Pyridylamido hafnium and zirconium complexes: Synthesis, dynamic behavior, and ethylene/1-octene and propylene polymerization reactions

Article abstract of DOI:10.1021/om200167h

Hafnium and zirconium pyridylamido complexes were prepared by the reaction of deprotonated ligand with MCl₄ followed by alkylation with MeMgBr. ¹H NMR analysis of the isolated products revealed the presence of two complexes in each s

Full text of DOI:10.1021/om200167h

ARTICLE
pubs.acs.org/Organometallics
Pyridylamido Hafnium and Zirconium Complexes: Synthesis,
Dynamic Behavior, and Ethylene/1-Octene and Propylene
Polymerization Reactions
Kevin A. Frazier, Robert D. Froese, Yiyong He, Jerzy Klosin,* Curt N. Theriault, Paul C. Vosejpka,
and Zhe Zhou
Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States
Khalil A. Abboud
Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
S Supporting Information
b
ABSTRACT: Hafnium and zirconium pyridylamido complexes
were prepared by the reaction of deprotonated ligand with
MCl4 followed by alkylation with MeMgBr. 1H NMR analysis of
the isolated products revealed the presence of two complexes in
each sample in about a 93:7 ratio. Both complexes were shown
by 1D NOESY experiments to be in dynamic equilibrium with
each other at ambient temperature. An analysis of the chemical
shift differences between major and minor isomers together with low-temperature NOE experiments revealed that the difference
between major and minor isomers is due to the rotation of the 2-iPr-phenyl group attached to the chiral center. Magnetization
transfer experiments conducted at temperatures between 10 and 40 °C yielded ΔH‡ and ΔS‡ of 14.3(6) kcal/mol and ꢀ11(2) cal/
mol K, respectively. Density functional theory calculations resulted in very similar activation parameters. Additionally, this fluxional
3
process was calculated to occur in the cationic species with a rate comparable to that of propylene propagation kinetics. Both
complexes have been studied as procatalysts for ethylene/1-octene copolymerization and propylene polymerization reactions. 13C
NMR analysis of polypropylene obtained under high-temperature polymerization conditions allowed for the unequivocal
determination of the identity of a second 2,1-regioerror.
’ INTRODUCTION
recently reported to exhibit living character.11 Interestingly, the
formation of a multimodal polymer is often observed with
catalysts of this type, indicating the lack of a single site. The
activation mechanism of these catalysts is unusual and has
been studied extensively via experimental and computational
methods.13,14 It has been hypothesized that the active catalytic
species is formed by insertion of an ethylene or R-olefin into the
Hfꢀaryl bond, leading to a modified catalyst, 1a (Figure 1). In
ethylene/1-octene and propylene polymerization reactions, in-
sertion of the olefin(s) into the Hfꢀaryl bond can lead to
multiple species, which results in the formation of multiple active
polymerization sites generating a mixture of polymers.
Most of the catalytic and mechanistic work reported thus far
has focused on the study of chiral and achiral hafnium complexes.
It was of interest to us to evaluate the zirconium8,15 analogue of 1
for both ethylene/1-octene and propylene polymerizations and
compare its polymerization characteristics to that of 1. Depend-
ing on the ligand framework, zirconium and hafnium complexes
can exhibit quite different polymerization behaviors; thus
The last two decades have seen extensive research devoted to
the development of non-Cp-based molecular catalysts for olefin
polymerization.1ꢀ3 We have been interested recently in imino-
amido4ꢀ6 and imino-enamido7 type catalysts and uncovered an
interesting diversity of polymerization characteristics. Closely
related to the imino-amido catalyst family are catalysts contain-
ing the pyridylamido ligand framework, which were developed
initially at Union Carbide8 (generation 1) and further elabo-
rated via a joint collaboration between Symyx Technologies and
The Dow Chemical Company9,10 (generation 2). The general
structures of the pyridylamido catalysts and the chiral procata-
lyst 1 used in this work are depicted in Figure 1. This catalyst
family has been the subject of much research due to unusual
catalyst and polymer properties.
Pyridylamido catalysts form high molecular weight, isotactic
polypropylene, which is very unusual for the C1/Cs-symmetric
catalysts.2d,11 This catalyst family was also identified as very
effective for the preparation of olefin block copolymers due to
their ability to undergo reversible and efficient chain-transfer
reactions with some metal alkyl complexes (e.g., ZnEt2) during
olefin polymerization.3,12 Pyridylamido catalysts were also
Received: February 21, 2011
Published: May 25, 2011
r
2011 American Chemical Society
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synthesis and evaluation of 3 was warranted. In addition to the
complications with catalyst activation mentioned above, it
has been known that there is a persistent additional species in
procatalyst 1, composition of which was unknown. This work
will shed light on the identity of this additional species,
ultimately adding an additional level of complexity to this
intriguing catalyst family.
’ RESULTS AND DISCUSSION
Previously, complex 1 was prepared by refluxing the corre-
sponding ligand (2) with Hf(NMe2)4 followed by the reaction of
the isolated triamide derivative, 2-Hf(NMe2)3, with AlMe3. We
desired to prepare 1 and its Zr analogue by a more easily scalable
Figure 3. Thermal ellipsoid drawing of 3 at the 40% probability level.
Hydrogen atoms have been removed for clarity.
Figure 1. Pyridylamido procatalysts and their activation.
Scheme 1. Synthesis of Procatalysts 1 and 3
Figure 2. 1H NMR spectrum of 1. Asterisks indicate some resonances of the minor component.
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method and developed an improved synthesis as outlined in
Scheme 1. Ligand 216 was reacted with one equivalent of n-BuLi
at ambient temperature in toluene followed by the reaction of the
resulting anion with hafnium or zirconium tetrachloride at
110 °C for 1 h. The in situ formed trichloride intermediate was
reacted with three equivalents of MeMgBr at ambient tempera-
ture to produce the desired complexes, 1 and 3. Both complexes
were characterized by elemental analysis, 1D (Figure 2) and 2D
NMR spectroscopy, and single-crystal X-ray analysis. X-ray
structures of 1 and 3 are isostructural, and only the molecular
structure of 3 is shown here (Figure 3).16 Interestingly, all regions
of the 1H NMR spectra of both complexes 1 and 3 revealed the
presence of a minor component at a level of about 7% (Figure 2).
Since ethylene/1-octene copolymers with a broad polydispersity
index (PDI) have been observed previously with 1, it was
reasoned that the minor component might be catalytically active
and directly responsible for polymer bimodality. Thus, it was
important to us to determine the identity of this minor
component.
This minor component appeared to be structurally similar to
1, as all of its resonances exhibited very similar chemical shifts
and multiplicity to those observed in 1. In an effort to identify
these resonances, a comprehensive NMR analysis was carried
out. The most important and unexpected piece of information
that allowed for determining the structure of this minor
component in the spectra of 1 came from 1D NOESY experi-
ments. In addition to the expected positive NOEs, 1D NOESY
spectra also revealed negative EXSY peaks between 1 and the
minor component. This fact clearly indicates that the minor
component is in chemical exchange with 1. Full analysis of the
NOE and TOCSY data allowed for the full assignment of all
resonances of the minor component, which from now on will be
Figure 4. Rotational isomers 1 and 10.
