Nickel catalysts bearing bidentate α-aminoaldimines for ethylene polymerization - Independent and cooperative structure/reactivity relationship resulting from unsymmetric square planar coordination

Article abstract of DOI:10.1039/b814423k

Ethylene polymerization catalyzed by Ni(ii) complexes that bear new bidentate ligands with a functional hybrid of amine and imine has been studied. A class of new α-aminoaldimines and their nickel complexes [R ¹R²NCMe₂CHN(

Full text of DOI:10.1039/b814423k

PAPER
www.rsc.org/dalton | Dalton Transactions
Nickel catalysts bearing bidentate a-aminoaldimines for ethylene
polymerization—independent and cooperative structure/reactivity
relationship resulting from unsymmetric square planar coordination†
Feng-Zhao Yang, Yi-Chun Chen, Ya-Fan Lin, Kuo-Hsuan Yu, Yi-Hung Liu, Yu Wang, Shiuh-Tzung Liu and
Jwu-Ting Chen*
Received 19th August 2008, Accepted 30th October 2008
First published as an Advance Article on the web 8th January 2009
DOI: 10.1039/b814423k
Ethylene polymerization catalyzed by Ni(II) complexes that bear new bidentate ligands with a
functional hybrid of amine and imine has been studied. A class of new a-aminoaldimines and their
1
2
3
1
2
3
3
i
=
nickel complexes [R R NCMe2CH N(2,6-R C6H3)]NiBr2 (R = R = Me, R = Me (Ni-1b); R = Pr
2
n
i
(Ni-1c); R1 = R2 = Et, R3 = H (Ni-2a); Me (Ni-2b); iPr (Ni-2c); R1 = R2 = Pr, R3 = Pr (Ni-3c);
i
i
(R1R2) = c-C3H6 R3 = Pr (Ni-4c); (R1R2) = c-C4H8, R3 = Pr (Ni-5c)) were synthesized. The molecular
structures of six nickel complexes were determined by X-ray crystallography, showing distorted
tetrahedral configurations. The SQUID data of Ni-1c confirms its ground state of triplet spin. Using
methylaluminoxanes (MAO) as the activator, the nickel complexes are found to catalyze ethylene
polymerization under moderate pressure and ambient temperature. The activity reaches to 106 g PE mol
Ni-1 h-1, and increases with the ethylene pressure in the range of 14–28 bar. The highly branching PE
products have Mn ~ 105 with PDI < 2. The amine and imine functionalities demonstrate independent
control to the polymerization reactions, wherein the activity appears to be facilitated by using the
catalysts installed with bulky imino substituents as well as with less sterically hindered amino
substituents. This is ascribed to the C2 unsymmetric coordination in the square planar resting state in
which the bulky polymer chain prefers cis to the imine and the small ethylene monomer is cis to the
amine.
comprising amine and imine are left as a relatively unripe field
Introduction
in catalysis.10 We report herein that nickel catalysts bearing
new a-aminoaldimine ligands are found to be highly active
to ethylene polymerization.11 In such a complex system, each
coordinating functionality displays independent but cooperative
structure-to-reactivity relationship. These ligands thus provide the
rare examples of different donor functionalities that can convey
selective geometrical isomerism, and further affect the reactivity
of ethylene polymerization.
The usage of late transition metal catalysts bearing the designed
ligands with constrained geometry for olefin polymerization has
acquired tremendous attention.1 Such catalysts are expected to
not only demonstrate promising activity, but also to confer a
characteristic control to the reaction course as well as to the
polymer properties, particularly distinguishable from the reactions
caused by the known catalysts of early transition metals.2 Among
the studied systems, the catalysts with diimine ligands with the
bulky substituents have been proved to represent a paradigm. It
leads to immense research in seeking for the ligand control with
steric bulkiness.3
In another aspect, the quest for new ligands with the hybrid
donating functionalities still remains a rising field since the
discovery of the SHOP process.4 It is generally believed that the
unsymmetric bidentate ligands potentially enable to afford the
distinct influence to the metal in the regards of both structure
and reactivity control.5,6 Some recent studies reveal that ethylene
polymerization may be catalyzed by the bidentates with N–O,
P–N and N–N’ donor combination.7–9 Curiously, the bidentates
Results and discussion
Synthesis and spectroscopic characterization
1
2
=
New a-aminoaldimines in the form of R R NCMe2CH N(2,6-
2
R3 C6H3) (L) were synthesized via amination of a-bromoaldehyde
followed by condensation with the aniline derivatives as shown in
Scheme 1.12
The substitution reactions of (DME)NiBr2 (DME = 1,2-
dimethoxyethane) with L generates the neutral complexes
1
2
3
1
2
3
=
[R R NCMe2CH N(2,6-R C6H3)]NiBr2 (R = R = Me, R =
2
Me (Ni-1b); R3 = Pr (Ni-1c); R1 = R2 = Et, R3 = H (Ni-2a); Me
i
(Ni-2b); Pr (Ni-2c); R1 = R2 = Pr, R3 = Pr (Ni-3c); (R1R2) =
i
n
i
Department of Chemistry, National Taiwan University, No 1, Section 4,
Roosevelt Road, Taipei, Taiwan 106. E-mail: jtchen@ntu.edu.tw; Fax: +886
2 2363 6359; Tel: +886 2 3366 1659
† Electronic supplementary information (ESI) available: SQUID data of
Ni-1c. CCDC reference numbers 682282 and 699109–699113. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b814423k
c-C3H6, R3 = Pr (Ni-4c); (R1R2) = c-C4H8, R3 = Pr (Ni-5c)). The
violet dibromonickel complexes are generally soluble in CH2Cl2 or
CHCl3, and appear to be hygroscopic. The SQUID measurement
for Ni-1c gives m = 3.18 BM at 295 K, indicating a ground state
of triplet spin.
i
i
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1243–1250 | 1243
©

Scheme 1 Synthesis of ligands and nickel catalysts.
