Single-component α-iminocarboxamide nickel ethylene polymerization and copolymerization initiators

Article abstract of DOI:10.1021/om070155g

The reaction of Ni(COD)₂, benzyl chloride, potassium N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidate, and pyridine or 2,6-lutidine yields N,O-bound α-iminocarboxamide complexes that can be used as single-component initiators for the homopolymerization of ethylene or the copolymerization of ethylene with functionalized norbornene monomers. Comparison of the Py versus 2,6-lutidine complexes highlights how the nitrogen ligand lability influences polymerization activity. It is also possible to synthesize η¹-CH₂COPh complexes via these procedures, which are less stable to the presence of monomer functionalities.

Full text of DOI:10.1021/om070155g

Organometallics 2007, 26, 5339-5345
5339
Single-Component r-Iminocarboxamide Nickel Ethylene
Polymerization and Copolymerization Initiators
Rene S. Rojas,† Griselda Barrera Galland,‡ Guang Wu,§ and Guillermo C. Bazan*,§
Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, Pontificia UniVersidad Cato´lica de Chile,
Santiago, Chile, Instituto de Qu´ımica da UFRGS, AVenida Bento Gonc¸alVes, 9500-CEP 91501-970, Brazil,
and Mitsubishi Chemical Center for AdVanced Materials, Institute for Polymer and Organic Solids,
Departments of Chemistry and Materials, UniVersity of California, Santa Barbara, California 93106
ReceiVed February 20, 2007
The reaction of Ni(COD)2, benzyl chloride, potassium N-(2,6-diisopropylphenyl)-2-(2,6-diisopropy-
lphenylimino)propanamidate, and pyridine or 2,6-lutidine yields N,O-bound R-iminocarboxamide
complexes that can be used as single-component initiators for the homopolymerization of ethylene or the
copolymerization of ethylene with functionalized norbornene monomers. Comparison of the Py versus
2,6-lutidine complexes highlights how the nitrogen ligand lability influences polymerization activity. It
is also possible to synthesize η1-CH2COPh complexes via these procedures, which are less stable to the
presence of monomer functionalities.
polyethylene from ethylene alone.5 Additionally, upon activation
with Ni(COD)2, these complexes provide sites that show quasi-
living characteristics for the polymerization of ethylene with
5-norbornen-2-yl-acetate (NBA).6 Significantly, activation with
Ni(COD)2 occurs only in the presence of ethylene. This feature
of the reaction allows for the synthesis of tapered, or gradient,
copolymer structures, although the mechanistic details of how
the Ni(COD)2/ethylene mixture activates the R-iminocarboxa-
mide complex remain uncertain at this stage. Structure-
reactivity relationship studies have shown that only N,O-bound
species (see Scheme 1) are useful in quasi-living polymeriza-
tions; negligible reactivity is seen with N,N-isomers under
Introduction
Interest in late transition metal initiators for the copolymer-
ization of ethylene with functionalized monomers stems from
the opportunity to access new commodity plastics and specialty
materials with unique properties.1 The ultimate utility of such
initiators is determined in part by whether preparative methods
are amenable for scale-up and incorporation into large-scale
manufacturing processes and by the potential applications and
cost of the resulting materials. Despite substantial progress in
the control of coactivator species,2 single-component systems
should provide better control over the polymerization reaction
conditions.3 Initiators that incorporate functionalities, are single
component, and provide living polymerization characteristics
are relatively rare and provide optimum control over polymer
chain composition and architecture.4
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Hu, T.; Tang, L.-M.; Li, X.-F.; Li, Y.-S.; Hu, N.-H. Organometallics 2005,
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Waltman, A. W.; Grubbs, R. H. Chem. Commun. 2003, 2272.
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Grubbs R. H.; Bansleben, D. A. Science 2000, 287, 460. (b) Connor, E. F.;
Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts, W.
P.; Litzau, J. J. J. Polym. Sci.: Part A: Polym. Chem. 2002, 40, 2842. (c)
Benedikt, G. M.; Elce, E.; Goodall, B. L.; Kalamarides, H. A.; McIntosh,
L. H.; Rhodes, L. F.; Selvy, K. T.; Andes, C.; Oyler, K.; Sen, A.
Macromolecules 2002, 35, 8978. (d) Yasuda, H.; Desurmont, G. Polym.
Int. 2004, 53, 1017. (e) Desjardins, S. Y.; Cavell, K. J.; Hoare, J. L.; Skelton,
B. W.; Sobolev, A. N.; White, A. H. Keim, W. J. Organomet. Chem. 1997,
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Bochmann, M. Organometallics 2005, 24, 3792.
R-Iminocarboxamide-Ni(η1-CH2Ph)(PMe3) complexes have
been used for concurrent tandem polymerization of branched
* Corresponding author. Fax: +1 805 893 4120. Tel: +1 805 893 5538.
E-mail: bazan@chem.ucsb.edu.
† Pontificia Universidad Cato´lica de Chile.
‡ Instituto de Qu´ımica da UFRGS.
§ University of California.
(1) (a) Rieger, B.; Baugh, L.; Striegler, S.; Kacker, S. Late Transition
Metal Polymerization Catalysis; John Wiley & Sons: New York, 2003.
