Synthesis of imino-enamido hafnium and zirconium complexes: A new family of olefin polymerization catalysts with ultrahigh-molecular-weight capabilities

Article abstract of DOI:10.1021/om101207a

Bidentate, nitrogen-containing molecules are of interest as ligands in transition-metal-catalyzed olefin polymerization. A computational evaluation of a series of 1,2-bis-imines, 1,2-imine-enamines, and 1,2-bis-enamines of cyclic and acyclic derivatives w

Full text of DOI:10.1021/om101207a

ARTICLE
pubs.acs.org/Organometallics
Synthesis of Imino-Enamido Hafnium and Zirconium Complexes:
A New Family of Olefin Polymerization Catalysts with
Ultrahigh-Molecular-Weight Capabilities
Ruth Figueroa, Robert D. Froese, Yiyong He, Jerzy Klosin,* and Curt N. Theriault
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: Bidentate, nitrogen-containing molecules are of
interest as ligands in transition-metal-catalyzed olefin polymer-
ization. A computational evaluation of a series of 1,2-bis-imines,
1,2-imine-enamines, and 1,2-bis-enamines of cyclic and acyclic
derivatives was conducted to understand the relative thermo-
dynamic stabilities of these compounds. The five- and six-
membered-ring 1,2-imine-enamines were found to be more
stable than the other tautomers, while the 1,2-bis-imines were calculated to have the lowest energy among four- and seven-
membered-ring and acyclic derivatives. On the basis of the computational results, literature examples, and prior experience with
imino-amido catalysts, 1,2-imine-enamines containing a cyclohex-2-enylidene backbone were targeted as ligands for a new family of
polyolefin catalysts. The desired ligands were prepared in three steps, starting from the commercially available 1,2-cyclohexane-
dione, and subsequently converted into hafnium and zirconium complexes. An ethylene/1-octene copolymerization study
conducted at 120 °C demonstrated that the hafnium complex possessed very good activity for the production of polymers with
ultrahigh molecular weight (Mw of 1037 kDa) and moderate 1-octene incorporation. This molecular weight is 20 times higher than
that produced by the titanium constrained geometry catalyst (CGC) under the same polymerization conditions. The imino-
enamido zirconium complex exhibited slightly lower activity than that observed for the hafnium catalyst, yielding an ethylene/
1-octene copolymer with Mw and mol % 1-octene incorporation of 509 kDa and 6.4, respectively. The polymerization reactions with
these catalysts conducted in the presence of diethylzinc led to a sharp decrease in the observed polymer molecular weights, indicative
of effective chain transfer. These imino-enamido complexes exhibit higher activity, produce higher molecular weight polymers,
incorporate higher levels of 1-octene, and demonstrate significantly improved thermal stability relative to analogous imino-amido
complexes reported previously.
’ INTRODUCTION
polymerization reactions.8 Imino-amido complexes are attrac-
tive, as they are readily prepared from commonly available
starting materials and a large and diverse library of such com-
plexes is accessible. More importantly, they exhibit good catalytic
activities at industrially relevant temperatures (greater than
100 °C), are capable of producing very high molecular weight
ethylene-based copolymers, and have the ability to undergo
reversible chain transfer with diethylzinc to produce olefin block
copolymers.5 A few representative imino-amido complexes in-
vestigated in our laboratory are displayed in Scheme 1.
There has been continued research aimed at the discovery of
new olefin polymerization catalysts1 that would allow for either
the production of new polyolefin products2 or lead to significant
improvements to current polymerization processes.3 Some im-
portant characteristics of olefin polymerization catalysts for the
synthesis of polyolefin copolymers, specifically poly(ethylene-co-
R-olefin), include molecular weight capabilities, reactivity toward
R-olefins, catalytic activity, and reactivity toward chain transfer
agents such as hydrogen and alkylaluminum or -zinc compounds.
Equally important is how these characteristics are influenced by
reaction conditions, such as concentration of monomers and
temperature.
Despite the advantages of imino-amido precatalysts, their in-
dustrial utility might be limited due to the thermal instability of
these materials. For example, precatalysts such as 1 were found to
decompose at elevated temperature to form ene-diamido
Recently, we4-6 and others7 have reported the use of group 4
imino-amido complexes, a class of compounds originally intro-
duced by Union Carbide Corp., as precatalysts for olefin
Received: December 28, 2010
Published: March 11, 2011
r
2011 American Chemical Society
1695
dx.doi.org/10.1021/om101207a Organometallics 2011, 30, 1695–1709
|

Organometallics
ARTICLE
Scheme 3. Synthesis of Imino-Enamines 7 and 9
Scheme 1. Examples of Previously Studied Imino-Amido
Complexesa
a DIP = 2,6-i-Pr2C6H3, Bn = CH2Ph.
These imino-enamines attracted our interest because they are
structurally similar to the imino-amine ligands and contain the
cyclohex-2-enylidene backbone which, in principle, should yield
configurationally stable complexes. Ligand 9 has been used in
the preparation of nickel,10,11 palladium,14 and aluminum
compounds15 but had not been yet reported in the synthesis of
group 4 transition metal complexes.16 Neutral and cationic nickel
complexes with acyclic imino-enamido ligands were reported as
well.17 Herein, we report a study of the computational stability of
various 1,2-bis-imines, 1,2-imino-enamines, and 1,2-bis-enam-
ines and the preparation of hafnium and zirconium complexes
containing imino-enamido ligands with a cyclohex-2-enylidene
backbone and their olefin polymerization characteristics.18
Scheme 2. Structural Rearrangement of Imino-Amido
Complexes 1 and 5a
’ RESULTS AND DISCUSSION
Computational Study of Bis-Imines vs Imino-Enamines. It
is not intuitively obvious why the reaction between primary
amines and acyclic 1,2-diones leads to the formation of 1,2-bis-
imines, whereas the analogous reaction with 1,2-cyclohexane-
dione produces the 1,2-imino-enamine isomer, as described
above. It was also reported13 that the reaction of isopropylamine
with cycloheptane-1,2-dione gives the corresponding bis-imine,
whereas the reaction of the same amine with 1,2-cyclohexane-
dione leads to the imino-enamine. These observations clearly
indicate that there are subtle thermodynamic preferences that
exist between such 1,2-bis-imines and 1,2-imino-enamines. To
understand the factors that control these preferences and to help
us determine which elements are critical to produce stable imine-
enamines suitable for complexation with early transition metals,
a computational study was carried out on the molecules shown
in Scheme 4. Ground-state energies for alkyl (i-Pr)- and aryl-
based (DIP) bis-imines (trans/trans (a), trans/cis (b), and cis/
cis (c) isomers), imino-enamines (d), and bis-enamines (e)
were calculated using density functional theory (DFT) and
G3MP2B3 methods19,20 for the four-, five-, six-, and seven-
membered-ring and acyclic derivatives (Scheme 4). These data
indicate that the nitrogen substitution (alkyl vs aryl) only has a
minor effect on the relative energies in each series. For this
reason, the following discussion will include only the data for
the i-Pr derivatives calculated using the high-level G3MP2B3
method.
complexes (4) via dibenzyl elimination (Scheme 2).4 The rate of
decomposition was found to be dependent on the nature of the
metal, with faster rates observed for zirconium derivatives than for
hafnium analogues. A second subclass of imino-amido complexes
containing the trimethylethylidene ligand bridge (e.g., 3, 5a) also
was found to be thermally unstable, decomposing via a 1,2-methyl
backbone rearrangement. This reaction results in the production of
a more stable isomeric precatalyst 5b (Scheme 2), but one that
exhibits poorer polymerization performance.6 We desired to pre-
pare imino-amido complexes with a ligand framework resistant to
the aforementioned deactivation pathways while maintaining po-
lymerization attributes of the best examples from this family of
catalysts.
Over a decade ago, van Asselt and co-workers9 described the
reaction of 1,2-cyclohexanedione (6) with excess isopropylamine
to yield imino-enamine 7, rather than the expected bis-imine
8 product (Scheme 3). Subsequently, groups from Mitsui
Petrochemical Industries10 and DuPont11 reported the analo-
gous reaction between 1,2-cyclohexanedione and 2 equiv of 2,6-
diisopropylaniline to form imino-enamine 9 (Scheme 3). Again,
formation of the bis-imine isomer was not observed. Other
imino-enamines with the cyclohex-2-enylidene backbone con-
taining alkyl substituents on the nitrogen atoms have been also
reported.12,13
There is a clear effect of the bridging unit on the relative
stability of 1,2-bis-imines and 1,2-imine-enamines. For five- and
six-membered-ring derivatives, the imino-enamine tautomers
(11d, 7) are favored considerably. Within five-membered-ring
derivatives, the imino-enamine isomer 11d is lowest in energy
and is favored over the next lowest trans/cis bis-imine 11b by 5.9
1696
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
Scheme 4. Calculated Ground-State Energy Differences between Various Isomersa
a Calculations were performed using the G3MP2B3 method. Relative enthalpies are in kcal/mol. Structures in blue and red correspond to the lowest and
highest energy compounds within each series. b Optimized with the NdC-CdN fragment constrained in a coplanar σ-cis configuration.
kcal/mol. Within six-membered-ring compounds, the imino-
enamine 7 is favored over the cis/cis bis-imine 12c by 4.4
kcal/mol. Five and six-membered-ring trans/trans bis-imines
11a and 12a are higher in energy than the corresponding
imino-enamine by 8.0 and 8.5 kcal/mol, respectively.21 Interest-
ingly, within the seven-membered-ring compounds, the relative
stability of bis-imine and imino-enamine is reversed, with the bis-
imine tautomer 13c being lower in energy by 5.5 kcal/mol. For
the four-membered-ring series, the bis-imine 10b is preferred
over imine-enamine 10d by 3.2 kcal/mol. In all cases, bis-
enamine isomers are higher in energy compared to imine-
enamines, with the largest difference calculated for the four-
membered-ring analogue 10e due to the formation of the
antiaromatic structure.
analogues, where 1-methylcycloalkenes are more stable than the
corresponding methylenecycloalkanes by at least 2 kcal/mol.23
Two factors appear critical for the relative stability of trans/trans
bis-imine and imino-enamine tautomers, and both are related to
the relative arrangement of the N-C-C-N fragment. One of
those factors is the hydrogen bonding between the imine
nitrogen and enamine NH group, which would be expected to
be strongest for the five- and six-membered-ring derivatives, due
to the close proximity of these groups resulting from the nearly
coplanar arrangement of the N-C-C-NH fragment. The
NdC-C-NH torsion angles in the five-, six- and seven-
membered-ring imino-enamines are approximately 4, 5, and
44°, respectively. For the six-membered-ring imine-enamine 9,
this torsion angle was determined crystallographically to be 3.7°
(vide infra). The hydrogen bond, however, would not be
expected to be stronger than 3-6 kcal/mol in compounds of
this type,24 which is still less than the energy difference between
the trans/trans bis-imine and imino-enamine tautomers for
the five- and six-membered-ring derivatives. Thus, hydrogen
There are a few important factors that determine the relative
stability of isomers shown in Scheme 4. For the following
discussion, it is important to point out that cyclic mono-imines
are more stable than the corresponding enamines by a few kcal/
mol.22 This trend is opposite to that observed for hydrocarbon
1697
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
bonding cannot be the sole contributing factor to the stability of
the five- and six-membered-ring imino-enamines.