X-Ray structural analysis
The single crystals of the nickel complexes were grown from
CH2Cl2–Et2O. The X-ray diffraction data, listed in Table 3, were
˚
collected using 3 kW sealed-tube MoKa radiation (l = 0.7103 A).
The data were processed using the DENZO method and the
structure were solved and refined by the SHELXTL program.13
Multi-scan absorption correction was applied, and decay was
negligible. All refinements were carried out by full-matrix least-
squares using anisotropic displacement parameters for all non-
hydrogen atoms. All the hydrogen atoms were added at calculated
positions.
ORTEP drawings of Ni-1b, Ni-1c, Ni-2a, Ni-2b, Ni-4c and Ni-
5c with thermal ellipsoids at 50% probability are shown in Fig. 1.
The four-coordinate molecular structures in distorted tetrahedral
geometry are confirmed. Such results explains the paramagnetism
shown by Ni-1c. The bond parameters are listed in Table 4.
The distances of the Ni–N1(sp2) bonds are in the range of
3
˚
˚
1.991–2.011 A and 2.049–2.080 A for the Ni–N2(sp ) bonds.
The data are consistent with the nickel–nitrogen bonds with the
imine and amine ligands, respectively.14 The angles of N1–Ni–N2
are in the range of 81.7–83.3◦, which are comparable with those
in the diimine complexes.3c,g,14c,d The angles of Br1–Ni–Br2 are
in the larger range of 116.1–123.6◦. Complex Ni-2a has the
particularly large Br1–Ni–Br2 angle. The average distances of the
˚
Ni–Br bonds are in the range of 2.3338–2.3654 A. The Ni–Br
˚
distance of Ni-2a (2.3536 and 2.3772 A) are also longer than
those in other analogues. The Ni–N1–C1 angles are in the range
of 111.5–114.5◦ and 103.3–108.3◦ for the Ni–N2–C2 angles. All
these structural features give solid support to the authentic amine–
imine bidentate coordination to the nickel(II) center. The non-
planar five-membered metallacycles imply that the amino and
imino substituents will be able to provide quite different steric
effect to their cis coordination sites.12
Fig. 1 ORTEP drawings of the nickel complexes. All hydrogen atoms
are omitted for clarity. Ni-1b (the one that does not have disorder in the
asymmetric unit is shown).
Ethylene polymerization
The nickel complexes have been found to be active catalysts for
ethylene polymerization with the assistance of methylaluminox-
anes at ambient temperature. The data are presented in Table 1.
At a pressure of 28 bar and 25 ◦C, the activity of Ni-1b reaches to
106 g mol Ni-1 h-1. In general, the PE products are of hyperbranch
and have Mn of 105 with Mw/Mn < 2. The Tg of PE are in the
◦
region of -40 to -50 C, but no observable Tm. TGA data show
less than 10% weight loss until 390 ◦C.
Entries 1–5 show that the catalysts Ni-1b are active within
10 min. For Ni-2b, as illustrated in the entries 9 and 10, the
1244 | Dalton Trans., 2009, 1243–1250
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The Royal Society of Chemistry 2009
©

Table 1 Data of ethylene polymerization
c
Catalyst/mmola
C2H4/bar
T
rxn/h
TOFb ¥ 10-3
Mn ¥ 10-3
PDI
Branch/ ¥ 103 Cd
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Ni-1b (41)
Ni-1b (41)
Ni-1b (41)
Ni-1b (41)
Ni-1b (41)
Ni-1c (39)
Ni-1c (43)
Ni-2a (22)
Ni-2b (22)
Ni-2b (22)
Ni-2c (22)
Ni-3c (22)
Ni-4c (22)
Ni-5c (22)
14
17
21
24
28
28
28
17
17
17
17
17
17
17
1/6
1/6
1/6
1/6
1/6
1/6
1/2
3
3
24
3
3
334
516
890
1030
1106
1085
1186
9
98
25
52
74
236
279
257
291
226
356
378
12
164
393
238
108
297
227
1.38
1.35
1.17
1.32
1.66
1.21
1.44
1.88
1.31
1.23
1.69
2.58
1.25
1.26
62
121
109
112
78
112
106
152
149
118
143
103
86
1/3
1/3
682
500
79
a All runs were carried out in 100 mL toluene at 25 ◦C, [Al]/[Ni] = 480. b TOF = g PE mol Ni-1 h-1. c Determined by GPC. d Determined by NMR
integration.
Table 2 Selected parameters from calculations
Complex cis-Ni-1b¢ trans-Ni-1b¢ cis-Ni-2b¢
lengthened reaction time from 3–24 h, although causing the
depletion of the activity, could increase the yields (6.4 and 13.2 g,
respectively) and Mn, but leave the PDI and branch number nearly
unchanged, indicating the reasonable stability of the catalyst
system at 25 ◦C. The activity increases with the ethylene pressure
in the range of 14–28 bar in the entries 1–5. It suggests that the
coordination of ethylene to the metal site ought to be crucial to
the catalysis.