1
Figure 5. H NMR and 1D NOESY spectra of 1 and 10 (in C6D6) at 7 °C (mixing time = 0.7 s). Asterisk designates residual toluene.
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Figure 6. 1D NOE array spectra of 1 and 10 (in toluene-d8) at 30 °C.
Figure 7. Calculated structure of 1 (major isomer).
Figure 9. Calculated transition state (TS) for the interconversion of
1 and 10.
H14.17 For example, the difference between the chemical shifts
of H10/H100, H11/H110, H14/H140, and H18/H180 are 0.68,
0.26, 0.44, and 0.56 ppm, respectively.
If the (2-iPr)Ph fragment has two different orientations as
depicted in Figure 4, then the NOE experiments might be able to
provide unequivocal evidence for it. To minimize contributions
from EXSY peaks, NOE NMR experiments were conducted at a
lower temperature (7 °C). The 1H NMR and 1D NOESY spectra
obtained at 7 °C are shown in Figure 5. Fortuitously, at 7 °C the
H14 and H9 resonances are adequately separated (they overlap
at 30 °C) such that they can be independently irradiated. Since
the distance between protons H9/H14 in the major isomer is
approximately the same as that of H90/H140 in the minor isomer
(the DFT-calculated distances are 2.67 Å for H9/H14 and 2.68 Å
for H90/H140), it was expected that irradiation of H14 and H140
would result in a similar intensity of NOEs for H9 and H90,
respectively (internal check). In the first NOE experiment, the
H14 resonance was irradiated, resulting in strong NOEs of H9,
H18, H20, and H25 (Figure 5, middle spectrum). It is important
to note that strong NOEs are observed for two out of three
methine resonances. There is also NOE enhancement for the
H10 resonance, but its intensity is very small. On the other hand,
irradiation of H140 resulted in very strong NOEs for H90, H100,
H200, and H250 (Figure 5, bottom spectrum). The appearance of
Figure 8. Calculated structure of 10 (minor isomer).
referred to as either the minor isomer or 10. The three-
dimensional structures of 1 and 10 were shown to differ in the
orientation of the (2-iPr)Ph group relative to the remaining part
of the ligand framework (Figure 4). This conclusion was
reached from several independent pieces of data. The first clue
as to the three-dimensional structure of the minor isomer came
from the analysis of the chemical shift differences between both
isomers. The chemical shift difference between most of the
resonances of 1 and 10 was found to be small (within 0.05 ppm)
except for the resonances associated with the (2-iPr)Ph group
attached to the chiral center (C14) and its neighboring proton
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Table 1. Selected Bond Lengths and Angles for the Calcu-
lated and Experimentally Determined Molecular Structuresa
bond/angle
1
1 (X-ray)
10
TS
HfꢀN2
2.325
2.094
2.220
2.230
2.287
1.469
1.442
1.515
1.399
1.480
107.8
69.6
2.295(2)
2.081(2)
2.223(3)
2.210(3)
2.256(2)
1.475(3)
1.444(3)
1.501(3)
1.391(3)
1.489(3)
105.7(2)
69.56(8)
72.12(7)
109.2(2)
114.1(2)
2.331
2.099
2.218
2.226
2.288
1.469
1.444
1.514
1.398
1.480
106.2
69.4
2.328
2.122
2.220
2.217
2.294
1.491
1.443
1.522
1.395
1.478
111.1
69.6
HfꢀN1
HfꢀC27
HfꢀC28
HfꢀC32
N2ꢀC14
N2ꢀC38
C14ꢀC34
C31ꢀC32
C31ꢀC33
C27ꢀHfꢀC28
N1ꢀHfꢀC32
N1ꢀHfꢀN2
C34ꢀC14ꢀN2
C35ꢀC14ꢀN2
71.5
71.5
72.3
108.7
109.1
105.2
114.6
117.2
112.7
a Metric parameters are based on the geometries shown in Figure 7ꢀ9
for the calculated structures.
a strong NOE for H100 and the disappearance of the NOE for
H180 is a strong indication that the difference between 1 and 10 is
due to the different disposition of the (2-iPr)Ph fragment relative
to the rest of the molecule.
To evaluate the activation parameters for this fluxional pro-
cess, a series of magnetization transfer experiments was con-
ducted between 10 and 40 °C. An example set of arrayed 1D
NOESY spectra is shown in Figure 6.18 The obtained rate
constants and corresponding Eyring plot are shown in the
Supporting Information. Data analysis results in ΔH‡ and ΔS‡
Figure 10. Isomerization of 1/10 and the anticipated activation steps
and possible isomerizations of various cationic species.
involves a windshield wiper motion (back and forth) rather than a
full rotation.
The enthalpy and entropy of activation as calculated using
density functional theory are ΔH‡ = 16.9 kcal/mol and ΔS‡ =
ꢀ9.9 cal/mol K. These values agree well with the experimentally
3
determined kinetic parameters of ΔH‡ = 14.3 kcal/mol and
of 14.3(6) kcal/mol and ꢀ11(2) cal/mol K, respectively. In-
ΔS‡ = ꢀ11 cal/mol K. Reaction thermodynamics for the iso-
3
3
tegration of the resonances corresponding to the major and
merization process from 1 to 10 are computed to be ΔH° = 1.7
1
minor isomers in the H NMR spectrum gives an equilibrium
kcal/mol and ΔS° = ꢀ1.5 cal/mol K, which at room tempera-
3
constant (Keq) of 14 at 30 °C, which corresponds to a free energy
(ΔG°) difference of 1.6 kcal/mol. For comparison, the rate
constant for interconversion of 3 and 30 was measured at 30 °C
using magnetization transfer experiments. The measured rate of
1.66(3) sꢀ1 is slightly faster than that of interconversion between
1 and 10, which was determined to be 1.22(2) sꢀ1 at the same
temperature.
ture equates to an equilibrium mixture of 97:3. This value agrees
very well with the experimentally determined equilibrium ratio
(93.3:6.7).
These same isomerization barriers were also determined for
the cationic catalyst, formed by the removal of one methyl
group, as well as the likely active catalyst,13 the olefin appended
species (see 1a in Figure 1). The methyl cation is not necessarily
the best representation of the active catalyst, as the open
coordination site could be occupied by a solvent molecule,
olefin, β-agostic interaction (in a longer polymer chain), or the
counterion. However, our goal was to determine if there were
gross differences for the rotation of the (2-iPr)Ph fragment in
the dimethyl neutral catalyst (1) and the two cationic repre-
sentations of active species. The isomerization processes for the
neutral procatalysts 1 and 10 and their corresponding cationic
species are depicted in Figure 10. The computed barrier for the
cationic systems were determined to be even lower than that of
the neutral species with ΔH‡ = 12.9 kcal/mol for activated 1
and ΔH‡ = 13.9 kcal/mol for ethylene-appended 1 (Figure 10).