A second major contributor to the enhanced stability of five-
and six-membered-ring imino-enamines over the corresponding
trans/trans bis-imines is the destabilization of the latter caused by
repulsion between the lone-pair electrons of the bis-imine
nitrogen atoms. Bis-imine destabilization should be the strongest
for five- and six-membered-ring derivatives due to the close
proximity of two imine nitrogen atoms, reduced in the four-
membered system as the nitrogen atoms are further apart and the
angle directs the lone pairs somewhat away from each other,
reduced also in the seven-membered-ring system where the ring
twist allows the lone pairs to avoid one another, and nonexistent
in the acyclic derivative which assumes a σ-trans configuration.
The NdC-CdN torsion angles in the five-, six-, and seven-
membered-ring trans/trans bis-imines are approximately 0, 46,
and 91°, respectively. Thus, the five- and six-membered-ring
trans/trans bis-imines are disfavored due to lone-pair-lone-pair
repulsions and imine-enamines are favored due to stronger
hydrogen bonding. Consistent with the bis-imine destabilization
hypothesis is that cyclic mono-imines are more stable than their
enamine counterparts.21 Another piece of supporting informa-
tion that the lone-pair-lone-pair interaction is a destabilizing
feature is that the five- and six-membered-ring bis-imines gen-
erally do not exist in the trans/trans form unless large steric
groups such as DIP reside on the imine nitrogen atoms.25 For
example, trans/cis bis-imines 11b and 12b are more stable than
their trans/trans counterparts 11a and 12a by 2.1 and 2.6 kcal/
mol, respectively.26,27 Additionally, for acyclic bis-imines, the
σ-trans isomer 14a is lower in energy than the σ-cis rotamer
14b by ca. 10 kcal/mol. Another piece of intriguing evidence
comes from the Cambridge Crystallographic Database, where
acyclic bis-imines were examined. All acyclic 1,2-bis-imines were
found to exist in the σ-trans conformation,25b,28 except for
three,29 which contain CF3 groups in the 2- and 3-positions of
the 1,4-diazabutadiene fragment. In the σ-trans configuration,
the lone pairs of the fluoride atoms appear capable of having a
strong repulsive interaction with the imine lone pair, leading to
considerable rotation of the two imine fragments away from each
other, as observed experimentally (NdC-CdN torsion angle
between 55 and 64°).29
Six- and seven-membered-ring bis-imines are intriguing in that
the cis/cis isomers are lower in energy than their trans/trans and
trans/cis counterparts. Since only one of the imines needs to
adopt the cis configuration to avoid the lone-pair-lone-pair
interaction, it is surprising that both bis-imines adopt the cis/cis
configuration. However, the severely twisted NdC-CdN frag-
ment allows for the reduction of steric interaction between the
two i-Pr groups. The seven-membered-ring cis/cis bis-imine
13c has the lowest ground-state energy among all seven-mem-
bered-ring derivatives. Published 1H and 13C NMR data13 for the
seven-membered-ring bis-imine are most consistent with the C2-
symmetric (chiral) structure 13c.30 Within the four-membered-
ring series, the trans/cis bis-imine 10b has the lowest energy,
with the trans/trans isomer 10a being 1.8 kcal/mol higher in
energy.
The relative energy trends shown in Scheme 4 are comparable
to energy differences calculated for the cyclic 1,2-keto-enamine/
1,2-keto-imine and 1,2-keto-enol/1,2-diketone pairs, pointing to
a common reason for the observed stability trends.31
The most significant result from this computational study is
that the five- and six-membered-ring imino-enamines are
Figure 1. Molecular structure of 9. Hydrogen atoms, except H1, are
omitted for clarity. Thermal ellipsoids are shown at the 40% probability
level. Atoms refined isotropically are represented by open spheres.
Selected bond lengths (Å) and angle (deg): C1-N2 = 1.306(2), C6-
N1 = 1.352(2), C5-C6 = 1.390(2), N1-H1 = 0.85(3), N2-H1 =
2.175; N1-H1-N2 = 111.5.
Scheme 5. Synthesis of Hafnium Complex 15
considerably lower in energy than any other derivative in the
five- and six-membered-ring series. This indicates that these two
imino-enamines should exist exclusively as a single isomer and
thus be good candidates for complexation with early-transition-
metal precursors.
Synthesis of Ligands and Complexes. It was of interest to us
to prepare hafnium and zirconium complexes containing cyclohex-
2-enylidene-bridged imino-enamido ligands, direct analogues of the
imino-amido complexes 2 and 3, and evaluate their olefin polym-
erization characteristics. Since ligand 9 is readily accessible, pre-
paration of its hafnium complex was undertaken initially to compare
properties of this precatalyst with those of the imino-amido
analogue 2. The desired ligand, (E)-N-(2-((2,6-diisopropylphe-
nyl)amino)cyclohex-2-enylidene)-2,6-diisopropylbenzenamine (9),
was prepared in 50% yield by following a literature procedure.11b
Single-crystal X-ray analysis of 9 confirms the planar arrangement of
the NdC-CdNH fragment (Figure 1). The reaction of 9 with
Hf(CH2Ph)4 in toluene produced, after 5 days at 76 °C, the desired
complex 15 in about 90% yield by NMR (Scheme 5). Complex 15
was obtained in pure form in 53% yield after crystallization from
toluene/hexane. The NMR spectra of 15 are consistent with Cs
1
symmetry in solution. Resonances of interest observed in the H
NMR spectrum32 of 15 include two septets appearing at 2.74 and
3.51 ppm, which are assigned to the i-Pr methine protons of the 2,6-
diisopropylphenyl groups of the imine and enamine nitrogen
substituents, respectively. These assignments were confirmed by
1698
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
Scheme 6. General Strategy for the Synthesis of Unsymme-
trical Imino-Enamines
also in the solid state, as shown by single-crystal X-ray analysis.34
DFT calculations indicate that keto-enamine 17 is 7.9 kcal/mol
more stable than the isomeric keto-imine. This energy difference
is similar to that calculated for the six-membered-ring imino-
enamine 9 and its bis-imine tautomer. The presence of only one
doublet for the i-Pr methyl groups at 1.10 ppm is indicative of
rapid rotation of the 2,6-diisopropylphenyl fragment on the
NMR time scale. To access the desired ligand, several different
conditions were evaluated for the imine formation step. The best
conversion was obtained when 7 was reacted with 1.0 equiv of n-
octylamine and 1.0 equiv of formic acid. The product was isolated
in 59.5% yield by column chromatography using silica buffered
with triethylamine. However, the structure of the isolated imino-
enamine (18b) was different from that of the desired ligand
(18a), as shown by NOE analysis. Irradiation of the triplet at 5.04
ppm (3J = 4.6 Hz) corresponding to the vinyl proton (H2)
resulted in a strong NOE of a quartet (3J = 7.0 Hz) at 2.91
ppm corresponding to the methylene protons H7 and no
detectable NOE enhancement of the i-Pr groups. Additionally,
irradiation of the pseudotriplet at 2.06 ppm assigned to the H5
methylene (assignment based on 1D TOCSY and COSY)
showed strong enhancement to the resonances of the i-Pr groups.
These measurements clearly indicate that the structure of the
obtained ligand is that of 18b instead of the desired 18a.
1D NOESY measurements.32 Irradiation of the vinyl proton H5
resonating at 4.96 ppm shows a strong NOE of the i-Pr methine at
3.51 ppm, the i-Pr methyl groups at 1.14 ppm, and the cyclohex-2-
enylidene allylic protons resonating at 1.81 ppm. All benzyl
methylene protons appear as a singlet at 2.10 ppm, indicating fast
exchange of all three benzyl groups on the NMR time scale. In
addition to NMR and elemental analysis, complex 15 was also
characterized by X-ray single crystal analysis (vide infra).
1
Interestingly, the H NMR spectrum shows two doublets for
the i-Pr methyl groups, indicating restricted rotation of the 2,6-
diisopropylphenyl fragment on the NMR time scale. Reaction of
18b with Hf(CH2Ph)4 quantitatively yielded 19 within 1 h at
ambient temperature (Scheme 7). Complex 19 crystallized
slowly from a hexane solution at -35 °C over a period of 2
weeks. In addition to 1D and 2D NMR spectroscopy, complex 19
was characterized by elemental analysis and single-crystal X-ray
analysis (vide infra). The NOE experiments and X-ray analysis of
19 validated that the configuration of the imino-enamido
fragment in this complex is the same as in the corresponding
ligand 18b.
The most likely reason for the observed outcome of the imine-
formation reaction to produce 18b is that the condensation
reaction gives the desired ligand 18a, which under acidic condi-
tions isomerizes to the thermodynamically more stable 18b. This
is consistent with DFT calculations, which confirmed that 18b is
more stable than the desired ligand 18a by 1.9 kcal/mol. This
result suggests that perhaps this isomerization can be slowed
down or eliminated if the imine-formation step is conducted
under acid-free conditions. We turned our attention to titanium-
induced imine formation reactions,36 as this method does not
Due to the higher polymerization activity of imino-amido
complex 3 relative to that of 2, preparation of an imino-enamine
complex analogous to 3 was highly desired. Preparation of imino-
enamine ligands with two different substituents at the imine and
enamine nitrogen atoms requires a different synthetic approach,
as both groups need to be introduced sequentially. The general
strategy for the preparation of such unsymmetrical imino-enam-
ine ligands is outlined in Scheme 6 and involves preparation of
keto-enamine via transamination of morpholino-ketone 16 with
a primary amine to give a keto-enamine with the desired R1
group, followed by condensation of the product with another 1
equiv of primary amine to form the desired imino-enamines.
The synthesis was initiated with the preparation of the
morpholine derivative 16, which was synthesized in 95% yield
via condensation of 1,2-cyclohexanedione with morpholine
(Scheme 6).33 Compound 16 was fully characterized by both
NMR spectroscopy and single-crystal X-ray analysis.34 Transa-
mination of enamine 16 using p-toluenesulfonic acid hydrate
(PTSA) was used previously to form aryl-based keto-enamines.35
Transamination of 16 under similar reaction conditions to those
previously reported35b with 1 equiv of 2,6-diisopropylaniline and
0.1 equiv of acid at 50 °C resulted in a poor yield of 2-((2,6-
diisopropylphenyl)amino)cyclohex-2-enone (17) after 24 h.
Alternatively, we found that when the reaction was conducted
at 80 °C using 1.0 equiv of PTSA, 17 can be isolated in high yield
as a yellow solid. The transamination route is necessary to obtain
clean product 17, as direct condensation of 6 with 1 equiv of 2,6-
involve acidic reaction conditions. Imine and enamine formation
36a-d
reactions were reported using both TiCl4
or premade
titanium amido36e reagents.
