Synthesis, molecular structure and norbornene polymerization behavior of three-coordinate nickel(I) complexes with chelating anilido-imine ligands

Article abstract of DOI:10.1039/b516203c

Reaction of lithium salts of anilido-imine ligands bearing bulky substituentes on the nitrogen donor atoms with trans-chloro(phenyl) bis(triphenylphosphane)nickel(ii) results in the formation of two rare three-coordinate nickel(i) complexes [(Ar₁

Full text of DOI:10.1039/b516203c

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www.rsc.org/dalton | Dalton Transactions
Synthesis, molecular structure and norbornene polymerization behavior of
three-coordinate nickel(I) complexes with chelating anilido-imine ligands
Hai-Yu Wang, Xia Meng and Guo-Xin Jin*
Received 15th November 2005, Accepted 20th February 2006
First published as an Advance Article on the web 7th March 2006
DOI: 10.1039/b516203c
Reaction of lithium salts of anilido-imine ligands bearing bulky substituentes on the nitrogen donor
atoms with trans-chloro(phenyl)bis(triphenylphosphane)nickel(II) results in the formation of two rare
=
three-coordinate nickel(I) complexes [(Ar1N CHC6H4NAr2)Ni(I)PPh3] (1: Ar1 = Ar2 = 2,6-i-Pr2C6H3;
2: Ar1 = 2,6-Me2C6H3, Ar2 = 2,6-i-Pr2C6H3). The molecular structures of complexes 1 and 2 have been
confirmed by single crystal X-ray analyses. These two complexes exhibit paramagnetic properties as
measured by their EPR and 1H NMR spectra. After being activated with methylaluminoxane (MAO)
these complexes could polymerize norbornene to afford addition-type polynorbornene (PNB) with high
molecular weight Mw (106 g mol−1), catalytic activities being high, up to 2.82 × 107 gPNB mol−1 h−1.
Ni
Janiak and Lassahn11 gave an overall review on the addition
Introduction
polymerization of norbornene using various metal complexes
as catalysts, including early transition metals (zirconium and
titanium), and late transition metals (palladium and nickel).11
After Deming and Novak introduced the first nickel complex
for the addition polymerization of norbornene,12 several other
catalyst systems13,14e,g have also been applied to this polymerization
reaction.
Three-coordinate complexes of the transition metals with non-d10
electron configuration are generally believed to be rare,1 because it
is difficult with only three ligand donors to reach the preferred
configurations with 16 or 18 electrons in the metal bonding
and nonbonding orbitals.2 In all solution-phase three-coordinate
transition metal complexes, the metal center is protected with
extremely bulky ligands. In the past decade bulky aryl-substituted
b-diketiminate ligands (I) have experienced a renaissance, in part
for their ability to stabilize low-coordinate main group and late
transition metal complexes.3 A chelating anilido-imine ligand (III)
has recently attracted increasing attention because it combines
the steric and electronic features of the b-diketiminate and
salicylaldiminato (II) ligand frameworks. In 2003, Piers et al.4 first
reported organoyttrium complexes with a chelating anilido-imine
donor. Subsequently, the groups of Wu and Mu5,6 synthesized
nickel and aluminium complexes bearing ligand III, respectively.
However, the isolable low-coordinate nickel(I) complexes with
bulky anilido-imine donors were unknown prior to our work.2,7,14e
During the past few years, we have designed and synthesized
several series of nickel catalysts supported by [N,O], [N,N]
and [N,P] ligands,14 including self-immobilized neutral nickel
catalysts and binuclear 2,5-disubstituted amino-p-benzoquinone
nickel complexes. The present contribution describes the synthesis
and structure of two rare three-coordinate nickel(I) complexes
with chelating anilido-imine ligands. More importantly, we show
that these electronically unsaturated organometallic complexes are
stable in the solid state and display good catalytic activity towards
norbornene polymerization upon activation with methylalumi-
noxane (MAO). Moreover, the catalytic activity of the addition
polymerization of norbornene is up to 107 gPNB mol−1 h−1.