Entries 8–11 show that the ortho-substituted phenyl on the imino
nitrogen can substantially help the activity. This is as expected
and is consistent with the structure-to-reactivity relationship
discovered in the diimine systems.3
trans-Ni-2b¢
˚
(Ni–N1)/A
2.201
1.916
1.278
1.969
2.034
1.978
81.95
2.17
2.085
1.926
1.278
1.995
2.063
1.985
81.47
0
2.106
1.928
1.276
1.947
2.035
1.992
83.51
21.07
2.162
1.921
1.279
2.004
2.073
1.976
82.40
0
˚
(Ni–N2)/A
˚
(C1–N1)/A
˚
(Ni–C11)/A
˚
(Ni–C14)/A
˚
(Ni–C15)/A
N1–Ni–N2/◦
Rel. E/KJ mol-1
Most intriguingly, the data of the entries 7 and 11–14 clearly
exhibit that the less bulky amino substituents are favored by the
ethylene polymerization. Further more, the activity of polymer-
ization is rather susceptible to the conformational variation of the
amino substituents. As shown in the entries 13 and 14, the catalysts
of Ni-4c and Ni-5c, which have the cyclic amino substituents afford
much better activity than those with acyclic substituents of the
comparable carbon numbers as shown in entries 9–11.
Such an independent but still cooperative structure-to-reactivity
relationship from the unsymmetric aminoaldimine ligands is
in contrast to the general understanding concluded from the
symmetric diimine systems in which the ethylene coordination is
not rate determining.3a–c In these amine–imine catalysts, although
the ortho-substituents on the imino phenyl ring remains important,
however, the polymerization activity appears to be more dependent
to the amino substituents.
Calculation analysis
Theoretical calculations also supports the assertion of steric con-
cern. The relative stability for two geometrical isomers correspond-
ing to (L-1b)Ni(C2H4)(nPr) (Ni-1b¢) and (L-2b)Ni(C2H4)(nPr) (Ni-
2b¢) have been calculated. Some bonding data are listed in Table 2.
The calculated structures are illustrated in Fig. 2. It is worthy of
noting that the trans form is 2.17 kJ mol-1 more stable than the
cis form for (L-1b)Ni(C2H4)(nPr). Whilst for (L-2b)Ni(C2H4)(nPr),
the trans form is 21.07 KJ mol-1 more stable than the cis derivative.
Unlike the symmetric diimine systems, the bidentate a-
aminoaldimines can lead to selective geometrical isomerism in
square planar configuration.11 In the square-planar resting state,
the polymer chain and ethylene monomer are considered to
coordinate to the Ni(II) center, besides the auxiliary bidentate
ligand.3a,b Concerning the stereoselectivity in the more stable
trans form, the bulky polymer chain may be cis to the imino
functionality; and the small ethylene is seated cis to the amine.
This is because the Ni–N1–C21 angle (generally > 120◦) around
the imino sp3 nitrogen may accommodate greater steric tolerance
than the Ni–N2–C angles (<110◦) around the amino sp3 nitrogen.
Therefore, the bulkier amino substituents tend to destabilize the
resting state by hampering the ethylene coordination.
Fig.
2
Calculated structures for the geometrical isomers of
(L-1b)Ni(C2H4)(nPr) (Ni-1b¢) and (L-2b)Ni(C2H4)(nPr) (Ni-2b¢).
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Dalton Trans., 2009, 1243–1250 | 1245
©

1
It is indicated that the geometrical isomerism in Ni-1b¢ probably
makes little difference to ethylene polymerization. However in Ni-
2b¢, the steric hindrance resulting from the methyl groups on the
C2 could cause the N-bound ethyl groups to interfere the ethylene
coordination, specifically in the trans configuration.
In addition, the steric hindrance between the two amino ethyl
groups could enlarge the N1–Ni–N2 bite angle, which is known to
be crucial to the polymerization activity.15 This can also explain
why the small cyclic ring on the amino functionality can facilitate
the ethylene polymerization.
n/cm-1: nC 1662. H NMR (CDCl3, 400 MHz) d/ppm: 7.59
=
N
=
(s, 1H, CH N), 7.01–6.86 (m, 3H, C6H3), 2.34 (s, 6H, NCH3),
2.07 (s, 6H, (C6H3)CH3), 1.31 (s, 6H, CCH3). 13C NMR (CDCl3,
=
100.625 MHz) d/ppm: 173.2 (CH N), 150.5, 128–123 (phenyl-
C), 61.5 (CCH3), 39.2 (NCH3), 20.0 (CCH3), 18.4 ((C6H3)CH3);
HR-FAB-MS m/z: calcd for C14H23N2 219.1861, found 219.1862.
i
=
Me2NCMe2CH N(2,6- Pr2C6H3) (L-1c)
Following the same procedure used for L-1b, the reaction of
Me2NCMe2CHO (4.6 g, 0.04 mol) and 2,6-iPr2C6H3NH2 (8.8 g,
0.05 mol) gave L-1c as a viscous yellow liquid in 47% yield (11.5 g).
Concluding remarks
IR (KBr) n/cm-1: nC N 1626. 1H NMR (CDCl3, 300 MHz) d/ppm:
=
=
7.60 (s, 1H, CH N), 7.10–7.01 (m, 3H, C6H3), 2.90 (h, JH–H
=
In conclusion, the nickel catalysts bearing the amino and imino hy-
brid bidentate ligand are proved to afford a rare example wherein
two coordinating functionalities confer the steric differentiation
to the coordination that further resulting in the reactivity control
to ethylene polymerization.
6.9 Hz, 2H, (CH(CH3)2), 2.35 (s, 6H, NCH3), 1.32 (s, 6H, CCH3),
1.15 (d, JH–H = 6.9 Hz, 12H, CH(CH3)2). 13CNMR (CDCl3,
=
100.625 MHz) d/ppm: 170.3 (CH N), 148.2–122.8 (phenyl-C),
61.8 (CCH3), 39.2 (NCH3), 27.6 (CH(CH3)2), 22.2 (CCH3), 20.0
(CH(CH3)2); MS (FAB, m/z): 275.2 (M+ + 1). Anal. calcd for
C18H30N2: C 78.78, H 11.02, N 10.20. Found: C 77.73, H 11.19,
N 9.31.
