Synthesis, molecular structures, and norbornene addition polymerization activity of the neutral nickel catalysts supported by β-diketiminato [N, N], ketiminato [N, O], and schiff-base [N, O] ligands

Article abstract of DOI:10.1021/om0499658

A series of neutral nickel complexes [Ni(Ph)(PPh₃)(N, O)] with Schiff-base ligands (N, O) [N, O = 5-Me-3-tert-Bu-(Ar-N=CH)C₆H ₂O (1, Ar = 2,6-Me₂C₆H₃; 2, Ar = 2,6-i-Pr₂C₆H₃)], [Ni(Ph)(PPh ₃)(N,O)], with β-ketiminato ligands (N, O) [N, O = CH ₃COCHC=(CH₃)N-Ar (3, Ar = 2,6-Me₂C ₆H₃; 4, Ar = 2,6-i-Pr₂C₆H ₃)] and [Ni(N, N)(PPh₃)], and with β-diketiminato ligands (N, N) [5, N, N = [2,6-i-Pr₂(C₆H ₃)N=C(CH₃)]₂CH] have been synthesized and characterized. The molecular structures of complexes 1, 4, and 5 have been confirmed by X-ray single-crystal analyses. Although their ligands have similar structures, complex 4 possesses a structure similar to that of four-coordination nickel with complex 1, while complex 5 reveals a rare three-coordination nickel geometry. These compounds show high catalytic activities of up to 3.16 × 10⁷ g PNB mol^-1 Ni h^-1 for the addition polymerization of norbornene in the presence of modified methylaluminoxane (MMAO) as cocatalyst. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polyborbornene have been investigated under various reaction conditions.

Full text of DOI:10.1021/om0499658

3270
Organometallics 2004, 23, 3270-3275
Syn th esis, Molecu la r Str u ctu r es, a n d Nor bor n en e
Ad d ition P olym er iza tion Activity of th e Neu tr a l Nick el
Ca ta lysts Su p p or ted by â-Dik etim in a to [N, N],
Ketim in a to [N, O], a n d Sch iff-Ba se [N, O] Liga n d s
Dao Zhang,‡ Guo-Xin J in,*,†,‡ Lin-Hong Weng,† and Fusong Wang†
Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry,
Fudan University, Shanghai, 200 433, China, and State Key Laboratory of Polymer Physics
and Chemistry, Changchun Institute of Applied Chemistry, The Chinese Academy of Sciences,
Changchun 130 022, China
Received J anuary 13, 2004
A series of neutral nickel complexes [Ni(Ph)(PPh3)(N, O)] with Schiff-base ligands (N, O)
[N, O ) 5-Me-3-tert-Bu-(Ar-NdCH)C6H2O (1, Ar ) 2,6-Me2C6H3; 2, Ar ) 2,6-i-Pr2C6H3)],
[Ni(Ph)(PPh3)(N,O)], with â-ketiminato ligands (N, O) [N, O ) CH3COCHCd(CH3)N-Ar
(3, Ar ) 2,6-Me2C6H3; 4, Ar ) 2,6-i-Pr2C6H3)] and [Ni(N, N)(PPh3)], and with â-diketiminato
ligands (N, N) [5, N, N ) [2,6-i-Pr2(C6H3)NdC(CH3)]2CH] have been synthesized and
characterized. The molecular structures of complexes 1, 4, and 5 have been confirmed by
X-ray single-crystal analyses. Although their ligands have similar structures, complex 4
possesses a structure similar to that of four-coordination nickel with complex 1, while complex
5 reveals a rare three-coordination nickel geometry. These compounds show high catalytic
activities of up to 3.16 × 107 g PNB mol-1 Ni h-1 for the addition polymerization of norbornene
in the presence of modified methylaluminoxane (MMAO) as cocatalyst. Catalytic activities,
polymer yield, molecular weights, and molecular weight distributions of polyborbornene have
been investigated under various reaction conditions.
In tr od u ction
organic solvents, and excellent optical transparency.
However, the addition polymerization is much less
developed for norbornene than ROMP (ring-opening
metathesis polymerization). J aniak et al.4 gave a full
literature and patent account on the work describing
the addition polymerization to homo-polynorbornene.
The olefin polymers of norbornene were obtained with
early transition metals (titanium, zirconium, and chro-
mium) and late transition metals (cobalt, nickel, and
palladium). Deming and Novak introduced the first
nickel complexes for the addition polymerization of
norbornene in 19935 and recently several other catalyst
systems were presented.6
Olefin polymerization based on late transition metal
catalysts has been one of the most exciting develop-
ments in the area of catalysis, organometallic chemistry,
and polymer science in recent years.1 Ni-based catalysts
are best known to oligomerize ethylene and dimerize
propylene and higher R-olefins because nickel metal was
usually thought to generally prefer â-hydride elimina-
tion followed by reductive elimination before 1995.2 Now
a large number of papers and patents published on this
field show the intense exploration and commercializa-
tion of new polymerization technologies in both indus-
trial and academic fields.3
During the past few years most of our effort has
focused on neutral, single-component nickel ethylene-
polymerization catalysts before we began our cyclo-
olefin polymerization study. Several series of nickel
catalysts supported by [N, O] monoanionic and bis-
anionic ligands, including salicylaldiminato phenyl nickel
complexes7 and binuclear 2,5-disubstituted amino-p-
benzoquinone nickel(II) complexes,8 were designed and
synthesized on the basis of recent developments. These
Homo-polymer addition of polynorbornenes are of
considerable interest because of their unique physical
properties, including heat resistivity, good solubility in
Dedicated to Prof. Li-Xin Dai on the occasion of his 80th birthday.
* Corresponding author. E-mail: gxjin@fudan.edu.cn. Fax: +86-21-
65641740. Tel: +86-21-65643776.
† Fudan University.
‡ Changchun Institute of Applied Chemistry, The Chinese Academy
of Sciences.
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Publication on Web 05/19/2004

