α-Iminocarboxamide nickel complexes: Synthesis and uses in ethylene polymerization

Article abstract of DOI:10.1021/om050640g

A series of nickel complexes containing α-iminocarboxamide, η¹-benzyl, and PMe₃ ligands were synthesized to identify structural features of neutral Ni complexes that are employed in ethylene polymerization and ethylene/functionalized norbornene copolymerizations. Variations in steric bulk on aryl substituents in the α-iminocarboxamide framework were used to probe N,N- versus N,O-binding modes. When the steric bulk is sufficiently large, as in [N-(2,6- diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato- κ²N,O]Ni(η¹-CH₂-Ph)(PMe₃) (1), [N-(2,6-diethylphenyl)-2-(2,6-diethylphenylimino)propanamidato- κ²N,O](η¹-CH₂Ph)(PMe ₃)nickel (2), and [N-(2,6-methyl-isopropylphenyl)-2-(2,6- methylisopropylphenylimino)propanamidato-κ²N,O] (η¹-CH₂Ph)(PMe₃)nickel (3), one observes N,O-binding. In the case of [N-(2,6-dimethylphenyl)-2-(2,6-dimethylphenylimino) propanamidato]((η¹-CH2Ph)(PMe₃)nickel (4), both, N,O- and N,N-bound modes can be obtained and isolated; the N,N structure is the thermodynamic product. N,N products are observed with smaller ligands, as in [N-phenyl-2-(2,6-diisopropylphenylimino)propanamidato-κ: ²N,N](η¹-CH₂Ph)(PMe₃)nickel (5) and [N-(2,6-diisopropylphenyl)-2-(phenylimino)propanamidato- κ²N,N] (η¹-CH₂Ph)(PMe ₃)-nickel (6). Ethylene polymerization, upon activation with Ni(COD)₂, is observed only with the N,O-bound species. NMR spectroscopy shows that addition of Ni(COD)₂ to 5 and 6 results in removal of the phosphine and the formation of an η³-benzyl fragment. Furthermore, the phosphine-free complex [N-(2,6-diisopropylphenyl)-2- (2,6-diisopropylphenylimino)propanamidato-κ²N,N] (η³-CH₂Ph)nickel (7) is also inactive toward ethylene polymerization. These observations suggest that ethylene polymerization is preferentially initiated by nickel complexes with N,O-bound α- iminocarboxamide ligands.

Full text of DOI:10.1021/om050640g

5644
Organometallics 2005, 24, 5644-5653
r-Iminocarboxamide Nickel Complexes: Synthesis and
Uses in Ethylene Polymerization
Rene S. Rojas,† Julia-Christina Wasilke,† Guang Wu,† Joseph W. Ziller,‡ and
Guillermo C. Bazan*,†
Mitsubishi Chemical Center for Advanced Materials, Institute for Polymer and Organic Solids,
Departments of Chemistry and Materials, University of California, Santa Barbara, California
93106, and Department of Chemistry, University of California, Irvine, California 92697
Received July 27, 2005
A series of nickel complexes containing R-iminocarboxamide, η1-benzyl, and PMe3 ligands
were synthesized to identify structural features of neutral Ni complexes that are employed
in ethylene polymerization and ethylene/functionalized norbornene copolymerizations.
Variations in steric bulk on aryl substituents in the R-iminocarboxamide framework were
used to probe N,N- versus N,O-binding modes. When the steric bulk is sufficiently large, as
in [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ2N,O]Ni(η1-CH2-
Ph)(PMe3) (1), [N-(2,6-diethylphenyl)-2-(2,6-diethylphenylimino)propanamidato-κ2N,O](η1-
CH2Ph)(PMe3)nickel (2), and [N-(2,6-methyl-isopropylphenyl)-2-(2,6-methylisopropylphe-
nylimino)propanamidato-κ2N,O](η1-CH2Ph)(PMe3)nickel (3), one observes N,O-binding. In
the case of [N-(2,6-dimethylphenyl)-2-(2,6-dimethylphenylimino)propanamidato]((η1-CH2Ph)-
(PMe3)nickel (4), both, N,O- and N,N-bound modes can be obtained and isolated; the N,N
structure is the thermodynamic product. N,N products are observed with smaller ligands,
as in [N-phenyl-2-(2,6-diisopropylphenylimino)propanamidato-κ2N,N](η1-CH2Ph)(PMe3)nickel
(5) and [N-(2,6-diisopropylphenyl)-2-(phenylimino)propanamidato-κ2N,N](η1-CH2Ph)(PMe3)-
nickel (6). Ethylene polymerization, upon activation with Ni(COD)2, is observed only with
the N,O-bound species. NMR spectroscopy shows that addition of Ni(COD)2 to 5 and 6 results
in removal of the phosphine and the formation of an η3-benzyl fragment. Furthermore, the
phosphine-free complex [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propan-
amidato-κ2N,N](η3-CH2Ph)nickel (7) is also inactive toward ethylene polymerization. These
observations suggest that ethylene polymerization is preferentially initiated by nickel
complexes with N,O-bound R-iminocarboxamide ligands.
Introduction
use of multiple catalysts in a tandem process so that
branched polyethylene can be obtained from ethylene
alone.3 Initiators that provide for the living polymeri-
zation of ethylene and 1-alkenes4 constitute a special
Interest in metal-mediated polymerization of olefins
remains unabated in academic and industrial labora-
tories.1 Recent advances in stereocontrol and improved
functionality tolerance, together with insight from
mechanistic and theoretical studies, have considerably
improved control over the final polymer structures and
thereby the bulk properties of the resulting materials.
High-throughput techniques for screening metal-ligand
combinations and polymerization conditions2 have led
to improved initiator structures and have enabled the
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* To whom correspondence should be addressed. E-mail: bazan@
chem.ucsb.edu.
† Mitsubishi Chemical Center for Advanced Materials.
‡ Department of Chemistry.
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10.1021/om050640g CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/11/2005

R-Iminocarboxamide Nickel Complexes
Organometallics, Vol. 24, No. 23, 2005 5645
Scheme 1. General Synthesis of r-Iminocarboxamide Ligandsa
a (i) Benzene, 25 °C, 2 h; (ii) toluene, p-toluenesulfonic acid, 24 h.
area of attention, since they allow for accessing macro-
molecular architectures such as block and tapered
copolymers,5 star-shaped structures,6 end-functionalized
polymers,7 and grafted backbones.8,9 Macromolecular
structure impacts the solid state arrangement of the
polymer chains and therefore physical and mechanical
properties.
coordinated compounds provide active sites at room
temperature, i.e., conditions that allow the quasi-living
polymerization of ethylene.
Results and Discussion
Synthesis and Characterization of r-Iminocar-
boxamide Nickel Complexes. R-Iminocarboxamide
ligands can be synthesized following standard conden-
sation reaction procedures.11 An improved synthesis
employs oxalyl chloride and pyruvic acid in benzene at
room temperature in the presence of triethylamine to
generate pyruvic acid chloride in situ (Scheme 1).
Addition of 1 equiv of aniline results in reaction at the
acid chloride site. This reaction takes place over a period
We recently disclosed that the activation of [N-
(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-
propanamidato-κ2N,O]Ni(η1-CH2Ph)(PMe3) (1) with Ni-
(COD)2 (Ni(COD)2 ) bis(1,5-cyclooctadiene)nickel) gen-
erates an active site that is capable of copolymerizing
ethylene and 5-norbornen-2-yl acetate in a quasi-living
fashion (eq 1).10 The polymerization reaction shows a
linear increase in molecular weight with increasing
reaction time; however the molecular weight distribu-
tions of the products show polydispersities (PDIs) that
are larger than the ones expected from a living system.
Deviations from a living behavior are likely due to the
precipitation of the product as the reaction proceeds and
to inefficient initiation, as determined by NMR spec-
troscopy experiments. Polymerizations with 1/Ni(COD)2
are sufficiently well-behaved, and they can produce
block copolymers containing segments of random se-
quences of ethylene and 5-norbornen-2-yl acetate with
different molar compositions. These structures have
been synthesized by a simple procedure that involves
an ethylene pressure jump. The resulting materials
show microphase separation and have the potential to
reduce the interfacial energy between polyolefins and
polar plastics, such as polycarbonates.