Experimental
General procedure
=
Et2NCMe2CH NPh (L-2a)
Commercially available reagents were purchased and used without
further purification unless otherwise indicated. Toluene and
diethyl ether were distilled from purple solutions of benzophenone
ketyl under nitrogen and dichloromethane was dried over P2O5
and distilled immediately prior to use. Air-sensitive materials were
manipulated under a nitrogen atmosphere in a glove box or by
standard Schlenk techniques. The IR spectra were recorded on
a Bio-Rad FTS-40 spectrophotometer. The NMR spectra were
measured on a Bruker AC-300 or a Bruker AC-400 spectrometer.
The corresponding frequencies for the 13C NMR spectra were
75.469 MHz and 100.625 MHz, respectively. Values upfield of 1H
and 13C data are given in d (ppm) relative to tetramethylsilane
(d 0.00) in CDCl3. Mass spectrometric analyses were collected on
a JEOL SX-102A spectrometer. Elemental analysis was done on
a Perkin-Elmer 2400 CHN analyzer. Gel perm◦eation chromatog-
raphy (GPC) was performed in toluene at 25 C using a Kratos
model spectroflow 400 equipped with PL-mixed D exclusion limit
400k columns. Differential scanning calorimetry was measured
under a continuous nitrogen purge (20 mL min-1) on a Perkin-
Elmer Pyris 6 DSC instrument. The data were gathered on the
third heating cycle using a heating and cooling scan rate of
10–15 ◦C min-1. Thermogravimetric analysis was carried out using
a TA Instruments TGA5100 with a hating rate of 10 ◦C min-1 from
0–800 ◦C under a continuous nitrogen purge. Magnetic moments
were measured between 2–300 K with an applied field up to 7 T,
using a MPMS7 SQUID magnetometer (Quantum Design, USA).
Following the same procedure used for L-1b, the reaction of
Et2NCMe2CHO (11.4 g, 0.08 mol) and aniline (7.4 g, 0.08
mol) gave a viscous yellow liquid in 66% yield (11.5 g). IR
1
(KBr) n/cm-1: nC 1648. H NMR (CDCl3, 300 MHz) d/ppm:
=
N
=
7.76 (s, 1H, CH N), 7.36–7.0 (m, 5H, C6H5), 2.70 (q, JH–H
=
7.1 Hz, 4H, NCH2CH3), 1.34 (s, 6H, CCH3), 1.05 (t, JH–H
=
7.1 Hz, 6H, NCH2CH3). 13C NMR (CDCl3, 75.469 MHz) d/ppm:
=
172.6 (CH N), 151.8, 130–112 (phenyl-C), 63.0 (CCH3), 43.8
(NCH2CH3), 21.8 (CCH3), 15.8 (NCH2CH3). MS (FAB, m/z):
219.2 (M+ + 1). Anal. calcd for C14H22N2: C 77.01, H 10.16, N
12.83. Found: C 76.43, H 10.01, N 12.32.
=
Et2NCMe2CH N(2,6-Me2C6H3) (L-2b)
Following the same procedure used for L-1b, the reaction of
Et2NCMe2CHO (10.0 g, 0.07 mol) and 2,6-Me2C6H3NH2 (8.5 g,
0.07 mol) gave a viscous yellow liquid of L-2b in 50% yield (8.6
1
g). IR (KBr) n/cm-1: nC 1667. H NMR (CDCl3, 300 MHz)
=
N
=
d/ppm: 7.58 (s, 1H, CH N), 7.01–6.88 (m, 3H, C6H3), 2.66 (q,
JH–H = 7.1 Hz, 4H, NCH2CH3), 2.07 (s, 6H, (C6H3)CH3), 1.34
(s, 6H, CCH3), 1.06 (t, JH–H = 7.1 Hz, 6H, NCH2CH3). 13C
=
NMR (CDCl3, 75.469 MHz) d/ppm: 174.3 (CH N), 150.5, 128–
123 (phenyl-C), 63.0 (CCH3), 43.7 (NCH2CH3), 22.1 (CCH3),
18.3 ((C6H3)CH3), 16.5 (NCH2CH3). HR-FAB-MS: m/z calcd for
C16H27N2 247.2174, found 247.2175. Anal. calcd for C16H26N2: C
78.00, H 10.64, N 11.37. Found: C 77.64, H 10.45, N 11.39.
Synthesis and characterization
i
=
Et2NCMe2CH N(2,6- Pr2C6H3) (L-2c)
=
Me2NCMe2CH N(2,6-Me2C6H3) (L-1b)
Following the same procedure used for L-1b, the reaction of
Et2NCMe2CHO (10.0 g, 0.07 mol) and 2,6-iPr2C6H3NH2 (12.4 g,
0.07 mol) gave a viscous yellow liquid of L-2c and was obtained in
44% yield (9.3 g). IR (KBr) n/cm-1: nC 1666. 1H NMR (CDCl3,
300 MHz) d/ppm: 7.56 (s, 1H, CH N), 7.09–7.05 (m, 3H, C6H3),
2.88 (h, JH–H = 7.1 Hz, 1H CH(CH3)2) 2.65 (q, JH–H = 7.1 Hz,
4H, NCH2CH3), 1.33 (s, 6H, CCH3), 1.13 (d, JH–H = 7.1 Hz,
Me2NCMe2CHO (4.6 g, 0.04 mol) and 2,6-dimethylaniline (6.0 g,
0.05 mmol) were placed in 30 mL of toluene. Formic acid (0.3 mL
99% v/v aqueous solution) was added, and the solution was
refluxed in a set-up with a Dean–Stark trap for 1 d. Toluene
was removed in vacuo. The product was isolated by distillation
to give a viscous yellow liquid in 58% yield (5.06 g). IR (KBr)
=
N
=
1246 | Dalton Trans., 2009, 1243–1250
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©

6H, CH(CH3)2), 1.05 (t, JH–H = 7.1 Hz, 6H, NCH2CH3). 13C
turned to violet within 10 min. The reaction was allowed to
complete at 25 ◦C. After removal of the supernatant solid, the
reaction solution was concentrated. The addition of dry Et2O
resulted in the solid product, and the yield of Ni-1b was 74% (321
mg) after recrystallization from CH2Cl2–Et2O. MS (FAB, m/z):
355.0 (M+ - Br). Anal. calcd for C14H22N2Br2Ni: C 38.49, H 5.08,
N 6.41. Found: C 38.57, H 5.06, N 6.04. Crystals suitable for X-ray
diffraction experiment were obtained by slow diffusion of diethyl
ether into a saturated dichloromethane solution of Ni-1b.