While the calculations for the active cationic catalysts are only
estimates, these barriers are low and one would expect the
corresponding rotation of the (2-iPr)Ph group to be as fast, if
not faster, than the rate of polymerization. The relative rate at
which the (2-iPr)Ph group rotates is important since the two
possible procatalysts, 1 and 10, are structurally different enough
The calculated structures of 1, 10, and the transition state (TS)
for their interconversion are shown in Figure 7ꢀ9, respectively.19
Selected bond lengths and angles for the calculated structures are
collected in Table 1. Except for the orientation of the (2-iPr)Ph
fragment, both structures 1 and 10 are very similar. However,
the transition state is distorted significantly compared to the
two minima. First, the five-membered ring containing Hfꢀ
N1ꢀC34ꢀC14ꢀN2 is relatively planar in 1 and 10 but is
noticeably puckered in the TS. The HfꢀN1ꢀC34ꢀC14 torsion
angles for 1, 10, and TS are ꢀ14.9°, ꢀ8.4°, and ꢀ38.7°,
respectively. Second, the 2,6-diisopropylphenyl fragment is tilted
away from the (2-iPr)Ph fragment in the TS. The C30ꢀ
C38ꢀN2ꢀC14 torsion angles for 1, 10, and TS are 105.7°,
107.7°, and 122.8°, respectively. Another notable aspect is that
the (2-iPr)Ph fragment could rotate in either direction in the TS,
but prefers to reside toward the pyridine rather than being
directed toward the sterically encumbered 2,6-diisopropylphenyl
group (see Figure 9). Thus the equilibrium process, 1 T 10,
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Table 2. Ethylene/1-Octene Copolymerization Data for Complexes 1, 3, and CGCa
run #
poly. temp (°C)
catalyst (μmol)
yield (g)
catalyst activityb
Tm (°C)
Mw ꢁ 10ꢀ3 (kDa)
Mw/Mn
octene content (mol %)
1
2
3
4
5
6
120
120
120
150
150
150
1 (1.5)
19.9
8.4
13 267
8400
53.8
1420
867
3.1
3.3
12.1
8.5
3 (1.5)
68/106
59.1
CGC (0.2)
1 (2.5)
46.7
17.5
7.6
233 500
7000
50.2
565
2.2
15.6
12.7
8.4
51.1
8.2
3 (2.0)
3800
71/114
55.4
301
136
1.8
CGC (0.4)
47.5
118 750
28.6
14.6
a Polymerization conditions: 533 mL of Isopar-E; 250 g of 1-octene; ethylene pressure = 460 psi; procatalyst:activator:MMAO = 1:1.2:10; activator:
[HNMe(C18H37)2][B(C6F5)4]; hydrogen = 10 mmol; reaction time 15 min. b Activity: g of polymer/mmol cat. CGC = {(η5-C5Me4)(SiMe2-N-
tBu)}TiMe2. 1-Octene content determined by FTIR.
Table 3. Propylene Polymerization Data for Complexes 1
and 3 (high propylene concentration)a
run catalyst
yield
(g)
catalyst
activityb
Tm
%
Mw ꢁ 10ꢀ3
#
(μmol)
(°C) mmmm (kDa) Mw/Mn
7
8
1 (1)
3 (1)
23.8
10.9
23 800
10 900
153.9 94.2
146.6 92.6
198
63.4
3.0
2.9
a Polymerization conditions: temp = 90 °C; 667 mL of Isopar-E; 286 g of
propylene; hydrogen = 8.3 mmol; procatalyst:activator:MMAO =
1:1.2:10; activator: [HNMe(C18H37)2][B(C6F5)4]; reaction time
10 min. b Activity: g of polymer/mmol cat.
that they are likely to produce different types of polymers. The
structural differences between the two isomers have already
been discussed, but as an example of the contrasting geome-
tries, one can compare the distance between the methine
proton of the (2-iPr)Ph group and the hafnium atom. In 1,
this distance is 5.570 Å, while in 10 this distance has been
reduced to 3.050 Å, indicating a more sterically crowded
environment. Since even achiral versions of pyridylamide
catalysts {without (2-iPr)Ph)} produce multimodal polymers
as a result of ligand modification,13 it is unclear what the role of
the (2-iPr)Ph rotation is in 1 and 3 with regard to polymer
properties.
Ethylene/1-Octene Copolymerization Study. Ethylene/1-
octene copolymerization reactions was also conducted in a 2 L
batch reactor at 120 °C containing 460 psi ethylene pressure
and 250 g of 1-octene. In addition to complexes 1 and 3, (η5-
C5Me4)(SiMe2-N-tBu)TiMe2 (CGC) was also included in the
study for comparison. Procatalysts were activated with 1.2
equivalents (relative to procatalyst) of [HNMe(C18H37)2]-
[B(C6F5)4] activator. All polymerization reactions were car-
ried out for 15 min and stopped by venting the ethylene
pressure. At a polymerization temperature of 120 °C, the
catalytic activity of 1 is about 60% higher than that of the
zirconium analogue 3, but is 18 times lower than the catalytic
activity of CGC. At 150 °C, the activity decreases but the
relative activity trends between catalysts remain almost the
same. The hafnium complex 1 is a good 1-octene incorporator,
leading to polymers with 1-octene levels that are higher than
those produced by 3 but somewhat lower than those produced
by CGC (at both polymerization temperatures). The same
1-octene incorporation trends (hafnium leads to higher in-
corporation of 1-octene than the zirconium analogue) were
observed also within the imino-amido and imino-enamido
families of catalysts.4,7 Pyridylamido complex 1 is a better
1-octene incorporator than hafnium imino-amido and
Figure 11. 3D structures of four possible 2,1-insertion regioerrors
in iPP.
imino-enamido catalysts.4,7 The most remarkable polymeriza-
tion data included in Table 2 are the molecular weight of
polymers produced by 1 and 3. At a polymerization tempera-
ture of 120 °C, procatalyst 1 gives an ultrahigh molecular
weight ethylene/1-octene copolymer with a Mw of 1422 kDa,
which is about 30 times higher than that produced by the CGC
catalyst. The molecular weights of polymers produced by 1 at
120 °C are not only higher than those produced by CGC but
also higher than those generated by hafnium imino-enamido
complexes, which have Mw of about 1000 kDa under very
similar polymerization conditions. The zirconium complex 3
results in polymers with high Mw that is about half of that
produced by the Hf analogue. Procatalyst 1 is a very rare
example of a catalyst that is capable of producing ethylene/
1-octene copolymers at 120 °C with a Mw above 1000 kDa.
Propylene Polymerization Study. Propylene polymeriza-
tion reactions were conducted in a 1.8 L batch reactor under
two different sets of conditions. The first set of experiments
was conducted under high propylene concentration and
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90 °C reactor temperature (Table 3). The data indicate that
the zirconium complex 3 exhibits about 50% lower activity
than 1. The Zr catalyst yields isotactic polypropylene (iPP)
with significantly lower Mw and slightly lower tacticity
as shown by a reduced melting point and 13C NMR
analysis.
minor regioerror (Figure 12, label with # symbol). Chemical shift
analysis of resonances of this minor regioerror suggests that they
belong to either the RE1 or the RE4 microstructure. In order to
assign this regioerror, a 2D HOESY experiment of iPP from run 9
was conducted (Figure 13). It was expected that the chemical
shift difference of the two protons attached to carbons F and f
(Figure 12) in RE1 and RE4, respectively, should be about
0.4 and 0.13 ppm, respectively. The chemical shift difference
found in the sample from run 9 is 0.48 ppm (Figure 13), which
indicates that this minor 2,1-regioerror belongs to the RE1
Previous studies2d,20 showed that pyridylamido catalyst 1
led to a 2,1-insertion regioerror (RE3, Figure 11), which is
structurally different from the regioerrors observed in poly-
mers prepared by standard C2-symmetric metallocene catalysts
(RE1 and RE2). Initially, very low levels of the minor 2,1-
insertion regioerror in the polymers from 1 made it impossible
to determine conclusively its nature. We decided to prepare
several iPP samples under different reaction conditions
using catalysts 1 and 3 in an effort to generate samples with
significantly higher amounts of secondary minor 2,1-regioerrors,
in order to allow us to establish its stereochemistry unambigu-
ously. The second set of propylene polymerization reactions was
performed at lower propylene pressure and two different reactor
temperatures (60 and 120 °C), as shown in Table 4. Gratifyingly,
13C NMR analysis of polymers produced at the higher tempera-
ture (120 °C) (runs 9 and 10) reveals significant formation of the
Table 4. Propylene Polymerization Data for Complexes 1
and 3 (low propylene concentration)a
run temp
catalyst
yield
(g)
catalyst
activityb (°C)
Tm
Mw ꢁ 10ꢀ3 Mw/
#
(°C)
(μmol)
(kDa)
Mn
9
120
1 (0.5)
3 (2.0)
1 (0.5)
3 (1.0)
4.9
2.8
2.2
7.2
9800
1400
4400
7200
144.7
139.1
156.7
150.2
88.7
67.4
702
2.7
4.3
2.2
1.9
10 120
11 60
12 60
168
a Polymerization conditions: 300 mL of Isopar-E; propylene = 80 g;
hydrogen = 9.6 mmol; procatalyst:activator:MMAO = 1:1.2:10; activa-
tor: [HNMe(C18H37)2][B(C6F5)4]; reaction time 10 min. b Activity:
g of polymer/mmol cat.
Figure 13. HOESY (1Hꢀ C) of iPP (resonances F and f) prepared at
13
120 °C (run 9). Mixing time is 100 ms.
Figure 12. 13C NMR of iPP prepared at 120 °C (run 9, top spectrum) and iPP prepared at 60 °C (run 13, bottom spectrum). Asterisks and number
symbols designate RE3 and RE1 2,1-insertions, respectively.
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microstructure.20 The presence of RE1 and RE3 regioerrors in
iPP produced by 1 and 3 indicates that these misinsertions are
not triggered by the preceding stereoerror in the growing
polymer chain and are formed by enchainment of 2,1-propylene
coordinated with both enantiofaces to the metal center. Since
procatalysts 1 and 3 can result in the formation of more than one
active catalyst under polymerization conditions, it is not obvious
if both regioerrors (RE3 and RE1) are formed by the same or
different catalytic species.
methylethyl)-N-[[6-(1-naphthalenyl)-2-pyridinyl]methylene]benzenamine
(2.20 g, 5.6 mmol) was magnetically stirred as a slurry in 60ꢀ70 mL of dry
ether under a nitrogen atmosphere. An ether solution of 2-isopropylphe-
nyllithium (1.21 g, 9.67 mmol in 25 mL of dry ether) was added slowly using
a syringe over a period of 4ꢀ5 min. After the addition was complete, a small
sample was removed and quenched with 1 N NH4Cl, and the organic layer
was analyzed by high-pressure liquid chromatography (HPLC) to check for
complete consumption of starting imine. The remainder of the reaction
mixture was quenched by the careful, slow addition of 1 N NH4Cl (10 mL).
The mixture was diluted with more ether, and the organic layer was washed
twice with brine, dried (anhydrous Na2SO4), filtered, and stripped of solvent
under reduced pressure. The crude product, obtained as a thick red oil (2.92
g; 100% yield), was used without further purification. 1H NMR (500 MHz,
toluene-d8): δ 8.14 (m, 1H), 7.68 (dd, 1H, J = 7.5, 1.5 Hz), 7.64ꢀ7.56 (m,
2H), 7.46 (dd, 1H, J= 7.1, 1.2 Hz), 7.29ꢀ7.20(m, 3H), 7.19ꢀ7.09 (m, 4H),
7.08ꢀ7.00 (m, 5H), 5.66 (s, 1H, H14), 4.80 (s, 1H, NH), 3.29 (hept, 1H, J=
6.8 Hz, CH(CH3)2), 3.22 (hept, 2H, J = 6.8 Hz, CH(CH3)2), 1.08ꢀ1.03
(m, 6H, CH(CH3)2), 1.01 (d, 3H, J = 6.9 Hz, CH(CH3)2), 1.00 (d, 6H,
J = 6.9 Hz, CH(CH3)2), 0.95 (d, 3H, J = 6.8 Hz, CH(CH3)2). 1H NMR
(500 MHz, C6D6): δ 8.20 (m, 1H), 7.75 (m, 1H), 7.68ꢀ7.60 (m, 2H),
7.51 (dd, J = 7.1, 0.9 Hz, 1H), 7.30ꢀ7.23 (m, 3H), 7.21ꢀ7.05 (m, 8H),
7.02 (d, J = 7.6 Hz, 1H), 5.73 (s, 1H), 4.87 (s, 1H), 3.33 (hept, J = 6.8 Hz,
1H), 3.27 (hept, J = 6.7 Hz, 2H), 1.07 (d, J = 6.8 Hz, 6H), 1.02 (d, J = 6.8
Hz, 9H), 0.97 (d, J = 6.8 Hz, 3H). 13C{1H} NMR (126 MHz, C6D6):
δ 163.01, 159.07, 146.71, 143.44, 143.41, 141.00, 138.86, 136.78, 134.55,
131.85, 129.24, 128.64, 128.52, 127.78, 127.68, 126.55, 126.53, 126.27,
126.00, 125.81, 125.33, 124.41, 123.96, 122.91, 120.19, 67.10, 28.85, 28.12,
24.36, 24.23, 23.81. 13C{1H} NMR (126 MHz, toluene-d8): δ 162.98
(quat), 159.06 (quat), 146.69 (quat), 143.47 (quat), 143.34 (quat), 141.04
(quat), 138.80 (quat), 136.73 (CH), 134.55 (quat), 131.83 (quat), 129.20
(CH), 128.62 (CH), 128.48 (CH), 127.70 (CH), 127.63 (CH), 126.54
(CH), 126.45 (CH), 126.22 (CH), 125.90 (CH), 125.73 (CH), 125.22
(CH), 124.37 (CH), 123.86 (CH), 122.84(CH), 120.09 (CH), 67.12 (CH),
28.85 (CH(CH3)2), 28.11 (CH(CH3)2), 24.32 (CH(CH3)2), 24.23
(CH(CH3)2), 24.20 (CH(CH3)2), 23.78 (CH(CH3)2). ES-HRMS (m/e):
calcd for C37H41N2 (M þ H)þ 513.326, found 513.327.
’ CONCLUSIONS
This work revealed that the second component present in the
hafnium and zirconium pyridylamido procatalysts is a result of the
presence of a minor diastereoisomer that is in dynamic equilibrium
with the primary complex at ambient temperature. Analysis of
chemical shift differences between the isomers together with low-
temperature NOE experiments and computational work showed
that the difference between the major and minor isomers is due to
the rotation of the 2-isopropylphenyl ring attached to the chiral
center. Activation barriers obtained experimentally (ΔH‡ and ΔS‡
of 14.3(6) kcal/mol and ꢀ11(2) cal/mol K, respectively, for the Hf
3
complex) for this fluxional process compared favorably with
computational data. Copolymerization studies of ethylene and
1-octene showed pyridylamide hafnium procatalyst 1 exhibits
moderate activity at 120 °C, but it produces ultrahigh molecular
weight (1420 kDa) copolymers at this temperature. Complex 1 is a
very rare example of a procatalyst capable of producing such high
molecular weight copolymers at temperatures above 100 °C. The
zirconium analogue 3 gives lower activity and leads to polymers with
a lower molecular weight and reduced 1-octene content compared
to 1. Polypropylene produced by the pyridylamido zirconium 3 has
slightly lower tacticity and lower molecular weight than the polymer
prepared by the hafnium complex 1. Propylene polymerization at
higher reactor temperature (120 °C) resulted in the formation of
polypropylene with two distinct 2,1 insertion regioerrors. The minor
regioerror was determined to be the same regioerror as the one
observed in iPP produced by metallocene catalysts.
Preparation of [N-[2,6-Bis(1-methylethyl)phenyl]-R-[2-(1-methylethyl)-
phenyl]-6-(1-naphthalenyl-kC2)-2-pyridinemethanaminato(2-)-kN1,
kN2]dimethylhafnium (1, 10). Inside a nitrogen-filled glovebox a glass
jar was charged with N-[2,6-bis(1-methylethyl)phenyl]-R-[2-(1-methyl-
ethyl)phenyl]-6-(1-naphthalenyl)-2-pyridinemethanamine (10.21 g,
19.92 mmol) dissolved in 100 mL of toluene. To this solution was added
nBuLi (8.4 mL of 2.5 M solution in hexanes, 21.0 mmol) by syringe. This
solution was stirred for 1 h; then solid HfCl4 (6.41 g, 20.00 mmol) was
added. The jar was capped with an air-cooled reflux condenser, and the
mixture was heated to 100 °C for 2 h. After cooling, MeMgBr (23.2 mL of
3 M solution in diethyl ether, 69.7 mmol, 3.5 equivalents) was added by
syringe, and the resulting mixture stirred overnight at ambient temperature.
Solvent was removed from the reaction mixture using a vacuum system
attached to the drybox. To the residue was added toluene and the mixture
was filtered. The residue was washed with additional toluene (8 washes of
∼50 mL; until the eluent flow was colorless). Recovered eluent was stripped
to dryness under vacuum, and hexane (30 mL) was added, then removed by
vacuum. Hexane (50 mL) was again added, and the resulting slurry was
stirred for 30 min. The suspension was filtered and the collected product
was washed with cold hexane (50 mL) to give the desired product as a
’ EXPERIMENTAL SECTION
General Considerations. All syntheses and manipulations of air-
sensitive materials were carried out in a nitrogen-filled glovebox. Solvents
were first saturated with nitrogen and then dried by passage through
activated alumina and Q-5 catalyst prior to use. Deuterated NMR solvents
(toluene-d8, C6D6) were dried over sodium/potassium alloy and filtered
prior to use unless otherwise noted. NMR spectra were recorded on Varian
Inova 300 (FT 300 MHz, 1H; 75 MHz, 13C) and VNMRS 500 (FT 500
MHz, 1H; 126 MHz, 13C) spectrometers. 1H NMR data are reported as
follows: chemical shift, integration, multiplicity (br = broad, s = singlet, d =
doublet, t = triplet, q = quartet, p = pentet, hept = heptet, and m = multiplet)
and assignment. Chemical shifts for 1H NMR data are reported in
ppm downfield from tetramethylsilane (TMS, δ scale) using residual protons
in the deuterated solvents (C6D6, 7.15 ppm, C6D5CD3, 2.09 ppm) as
1
references. 13C NMR data were determined with H decoupling, and the
1
bright yellow powder (11.2 g, 15.46 mmol, 78%). 1: H NMR (500
chemical shifts are reported in ppm vs tetramethylsilane (C6D6, 128 ppm,
toluene-d8, 20.4 ppm). 2,6-Bis(1-methylethyl)-N-[[6-(1-naphthalenyl)-2-pyr-
idinyl]methylene]benzenamine and 2-isopropylphenyllithium were prepared
according to published procedures.10c Sublimed grade HfCl4 was obtained
from Strem, and the naphthylboronic acid used was obtained from Frontier
Scientific. Elemental analyses were performed by Midwest Microlab, LLC.
Preparation of N-[2,6-Bis(1-methylethyl)phenyl]-R-[2-(1-methylethyl)-
phenyl]-6-(1-naphthalenyl)-2-pyridinemethanamine (2). The 2,6-bis(1-
MHz, C6D6, 30 °C): δ 8.57 (d, 1H, 3J = 7.5 Hz, H1), 8.25 (d, 1H, 3J = 8.5
Hz, H6), 7.81 (d, 1H, 3J = 7.5 Hz, H2), 7.71 (dd, 1H, 3J = 7.7 Hz, 3J = 1.7
Hz, H3), 7.51 (d, 1H, 3J = 8.0 Hz, H7), 7.34 (m, 1H, H10), 7.30 (m, H5),
7.27 (m, H4), 7.17 (dd, 1H, 3J = 7.5 Hz, 4J = 1.9, H17), 7.13 (t, 1H, 3J =
7.5 Hz, H16), 7.07 (dd, 1H, 3J = 7.5 Hz, 4J = 1.9, H15), 7.07 (m, 1H,
H13), 7.00 (m, 2H, H11/H12), 6.84 (t, 1H, 3J = 7.5 Hz, H8), 6.57 (s,
3
3
1H, H14), 6.55 (d, 1H, J = 7.5 Hz, H9), 3.82 (sep., 1H, J = 6.8
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Organometallics
ARTICLE
Hz, H19), 3.37 (sep., 1H, 3J = 7.0 Hz, H20), 2.89 (sep., 1H, 3J = 6.8 Hz,
H18), 1.38 (d, 3H, 3J = 7.0 Hz, H25), 1.36 (d, 3H, 3J = 7.5 Hz, H24), 1.17
(d, 3H, 3J = 6.5 Hz, H21), 1.14 (d, 3H, 3J = 6.5 Hz, H26), 0.94 (s, 3H,
H27), 0.689 (d, 3H, 3J = 6.5 Hz, H22), 0.685 (s, 3H, H28), 0.38 (d, 3H,
3J = 6.5 Hz, H23). 10: 1H NMR (C6D6, 30 °C): δ 8.55 (d, 1H, 3J = 7.5
Hz, H10), 8.30 (d, 1H, 3J = 8.5 Hz, H60), 7.77 (d, 1H, 3J = 8.0 Hz, H20),
7.69 (d, 1H, 3J = 8.0 Hz, H30), 7.55 (d, 1H, 3J = 8.0 Hz, H70), 7.30 (tm,
1H, 3J = 8.5 Hz, H50), 7.25 (tm, 1H, 3J = 7.0 Hz, H40), 7.18 (d, 1H, 3J =
7.5 Hz, H130), 7.07 (tm, 1H, 3J = 7.0 Hz, H120), 6.86 (t, 1H, 3J = 7.5 Hz,
H80), 6.75 (t, 1H, 3J = 7.5 Hz, H110), 6.68 (d, 1H, 3J = 8.0 Hz, H100),
(d, 3H, J = 6.8 Hz, H26), 0.85 (s, 3H), 0.69 (d, 3H, J = 6.7 Hz, H22), 0.38
(d, 3H, J = 6.7 Hz, 3H). 13C{1H} NMR (126 MHz, C6D6): δ 192.35
(C32), 170.24 (C34), 164.34 (C33), 147.42 (quat), 146.47 (quat),
146.43 (quat), 144.71 (quat), 142.74 (quat), 140.78 (quat), 140.74
(C8), 135.76, 133.34 (C1), 130.25 (C10), 130.00, 129.89, 129.38,
127.93, 126.85, 126.82, 126.29, 125.45, 125.32, 125.23, 124.56, 124.18
(C6), 120.16 (C7), 119.65 (C9), 76.71 (C14), 53.61 (ZrCH3), 49.77
(ZrCH3), 28.86 (C20), 28.68 (C18), 28.17 (C19), 27.47 (C24), 25.83
(C25), 25.33 (C26), 25.04 (C21), 23.84 (C23), 23.15 (C22). Anal. Calcd
for C39H4ZrN2: C, 74.12; H, 7.02; N, 4.43. Found: C, 74.22; H, 7.15,
N, 4.42.