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In this contribution, we report on the synthesis of
nonionic structural variations of 1, which were designed
to obtain insight into the active species in the reaction
shown in eq 1. We anticipated that the size of the
aromatic substituents on the imine and carboxamide
nitrogens would influence ligand coordination mode (i.e.,
N,N vs N,O). Examination of the reactivity toward
ethylene, coupled with the targeted synthesis of a
phosphine-free analogue of 1, suggests that only N,O-
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Chem. Soc. 2001, 123, 5352.

5646 Organometallics, Vol. 24, No. 23, 2005
Rojas et al.
of 2 h and requires the addition of 1 equiv of triethyl-
amine. A different aniline may be added at this stage
to generate R-iminocarboxamide ligands with different
substituents at the two nitrogen sites. The second step
requires overnight heating to ∼110 °C. Two equivalents
of aniline are added to pyruvic acid chloride in cases
where identical substitution is desired. Purification can
be accomplished by chromatography or crystallization,
depending on the aryl substituents. Deprotonation is
readily accomplished using KH in THF. Addition of the
potassium salts to Ni((η1-CH2Ph)Cl(PMe3)212 yields the
desired complexes.
The reaction of potassium N-(2,6-diethylphenyl)-2-
(2,6-diethylphenylimino)propanamide with Ni(η1-CH2-
Ph)Cl(PMe3)2 yields a single organometallic product,
which was characterized by NMR spectroscopy. The 1H
and 13C NMR spectra are consistent with the formation
of a single isomer containing a nickel center ligated by
R-iminocarboxamide, η1-CH2Ph, and PMe3 ligands (1H
NMR: 1.03, CH2-Ph; 0.53, P(CH3)3; 13C NMR: 12.65,
PCH3; 8.3, CH2-Ph). The 31P NMR spectrum reveals a
single peak at δ ) -7.7 ppm, which indicates N,O-
coordination of the R-iminocarboxamide fragment to
nickel (N,N-coordination gives rise to peaks in the -18
to -20 ppm range).11 The product is therefore [N-(2,6-
diethylphenyl)-2-(2,6-diethylphenylimino)propanamidato-
κ2N,O](η1-CH2Ph)(PMe3) nickel (2), as shown in eq 2.
temperature into a toluene solution of the crude product
gave a crystalline product. Optical microscopy revealed
that single crystals with different colors were obtained.
The majority of the crystals were red (4r), while the
second fraction was pale orange (4o). Successive recrys-
tallization at -35 °C provided mostly the pale orange
crystals (4o). The 31P NMR shifts for the red fraction
occur at -18.6 and -19.7 ppm, in a 3:1 ratio, while the
orange product displays a single peak at -8.1 ppm.
These data are consistent with 4r corresponding to two
isomers of the N,N-bound product, which differ in the
orientation of the η1-benzyl and phosphine ligands,
relative to the imine and carboxamide nitrogens. The
structure of 4o corresponds to the N,O-bound structure,
with the bulkier phosphine ligand opposite the imine
nitrogen, as shown in eq 4.
The stability of 4o was investigated by 1H NMR
spectroscopy starting with a sample of 90% purity. Over
a period of 60 min at 40 °C, the methyl peak of PMe3 (δ
) 0.56 ppm) is reduced in intensity by more than 50%
with a concomitant increase of two signals at 0.34 and
0.22 ppm, which correspond to the phosphine reso-
nances in 4r. Complete conversion from 4o to 4r takes
place after 2 h at 50 °C. The rearrangement is irrevers-
ible. These studies led to fine-tuning of the reaction
conditions so that each isomer could be produced
directly. Compound 4o was isolated in greater than 95%
purity by running the reaction at -10 °C for 4 h, while
4r was isolated by running the reaction at 50 °C for 4
h. It should be noted here that there is no change in
the binding mode of the R-iminocarboxamide ligands in
compounds 1, 2, and 3 after heating to 60 °C for 1 h.
Solid state characterization of 4o by single-crystal
X-ray diffraction (Figure 1) is consistent with the
structure in eq 4. Compound 4o adopts a square-planar
coordination geometry around the nickel center with a
cis relationship between PMe3 and the carboxamide
oxygen. The PMe3 is displaced by 10° below the N-Ni-N
plane, while the benzyl ligand is 4° is above the plane
(Table 1).
Equation 3 shows the synthesis of [N-(2,6-methyliso-
propylphenyl)-2-(2,6-methylisopropylphenylimino)pro-
panamidato-κ2N,O](η1-CH2Ph)(PMe3)nickel (3) by addi-
tion of potassium N-(2,6-methylisopropylphenyl)-2-(2,6-
methylisopropylphenylimino)propanamide to Ni(η1-
1
CH2Ph)Cl(PMe3)2. H and 31P NMR spectroscopy and
elemental analysis are consistent with the molecular
structure and N,O-coordination of the R-iminocarboxa-
mide ligand (31P NMR: δ ) -7.8 pm).
The steric bulk of the ligand was further reduced by
employing N-(2,6-dimethylphenyl)-2-(2,6-dimethylphe-
nylimino)propanamide to synthesize [N-(2,6-dimeth-
ylphenyl)-2-(2,6-dimethylphenylimino)propanamidato]-
(η1-CH2Ph)(PMe3)nickel (4). The product is obtained as
a mixture of three isomers, as determined by NMR
spectroscopy. In particular, the 31P NMR spectrum in
C6D6 exhibits three PMe3 signals (31P NMR: δ -8.1,
-18.6, and -19.7 ppm). Diffusion of pentane at room
Single crystals of 4r suitable for X-ray diffraction
studies were obtained by diffusion of pentane into a
toluene solution, and the resulting structure is shown
in Figure 2. The molecular structure confirms the N,N-
binding mode determined by 31P NMR spectroscopy.
There is a distortion of the square-planar geometry
(12) Carmona, E.; Paneque, M.; Poveda, M. L. Polyhedron 1989, 8,
285.

R-Iminocarboxamide Nickel Complexes
Organometallics, Vol. 24, No. 23, 2005 5647
Equation 5 shows the synthesis of two complexes with
R-iminocarboxamide ligands featuring unsubstituted
and substituted aromatic rings. The two compounds are
[N-phenyl-2-(2,6-diisopropylphenylimino)propanamidato-
κ2N,N](η1-CH2Ph)(PMe3)nickel (5) and [N-(2,6-diisopro-
pylphenyl)-2-(phenylimino)propanamidato-κ2N,N](η1-
CH2Ph)(PMe3)nickel (6). In both compounds N,N-
1
coordination is observed. For compound 5, the H and
31P NMR spectra are consistent with a single isomer
containing R-iminocarboxamide, η1-benzyl, and PMe3
ligands (31P NMR: δ -20.3 ppm). Compound 6 displays
three sets of signals in the 1H and 31P NMR spectra that
can be attributed to two N,N-coordinated isomers in a
3:1 ratio, which together account for 90% of the product,
and an N,O-coordinated isomer (10%) (31P NMR: δ
-20.4, -18.5, -7.1 ppm). There is no change in the
isomeric distribution in 6 upon heating to 60 °C for 1 h.
Figure 1. ORTEP drawing of 4o drawn at 50% probability.
Hydrogen atoms were omitted for clarity.
Diffusion of pentane into toluene solutions of 5 or 6
at room temperature yields single crystals suitable for
X-ray studies. As shown in Figure 3, the nickel atom in
both complexes is contained within a square-planar
arrangement. The phosphine and benzyl groups show
distortions above and below the plane. The N(2)-Ni-
P(1) angles are 148.92(5)° for 5 and N(1)-Ni-P(1)
155.21(4)° for 6. The N(1)-Ni-C(4) angles amount to
161.14(8)° and N(2)-Ni-C(4) to 156.18(7)° for 5 and 6,
respectively (Table 1). The benzyl ligand binds trans to
the carboxamide nitrogen in 5 and cis to the carboxa-
mide in 6. The PMe3 ligand coordinates trans to the
substituted aromatic ring in both cases, indicating that
steric demands are more important than electronic
preferences. The Ni-N(1), Ni-N(2), Ni-C(4), and Ni-
(P1) bond lengths are similar in both complexes.