Ni
Results and discussion
Synthesis of nickel complexes
The syntheses of the nickel complexes as catalytic precursors
are shown in Scheme 1. The free ligands L1–L3 were prepared
according to a literature procedure.4 It was noteworthy that the
steric bulkiness of the ligands could be easily adjusted by changing
various arylamines. These two ligands were characterized by H
NMR and IR spectroscopy. The NH resonances characteristically
Late transition metal catalysts for olefin polymerization have
received increasing attraction in the academic and industrial
fields over the past decades, for they are much less oxophilic
and more tolerant of polar functional groups than the catalysts
ordinarily used.8 Among these numerous catalysts, interest in
nickel-based catalytic systems has been on the rise stimulated in
part by the discovery of a-diimine-based cationic nickel catalysts,9
especially single-component neutral nickel catalysts.10 In 2001,
1
appear at low field (d ca 10.5). The infrared absorption bands of
−1
=
the imine C N stretch occur in the region 1621–1623 cm .
After the anilido-imine ligands (L1 and L2) were treated with
n-BuLi in THF, 0.96 equiv. of trans-chloro(phenyl)bis(tripheny-
lphosphane)nickel(II) was added to give a dark red solution and
nickel(I) complexes 1 and 2 as red prismatic crystals were obtained
in high yields by recrystallizing from a solution of THF/n-
hexane. The reaction was quite clean and no corresponding
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials,
Department of Chemistry, Fudan University, Shanghai, 200 433, China
E-mail: gxjin@fudan.edu.cn; Fax: +86-21-65641740; Tel: +86-21-
65643776
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Scheme 1 Synthesis of nickel complexes 1 and 2.
=
four-coordinate Ni(II) complexes [(Ar1N CHC6H4NAr2)Ni(Ph)-
=
(PPh3)] or [(Ar1N CHC6H4NAr2)2Ni] were isolated. Meanwhile,
biphenyl was formed in the reaction solution and could be
monitored by GC-MS. Hence it was speculated that phenyl
radicals were the product of phenyl oxidation by nickel. The
complexes were well characterized by EPR, IR spectroscopy as
well as elemental analysis. The spectroscopic properties of 1 and
2 are consistent with the d9 electronic configuration. Complexes
have only broad peaks in their 1H NMR spectrum, and their EPR
spectra both show a slightly rhombic signal, as shown in Fig. 1 and
2. However, there exist great differences between the EPR signals
of these two complexes, indicating that the microenvironment of
the ligands greatly influences the spectroscopic properties of the
Fig. 2 EPR spectrum of complex 2.
complexes. The IR spectra of these complexes show absorption
−1
=
bands of the imine C N at 1606–1608 cm , which are obviously
In order to compare the steric influence of substituted groups
on the 2,6-positions of phenyl in anilido-imine ligands, the ligand
L3 with phenyl substituents on two nitrogen atoms was used as
ligand and reacted with trans-[Ni(PPh3)2(Ph)Cl]. In the process
of complex preparation, it was difficult to obtain pure nickel
complexes because of the very similar solubility of the nickel
complexes and triphenylphosphine (PPh3). By repeated attempts,
product 3 (L3)2Ni (ca 5% yield, Scheme 2) was isolated by
recrystallization from hexane solution at −20 ◦C.
blue shifted in comparison with the free ligands.
Fig. 1 EPR spectrum of complex 1.
Scheme 2 Synthesis of nickel complex 3.
