Synthesis and characterization of group 4 fluorinated bis(amidinates) and their reactivity in the formation of elastomeric polypropylene

Article abstract of DOI:10.1021/om300702s

Bis(amidinate) titanium and zirconium bis(dimethylamido) complexes were prepared, and the dynamic behavior of the titanium complex containing perfluorinated amidinate ligand (11) was studied in detail. The variable-temperature NMR revealed the presence of

Full text of DOI:10.1021/om300702s

Article
pubs.acs.org/Organometallics
Synthesis and Characterization of Group 4 Fluorinated
Bis(amidinates) and Their Reactivity in the Formation of Elastomeric
Polypropylene
Tatyana Elkin, Sinai Aharonovich, Mark Botoshansky, and Moris S. Eisen*
Schulich Faculty of Chemistry, TechnionIsrael Institute of Technology, Haifa 32000, Israel
S
* Supporting Information
ABSTRACT: Bis(amidinate) titanium and zirconium bis-
(dimethylamido) complexes were prepared, and the dynamic
behavior of the titanium complex containing perfluorinated
amidinate ligand (11) was studied in detail. The variable-
temperature NMR revealed the presence of two species in
solution, in line with the different connection modes of the
ligand to the metal center. The resulting complexes were tested
as catalysts in the polymerization of propylene, and the resulting
polymers were consistent with elastomeric high-molecular-
weight atactic polypropylenes.
bis(phenylamidinate) titanium dichloride to the bis(p-tolylamidi-
nate) titanium dichloride complex, a polypropylene with much
higher molecular weight and a complex with a reduced catalytic
activity are obtained in the latter case, thus corroborating our
observations.9 This substituent effect is extraordinary in view of
the distant location of the para substituent from the active
metal center in the κ2-bonded amidinate, which precludes
significant steric, inductive, field, or resonance effects and
supports the observed ligand rearrangement (Scheme 1).
In addition to the benzamidinates, myriads of ancillary
ligands have attracted considerable attention in the last 25
years, and in combination with transition metals, designed
complexes have been obtained for the catalytic polymerization
of α-olefins.3,10 One type of these elegant ligands that has
attracted our attention is the phenoxyimine ligands and their
corresponding group 4 catalysts (FI catalysts). The use of these
complexes in the polymerization of ethylene containing a
fluorine atom at the ortho position of the N-aryl moiety
surprisingly led to a living polymerization.11 On the basis of
theoretical studies it was suggested that the chain termination is
avoided due to the preferential F···H interaction between the
fluorine atom of the ancillary ligand and a β-hydrogen of the
growing polymer chain.12 Interestingly, the suppression of a β-
hydride chain transfer was observed very recently in a Ni(II)
complex in the polymerization of ethylene due to a weak
fluorocarbon ligand−product interaction.12d
INTRODUCTION
■
In the last two decades, the search for new polymeric materials
and specially polyolefins with valuable physical and mechanical
properties has seen impressive growth. Considerable attention
was drawn to the design and synthesis of homogeneous
nonmetallocene group IV catalysts, which have reached a high
level of sophistication.1−3 Polypropylene is among the most
commercially important polyolefins, with a worldwide
production of ca. 4 × 107 tons/y, about 6 kg per capita in
2006, with an additional 17% growth expected until 2020.1
Catalysts generated from early-transition-metal complexes
containing the amidinate ligands [NR1CR2NR3]− have been
found to be active in the polymerization of α-olefins. The
amidinates are attractive ancillary ligands due to their rich
coordination chemistry, their facile synthesis, and the
opportunity to tune their electronic and steric properties.4−6
We have shown that when the bis(p-arylamidinate) group 4
dichloride/dialkyl complexes are activated by methylaluminox-
ane (MAO), the resulting active species polymerize propylene,
affording a mixture of two polypropylene fractions: a minor
isotactic fraction and a nonstereospecific elastomeric fraction.
These two fractions are obtained by a bis(p-arylamidinate)
group 4 cationic monoalkyl complex and a corresponding
cationic mono(p-arylamidinate) group 4 complex, respectively.7
Mechanistic studies have suggested that the mono(p-
arylamidinate) titanium trialkyl complex is obtained via the
dynamic behavior of the arylamidinate ligands, resulting in the
migration of one of the two amidinate ligands to MAO.7a,8 This
new highly coordinatively unsaturated complex responds to the
ligand migration by rearranging the additional (p-arylamidi-
nate) ligand, resulting in the reattachment of the ligand to the
metal via one nitrogen atom and a π-bonded phenyl ring
(Scheme 1). We have shown that, when comparing the simple
Hence, it was conceptually interesting to study if such a
unique interaction can also be applied to fluorinated amidinate
ligands. We present herein the preparation of various Ti and Zr
complexes decorated with several N-fluoroaryl amidinates, their
Received: July 25, 2012
© XXXX American Chemical Society
A
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Scheme 1. Active Species Formed during the Activation of Titanium Bis(p-arylamidinate) Dichloride Complex with MAO
solution and solid-state structures, and their propylene
polymerization behavior.
imidazole 6 (70% isolated yield) were obtained (Scheme 2)
in the condensation of pentafluoroaniline with isobutyric acid,
in the presence of PPSE.13 Interestingly, we have found that the
order of addition of the reagents to the reaction mixture has a
dramatic influence on the obtained ratio for the two products. If
the pentafluoroaniline is added first to the PPSE, the imidazole
6 is the only observed product, isolated in 96% yield. However,
if the isobutyric acid is added first to the PPSE, followed by the
addition of the pentafluoroaniline, a mixture of the amidine 5
and the imidazole 6 is obtained. Addition of a slight excess of
isobutyric acid (beyond 1 equiv) results in the production of
the corresponding amide and the imidazole without formation
of the amidine. These results indicate that the amide can be
attacked by the amine either at the carbonyl group, affording
the amidine 5, or at the ortho position of the C6F5 ring,
removing a fluorine atom followed by an intramolecular ring
closure to form the imidazole 6. Interestingly, a mixture of the
amidine with PPSE does not produce imidazole.