Figure 2. ORTEP drawing of 4r drawn at 50% probability.
Hydrogen atoms were omitted for clarity.
around nickel (the N(1)-Ni-P(1) angle (168.56(4)°)
being smaller than 180° and the P(1) atom is ∼11° out
of the N(1)-Ni-N(2) plane). The benzyl group is located
cis to the carboxamide nitrogen with a N(2)-Ni-C(4)
angle of 161.56(6)° and is tilted 18.5° out of the plane.
The Ni-P, Ni-N(1), and Ni-C(4) bond distances are
similar in 4ï and 4r (Table 1).
Activation with Ni(COD)2 and Reactivity toward
Ethylene. A study of the polymerization of ethylene
with the family of N,O- and N,N-bound nickel complexes
([Ni-R-iminocarboxamide] ) 3.43 × 10-4 M) activated
with 2.5 equiv of Ni(COD)2 was carried out, and the
results are summarized in Table 2. The [Ni(COD)2]/[Ni-
Table 1. Selected Bond Distances (Å) and Angles (deg) for r-Iminocarboxamide Nickel Complexes
4o
4r
5
6
7
Ni(1)-N(1)
1.9415(12)
1.9350(16)
1.9633(13)
1.888(2)
Ni(1)-O(1)
1.920(2)
1.960(3)
1.972(3)
2.1429(9)
1.307(4)
Ni(1)-C(4)
1.9714(14)
1.9922(11)
2.1885(4)
1.2454(17)
1.9479(19)
1.9793(15)
2.1555(6)
1.237(2)
1.9533(17)
1.9721(13)
2.1607(5)
1.2427(19)
1.946(3)
1.950(2)
Ni(1)-N(2)
Ni(1)-P(1)
O(1)-C(1)
1.237(3)
2.035(3)
2.155(2)
83.63(8)
Ni(1)-C(5)
Ni(1)-C(6)
N(1)-Ni(1)-N(2)
N(2)-Ni(1)-O(1)
C(4)-Ni(1)-P(1)
N(1)-Ni(1)-C(4)
N(2)-Ni(1)-P(1)
O(1)-Ni(1)-C(4)
N(1)-Ni(1)-P(1)
C(4)-Ni(1)-N(2)
O(1)-Ni(1)-P(1)
N(1)-Ni-C(6)
81.01(5)
81.94(7)
81.87(5)
83.17(10)
89.10(10)
88.79(5)
91.38(6)
101.98(4)
92.50(6)
161.14(8)
148.92(5)
92.47(6)
94.64(7)
100.52(4)
98.88(10)
169.98(9)
176.17(12)
168.56(4)
161.56(6)
98.12(5)
96.90(8)
155.21(4)
156.18(7)
96.16(12)
92.13(7)
176.31(11)
167.00(10)

5648 Organometallics, Vol. 24, No. 23, 2005
Rojas et al.
Figure 3. ORTEP drawing of 5 and 6 drawn at 50% probability.
Table 2. Ethylene Polymerization Reactionsa
time
reaction
Mn
Tm
entry
precatalyst
(min)
temp (°C)
activityb
(× 10-3
)
Mw/Mn
1.4
(°C)
1
2
110
1
20
20
10
20
30
40
20
20
40
20
40
20
20
20
20
20
20
20
20
70
20
20
20
20
70
20
20
20
20
20
70
20
70
20
20
70
55
186
35
110
7
125
6.1
2.0
1.8
2.0
1.9
5.0
1.7
1.8
1.9
2.0
3
2
59
73
77
85
7
130
130
130
130
4
2
28
5
2
31
6
2
21
7
2
112
30
8
3
76
104
61
79
130
131
132
132
9
3
26
10
11
12
13
14
15
16
17
18
4ï
4ï
4r
4r
5c
5
19
22
3
oligomers
oligomers
11
6
6
7
18
multimodal
6
oligomers
a Polymerizations were carried out in 100 mL autoclave reactors with 10 µmol of precatalyst, 25 µmol of Ni(COD)2 in 30 mL of toluene;
reaction time, 20 min; temperature controlled by using a water bath, pressure 100 psi. b kg polymer/(mol Ni)(h)(atm); entry 17 run with
40 µmol of 6, 100 µmol of Ni(COD)2. c Reaction run under the same conditions as entry 17 did not show ethylene consumption; entries 12,
14, and 16 were repeated at 500 and 1000 psi: none showed ethylene consumption.
R-iminocarboxamide] ratio of 2.5 was determined in
previous studies.10 Reactions were performed inside a
100 mL autoclave reactor in toluene at an ethylene
pressure of 100 psi. The reactions used an external
water bath kept constant at 20 °C. Entry 1 corresponds
to the reactivity previously reported for 1/Ni(COD)2 and
is provided for comparison.10 Entries 3-6 show the
results obtained at different reaction times with 2/Ni-
(COD)2. Comparison of these entries shows that the
ethylene consumption is constant up to 30 min, with
the molecular weights of the resulting polymers increas-
ing with longer reaction times. However, the PDIs (Mw/
Mn ratios) are approximately 2, while the PDI of the
polyethylene obtained by using complex 1 is more
narrow (entry 1). Entries 2 and 7 show that at higher
temperatures compounds 1/Ni(COD)2 and 2/Ni(COD)2
provide higher activity, compared to room-temperature
reactions (entries 1 and 3), but result in low molecular
weight products with broad PDIs.
tions also yield ethylene polymerization sites. A com-
parison of entries 1, 4, 8, and 10 performed with 1, 2,
3, and 4o, respectively, under similar reaction conditions
shows that the polymerization activity decreases with
a reduction of the steric bulk on the R-iminocarboxamide
ligand. Entries 6, 9, and 11 show that increasing the
reaction time to 40 min, while keeping the temperature
at approximately 20 °C, results in a decrease in the
overall integrated polymerization activity and an in-
crease in the molecular weight of the polyethylene
product; interestingly the PDIs do not change. For all
precatalyst/Ni(COD)2 combinations there was no change
in the ethylene consumption rate when the ethylene
pressure was varied between 200 and 1000 psi (Sup-
porting Information).
Entries 12-18 show the results obtained with the
N,N-bound complexes 4r, 5, and 6. Negligible reactivity
was observed at 20 °C (entries 12, 14, and 16). Ethylene
consumption is observed when the reactions are carried
out at 70 °C (entries 13, 15, and 18), however at rates
substantially lower than that obtained with the N,O-
Entries 8 and 9 with 3/Ni(COD)2 and entries 10 and
11 with 4o/Ni(COD)2 demonstrate that these combina-

R-Iminocarboxamide Nickel Complexes
Organometallics, Vol. 24, No. 23, 2005 5649
bound counterparts under the same reaction conditions
(entries 2 and 7).13 At the higher temperature, com-
pounds 5 and 6 provide low molecular weight ethylene
oligomerization products. In the case of 6 (entry 17)
performing the reactions at higher Ni concentrations ([6]
≈ 1.4 × 10-3 M, [6]/[Ni(COD)2] ) 2.5) yields a mixture
of polyethylene and oligomeric products. Additionally,
there is no perturbation on the activity of any combina-
tion (either N,O- or N,N-bound) upon increasing the
ethylene pressure (500 and 1000 psi) at 20 °C.
NMR Spectroscopy of Reactions with Ni(COD)2.