Due to the high solubility of the n-octyl Hf complex 19, the
preparation of ligands with the shorter n-butyl chain on the imine
nitrogen was considered to decrease solubility. The titanium
reagent was prepared by refluxing Ti(NMe2)4 with 6 equiv of n-
butylamine in toluene for 6 h under a constant nitrogen sweep to
remove dimethylamine. Removal of the solvent gave the Ti-
imido reagent as a brown-red glossy solid. The structure of the
product is polymeric in nature ((Ti(N-n-Bu)2)n), as suggested by
1
the broad features in the H NMR spectrum32 and results
1
diisopropylaniline gives a mixture of products. The H NMR
described previously by Bradley and Torrible.37
spectrum of 17 shows the presence of a triplet at 4.95 ppm,
indicating that the compound exists as the keto-enamine rather
than the keto-imine. The keto-enamine form of 17 is maintained
The reaction of 17 with the Ti-imido reagent at room tempera-
ture in toluene led to the formation of the desired product 20a in
good yield (Scheme 8). However, this reaction took about 2 days
1699
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
Scheme 7. Synthesis of Hafnium Complex 19
4.78 ppm (3J = 4.6 Hz) corresponding to the vinyl proton H5
leads to a strong NOE of the septet at 3.39 ppm corresponding to
i-Pr methine protons and a quartet at 1.96 ppm assigned to the
methylene protons H4 and no detectable NOE enhancement of
methylene protons H7. Unlike the case of 18b, there is only one
doublet present in the 1H NMR spectrum of 20a corresponding
to the i-Pr methyl groups. The 13C{1H} NMR spectrum features
a broad signal at 24.23 ppm (Δν1/2 = 160 Hz) corresponding to
the i-Pr methyl groups. This broad signal is an indication of
hindered rotation about the 2,6-diisopropylphenyl fragment
along the N-C(ipso) bond. The presence of only one doublet
in the 1H spectrum for the i-Pr methyl groups is most likely due
to small chemical shift differences (smaller than in the case of the
analogous resonances observed in the 13C{1H} spectrum)
between the i-Pr methyl groups in the 1H spectrum at the low-
exchange regime. This leads to coalescence at temperatures
lower than in the case of resonances in the 13C{1H} spectrum.
To test if ligand 20a is stable to isomerization under neutral
conditions, it was heated to 71 °C for 39 h in C6D6. 1H NMR
showed no indication of isomerization. On the other hand,
addition of 3% HCl (in diethyl ether) relative to 20a, dissolved
in C6D6, led to complete and clean isomerization to produce 20b
within 10 min at ambient temperature. These experiments clearly
indicate that these alkyl-imino-aryl-enamines are thermally stable
but can be converted readily to thermodynamically more stable
aryl-imino-alkyl-enamine isomers in the presence of a catalytic
amount of acid.
Scheme 8. Synthesis of Hafnium and Zirconium Complexes
21 and 22
to reach full completion. It is important to maintain good stirring,
which is made difficult by the formation of a thick brown
byproduct during the course of the reaction. Despite the long
reaction times, this synthetic method was found to be reliable and
allowed preparation of this ligand on a multigram scale. The
NMR spectra, including 1D NOESY data, are consistent with the
desired structure 20a. For example, irradiation of the triplet at
Reaction of ligand 20a with M(CH2Ph)4 (M = Hf, Zr) leads to
clean formation of the desired complexes 21 and 22 in good
yields at ambient temperature within 1 h (Scheme 8). No
isomerization of the ligand framework was observed during
1700
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
Figure 2. Schematic representation of possible low-temperature solu-
tion structure of 21.
preparation of 21 and 22, as confirmed by NOE experiments and
X-ray crystallography. Both complexes exhibit Cs symmetry in
solution, as shown by NMR spectroscopy. For example, the 1H
NMR spectrum of 21 shows only one i-Pr methine signal at 3.24
ppm and two doublets at 1.11 and 1.31 ppm corresponding to the
i-Pr methyl groups, indicating that both i-Pr groups have the
same chemical environment. The appearance of two separate
resonances for the i-Pr methyl groups is due to the hindered
rotation of the 2,6-diisopropylphenyl fragment along the N-
C(ipso) bond, which leads to a different chemical environment of
the methyl groups pointed toward and away from the cyclohex-2-
enylidene bridge. This is a very common phenomenon in
complexes containing the bulky 2,6-diisopropylphenyl
fragment.6,38 NOE experiments indicate that the upfield doublet
(1.11 ppm) corresponds to the methyl groups pointing toward
the bridge of the ligand. As hoped, both complexes are highly
crystalline compared to 19 and can be crystallized easily from a
toluene/hexane solvent mixture. In addition to other NMR
techniques, all new ligands and complexes were studied by 1D
TOCSY, which allows for unequivocal identification of protons
associated with the two separate spin systems of cyclohex-2-
enylidene and N-n-alkyl fragments. For example, irradiation of
the methylene protons R to the N(imine) atom at 2.80 ppm in 21
clearly identified the remaining protons of the butyl chain
resonances at 1.17, 1.06, and 0.77 ppm. The 1H NMR spectrum
of 21 contains a broad singlet at 2.11 ppm assigned to the three
benzyl methylene groups. The broadness of this resonance
indicates that the rate of chemical exchange of the three benzyl
groups is reduced from a fast chemical exchange regime and
suggested the possibility of freezing out this fluxional process at
low temperature. When a solution of 21 in toluene-d8 is cooled
to -70 °C, three separate resonances for the benzyl groups are
observed. The variable-temperature NMR spectra show coales-
cence of all three benzyl resonances at around -20 °C.32 The
most likely mechanism of this fluxional process is the rotation of
the imino-enamido ligand about a C3 axis of the HfBn3 fragment.
A static structure accounting for the appearance of three different
benzyl groups at low temperature is shown in Figure 2. This
structure is similar to solid-state structures of 21 and 22
determined by single-crystal X-ray crystallography (vide infra).
As mentioned earlier, the major motivation for the preparation
and investigation of complexes with the cyclohex-2-enylidene
backbone was to identify complexes with high thermal stability.
With a sample of 21 in hand, it was finally possible to answer the
question about its thermal stability. A solution of 21 in toluene-d8
was heated in the NMR probe to 89 °C for 42 h. To our delight,
the NMR spectra showed very little (less than 4%) decomposi-
tion, indicating the very high thermal stability of 21. This result
stands in sharp contrast to imino-amido complexes, which
undergo complete decomposition under the same conditions.
The high thermal stability of 21 indicates that either its double-
bond isomer is higher in energy and/or the pathway to reach the
double-bond isomer of 21 is not accessible at this tempera-
ture. The calculated ground-state energy difference between 21
Figure 3. Molecular structure of 15. Hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 40% probability level.
Selected bond lengths (Å) and angle (deg): Hf-N1 = 2.164(3), Hf-
N2 = 2.318(3), C1-N1 = 1.384(4), C6-N2 = 1.306(4), C1-C2 =
1.364(4), C5-C6 = 1.497(4); N2-Hf-N1 = 70.99(9).
Figure 4. Molecular structure of 19. Hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 40% probability level.
Selected bond lengths (Å) and angle (deg): Hf-N1 = 2.079(2), Hf-
N2 = 2.345(2), C1-N1 = 1.386(2), C6-N2 = 1.298(2), C1-C2 =
1.350(3), C5-C6 = 1.501(3); N2-Hf-N1 = 69.86(5).
and its isomer with the CdC and CdN double bonds transposed
is only 1.0 kcal favoring 21, whereas for the Zr analogue, the
CdC/CdN bond isomer is more stable by 0.5 kcal than 22.
These calculations suggest that the high stability of 21 can be
attributed to the lack of a kinetic pathway to access its double-
bond isomer.
Single-Crystal X-ray Structures. The molecular structures
of 15, 19, 21, and 22 are shown in Figures 3-6, respectively, and
selected bond lengths and angles are presented in Table 1. Metric
parameters obtained for 15, 19, 21, and 22 clearly confirm the
identity of individual isomers originally established by NOESY
experiments. For example, the C1-C2 bond length of 1.350(3)
Å in 19 clearly indicates the presence of the double bond in
the cyclohex-2-enylidene fragment bonded to the N-n-octyl
1701
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
Figure 6. Molecular structure of 22. Hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 40% probability level.
Selected bond lengths (Å) and angles (deg): Zr-N1 = 2.332(3), Zr-
N2 = 2.132(2), C1-N1 = 1.290(3), C6-N2 = 1.399(3), C1-C2 =
1.508(3), C5-C6 = 1.349(3); N2-Zr-N1 = 71.21(6).
Figure 5. Molecular structure of 21. Hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 40% probability level.
Selected bond lengths (Å) and angle (deg): Hf-N1 = 2.164(3), Hf-
N2 = 2.318(3), C1-N1 = 1.384(4), C6-N2 = 1.306(4), C1-C2 =
1.364(4), C5-C6 = 1.497(4); N2-Hf-N1 = 70.99(9).
weight capability is one of the most important characteristics of
polyolefin catalysts, as it allows for the preparation of a larger
array of products under various process conditions. It is simple to
reduce the molecular weight of polyolefins to a desired level by
the introduction of hydrogen during polymerization reactions,
but it is much harder to increase the polymer’s molecular weight
for catalysts which undergo frequent termination events.39
Complex 19 with its CdC and CdN double bonds transposed
as compared to 21 was not very active (21 kg of polymer/mmol
of catalyst) and gave a polymer with significantly reduced 1-octene
content compared to that of 21 (3.7 mol % octene vs 8.7 mol %
octene). The molecular weight of the copolymer produced by 19
was higher (Mw = 509 kDa) than that of 3 (Mw = 283 kDa) but
lower than that made by 21. Performance differences between 19
and 21 mirror those observed within the imino-amido catalyst
family (5a vs 5b).6 The polymerization activity of complex 22,
the Zr analogue of 21, was lower by 33% than that of 21 and was
almost identical with that of 3. 1-Octene incorporation is lower
for 22 than for 21, a trend also observed in related imino-amido
complexes. The molecular weight of polymer prepared by 22 is
lower than that of its Hf analogue 21 but higher than that of 3.
The catalytic performance of complex 21 at 150 °C (run 8) was
50% lower than at 120 °C, but it was still 3 times higher than that
of 3 (run 9), due to an even steeper decline in activity (75%) for
the latter. The molecular weight and 1-octene incorporation are
significantly higher for 21 (Mw = 386 kDa, 7.0 mol % octene)
than for 3 (Mw = 114 kDa, 4.4 mol % octene).
These data indicate that cyclohex-2-enylidene-bridged imino-
enamido complexes have intrinsically higher molecular weight
capabilities than the analogous trimethylethylidine-bridged imi-
no-amido complexes. This phenomenon is seen in both the DIP-
DIP (15 vs 2) and DIP-alkyl (21 vs 3) series of complexes. To
gain insight into why imino-enamido catalysts lead to higher
molecular weight polymers, end group analysis was performed by
1H NMR spectroscopy on polymers prepared at 150 °C (runs 8
and 9, Figure 7). End group analysis allows for evaluating the
identity and concentration of individual unsaturated functional
groups resulting from chain termination events. The higher the
fragment. The difference between the Hf-N(imino) and Hf-
N(enamido) bond lengths in 15 (0.154 Å) is significantly smaller
than that found in the imino-amido analogue 2 (0.283 Å). An
analogous trend is observed between imino-enamido derivatives
19 and 21 and their imino-amido counterparts 6 and 5, respec-
tively. Additionally, the differences between C-N(imino) and
C-N(enamido) bond lengths for 15, 19, 21, and 22 are 0.078,
0.088, 0.113, and 0.109 Å, respectively, which are smaller than the
differences found in 5 (0.227 Å) and 6 (0.163 Å). All this
information indicates that the bonding in the five-membered
metallacyclic rings in 15, 19, 21, and 22 complexes is more
symmetric than in the case of the imino-amido complexes. All
benzyl groups are bonded in an η1 fashion in these complexes.