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Structure analysis
Single crystals of complexes 1 and 2 suitable for X-ray crystal
structure determination were obtained by recrystallization from
THF/n-hexane solution at −5 ◦C for 3 days. The ORTEP diagrams
of the molecular structures of these two complexes are respectively
shown in Fig. 3 and 4 with selected bond lengths and angles. These
two complexes both crystallize in the monoclinic space group
P21/n. Molecular structure analysis reveals that the nickel center
exhibits a rare trigonal planar geometry with two nitrogen atoms
of the anilido-imine ligand and one triphenylphosphane group,
and the metal (Ni) deviates from the [N(1), N(2) and P(1)] plane
˚
˚
by ca 0.0436 A for 1 and ca 0.0396 A for 2, respectively. The
N1–C1–C6–C7–N2 atoms are almost located in a plane (mean
˚
˚
deviation 0.0180 A for 1, 0.0083 A for 2), and this plane is nearly
coplanar with the N1–N2–P1 chelating plane (bite angle between
two planes, 8.5◦ for 1 and 6.9◦ for 2). The distances between Ni and
the atoms bonding with it in 1 are slightly longer than those in 2.
The N(2)–Ni(1)–P(1) angle of 1 [118.08(13)◦] is wider than that in 2
[112.97(6)◦], with the other two angles at the metal center narrower
than those found in 2. In short, the above mentioned differences
in structure between 1 and 2 can be attributed to different steric
congestion, which is caused by the replacement of the bulkier 2,6-
diisopropylbenzene on the nitrogen atom of the imino in ligand
L1 by 2,6-dimethylbenzene in L2.
Fig. 4 Structure of complex 2 (thermal ellipsoids are d◦rawn at the 30%
˚
probability level). Selected bond lengths [A] and angles [ ]: Ni(1)–N(1) =
1.899(2), Ni(1)–N(2) = 1.933(2), Ni(1)–P(1) = 2.2096(9), N(1)–C(1) =
1.344(3), C(1)–C(6) = 1.433(3), C(6)–C(7) = 1.426(3), N(2)–C(7) =
1.298(3); N(1)–Ni(1)–N(2) = 95.27(8), N(1)–Ni(1)–P(1) = 151.49(6),
N(2)–Ni(1)–P(1) = 112.97(6), C(7)–N(2)–Ni(1) = 123.07(16), C(8)–N(2)–
Ni(1) = 121.61(16), C(7)–N(2)–C(8) = 115.3(2), C(1)–N(1)–Ni(1) =
127.67(15), C(16)–N(1)–Ni(1)
118.60(19).
=
113.72(14), C(1)–N(1)–C(16)
=
˚
A for 1 and 2, respectively. In addition, the bond lengths of Ni–N
˚
˚
(1.908(4)–1.970(4) A in 1, 1.899(2)–1.933(2) A in 2) in these two
complexes are longer than the values previously reported for [((2,6-
14e
˚
=
i-Pr2(C6H3)N C(CH3))2CH)Ni(I)(PPh3)] (1.889(3)–1.911(3) A)
=
and [((2,6-i-Pr2(C6H3)N C(t-Bu))2CH)Ni(I)(THF)] (1.876(1)–
1.882(1) A), and the Ni–P bond length (2.233(2)A in 1 and
2
˚
˚
˚
2.2096(9) A in 2) is also slightly longer than the value of complexes
in the literature.14e However, the N–Ni–N angle of these complexes
(94.56(17)◦ for 1, 95.27(8)◦ for 2) is narrower than 96.77(14) of
14e
=
[((2,6-i-Pr2(C6H3)N C(CH3))2CH)Ni(I)(PPh3)]
and 100.46(6)
2
=
of [((2,6-i-Pr2(C6H3)N C(t-Bu))2CH)Ni(I)(THF)]. When com-
paring complex 2 with the nickel(II) complex bearing the
same ligand framework, we find that the bond length Ni–
˚
˚
N(1) (1.899(2) A) in 2 is longer than that (1.888(2) A) in
5
=
[((Ar1N CHC6H4NAr2)Ni(II)Br)2] (Ar1 = 2,6-Me2C6H3, Ar2 =
=
2,6-i-Pr2C6H3), but the Ni–N(2) (nitrogen atom of imine C N)
˚
˚
bond length (1.933(2) A) in 2 is shorter than that (1.951(2) A)
Fig. 3 Structure of complex 1 (thermal ellipsoids are d◦rawn at the 30%
=
in [((Ar1N CHC6H4NAr2)Ni(II)Br)2]. These data indicate that
the valence of the central metal didn’t remarkably influence its
bonding with nitrogen atoms of the ligands.