1H NMR spectroscopy was used to investigate reactivity
differences between N,O- and N,N-coordinated com-
plexes. We previously reported that the 1H NMR spectra
of solutions of 1 and 2.5 equiv of Ni(COD)2 at room
temperature over a period of 1.5 h provide no observable
changes, except for the decomposition of Ni(COD)2.10a
We repeated these experiments at 40 and 60 °C and
obtained similar observations using compounds 2 and
3. The results are different when using 5 and 2.5 equiv
of Ni(COD)2 under similar reaction conditions. Reso-
nances attributed to free COD (5.58, 2.21 ppm) and an
η3-benzyl complex (between 5.8 and 6.8 ppm) are
observed. After 1 h at 65 °C, 75% of 5 is consumed and
two η3-benzyl isomers can be identified. Two separate
doublets are observed corresponding to the ortho-
hydrogens (6.0 and 5.9 ppm) on the benzyl ligand and
two triplets for the benzyl meta-hydrogens (6.2 and 6.4
ppm). The set of signals is attributed to two isomers,
which appear in a 3:2 ratio. Signals from the para-
substituted hydrogens are sharp at 7.33 and 7.28 ppm.
Other evidence supporting the formation of two η3-
benzyl isomers is the presence of new septets at 3.54,
3.33, and 2.86 ppm, which are associated with the
CHMe2 groups. Isolation of the product was not possible;
however there is no reaction upon addition of ethylene
to the mixture of isomers.
Figure 4. Molecular structure of 7 drawn at 50% prob-
ability. Hydrogen atoms were omitted for clarity.
product mixture was obtained including a zwitterionic
B(C6F5)3 adduct11 and insoluble B(C6F5)3-PMe3.
A neutral η3-benzyl complex, [N-(2,6-diisopropylphe-
nyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ2N,N]-
(η3-CH2Ph)nickel (7), was successfully synthesized by
direct reaction of potassium N-(2,6-diisopropylphenyl)-
2-(2,6-diisopropylphenylimino)propanamide with Ni-
(COD)2 and benzyl chloride in THF, as shown in eq 6.
Best results are obtained when exposure to light is
minimized and with the addition of dimethylaniline. The
role of dimethylaniline is not clear at this stage;
presumably it improves the product yield by stabilizing
reactive intermediates. Successive crystallization from
pentane allowed for isolation of 7 as thermally and air-
sensitive dark orange crystals in 70% yield. While
isopropyl substitution on both phenyl rings provides the
desired product, similar reactions with ligand frame-
works with lesser steric bulk failed.
At room temperature, the reaction between 6 and Ni-
(COD)2 provided approximately 20% of an η3-benzyl
complex, together with free COD. Signals characteristic
of η3-coordinated benzyl ligands are observed at 5.95
and 5.83 ppm (ortho-hydrogens) and 6.58 and 6.22 ppm
(meta-hydrogens), indicating the formation of two iso-
mers. Substantial amounts of starting material were
converted (∼75%) after increasing the temperature to
65 °C and allowing the reaction to proceed for an hour.
No ethylene polymerization was obtained with 5 or 6
in the presence of Ni(COD)2 at room temperature (Table
2). This observation and the results described above
from NMR spectroscopy experiments suggest that N,N-
coordinated η3-benzyl nickel complexes are not active
species at room temperature. Instead, the data are
consistent with only the N,O-coordinated nickel com-
plexes being the active species.
Synthesis and Isolation of a Phosphine-Free
r-Iminocarboxamide η3-Benzyl Nickel Complex.
Efforts to remove PMe3 from 1 and 2 by using CuCl or
(MeCN)3CuCl in toluene were not successful, as deter-
mined by 1H NMR spectroscopy. No reactivity was also
observed when these reactions were performed in the
presence of ethylene. Addition of 1 equiv of B(C6F5)3 to
1 or 2 did not result in a neutral η3-complex; instead a
Single crystals of 7 suitable for crystallographic
studies were obtained from pentane by slow evaporation
at -35 °C, and the results are shown in Figure 4. The
benzyl group is coordinated in an η3-fashion with the
methylene group in a trans orientation relative to the
imine nitrogen atom. A square-planar arrangement
surrounds the nickel center. The two aryl rings are
perpendicular to the square plane and are pushed
slightly toward the metal. The bond distances for Ni-
N(1) and Ni-N(2) (1.889(2) and 1.950(2) Å, respectively)
are slightly shorter compared to the values for the η1-
benzyl N,N-nickel complexes (Table 1) (the bond dis-
tances for Ni-N(1) and Ni-N(2) are 1.9415(12) and
1.9922(11) Å for compound 4r and 1.9350(16) and
1.9793(15) Å for compound 5), consistent with stronger
binding of the ligand. Comparison of metrical param-
eters with those of a polymerization-active zwitterionic
N,N-chelating R-iminocarboxamide nickel complex fea-
turing an η3-benzyl ligand and B(C6F5)3 attached to the
carbonyl functionality shows comparable bond distances
(13) Polymer formation was also observed when the ethylene
polymerization was run at 50 °C.

5650 Organometallics, Vol. 24, No. 23, 2005
Rojas et al.
between the Ni and the two nitrogen atoms.11 As
expected, the C(1)-O(1) bond is shorter in 7 (1.238(3)
Å), due to its double-bond character, while zwitterionic
compounds show more single-bond character.
mode. It is also informative that the narrowest poly-
dispersities are obtained with 1, which contains the
largest steric bulk around nickel. Differences in reactiv-
ity within the set of active species are not sufficiently
large to draw further structure/reactivity relationships.
Examination of reactions with compounds 5 and 6 and
Ni(COD)2 by 1H NMR spectroscopy indicates η3-benzyl
ligand formation and loss of PMe3. This information
supports the idea that loss of the phosphine is a
prerequisite for the initiation of ethylene polymeriza-
tion. No such indication could be observed with other
compounds. We note, however, that ethylene is present
in the polymerization reactions. It has been previously
suggested that ethylene may displace COD to form a
more active species that proceeds to extract phosphine.7a
Monitoring such reactions by NMR spectroscopy is not
feasible because the rate of propagation is faster than
that of initiation. Polyethylene forms and precipitates,
which renders such analysis uninformative.
1
Two isomers of 7 in a 5:8 ratio are observed by H
NMR spectroscopy. NOESY studies were carried out to
identify the structure of the isomers. Two possibilities
considered were N,N-ligand coordination and N,O-
ligand coordination versus η3-benzyl positional isomers,
with the CH2 group either cis or trans to the imine site.
The NOESY study is consistent with two N,N-coordi-
nated structures with different orientations of the
benzyl fragment. Full details for these experiments are
deposited in the Supporting Information. From a reac-
tivity perspective, it is important to note that there is
no ethylene consumption when 100 to 1000 psi ethylene
was added to 7, at temperatures ranging from 20 to 70
°C. Addition of Ni(COD)2 did not result in a change of
activity.
Compound 7 provides for a phosphine-free, η3-benzyl
structure. That it is unreactive toward ethylene is
consistent with the proposal that only N,O-bound spe-
cies are active. Putting together the structural and
reactivity observations provided in this study indicates
that the neutral initiators capable of quasi-living po-
lymerization of ethylene are [N,O-R-iminocarboxami-
dato](benzyl)nickel complexes. Two situations may be
further considered, one where the initiator is an η3-
benzyl complex that can be converted to Ni(C2H4)(η1-
benzyl) species, by dissociative or associative displace-
ment by ethylene of the π-component of the η3-benzyl
fragment. Alternatively, the Ni(C2H4)(η1-benzyl) species
may form directly after PMe3 displacement. There is
insufficient information at this stage to differentiate the
two possibilities. It is also interesting to note that the
polymerization reactions show no decrease in activity,
even after 30 min. Perhaps N,O f N,N isomerization
is slower for the phosphine-free species, or the resting
state of the active site is an olefin adduct in which
R-iminocarboxamide isomerization is restricted. Alter-
natively, it may be that N,N-bound species are incapable
of initiation but can insert ethylene once the polymer-
ization is underway. Having identified plausible initiat-
ing structures should allow for a more rational improve-
ment of the polymerization activity of this class of
complexes and therefore a better control of the product
structures.
Summary, Discussion, and Conclusion
As stated in the Introduction, our interest in examin-
ing a variety of nickel complexes with R-iminocarboxa-
mide ligands stems from the ability of 1/Ni(COD)2 to
generate block copolymers with ethylene and function-
alized norbornenes. The exact structure corresponding
to the initiating species has not been determined previ-
ously and is the main subject of this study.