Neutral Nickel Catalysts
Sch em e 1
Organometallics, Vol. 23, No. 13, 2004 3271
Sch em e 2. Syn th esis of Nick el Com p lexes 1-5
neutral nickel complexes based on anion ligands are
very reactive toward ethylene.
Our goal was to study nickel catalysts supported by
monoanionic ligands whose steric and electronic proper-
ties can be easily modified. Since â-ketiminato and
â-diketiminato ligands with bulky substitutes not only
have stronger π-bonding tendencies to the same acceptor
(Scheme 1) than Schiff-base ligands we have used but
also are able to stabilize metal complexes, we have been
examining some nickel compounds stabilized by these
ligands. Polymerization experiments show that these
nickel complexes are not reactive to ethylene or R-olefins
but display very high cyclo-olefin polymerization activi-
ties. The focus of this article is the synthesis of a series
of neutral nickel(II) complexes bearing Schiff-base
ligands [N, O], â-ketiminato ligands [N, O], and
â-diketiminato [N, N] ligands and the polymerization
of norbornene upon activation with modified methyla-
luminoxane (MMAO) (Scheme 2). Three typical molec-
ular structures of nickel catalysts were characterized
by an X-ray crystallographic study.
of â-diketone and corresponding anilines.9 The â-ke-
toamine ligand L4 continuously reacted with substituted
aniline hydrochloride to afford white â-iminoamine
ligand L5 as reported.10 The obtained organic ligands
were treated with n-BuLi in toluene (NaH in THF for
L1 and L2) and then reacted with trans-chloro(phenyl)
bis(triphenylphosphine) nickel(II) to give their corre-
sponding complexes 1-5. The [N, O] and [N, N] ligands
and corresponding complexes were characterized by 1H
NMR spectra and elemental analyses. Single crystals
of nickel complexes 1, 4, and 5 suitable for X-ray
structure determination were recrystallized from tolu-
ene at lower temperature. The collection data and
refinement data of the analyses are summarized in
Table 1. The ORTEP diagrams are shown in Figures 1,
2 and 3.
As depicted in Figure 1, complex 1 has a crystal
structure similar to the analogue complexes we previ-
ously reported.4 Complex 1 contains a chelating [N, O]
ligand, a triphenylphosphine group (PPh3), and a phenyl
group. The bulky [2,6-Me2(C6H3)-N] moiety occupies the
position trans to PPh3 with a nearly linear N(1)-Ni-
(1)-P(4) angle (177.67°), and the phenyl group bonded
to Ni(1) also lies in a position trans to O(1) with an
Resu lts a n d Discu ssion
The syntheses of the nickel complexes as catalytic
precursors are shown in Scheme 2. The ligands of
salicylaldimines, L1 and L2, were synthesized as yellow
oils via the condensation reaction of salicylaldehydes
and anilines in good yield as we previously reported.7
The â-ketoamine ligands L3 and L4 were also efficiently
obtained as white solids by the condensation reaction
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Wheeler, L. M. J . Polym. Sci., Part A: Polym. Chem. 2003, 41, 2095-
2106. (b) Li, X.-F.; Li, Y.-S. J . Polym. Sci., