321 (vs), 1273 (m), 1196 (s), 1169 (m),
1157 (w), 1146 (w), 1078 (w), 1061 (m), 1020 (m), 999 (w), 968
(w), 926 (w), 914 (w), 824 (m), 791 (m), 772 (s), 746 (s), 719 (s),
689 (vs), 667 (w), 611 (w), 565 (m). 1H NMR (300 MHz, CDCl3): δ
2.13 (s, 6H, CH3), 6.89−6.99 (m, 2H, CHarom.), 7.26−7.59 (m, 7H,
CHarom.), 7.88 (t, 3JHH = 7 Hz, 1H, CHarom.), 8.40 (d, 3JHH = 7 Hz, 1H,
CHarom.), 8.63 (br s, 1H, CHarom.), 8.97 (br s, 1H, NH). 13C NMR (75
MHz, CDCl3): δ 18.30 (2C, CH3), 122.9 (2C, CHarom.), 126.0 (2C,
CHarom.), 127.7, 127.9, 131.5 (2C, CHarom.), 134.3, 135.8, 136.7 (i-
Carom.), 137.4 (2C, CHarom.), 148.0 (2C, CHarom.), 148.8, 149.6 (i-
Carom.), 152.2 (CN), 177.2 (CO). MS (ESI): m/z 351 [M + Na]+,
329 [M + H]+. HRMS [M + H]+: calcd, 329.1648; found, 329.1640.
Formula: C22H20N2O (M = 328.16 g/mol). Anal. Calcd: C, 80.46; H,
6.14; N, 8.53. Found: C, 80.17; H, 6.22; N, 8.43. For details of the X-
ray diffraction study, see the Supporting Information.
1
(0.31 mmol, 92%), colorless powder. H NMR (600 MHz, THF-d8,
298 K): δ 6.24 (br s, 4H, CHCp), 7.39 (t, J = 7.4 Hz, 1H, CHarom.),
7.48−7.50 (m, 2H, CHarom.), 7.73−7.78 (m, 5H, CHarom.), 8.05 (td, J =
7.7, 1.6 Hz, 1H, CHarom.), 8.08−8.12 (m, 2H, CHarom.), 8.20 (d, J = 7.8
Hz, 1H, CHarom.), 8.89−8.90 (m, 1H, CHarom.), 9.76 (d, J = 4.6 Hz, 1H,
CHarom.), (the NH signal could not be detected). 13C NMR (151
MHz, THF-d8, 298 K): δ 118.7 (5C, CCp), 124.9 (2C, CHarom.), 127.1,
128.0, 129.1 (2C, CHarom.), 129.3, 130.2 (2C, CHarom.), 136.9 (i-Carom.),
139.3, 139.8 (CHarom.), 145.9, 150.5 (i-Carom.), 150.6, 150.9
(NCHa r o m . ), 167.4 (CN), 171.4 (CO). Formula:
C23H19Cl3N4OZr (M = 561.97 g/mol). Anal. Calcd: C, 48.89; H,
3.39; N, 9.92. Found: C, 49.28; H, 3.27; N, 9.91. For details of the X-
ray diffraction study, see the Supporting Information.
(((((2,6-Dimethylphenyl)imino)(phenyl)methyl)imino)(phenyl)-
methoxy)(cyclopentadienyl)zirconium(IV) Dichloride (9). A solution
of potassium salt 8 (150 mg, 1 equiv, 0.37 mmol) in THF (5 mL) was
added to a mixture of CpZrCl3 (100 mg, 1 equiv, 0.38 mmol) in THF
(20 mL), and the resulting mixture was stirred at room temperature
for 4 h. The resulting yellow solution was filtered over Celite. The
Potassium N-(((2,6-Dimethylphenyl)imino)(phenyl)methyl)-
benzimidate (8). A solution of compound 1c (203 mg, 1 equiv, 0.62
mmol) and potassium hydride (37 mg, 1.5 equiv, 0.93 mmol) was
stirred in 10 mL of dry THF for 4 h. The reaction showed rapid gas
evolution. The slightly cloudy mixture was filtered through Celite, and
H
DOI: 10.1021/acs.organomet.6b00240
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
solvent was evaporated, and the solid was washed with diethyl ether.