Scheme 1 provides a straightforward approach to
generating R-iminocarboxamide ligands in which the
steric bulk on the imine and carboxamide nitrogens can
be controlled by aromatic substituents. Deprotonation
of the ligand with potassium hydride, followed by
reaction with Ni(η1-CH2Ph)Cl(PMe3)2, yields the target
compounds with general structure [R-iminocarboxami-
dato](η1-CH2Ph)(PMe3)nickel. Structural characteriza-
tion, by 31P NMR spectroscopy and X-ray diffraction
structure determination, shows that the N,O-binding
mode is preferred when the steric bulk at both nitrogen
sites is sufficiently large, for example, compounds 1, 2,
and 3. In the case of compound 4, where 2,6-dimeth-
ylphenyl substituents are present, one obtains an
intermediate situation. The N,O-mode is kinetically
preferred, probably because of easier displacement by
the sterically unencumbered oxygen. The N,N isomer
is ultimately the thermodynamic product, which reflects
an electronic preference for nickel to bind to nitrogen
over oxygen. Examination of Figure 3 shows that the
N,N-bound compounds 5 and 6 are nearly isostructural,
in the sense that the overall molecular arrangements
differ only by the location of oxygen and methyl on the
ligand bridge. The PMe3 is situated trans to the bulky
2,6-diisopropylphenyl fragment and is adjacent to the
more accommodating phenyl fragment.
Experimental Section
General Remarks. All manipulations were performed
under an inert atmosphere using standard glovebox and
Schlenk-line techniques. All reagents were used as received
from Aldrich unless otherwise specified. Ethylene was pur-
chased from Matheson Tri-Gas (research grade, 99.99% pure)
and was further purified by passage 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 polymeri-
zation was distilled from sodium/potassium alloy. The syn-
thesis of compounds 2, 3, 4o, 4r, 5, and 6 used procedures
similar to the literature procedure for 110 and were purified
by recrystallization. NMR spectra were obtained using Varian
Unity 400 and 500 spectrometers. Polymers were dried
overnight under vacuum, and the polymerization activities
Reactions of ethylene with mixtures composed of
[R-iminocarboxamidato](η1-CH2Ph)(PMe3)nickel and 2.5
equiv of Ni(COD)2 have been summarized in Table 2.
The most important reactivity trend that can be ex-
tracted from these data is that only the N,O-bound
precursors give rise to effective ethylene polymerization
initiators. Particularly striking is the difference between
compounds 4o (N,O-bound and active) and 4r (N,N-
bound and inactive), which are supported by the same
R-iminocarboxamidato ligand and differ in the binding

R-Iminocarboxamide Nickel Complexes
Organometallics, Vol. 24, No. 23, 2005 5651
Table 3. Crystal Data and Structure Refinement for r-Iminocarboxamide Nickel Complexes
4o
4r
5
6
7
empirical formula
fw
C
29H37N2NiOP
C29H37N2NiOP
519.29
C31H41N2NiOP
547.34
C31H41N2NiOP
547.34
C34H44N2NiO
519.29
555.42
temp (K)
117 (1)
0.71073
monoclinic
P21/c
a ) 17.3082(13)
168 (2)
163 (2)
163 (2)
117(1)
wavelength (Å)
cryst syst
space group
unit cell dimens
(Å, deg)
0.71073
0.71073
0.71073
0.71073
monoclinic
C2/c
monoclinic
P21/n
orthorhombic
P212121
monoclinic
P21/n
a ) 10.0245(4)
a ) 10.2471(19)
a ) 10.9043(9)
a ) 32.086(3)
b ) 9.5254(7)
c ) 16.6458(13)
R ) 90
b ) 24.6120(10)
c ) 11.2350(5)
R ) 90
b ) 16.382(3)
c ) 17.047(3)
R ) 90
b ) 17.1985(15)
c ) 15.6966(13)
R ) 90
b ) 9.2402(7)
c ) 21.1912(17)
R ) 90
â ) 96.424(2)
γ ) 90
â ) 100.2400(10)
γ ) 90
â ) 90
â ) 93.937(2)
γ ) 90
â ) 104.209(2)
γ ) 90
γ ) 90
volume (Å3)
Z
density (calcd)
2727.1(4)
4
1.264
2727.8(2)
4
1.264
2861.6(9)
4
2936.8(4)
4
1.238
6090.5(8)
8
1.211
1.270
(Mg/m3)
absorp coeff (mm-1
F(000)
)
0.198
0.793
1104
0.760
1168
0.740
1168
0.665
2384
276
cryst size (mm3)
θ range (deg)
index ranges
0.2 × 0.15 × 0.1
1.18 to 29.44
-23 e h e 17
-13 e k e 12
-11 e l e 22
13 719
6581 [R(int) )
0.0423]
87.2
0.37 × 0.33 × 0.31 0.40 × 0.37 × 0.30 0.25 × 0.23 × 0.15 0.25 × 0.15 × 0.08
1.65 to 28.28
-12 e h e 13
-32 e k e 31
-14 e l e 14
27 928
6524 [R(int) )
0.0264]
96.4
2.32 to 28.29
-13 e h e 13
-21 e k e 21
-22 e l e 22
29 503
6933 [R(int) )
0.0416]
98.9
1.76 to 28.31
-14 e h e 14
-22 e k e 22
-20 e l e 20
35 747
7190 [R(int) )
0.0378]
98.3
1.31 to 26.50
-40 e h e 38
-11 e k e 11
-26 e l e 23
17 585
5851 [R(int) )
0.0392]
92.7
no. of reflns collected
no. of indep reflns
completeness to
θ ) 28.28° (%)
max. and min.
transmn
0.6922a
0.7911 and 0.7579 0.8042 and 0.7510 0.8971 and 0.8366 0.8482a
no. of data/restraints/ 6581/0/277
params
6524/0/455
6933/0/489
7190/0/489
5851/0/519
goodness-of-fit on F2
final R indices
0.908
1.042
1.050
1.063
1.051
R1 ) 0.0460,
wR2 ) 0.1122
R1 ) 0.0625, wR2 ) 0.1214
R1 ) 0.0511,
wR2 ) 0.1257
R1 ) 0.0894,
wR2 ) 0.1399
R1 ) 0.0287,
wR2 ) 0.0707
R1 ) 0.0361,
wR2 ) 0.0753
R1 ) 0.0302,
wR2 ) 0.0699
R1 ) 0.0385,
wR2 ) 0.0747
0.606 and -0.358
R1 ) 0.0309,
wR2 ) 0.0726
R1 ) 0.0485,
wR2 ) 0.0819
0.383 and -0.295
[I > 2σ(I)]b
R indices (all data)b
largest diff peak and
0.715 and -0.629 0.410 and -0.293
1.126 and -0.452
hole (e Å-3
)
a min./max. b R1 ) ∑||Fo| - |Fc||]/∑[|Fo|, wR2 ) [∑(Fo2 - Fc )2]/∑[w(Fo2)2]]1/2, GOF ) [∑[w(Fo2 - Fc )2]/(n - p)]1/2, where n is the number
2
2
of the reflections and p is the total number of parameters refined.
were calculated from the mass of product obtained. These
values were to within 5% of the calculated mass by measuring
the ethylene consumed by use of a mass flow controller. The
polymers were characterized by GPC analysis at 135 °C in
o-dichlorobenzene (in a Polymers Laboratories, high-temper-
ature chromatograph, Pl-GPC 200). Polymer melting points
were measured on a TA Instruments differential scanning
calorimeter (model DSC 2920) at a rate of 10 °C/min for two
cycles using a temperature range of 0-150 °C. 1H NMR spectra
of the polymers were obtained in a mixed solvent (C6D6/1,2,4-
trichlorobenzene in a 1:4 volume ratio) at 115 °C. Elemental
analysis was performed on a Leeman Labs Inc. CE440
elemental analyzer and a Control Equipment Corporation 440
elemental analyzer. FTIR spectra were recorded on a Bruker
Vector-22 spectrophotometer using KBr pellets and in solution
using C6D6 as solvent.
X-ray Crystallography. The monocrystal was mounted on
a glass fiber and transferred to a Bruker CCD platform
diffractometer. The SMART14 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 SAINT15 and SADABS16 to
yield the reflection data file. Subsequent calculations were
carried out using the SHELXTL17 program. The structure was
solved by direct methods and refined on F2 by full-matrix least-
squares techniques. The analytical scattering factors18 for
neutral atoms were used throughout the analysis. Hydrogen
atoms were located from a difference Fourier map and refined
(x, y, z and Uiso).19 The crystal data and refinement are
summarized in Table 3.
Synthesis and Characterization of Compounds. Po-
tassium N-(2,6-diethylphenyl)-2-(2,6-diethylphenylimi-
no)propanamide. N-(2,6-Diethylphenyl)-2-(2,6-diethylphe-
nylimino)propanamide (1.28 g, 3.63 mmol) and KH (145.6 mg,
3.63 mmol) were stirred in THF overnight. The reaction
showed rapid gas evolution. The suspension was filtered, and
the solvent was removed in a vacuum, providing a beige
powder in 81% yield.
1H NMR (399.95 MHz, [d3]-chloroform, 298 K): δ 7.06-7.00
3
3
(m, 3H, JHH ) 6.2 Hz, H-Ph), 7.86 (d, 2H, JHH ) 7.5 Hz,
H-Ph), 6.65 (t, 1H, 3JHH ) 7.5 Hz, H-Ph), 2.75 (m, 2H, 3JHH
)
3
7.2 Hz, CH2), 2.62 (m, 2H, JHH ) 7.2 Hz, CH2), 2.31 (m, 4H,
3JHH ) 7.2 Hz, CH2), 2.34 (s, 3H, CH3), 1.25 (t, 6H, 3JHH ) 7.2
3
Hz, CH3-Et), 1.08 (t, 6H, JHH ) 7.2 Hz, CH3-Et).
[N-(2,6-Diethylphenyl)-2-(2,6-diethylphenyl)propana-
midato-K2N,O](η1-CH2Ph)(PMe3)nickel (2). Potassium N-(2,6-
diethylphenyl)-2-(2,6-diethylphenylimino)propanamide (610
(14) SMART Software Users Guide, Version 5.1; Bruker Analytical
X-Ray Systems, Inc.; Madison, WI, 1999.
(17) Sheldrick, G. M. SHELXTL Version 6.12; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 2001.
(15) SAINT Software Users Guide, Version 6.0; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 1999.
(18) International Tables for X-ray Crystallography, Vol. C; Kluwer
Academic Publishers: Dordrecht. 1992.
(16) Sheldrick, G. M. SADABS, Version 2.05; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 2001.
(19) Flack, H. D. Acta Crystallogr. 1983, A39, 876.

5652 Organometallics, Vol. 24, No. 23, 2005
Rojas et al.
mg, 1.57 mmol) in toluene was added to Ni((η1-CH2Ph)Cl-
(PMe3)2 (529 mg, 1.57 mmol) in toluene and stirred for 4 h.
The suspension was filtered, and all volatiles were removed
under vacuum to give a light red solid. The latter was
triturated with pentane and left at -35 °C overnight. The
product in the form of an orange solid (73%) was filtered and
dried in a vacuum.
propanamide (200 mg, 0.6 mmol) in toluene was added to
Ni((η1-CH2Ph)Cl(PMe3)2 (203 mg, 0.6 mmol) in toluene and
stirred for 4 h at 40 °C. The suspension was filtered, and all
volatiles were removed under vacuum to give a red solid. The
crude material was triturated with pentane and crystallized
at -35 °C overnight. The product, in the form of a dark red
solid, was isolated by filtration and dried under vacuum in
84% yield. The 1H NMR spectrum shows two isomers in a 3:1
ratio.
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 7.21 (d, 2H,
3
3JHH ) 7.5 Hz, H-Ph), 7.18 (m, 1H, H-Ph), 7.10 (dd, 1H, JHH
) 7.5 Hz, H-Ph), 7.03 (dd, 1H, 3JHH ) 7.5 Hz, H-Ph), 6.96 (m,
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 7.50 (m, 2H,
H-Phminor), 7.36 (m, 2H, H-Phmajor), 7.25 (d, 2H, 3JHH ) 7.2 Hz,
H-Phminor), 7.14-6.87 (m, 13H, H-Ph), 6.72 (dd, 1H, 3JHH ) 6.8
3
6H, H-Ph), 2.84 (q, 4H, JHH ) 7.4 Hz, CH2-Et), 2.71 (dq, 4H,
3JHH ) 7.4 Hz, 5JHP ) 2.8 Hz, CH2-Et), 2.08 (s, 3H, CH3), 1.40
3
3
3
(t, 6H, JHH ) 7.4 Hz, CH3-Et), 1.15 (t, 6H, JHH ) 7.4 Hz,
Hz, H-Phminor), 6.64 (d, 2H, JHH ) 7.6 Hz, H-Phminor). Major
2
CH3-Et), 1.03 (s, 2H, CH2-Ph), 0.53 (d, 9H, JHP ) 10.1 Hz,
isomers: 2.70 (s, 6H, Ph- CH3), 2.24 (s, 6H, Ph- CH3), 1.86 (s,
P(CH3)3). 13C NMR (125.7 MHz, [d6]-benzene, 298 K): δ 181.40
(carbonyl), 149.92, 148.72, 143.35, 135.19, 134.66, 129.93,
128.69, 127.09, 126.62, 126.31, 123.56, 122.73 (imine, ph-C),
26.66, 24.87 (Et-CH2), 19.18 (CH3), 15.27, 13.99 (Et-CH3), 12.65
(d, J ) 28 Hz, PCH3), 8.3 (CH2-Ph). 31P{1H} NMR (161.91 MHz,
[d6]-benzene, 298 K, H3PO4): δ -7.7. Anal. Calcd for C33H45N2-
OPNi: C, 68.93; H, 7.89; N, 4.87. Found: C, 68.90; H, 7.72;
N, 4.91.
3H, CH3), 1.00 (d, 2H, JHP ) 6.4 Hz, CH2-Ph) 0.32 (d, 9H,
3
2JHP ) 9.6 Hz, P(CH3)3). Minor isomers: 2.90 (s, 6H, Ph-CH3),
2.02 (s, 6H, Ph-CH3), 1.70 (s, 3H, CH3), 1.52 (d, 2H, 3JHP ) 8.4
Hz, CH2-Ph) 0.20 (d, 9H, 2JHP ) 8.8 Hz, P(CH3)3). 31P{1H} NMR
(161.91 MHz, [d6]-benzene, 298 K, H3PO4): δ -18.6, -19.7.
Anal. Calcd for C29H37N2OPNi: C, 67.08; H, 7.18; N, 5.39.
Found: C, 67.20; H, 7.05; N, 5.31.
[N-Phenyl-2-(2,6-diisopropylphenylimino)propan-
amidato-K2N,N](η1-CH2Ph)(PMe3)nickel (5). Potassium
N-phenyl-2-(2,6-diisopropylphenylimino)propanamide (245 mg,
0.68 mmol) in toluene was added to Ni((η1-CH2Ph)Cl(PMe3)2
(230 mg, 0.68 mmol) in toluene and stirred for 4 h at room
temperature. The suspension was filtered, and all volatiles
were removed in a vacuum to give an orange solid. Trituration
with pentane and crystallization at -35 °C overnight gave the
product as a dark orange solid in 75% yield. The product was
isolated by filtration and dried in a vacuum. Single crystals
for X-ray crystallography were grown by layering pentane onto
a toluene solution of 5 at room temperature. For NMR data
see ref 11.