Perspective views of the molecular structures of the amidines
3−5 and the corresponding imidazole 6 are presented in
Figures 1−4, respectively. Notably, the methyl groups of the
isopropyl moiety are disposed in the solid structure to minimize
interactions with any nearby fluorine atoms. In addition, the
isopropyl group forms a dihedral angle with the N−C−N plane,
C15−C14−C13−N2 = 57.79 and 50.28° and C16−C14−
C13−N2 = 68.34 and 72.84°, for ligand 5 and compound 6,
respectively, similarly to the arylamidinates (vide infra). As can
be observed for all the amidine ligands, the NH−C(central)
and the NC bond lengths and the NC−NH bond of all of
the amidine ligands are alike, exhibiting no major differences.
Several titanium and zirconium complexes were prepared by
the reaction of 1 equiv of either Ti(NMe2)4 or Zr(NMe2)4
metal precursor with 2 equiv of the corresponding neutral
amidines (eq 2). For the corresponding titanium complexes (7,
9, and 11) and the zirconium complex (12) X-ray crystallo-
RESULTS AND DISCUSSION
■
We start the presentation of the results by disclosing why the
specific ligands were designed for this study. We have recently
shown (Scheme 1)9 that in the cationic mono aryl/phenyl
amidinate complexes the aromatic ring will rearrange,
producing a κ6 coordination structure and any substituent at
the para position will interact with a growing polymer chain,
retarding a chain transfer and allowing higher molecular
weights (the bigger the substituent, the larger the molecular
weight of the obtained polymer). This is a steric effect of the
para substituent exhibiting a linear free energy relationship with
the Taft parameter. Hence, to eliminate any π bonding of the
aryl/phenyl amidinate ring while keeping the steric environ-
ment similar to that of the arylamidinates, the ligands were
prepared with an isopropyl moiety, instead of the aryl group, at
the amidine carbon substituent. In addition, a range of
differently fluorinated aromatic rings were used as the
amidinate nitrogen substituents. The amidines were synthesized
using polyphosphoric acid trimethylsilyl esters (PPSE) as the
condensation reagent (eq 1).13
Our first attempts to prepare the ligand containing the
pentafluorophenyl ring by the condensation of the aniline with
the corresponding acyl chloride and the concomitant
condensation of the resulting amide with an additional 1
equiv of pentafluoroaniline, led to very low yields (2−5%) of
the desired amidine 5. Full conversion toward the desired
amidine 5 (30% isolated yield) and the corresponding
B
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Scheme 2. Synthesis of the Bis(pentafluorophenyl) Isopropyl Amidinate Ligand 5 and the Corresponding Benzimidazole 6
Figure 1. Mercury diagram of the molecular structure of amidine 3
Figure 2. Mercury diagram of the molecular structure of amidine 4
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): C(11)−N(1) =
1.374(4); C(11)−N(2) = 1.268(4); C(9)−N(1) = 1.408(4); C(15)−
N(2) = 1.422(4); C(1)−F(1) = 1.380(4); C(23)−F(2) = 1.356(4);
N(2)−C(1)−N(1) = 120.9(3).
and (25% probability ellipsoids). Hydrogen atoms are omitted for
clarity. Representative bond lengths (Å) and angles (deg): C(1)−
N(1) = 1.362(2); C(1)−N(2) = 1.287(2); C(11)−N(1) = 1.416(2);
C(5)−N(2) = 1.418(2); C(14)−F(2) = 1.366(3); C(8)−F(1) =
1.360(2); N(2)−C(1)−N(1) = 119.85(16).
graphic studies were performed, and the Mercury diagrams are
presented in Figures 5−8, respectively.
1.889(5) and 2.031(3) Å for complexes 11 and 12,
respectively) are shorter, as expected, than the M−N bond
lengths of the coordinated amidinate (2.1018(18), 2.1769(19),
2.091(2), and 2.222(2) Å for complex 7, 2.120(5), 2.214(5),
2.105(5), and 2.234(5) Å for complex 9, 2.124(6) and 2.247(5)
Å for complex 11, and 2.242(3) and 2.341(3) Å for complex
12, respectively). These latter M−N bond lengths are
comparable to those found in previously reported amidinate
complexes.14
In the solid state, complexes 7, 9, 11, and 12 all exhibit C2
symmetry, where the metal is situated in a pseudo-octahedral
environment that is formed by four nitrogen atoms from the
amidinate ligands and two nitrogen atoms from the
dimethylamido groups. In these complexes, the dimethylamido
groups are disposed in a cis position, and the M−N bond
lengths of the dimethylamido moieties (1.893(2) and 1.899(2)
Å for complex 7, 1.893(5) and 1.898(5) Å for complex 9, and
C
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Figure 3. Mercury diagram of the molecular structure of the amidine 5
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): C(13)−N(1) =
1.277(3); C(13)−N(2) = 1.376(3); C(1)−N(1) = 1.399(3); C(7)−
N(2) = 1.404(3); C(8)−F(6) = 1.343(4); C(12)−F(10) = 1.337(4);
C(2)−F(1) = 1.345(1); C(6)−F(5) = 1.349(3); N(2)−C(13)−N(1)
= 117.8(2).