(b) Blom, R.; Follestad, A.; Rytter, E.; Tilset, M.; Ystenes, M. Organo-
metallic Catalysts and Olefin Polymerization: Catalysts for a New
Millennium; Springer-Verlag: Berlin, Germany, 2001. (c) Galli, P.; Vecellio,
G. J. Polym. Sci. Part A: Polym. Chem. 2004, 42, 396. (d) Keim, W.;
Kowalt, F. H.; Goddard, R.; Kruger, C. Angew. Chem., Int. Ed. Engl. 1978,
17, 466. (e) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schultz, R. P.;
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(2) (a) Yang, Q.-Z.; Kermagoret, A.; Agostinho, M.; Siri, O.; Braunstein,
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White, P. S. Organometallics 2006, 25 (8), 1868. (c) Scha¨tz, A.; Scarel,
A.; Zangrando, E.; Mosca, L.; Carfagna, C.; Gissibl, A.; Milani, B.; Reiser,
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(5) (a) Bazan, G. C.; Rodriguez, G.; Ashe, A. J., III; Al-Ahmad, S.;
Mu¨ller, C. J. Am. Chem. Soc. 1996, 118, 2291. (b) Barnhart, R. W.; Bazan,
G. C.; Mourey, T. J. Am. Chem. Soc. 1998, 120, 1082. (c) Komon, Z. J.
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10.1021/om070155g CCC: $37.00 © 2007 American Chemical Society
Publication on Web 09/27/2007

5340 Organometallics, Vol. 26, No. 22, 2007
Rojas et al.
Scheme 1 . The Two Binding Modes of r-Iminocarboxamide
Ligands
reaction conditions where there is control over polymer struc-
ture.7 N,N-Binding appears to be favored by electronic reasons.
N,O-Binding is observed when bulky substituents are present
on the aryl groups. Additional isomers not shown in Scheme 1
arise from the position of PMe3 within the square plane, i.e.,
cis or trans to the imine coordination site. These observations
are consistent with an activation process that generates a
phosphine-free N,O-bound initiator species.
Figure 1. ORTEP drawing of N,N-1 (50% probability). Hydrogen
atoms were omitted for clarity.
In this contribution we disclose R-iminocarboxamide species
that are isoelectronic and isostructural adducts to the structures
in Scheme 1 but that take advantage of nitrogen ligands instead
of PMe3. These complexes can initiate ethylene homopolym-
erization and ethylene/NBA or 5-norbornen-2-ol NBO copo-
lymerization without the need to use Ni(COD)2, thereby simpli-
fying the polymerization procedures. Of particular interest is
the control required over the synthetic entry into these new
complexes to favor the N,O-bound isomers over the less reactive
N,N-bound species. We also show that these synthetic methods
are also suitable for making analogous complexes with η1-CH2-
COPh.
Results and Discussion
Synthesis, Characterization, and Reactivity of η1-Benzyl
Complexes. Initial efforts involved direct addition of excess
pyridine (Py) to the base-free compound [N-(2,6-diisopropy-
lphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ2N,N]-
Ni(η3-CH2Ph),7 as shown in eq 1. The strategy here was to force
dissociation of the benzyl π-component by Py, with a concomi-
tant rearrangement to the N,O-bound species. NMR spectroscopy
revealed that the product of the reaction contained two isomers
in a 1:1 ratio. Single crystals suitable for X-ray crystallography
studies were obtained by slow evaporation of a benzene solution.
As seen in Figure 1, the results show a square-planar arrange-
ment around the nickel center with an N,N-bound R-iminocar-
boxamide ligand, and Py trans to the imine nitrogen. The
products of the reaction are thus cis- and trans-[N-(2,6-
diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanami-
dato-κ2N,N]Ni(η1-CH2Ph)(Py) (N,N-1 in eq 1). We assign the
second isomer as the N,N-bound R-iminocarboxamide complex
with Py trans to the carboxamide nitrogen. On the basis of the
previously observed lack of reactivity from N,N-isomers, we
sought a different synthetic method.
Figure 2. ORTEP drawing of N,O-1 (50% probability). Hydrogen
atoms were omitted for clarity.
panamidate, Ni(COD)2, benzyl chloride, and Py in THF.
Running the reaction at 22 °C in the absence of light yields
two isomers in a 3:1 ratio, which, as determined by 1H and 13
C
NMR spectroscopies, do not correspond to the products in eq
1. Single crystals were obtained after workup by slow evapora-
tion of a benzene solution, and the results of subsequent X-ray
diffraction studies are shown in Figure 2. The room-temperature
reaction thus yields the desired N,O-bound structure, [N-(2,6-
diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-
κ2N,O]Ni(η1-CH2Ph)(Py) (N,O-1), as shown in eq 2. The two
isomers observed in solution are assigned to cis- versus trans-
binding of Py relative to the imine nitrogen.
A more direct approach involved the reaction of potassium
(7) Rojas, R. S.; Wasilke, J. C.; Wu, G.; Ziller, J. W.; Bazan, G. C.
N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)pro-
Organometallics 2005, 24, 5644.

R-Iminocarboxamide Nickel Ethylene Polymerization Initiators
Organometallics, Vol. 26, No. 22, 2007 5341
Table 1. Selected Bond Distances (Å) and Angles (deg)
N,N-1
1.9223(15) 1.915(2)
1.9267(19) 1.9453(11) 1.939(2)
N,O-1
N,O-2
N,O-3
Ni(1)-N(1)
Ni(1)-O(1)
Ni(1)-C(28)
Ni(1)-N(2)
Ni(1)-N(3)
O(1)-C(8)
C(28)-O(2)
1.9253(13) 1.912(3)
1.966(2)
1.943(3)
1.9647(17) 1.860(4)
1.9403(16)
1.9060(16) 1.888(2)
1.9132(13) 1.913(3)
1.2961(19) 1.298(4)
1.231(5)
1.251(2)
1.295(3)
N(1)-Ni(1)-N(2) 82.53(7)
N(1)-Ni(1)-O(1)
83.89(8)
96.39(11)
169.87(10) 171.51(5)
83.47(5)
94.20(7)
83.70(1)
94.52(14)
174.37(12)
C(28)-Ni(1)-N(1) 94.88(8)
N(1)-Ni(1)-N(3) 167.28(7)
N(2)-Ni(1)-C(28) 171.83(10)
O(1)-Ni(1)-C(28)
172.85(11) 175.80(7)
177.45(14)
91.04(14)
N(3)-Ni(1)-C(28) 89.54(8)
90.13(12)
90.60(9)
93.93(7)
88.57(5)
N(3)-Ni(1)-N(2)
N(3)-Ni(1)-O(1)
Ni(1)-C(28)-O(2)
94.62(7)
90.71(11)
120.1(3)
given in Table 2. Reactions were performed in a 100 mL
autoclave reactor in toluene at an ethylene pressure of 100 psi
with [Ni] ) 3.33 × 10-4 M. Temperatures were controlled by
either an external water bath or an internal heater and were
monitored by using an internal thermocouple. No reaction
occurred when using N,N-1 at either 20 or 40 °C (entries 1 and
2). In the case of N,O-1, negligible monomer consumption
occurs at 20 °C (entry 3); however polyethylene forms at
40 °C with an activity of 60 kg/(mol Ni)(h) (entry 4). Increasing
the ethylene pressure to 500 or 1000 psi results in no activity
for N,N-1 or change in the consumption of ethylene by N,O-1.