Polymerization Results. New precatalysts were evaluated in
ethylene/1-octene copolymerization reactions conducted in a 2
L batch reactor at both 120 and 150 °C. They were activated with
1.2 equiv (relative to precatalyst) of [HNMe(C18H37)2][B-
(C6F5)4] activator. All polymerization reactions were conducted
in the presence of 10 mmol of hydrogen. Complex 15 was
evaluated in comparison to the structurally similar imino-amido
complex 2 (Table 2). The activity of 15 was 27.7 kg of polymer/
mmol of catalyst, which is about 70% of that of 2. Complex 15
gave polymers with slightly higher 1-octene incorporation levels,
as shown by IR and polymer melting points (117.5 °C for 15 vs
121.3 °C for 2). Interestingly, the molecular weight of ethylene/
1-octene copolymer produced by 15 (Mw = 1002 kDa) was 3.5
times higher than that of 2 (Mw = 275 kDa). The activity of 21
(120 kg of polymer/mmol of catalyst), a direct analogue of 3, was
found to be about 1.5 times higher than that of 3. Complex 21
resulted in a higher 1-octene incorporation rate than 3 (8.7 mol %
1-octene for 21 vs 5.5 mol % 1-octene for 3). The polymer
melting point as determined by DSC is in agreement with the IR
measurements (74 °C for 21 vs 98 °C for 3). Most significantly,
the Mw value of polymer prepared by 21 was about 3.5 times
higher than that of 3 (1037 kDa vs 283 kDa, runs 3 and 5). The
ultrahigh molecular weights obtained for 15 and 21 are 20 times
higher than that produced by the CGC complex, {(η5-C5Me4)-
(SiMe2-N-t-Bu)}TiMe2, under the same conditions. Molecular
1702
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
Table 1. Bond Lengths (Å) and Angles (deg) for Complexes 15, 19, 21, and 22, as Well as the Previously Reported 2 and 5a,b
ARTICLE
bond length/angle
15
25
19
21
22
5a6
5b6
Hf(Zr)-N1
Hf(Zr)-N2
Hf(Zr)-Bn1
Hf(Zr)-Bn2
Hf(Zr)-Bn3
C1-C2
2.164(3)
2.318(3)
2.233(3)
2.286(3)
2.222(3)
1.364(4)
1.475(5)
1.505(5)
1.497(5)
1.497(4)
1.470(4)
1.384(4)
1.452(4)
1.306(4)
70.99(9)
2.093(3)
2.376(3)
2.208(5)
2.221(5)
2.225(6)
1.518(6)
2.079(2)
2.345(2)
2.247(2)
2.289(2)
2.235(2)
1.350(3)
1.503(3)
1.517(3)
1.530(3)
1.501(3)
1.462(2)
1.386(2)
1.471(2)
1.298(2)
69.86(5)
2.313(2)
2.100(2)
2.243(2)
2.288(2)
2.266(2)
1.498(3)
1.523(4)
1.518(4)
1.491(3)
1.347(3)
1.459(3)
1.290(3)
1.486(3)
1.403(2)
72.03(6)
2.332(2)
2.132(2)
2.266(2)
2.303(3)
2.286(2)
1.508(3)
1.517(4)
1.517(4)
1.487(3)
1.349(3)
1.460(3)
1.290(3)
1.478(3)
1.399(3)
71.21(6)
2.301(3)
2.074(3)
2.288(3)
2.259(3)
2.253(3)
1.509(5)
2.030(4)
2.380(4)
2.291(5)
2.272(5)
2.242(5)
1.515(6)
C2-C3
C3-C4
C4-C5
C5-C6
1.552(7)
1.433(8)
1.314(6)
1.448(6)
1.495(5)
69.99(13)
1.539(5)
1.508(4)
1.270(5)
1.489(4)
1.497(4)
72.6(1)
1.509(6)
1.515(6)
1.454(6)
1.475(5)
1.291(6)
68.9(1)
C1-C6
N1-C1
N1-C7
N2-C6
N1-Hf(Zr)-N2
Table 2. Polymerization Data for Complexes 2, 3, 15, 19, 21, 22, and CGCa
run
cat. (amt (μmol))
temp (°C)
amt of DEZ (μmol)
polymer yield (g)
cat. activityb
10-3Mw*/PDI
Tm (°C)
octene content (mol %)
1
2 (0.7)
120
120
120
120
120
120
120
150
150
120
120
120
120
120
120
26.7
19.4
58.7
14.7
48.1
32.0
39.1
20.2
24.7
63.5
72.2
81.3
31.9
21.9
27.7
38 100
27 700
275/2.3
1002/3.1
283/2.4
506/1.8
1037/2.4
509/2.8
47/2.3
121.3
117.5
96.9
104.7
76.0
91.9
58
2.4
5.4
5.5
3.4
8.7
7.2
14.8
4.4
7.0
5.0
5.0
5.0
7.0
6.0
5.6
2
15 (0.7)
3 (0.7)
3
83 900
4
19 (0.7)
21 (0.4)
22 (0.4)
CGC (0.2)
3 (1.0)
21 000
5
120 300
80 000
6
7
195 500
20 200
8
114/2.6
386/2.4
280/2.5
199/1.9
150/3.2
1100/2.4
499/1.9
309/2.1
104.5
79.8
99.5
102.3
102.8
80
9
21 (0.4)
3 (0.7)
61 800
10
11
12
13
14
15
0
140
350
0
90 700
3 (0.7)
103 100
116 100
159 500
109 500
138 500
3 (0.7)
21 (0.2)
21 (0.2)
21 (0.2)
40
89.7
88.9
100
a Polymerization conditions: 533 mL of Isopar-E; 250 g of 1-octene; ethylene pressure 460 psi; hydrogen 10 mmol; pre-catalyst:activator = 1:1.2;
activator [HNMe(C18H37)2][B(C6F5)4]; 1:10 MMAO; reaction time 10 min. CGC = {(η5-C5Me4)(SiMe2-N-t-Bu)}TiMe2. b Activity in units of g of
polymer/mmol of catalyst.
native molecular weight a polymer exhibits, the lower the con-
centration of unsaturated polymer end groups measured (relative
to polymer backbone). The total unsaturation found in polymers
produced by 21 was 2.3 times lower than that in 3, which is
consistent with the molecular weight data.40 The level of vinyl
groups, which is a result of β-hydrogen elimination/chain trans-
fer to monomer following a last inserted ethylene is virtually the
same for both polymers (21 and 3), but the level of cis-/trans-
vinylene (product of elimination after a 2,1-insertion of 1-octene)
and vinylidene (product of elimination after a 1,2-insertion of
1-octene) groups is 4.1 and 3.0 times higher, respectively, for 3.
This analysis clearly indicates that the main reason for the higher
molecular weight capability of 21 compared to that of 3 is the
higher barrier of β-hydride elimination/chain transfer to mono-
mer after 2,1- and 1,2-inserted 1-octene.
undergoing effective chain transfer reactions with diethylzinc
(DEZ) during polymerization. The addition of 200 and 500
equiv of DEZ (relative to 21) during polymerization resulted in a
significant reduction of Mw from 1100 kDa (no DEZ) to 499 and
309 kDa, respectively. This represents a 72% decrease of Mw for a
run with 500 equiv of DEZ. For 3, the addition of 200 or 500
equiv of DEZ during polymerization resulted in a reduction in
Mw from 280 kDa (no DEZ) to 199 and 150 kDa, respectively.
Complex 21, with its intermediate 1-octene incorporation, can be
used to prepare either the soft or hard segment of OBCs,
depending on the characteristics of the partnering catalyst and
the design of the OBC.
’ CONCLUSIONS
Since imino-amido complexes 2 and 3 were shown to produce
olefin block copolymers (OBC),5 it was of interest to us to
determine if imino-enamido complexes such as 21 are capable of
Theoretical calculations revealed interesting trends of stability
within cyclic and acyclic bis-imines and imine-enamines. Five- and
six-membered-ring imine-enamines are considerably more stable
1703
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
The high thermal stability of new imino-amido complexes, coupled
with their very good activity and ultrahigh-molecular-weight cap-
ability, makes them good candidates for the high-temperature
synthesis of block and random ethylene/R-olefin copolymers.
Imino-enamido ligands are highly modular in nature, and
various modifications to ligand structure should be possible
via substitution variation on the imine and enamine nitrogen
atoms and alterations to the ligand backbone. It is likely that
even better performing imino-enamido catalysts can be iden-
tified via a comprehensive structure-reactivity study. On the
mechanistic side, one wonders about the polymerization
mechanism in these systems, since there are two alkyl groups
remaining following precatalyst activation which might lead
potentially to two polymeryl chains growing simultaneously
at the metal center. These topics will be the subject of future
reports.
’ EXPERIMENTAL SECTION
Figure 7. Fragment of 1H NMR spectra of ethylene/1-octene copoly-
mers obtained at 150 °C for 3 (run 8, top spectrum) and 21 (run 9,
bottom spectrum). The asterisk designates an impurity from the
antioxidant package.
General Considerations. All solvents and reagents were ob-
tained from commercial sources and used as received unless otherwise
noted. Toluene, hexanes, CH2Cl2, and C6D6 were dried and degassed
according to published procedures. NMR spectra were recorded on
Varian Mercury-Vx-300 and VNMRS-500 spectrometers. 1H NMR data
are reported as follows: chemical shift (multiplicity (br = broad, s =
singlet, d = doublet, t = triplet, q = quartet, p = pentet, and m =
multiplet), integration, and assignment). Chemical shifts for 1H NMR
data are reported in ppm downfield from internal tetramethylsilane
(TMS, δ scale) using residual protons in the deuterated solvent (C6D6,
7.15 ppm; toluene-d8, 2.09 ppm) as references. 13C NMR data were
determined with 1H decoupling, and the chemical shifts are reported in
ppm vs tetramethylsilane (C6D6, 128 ppm; toluene-d8, 20.4 ppm).
Elemental analyses were performed at Midwest Microlab, LLC.
Preparation of N-[2-[[2,6-Bis(1-methylethyl)phenyl]amino]-
2-cyclohexen-1-ylidene]-2,6-bis(1-methylethyl)benze-
namine (9). This synthesis is based on a literature procedure.11a 1,
2-Cyclohexanedione (2.062 g, 18.39 mmol) and 2,6-diisopropylaniline
(6.52 g, 36.78 mmol) were dissolved in 70 mL of methanol. To this
solution was added 1 mL of formic acid, and the mixture was stirred for
3 days at room temperature. Precipitated white crystalline solid was
collected on the frit, washed with methanol (2 ꢀ 15 mL), and dried
under reduced pressure to give 4.101 g (51.8%) of product.
than their corresponding bis-imines, due to favorable hydrogen
bonding in imine-enamines and unfavorable lone-pair-lone-pair
repulsions or steric interactions that exist in bis-imines. On the other
hand, the lowest energy tautomer of the four- and seven-membered
rings as well as the acyclic structures is the bis-imine. New imino-
enamido complexes containing cyclohex-2-enylidene backbones
were prepared in four steps, starting from the commercially available
compound 1,2-cyclohexanedione. The last step in the ligand syn-
thesis, imine formation, was the most challenging due to the
unexpected ligand isomerization under acidic conditions. This
difficulty was overcome by employing a Ti-imido reagent to
introduce the imine functionality. As hoped, the imino-enamido
complexes (e.g., 21) bearing alkyl and aryl substituents on the imido
and enamido nitrogen atoms, respectively, are thermally stable at
90 °C for many hours. This high thermal stability is in sharp contrast
to that observed in analogous imino-amido complexes, which
undergo a facile 1,2-Me shift at this temperature, producing iso-
meric complexes exhibiting poor polymerization characteristics. An
ethylene/1-octene copolymerization study conducted at 120 °C
demonstrated that the imino-enamido hafnium complex 21 has an
activity 50% higher than that of the analogous imino-amido
complex 3 and, more significantly, it produces polymers with higher
molecular weight (Mw of 1037 kDa vs 283 kDa) and higher 1-octene
content (8.0 vs 5.0 mol %) than for 3. To a great extent, the
molecular weight capability of a catalyst determines what type of
polyolefin can be produced under given reactor conditions and is
often a limiting factor for many catalysts. The ultrahigh-molec-
ular-weight capability discovered for 15 and 21 is of importance,
as catalysts capable of producing very high molecular weight
polyolefins can be utilized at very high reactor temperatures,
which is advantageous in the solution process. This very high
molecular weight capability of 21 is a result of higher barriers for
β-hydride elimination/chain transfer to monomer following
1-octene insertion as compared to the analogous imino-amido
complex 3, as shown by end group analysis. A polymerization
study with 21 conducted in the presence of diethylzinc resulted
in a sharp decrease of polymer molecular weight (from 1100 kDa
to 309 kDa), indicating a very effective chain transfer reaction.
Preparation of [N-[2-[[2,6-Bis(1-methylethyl)phenyl]-
amino-KN]-2-cyclohexen-1-ylidene]-2,6-bis(1-methyl-
ethyl)benzenaminato-KN]tris(phenylmethyl)hafnium
(15). N-[2-[[2,6-Bis(1-methylethyl)phenyl]amino]-2-cyclohexen-1-
ylidene]-2,6-bis(1-methylethyl)benzenamine (0.439 g, 1.0 mmol) and
tetrabenzylhafnium (0.554 g, 1.0 mmol) were dissolved in 6 mL of C6D6.
The solution was heated for 4 days at 76 °C. NMR showed complete
conversion of tetrabenzylhafnium with a product to ligand ratio of 9:1.
Solvent was removed under reduced pressure. The remaining residue
was dissolved in 3 mL of toluene and filtered. To the filtrate was added
8 mL of hexane. Within minutes yellow crystals appeared. After standing at
ambient temperature for 3 h, 10 mL of hexane was added and the
solution was put into a freezer (-26 °C) overnight. The solvent was
decanted, and the yellow crystals were washed with hexane (2 ꢀ 10 mL)
and dried under reduced pressure to give 0.486 g (54.5%) of product. 1H
NMR (C6D6, 500 MHz, 30 °C): 7.25 (m, 3H, i-Pr2-Ph), 7.11 (tm, 6H,
3JH-H = 7.5 Hz, m-CH2Ph), 7.06 (m, 3H, i-Pr2-Ph), 6.84 (m, 3H, 3JH-H
=
3
7.5 Hz, p-CH2Ph), 6.61 (d, 6H, JH-H = 7.5 Hz, o-CH2Ph), 4.96 (t,
1H, 3JH-H = 5.0 Hz, H5), 3.51 (sept. 2H, 3JH-H = 7.0 Hz, CH(CH3)2),
3
2.74 (sept. 2H, JH-H = 7.0 Hz, CH(CH3)2), 2.11 (br s, 6H, Hf-
CH2Ph), 1.98 (t, 2H, 3JH-H = 6.5 Hz, H2), 1.81 (q, 2H, 3JH-H = 5.6 Hz,
1704
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
H4), 1.25 (p, 2H, 3JH-H = 6.0 Hz, H3), 1.22 (d, 6H, 3JH-H = 7.0 Hz,
CH(CH3)2), 1.16 (d, 6H, 3JH-H = 6.5 Hz, CH(CH3)2), 1.14 (d, 6H,
acetate/98.5% hexanes to afford 0.9332 g (59.48%) of the product as a
thick yellow oil. Note: TLC plates were buffered by treating with a
solution of 5% triethylamine/95% hexanes for about 5 min and then
allowed to dry. The silica gel for the column was also treated with a 5%
triethylamine/95% hexanes solution and loaded in the column in that
3
3JH-H = 6.5 Hz, CH(CH3)2), 0.98 (d, 6H, JH-H = 7.0 Hz, CH-
(CH3)2) ppm. 13C{1H} NMR (C6D6, 500 MHz, 30 °C): 181.90
(NdC), 150.03 (quat), 146.48 (quat, 145.91 (quat, 145.78 (quat,
144.12 (quat, 140.39 (quat), 128.57 (m-CH2Ph), 128.26 (o-CH2Ph),
1
solution. H NMR (C6D6, 500 MHz, 30 °C): δ 7.11-7.18 (m, 2H),
128.00 (i-Pr2-Ph), 126.89 (i-Pr2-Ph), 125.07 (i-Pr2-Ph), 124.87 (i-Pr2-
7.05-7.09 (m, 1H), 5.10 (t, 1H, 3J = 5.3 Hz, NH), 5.04 (t, 1H, 3J = 4.6
Hz, H2), 2.91 (q, 2H, 3J = 7.0 Hz, H7), 2.87 (septet, 2H, 3J = 7.0 Hz,
CH(CH3)2), 2.17 (q, 2H, 3J = 5.9 Hz, H3), 2.06 (pseudo t, 2H, 3J = 6.5
Hz, H5), 1.54 (quintet, 2H, 3J = 6.2 Hz, H4), 1.49 (quintet, 2H, 3J = 7.2
Hz, H8), 1.19-1.32 (CH2 overtone m, 10H), 1.19 (d, 6H, 3J = 6.8 Hz,
CH(CH3)2)), 1.15 (d, 6H, 3J = 7.0 Hz, CH(CH3)2), 0.87 (t, 3H, 3J = 7.0
Hz, H14) ppm. 13C{1H} NMR (C6D6, 125 MHz, 30 °C): δ 162.97,
146.38, 140.45, 136.59, 123.94, 123.34, 102.65, 43.62, 32.21, 29.83,
29.81, 29.70, 29.43, 28.56, 27.74, 24.94, 23.75, 23.64, 23.12, 23.05, 14.32
ppm. GC/MS (CI) mass spectrum: m/z 383 (M þ H). HRMS (ESI,
(M þ H)þ): m/z calcd for C26H43N2 383.342, found 383.340.
1
Ph), 122.45 (C5), 122.38 (p-CH2Ph), 89.82 (Hf-CH2Ph, JC-H
=
116.9 Hz), 32.23 (C2), 29.15 (CH(CH3)2), 28.70 (CH(CH3)2), 26.93
(CH(CH3)2), 25.34 (C4), 25.10 (CH(CH3)2), 24.13 (CH(CH3)2),
23.80 (CH(CH3)2), 22.98 (C3) ppm. Anal. Calcd for C51H62HfN2: C,
69.49; H, 7.09; N, 3.18. Found: C, 69.36; H, 6.96, N, 3.06.
Preparation of 2-(4-Morpholinyl)-2-cyclohexen-1-one
(16). This synthesis is modified from a literature procedure.32 A 500
mL round-bottom flask was equipped with a Dean-Stark trap, con-
denser, stir bar, and gas inlet (N2 atmosphere). The flask was charged
with of 1,2-cyclohexanedione (15.14 g, 135.00 mmol), morpholine
(14.82 g, 170.10 mmol), and toluene (330 mL). The resulting yellow
solution was heated at reflux for 5 h, resulting in the collection of about
3.0 mL of water in the Dean-Stark trap. The brown solution was
decanted from thick oil and rinsed with toluene. The solution was
concentrated under high vacuum to afford 23.33 g (95.34%) of a brown
solid. 1H NMR (C6D6, 300 MHz, 30 °C): δ 5.35 (t, 1H, 3J = 4.6 Hz),
3.67-3.64 (m, 4H), 2.70-2.66 (m, 4H), 2.18-2.13 (m, 2H, H2),
Preparation of [2,6-Bis(1-methylethyl)-N-[(1E)-2-(octyla-
mino-KN)-2-cyclohexen-1-ylidene]benzenaminato-KN]tris-
(phenylmethyl)hafnium (19). In the glovebox, a vial was charged
with 2,6-bis(1-methylethyl)-N-[(1E)-2-(octylamino)-2-cyclohexen-1-
ylidene]benzenamine (0.3341 g, 0.8732 mmol), benzene (5.0 mL),
and tetrabenzylhafnium (0.4741 g, 0.8731 mol). The solution became
1
reddish brown. After about 5-10 min, H NMR showed the desired
3
complex and some HfBn4 remaining. Therefore, a drop of the ligand was
added. The mixture was stirred. The reaction mixture was concentrated
under reduced pressure to afford 724 mg (99.5%) of the crude complex
as a reddish sticky solid. The complex was further purified by recrys-
tallization from hexanes at -40 °C to produce 346 mg of clean complex.
1H NMR (toluene-d8, 500 MHz, 30 °C): 7.20 (tm, 6H, 3JH-H = 8.0 Hz,
m-CH2Ph), 6.99-7.06 (m, 12H, i-Pr2-Ph and o-CH2Ph), 6.88 (tm, 3H,
3JH-H = 7.5 Hz, p-CH2Ph), 5.13 (t, 1H, 3JH-H = 5.0 Hz, H2), 3.33 (m,
2H, H7), 2.35 (septet, 2H, 3JH-H = 6.5 Hz, CH(CH3)2), 2.12 (br s, 6H,
Hf-CH2Ph), 2.10 (q, 2H, 3JH-H = 5.6 Hz, H3), 1.89 (t, 2H, 3JH-H = 6.2
1.87-1.81 (m, 2H, H4), 1.42 (quintet, 2H, J = 6.4 Hz, H3) ppm.
13C{1H} NMR (C6D6, 75 MHz, 30 °C): δ 194.30, 147.03, 124.72,
67.32, 50.81, 40.49, 25.89, 23.63 ppm. GC/MS (CI) mass spectrum:
m/z 182 (M þ H).
Preparation of 2-[[2,6-Bis(1-methylethyl)phenyl]amino]-
2-cyclohexen-1-one (17). A 250 mL three-necked round-bottom
flask equipped with a condenser, gas inlet, and septum was placed under
an N2 atmosphere. The flask was charged with 2-(4-morpholinyl)-2-
cyclohexen-1-one (7.0046 g, 38.65 mmol), toluene (80 mL), and 2,6-
diisopropylaniline (6.8521 g, 38.65 mmol). To the yellow solution was
added p-toluenesulfonic acid hydrate (7.3520 g, 38.65 mmol). The
reaction mixture became very thick, due to heavy precipitate formation.
The mixture was heated to 80 °C (oil bath temperature) and stirred for 2
h. After it was cooled to ambient temperature, the mixture was filtered.
The filtrate was concentrated under vacuum to afford 10.09 g of a yellow
solid. The solid was dissolved in hot hexanes (∼30 mL) and filtered.
After it was cooled to ambient temperature, the solution was placed in
the freezer (-10 °C) overnight. The product was collected on a frit,
washed with cold hexanes (2 ꢀ 6 mL), and dried under vacuum to give
4.0550 g of yellow solid. The filtrate was concentrated, and the resulting
solid was recrystallized two more times, giving two additional crops
(1.0785 and 0.6919 g). The combined yield was 5.8254 g (55.54%). 1H
NMR (C6D6, 300 MHz): δ 7.17-7.06 (m, 3H), 6.00 (broad s, 1H), 4.95
(t, 1H, J = 4.7 Hz), 3.15 (septet, 2H, J = 6.9 Hz), 2.21-2.16 (m, 2H, H2),
1.75 (q, 2H, J = 5.5 Hz, H4), 1.41 (quintet, 2H, J = 6.3 Hz, H3), 1.10 (d,
12H, J = 6.9 Hz) ppm. 13C{1H} NMR (C6D6, 75 MHz): δ 194.09, 147.17,
140.82, 135.90, 127.47, 124.04, 112.08, 38.15, 28.91, 24.53, 24.36, 24.04
ppm. GC/MS (CI) mass spectrum: m/z 272 (M þ H). HRMS (ESI, (M þ
Na)þ): m/z calcd for C18H25NONa 294.180, found 294.183.