=
NMR (CDCl3, 75.469 MHz) d/ppm: 173.7 (CH N), 148.3, 137.4,
123.7, 122.8 (phenyl-C), 63.2 (CCH3), 43.8 (NCH2CH3), 27.6
(CH(CH3)2), 23.5 (CH(CH3)2), 22.2 (CCH3), 16.5 (NCH2CH3).
MS (FAB, m/z): 275.2 (M+ + 1). Anal. calcd for C20H34N2: C
79.41, H 11.32, N 9.26. Found: C 79.70, H 11.62, N 9.15.
n
i
=
Pr2NCMe2CH N(2,6- Pr2C6H3) (L-3c)
Following the same procedure used for L-1b, the reaction of
nPr2NCMe2CHO (3.42 g, 0.02 mol) and 2,6-iPr2C6H3NH2 (3.55 g,
0.02 mol) gave a yellow solid L-3c in 40% yield (2.74 g). IR
i
=
[Me2NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-1c)
1
(KBr) n/cm-1: nC 1666. H NMR (CDCl3, 300 MHz) d/ppm:
=
N
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (100 mg, 0.32 mmol) and L-1c (134 mg, 0.49 mmol)
gave violet solid of Ni-1c in 57% yield (92 mg). MS (FAB, m/z):
411.1 (M+ + 1 - Br). Anal. calcd for C18H30N2Br2Ni: C 43.86, H
6.11, N 5.68. Found: C 43.68, H 6.12, N 5.34.
=
7.59 (s, 1H, CH N), 7.12–7.04 (m, 3H, C6H3), 2.90 (h, JH–H
=
6.7 Hz, 2H, CH(CH3)2), 2.51 (m, 4H, CH2CH2CH3), 1.47 (m,
JH–H = 7.2 Hz, 4H, NCH2CH2CH3), 1.33 (s, 6H, CCH3), 1.60
(d, JH–H = 6.7 Hz, 12H, CH(CH3)2) 0.85 (t, JH–H = 7.2 Hz, 6H,
NCH2CH2CH3). 13C NMR (CDCl3, 75.469 MHz) d/ppm: 173.8
=
(CH N), 148.3, 137.4, 123.7, 122.8 (phenyl-C), 63.1 (CCH3), 53.3
=
[Et2NCMe2CH NPh]NiBr2 (Ni-2a)
(NCH2CH2CH3), 27.5 (CH(CH3)2), 24.5 (NCH2CH2CH3), 23.5
(CH(CH3)2), 22.1 (CCH3), 11.7 (NCH2CH2CH3). MS (FAB, m/z):
329.3 (M+ + 1). Anal. calcd for C22H38N2: C 79.95, H 11.59, N 8.47.
Found: C 79.40, H 11.60, N 8.24.
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (300 mg, 1.0 mmol) and L-2a (327 mg, 1.5 mmol)
gave a violet solid Ni-2a in 62% yield (264 mg). 1H NMR (CDCl3,
=
300 MHz) d/ppm: 8.56 (s, 1H, CH N), 7.44–7.18 (m, 5H, phenyl-
i
=
(c-C3H6)NCMe2CH N(2,6- Pr2C6H3) (L-4c)
H), 3.37, 2.96 (m, m, 2H, 2H, NCH2CH3), 1.74 (s, 6H, CCH3),
1.59 (t, JH–H = 7.1 Hz, 6H, NCH2CH3). 13C NMR (CDCl3,
Following the same procedure used for L-1b, the reaction of
c-C3H6NCMe2CHO (5.0 g, 0.04 mol) and 2,6-iPr2C6H3NH2 (8.8 g,
0.05 mol) gave the product L-4c. Isolation gives a yellow liquid in
=
75.469 MHz) d/ppm: 161.1 (CH N), 148.4, 128.8, 126.9, 120.8
(phenyl-C), 69.0 (CCH3), 46.2 (NCH2CH3), 21.2 (CCH3), 11.8
(NCH2CH3). MS (FAB, m/z): 355.0 (M+ + 1 - Br). Anal. calcd
for C14H22Br2N2Ni: C 38.49, H 5.08, N 6.41. Found: C 38.78, H
5.03, N 6.37.
1
47% yield (5.4 g). H NMR (CDCl3, 300 MHz) d/ppm: 7.60 (s,
=
1H, CH N), 7.05 (m, 3H, C6H3), 3.39 (t, JH–H = 7.2 Hz, 4H,
N(CH2)2CH2), 2.87 (m, JH–H = 6.7 Hz, 4H, CH(CH3)2), 2.05 (m,
JH–H = 7.2 Hz, 2H, N(CH2)2CH2), 1.22 (s, H, C(CH3)2), 1.13
(d, JH–H = 6.7 Hz, 12H, CH(CH3)2). 13C NMR (CDCl3, 75.469
=
[Et2NCMe2C N(2,6-Me2C6H3)]NiBr2 (Ni-2b)
=
MHz) d/ppm: 170.8 (CH N), 137.2, 123.9, 122.8 (phenyl-C), 59.1
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (300 mg, 1.0 mmol) and L-2b (358 mg, 1.5 mmol)
gave a violet solid of Ni-2b in 57% yield (264 mg). H NMR
(CCH3), 47.6 (NCH2), 27.6 (CH(CH3)2), 23.4 (CH(CH3)2), 20.0
(CCH3), 16.5 (CH2(CH2)2).