Figure 5. Mercury diagram of the molecular structure of complex 7
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): Ti(1)−N(1) =
2.1018(18); Ti(1)−N(2) = 2.1769(19); Ti(1)−N(5) = 1.893(2);
Ti(1)−N(4) = 2.091(2); Ti(1)−N(3) = 2.222(2); Ti(1)−N(6) =
1.899(2); C(1)−N(1) = 1.340(3); C(1)−N(2) = 1.312(3); C(17)−
N(3) = 1.308(3); C(17)−N(4) = 1.330(3); N(2)−Ti(1)−N(1) =
60.92(7); N(1)−Ti(1)−N(5) = 94.84(8); N(4)−Ti(1)−N(6) =
96.97(10); N(1)−Ti(1)−N(2)-C(1) = 0.01; N(4)−Ti(1)−N(3)−
C(17) = 2.09.
Figure 4. Mercury diagram of the molecular structure of the amidine 6
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): C(13)−N(1) =
1.397(3); C(13)−N(2) = 1.297(3); C(1)−N(1) = 1.412(3); C(7)−
N(1) = 1.388(3); C(8)−F(6) = 1.353(3); C(11)−F(9) = 1.348(3);
C(2)−F(1) = 1.334(3); C(6)−F(5) = 1.335(3); N(2)−C(13)−N(1)
= 112.4(2).
Figure 6. Mercury diagram of the molecular structure of complex 9
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): Ti(1)−N(1) =
2.214(5); Ti(1)−N(2) = 2.120(5); Ti(1)−N(5) = 1.893(5); Ti(1)−
N(4) = 2.105(5); Ti(1)−N(3) = 2.234(5); Ti(1)−N(6) = 1.898(5);
C(1)−N(1) = 1.322(7); C(1)−N(2) = 1.344(7); C(17)−N(3) =
1.334(7); C(17)−N(4) = 1.350(7); N(2)−Ti(1)−N(1) = 60.55(17);
N(1)−Ti(1)−N(5) = 91.3(2); N(3)−Ti(1)−N(6) = 103.6(2);
N(1)−Ti(1)−N(2)−C(1) = 2.23; N(4)−Ti(1)−N(3)−C(17) = 3.07.
The shortest distances between an o-F atom and the metal
center in complexes 11 and 12 exceed the sum of their
D
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ligand mechanism) is operative even at low temperatures.
Interestingly, for the rest of the complexes the same rapid
dynamic behavior was also observed at low temperatures. From
the crystal structure it is apparent that a significant barrier to
the rotation of the pentafluorophenyl ring exists in both
complexes, since the overlap of the o-F with the methyl groups
of the isopropyl moiety; however, this interaction is observed
only for complex 11. For complex 11, a very informative and
1
complex comprehensive spectrum in both H and 19F NMR is
obtained at low temperature. The dynamic process for complex
11 was studied with variable-temperature 19F and 1H
measurements, and the respective spectra are presented in
Figures 9 and 10.
The outcome of the variable-temperature NMR analysis (1H,
19F) indicates that only two species (11A,B) are present in
solution and their ratio, in addition to the different temperature
measurements, is kept constant (Figures 9−11 and Table 1).
Complex 11A shows a dynamic behavior as a function of the
temperature, whereas complex 11B exhibits no dynamic
behavior in solution over the examined temperature range.
From the line broadening analysis, complex 11A exhibits the
dynamic processes (i) rotation of the methyl groups within
each isopropyl group and (ii) dynamic equilibration of the
isopropyl groups between the two amidinate ligands within the
complex with the thermodynamic value measured of ΔH⧧ =
13.4(0.4) kcal mol−1 (see the corresponding Eyring plot in the
Supporting Information), together with the equilibration of the
perfluorinated aromatic rings. Hence, it seems plausible that
complex 11A has one open ligand (κ1) and one closed chelated
ligand (κ2), whereas in complex 11B both ligands are
connected to the metal center in a κ2 fashion (at high
temperature a broadening of all the spectra lines is appreciable,
suggesting a high energy of activation toward the interconver-
sion of 11A to 11B). The two complexes 11A,B were
Figure 7. Mercury diagram of the molecular structure of complex 11
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): Ti(1)−N(1) =
2.124(6); Ti(1)−N(2) = 2.247(5); Ti(1)−N(3) = 1.889(5); C(13)−
N(1) = 1.356(8); C(13)−N(2) = 1.289(8); F(10)−Ti(1) = 4.546;
N(2)−Ti(1)−N(1) = 59.5(2); N(2)−Ti(1)−N(3) = 90.90(2);
N(2)−Ti(1)−N(1)−C(13) = 4.78.
1
characterized by H and 19F COSY at 227 K (Figures 11 and
12) and also at 365 K (see the Supporting Information). It is
important to point out that the presence of the symmetric C2v
complex 11, having two κ1 chelating ligands, was not observed
in solution even when one crystal was dissolved (based on the
1
1H and 19F NMR correlating data). In the H NMR at 365 K
the signals were broadened, and no final product (coalescence
process/correlation among the two complexes) was obtained.
Heating beyond 365 K induces a rapid decomposition of the
complexes. It is very interesting to follow the signals of the
isopropyl moieties in both complexes, showing a nice crossover
of the signals, which are also verified in the COSY spectra at the
different temperatures. The ratio among the complexes 11A,B
is maintained constant, 70:30, respectively, regardless of the
Figure 8. Mercury diagram of the molecular structure of complex 12
(25% probability ellipsoids). Hydrogen atoms are omitted for clarity.