3
Hz, H5), 1.64 (m, 2H, H8), 1.27 (p, 2H, JH-H = 6.1 Hz, H4-
determined by TOCSY1D), 1.27 (m, 10H, H9-H13), 1.15 (d, 6H,
3JH-H = 7.0 Hz, CH(CH3)2), 0.92 (d, 6H, 3JH-H = 6.5 Hz, CH(CH3)2),
0.91 (t, 3H, 3JH-H = 7.0 Hz, H10) ppm. 13C{1H} NMR (toluene-d8, 125
MHz, 30 °C): 183.99 (NdC), 148.12 (quat), 146.08 (quat), 144.54
(quat), 139.94 (quat), 128.58 (m-CH2Ph), 128.12 (o-CH2Ph), 127.40
(i-Pr2-Ph), 124.47 (i-Pr2-Ph), 122.14 (p-CH2Ph), 113.25 (C2), 85.23
(Hf-CH2Ph, 1JC-H = 119.0 Hz), 45.72 (C7), 32.21, 31.80 (C5), 29.96,
29.89, 29.03 (CH(CH3)2), 28.09, 27.24 (C8), 25.33 (C3), 24.56
(CH(CH3)2), 24.19 (CH(CH3)2), 23.49, 23.04, 14.31 (C14).
HSQCAD (toluene-d8, 500 MHz): (7.20, 128.58), (6.99-7.06,
128.12/127.40/124.47), (6.88, 122.14), (5.13, 113.25), (3.33, 45.72),
(2.35, 29.03), (2.12, 85.23), (2.10, 25.33), (1.89, 31.80), (1.64, 27.24),
(1.28, 32.31/29.96/29.90/28.09/23.49/23.04), (1.15, 24.19), (0.92,
24.56), (0.91, 14.31) ppm. Anal. Calcd for C47H62HfN2: C, 67.73; H,
7.50; N, 3.36. Found: C, 67.63; H, 7.47, N, 3.39.
Preparation of n-Butylamino-Titanium Reagent (Ti(N-n-
Bu)2)n. Ti(NMe2)4 (26 g, 0.116 mol) was dissolved in 500 mL of
toluene in a drybox in a Schlenk flask. The flask was taken into the hood.
To this solution was added 68.8 mL (0.696 mol) of n-butylamine, which
resulted in the formation of an orange solid. The mixture was heated at
gentle reflux with a nitrogen sweep at the top of the condenser. The
yellow solution became deep red within minutes after heating. After 6 h
of reflux, the solution was cooled to room temperature and the solvent
was removed under reduced pressure to give a deep red-black glassy
solid. The product was transferred into the drybox for storage. A 23.29 g
amount of product was obtained.
Preparation of 2,6-Bis(1-methylethyl)-N-[(1E)-2-(octyla-
mino)-2-cyclohexen-1-ylidene]benzenamine (18b). In the
purge box,
a 40.0 mL vial was charged with 2-[[2,6-bis(1-
methylethyl)phenyl]amino]-2-cyclohexen-1-one (1.1128 g, 4.1003
mmol), toluene (20.0 mL), n-octylamine (0.680 mL, 4.1090 mmol),
molecular sieves, and formic acid (0.16 mL, 4.1364 mmol). The mixture
was shaken at 75 °C overnight. After it was cooled to ambient
temperature, the solution was filtered to remove the molecular sieves
and solvent was removed under reduced pressure to afford 1.5337 g of a
thick yellow oil with some solid. The crude product was chromato-
graphed using buffered silica gel and eluted with 1% Et3N/0.5% ethyl
Preparation of N-[(6E)-6-(Butylimino)-1-cyclohexen-1-yl]-
2,6-bis(1-methylethyl)benzenamine (20a). The reaction was
carried out in a glovebox under an N2 atmosphere. 2-[[2,6-Bis(1-
1705
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
methylethyl)phenyl]amino]-2-cyclohexen-1-one (9.030 g, 33.273 mmol)
was dissolved in toluene (400 mL) in a 1 L flask containing a stir bar. To
the solution was added the titanium reagent (8.378 g, 24.905 mmol)
followed by toluene (50 mL), giving a deep red-brown solution. The
mixture was stirred for 2 days, resulting in the formation of copious
amounts of brown precipitate. The mixture was filtered using a medium-
porosity fritted-glass funnel. The brown solid was washed with toluene
(4 ꢀ 50 mL). Solvent was removed under reduced pressure, leaving
(d, 6H, 3JH-H = 6.9 Hz, CH(CH3)2), 1.29 (p, 2H, 3JH-H = 6.3 Hz, H3),
1.17 (m, 2H, H8), 1.11 (d, 6H, 3JH-H = 6.9 Hz, CH(CH3)2), 1.06 (sext,
3
3
2H, JH-H = 7.4 Hz, H9), 0.77 (t, 3H, JH-H = 6.9 Hz, H10) ppm.
13C{1H} NMR (toluene-d8, 125 MHz, 30 °C): 175.87 (NdC), 151.58
(quat), 146.07 (quat), 145.00 (quat), 144.71 (quat), 128.61 (m-
CH2Ph), 127.25 (CH2Ph), 126.29 (i-Pr2-Ph), 124.36 (i-Pr2-Ph),
121.80 (CH2Ph), 116.93 (C5), 85.07 (Hf-CH2Ph, 1JC-H = 117.4 Hz),
49.50 (N-CH2), 30.46 (C8), 28.61 (CH(CH3)2), 28.28 (C2), 26.30
(CH(CH3)2), 24.87 (C4), 24.36 (CH(CH3)2), 22.88 (C3), 20.91 (C9),
13.74 (CH3). HSQC (toluene-d8, 500 MHz, 30 °C): (7.11, 128.61),
(6.80, 127.25), (7.18, 126.29), (7.18, 124.36), (6.82, 121.80), (4.57,
116.93), (2.11, 85.07), (2.80, 49.50), (1.17, 30.46), (3.24, 28.61), (1.89,
28.28), (1.11, 26.30), (1.83, 24.87), (1.31, 24.36), (1.29, 22.88), (1.06,
20.91), (0.77, 13.74) ppm. HRMS (ESI, (M - Bn)þ): m/z calcd for
C36H47N2Hf 687.321, found 687.324. Anal. Calcd for C43H54HfN2: C,
66.43; H, 7.00; N, 3.60. Found: C, 66.58; H, 6.89, N, 3.65.
1
9.005 g (82.9%) of the product as a yellow oil. H NMR (C6D6, 500
MHz, 30 °C): δ 7.23-7.17 (m, 3H, i-Pr2-Ph), 6.89 (s, 1H, NH), 4.78 (t,
1H, J = 4.6 Hz, H5), 3.39 (septet, 2H, 3J = 6.9 Hz, CH(CH3)2), 3.26 (t,
2H, 3J = 6.8 Hz, H7), 2.09 (pseudo t, 2H, 3J = 6.6 Hz, H2), 1.96 (q, 2H,
3J = 5.5 Hz, H4), 1.69 (pentet of multiplets, 2H, 3J = 7.8 Hz, H8), 1.53
(quintet, 2H, 3J = 6.5 Hz, H3), 1.44 (sextet of multiplets, 2H, 3J = 7.0 Hz,
H9), 1.22 (d, 12H, 3J = 6.8 Hz, CH(CH3)2), 0.94 (t, 3H, 3J = 7.3 Hz,
H10) ppm. 13C{1H} NMR (C6D6, 125 MHz, 30 °C): δ 160.61, 147.38,
140.90, 137.89, 126.83, 123.80, 103.26, 49.84, 33.71, 28.69, 26.80, 24.23,
23.92, 23.39, 21.03, 14.21. HSQC (C6D6, 500 MHz): δ (7.23-7.17,
126.83/123.80), (4.78, 103.26), (3.39, 28.69), (3.26, 49.84), (2.09,
26.80), (1.96, 23.92), (1.69, 33.71), (1.52, 23.39), (1.44, 21.03), (1.22,
24.23), (0.94, 14.21) ppm. HRMS (ESI, (M þ H)þ): m/z calcd for
C22H35N2 327.277, found 327.280.
Preparation of (E)-2,6-Diisopropyl-N-[2-(butylamino)-
cyclohex-2-enylidene]aniline (20b). N-[(6E)-6-(Butylimino)-1-
cyclohexen-1-yl]-2,6-bis(1-methylethyl)benzenamine (108 mg) was
dissolved in 587 mg of C6D6. To this solution was added 10 μL of 1.0
M HCl in diethyl ether, and the NMR tube was inserted into the NMR
probe within 30 s. NMR spectra of this reaction mixture were followed
over the course of 10 min. Isomerization was complete and quantitative
Preparation of [N-[(6E)-6-(Butylimino-KN)-1-cyclohexen-
1-yl]-2,6-bis(1-methylethyl)benzenaminato-KN]tris(phenyl-
methyl)zirconium (22). N-[(6E)-6-(Butylimino)-1-cyclohexen-1-
yl]-2,6-bis(1-methylethyl)benzenamine (0.350 g, 1.07 mmol) and tetra-
benzylzirconium (0.4885 g, 1.07 mmol) were dissolved in 3 mL of
benzene at room temperature to give a light red solution. After the
1
mixture was stirred for 1 h, H NMR showed that the reaction had
reached completion. To the reaction mixture was added 8 mL of hexane;
the solution was filtered and put into a freezer (-45 °C) overnight. The
solvent was decanted, and the resulting yellow crystals were washed with
cold hexane (2 ꢀ 4 mL) and dried under reduced pressure to give 0.566
g (68.1%) of product. 1H NMR (C6D6, 500 MHz, 30 °C): 7.22
(pseudotriplet, 3H, i-Pr2-Ph), 7.12 (tm, 6H, 3JH-H = 7.8 Hz, m-CH2Ph),
6.88 (tm, 3H, 3JH-H = 7.0 Hz, p-CH2Ph), 6.88 (dm, 6H, 3JH-H = 8.0 Hz,
o-CH2Ph), 4.64 (t, 1H, 3JH-H = 5.0 Hz, H5), 3.30 (sept, 2H, 3JH-H = 7.0
Hz, CH(CH3)2), 2.83 (m, 2H, H7), 2.24 (br s, 6H, Hf-CH2Ph), 1.95 (t,
2H, 3JH-H = 6.3 Hz, H2), 1.78 (q, 2H, 3JH-H = 5.8 Hz, H4), 1.32 (d, 6H,
3JH-H = 6.5 Hz, CH(CH3)2), 1.28 (p, 2H, 3JH-H = 6.5 Hz, H3), 1.21 (m,
within 10 min. 1H NMR (C6D6, 500 MHz, 30 °C): 7.144 (d, 1H, 3JH-H
=
8 Hz, i-Pr2-Ph), 7.143 (d, 1H, 3JH-H = 7 Hz, i-Pr2-Ph), 7.09 (dd, 1H,
3JH-H = 8.8 Hz, 3JH-H = 6.5 Hz, i-Pr2-Ph), 5.11 (br s, 1H, NH), 5.04 (t,
1H, 3JH-H = 4 Hz, H2), 2.886 (t, 2H, 3JH-H = 7 Hz, H7), 2.881 (sept,
2H, 3JH-H = 6.9 Hz, CH(CH3)2), 2.16 (q, 2H, 3JH-H = 5.5 Hz, H3),
3
3
2H, H8), 1.14 (d, 6H, JH-H = 6.5 Hz, CH(CH3)2), 1.05 (sext, 2H,
2.07 (m, 2H, H5), 1.53 (p, 2H, JH-H = 6.5 Hz, H3), 1.43 (pm, 2H,
3JH-H = 7.5 Hz, H9), 0.73 (t, 3H, 3JH-H = 7.5 Hz, H10) ppm. 13C{1H}
NMR (C6D6, 125 MHz, 30 °C): 175.42 (NdC), 151.91 (quat), 146.44
(quat), 145.93 (quat), 144.73 (quat), 129.35 (m-CH2Ph), 127.44 (o-
CH2Ph), 126.30 (i-Pr2-Ph), 124.57 (i-Pr2-Ph), 122.30 (p-CH2Ph),
3JH-H = 7.8 Hz, H8), 1.28 (sext-m, 2H, 3JH-H = 7.8 Hz, H9), 1.16 (d,
3
3
6H, JH-H = 6.9 Hz, CH(CH3)2), 1.13 (d, 6H, JH-H = 6.9 Hz,
CH(CH3)2), 0.80 (t, 3H, 3JH-H = 7.4 Hz, H10) ppm. 13C{1H} NMR
(C6D6, 125 MHz, 30 °C): 163.00 (NdC), 146.39 (quat), 140.42 (quat),
136.63 (quat), 123.95 (CH), 123.37 (CH), 112.83 (C2), 43.35 (C7),
31.47 (C8), 29.82 (C5), 28.56 (CH(CH3)2), 24.89 (C3), 23.71 (C4),
23.60 (CH(CH3)2), 23.09 (CH(CH3)2), 20.76 (C9), 14.02 (C10) ppm.