1
=
(CDCl3, 300 MHz) d/ppm: 8.29 (s, 1H, CH N), 7.06–6.98 (m, 3H,
i
=
(c-C4H8)NCMe2CH N(2,6- Pr2C6H3) (L-5c)
phenyl-H), 3.45, 3.07 (m, m JH–H = 7.1 Hz, 2H, 2H, NCH2CH3),
2.10 (s, 6H, (C6H3)CH3), 1.83 (s, 6H, CCH3), 1.70 (t, JH–H
= 7.1 Hz, 6H, NCH2CH3). 13C NMR (CDCl3, 75.469 MHz)
Following the same procedure used for L-1b, the reaction of
c-C4H8NCMe2CHO (10.0 g, 0.07 mol) and 2,6-iPr2C6H3NH2
(14.1 g, 0.08 mol) gave the product L-5c. Isolation was done
by crystallization to give a yellow solid in 50% yield (10.5 g).
IR (KBr) n/cm-1: nC 1666. 1H NMR (CDCl3, 300 MHz)
=
d/ppm: 164.4 (CH N), 147.9, 127.9, 125.6, 124.1, (phenyl-C),
69.8 (CCH3), 46.6 (NCH2CH3), 21.4 (CCH3), 18.3 ((C6H3)CH3),
11.9 (NCH2CH3). MS (FAB, m/z): 383.1 (M+ - Br). Anal. calcd
for C16H26Br2N2Ni·0.324CH2Cl2: C 45.92, H 6.41, N 6.03. Found:
C 45.92, H 6.40, N 6.48.
=
N
=
d/ppm: 7.67 (s, 1H, CH N), 7.10–7.01 (m, 3H, C6H3), 2.89 (h,
2H, JH–H = 7.1 Hz, 2H, CH(CH3)2), 2.78 (m, 4H, NCH2CH2),
1.77 (m, 4H, NCH2CH2), 1.38 (s, 6H, CCH3), 1.13 (d, JH–H
=
7.1 Hz, 12H, CH(CH3)2). 13C NMR (CDCl3, 75.469 MHz)
i
=
[Et2NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-2c)
=
d/ppm: 172.1 (CH N), 148.3, 137.4–122.8 (phenyl-C), 59.7
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (300 mg, 1.0 mmol) and L-2c (453 mg, 1.5 mmol)
(CCH3), 46.5 (NCH2CH2), 27.6 (CH(CH3)2), 24.1 (NCH2CH2),
23.5 (CH(CH3)2), 21.8 (CCH3). MS (FAB, m/z): 301.2 (M+ + 1).
Anal. calcd for C20H32N2: C 79.94, H 10.73, N 9.32. Found: C
80.32, H 11.12, N 9.27.
1
gave violet Ni-2c in 56% yield (291 mg). H NMR (CDCl3, 300
=
MHz) d/ppm: 8.29 (s, 1H, CH N), 7.14 (br, 3H, phenyl-H),
3.49, 3.12 (br, 2H, 2H, NCH2CH3), 2.73 (br, 1H, CH(CH3)2)),
1.85 (s, 6H, CCH3), 1.74 (br, 6H, NCH2CH3), 1.19 (br, 6H,
CH(CH3)2)). 13C NMR (CDCl3, 75.469 MHz) d/ppm: 163.9
=
[Me2NCMe2C N(2,6-Me2C6H3)]NiBr2 (Ni-1b)
=
(DME)NiBr2 (300 mg, 1.0 mmol) and L-1b (327 mg, 1.5 mmol)
were placed in a round-bottomed flask under nitrogen. Pre-dried
CH2Cl2 (15 mL) was transferred in vacuo. The orange solution
(CH N), 150.3, 136.0, 124.5 122.5 (phenyl-C), 70.0 (CCH3), 46.6
(NCH2CH3), 27.5 (CH(CH3)2), 23.1 (CH(CH3)2), 21.4 (CCH3),
12.0 (NCH2CH3). MS (FAB, m/z): 439.1 (M+ - Br). Anal. calcd
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1243–1250 | 1247
©

Table 3 X-Ray crystal parameters and data collection
Compound
Ni-1b
Ni-1c
Ni-2a
Ni-2b
Ni-4c
Ni-5c
Formula
C14H22Br2N2Ni
436.87
0.25 ¥ 0.20 ¥ 0.15 0.25 ¥ 0.20 ¥ 0.15
Monoclinic
P21/c
17.3020(4)
13.8610(3)
15.2240(3)
90
108.879(2)
90
3454.65(13)
8
1.680
C18H30Br2N2Ni
492.97
C14H22Br2N2Ni
436.87
0.20 ¥ 0.20 ¥ 0.15
Monoclinic
P21/c
7.3858(3)
14.1749(4)
16.5776(6)
90
95.731(1)
90
1726.85(11)
4
1.680
872
150(1)
C16H26Br2N2Ni
464.92
0.20 ¥ 0.10 ¥ 0.03 0.25 ¥ 0.20 ¥ 0.15 0.25 ¥ 0.20 ¥ 0.15
Triclinic
¯
P1
7.9039(3)
8.6754(3)
15.4932(4)
102.012(1)
95.157(1)
113.542(1)
934.71(6)
2
1.652
468
150(2)
5.308
C19H30Br2N2Ni
504.98
C20H32Br2N2Ni
519.01
Mr/g mol-1
Crystal size/mm
Crystal system
Space group
Orthorhombic
Pna21
15.225(3)
10.217(2)
14.312(3)
90
90
90
2226.3(8)
4
1.471
1000
295(2)
4.462
0.403–0.519
2.40–27.47
-16–19, -12–13, 18
Orthorhombic
Pna21
15.1090(3)
10.4250(3)
14.4930(3)
90
Monoclinic
P21/c
8.66900(10)
14.1770(2)
19.0860(3)
90
101.9170(10)
90
2295.12(6)
4
1.502
1056