3
6.48 (d, 1H, J = 7.5 Hz, H90), 6.13 (s, 1H, H140), 3.92 (sep., 1H,
3J = 7.0Hz, H190), 3.45 (sep., 1H, 3J=6.8Hz, H180), 3.18 (sep., 1H, 3J=6.8
Hz, H200), 1.41 (d, 3H, 3J = 7.0 Hz, H240), 1.40 (d, 3H, 3J = 7.0 Hz, H250),
1.27 (d, 3H, 3J = 6.5 Hz, H220), 1.18 (d, 3H, 3J = 6.5 Hz, H260), 0.88 (s, 3H,
H270), 0.67 (s, 3H, H280), 0.48 (d, 3H, 3J = 6.5 Hz, H210), 0.29 (d, 3H, 3J =
7.0 Hz, H230). 1: 13C{1H} NMR (126 MHz, C6D6, 30 °C): δ 206.04
(C32), 170.53 (C34), 164.32 (C33), 147.35 (C37), 146.68 (36), 146.36
Polymerization ProceduresandPolymer Characterizations.
Ethylene/1-Octene Copolymerization. A 2 L Parr reactor was used
in the polymerizations. All feeds were passed through columns of
alumina and Q-5 catalyst (available from Engelhard Chemicals Inc.)
prior to introduction into the reactor. Procatalyst and cocatalyst
(activator) solutions were handled in the glovebox. A stirred 2 L reactor
was charged with about 533 g of mixed alkanes solvent and 250 g of
1-octene comonomer. Hydrogen was added as a molecular weight
control agent by differential pressure expansion from a 75 mL addition
tank at 300 psi (2070 kPa). The reactor contents were heated to the
polymerization temperature of 120 °C and saturated with ethylene at
460 psig (3.4 MPa). Catalysts and cocatalysts, as dilute solutions in
toluene, were mixed and transferred to a catalyst addition tank and
injected into the reactor. The polymerization conditions were main-
tained for 10 min with ethylene added on demand. Heat was continu-
ously removed from the reaction vessel through an internal cooling coil.
The resulting solution was removed from the reactor, quenched with
isopropyl alcohol, and stabilized by addition of 10 mL of a toluene
solution containing approximately 67 mg of a hindered phenol anti-
oxidant (Irganox 1010 from Ciba Geigy Corporation) and 133 mg of a
phosphorus stabilizer (Irgafos 168 from Ciba Geigy Corporation).
Between polymerization runs, a wash cycle was conducted in which
850 g of mixed alkanes was added to the reactor and the reactor was
heated to 150 °C. The reactor was then emptied of the heated solvent
immediately before beginning a new polymerization run. Polymers were
recovered by drying for about 12 h in a temperature-ramped vacuum
oven with a final set point of 140 °C. Melting and crystallization
temperatures of polymers were measured by differential scanning
calorimetry (DSC 2910, TA Instruments, Inc.). Samples were first
heated from room temperature to 180 at 10 °C/min. After being held
at this temperature for 2ꢀ4 min, the samples were cooled to ꢀ40 at
10 °C/min, held for 2ꢀ4 min, and then heated to 160 °C. Weight
average molecular weights (Mw) and polydispersity values (PDI) were
determined by analysis on a Viscotek HT-350 gel permeation chroma-
tographer (GPC) equipped with a low-angle/right-angle light-scattering
detector, a 4-capillary inline viscometer, and a refractive index detector.
The GPC utilized three Polymer Laboratories PLgel 10 μm MIXED-B
columns (300 ꢁ 7.5 mm) at a flow rate of 1.0 mL/min in 1,2,4-
trichlorobenzene at either 145 or 160 °C. To determine octene
incorporation, 140 μL of each polymer solution was deposited onto a
silica wafer, heated at 140 °C until the trichlorobenzene had evaporated,
and analyzed using a Nicolet Nexus 670 FTIR with 7.1 version software
equipped with an AutoPro auto sampler.
(C39), 145.55 (C38), 143.98 (C31), 140.81 (C35), 140.75 (C8, 1JCH
=
163.6 Hz), 135.70 (C29), 134.11 (C1, 1JCH = 158.6 Hz), 130.72 (C30),
130.09 (C10), 129.92 (C3), 129.86 (C2), 127.95 (CH), 126.90 (C5),
126.79 (CH), 125.99 (C16), 125.46 (CH), 125.41 (C4), 125.14
(C17), 124.47 (CH), 124.17 (C6), 120.36 (C7, 1JCH = 166.2 Hz, 2JCH
6.7 Hz),), 119.48 (C9, 1JCH = 166.4 Hz, 2JCH = 6.7 Hz), 76.75 (C14, 1JCH
=
=
133.5 Hz), 66.89 (C28, 1JCH = 111.6 Hz), 62.85 (C27, 1JCH = 112.8 Hz),
28.70 (C20), 28.63 (18), 28.12 (C19), 27.44 (C24), 25.77 (C25), 25.44
(C26), 25.16 (C21), 23.73 (C23), 23.02 (C22). Anal. Calcd for
C39H4HfN2: C, 65.12; H, 6.17; N, 3.89. Found: C, 65.56; H, 5.93, N, 3.73.