[N-(2,6-Methylisopropylphenyl)-2-(2,6-methylisopro-
pylphenylimino)propanamidato-K2N,O](η1-CH2Ph)(PMe3)-
nickel (3). Potassium N-(2,6-methylisopropylphenyl)-2-(2,6-
methylisopropylphenylimino)propanamide (300 mg, 0.77 mmol)
in toluene was added to Ni((η1-CH2Ph)Cl(PMe3)2 (260 mg, 0.77
mmol) in toluene and stirred for 4 h at room temperature. The
suspension was filtered, and all volatiles were removed under
vacuum to give a red solid. Trituration with pentane and
crystallization at -35 °C overnight gave the product as a dark
orange solid in 69% yield. The product was isolated by
filtration and was dried under vacuum.
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 7.23 (m, 4H,
H-Ph), 7.07 (m, 2H, H-Ph), 6.96 (m, 4H, H-Ph), 6.81 (d, 1H,
3JHH ) 7.2 Hz, H-Ph), 3.92 (sep., 2H, 3JHH ) 6.8 Hz, CHMe2),
3.54 (sep, 2H, 3JHH ) 6.8 Hz, CHMe2), 2.44 (s, 3H, CH3), 2.09
[N-(2,6-Diisopropylphenyl)-2-(phenylimino)propana-
midato-K2N,N](η1-CH2Ph)(PMe3)nickel (6). Potassium N-
(2,6-diisopropylphenyl)-2-(phenylimino)propanamide (200 mg,
0.55 mmol) in toluene was added to Ni((η1-CH2Ph)Cl(PMe3)2
(187 mg, 0.55 mmol) in toluene and stirred for 4 h at room
temperature. Purification similar to that for 5 gave the
compound 6 in 72% yield. The product was isolated by
filtration and dried in a vacuum. Single crystals for X-ray
crystallography were grown by layering pentane onto a toluene
solution of compound 6 at room temperature.
3
(s, 3H, CH3), 2.01 (s, 3H, CH3), 1.44 (d, 3H, JHH ) 6.8 Hz,
3
i
iPr-CH3), 1.43 (d, 3H, JHH ) 6.8 Hz, Pr-CH3), 1.34 (d, 3H,
3JHH ) 6.8 Hz, iPr-CH3), 1.09 (d, 3H, 3JHH ) 6.8 Hz, iPr-CH3),
1.12 (s, 2H, CH2), 0.55 (d, 9H, JHP ) 10 Hz, PMe3). 31P{1H}
2
NMR (161.91 MHz, [d6]-benzene, 298 K, H3PO4): δ -7.8. Anal.
Calcd for C33H45N2OPNi: C, 68.93; H, 7.89; N, 4.87. Found:
C, 68.58; H, 7.60; N, 4.71.
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 7.67 (d, 2H,
3JHH ) 6.8 Hz, H-Ph), 7.36 (m, H-Ph), 7.06 (m, H-Ph), 6.91
(m, H-Ph), 6.78 (m, H-Ph), 6.69 (m, H-Ph), 6.57 (m, H-Ph), 4.73
[N-(2,6-Dimethylphenyl)-2-(2,6-dimethylphenylimino)-
propanamidato-K2N,O](η1-CH2Ph)(PMe3)nickel (4o). Po-
tassium N-(2,6-dimethylphenyl)-2-(2,6-dimethylphenylimino)-
propanamide (300 mg, 0.9 mmol) in toluene was added to
Ni((η1-CH2Ph)Cl(PMe3)2 (305 mg, 0.9 mmol) in toluene and
stirred for 4 h at -30 °C. The suspension was filtered, and all
volatiles were removed under vacuum to give an orange solid.
Trituration with pentane and crystallization at -35 °C over-
night gave the product as a light orange solid in 78% yield.
The product was isolated by filtration and was dried under
vacuum.
3
3
(sep, 2H, JHH ) 6.8 Hz, CHMe2), 4.18 (sep, 2H, JHH ) 6.8
3
Hz, CHMe2), 3.47 (sep, 2H, JHH ) 6.8 Hz, CHMe2), 2.12 (s,
3H, CH3), 2.93 (s, 3H, CH3), 1.79 (s, 3H, CH3), 1.68 (d, 6H,
3JHH ) 6.8 Hz, iPr-CH3), 1.63 (d, 6H, 3JHH ) 6.4 Hz, iPr-CH3),
3
i
1.54 (s, 2H, CH2Ph), 1.527 (d, 6H, JHH ) 7.2 Hz, Pr-CH3),
3
i
3
1.46 (d, 12H, JHH ) 5.6 Hz, Pr-CH3) 1.27 (d, 6H, JHH ) 6.8
i
2
Hz, Pr-CH3), 1.19 (s, 2H, CH2Ph), 0.53 (d, 9H, JHP ) 10.0
2
Hz, PMe3), 0.51 (d, 9H, JHP ) 14.8 Hz, PMe3), 0.30 (d, 9H,
1H NMR (399.95 MHz, [d6]-benzene, 298 K): δ 7.19 (d, 2H,
3JHH ) 7.6 Hz, para-H-Ph), 7.13 (m, 2H, H-Ph), 7.03 (dd, 1H,
3JHH ) 7.6 Hz, meta-H-Ph), 6.97 (m, 3H, H-Ph), 6.87 (m, 3H,
H-Ph), 2.43 (s, 6H, Ph-CH3), 2.11 (s, 6H, Ph-CH3), 2.00 (s, 3H,
2JHP ) 8.8 Hz, PMe3). 13C NMR (125.7 MHz, [d6]-benzene, 298
K): δ 182.04, 178.75 (carbonyl), 149.74, 149.46, 148.05, 147.61,
145.39, 144.39, 138.67, 129.71, 129.55, 129.48, 129.32, 129.05,
126.55, 126.48, 125.53, 124.04, 123.84, 123.61, 122.97. 122.90,
122.82 (imine, ph-C), 29.92, 29.61 (iPr-CH), 26.12, 24.47 (iPr-
CH3), 19.16, 18.55 (CH3) 13.96 (d, J ) 25, PCH3), 12.45 (d, J
) 27, PCH3). 31P{1H} NMR (161.91 MHz, [d6]-benzene, 298
K, H3PO4): δ -20.4, -18.46, -7.13. Anal. Calcd for C31H41N2-
OPNi: C, 68.03; H, 7.55; N, 5.12. Found: C, 68.18; H, 7.30;
N, 5.22.
[N-(2,6-Diisopropylphenyl)-2-(2,6-diisopropylphenyl)-
propanamidato-K2N,N](η3-CH2Ph)nickel (7). The synthesis
of 7 was carried out while minimizing exposure to light. A Ni-
(COD)2 solution (124 mg, 0.46 mmol) in 5 mL of THF was
treated with potassium N-(2,6-diisopropylphenyl)-2-(2,6-diiso-
propylphenylimino)propanamide (200 mg, 0.46 mmol, in 4 mL
2
CH3), 0.97 (s, 2H, CH2-Ph) 0.56 (d, 9H, JHP ) 10.0 Hz,
P(CH3)3). 13C NMR (125.7 MHz, [d6]-benzene, 298 K): δ 181.22
(carbonyl), 163.4 (CdN), 149.56, 149.18, 144.38, 134.60, 130.14,
129.98, 129.83, 129.66, 129.08, 128.82, 127.95, 126.61, 123.86,
122.34 (imine, ph-C), 19.46, 18.45 (Ph-CH3), 18.37 (CH3), 12.72
(d, J ) 28 Hz, PCH3), 8.27 (CH2-Ph). 31P{1H} NMR (161.91
MHz, [d6]-benzene, 298 K, H3PO4): δ -8.1. Anal. Calcd for
C29H37N2OPNi: C, 67.08; H, 7.18; N, 5.39. Found: C, 66.98;
H, 7.06; N, 5.31.
[N-(2,6-Dimethylphenyl)-2-(2,6-dimethylphenylimino)-
propanamidato-K2N,N](η1-CH2Ph)(PMe3)nickel (4r). Po-
tassium N-(2,6-dimethylphenyl)-2-(2,6-dimethylphenylimino)-

R-Iminocarboxamide Nickel Complexes
Organometallics, Vol. 24, No. 23, 2005 5653
of THF) and DMA (∼1 g) at -35 °C. Benzyl chloride (60 mg in
5 mL of THF at -35 °C, 0.48 mmol) was added immediately
after. The reaction mixture was allowed to reach room tem-
perature and was stirred overnight. The volatiles were then
removed under vacuum. The resulting oil was extracted with
pentane (15 mL) and filtered. The solvent volume was reduced,
and crystallization took place at -35 °C overnight. The product
of the first crystallization contains 7 and unreacted Ni(COD)2.