Representative bond lengths (Å) and angles (deg): Zr(1)−N(2) =
2.242(3); Zr(1)−N(3) = 2.341(3); Zr(1)−N(1) = 2.031(3); C(1)−
N(2) = 1.351(4); C(1)−N(3) = 1.331(4); F(5)−Zr(1) = 3.947;
N(2)−Zr(1)−N(3) = 56.78(9); N(2)−Zr(1)−N(1) = 94.65(11);
N(2)−Zr(1)−N(3)−C(1) = 6.62.
1
temperature, as was confirmed by both the H and 19F NMR
(see the integration of signals in Table 1). The variable-
temperature 19F NMR spectra were very informative, and full
assignment of the two complexes was possible via their
chemical shifts, 2D correlations at the different temperatures,
and the corresponding integrations. It is important to point out
that two possible geometrical isomers (cis and trans isomers)
could be responsible for the signals obtained in complex 11A as
presented in Figure 11. Our attempts to obtain crystals of just
11A were unsuccessful; however, for the trans isomer a high
energy of activation toward its equilibration to complex 12
would be expected.
corresponding van der Waals radii (4.546 Å in complex 11 and
3.947 Å in complex 12),15 indicating the absence of any notable
interaction between the metal center and the F atoms of the
fluorinated aryl substituents.
Despite their similar solid-state structures, complexes 11 and
12 display a completely different behavior in solution. In the
19F NMR of complex 12, only three signals are observed, and in
1
the H NMR only one set of signals corresponding to the
isopropyl moieties is detected. The persistence of these
observations even at low temperatures (−50 °C precipitating
temperature of the complex) indicates that a rapid dynamic
behavior of the complex 12 (from Δ to Λ via an open−close
All of the complexes were tested as suitable catalysts for the
polymerization of propylene. Catalytically active species were
generated by the reaction of the complexes with methyl-
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Figure 9. Variable-temperature 19F NMR spectra for complex 11. The labels in the spectrum correspond to the different fluorine atoms as defined in
Figure 11.
1
Figure 10. Variable-temperature H NMR for complex 11. The labels in the spectrum correspond to the different atoms in the corresponding
complexes as defined in Figure 11.
alumoxane (MAO) in a 1:1000 ratio in toluene. The
polymerizations were performed with an excess of propylene
at room temperature for 3 h (Table 2). The precatalyst 11
exhibits an activity of 97 kg mol−1 h−1 at room temperature,
while complex 12 showed a similar reactivity of 113 kg mol−1
h−1, but only at elevated temperature (60 °C), since at room
temperature no polymerization was obtained. Unlike the case
for the benzamidinates, no stereospecific fraction was obtained,
F
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Figure 11. Assignment of fluorine atoms in 11A (both plausible isomers) and 11B at 227.2 K.
with a higher molecular weight as compared to that for complex
7, presumably due to chain transfer suppression, whereas the p-
fluorine complex 9 induces a higher insertion rate as compared
to complex 7. The most interesting result is obtained with the
fluoronaphthyl complex 10, which exhibits low activity but
affords high-molecular-weight polymer, suggesting that the
interaction of the fluorine atom with the metal center or the
growing chain may be impeding chain termination as well as
monomer insertion.
Table 1. Integration of H and F (Ortho) Atoms of Species
11A,B at the Lowest and the Highest Temperatures with No
Coalescences
a
1H NMR
19F NMR
temp
(K)
group integration
group
integration
227.2 A(CH),
B(CH)
1.00, 0.31 B(Fd), B(Fa)
0.628, 0.654
A(CH3),
B(CH3)
3.00, 1.84 A(Fa), A(Fb),
A(Fe), A(Fh)
1.03, 1.00, 1.03,
1.01
CONCLUSIONS
365.3 A(CH),
B(CH)
1.00, 0.35 B(ortho) left,
B(ortho) left
1.00, 1.01
■
In this work we reported a series of new fluorinated titanium
and zirconium bis(amidinates). Variable-temperature H NMR
A(CH3),
B(CH3)
5.87, 1.94 A(ortho)
3.15
1
revealed the dynamic behavior of the titanium complex 11A
with rearrangement of the ligand about the metal center. The
dynamic behavior of the resulting fluorinated zirconium and
titanium bis(amidinates) leads to the complete loss of C2
symmetry followed by loss of stereospecificity in the polymer-
ization of propylene. Substitution with fluorine atoms on
different positions of the N-aryl substituent revealed that
fluorine atoms at the meta position suppress termination of the
growing chain, while p-F accelerates the insertion of monomer.
a
The legends at the spectrum correspond to the different atoms in the
corresponding complexes as defined in Figure 11.
presumably due to the dynamic behavior of the complex 11A
forming various active species, as corroborated by the large
molecular weight distribution of the obtained polymers. The
mmmm pentad frequency (6−7%) was found in all cases, and in
some cases the polymers were obtained as elastomeric
materials, due to their molecular weight.16 The polymers that
were obtained with complex 12 were atactic, and due to their
low molecular weight, the consistency of these resulting
materials was a tacky liquid. End group analysis has revealed
that β-H-elimination/transfer to a monomer is responsible for
the chain transfer process.
EXPERIMENTAL SECTION
■
All manipulations of air-sensitive materials were carried out with the
rigorous exclusion of oxygen and moisture in oven-dried or flamed
Schlenk-type glassware on a dual-manifold Schlenk line or interfaced
to a high-vacuum (10−5 Torr) line or in a nitrogen-filled glovebox (M.