Preparation of [N-[(6E)-6-(Butylimino-KN)-1-cyclohexen-
1-yl]-2,6-bis(1-methylethyl)benzenaminato-KN]tris(phenyl-
methyl)hafnium (21). N-[(6E)-6-(Butylimino)-1-cyclohexen-1-
yl]-2,6-bis(1-methylethyl)benzenamine (0.3005 g, 0.92 mmol) and
tetrabenzylhafnium (0.4997 mmol) were dissolved in toluene (6 mL)
at room temperature, giving a light red solution. After this solution was
stirred overnight (yellow solution), solvent was removed under reduced
pressure, giving a highly crystalline yellow solid. The residue was
dissolved in toluene (2 mL), followed by addition of hexane (8 mL).
The solution was filtered and allowed to stand overnight at ambient
temperature, resulting in the formation of large yellow crystals. The
mother liquor was decanted, and the large yellow crystals were washed
with cold hexane (5 mL) and dried under reduced pressure to give 331
mg of product. The mother liquor and hexane wash were combined and
put into a freezer (-20 °C) overnight. The solvent was decanted and the
resulting yellow crystals were washed with cold hexane (2 ꢀ 2 mL) and
dried under reduced pressure to give 211 mg of product. Combined
yield: 0.542 mg, 75.8%. 1H NMR (toluene-d8, 500 MHz, 30 °C): 7.18 (s,
3H, i-Pr2-Ph), 7.11 (tm, 6H, 3JH-H = 7.6 Hz, m-CH2Ph), 6.81, (m, 9H,
1
115.83 (C5), 75.11 (Hf-CH2Ph, JC-H = 123.2 Hz), 50.20 (N-CH2),
30.60 (C8), 28.55 (CH(CH3)2), 28.30 (C2), 26.55 (CH(CH3)2), 25.06
(C4), 24.23 (CH(CH3)2), 22.92 (C3), 20.75 (C9), 13.72 (CH3) ppm.
Information about C-H coupling constants comes from the proton-
coupled 13C experiment. HSQC (toluene-d8, 300 MHz; 1H resonance in
ppm, 13C resonance in ppm): (7.12, 129.35), (6.88, 127.44), (7.22,
126.30), (7.22, 124.57), (6.88, 122.30), (4.64, 115.83), (2.24, 75.11),
(2.83, 50.20), (1.21, 30.60), (3.30, 28.55), (1.95, 28.30), (1.14, 26.55),
(1.78, 25.06), (1.32, 24.23), (1.28, 22.92), (1.05, 20.75), (0.73, 13.72).
HRMS (ESI, (M - Bn)þ): m/z calcd for C36H47N2Zr 597.279, found
597.282. Anal. Calcd for C43H54ZrN2: C, 74.84; H, 7.89; N, 4.06.
Found: C, 74.60; H, 7.73, N, 4.28.
Ethylene/1-Octene Polymerization Procedures and Poly-
mer 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 or 150 °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
o-/p-CH2Ph), 4.57 (t, 1H, 3JH-H = 5.0 Hz, H5), 3.24 (sept, 2H, 3JH-H
=
6.6 Hz, CH(CH3)2), 2.80 (m, 2H, H7), 2.11 (br s, 6H, Hf-CH2Ph), 1.89
(t, 2H, 3JH-H = 6.7 Hz, H2), 1.83 (q, 2H, 3JH-H = 5.6 Hz, H4), 1.31
1706
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
tank and injected into the reactor. The polymerization conditions were
maintained for 10 min with ethylene added on demand. Heat was
continuously 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
antioxidant (Irganox 1010 from Ciba Geigy Corp.) and 133 mg of a
phosphorus stabilizer (Irgafos 168 from Ciba Geigy Corp.).
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.
Structure Determinations of 16 and 17. Crystals, mounted
on a Mitegen Micromount, were automatically centered on a Bruker
SMART X2S benchtop crystallographic system. Intensity measurements
were performed using monochromated (doubly curved silicon crystal)
Mo KR radiation (0.710 73 Å) from a sealed microfocus tube. Generator
settings were 50 kV and 1 mA. Data were acquired using three sets of ω
scans at different ψ 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 structures were solved with XS, and subsequent structure
refinements were performed with XL.
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 2-4 min, the samples were cooled to -
40 °C at 10 °C/min, held for 2-4 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 permea-
tion chromatograph (GPC) equipped with a low-angle/right-angle light
scattering detector, a four-capillary inline viscometer, and a refractive
index detector. The GPC utilized three (3) 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 1-octene
incorporation, 140 μL of each polymer solution was deposited onto a
silica wafer, heated to 140 °C until the trichlorobenzene had evaporated,
and analyzed using a Nicolet Nexus 670 FTIR with version 7.1 software
equipped with an AutoPro auto sampler.
’ ASSOCIATED CONTENT
S
Supporting Information. Tables with total energies for
b
all computed structures, NMR spectra, X-ray data including
CIF files, and a Mol file containing xyz data for all computed
structures. This material is available free of charge via the Internet
at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*To whom correspondence should be addressed. E-mail: jklosin@
dow.com.
’ ACKNOWLEDGMENT
We thank Francis Timmers for help with cover art design.
End Group Analysis. Samples were dissolved in 8 mm NMR tubes in
a solvent mixture, tetrachloroethane-d2/perchloroethylene (50/50 v/v),
with concentrations of 0.10 g/1.8 mL. The tubes were then heated in a
heating block set at 120 °C. The sample tubes were repeatedly vortexed
’ REFERENCES
(1) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428–447. (b) Gibson, V. C.; Spitzmesser, S. K. Chem.
Rev. 2003, 103, 283–316. (c) Makio, H.; Kashiwa, N.; Fujita, T. Adv.
Synth. Catal. 2002, 344, 477–493. (d) Park, S.; Han, Y.; Kim, S. K.; Lee,
J.; Kim, H. K.; Do, Y. J. Organomet. Chem. 2004, 689, 4263–4276.
(2) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169–1203. (b) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am. Chem.
Soc. 2001, 123, 5134–5135. (c) Bollmann, A.; Blann, K.; Dixon, J. T.;
Hess, F. M.; Killian, E.; Maumela, H.; McGuinness, D. S.; Morgan, D. H.;
Neveling, A.; Otto, S.; Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.;
Kuhlmann, S. J. Am. Chem. Soc. 2004, 126, 14712–14713. (d) Boussie,
T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc,
M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.; Rosen, R. K.;
Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.; Talarico, G. Angew.
Chem., Int. Ed. 2006, 45, 3278–3283. (e) Arriola, D. J.; Carnahan, E. M.;
Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Science 2006, 312, 714–
719.
(3) (a) Klosin, J.; Kruper, W. J.; Nickias, P. N.; Roof, G. R.; De
Waele, P.; Abboud, K. A. Organometallics 2001, 20, 2663–2665.
(b) Konze, W. V.; Vanderlende, D. D. Int. Pat. Appl. 2007136497, 2007.
(c) Nabika, M.; Katayama, H.; Watanabe, T.; Kawamura-Kuribayashi, H.;
Yanagi, K.; Imai, A. Organometallics 2009, 28, 3785–3792.
(4) De Waele, P.; Jazdzewski, B. A.; Klosin, J.; Murray, R. E.;
Petersen, J. L.; Theriault, C. N.; Vosejpka, P. C. Organometallics 2007,
26, 3896–3899.
1
and heated to achieve a homogeneously flowing fluid. The H NMR
spectra were taken on a Varian Inova 600 MHz spectrometer. The
following acquisition parameters were used: 25 s relaxation delay, 1 s
presaturation (satpwr 1) on backbone (CH2) protons, 90° pulse of 7.25
μs, 128 scans. All measurements were taken without sample spinning at
110 ( 1 °C. The 1H NMR spectra were referenced at 5.99 ppm for the
peak of residual tetrachloroethane-d1.
Computational Details. Calculations used the Gaussian03
program.41 Geometry optimizations and energies on ligands were done
using two methods: (i) the hybrid density functional theory (DFT)
method, B3LYP,42 with the 6-311þG** basis set43 and (ii) the
G3MP2B3 level of theory.44 For the metal-ligand complexes, structures
were optimized with the B3LYP method and the LANL2TZ(F) basis set45
on Hf/Zr along with 6-31G*(5d) on the remaining atoms. Single-point
energies were done with the B3LYP/LANL2TZ(F)/6-311þG** method.
Structure Determinations of 10, 15, 19, 21, and 22. X-ray
intensity data were collected on a Bruker SMART diffractometer using
Mo KR radiation (λ = 0.710 73 Å) and an APEXII CCD area detector.
Raw data frames were read by the program SAINT46 and integrated
using 3D profiling algorithms. The resulting data were reduced to
produce hkl reflections and their intensities and estimated standard
deviations. The data were corrected for Lorentz and polarization effects,
and numerical absorption corrections were applied on the basis of
indexed and measured faces. The structure was solved and refined in
SHELXTL6.1, using full-matrix least-squares refinement. The non-H
atoms were refined with anisotropic thermal parameters, and all of the H
atoms were calculated in idealized positions and refined riding on their
parent atoms. The refinement was carried out using F2 rather than F
values. R1 was calculated to provide a reference to the conventional R
value, but its function was not minimized.
(5) Kuhlman, R. L.; Klosin, J. Macromolecules 2010, 43, 7903–7904.
(6) Froese, R. D.; Jazdzewski, B. A.; Klosin, J.; Kuhlman, R. L.;
Theriault, C. N.; Welsh, D. M.; Abboud, K. A. Organometallics 2011,
30, 251–262.
(7) (a) Mashima, K.; Ohnishi, R.; Yamagata, T.; Tsurugi, H. Chem.
Lett. 2007, 36, 1420–1421. (b) Tsurugi, H.; Ohnishi, R.; Kaneko, H.;
Panda, T. K.; Mashima, K. Organometallics 2009, 28, 680–687.
(c) Kaneko, H.; Tsurugi, H.; Panda, T. K.; Mashima, K. Organometallics
2010, 29, 3463–3466.
1707
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
(8) (a) Murray, R. E. U.S. Patent 6,096,676, 2000. (b) Murray, R. E.;
George, V. M.; Nowlin, D. L.; Schultz, C. C.; Petersen, J. L. Polym. Prepr.