˚
probability level). Selected bond lengths [A] and angles [ ]: Ni(1)–N(1) =
1.908(4), Ni(1)–N(2) = 1.970(4), Ni(1)–P(1) = 2.233(2), N(1)–C(1) =
1.345(6), C(1)–C(6) = 1.436(7), C(6)–C(7) = 1.447(8), N(2)–C(7) =
1.274(7); N(1)–Ni(1)–N(2) = 94.56(17), N(1)–Ni(1)–P(1) = 147.08(13),
N(2)–Ni(1)–P(1) = 118.08(13), C(7)–N(2)–Ni(1) = 122.5(3), C(8)–N(2)–
Ni(1) = 122.2(4), C(7)–N(2)–C(8) = 115.2(5), C(1)–N(1)–Ni(1) = 128.0(3),
C(20)–N(1)–Ni(1) = 114.3(3), C(1)–N(1)–C(20) = 117.7(4).
Complex 3 (Fig. 5) also crystallizes in the monoclinic space
group P21/n. Different from the three-coordinate nickel com-
plexes, the metal center of complex 3 exhibits a distorted tetra-
hedral geometry with four nitrogen atoms of two anilido-imine
ligands, and the N1–C7–C12–C13–N2 and N3–C26–C31–C32–
N4 two “planes” are nearly perpendicular (bite angle 99.8◦).
Owing to the structural similarity in anilido-imine ligands with
different substituent groups complex 3 has similar bond length
and angle parameters to complex 1 and 2. For instance, the imino
Unlike b-diketiminato complexes, the anilido-imino complexes
=
1 and 2 are more localized and the imino C N bonds in these com-
plexes retain double bond character, being 1.274(7) and 1.298(3)
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stabilized.2,3 Therefore, it is likely that bulkier substituents on
the donor atoms in b-diketiminate and anilido-imine ligands
than salicylaldiminato ligands lead to the formation of three-
coordinate, instead of four-coordinate, complexes. It has been
reported that attempted alkylation induced the reduction of
Ni(II) complexes to Ni(I).2 X-Ray analysis also clearly shows that
reduction occurred to give a nickel(I) complex with PPh3 as the
second ligand. Support for the nickel(I) oxidation state comes
from the EPR spectra of 1 (Fig. 1) and 2 (Fig. 2) in the solid
state. In addition, these two complexes are stable over a period of
3 days exposure to air in the solid state. An investigation on the
mechanism of reduction will require further study.
Addition polymerization of norbornene
Preliminary experiments showed that complexes 1 and 2 were not
able to catalyze ethylene polymerization with or without methy-
laluminoxane (MAO) as cocatalyst at high pressures of ethylene.
However, these two catalytic precursors could polymerize nor-
bornene to afford addition-type polynorbornene (PNB) after be-
Fig. 5 Structure of complex 3 (thermal ellipsoids are drawn at the
ing activated with MAO, with high activities (107 gPNB mol−1 h−1)
Ni
30% probability level). Selected bond lengths [A] and angles [◦]:
˚
and high molecular weight Mw (106 g mol−1).
Ni(1)–N(3)
=
1.9141(19), Ni(1)–N(1)
=
1.9196(19), Ni(1)–N(4)
=
The norbornene polymerization results are collected in Table 1.