Braun) with a medium-capacity recirculator (1−2 ppm O2). Argon and
nitrogen were purified by passage through a MnO oxygen removal
Interestingly, introduction of a fluorine atom at the meta
position in complex 8 causes the formation of polypropylene
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1
Figure 12. 19F COSY (left) and H COSY (right) of complex 11 at 227.2 K.
column and a Davison 4 Å molecular sieve column. Analytically pure
CH2Cl2 and CDCl3 were used without any purification, and all other
solvents (toluene, hexane, toluene-d8, C6D6) were dried over Na/K
alloy, degassed by three freeze−pump−thaw cycles and vacuum-
transferred prior to use. The final products 1−6 are air stable and do
not need to be stored under inert conditions. All anilines and
hexamethyldisiloxane (TMS2O) were purchased from Sigma-Aldrich
and used without further purification. Ti(NMe2)4, Zr(NMe2)4,17 and
8-fluoronaphthalen-1-ylamine18 were prepared by literature proce-
dures. NMR spectra were recorded on a Bruker Avance 300
spectrometer. NMR spectra for variable-temperature experiments
were recorded on a Bruker Avance 600 spectrometer; the temperature
was calibrated with MeOH (low temperature) and ethylene glysol
(high temperature). 1H and 13C chemical shifts are referenced to
internal solvent resonances and reported relative to TMS. 19F chemical
shifts were referenced according to IUPAC recommendations.19 The
experiments with metal complexes were conducted in Teflon-sealed
NMR tubes (J. Young) after the preparation of the sample under
Table 2. Propylene Polymerization Results with the
Bis(amidinate)dimethylamido Titanium and Zirconium
Complexes 7−12
a
b
precat.
activity
Mw
PD
Ri
Rt
c
11
7
97.0
33.5
35.0
63.2
1.7
251 000
8.3
3.9
3.9
3.7
2.6
4.4
4.5
2.4 × 10−3
1.3 × 10−3
1.3 × 10−3
2.5 × 10−3
5.2 × 10−5
1.3 × 10−4
3.1 × 10−3
3.4 × 10−5
3.9 × 10−5
1.5 × 10−5
4.7 × 10−5
6.6 × 10−8
2.7 × 10−6
1.3 × 10−3
55 000
142 500
82 000
82 000
91 500
4 500
8
9
10
d
10
4.9
d
12
113.0
a
Reaction conditions: catalyst:MAO 1:1000 in 6 mL of toluene, 30 mL
b
of propylene, room temperature, 3 h. Activity in kg (mol of
c
d
catalyst)−1 h−1. Bimodal signal in GPC analysis. Polymerization
temperature 60 °C.
Table 3. Crystallographic Data for Amidine Ligands 3−5 and Imidazole 6
amidine 3
amidine 4
amidine 5
imidazole 6
empirical formula
formula wt
T (K)
C16H16F2N2
274.31
C24H20F2N2
374.42
C16H8F10N2
418.24
C16H7F9N2
398.24
293(2)
293(2)
293(2)
293(2)
λ (Å)
0.710 73
triclinic
0.710 73
triclinic
0.710 73
monoclinic
P21/c
0.710 73
monoclinic
C2/c
cryst syst
space group
a (Å)
P1
̅
P1
̅
8.579(2)
11.799(2)
14.702(3)
101.20(3)
90.71(3)
91.07(3)
1459.4(5)
4
11.659(2)
11.707(3)
15.017(3)
93.24(2)
112.97(3)
100.56(3)
1993.4(7)
4
8.029(2)
12.698(2)
16.824(3)
16.809(3)
16.277(3)
11.616(2)
b (Å)
c (Å)
α (deg)
β (deg)
97.21(3)
99.09(3)
γ (deg)
V (Å3)
1701.7(6)
4
3138.2(10)
8
Z
ρ (g/cm3)
μ(Mo Kα) (mm−1
1.248
1.248
1.633
1.686
)
0.092
0.086
0.175
0.176
R1, wR2 (I >2σ(I))
R1, wR2 (all data)
GOF on F2
0.0536, 0.1350
0.0831, 0.1482
1.052
0.0750, 0.1898
0.1616, 0.2191
1.051
0.0489, 0.1258
0.1113, 0.1494
0.915
0.0457, 0.1155
0.0936, 0.1322
0.94
F(000)
576
784
832
1584
θ range for data collecn (deg)
no. of collected/unique rflns
largest diff peak, hole (e/Å3)
2.03−25.02
14 056/5121
0.131, −0.167
1.65−24.96
15 985/6911
0.449, −0.185
2.44−25.86
12 426/3166
0.268, −0.215
2.35−25.01
2769/2769
0.164, −0.132
H
dx.doi.org/10.1021/om300702s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Crystallographic Data for Complexes 7, 9, 11, and 12
complex 7
complex 9
complex 11
complex 12
C18H13F10N3Zr0.50
empirical formula
formula wt
T (K)
C36H46N6Ti
610.69
C54H63F6N9Ti1.50
1023.98
C36H26F20N6Ti
970.53
506.92
293(2)
240(2)
240(2)
240(2)
λ (Å)
0.710 73
monoclinic
P21/c
0.710 73
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
C2/c
cryst syst
space group
a (Å)
triclinic
P1
̅
16.370(3)
10.527(2)
20.018(4)
11.411(2)
19.071(4)
26.934(5)
101.71(3)
97.29(3)
11.929(2)
17.908(3)
18.271(4)
12.079(2)
17.913(4)
18.634(4)
b (Å)
c (Å)
α (deg)
β (deg)
98.81(3)
98.15(3)
98.97(3)
γ (deg)
100.20(3)
5567.4(18)
4
V (Å3)
3408.9(11)
4
3863.7(12)
4
3982.6(14)
8
Z
ρ (g/cm3)
μ(Mo Kα) (mm−1
1.19
1.222
1.668
1.691
)
0.284
0.283
0.356
0.407
R1, wR2 (I >2σ(I))
R1, wR2 (all data)
GOF on F2
0.0509, 0.1310
0.0736, 0.1398
1.056
0.0866, 0.2483
0.1403, 0.2695
0.949
0.0754, 0.1504
0.2288, 0.1926
0.846
0.0428, 0.0920
0.0727, 0.1011
0.928
F(000)
1304
2148
1944
2016
θ range for data collecn (deg)
no. of collected/unique rflns
largest diff peak, hole (e/Å3)
2.06 to 25.02
19 688/5917
0.483, −0.341
1.70 to 25.02
70 805/19 135
0.923, −0.407
2.07 to 25.00
20 758/3242
0.519, −0.359
2.05 to 25.05
19 661/3497 (R(int) = 0.098)
0.268, −0.871
1
anaerobic conditions, with dried toluene-d8 or C6D6. The molecular
weights and polydispersities of the polymers were determined by the
gel permeation chromatography (GPC) method on a Varian PL-GPC
220 instrument using 1,2,4-trichlorobenzene as the mobile phase at
160 °C. Polystyrene standards were used for the standard calibration
curve of GPC.