Preparation of [N-[2,6-Bis(1-methylethyl)phenyl]-R-[2-(1-methylethyl)-
phenyl]-6-(1-naphthalenyl-kC2)-2-pyridinemethanaminato(2-)-kN1,-
kN2]dimethylzirconium (3, 30). A solution of N-[2,6-bis(1-methylethyl)-
phenyl]-R-[2-(1-methylethyl)phenyl]-6-(1-naphthalenyl)-2-pyridi-
nemethanamine (2.25 g, 4.39 mmol) in hexane (40 mL) was cooled in a
glovebox freezer (ꢀ40 °C). nBuLi solution (1.93 mL of 2.5 M nBuLi in
hexane, 4.83 mmol) was added by syringe, and the suspension was stirred
for about 2 h after reaching ambient temperature. The reaction mixture
was cooled again in the freezer, filtered, washed with cold hexane, and
vacuum-dried overnight. The lithium amide product (2.38 g) as a light tan
solid powder was carried on to the next step without further treatment or
purification (quantitative recovery was assumed). This lithium salt (2.38 g
crude from the previous reaction, 4.38 mmol) was stirred in toluene
(∼50 mL) with ZrCl4 (1.02 g, 4.38 mmol). After mixing, the mixture
became clear and darkened. The solution was heated to reflux for 2 h, then
was allowed to cool to ambient temperature. The reaction solution was
chilled slightly below ambient temperature in the glovebox freezer just
prior to the addition of MeMgBr solution (5.06 mL of 3 M solution in
ether, 15.18 mmol), which was added via syringe. This mixture was stirred
atambient temperature overnight. The solvents wereremoved completely
under vacuum; then toluene (50 mL) was re-added and the mixture was
filtered. The residualdark sludge waswashedwithtoluene untilthe washes
were almost colorless. The collected toluene solution was stripped to
dryness under vacuum, and a crude product was obtained as a dark brown
powder. Hexane (∼30 mL) was added to the crude product, and it was
triturated briefly at ambient temperature before being cooled to ꢀ40 °C,
filtered, and washed with additional cold hexane. The solid product
recovered from the hexane filtering (1.36 g, 49% yield) was further
purified by recrystallization (toluene/hexane) to provide X-ray quality
crystals. 1H NMR (500 MHz, C6D6) δ 8.59 (d, 1H, J = 7.6 Hz, H1), 8.24
(d, 1H, J = 7.6 Hz, H6), 7.76ꢀ7.69 (m, 2H, H2/H3), 7.50 (d, 1H, J =
7.9 Hz, H7), 7.36 (m, 1H, H10), 7.32ꢀ7.25 (m, 2H, H4/H5), 7.19ꢀ7.10
(m, 2H, H16/H17), 7.09ꢀ7.05 (m, 2H, H13/H15), 7.04ꢀ6.97 (m, 2H,
H11/H12), 6.83 (t, 1H, J = 7.8 Hz, H8), 6.54 (d, 1H, J = 7.7 Hz, H9), 6.44
(s, 1H, H14), 3.84 (hept, 1H, J = 6.9 Hz, H19), 3.40 (hept, 1H, J = 6.7 Hz,
H20), 2.92 (hept, 1H, J = 6.7 Hz, H18), 1.38(d, 3H, J = 6.8 Hz, H25), 1.36
(d, 3H, J = 6.9 Hz, H24), 1.19 (s, 3H), 1.18 (d, 3H, J = 7.3 Hz, H21), 1.13
Propylene Polymerization. Propylene polymerization was con-
ducted in a 1.8 L SS batch reactor. This reactor was manufactured by
Buchi AG and sold by Mettler and is heated/cooled via the vessel jacket
and reactor head. Syltherm 800 was the heat transfer fluid used and was
controlled by a separate heating/cooling skid. Both the reactor and the
heating/cooling system are controlled and monitored by a Camile TG
process computer. The bottom of the reactor was fitted with a large
orifice bottom dump valve, which empties the reactor contents into a 6 L
SS dump pot. The dump pot was vented to a 30 gal blowndown tank,
with both the pot and the tank N2 purged. All chemicals used for
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Organometallics
ARTICLE
ꢃ
ꢂ
ka
polymerization or catalyst makeup were run through purification
columns, to remove any impurities that may effect polymerization.
The propylene, toluene, and IsoparE were passed through two columns,
the first containing A2 alumna, the second containing Q5 reactant. The
N2 and H2 were passed through a single Q5 reactant column. The
reactor was cooled to 50 °C for chemical additions. The Camile controls
the addition of IsoparE, using a micromotion flowmeter to accurately
add the desired amount. The addition of H2 was accurately achieved by
pressuring up a 50 mL shot tank to 240 psi and slowly adding H2 until
the desired decrease was reflected in the shot tank pressure. The
propylene was then added through the micromotion flowmeter.
After the chemicals were in the reactor, the reactor was heated to the
polymerization temperature. The activator(s) and catalyst were handled in
an inert glovebox, mixed together in a vial, drawn into a syringe, and pressure
transferred into the catalyst shot tank. This was followed by three rinses of
toluene, 5 mL each. Immediately after catalyst/activator addition, the run
timer began. Usually within the first 2 min of successful catalyst runs, an
exotherm was observed, as well as decreasing reactor pressure. These
polymerizations were run for 10 min; then the agitator was stopped, the
reactor pressured up to ∼500 psi with N2, and the bottom dump valve
opened to empty reactor contents to the dump pot. The dump pot contents
were poured into trays placed in a lab hood, where the solvent was
evaporated off overnight. The trays containing the remaining polymer were
then transferred to a vacuum oven, where they were heated to 145 °C under
vacuum to remove any remaining solvent. After the trays cooled to ambient
temperature, the polymers were weighed for yield/efficiencies and sub-
mitted for polymer testing. Weight average molecular weights (Mw) and
polydispersity values were determined by analysis on a SYMYX
high-throughput gel permeation chromatographer. The GPC utilized three
Polymer Laboratories PLgel 10 μm MIXED-B columns (300 ꢁ 10 mm) at
a flow rate of 2.5 mL/min in 1,2,4-trichlorobenzene at 160 °C. Melting and
crystallization temperatures of polymers were measured by differential
scanning calorimetry (DSC 2910, TA Instruments, Inc.). Samples were
first heated from room temperature to 210 at 10 °C/min. After being
held at this temperature for 4 min, the samples were cooled to ꢀ40 at
10 °C/min and were then heated to 215 at 10 °C/min after being held
at ꢀ40 °C for 4 min.
b
a
Bt ¼ A0
ðeꢀL ꢁt ꢀ eꢀL ꢁt
Þ
La ꢀ Lb
"
#
ꢀ
ꢁ
ꢀ
ꢁ
1
Ra ꢀ Rb þ ka ꢀ kb
La ꢀ Lb
Ra ꢀ Rb þ ka ꢀ kb
eꢀL ꢁt
þ
1 ꢀ
eꢀL ꢁt
b
a
þ
Bo 1 þ
ꢄ
2
La ꢀ Lb
ꢅ
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1
2
La¼
Lb ¼
ðRa þ Rb þ ka þ kbÞ þ ½ðRa ꢀ Rb þ ka ꢀ kbÞ þ4kakbꢂ
2
1
2
ꢄ
ꢅ
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
ðRa þ Rb þ ka þ kbÞ ꢀ ½ðRa ꢀ Rb þ ka ꢀ kbÞ þ4kakbꢂ
ð5Þ
Magnetization transfer experiments were performed on a Varian
VNMRS 500 (FT 500 MHz) spectrometer equipped with a pulse-field
gradient probe using NOESY1D pulse sequences (double pulse field
gradient spin echo NOE (DPFGSE-NOE) method22). Magnetization
transfer data were collected at 10, 20, 30, and 40 °C. The resonance at
6.12ꢀ6.15 ppm was selectively excited in each of these experiments, and
its return to equilibrium together with its exchange with the peak at
6.57ꢀ6.59 ppm was followed as a function of time (mixing time). Probe
temperature was calibrated using ethylene glycol. Acquisition time was
set to 2 s with a delay time of 1 s. Line broadening of 0.5 was used. The
number of transients collected for each spectrum was set from 128 to
856. All the resonances were integrated and tabulated. Chemical
exchange rate constants (k) were obtained by fitting time-dependent
integrated values of both signals to eqs 4 and 5 using a nonlinear least-
squares routine. Five parameters (Ao, Bo, ka, kb, Ra, and Rb) were varied
in order to minimize the sum of the squared deviations between the
experimental and calculated data. Microsoft Excel solver was used to
perform this least-squares analysis. Thermodynamic parameters (ΔH‡
and ΔS‡) were obtained by least-squares analysis of the nonlinear form
of the Eyring equation.23 In this procedure, rate constants are calculated
using the nonlinear form of the Eyring equation, and the ΔH‡ and ΔS‡
are adjusted until the sum of the error squared between the observed and
calculated rate constants reaches a minimum. Microsoft Excel solver was
used to perform this least-squares analysis. Errors were obtained by
nonlinear error analysis using SolvStat macro.24
13C NMR Analysis of Polypropylene Samples. The sample
was prepared by adding approximately 2.7 g of stock solvent to a
0.21ꢀ1.2 g sample in a 10 mm NMR tube and then purging in an N2 box
for 2 h. The stock solvent was made by dissolving 4 g of PDCB para-
dichlorobenzene in 39.2 g of ortho-dichlorobenzene with 0.025 M
chromium acetylacetonate (relaxation agent). The sample was dissolved
and homogenized by heating the tube and its contents at 140ꢀ150 °C.