In no case has PNB been obtained using 1 or 2 in the absence
of MAO, whilst the use of up to 5000 equivalents of MAO in the
absence of any nickel species, under the polymerization conditions
employed here, afforded only negligible polymer. Therefore MAO
was essential for the polymerization catalyzed by 1 or 2. Varying
the MAO : complex 1 ratio (expressed here as Al : Ni ratio) has
considerable effects on catalytic activity and Mw.13k When Al :
Ni = 1000 (entry 1, Table 1), the obtained polymer is negligible;
1.960(2), Ni(1)–N(2) = 1.965(2), N(1)–C(7) = 1.353(3), C(7)–C(12) =
1.423(3), C(12)–C(13) = 1.421(3), N(2)–C(13) = 1.302(3), N(3)–C(26) =
1.354(3), C(26)–C(31) = 1.423(3), C(31)–C(32) = 1.418(3), N(4)–C(32) =
1.300(3); N(3)–Ni(1)–N(1) = 117.27(8), N(3)–Ni(1)–N(4) = 93.24(9),
N(1)–Ni(1)–N(4) = 130.39(8), N(3)–Ni(1)–N(2) = 118.52(8), N(1)–Ni(1)–
N(2) = 94.81(8), N(4)–Ni(1)–N(2) = 103.96(8).
=
C N bonds of complex 3 still retain double bond character, being
1.302(3) and 1.300(3) A.
˚
Interestingly, the reaction of salicylaldiminato ligands with
trans-[Ni(PPh3)2(Ph)Cl] results in the formation of four-
coordinate salicylaldimine nickel(II) complexes.10a,b However, when
the b-diketiminate14e and anilido-imine ligands bearing 2,6-
diisopropylbenzene on the nitrogen atoms react with nickel com-
plex trans-[Ni(PPh3)2(Ph)Cl], three-coordinate nickel(I) complexes
are obtained. As we know that the b-diketiminate ligands have
emerged as one of the most versatile ligand families in coordination
chemistry,15 anilido-imine ligands are similar to them in their
steric and electronic properties. In particular, the use of bulky
substituents on the nitrogen donor atoms of the b-diketiminate
ligands has allowed low coordination metal complexes to be
but the activity of 1 is up to 107 gPNB mol−1 h−1 when Al : Ni >
Ni
2000. Moreover, the activity of complex 1 always increases with
increasing Al : Ni ratio and herein we do other polymerization
reactions at Al : Ni = 5000. The Mw of polymers likewise
exhibits remarkable changes with Al : Ni, and is highest at Al :
Ni = 5000. The reaction temperature also affects considerably
the catalytic activities and Mw (entries 5 and 7–9, Table 1).
With increasing reaction temperature, the catalytic activities first
increase and then decrease—the highest activity is at 60 ◦C (2.71 ×
107 gPNB mol−1 h−1). In contrast, Mw decreases with increasing
Ni
temperature while Mw/Mn varies irregularly. Comparing entries
5 and 10 in Table 1, we found that complex 1 displayed lower
Table 1 Addition polymerization of norbornene with nickel(I) complexes 1 and 2 activated by methylaluminoxane(MAO)a
T/◦C
Al/Ni
Polymer/g
Activityb
Mw
Mw/Mn
c
c
Entry
Complex
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
2
30
30
30
30
30
30
0
60
90
30
1000
2000
3000
4000
5000
10000
5000
5000
5000
5000
Trace
0.408
0.574
0.788
0.865
0.940
0.788
0.902
0.595
0.941
—
1.22
1.72
2.36
2.60
2.82
2.36
2.71
1.79
2.82
2.09
2.34
2.39
2.72
2.62
3.05
1.87
1.31
2.00
4.2
3.8
4.0
7.0
3.4
2.9
2.7
3.5
2.6
10
a Polymerization conditions: solvent, chlorobenzene; total volume, 10 mL; nickel complex, 0.2 lmol; norbornene, 1.88 g [norbornene/nickel(molar) =
100 000]; reaction time, 10 min. b 107 gPNB mol−1 h−1 c Mw (106 g mol−1) and Mw/Mn values were determined by GPC.
.