Successive crystallization from pentane allows the isolation
of 7 as dark orange crystals in 70% yield. 1H NMR spectroscopy
showed two isomers.
4b); 3.61 (p, 2H, CH-3/4s)/5.92 (d, ortho-Bns), 1.41 (d, CH3-3/
4s), 1.28 (d, CH3-3/4s); 3.39 (p, CH-1/2s)/1.78 (s, CH3 ), 1.30 (d,
s
CH3-1/2s), 1.26 (s, CH2 ), 0.96 (d, CH3-1/2s); 2.94 (p, CH-1/2b)/
s
5.98 (d, ortho-Bnb), 1.75 (s, CH3 ), 1.05 (d, CH3-1/2b), 0.84 (d,
b
CH3-1/2b); 1.53 (s, CH2 )/5.98 (d, ortho-Bnb), 4.08 (p, CH-3/4b);
b
1.50 (dd, CH3-3/4b)/7.30 (m, meta-Ph-3/4b), 5.98 (d, ortho-Bnb);
1.41 (d, CH3-3/4s)/7.18 (m, meta-Ph-3/4s), 3.61 (p, 2H, CH-3/
4s), 1.28 (d, CH3-3/4s); 1.30 (d, CH3-1/2s), 1.28 (d, CH3-3/4s)/
7.18 (m, meta-Ph-3/4s), 7.01 (m, meta-Ph-1/2s), 6.35 (t, meta-
Bns), 5.92 (d, ortho-Bns), 3.61 (p, 2H, CH-3/4s), 3.39 (p, CH-1/
2s), 1.41 (d, CH3-3/4s), 0.96 (d, CH3-1/2s); 1.05 (d, CH3-1/2b)/
6.90 (d, meta-Ph-1/2b), 6.57 (t, para-Bnb), 6.25 (t, meta-Bnb),
5.98 (d, ortho-Bnb), 2.94 (p, CH-1/2b), 0.84 (d, CH3-1/2b); 0.96
(d, CH3-1/2s)/7.01 (m, meta-Ph-1/2s), 3.39 (p, CH-1/2s), 1.78 (s,
FTIR (KBr, cm-1): ν 3058 s, 2957br, 1624s, 1584 s, 1473br,
1437 s, 1381 s, 1361s, 1323s, 1255m, 899m, 795br, 747s. FTIR
(C6D6, cm-1): ν 3061 s, 2960br, 1628s, 1586 s, 1465br, 1439 s,
1
1
s
1380 m, 1358s, 1255m, 899m, 790br, 745s. H NMR and H-
{NOE} NMR, assignment according to figure below. 1H NMR
(499.86 MHz, [d6]-benzene, 298 K): δ 7.30 (m, 3H, meta-Ph-
3/4b, para-Ph), 7.18 (m, 2H, meta-Ph-3/4s), 7.01 (m, 3H, meta-
CH3 ), 1.30 (d, CH3-1/2s); 0.84 (d, CH3-1/2b)/6.90 (d, meta-Ph-
1/2b), 2.94 (p, CH-1/2b), 1.75 (s, CH3 ), 1.05 (d, CH3-1/2b). 13C
b
NMR (125.7 MHz, [d6]-benzene, 298 K): δ 182.04, 179.23
(carbonyl), 169.85, 168.62 (CdN), 147.74, 146.21, 145.55,
144.16, 143.87, 143.77, 138.97, 138.92, 135.79, 134.86, 127.69,
127.57, 127.26, 127.03, 125.64, 125.16, 124.55, 124.15, 123.63,
123.09 (imine, ph-C), 118.58, 118.35 (ortho-Bn), 103.06, 102.17
(ortho-Bn), 37.54, 35.90 (iPr-CH), 29.90, 29.87, 29.34, 29.18,
26.02, 25.68, 24.49, 24.33, 23.94, 23.75(iPr-CH3), 24.36, 24.22
(CH2-Ph), 19.89, 19.32 (CH3). Anal. Calcd for C34H44N2ONi:
C, 73.52; H, 7.98; N, 5.04. Found: C, 73.38; H, 7.90; N, 5.02.
Typical Reaction with Ethylene. An autoclave reactor
was loaded inside a glovebox with an R-iminocarboxamide
complex (10 µmol) and Ni(COD)2 (25 µmol) and toluene, such
that the final volume of the toluene solution was 30 mL. The
reactor was sealed inside the glovebox. The reactor was
attached to an ethylene line, and the gas was fed continuously
into the reactor at a specific pressure. The pressurized reaction
mixture was stirred at a temperature controlled by an external
water bath. After a specific reaction time, the ethylene was
vented and acetone was added to quench the polymerization.
The precipitated polymer was collected by filtration and dried
overnight under vacuum.
3
Ph-1/2s, para-Ph), 6.90 (d, 2H, JHH ) 7.7 Hz, meta-Ph-1/2b),
3
3
6.72 (t, 1H, JHH ) 7.6 Hz, para-Bns), 6.57 (t, 1h, JHH ) 7.7
Hz, para-Bnb), 6.35 (t, 2H, JHH ) 7.6 Hz, meta-Bns), 6.25 (t,
3
2H, 3JHH ) 7.7 Hz, meta-Bnb), 5.98 (d, 2H, 3JHH ) 7.7 Hz, ortho-
Bnb), 5.92 (d, 2H, 3JHH ) 7.6 Hz, ortho-Bns), 4.08 (p, 2H, 3JHH
) 6.9 Hz, CH-3/4b), 3.61 (p, 2H, 3JHH ) 6.9 Hz, CH-3/4s), 3.39
(p, 2H, JHH ) 6.9 Hz, CH-1/2s), 2.94 (p, 2H, JHH ) 6.8 Hz,
3
3
CH-1/2b), 1.78 (s, 3H, CH3 ), 1.75 (s, 3H, CH3 ), 1.53 (s, 2H,
s
b
CH2 ), 1.50 (dd, 12H, JHH ) 6.9 Hz, CH3-3/4b), 1.41 (d, 6H,
b
3
3JHH ) 6.9 Hz, CH3-3/4s), 1.30 (d, 6H, JHH ) 6.9 Hz, CH3-1/
3
2s), 1.28 (d, 6H, JHH ) 6.9 Hz, CH3-3/4s), 1.26 (s, 2H, CH2 ),
3
s
3
3
1.05 (d, 6H, JHH ) 6.8 Hz, CH3-1/2b), 0.96 (d, 6H, JHH ) 6.9
Hz, CH3-1/2s), 0.84 (d, 6H, JHH ) 6.8 Hz, CH3-1/2b).
3
Acknowledgment. The work was funded by the
DOE (grant no. DE-FG03098ER14910) and the Mitsub-
ishi Chemical-Center for Advanced Materials. The
authors are grateful for useful discussions with Profes-
sors Ed Kramer, Susannah Scott, and Glenn Fredrick-
son.
Supporting Information Available: Additional polym-
erization reaction results, summary of NOSEY 1H NMR
spectroscopy results for compound 7, and the complete details
for crystallographic studies of 4o, 4r, 5, 6, and 7.
1H{NOE} NMR (499.86 MHz, [d6]-benzene, 298K): δH(ir)
/
δH(res) 5.98 (d, ortho-Bnb)/6.25 (t, meta-Bnb), 2.94 (p, CH-1/2b),
1.53 (s, CH2 ), 1.05 (d, CH3-1/2b); 5.92 (d, ortho-Bns)/6.35 (t,
b
meta-Bns), 3.61 (p, 2H, CH-3/4s), 1.26 (s, CH2 ); 4.08 (p, CH-
s
3/4b)/7.30 (m, meta-Ph-3/4b), 1.53 (s, CH2 ), 1.50 (dd, CH3-3/
OM050640G
b