X-ray Crystallographic Measurements. The single-crystal
material was immersed in Paratone-N oil and was quickly fished
with a glass rod and mounted on a Kappa CCD diffractometer under a
cold stream of nitrogen. Data collection was performed using
monochromated Mo Kα radiation using φ and ω scans to cover the
Ewald sphere.20 Accurate cell parameters were obtained with the
amount of indicated reflections (Tables 3 and 4).21 The structure was
solved by SHELXS-97 direct methods22 and refined by the SHELXL-
97 program package.23 The atoms were refined anisotropically.
Hydrogen atoms were included using the riding model. Software
used for molecular graphics: Mercury 2.4. The cell parameters and
refinement data are presented in Tables 3 and 4.
1 (amidine): yield 85.2%; H NMR (CDCl3) δ 7.27−7.163 (5H,
3
m), 6.98−6.84 (5H, m), 5.72 (1H, br), 2.84 (1H, m, J = 6.87 Hz),
0.71 (6H, d, J = 6.87 Hz); 13C NMR δ 158.2, 150.7, 140.6, 128.9,
3
128.5, 122.2, 121.5, 119.3, 29.0, 19.9.
1
2 (amidine): yield 89.8%; H NMR (tol-d8) δ 7.02 (4H, m), 6.71
(4H, m), 5.76 (1H, br), 2.76 (1H, sept, 3J = 7.32 Hz), 0.72 (6H, d, 3J =
7.33 Hz); 19F NMR δ −112.85 (1F, s), −111.81 (1F, s); 13C NMR δ
164.4, 159.3, 151.8, 141.5, 129.9, 117.0, 114.6, 109.1, 108.9, 108.3,
106.7, 29.5, 20.7.
3: yield 91.5%; 1H NMR (CDCl3) δ 7.29 (4H, t, 3J = 7.65 Hz), 7.02
3
3
(2H, t, J = 7.53 Hz), 6.84 (2H, t, J = 7.6 Hz), 6.09 (1H, br), 2.94
(1H, sept, J = 6.03 Hz), 0.85 (6H, d, J = 6.06 Hz); 19F NMR δ
−122.72 (1F, s), −120.27 (1F, s); 13C NMR δ 171.9, 159.3, 150.1,
140.5, 137.1, 129.0, 122.5, 121.4, 119.5, 29.3, 20.0.
3
3
1
4: yield 83.5%; H NMR (CDCl3) δ 9.75 (1H, br) 7.55 − 6.73
3
3
(12H, m), 2.98 (1H, sept, J = 6.92 Hz), 1.12 (6H, d, J = 6.92 Hz);
19F NMR δ −112.85 (1F, s), −111.81 (1F, s); 13C NMR δ 175.2,
160.2, 157.8, 136.4, 136.4, 132.5, 132.5, 127.1, 125.4(d, 1J = 10.25 Hz),
1
125.2 (d, J = 3.32 Hz), 123.7, 118.7, 111.2, 110.9, 37.3, 19.5.
Synthesis of PPSE. A mixture of 14.2 g of phosphorus pentoxide
(P2O5), 25.6 g of hexamethylsiloxane (TMS2O), and 30 mL of CH2Cl2
was refluxed for 30 min under a slow flow of N2. After the mixture
became a colorless liquid, the flask was placed under vacuum and
slowly heated to 160 °C. The resulting viscous oil was used
immediately for the synthesis of the corresponding amidine.
1
5 (amidine): yield 28%; H NMR (CDCl3) δ 4.80 (broad, 1H),
2.19 (sept, J = 6.9 Hz), 0.71 (d, J = 6.9 Hz); 19F NMR δ −165.50
3
3
(1F, t, 3J = 22.92 Hz), −164.64 (2F, t, 3J = 20.78 Hz), −164.10 (2F, t,
3J = 20.25 Hz), −157.64 (1F, t, J = 22.38 Hz), −154.20 (2F, d, J =
21.32 Hz), −146.09 (2F, d, 3J = 21.29 Hz); 13C NMR δ 165.2, 145.4−
136.4 (C-Fs, low broad signals), 30.9, 19.4. Anal. Calcd for
C16H8F10N2: C, 45.95; H, 1.93; N, 6.70. Found: C, 46.33; H, 1.95;
N, 6.40.
3
3
General Procedure for the Synthesis of Amidines. To the
PPSE prepared from 14.2 g of P2O5 at 180 °C under an N2 flow was
added 1 equiv (1.25 mmol) of isobutyric acid, and the mixture was
stirred for 5 min; during this time the reaction was heated to 200 °C.