Ni
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catalytic activity than complex 2. Plausible reasons could be
attributed to bulkier hindrance in complex 1 than 2, which made
more difficult the insertion of norbornene into the Ni–C bond.13g,i
age molecular weight (Mw) and molecular weight distribution
(Mw/Mn) values of PNB products were determined using a
PL GPC-220 gel permeation chromatograph at 150 ◦C using a
narrow standards calibration and equipped with three PL gel
columns (sets of PL gel 10 m MIXED-B LS). Trichlorobenzene
was employed as a solvent at a flow rate of 1.00 mL min−1.
Differential scanning calorimetric (DSC) measurements were
performed with a PerkinElmer Pyris 1 DSC. The X-ray diffraction
(XRD) diagram of the polymer powder was obtained using a
Bruker D4 Endeavor X-ray diffractometer with monochromatic
1
The polymers obtained were characterized by IR, H NMR,
1
DSC and XRD analyses. All IR spectra and H NMR spectra
were similar and characteristic of the addition-type PNB, and
revealed no traces of double bonds which are typical for ROMP
(ring-opening metathesis polymerization) PNB.16,13i Our attempts
to determine the glass transition temperature (Tg) of PNB failed,
and the DSC studies did not give an endothermic signal upon
heating to the decomposition temperature (above 450 ◦C).
Fig. 6 shows the XRD spectra of the obtained PNB. The
spectra display two broad halos at 2h of ca 10 and 18◦ that can
be regarded as a reflection of the interchain/intersegment and
intrachain distance of PNB. This is mostly consistent with the
results reported by our and other groups.14g,17 No traces of Bragg
refractions are revealed at crystalline regions. Therefore the PNB
obtained here is non-crystalline.
˚
radiation at a wavelength of 1.54 A. Scanning was performed with
2h ranging from 5 to 70◦.
Syntheses
Synthesis of complex 1. To a stirred solution of ligand L1
(0.486 g, 1.1 mmol) in THF (15 mL) at −78 ◦C was added a
2.82 M n-BuLi hexane solution (0.43 mL, 1.21 mmol) dropwise
over a 3 min period. The mixture was allowed to warm to room
temperature and stirred for 3 h. The resultant mixture containing
the lithium salt of L1 was slowly channeled to a 50 mL flask with
0.736 g of trans-[Ni(PPh3)2(Ph)Cl] (1.06 mmol) in 10 mL of THF
and continuously stirred overnight at room temperature. After
the dark red solution was concentrated to about 3 mL, 20 mL of
hexane was added and after filtering the resulting solution was kept
at −5 ◦C for 3 days to isolate red crystals of 1 (0.361 g). Isolating
the crystals and subsequent partial removal of the solvent from
the mother liquor afforded an additional crop of 1 (0.121 g) at
−20 ◦C for a week. Yield 0.482 g (59.8%). IR (KBr): 3055(m),
2960(s), 2925(m), 2865(m), 1606(s), 1580(m), 1520(m), 1483(w),
1463(m), 1437(s), 1343(m), 1255(w), 1197(s), 1157(m), 1119(s),
1071(w), 1028(w), 997(w), 922(w), 789(w), 747(s), 721(s), 694(s),
1
542(s) cm−1. No clearly discernable signals were seen in the H
NMR spectrum. Anal. Calcd for C49H54PN2Ni (760.62): C, 77.38,
H, 7.16, N, 3.68. Found: C, 77.08, H, 7.28, N, 3.65%. EPR (9.4450
GHz, 293 K): g = 2.36, 2.22, 2.14, 2.10, 2.05, 1.97.
Fig. 6 XRD diagram of PNB.
Synthesis of complex 2. In a procedure similar to that for the
preparation of 1, the resulting dark red solution was kept at −5 ◦C
for 3 days to isolate red crystals of 2 (0.231 g). After concentration
Experimental
General considerations
◦
of the filtrate to ca 10 mL, the solution was kept at −20 C for
All manipulations of air- and/or water-sensitive compounds were
carried out under dry nitrogen using standard Schlenk and
vacuum-line techniques. Solvents were dried by refluxing with
appropriate drying agents and distilled under nitrogen prior to
use. Ligands L4 and trans-[Ni(PPh3)2(Ph)Cl]18 were prepared ac-
cording to literature procedures. Norbornene (bicyclo[2.2.1]hept-
2-ene, Acros) was purified by distillation over sodium and used
as a chlorobenzene solution. Methylaluminoxane (MAO) was
purchased from Aldrich as 10% weight of a toluene solution and
used without further purification. 2-Fluorobenzaldehyde (98%)
was purchased from Lancaster. Other commercially available
reagents were purchased and used without purification.