Higher activities are observed when the nitrogen ligand is
changed from Py to 2,6-Lu, at both 20 and 40 °C (compare
entries 3 and 4 vs 5 and 6). Gel permeation chromatography
measurements calibrated against polystyrene standards show that
the weight average molecular weights of the resulting polyeth-
ylenes are in the range 63 000 to 183 000 with polydispersities
centered around 2.
The differences in reactivity and structure between N,O-1
and N,O-2 suggest that the rate of Py or 2,6-Lu dissociation
influences the rate of initiation. Addition of an equivalent of
2,6-Lu shuts down the polymerization activity. The choice of
2,6-Lu over Py thus may be useful in two ways: it provides
for a faster initiation step (more labile) and it has a lower
tendency to bind to the propagating species and block ethylene
coordination (see Figure S-2 in the Supporting Information).
1H NMR spectroscopy analysis in C6D6 at 60 °C of N,O-1 and
N,O-2 up to 1 h shows no evidence of Py or 2,6-Lut loss; the
formation of only a small fraction of the η3-complex takes place.
These observations are consistent with an equilibrium constant
that favors the Py or 2,6-Lut adducts. Two possibilities ensue.
The first involves ethylene coordination/insertion on the small
fraction of unbound species, the concentration of which increases
at higher temperatures. Alternatively, ethylene displaces the
nitrogen ligand via an associative mechanism. Under these
circumstances, the more important factor is that lutidine is more
weakly bound instead of its increased ability to sterically protect
the nickel center.
Figure 3. ORTEP drawing of N,O-2 (50% probability). Hydrogen
atoms were omitted for clarity.
Comparison of 1H NMR spectra shows that heating a solution
of N,O-1 in C6D6 at 60 °C for 14 h produces N,N-1 in nearly
quantitative yield. The transformation is irreversible. Thus,
N,O-1 is a kinetic product, formed presumably because the
oxygen in the carboxamidate functionality is more open than
the nitrogen site and therefore more likely to participate in
displacement reactions.
A reaction similar to that in eq 2 using 2,6-lutidine (2,6-Lu)
instead of Py yields, after purification by recrystallization from
a 1:4 ether-pentane mixture, a single organometallic product
in higher than 85% yield. The composition of the product is
[N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)pro-
panamidato-κ2N,O]Ni(η1-CH2Ph)(2,6-Lu) (N,O-2 in eq 3), as
determined by NMR spectroscopy and single-crystal diffraction
studies (Figure 3). Reactions analogous to those in eqs 1 and 2,
with the bulkier 2,6-di(tert-butyl)pyridine, did not yield the
desired benzyl complexes. Instead, one obtains the base-free
compound [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphe-
nylimino)propanamidato-κ2N,N](η3-CH2Ph)nickel complex, i.e.,
the starting material in eq 1.
Statistically significant differences are observed in the
structures of N,O-1 and N,O-2. Table 1 contains a summary of
relevant metrical data. As a result of the increased bulk of 2,6-
Lu compared to Py, the coordination sphere around Ni is more
crowded in N,O-2. For example, when comparing N,O-2 with
N,O-1, longer Ni-ligand distances are found: Ni-C(28)
(1.9647(17) vs 1.943(3) Å), Ni-N(3) (1.9132(13) vs 1.888(2)
Å), Ni-O (1.9453(11) vs 1.9267(19) Å), and Ni-N(1) (1.9253-
(13) vs 1.915(2) Å). On the basis of these distances, it is
reasonable to expect that 2,6-Lu is more weakly bound than
Py.
The last four entries in Table 2 show that N,O-2 can initiate
the copolymerization of ethylene with NBA or 5-norbornen-2-
ol (NBO). Similar efforts using N,O-1 were not as successful.
In these reactions fixed concentrations of the comonomer and
the initiator source are mixed inside the glovebox, placed in
the reactor, and subsequently attached to an ethylene feed line.
The percent incorporation of the comonomers into the polymer
chain is controlled by the initial concentration in the reaction
medium prior to polymerization. For example, when the
Polymerization Activity with η1-Benzyl Complexes. A
series of ethylene homopolymerization and copolymerization
reactions were conducted, and the summary of the results is

5342 Organometallics, Vol. 26, No. 22, 2007
Table 2. Summary of Polymerization Reactions with N,O-1 and N,O-2a
Rojas et al.
entry
initiator
comonomer
[M]
T (°C)
activityb
Mw
Mw/Mn
% inc.
1
2
3
4
5
6
7
8
9
N,N-1
N,N-1
N,O-1
N,O-1
N,O-2
N,O-2
N,O-2
N,O-2
N,O-2
N,O-2
20
40
20
40
20
40
40
40
40
40
60
43
63 000
125 000
143 000
96 000
93 000
88 000
1.8
1.8
2.2
1.9
1.8
2.0
5.7
304
160
170
147
48
NBA (0.075)
NBA (0.150)
NBO (0.075)
NBO (0.150)
9
13
8
10
183 000
14
aPolymerizations were carried out in a 100 mL autoclave reactor with 10 µmol of Ni in 30 mL of toluene ([Ni] ) 3.33 × 10 -4 M); reaction time 20 min;
b
PC2H4 ) 100 psi; temperature controlled by using a water bath. kg polymer/(mol Ni)(h), as determined by the mass of the polymer product. Yield ) activity
× mol Ni × 0.333 h.