Two equivalents (2.5 mmol) of the corresponding aniline was then
added dropwise with syringe to the reaction mixture, and the resulting
viscous liquid was stirred at this temperature for 5 h. After that time
the reaction mixture was made strongly basic (pH about 12) by adding
a 1 M solution of NaOH. The resulting biphasic mixture was extracted
three times with CH2Cl2; the combined organic fractions were washed
with water, dried over Na2SO4, filtered and all volatiles removed under
reduced pressure. The resulting crude product was purified by column
chromatography on silica using a 1/1 hexane/CH2Cl2 mixture as
eluent. Alternatively, the crude mixture may be separated by silica gel
chromatography using 80/20 hexane/ethyl acetate as eluent.
1
3
6 (imidazole): yield 69%; H NMR (CDCl3) δ 1.06 (6H, d, J =
6.82 Hz), 1.99 (1H, m, J = 6.87 Hz); 19F NMR (CDCl3) δ −164.10
3
(2F, t, 3J = 22.61 Hz), −164.07 (1F, t, 3J = 19.21 Hz), −163.39 (1F, q,
3J = 22.65 Hz), −157.19 (1F, q, J = 22.67 Hz), −154.20 (1F, d, J =
3
3
21.32 Hz), −153.21 (1F, d, 3J = 22.17 Hz), −145.65 (2F, d, 3J = 19.17
Hz); 13C NMR δ 162.3, 145.4−136.4 (C-Fs, low broad signals), 26.5,
20.5. Anal. Calcd for C16H7F9N2: C, 48.26; H, 1.77; N, 7.03. Found: C,
48.15; H, 1.68; N, 6.89.
General Procedure for the Synthesis of L2M(NMe2)2
Complexes (7−12). A toluene solution of 2 equiv (0.88 mmol) of
the corresponding ligand was added dropwise to a solution of 1 equiv
of M(NMe2)4 (0.44 mmol) in toluene at room temperature, and the
reaction mixture was stirred overnight. After this period of time all
I
dx.doi.org/10.1021/om300702s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
volatiles were removed under reduced pressure, and to the resulting
residue was added hexane, causing precipitation of solid material. The
mixture was filtered, the resulting cake was washed with hexane, and
the resulting solid was dried in vacuo to give the complexes as pure
products. X-ray-quality crystals were obtained by slow evaporation of
toluene from the toluene/complex solution, unless stated otherwise.
7: yield 87.3%; 1H NMR (tol-d8) δ 7.18 (4H, t, 3J = 7.74 Hz), 7.07
ACKNOWLEDGMENTS
■
This research was supported by the USA-Israel Binational
Science Foundation under Contract 2008283. S.A. thanks
Raymond Rosen for his fellowship.
REFERENCES
3
3
■
(4H, br), 6.96 (2H, t, J = 7.15), 3.07 (12H, s), 2.95 (2H, m, J =
3
7.22), 0.91 (12H, d, J = 7.22 Hz); 13C NMR δ 174.4, 149.2, 137.5,
(1) Kissin, Y. V. Alkene Polymerization Reactions with Transition Metal
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Coord. Chem. Rev. 2009, 253, 2082−2097. (b) Takeuchi, D. Dalton
Trans. 2010, 39, 311−328. (c) Baugh, L. S.; Canich, J.-A. M. In:
Stereoselective Polymerization with Single-Site Catalysts; CRC Press:
Boca Raton, FL, 2008. (d) Givson, V. C.; Redshaw, C.; Solan, G. A.
Chem. Rev. 2007, 107, 1745−1776.
(3) (a) Delferro, M.; Marks, T. J. Chem. Rev. 2011, 111, 2450−2485
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2009, 42, 1532−1544. (d) Amin, S. B.; Marks, T. J. Angew. Chem., Int.
Ed. 2008, 47, 2006−2025. (e) Vanka, K.; Xu, Z.; Seth, M.; Ziegler, T.
Top. Catal. 2005, 34, 143−164.
(4) (a) Edelmann, F. T. Adv. Organomet. Chem. 2008, 57, 183−352.
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F. T. Struct. Bonding (Berlin) 2010, 137, 109−163.
(5) (a) Volkis, V.; Shmulinson, M.; Averbuj, C.; Lisovskii, A.;
Edelmann, F. T.; Eisen, M. S. Organometallics 1998, 17, 3155−3157.
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(c) Zhang, Y.; Sita, L. R. Chem. Commun. 2003, 2358−2359.
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D. A. Russ. Chem. Rev. 2006, 75, 351−374.
(6) Volkis, V.; Nelkenbaum, E.; Lisovskii, A.; Hasson, G.; Semiat, R.;
Kapon, M.; Botoshansky, M.; Eishen, Y.; Eisen, M. S. J. Am. Chem. Soc.
2003, 125, 2179−2194.
(7) (a) Volkis, V.; Lisovskii, A.; Tumanskii, B.; Shuster, M.; Eisen, M.
S. Organometallics 2006, 25, 2656−2666. (b) Aharonovich, S.; Volkis,
V.; Eisen, M. S. Macromol. Symp. 2007, 260, 165−171.
(8) (a) Volkis, V.; Aharonovich, S.; Eisen, M. S. Macromol. Res. 2010,
18, 967−973. (b) Volkis, V.; Lisovskii, A.; Tumanskii, B.; Shuster, M.;
Eisen, M. S. Organometallics 2006, 25, 2656−2666.
(9) (a) Aharonovich, S.; Botoshansky, M.; Balazs, Y. S.; Eisen, M. S.
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aza-allyl Complexes of Li, Ti, Zr, and V: Structure, Reactivity and
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Institute of Technology, 2010.
126.5, 123.4, 121.6, 47.5, 30.7. Anal. Calcd for C36H46N6Ti: C, 70.57;
H, 7.90; N, 13.72. Found: C, 70.21; H, 7.28; N, 12.08.