1H NMR spectra were recorded with a Varian Unity-400
spectrometer. Elemental analyses were performed on an Elementar
vario EL III Analyzer. FT-IR analyses were detected with a
Nicolet-FT-IR-50X spectrometer. NMR data for PNB were
obtained at ambient temperature on Bruker AC 500 spectrometer
instrument using o-chlorobenzene-d4 as solvent. EPR spectra
were recorded with a Bruker ER200D-SRC spectrometer. Aver-
a week. An additional crop of 2 (0.186 g) was obtained. Yield
0.417 g (61.5%). IR (KBr): 3055(w), 2960(m), 2925(w), 2865(w),
1608(s), 1580(m), 1519(m), 1465(m), 1435(s), 1378(w), 1343(m),
1210(w), 1179(m), 1159(m), 1119(m), 1094(w), 1028(w), 997(w),
922(w), 801(w), 745(s), 722(m), 696(s), 541(s) cm−1. No clearly
1
discernable signals were seen in the H NMR spectrum. Anal.
Calcd for C45H46PN2Ni (704.52): C, 76.72, H, 6.58, N, 3.98. Found:
C, 76.45, H, 6.52, N, 3.86%. EPR (9.4430 GHz, 293 K): g = 2.30,
2.22, 2.12, 2.05.
Synthesis of complex 3. In a procedure similar to that for
the preparation of 1, only a few red crystals of 3 were obtained
after the resulting dark red n-hexane solution was kept at −5 ◦C
for 3 days. Yield 0.030 g (5.0%). About 10 mL of concentrated
filtrate was kept at −20 ◦C for a week, and a lot of solid was
separated out, but the mixture of nickel complexes and PPh3
could not be successfully separated. IR (KBr): 3056(w), 1607(s),
1573(s), 1524(m), 1487(m), 1463(m), 1431(s), 1384(w), 1340(m),
1266(w), 1226(w), 1206(w), 1180(m), 1161(s), 1132(w), 1037(w),
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Table 2 Crystal data and structural refinement details for 1, 2 and 3
Formula
C49H54N2NiP
C45H46N2NiP
C38H30N4Ni
M
760.62
Monoclinic
P21/n
10.695(3)
23.306(6)
17.182(4)
4259.5(18)
90
95.975(4)
90
4
Red
704.52
Monoclinic
P21/n
12.006(5)
17.966(7)
18.475(7)
3886(3)
90
102.793(5)
90
4
Red
601.37
Monoclinic
P21/n
11.050(3)
19.819(5)
13.814(3)
3024.9(12)
90
Crystal system
Space group
˚
˚
˚
a/A
b/A
c/A
3
˚
V/A
a/◦
b/◦
c /◦
Z
91.116(4)
90
4
Color
Red
Crystal size/mm
0.10 × 0.15 × 0.25
0.20 × 0.15 × 0.10
0.30 × 0.10 × 0.05
D
calcd/g cm−3
1.186
1.204
1.320
l/mm−1
0.527
1.48/25.01
1620
0.573
1.85/25.01
1492
0.675
1.80/27.12
1256
h limits/◦
F (000)
No. of obsd reflns
No. of params refnd
Final R indices [I > 2r(I)]a
R indices (all data)
7479 (Rint = 0.0513)
6851 (Rint = 0.0238)
6629 (Rint = 0.0429)
486
448
388
R1 = 0.0883,wR2 = 0.2292
R1 = 0.1343,wR2 = 0.2658
1.007
R1 = 0.0421,wR2 = 0.1076
R1 = 0.0587,wR2 = 0.1182
1.030
R1 = 0.0436,wR2 = 0.0670
R1 = 0.0989,wR2 = 0.0774
0.799
b
GOF on F2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
a R1 = ꢀFo| − |Fcꢀ/ |Fo|; wR2 = [ w(|Fo2| − |Fc2|)2/ w|Fo2|2]1/2
.
b S = [ (w(Fo − Fc2))2]/(n − p)1/2
.