N,O-2, as shown in eq 4. Under minimal exposure to light,
benzoyl chloride and Py were mixed and added to a solution of
Ni(COD)2 in THF at -35 °C. The reaction was allowed to warm
to room temperature, and after 20-30 min of stirring the
originally clear reaction mixture turned slightly cloudy. At this
stage, potassium N-(2,6-diisopropylphenyl)-2-(2,6-diisopropy-
lphenylimino)propanamidate in THF was added dropwise to the
reaction mixture over a 45 min period and the mixture was
stirred overnight. After workup by filtration, the product of the
first crystallization effort contained N,O-3 with an impurity
corresponding to bis[N-(2,6-diisopropylphenyl)-2-(2,6-diisopro-
pylphenylimino)propanamidato-κ2N,O]Ni (see Supporting In-
formation). Successive crystallizations from pentane-ether
solvent mixtures allowed the isolation of N,O-3 as dark orange
crystals in 54% yield. 1H NMR and 13C NMR spectra are
consistent with the presence of a single isomer.
Figure 4. ORTEP drawing of N,O-3 (50% probability). Hydrogen
atoms were omitted for clarity.
concentration of NBA is increased from 0.075 to 0.15 M and
the reaction is allowed to proceed for 20 min, the molar
incorporation increases from 9% to 13%, as determined by 1H
NMR spectroscopy of the isolated products. A qualitatively
similar increase is also observed with NBO. However, higher
initial concentrations of NBO result in a decrease of net activity
and a broadening of molecular weight (compare entries 6 and
9 vs 10), possibly as a result of deactivation or competitive
binding by the hydroxyl functionalities.
Microstructure characterization of the products in Table 2
by 13C NMR spectroscopy reveals that the ethylene homopoly-
mers contain only methyl branches. The copolymers also
contained only methyl branches, and there is no evidence that
the functionalized monomers are found adjacent to each other
along the polymer backbone (see Supporting Information).
Synthesis, Characterization, and Reactivity of an η1-
Benzoyl Complex. Previous studies demonstrated that, com-
pared to η3-benzyl, the stronger binding to nickel of the η3-
methallyl fragment results in a decrease of initiation rates for
ethylene oligomerization reactions.8 On the basis of these
observations, we sought to synthesize an isostructural analogue
of N,O-1 with η1-benzoyl instead of η1-benzyl. The η1-benzoyl
fragment was chosen, in part, because of the expected ease of
oxidative addition to Ni(COD)2, a primary requirement for the
synthetic entry into R-iminocarboxamide complexes and because
of the electron-withdrawing ability of the carbonyl group. The
synthesis of [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphe-
nylimino)propanamidato-κ2N,O]Ni(η1-COPh)(Py) (N,O-3) was
carried out by adapting the procedures developed for N,O-1 and
Figure 4 provides the results of X-ray diffraction studies from
single crystals of N,O-3 obtained by slow evaporation of an
ether solution. The desired N,O-bonding mode is observed with
the benzoyl ligand coordinated in an η1-fashion trans to the
amide nitrogen (similar orientation as in N,O-1). Note that the
benzoyl carbonyl is “perpendicular” to the nickel square plane.
The C(28)-O(2) bond distance (1.231(5) Å) and the O(2)-
C(28)-Ni angle (120.1(3)°) (Table 1) indicate sp2 hybridization
and that no strong interaction between the benzoyl carbonyl
and nickel occurs. The two aryl rings on the R-iminocarboxa-
mide are also perpendicular to the square plane. The bond
distances for Ni-N(1) and Ni-O(1) (1.912(3) and 1.939(2) Å,
respectively) are similar to those in compound N,O-1 (Table
(8) Komon, Z. J. A.; Bu, X. H.; Bazan, G. C. J. Am. Chem. Soc. 2000,
122, 12379.

R-Iminocarboxamide Nickel Ethylene Polymerization Initiators
Organometallics, Vol. 26, No. 22, 2007 5343
Table 3. Summary of Polymerization Reactions with N,O-3a
entry
initiator
comonomer [M]
T (°C)
activityb
Mw
Mw/Mn
% inc.
1
2
3
4
5
6
7
8
N,O-3
N,O-3
N,O-3
N,O-3
N,O-3c
N,O-3c
N,O-3
N,O-3
20
40
50
60
50
40, 50
50
270
301
131
145 000
160 000
183 000
1.7
2.0
2.4
NBA (0.075)c
NBO (0.075)c
NBA (0.075)
NBO (0.075)
261
323
125 000
112 000
2.5
2.6
2.5
3.0
50
aPolymerizations were carried out in a 100 mL autoclave reactor with 10 µmol of Ni in 30 mL of toluene; [Ni] ) 3.33 × 10-4 M; reaction time, 20 min;
b
c
ethylene pressure 400 psi; temperature controlled by using a water bath. kg polymer/(mol Ni)(h). Yield ) activity × mol Ni × 0.333 h. Method 1: initial
addition of comonomer. In these reactions fixed concentrations of the comonomer and the initiator source are mixed inside the glovebox, placed in the
reactor, and subsequently attached to an ethylene feed line. Method 2: Addition of comonomer after initiation with ethylene. Initiator solutions (N,O-3) and
toluene are placed in the reactor, subsequently attached to an ethylene feed line, and the polymerization is run for 5 min. After this time the comonomer was
added via an addition funnel and the copolymerization reaction was allowed to run for an additional 15 min.