8: yield 91.5%; 1H NMR (tol-d8) δ 6.99 (8H, m, 3J = 7.65 Hz), 6.79
3
3
(8H, m, J = 8.24 Hz), 3.11 (12H, s), 2.94 (2H, sept, J = 7.08 Hz),
0.90 (12H, d, J = 7.06 Hz); 19F NMR δ −113.02 (2F, q, J = 8.68
Hz); 13C NMR δ 174.6, 165.8, 160.9, 150.3, 150.1, 129.5, 129.3, 47.0,
20.4. Anal. Calcd for C36H42F4N6Ti: C, 63.16; H, 6.48; N, 12.28.
Found: C, 61.66; H, 6.26; N, 11.34.
3
3
1
9: yield 86.7%; H NMR (tol-d8) δ 6.92 (8H, br), 3.16 (12H, s),
2.88 (2H, sept, 3J = 7.34 Hz), 0.89 (12H, d, 3J = 7.35 Hz); 19F NMR δ
−119.83; 13C NMR δ 174.8, 162.0, 157.2, 144.6, 144.2, 115.3, 114.8,
47.1, 30.2, 20.5. Anal. Calcd for C36H42F4N6Ti: C, 63.16; H, 6.48; N,
12.28. Found: C, 62.11; H, 7.10; N,11.52.
1
3
10: yield 92.3%; H NMR (tol-d8): δ 0.99 (12H, d, J = 6.94 Hz),
2.29 (2H, s), 2.91 (12H, m, 3J = 6.9 Hz), 7.448−6.733 (24H, m); 19
F
NMR δ −111.39 (dd, J = 12.87 Hz, J = 4.37 Hz); 13C NMR δ
172.81, 162.80, 162.16, 158.0, 157.3, 145.9, 137.5, 136.9, 136.9, 135.7,
128.3, 127.8, 125.6, 124.9, 124.2, 121.6, 121.4, 118.4, 117.3, 110.6,
110.17, 31.0, 20.0. Anal. Calcd for C52H50F3N6Ti: C, 70.58; H, 5.92;
N, 9.50. Found: C, 76.58; H, 6.54; N, 10.11.
3
4
11: yield 84.0%; X-ray-quality crystals obtained by cooling the
saturated toluene solution from 50 °C to room temperature; 1H NMR
(C6D6) δ 2.86 (s, 12H), 2.32 (sept, 3J = 7.2 Hz, 2H), 0.74 (d, 3J = 7.2
Hz, 12H); 19F NMR spectrum at room temperature consists of broad
signals that cannot be assigned properly; 13C NMR δ 179.6, 45.1, 31.5,
17.4. Anal. Calcd for C36H28F20N6Ti: C, 44.46; H, 2.90; N, 8.64.
Found: C, 44.93; H, 2.56; N, 8.17.
1
3
12: yield 76.2% H NMR (C6D6) δ 2.59 (s, 12H), 2.33 (sept, J =
6.9 Hz, 2H), 0.74 (d, J = 6.9 Hz, 12H); 19F NMR δ −148.5 (d, J =
21.5 Hz, 8F), −160.30 (t, 3J = 21.7 Hz, 4F). −163.87 (t, 3J = 18.9 Hz,
8F); 13C NMR δ 184.6, 40.3, 32.6, 19.4. Anal. Calcd for
C36H28F20N5Zr: C, 42.56; H, 2.78; N, 8.27. Found: C, 44.93; H,
2.30; N, 6.89.
3
3
Typical Procedure for Propylene Polymerization. Inside the
glovebox, 10 mg of the complex, the appropriate amount of the MAO
(1:1000 metal:Al ratio), and 6 mL of toluene were mixed and loaded
into a stainless steel reactor. The reactor was connected to the high-
vacuum line, and 30 mL of propylene was transferred into the reactor.
The reaction mixture was warmed to the desired temperature and
stirred for 3 h. The reaction was quenched with acetylacetone, and the
resulting polymer was washed with methanol followed by acetone. The
solvents were dried out in the vacuum oven at 50 °C. The resulting
material was fractionalized with hexane in a Soxhlet apparatus.
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Matsukawa, N.; Matsui, S.; Mohri, J.; Furuyama, R.; Terao, H.;
Bando, H.; Tanaka, H.; Fujita, T. Chem. Rec. 2004, 4, 137−158.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, tables, and CIF files giving an Eyring plot for the
dynamic process in complex 11, COSY of complex 11 at high
(365 K) and low (227 K) temperatures, and crystallographic
data for ligands 3−6 and complexes 7, 9, 11, and 12. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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(b) Chan, M. C. W.; Kui, S. C. F.; Cole, J. M.; McIntyre, G. J.; Matsui,
S.; Zhu, N.; Tam, K.-H. Chem. Eur. J. 2006, 12, 2607−2619. (c) Kui, S.
C. F.; Zhu, N.; Chan, M. C. W. Angew. Chem., Int. Ed. 2003, 42, 1628−
1632. (d) Weberski, M. P.; Chen, C.; Delferro, M.; Zuccaccia, C.;
Macchioni, A.; Marks, T. J. Organometallics 2012, 31, 3773−3789.
(13) Ogata, S.; Mochizuki, A.; Kakimoto, M.; Imai, Y. Bull. Chem. Soc.
Jpn. 1986, 59, 2171−2177.
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Weitershaus, K.; Bellemin-Laponnaz, S.; Wadepohl, H.; Gade, L. H.
Inorg. Chem. 2006, 45, 7777−7787. (c) Cortright, S. B.; Huffman, J.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: chmoris@tx.technion.ac.il.
Notes
The authors declare no competing financial interest.
J
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