295(2)
4.333
0.325–0.534
3.75–27.49
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
90
90
3
˚
V/A
2282.81(9)
4
1.469
1024
295(2)
4.354
0.338–0.533
2.73–27.49
Z
r
calcd/Mg m-3
F(000)
T/K
m/mm-
Transmission
q range/◦
h, k, l
1744
295(2)
5.739
0.260–0.446
1.24–27.47
1
5.741
0.3691–0.4921
1.89–27.50
0.4790–0.6944
2.64–27.50
22, 17, 19
26 721
7918
9, -18–16, -19–21
10 220
3919
10, 11, 20
10 492
4155
19, 13, 18
13 320
4895
11, 18,-23–24
17 428
5242
Reflections collected
Independent
reflections
12 969
4515
Rint
0.0970
7918/3
335
0.0479
4515/1
209
0.0371
3919/0
176
0.0420
4155/0
196
0.0484
4895/1
218
0.0456
5242/0
227
Data/restraints
Parameters
R1 [I > 2s(I)]
wR2 [I > 2s(I)]
R1 (all data)
wR2 (all data)
0.0942
0.2648
0.1728
0.2911
0.0583
0.1458
0.1057
0.1713
1.023
0.698 and -0.549
0.0506
0.1113
0.0680
0.1185
1.092
0.727 and -1.442
0.0451
0.0785
0.0687
0.0853
1.057
0.473 and -0.634
0.0436
0.0974
0.0814
0.1141
0.994
0.585 and -0.465
0.0408
0.1046
0.0649
0.1210
1.025
0.467 and -0.559
Goodness of fit on F2 1.543
Largest diffraction
peak and hole, e A
1.518 and -0.939
-3
˚
for C20H34N2Br2Ni: C 46.11, H 6.58, N 5.38. Found: C 46.33, H
6.47, N 5.11.
Br). UV-vis, lmax/nm (e/M-1 cm-1): 519 (107). Anal. calcd for
C20H32N2Br2Ni: C 46.29, H 6.21, N 5.40. Found: C 45.93, H 6.12,
N 5.20.
n
i
=
[ Pr2NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-3c)
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (100 mg, 0.32 mmol) and L-3c (160 mg, 0.49 mmol)
gave violet Ni-3c in 40% yield (72 mg). MS (FAB, m/z): 413 (M+ -
Br). UV-vis, lmax/nm (e/M-1 cm-1): 515 (22.4). Anal. calcd for
C22H38N2Br2Ni: C 48.13, H 6.98, N 5.10. Found: C 48.78, H 7.51,
N 4.71.
General procedure for polymerization of ethylene
Into a 600 mL Parr autoclave was placed the nickel complexes
(22–42 mg) and MAO (6–8 mL) in dried toluene (100 mL). The au-
toclave was sealed. Upon flushing with ethylene gas several times,
the ethylene gas was pressurized. During the reaction, ethylene
was refilled when the pressure was found to drop. The mixture was
stirred for a period of time. The reaction was quenched by venting
the autoclave followed by the addition of methanol–HCl (4 : 1).
The precipitated polymers were filtered from solution and dried in
vacuo.
In a typical run, to a 600 mL autoclave was placed 22 mg of the
catalyst and 6 mL MAO (10 wt%) in 100 mL of pre-dried toluene.
The thermostated autoclave was sealed and flushed several times
with ethylene. The ethylene was then pressurized up to 17 bar.
According to Henry’s law and the ideal gas law, the reaction was
run with the presence of 6.4 g ethylene in toluene and 9.7 g in the
free space in the reactor.16 The reaction ran for 3 h at 25 ◦C, then
quenched by venting the autoclave. To the solution, was added
methanol–HCl in 4 : 1 v/v ratio. Toluene was used to extract
the organics and methanol or acetone was used to precipitate the
i
=
[(c-C3H6)NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-4c)
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (100 mg, 0.32 mmol) and L-4c (140 mg, 0.49 mmol)
gave violet Ni-4c in 42% yield (48 mg). MS (FAB, m/z): 425.1
(M+ - Br). UV-vis, lmax/nm (e/M-1 cm-1): 517 (15.5). Anal. calcd
for C19H30N2Br2Ni: C 45.19, H 5.99, N 5.55. Found: C 44.37,
H 5.77, N 5.28.