The data were collected using a Bruker 400 MHz spectrometer equipped
with a Bruker Dual DUL high-temperature CryoProbe.25 For 1D 13C
NMR, the data were acquired using 320 transients per data file, a 7.3 s
pulse repetition delay (6 s delay þ1.3 s acq. time), 90 degree flip angles,
and a modified inverse gated decoupling26 with a sample temperature of
120 °C. All measurements were made on nonspinning samples in locked
mode. Samples were homogenized immediately prior to insertion into
the heated (125 °C) NMR changer and were allowed to thermally
equilibrate in the probe for 7 min prior to data acquisition.
Magnetization Transfer Experiments.18 NMR measurements
were performed on a Varian VNMRS 500 (FT 500 MHz) spectrometer
using toluene-d8. The rate of this chemical exchange was measured by
following transfer of magnetization (by measuring areas under the
exchanging resonances) as a function of mixing time. A two-site
exchange process is illustrated in eq 1. The rate laws for this two-site
exchange are shown in eqs 2 and 3. Integration of these rate laws leads to
expressions 4 and 5, where At and Bt are peak intensities (integrals) of
resonances A and B at time t, Ao and Bo are peak intensities (integrals) of
A and B at t = 0, k is the chemical exchange rate constant, t is the mixing
time, and Ra and Rb are relaxation rates for A and B.21
ka
Ra
r
Rb
f
s
relaxation
AhB
s
relaxation
Keq ¼ ka=kb
ð1Þ
ð2Þ
ð3Þ
kb
DA
Dt
¼ kb½Bꢂ ꢀ ka½Aꢂ ꢀ Ra½Aꢂ
DB
Dt
¼ ka½Aꢂ ꢀ kb½Bꢂ ꢀ Rb½Bꢂ
’ COMPUTATIONAL DETAILS
Calculations were carried out with the Gaussian0327 program. All
optimizations and frequencies used the hybrid density functional theory
(DFT) method, B3LYP.28 These calculations were performed with the
LANL2TZ(f)29 basis set on hafnium, which includes triple-ζ functions
on the valence and added f-functions, while the inner electrons are
approximated by the LANL2DZ effective core potential. All other atoms
utilize the 6-311G** basis set.30 Unless otherwise stated, energies are
compiled in kcal/mol, and free energies are quoted at 298 K.
"
ꢀ
ꢁ
1
Ra ꢀ Rb þ ka ꢀ kb
At ¼ Ao 1 þ
eꢀL ꢁt
b
2
La ꢀ Lb
ꢀ
ꢁ
ꢂ
ꢃ
ꢂ
Ra ꢀ Rb þ ka ꢀ kb
kb
La ꢀ Lb
eꢀL ꢁt þB0
ðeꢀL ꢁt ꢀeꢀL ꢁt
Þ
a
b
a
þ 1þ
La ꢀ Lb
ð4Þ
3327
dx.doi.org/10.1021/om200167h |Organometallics 2011, 30, 3318–3329

Organometallics
ARTICLE
Structure Determination of 1 and 3. Data for both structures
were collected at 173 K on a Siemens SMART PLATFORM equipped
with a CCD area detector and a graphite monochromator utilizing Mo
KR radiation (λ = 0.71073 Å). Cell parameters were refined using up to
8192 reflections in each case. A hemisphere of data (1381 frames) was
collected using the ω-scan method (0.3° frame width) for each structure.
The first 50 frames were remeasured at the end of data collection to
monitor instrument and crystal stability (maximum correction on I was
<1%). Absorption corrections by integration were applied on the basis of
measured indexed crystal faces.
(3) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.;
Wenzel, T. T. Science 2006, 312, 714–719.
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Petersen, J. L.; Theriault, C. N.; Vosejpka, P. C. Organometallics 2007,
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Kuhlman, R. L.; Theriault, C. N.; Welsh, D. M.; Abboud, K. A.
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The structures were solved by the direct methods in SHELXTL631
and refined using full-matrix least-squares. The non-H atoms were
treated anisotropically, whereas the hydrogen atoms were calculated in
ideal positions and were riding on their respective carbon atoms. For 1,
in the final cycle of refinement, 6234 observed reflections with I > 2σ(I)
were used to refine 387 parameters, and the resulting R1, wR2, and S
(goodness of fit) were 2.31%, 5.33%, and 1.03, respectively. A correction
for secondary extinction was not applied. For 3, in the final cycle of
refinement, 21 193 observed reflections with I > 2σ(I) were used to refine
379 parameters, and the resulting R1, wR2, and S (goodness of fit) were
3.7%, 8.54%, and 0.924, respectively. A correction for secondary extinction
was not applied due to the small crystal size. Refinement was done using F2.
Structure Determination of 2. The crystal, mounted on a Mitegen
Micromount, was automatically centered on a Bruker SMART X2S bench-
top crystallographic system. Intensity measurements were performed using
monochromated (doubly curved silicon crystal) Mo KR radiation (0.71073
Å) from a sealed microfocus tube. Generator settings were 50 kV, 30 mA.
Data were acquired using three sets of omega scans at different phi settings.
APEX2 software was used for preliminary determination of the unit cell.
Determinations of integrated intensities and unit cell refinement were
performed using SAINT. Data were corrected for absorption effects with
SADABS using the multiscan technique. The structure was solved with XS,
and subsequent structure refinements were performed with XL.
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’ ASSOCIATED CONTENT
S
Supporting Information. NMR spectra, X-ray data for 1,
b
2, and 3 including CIF file, table with total energies for all
computed structures, mol file containing xyz data for all com-
puted structures, and Excel spreadsheet containing magnetiza-
tion transfer calculations. This material is available free of charge
via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: jklosin@dow.com.
(12) Alfanso, F.; Boone, H. W.; Busico, V.; Cipullo, R.; Stevens, J. C.
Macromolecules 2007, 40, 7736–7738.
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K. A. J. Am. Chem. Soc. 2008, 130, 10354–10368. (c) Busico, V.; Cipullo,
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dx.doi.org/10.1021/om200167h |Organometallics 2011, 30, 3318–3329

Organometallics
ARTICLE
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