1). The Ni-N(3) bond distance for N,O-1 is slightly shorter
than that in N,O-3 (1.888(2) vs 1.913(3) Å), while the Ni-
C(28) (η1-benzoyl) is 0.083(4) Å shorter than Ni-C28
(η1-benzyl).
η1-benzoyl complex N,O-3. We anticipate similar success with
other R-iminocarboxamide frameworks that have sufficiently
bulky aryl substituents to inhibit N,N-binding and with pyridine
derivatives that can bind tightly to nickel. Structural analysis
shows that the 2,6-Lu ligand in N,O-2 is more weakly bound
than Py in N,O-1. Consistent with a more weakly bound 2,6-
Lu ligand, we find that polymerizations with N,O-2 can be
accomplished milder reaction conditions, relative to N,O-1. We
find that N,O-3 is unstable to the presence of NBA or NBO.
Successful copolymerizations with ethylene can be achieved
only when the functionalized norbornenes are added after
initiation with ethylene.
Table 3 provides the results for a series of polymerization
reactions at ethylene pressures of 400 psi when carried out with
N,O-3. No reaction occurs at 20 °C (entry 1). However, at
40 °C (entry 2) an ethylene consumption activity of 270 kg/
(mol Ni)(h) is observed. Increasing the temperature from 40 to
50 °C (entry 3), without changing reaction time or ethylene
pressure, results in a slight increase of activity. However,
increasing the temperature to 60 °C (entry 4) decreases the
activity, perhaps as a result of thermal decomposition. An
increase in the molecular weight and PDIs of the resulting
polyethylene was also seen with increasing temperature.
Copolymerization tests with N,O-3 are contained in entries
5 to 8 in Table 3. For the results in entries 5 and 6, where no
reactivity was observed, the same technique as for the polym-
erization reactions using N,O-2 were used. That is, N,O-3 was
mixed in the presence of comonomer prior to ethylene addition.
Separate tests, where N,O-3 and NBA were mixed in C6D6,
Experimental Section
General Remarks. All manipulations were performed in an inert
atmosphere using standard glovebox and Schlenk-line techniques.
Unless otherwise specified, all reagents were used as received from
Aldrich. Ethylene was purchased from Matheson Tri-Gas (research
grade, 99.99% pure) and was further purified by passing through
an oxygen/moisture trap (Matheson model 6427-4S). Toluene, THF,
hexane, and pentane were distilled from benzophenone ketyl. All
polymerization reactions were carried out in a Parr autoclave reactor
as described below. Toluene for polymerization was distilled from
sodium/potassium alloy. Compound N,N-1 was prepared by the
addition of Py to the previously reported compound [N-(2,6-
diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-
κ2N,N]Ni(η3-CH2Ph).7 Compounds N,O-1 and N,O-2 were prepared
by direct reaction of potassium N-(2,6-diisopropylphenyl)-2-(2,6-
diisopropylphenylimino)propanamidate with Ni(COD)2, benzyl
chloride, and pyridine or 2,6-lutidine in THF. NMR spectra were
run on Varian Unity 400 and 500 spectrometers. Polymers were
dried overnight under vacuum, and the polymerization activities
were calculated from the mass of product obtained. These values
were within 5% of the mass calculated by measuring the ethylene
consumed using a mass flow controller. The polymers were
characterized by GPC at 135 °C in o-dichlorobenzene (in a Polymer
1
revealed by H NMR spectroscopy that quick decomposition
took place, leading to the formation of a complex mixture of
unassignable products. A different copolymerization method was
thus explored. Here NBA or NBO was added via a pressurized
addition funnel after 5 min of exposing N,O-3 to ethylene and
the temperature was increased to 50 °C. Entries 7 and 8 show
that this post-initiation addition method leads to a high molecular
weight polymer that incorporates the desired functionalized
norbornenes. The lower incorporation under these conditions,
relative to those in Table 2, may be attributed to the higher
ethylene pressures.9 Polymer microstructures are similar to those
observed for the products in Table 2 (Supporting Information).
Conclusions
1
In summary, we report on the synthetic access to compounds
N,O-1 and N,O-2, which are single-component initiators for the
polymerization of ethylene and copolymerization of ethylene
with NBA or NBO. There is no need to use Ni(COD)2 for
activation, as is the case for the PMe3 analogues. Thermal
activation is required, possibly for dissociation of Py or 2,6-
Lu, which reduces the control over the polymer structure; that
is, it was not possible to find polymerization conditions with
quasi-living characteristics. The syntheses of N,O-1 and N,O-2
require the methods shown in eqs 2 and 3, which are simple
and of high yield and can be extended to the preparation of the
Laboratories high-temperature chromatograph, Pl-GPC 200). H
NMR spectra of the polymers were obtained in a mixed solvent
(C6D6/1,2,4-trichlorobenzene in a 1:4 ratio by volume) at 115 °C.
Elemental analysis was performed on a Leeman Labs Inc. CE440
elemental analyzer and a Control Equipment Corporation 440
elemental analyzer.
X-ray Crystallography. The monocrystal was mounted on a
glass fiber and transferred to a Bruker CCD platform diffractometer.
The SMART10 program package was used to determine the unit-
cell parameters and for data collection (25 s/frame scan time for a
sphere of diffraction data). The raw frame data were processed using
(9) Chen, G.; Ma, X. S.; Guan, Z. J. Am. Chem. Soc. 2003, 125 (22),
6697.
(10) SMART Software Users Guide, Version 5.1; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 1999.

5344 Organometallics, Vol. 26, No. 22, 2007
Rojas et al.