Single crystals of compound 9 suitable for X-ray diffraction analysis
were grown by slow diffusion of pentane into a trichloromethane
solution at room temperature. Yield: 215 mg (0.18 mmol, 47%),
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1
yellow solid. H NMR (500 MHz, CD2Cl2, 223 K): δ 1.82 (s, 3H,
CH3), 1.91 (s, 3H, CH3), 2.19 (s, 12H, CH3), 2.45 (s, 3H, CH3), 2.58
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3
(t, JHH = 9.2 Hz, 1H, CHarom.), 8.72−8.76 (m, 1H, CHarom.
)
(unambiguous assignment was difficult because of overlap of
resonances and the complicated splitting patterns). 13C NMR (125.7
MHz, CD2Cl2, 223 K): δ 19.3 (CH3), 19.4 (CH3), 19.6 (4C, CH3),
20.7 (CH3), 21.5 (CH3), 118.3 (5C, CHCp), 119.0 (10C, CHCp), 119.1
(5C, CHCp), 125.3 (3C, CHarom), 126.6, 126.7, 127.2, 127.5 (CHarom),
127.7 (2C, CHarom), 127.8, 128.0, 128.1, 128.4, 128.5, 128.6, 128.8
(CHarom), 129.0 (2C, CHarom), 129.1, 129.5, 129.8, 129.9 (CHarom),
130.1 (2C, CHarom), 130.5 (2C, CHarom), 130.6, 131.1 (CHarom), 130.5
(2C, CHarom), 131.3 (i-Carom), 131.5 (i-Carom), 131.8 (2C, i-Carom),
132.1 (i-Carom), 132.3 (2C, i-Carom), 132.9 (i-Carom), 133.5 (2C,
CHarom), 134.9, 135.0 (3C, CHarom), 135.1, 135.9 (CHarom), 136.6 (i-
Cphen), 137.0 (3C, i-Cphen.), 142.9 (4C, i-C−CH3), 142.3 (2C, i-C−
CH3), 142.7 (2C, i-C−CH3), 170.5 (CN), 174.8 (C−O), 176.2 (2C,
CN), 180.0 (2C, C−O), 180.9 (CN), 185.2 (C−O). Formula:
C54H48N4O2Zr2Cl4·CHCl3 (M = 1221.98 g/mol). Anal. Calcd: C,
53.77; H, 4.02; N, 4.56. Found: C, 53.46; H, 3.98; N, 4.57. For details
of the X-ray diffraction study, see the Supporting Information.
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ASSOCIATED CONTENT
* Supporting Information
■
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S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00240.
Crystallographic data for 1a (CIF)
Crystallographic data for 1b (CIF)
Crystallographic data for 1c (CIF)
Crystallographic data for 7a (CIF)
Crystallographic data for 7b (CIF)
Crystallographic data for 8 (CIF)
Crystallographic data for 9 (CIF)
Crystallographic data for 4 (CIF)
NMR spectra, detailed X-ray data, GPC diagrams, and
quantum-chemical results (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: rrojasg@uc.cl.
*E-mail: wurthwe@uni-muenster.de.
■
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ACKNOWLEDGMENTS
■
This article is dedicated to Prof. Dr. Gerhard Erker on the
occasion of his 70th birthday. We are grateful for financial
support from the Deutsche Forschungsgemeinschaft (SFB
858), the Fonds der Chemischen Industrie (Frankfurt),
FONDECYT Chile, Project 1130077, ICM no. 120082
(Nucleus Millenium CPC), and the Alexander von Humboldt
Foundation auspices through the Experience Research Program
(to R.S.R.). R.S.R. is grateful to Prof. Dr. G. Erker for providing
laboratory facilities and reagents for the synthesis of the
compounds.
Valderrama, S.; Antinolo, M.; Carrillo-Hermosilla, A.; Fer
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nadez-Galan,
F. J. Mol. Catal. A: Chem. 2014, 391, 130−138.
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