1
970(w), 851(w), 747(m), 722(m), 695(s), 543(m) cm−1. H NMR
vacuum. For all polymerization procedures, the total reaction
volume was 10.0 mL, which can be achieved by varying the
amount of chlorobenzene when necessary. IR (KBr): 2944, 2868,
1474, 1453, 1375, 1294, 1257, 1222, 1189, 1146, 1107, 1040, 942,
891 cm−1. 1H NMR: d 0.9–2.9 (m, maxima at 1.34 1.77 2.11 2.46
ppm).
=
(CDCl3): d = 7.26–7.69 (m, 30H, Ph–H and C NH). Anal. Calcd
for C38H30N4Ni (601.37): C, 75.90, H, 5.03, N, 4.66. Found: C,
76.33, H, 5.52, N, 4.19%.
X-Ray crystallography
For complexes 1, 2 and 3, a single crystal suitable for X-ray analysis
was sealed into a glass capillary, and the intensity data of the
single crystal were collected on the CCD-Bruker Smart APEX
system. All determinations of the unit cell and intensity data
were performed with graphite-monochromated Mo-Ka radiation
Conclusion
Anilido-imine ligands have attracted more and more attention
because of their steric and electronic features. Moreover, these
ligands with bulky substituents on the nitrogen atoms can be
conveniently prepared and their steric protection can stabilize elec-
tronically unsaturated low-coordinate metal complexes. Therefore
it is possible to synthesize some rare three-coordinate nickel(I)
complexes in the presence of anilido-imine ligands bearing bulky
substitute groups. Herein, we have successfully synthesized two
rare, three-coordinate nickel(I) complexes bearing a chelating
anilido-imine ligand and examined their catalytic behavior for the
addition polymerization of norbornene with MAO as cocatalysts.
The molecular structures of complex 1 and 2 were characterized
by single crystal X-ray diffraction in the solid state. These two
complexes exhibited paramagnetic properties as measured by their
EPR and 1H NMR spectra. An investigation on the mechanism of
reduction of Ni(II) complexes to Ni(I) will require further study.
˚
(k = 0.71073 A). All data were collected at room temperature
using the x scan technique. These structures were solved by direct
methods, using Fourier techniques, and refined on F2 by a full-
matrix least-squares methods. All the non-hydrogen atoms were
refined anisotropically, and all the hydrogen atoms were included
but not refined. Crystallographic data are summarized in Table 2.
CCDC reference numbers 289503–289505.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b516203c
Polymerization of norbornene
In a typical procedure (entry 5, Table 1), 0.2 lmol of nickel complex
1 in 1.0 mL of chlorobenzene, 1.88 g of norbornene in 3.0 mL of
chlorobenzene and another 3.0 mL fresh chlorobenezene were
added into a special polymerization bottle (20 mL) with a strong
stirrer under a nitrogen atmosphere. After the mixture was kept
at 30 ◦C for 10 min, 0.66 mL of MAO was charged into the
polymerization system via syringe and the reaction was initiated.
Ten minutes later, acidic ethanol (Vethanol : Vconcd.HCl = 20 : 1)
was added to terminate the reaction. The PNB was isolated by
filtration, washed with ethanol and dried at 80 ◦C for 48 h under
Acknowledgements
Financial support by the National Science Foundation of China
for Distinguished Young Scholars (20421303, 20531020) and by
the National Basic Research Program of China (2005CB623800)
is gratefully acknowledged.
2584 | Dalton Trans., 2006, 2579–2585
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