Table 4. Crystal Data and Structure Refinement for Phosphine-Free r-Iminocarboxamide Nickel Complexes
N,N-1
N,O-1
N,O-2
N,O-3
empirical formula
fw
C39H49N3ONi
634.52
C39H49N3ONi
634.52
C41H53N3ONi
662.58
C39H47N3O2Ni
648.51
temperature (K)
wavelength (Å)
cryst syst
space group
unit cell dimensions
(Å, deg)
118 (1)
0.71073
orthorhombic
P212121
a ) 9.1867(7)
119(1)
0.71073
monoclinic
P21/n
a ) 12.3182(13)
118 (1)
0.71073
monoclinic
P21/n
a ) 12.8214(9)
117 (1)
0.71073
monoclinic
P21/c
a ) 37.976(3)
b )16.0857(11)
c ) 23.3613(18)
R ) 90
b ) 17.9079(19)
c ) 17.6910(19)
R ) 90
b ) 18.6216(13)
c ) 17.7596(13)
R ) 90
b ) 14.4551(12)
c ) 14.8230(12)
R ) 90
â ) 90
â ) 93.588(3)
γ ) 90
â )101.519(2)
γ ) 90
â ) 98.536(2)
γ ) 90
γ ) 90
3452.2(4)
4
volume (Å3)
Z
3894.9(7)
4
4154.8(5)
4
8046.9(12)
4
density (calcd) (Mg/m3)
1.221
0.596
1360
0.3 × 0.15 × 0.08
1.54 to 28.57
-12 e h e 9
-21 e k e 20
-30 e l e 30
30 092
1.215
0.535
1528
0.2 × 0.1 × 0.06
1.62 to 26.48
-15 e h e 15
-20 e k e 22
-22 e l e 21
30 670
1.184
0.504
1592
0.3 × 0.3 × 0.20
1.60 to 28.52
-17 e h e 17
-23 e k e 24
-21 e l e 22
36 086
1.147
0.518
2968
0.35 × 0.3 × 0.15
5.10 to 26.37
-29 e h e 47
-17 e k e 17
-17 e l e 15
60 995
absorp coeff (mm-1
F(000)
)
cryst size (mm3)
θ range (deg)
index ranges
no. of reflns collected
no. of indep reflns
completeness to the
respective θ
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]a
8123 [R(int) ) 0.0430]
95.2
7976 [R(int) ) 0.0787]
99.0
9768 [R(int) ) 0.0386]
92.6
15 837 [R(int) ) 0.0618]
96.2
8123/0/593
0.978
7976/0/672
1.012
9768/0/705
1.039
15 837/25/889
1.063
R1 ) 0.0353,
wR2 ) 0.0722
R1 ) 0.0482,
wR2 ) 0.0753
0.448 and -0.205
R1 ) 0.0533,
wR2 ) 0.1191
R1 ) 0.0873,
wR2 ) 0.1348
0.854 and -0.489
R1 ) 0.0381,
wR2 ) 0.0902
R1 ) 0.0580,
wR2 ) 0.0974
0.419 and -0.323
R1 ) 0.0613,
wR2 ) 0.1474
R1 ) 0.1021,
wR2 ) 0.1660
1.297 and -0.533
R indices (all data)a
largest diff peak and
hole (e Å-3
)
a R1) ∑||Fo| - |Fc||]/∑[|Fo|; wR2 ) [∑(Fo - Fc )2]/∑[w(Fo )2]]1/2, GOF ) [∑[w(Fo - Fc )2]/(n - p)]1/2, where n is the number of reflections and p
2
2
2
2
2
is the total number of refined parameters.
SAINT11 and SADABS12 to yield the reflection data file. Subsequent
calculations were carried out using the SHELXTL13 program. The
structure was solved by direct methods and refined on F2 by full-
matrix least-squares techniques. Analytical scattering factors14 for
neutral atoms were used throughout the analysis. Hydrogen atoms
were located from a difference Fourier map and refined (x,y,z and
Uiso).15 Single crystals of N,N-1, N,O-1, N,O-2, and N,O-3 suitable
for X-ray diffraction studies were obtained by evaporation of
benzene or diffusion of pentane into a benzene or toluene solution.
The crystal data and refinement are summarized in Table 4.
Synthesis and Characterization of Compounds. [N-(2,6-
Diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-
κ2N,N](η1-CH2Ph)nickel(pyridine) (N,N-1). The synthesis of
N,N-1 was carried out by addition of 4 equiv of pyridine to a
[N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propan-
amidato-κ2N,N](η3-CH2Ph)nickel toluene solution (50 mg, 0.09
mmol in 5 mL of toluene). The reaction mixture was stirred for 1
h; volatiles were then removed under vacuum. The solid was
extracted with a 1:2 ether-pentane mixture (5 mL), and crystal-
lization took place at room temperature overnight. Compound N,N-1
6.79 (m, 4H, H-Ph), 6.76-6.63 (m, 4H, H-Ph), 6,24-6.12 (m, 2H,
3
Hp-Py), 5.85-5.80 (m, 4H, JHH ) 6.4 Hz, H0-Py), 4.70 (sep 2H,
3
3JHH ) 6.8 Hz, CH-i-Pr), 4.21 (sep 2H, JHH ) 6.8 Hz, CH-i-Pr),
3
3
3.97 (sep 2H, JHH ) 6.8 Hz, CH-i-Pr), 3.48 (sep 2H, JHH ) 6.8
Hz, CH-i-Pr), 1.98 (s, 2H, CH2-Bn), 1.92 (s, 3.0, CH3), 1.88 (s,
3.0, CH3), 1.77 (d, 6H, 3JHH ) 7.2 Hz, CH3-i-Pr), 1.67 (s, 2H, CH2-
3
3
Bn), 1.67 (d, 6H, JHH ) 7.2 Hz, CH3-i-Pr), 1.63 (d, 6H, JHH
)
6.8 Hz, CH3-i-Pr), 1.54 (d, 6H, 3JHH ) 6.8 Hz, CH3-i-Pr), 1.27 (d,
3
3
6H, JHH ) 6.8 Hz, CH3-i-Pr), 1.11 (d, 6H, JHH ) 7.2 Hz, CH3-
i-Pr), 1.05 (d, 6H, 3JHH ) 6.8 Hz, CH3-i-Pr), 0.92 (d, 12H, 3JHH
6.8 Hz, CH3-i-Pr).
)
[N-(2,6-Diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-
propanamidato-κ2N,O](η1-CH2Ph)nickel(pyridine)(N,O-1). The
synthesis of N,O-1 was carried out under minimal light exposure.