(Am. Chem. Soc., Div. Polym. Chem.) 2002, 43, 294–295. (c) Murray,
R. E. Int. Pat. Appl. 2003051935, 2003.
(9) van Asselt, R.; Elsevier, C. J.; Smeets, W. J. J.; Spek, A. L.;
Benedix, R. Recl. Trav. Chim. Pays-Bas 1994, 113, 88–98.
(27) The energy difference between trans/trans and trans/cis bis-
imines based on acenaphthalene bearing smaller substituents on imine
nitrogen atoms must be small, as both isomers are seen in solid-state
structures. For acenaphthalene bis-imines with o-CF3-Ph substituents on
nitrogen atoms, both trans/trans and trans/cis isomers are observed in
the unit cell.26a
(10) Kiyotaka B.; Masatoshi, N.; Daisuke, F. JP Patent 10182679, 1998.
(11) (a) Johnson, L. K.; Bennett, A. M. A.; Ittel, S. D.; Wang, L.;
Parthasarathy, A.; Hauptman, E.; Simpson, R. D.; Feldman, J.; Coughlin,
E. B. Int. Pat. Appl. 9830609, 1998. (b) Gates, D. P.; Svejda, S. A.; Onate,
E.; Killian, C. M.; Johnson, L. K.; White, P. S.; Brookhart, M. Macro-
molecules 2000, 33, 2320–2334.
(28) For examples of acyclic bis-imines with σ-trans confor-
mation see:(a) Gerdes, G.; Chen, P. Organometallics 2003, 22, 2217–
2225. (b) Ionkin, A. S.; Marshall, W. J. Organometallics 2004, 23, 3276–
3283. (c) Gonsalvi, L.; Gaunt, J. A.; Adams, H.; Castro, A.; Sunley, G. J.;
Haynes, A. Organometallics 2003, 22, 1047–1054. (d) Ionkin, A. S.;
Marshall, W. J. J. Organomet. Chem. 2004, 689, 1057–1063.
(12) Lodochnikov, V. G.; Gryaznova, T. V.; Gryaznov, P. I.; Musin,
R. Z.; Kibardin, A. M. Russ. J. Gen. Chem. 2001, 71, 437–442.
(13) Al-Omari, M.; Banert, K.; Hagedorn, M. Angew. Chem., Int. Ed.
2006, 45, 309–311.
(14) Kiesewetter, J.; Kaminsky, W. Chem. Eur. J. 2003, 9, 1750–1758.
(15) Pappalardo, D.; Tedesco, C.; Pellecchia, C. Eur. J. Inorg. Chem.
2002, 621–628.
(16) Cationic, acyclic imido-enamido complexes of zirconium have
been previously reported by the reaction of buta-1,3-diene-2,3-diamido
complexes with strong Lewis acids: Kim, Y H.; Kim, T. H.; Kim, N. Y.;
Cho, E. S.; Lee, B. Y.; Shin, D. M.; Chung, Y. K. Organometallics 2003,
22, 1503–1511.
(29) Amii, H.; Kohda, M.; Seo, M.; Uneyama, K. Chem. Commun.
2003, 1752–1753. (b) Sadighi, J. P.; Henling, L. M.; Labinger, J. A.;
Bercaw, J. E. Tetrahedron Lett. 2003, 44, 8073–8076. (c) Lersch, M.;
Krivokapic, A.; Tilset, M. Organometallics 2007, 26, 1581–1587.
(30) The 13C{1H} NMR spectrum for the seven-membered-ring bis-
imine13 exhibits only one signal for the imine or methine carbons, but two
carbon resonances are recorded for the i-Pr methyl groups. Two methyl
groups and only one methine proton are also observed in the 1H NMR
spectrum. This indicates that the i-Pr methyl groups are diastereotopic,
which implies a chiral environment. Bis-imine 13c is chiral, and because of
its cis/cis configuration, the barrier for interconversion between enantio-
mers is expected to be high. The bis-imine with a trans/trans configuration
(13a) is also chiral in the ground state, but because of the significantly
lower steric congestion between the imine nitrogen atoms, it would be
expected to undergo fast interconversion between enantiomers at ambient
temperature, resulting in the appearance of only one signal for the i-Pr
methyl peak (C2v symmetry in solution).
(31) Structures and energies of various cyclic 1,2-keto-enamines/
1,2-keto-imines and 1,2-keto-enol/1,2-diketones are included in the
Supporting Information.
(32) See the Supporting Information for NMR spectra.
(33) Ohashi, M.; Takahashi, T.; Inoue, S.; Sato, K. Bull. Chem. Soc.
Jpn. 1975, 48, 1892–1896.
(34) See the Supporting Information for details.
(35) (a) Polozov, G. I.; Tishchenko, I. G. Vestn. Belorus. Un-ta, Ser. 2
1986, 1, 67–69. (b) Dounay, A. B.; Overman, L. E.; Wrobleski, A. D.
J. Am. Chem. Soc. 2005, 127, 10186–10187.
(36) (a) Carlson, R.; Nilsson, A. Acta Chem. Scand. 1984, B 38, 49–
53. (b) Armesto, D.; Bosch, P.; Gallego, M. G.; Martin, J. F.; Ortiz, M. J.;
Pꢀerez-Ossorio, R.; Ramos, A. Org. Prep. Proced. Int. 1987, 19, 181–186.
(c) De Kimpe, N.; D’hondt, L.; Stanoeva, E. Tetrahedron Lett. 1991,
32, 3879–3882. (d) Carlson, R.; Larsson, U.; Hansson, L. Acta Chem.
Scand. 1992, 46, 1211–1214. (e) Klosin, J. U.S. Patent 6,617,407, 2003.
(37) Bradley, D. C.; Torrible, E. G. Can. J. Chem. 1963, 41, 134–138.
(38) (a) Schleis, T.; Spaniol, T. P.; Okuda, J.; Heinemann, J.;
M€ulhaupt, R. J. Organomet. Chem. 1998, 569, 159–167. (b) Bianchini,
C.; Giambastiani, G.; Rios, I. G.; Mantovani, G.; Meli, A.; Segarra, A. M.
Coord. Chem. Rev. 2006, 250, 1391–1418.
(39) It is possible to increase Mw by decreasing the reactor tem-
perature, but this is usually not a practical and economical solution.
(40) The ratio of molecular weights of polymers generated by 21 and
3 is 3.6, which is measurably higher than that obtained from end group
analysis (2.3). This difference is most likely due to the slightly higher
reactivity of 3 toward hydrogen compared to 21.
(41) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, M. G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, H.; Ehara, M.; Toyota, M. K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.;
Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui,
(17) Kim, Y. H.; Kim, T. H.; Lee, B. Y.; Woodmansee, D.; Bu, X.;
Bazan, G. C. Organometallics 2002, 21, 3082–3084.
(18) Figueroa, R.; Klosin, J. Int. Pat. Appl. 2010022228, 2010.
(19) The relative energies (kcal/mol) discussed in the text are
enthalpies. DFT ground-state energies for i-Pr- and DIP-based deriva-
tives for compounds shown in Scheme 4 are presented in the Supporting
Information.
(20) Three-dimensional structures of all calculated compounds are
included in the Supporting Information (MOL file format). MOL files
can be read by many programs, including the Mercury program freely
available at http://www.ccdc.cam.ac.uk/products/mercury/.
(21) There is one example of a structurally characterized six-mem-
bered-ring derivative that exists as a bis-imine rather than an imine-
enamine. In this case, however, both imine nitrogen atoms bear an
unsaturated group (3-pentene-2-thione) that stabilizes the bis-imine
form via conjugation: Jensen, H. P.; Kristensen, B. S.; Mosbaek, H.;
Søtofte, I. Acta Chem. Scand. 1978, A32, 141–148.
(22) N-methyl mono-imines are calculated to be more stable than
the corresponding enamines by 3.0 (five-membered), 1.6 (six-mem-
bered), and 0.3 kcal/mol (seven-membered).
(23) 1-Methylcycloalkenes are more stable than methylenecycloalk-
anes by 3.3 (five-membered ring), 7.2 (six-membered ring), and 2.3
kcal/mol (seven-membered ring).
(24) Smith, M. B.; March, J. March’s Advanced Organic Chemistry:
Reactions, Mechanisms, and Structure; Wiley: Hoboken, NJ, 2007; p 107.
(25) For crystal structures of acenaphthalene-based bis-imines with
trans/trans configuration see:(a) Liu, H.-R.; Gomes, P. T.; Costa, S. I.;
Duarte, M. T.; Branquinho, R.; Fernandes, A. C.; Chien, J. C. W.; Singh,
R. P.; Marques, M. M. J. Organomet. Chem. 2005, 690, 1314–1323.
(b) Coventry, D. N.; Batsanov, A. S.; Goeta, A. E.; Howard, J. A. K.;
Marder, T. B. Polyhedron 2004, 23, 2789–2795. (c) Zou, H.; Hu, S.;
Huang, H.; Zhu, F.; Wu, Q. Eur. Polym. J. 2007, 43, 3882–3891.
(26) For crystal structures of cyclic bis-imines with trans/cis
configuration see: (a) Moore, J. A.; Vasudevan, K.; Hill, N. J.; Reeske,
G.; Cowley, A. H. Chem. Commun. 2006, 2913–2915. (b) Rosa, V.;
Avilꢀes, T.; Aullon, G.; Covelo, B.; Lodeiro, C. Inorg. Chem. 2008,
47, 7734–7744. (c) Schleis, T.; Heinemann, J.; Spaniol, T. P.; Mulhaupt,
R.; Okuda, J. Inorg. Chem. Commun. 1998, 1, 431–434. (d) Fedushkin, I.
L; Chudakova, V. N.; Skatova, A. A.; Khvoinova, N. M.; Kurskii, Y. A.;
Glukhova, T. A.; Fukin, G. K.; Dechert, S.; Hummert, M.; Schumann, H.
Z. Anorg. Allg. Chem. 2004, 630, 501–507. (e) Lentz, D. Z. Naturforsch.,
B: Chem. Sci. 1992, 47, 148–150. (f) Adams, C. J.; Anderson, K. M.;
Bartlett, I. M.; Connelly, N. G.; Orpen, A. G.; Paget, T. J.; Phetmung, H.;
Smith, D. W. Dalton Trans. 2001, 1284–1292.
1708
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709

Organometallics
ARTICLE
Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.;
Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc., Wallingford, CT,
2004.
(42) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.;
Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (c) Miehlich, B.; Savin,
A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200.
(43) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971,
54, 724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257. (c) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163.
(44) (a) Curtiss, L. A.; Redfern, P. C.; Raghavachari, K.; Rassolov, V.;
Pople, J. A. J. Chem. Phys. 1999, 110, 4703. (b) Baboul, A. G.; Curtiss,
L. A.; Redfern, P. C.; Raghavachari, K. J. Chem. Phys. 1999, 110, 7650.
(45) (a) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical
Chemistry; Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3,
p 1. (b) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (c) Wadt, W.
R; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (d) Hay, P. J.; Wadt, W. R.
J. Chem. Phys. 1985, 82, 299. (e) Roy, L. E.; Hay, P. J.; Martin, R. L.
J. Chem. Theory Comput. 2008, 4, 1029.
(46) Sheldrick, G. M. SHELXTL6.1 Crystallographic Software Pack-
age; Bruker AXS, Inc., Madison, WI, 2008.
1709
dx.doi.org/10.1021/om101207a |Organometallics 2011, 30, 1695–1709