i
=
[(c-C4H8)NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-5c)
Following the same procedure used for Ni-1b, the reaction of
(DME)NiBr2 (100 mg, 0.32 mmol) and L-5c (150 mg, 0.49 mmol)
gave violet Ni-5c in 53% yield (52 mg). MS (FAB, m/z): 413 (M+ -
1248 | Dalton Trans., 2009, 1243–1250
This journal is
The Royal Society of Chemistry 2009
©

◦
˚
Table 4 Selected bond distances (A) and angles ( )
=
[Me2NCMe2CH N(2,6-Me2C6H3)]NiBr2 (Ni-1b)
Ni–N1
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
2.001(8)
1.250(12)
1.507(13)
81.9(3)
107.8(6)
113.6(6)
Ni–N2
N2–C2
N2–C6
Br1–Ni–Br2
N1–C1–C2
C6–N2–Ni
2.050(8)
1.5000(13)
1.484(13)
116.80(7)
122.7(9)
106.1(6)
Ni–Br1
C1–C2
2.3408(18)
1.503(13)
Ni–Br2
N1–C21
2.3405(18)
1.455(12)
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
112.5(7)
105.6(8)
125.3(6)
i
=
[Me2NCMe2CH N(2,6- Pr2C6H3)]NiBr2 (Ni-1c)
Ni–N1
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
2.011(5)
1.267(8)
1.507(11)
81.7(2)
108.3(5)
112.5(6)
Ni–N2
N2–C2
N2–C6
Br1–Ni–Br2
N1–C1–C2
C6–N2–Ni
2.061(6)
1.463(11)
1.550(13)
118.20(6)
122.8(6)
105.9(5)
Ni–Br1
C1–C2
2.3290(13)
1.492(10)
Ni–Br2
N1–C21
2.3521(17)
1.439(8)
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
111.5(4)
106.6(5)
128.1(3)
=
[Et2NCMe2CH NPh]NiBr2 (Ni-2a)
Ni–N1
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
1.997(4)
1.263(6)
1.505(5)
82.41 (15)
106.0 (3)
108.1(3)
Ni–N2
N2–C2
N2–C6
Br1–Ni–Br2
N1–C1–C2
C6–N2–Ni
2.058(4)
Ni–Br1
C1–C2
2.3535(7)
1.508(7)
Ni–Br2
N1–C21
2.3772(7)
1.434(6)
1.530(5)
1.500(6)
123.61(3)
119.5(4)
111.0(3)
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
114.5(3)
106.7(3)
123.7(3)
=
[Et2NCMe2CH N(2,6-Me2C6H3)]NiBr2 (Ni-2b)
Ni–N1
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
1.991(3)
1.270(4)
1.504(5)
82.66 (11)
103.34 (19)
106.7(2)
Ni–N2
N2–C2
N2–C6
Br1–Ni–Br2
N1–C1–C2
C6–N2–Ni
2.080(3)
1.537(5)
1.499(4)
118.33(2)
120.9(3)
109.5(2)
Ni–Br1
C1–C2
2.3666(6)
1.516(5)
Ni–Br2
N1–C21
2.3514(6)
1.449(4)
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
112.3(2)
105.8(3)
127.7(2)
i
=
[(c-C3H6)NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-4c)
Ni–N1
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
2.002(3)
1.276(6)
1.517(7)
82.20(16)
107.8(3)
115.4(3)
Ni–N2
N2–C2
N2–C7
Br1–Ni–Br2
N1–C1–C2
C7–N2–Ni
2.049(4)
1.501(7)
1.504(8)
116.14(4)
121.6(4)
108.2(4)
Ni–Br1
C1–C2
2.3591(10)
1.494(7)
Ni–Br2
N1–C21
2.3307(10)
1.443(6)
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
112.6(3)
106.6(4)
128.2(3)
i
=
[(c-C4H8)NCMe2C N(2,6- Pr2C6H3)]NiBr2 (Ni-5c)
Ni–N1
N1–C1
N2–C5
N1–Ni–N2
Ni–N2–C2
C5–N2–Ni
1.996(2)
1.264(4)
1.500(5)
83.30(11)
106.2(2)
104.4(2)
Ni–N2
N2–C2
N2–C6
Br1–Ni–Br2
N1–C1–C2
C6–N2–Ni
2.076(3)
1.513(4)
1.501(4)
117.02(2)
122.3(3)
115.6(2)
Ni–Br1
C1–C2
2.3368(6)
1.504(5)
Ni–Br2
N1–C21
2.3307(6)
1.441(4)
Ni–N1–C1
N2–C2–C1
C21–N1–Ni
112.5(2)
107.4(3)
128.6(2)
PE. The GPC analysis was done to the soluble part in toluene
solutions, relative to polystyrene standards.
All the non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were identified by calculation and refined using a
riding mode, and their contributions to structure factors were
included. Atomic scattering factors were taken from the Inter-
national Tables of Crystallographic Data, vol. IV.17 Computing
programs are from the NRC VAX package. Crystallographic data
and selected atomic coordinates and bond parameters are collected
in Tables 3 and 4. One molecule of the asymmetric unit of Ni-
1b shows disorder in the amino moiety that has been refined
with restrains. The prime labelled atoms account for 50% of
occupancies. The rest of data are supplied in the supplementary
material.†
X-Ray crystallographic analysis
The diffraction data were measured on a Nonius CAD-4,
SmartCCD or Nonius KappaCCD diffractometer with graphite-
˚
monochromatized MoKa radiation (l = 0.7103 A). No significant
decay was observed during the data collection. The structures were
solved using the direct method and refined by full-matrix least-
squares on the F2 value.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1243–1250 | 1249
©

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Computational details
All geometries were accomplished with QM optimization by
means of the gradient techniques of Becke’s three parameter hybrid
functional incorporating the Lee–Yang–Parr correlation func-
tional (BLYP) with VWN (Vosko, Wilk, and Nusair parameter-
ization) local density approximation implemented in ADF(ADF
2000.02 and ADF 2004.01). The electronic configurations of the
molecular systems were treated by a triple-x STOs basis set with
the 2p frozen core on Nickel; double-x STOs basis set with the 1s
frozen core on nitrogen and carbon with a 3d single polarization
function, and double-x STOs basis set on hydrogen with a 2p
polarization function. The results of both (L-1b)Ni(C2H4)(nPr)
and (L-2b)Ni(C2H4)(nPr) show that the trans forms are 2.17 and
21.07 kJ mol-1 more stable than the cis forms, respectively.
Acknowledgements
We thank the National Science Council, Taiwan ROC,
NWO/NSC project for the financial support and thank Nan-Ya
Plastic Co. for the generous supply of MAO.
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1250 | Dalton Trans., 2009, 1243–1250
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