A Ni(COD)2 solution (68 mg, 0.25 mmol in 5 mL of THF) was
treated with a mixture of benzyl chloride (63 mg, 0.49 mmol) and
pyridine (234 mg, 2.96 mmol) in 2 mL of THF at -35 °C. The
potassium salt of the ligand (105 mg, 0.23 mmol dissolved in 3
mL of THF) was added after 10 min of reaction. The reaction
mixture was allowed to warm to room temperature and was stirred
overnight. Volatiles were then removed under vacuum. The resulting
oil was extracted with ether (15 mL) and filtered through Celite.
The solvent volume was reduced, and crystallization took place at
room temperature overnight. Compound N,O-1 was isolated from
1
was isolated as red crystals in 95% yield. H NMR spectroscopy
revealed two isomers in a 1:1 ratio.
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 8.02-7.99 (m,
4H, Ho-Bn), 7.36 (t, 2H, Bn), 7.09-7.00 (m, 12H, H-Ph, Bn), 6.92-
1
the first crystallization as dark orange crystals in 62% yield. H
(11) SAINT Software Users Guide, Version 6.0; Bruker Analytical X-Ray
Systems, Inc.: Madison, WI, 1999.
(12) Sheldrick, G. M. SADABS, Version 2.05; Bruker Analytical X-Ray
Systems, Inc.: Madison, WI, 2001.
(13) Sheldrick, G. M. SHELXTL Version 6.12; Bruker Analytical X-Ray
Systems, Inc.: Madison, WI, 2001.
(14) International Tables for X-Ray Crystallography, Vol. C; Kluwer
Academic Publishers: Dordrecht, 1992.
NMR spectroscopy showed two isomers in a 3:1 ratio.
Anal. Calcd for C39H49N3ONi: C, 73.82; H, 7.78; N, 6.62.
1
Found: C, 72.05; H, 7.80; N, 6.62. H NMR (399.95 MHz, [d6]-
3
benzene, 298 K): δ 8.24 (br), 7.91 (d, JHH ) 5.6 Hz), 7.24 (t,
3JHH ) 7.6 Hz), 7.08-6.96 (m), 6.80-6.63 (m), 6.25 (dd, 2H, 3JHH
3
) 7.8 Hz, H0-Pyminor), 5.83 (dd, 2H, JHH ) 6.8 Hz, H0-Pymajor);
(15) Flack, H. D. Acta Crystallogr. 1983 A39, 876.
Major isomers, δ 3.90 (sep 2H, 3JHH ) 6.8 Hz, CH-i-Pr), 3.54 (sep

R-Iminocarboxamide Nickel Ethylene Polymerization Initiators
2H, 3JHH ) 6.8 Hz, CH-i-Pr), 2.09 (s, 3H, CH3), 2.07 (s, 2H, CH2-
Organometallics, Vol. 26, No. 22, 2007 5345
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 8.58 (d, 2H),
8.39-8.36 (tt, 2H) 7.29 (d, 2H), 7.02 (t, 1H), 6.96-6.89 (m, 6H),
6,24 (t, 1H), 5.85 (t, 2H), 3.86 (broad-sep 2H), 3.61 (sep 2H), 2.12
(s, 3.0), 1.46 (d, 12H), 1.25 (m, 6H), 1.11(d, 6H). 13C NMR (125.7
MHz, [d6]-benzene, 298 K): δ 250.98, 184.67, 162.60, 152.58,
151.35, 147.13, 143.45, 140.22, 139.18, 137.17, 131.29, 127.71,
125.67, 124.41, 124.19, 123.09, 29.90, 29.56, 25.21, 24.14, 23.59,
21.20.
Typical Homopolymerization of Ethylene. Polymerizations
were conducted in the following manner using the initiators N,N-
1, N,O-1, N,O-2, or N,O-3. An autoclave reactor (100 mL) was
loaded inside a glovebox with an appropriate amount (10 µmol) of
a neutral nickel(II) R-iminocarboxamide initiator with toluene, for
a final volume of 30 mL of toluene solution. The reactor was sealed
inside the glovebox, and it was attached to an ethylene line. The
gas was fed continuously into the reactor at a pressure of 100 psi
(in specifics tests also to 400, 500, and 1000 psi). The pressurized
reaction mixture was stirred at variable temperatures ranging from
20 to 40 °C. After a specific reaction time, the ethylene was vented
and acetone was added to quench the polymerization. The precipi-
tated polymer was collected by filtration and dried overnight under
vacuum. (The molecular weight average and PDIs were determined
by GPC analysis in dichlorobenzene at 135 °C and are relative to
polystyrene standards.)
Copolymerization of Ethylene with Norbornene Derivatives.
Method 1: Initial Addition of Comonomer. A steel reactor was
loaded inside a glovebox with an appropriate amount (10 µmol) of
a neutral nickel(II) R-iminocarboxamide initiator (compound N,O-
2), 5-norbornen-2-yl acetate (NBA) or 5-norbornen-2-ol (NBO)
(0.075 to 0.15 M), and toluene (26 g) for a final volume of 30 mL
of toluene solution. The steel reactor was sealed inside the glovebox
and was attached to the ethylene line. Ethylene was fed continuously
into the reactor at 100 psi, and the pressurized reaction mixture
was stirred at 40 °C. Ethylene was vented after 20 min, and acetone
and methanol were added to quench the polymerization. The
precipitated polymer was collected by filtration and dried under
high vacuum for 12 h. The molecular weight of the polyethylene
polymer was calculated by refractive index GPC analysis (o-
dichlorobenzene, 135 °C) relative to universal calibration from
polystyrene standards. Mol % incorporation of the norbornenyl
group was calculated from 1H NMR spectroscopy (C6D6-o-
dichlorobenzene, 120 °C).
3
3
Bn), 1.58 (dd 12H, JHH ) 6.8 Hz, CH3-i-Pr), 1.39 (d, 12H, JHH
) 6.8 Hz, CH3-i-Pr); Minor isomers, 3.64 (sep 2H, 3JHH ) 6.8 Hz,
CH-i-Pr), 3.31 (sep 2H, 3JHH ) 6.8 Hz, CH-i-Pr), 2.53 (s, 3H, CH3),
3
3
1.17 (d, 12H, JHH ) 6.4 Hz, CH3-i-Pr), 0.98 (d, 6H, JHH ) 6.8
Hz, CH3-i-Pr), 0.92(d, 6H, JHH ) 6.4 Hz, CH3-i-Pr). 13C NMR
3
(125.7 MHz, [d6]-benzene, 298 K): δ 182.35 (carbonylmajor), 178.35
(carbonylminor), 165.05 (CdNminor), 163.76 (CdNmajor), 152.27,
152.04, 151.29, 150.89, 146.87, 141.97, 140,26, 139.26, 139.01,
138.77, 135.74, 135.25, 129.24, 127.94, 127.28, 124.60, 123.72,
123.29, 123.10, 123.01, 122.95, 122.29, 122.09, 29.90, 29.77, 29.27,
28.74, 24.71, 24.56, 24.31, 24.12, 23.51, 21.00, 15.12.
[N-(2,6-Diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-
propanamidato-κ2N,O](η1-benzyl)nickel(lutidine) (N,O-2). The
synthesis of N,O-2 was carried out under minimal light exposure.
A Ni(COD)2 solution (68 mg, 0.25 mmol in 5 mL of THF) was
treated with a mixture of benzyl chloride (63 mg, 0.5 mmol) and
2,6-lutidine (156 mg, 1.45 mmol) in 2 mL of THF at -35 °C.
Potassium salt (105 mg, 0.25 mmol dissolved in 3 mL of THF)
was added after 10 min. The reaction mixture was allowed to warm
to room temperature and was stirred overnight. Volatiles were
removed under vacuum. The resulting oil was extracted with ether
(15 mL) and filtered through Celite. The solvent volume was
reduced, pentane was added, and crystallization took place at room
temperature overnight. Compound N,O-2 was isolated from the first
crystallization as dark orange crystals in 85% yield. 1H NMR
spectroscopy showed a single isomer.
Anal. Calcd for C41H53N3ONi: C, 74.32; H, 8.06; N, 6.34.
1
Found: C, 74.10; H, 8.01; N, 6.38. H NMR (399.95 MHz, [d6]-
3
benzene, 298 K): δ 7.11-7.04 (m, 5H, Bn), 6.90 (t, 1H, JHH
)
7.2 Hz, Hp-Ph), 6.75 (t, 1H, 3JHH ) 7.2 Hz, Hp-Ph), 6.58-6.50 (m,
4H, Hm-Ph), 6,23 (t, 1H, 3JHH ) 7.6 Hz, Hp-Lu), 5.84 (d, 2H, 3JHH
) 7.6 Hz, Hm-Lu), 3.89 (sep 2H, 3JHH ) 6.8 Hz, CH-i-Pr), 3.66 (s,
3
6H, Me-Lu), 3.49 (sep 2H, JHH ) 7.2 Hz, CH-i-Pr), 2.09 (s, 3.0,
3
CH3), 1.61 (d, 6H, JHH ) 7.2 Hz, CH3-i-Pr), 1.42 (s, 2H, CH2-
3
3
Bn), 1.40 (d, 12H, JHH ) 6.8 Hz, CH3-i-Pr), 1.17(d, 6H, JHH
)
6.8 Hz, CH3-i-Pr). 13C NMR (125.7 MHz, [d6]-benzene, 298 K):
δ 182.34 (carbonyl), 158.79 (CdN), 152.24, 141.93, 140.13, 138.64,
136.29, 127.86, 127.04, 124.52, 122.96, 122.88, 122.07, 29.73,
29.20 (CH-i-Pr), 26.67 (CH3-Lut), 24.67, 24.34, 24.11 (CH3-i-Pr),
21.09 (CH2-Ph), 11.66 (CH3).
[N-(2,6-Diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-
propanamidato-κ2N,O](η1-COPh)nickel(pyridine) (N,O-3). The
synthesis of N,O-3 was carried out under an inert atmosphere with
minimum exposure to light. A Ni(COD)2 solution (112 mg,
0.41 mmol in 5 mL of THF) was treated with a mixture of benzoyl
chloride (58 mg, 0.41 mmol) and pyridine (130 mg, 1,65 mmol) in
2 mL of THF at room temperature. After 15 min, the potassium
salt of the ligand (140 mg, 0.31 mmol dissolved in 3 mL of THF)
was added over 45 min. The reaction mixture was stirred overnight,
and volatiles were removed under vacuum. The resulting oil was
extracted with ether (15 mL) and filtered. The solvent volume was
reduced, and crystallization took place at room temperature
overnight. The product of the first crystallization batch contained
N,O-3 with an impurity. Successive crystallizations from pentane-
ether allowed the isolation of N,O-3 as dark orange crystals in 54%
Method 2: Addition of Comonomer after Initiation with
Ethylene. Initiator solutions (N,O-3) were prepared as described
above; however the comonomer was added via an addition funnel
after the polymerization of ethylene was allowed to run for 5 min.
Polymerization was quenched as described in method 1.
Acknowledgment. This work was funded through the
Mitsubishi Chemical Center for Advanced Materials and the
Department of Energy. The authors are grateful to Professors
Ed Kramer, Susannah Scott, and Glenn Fredrickson for useful
discussions.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
1
yield. H NMR spectroscopy showed one isomer.
OM070155G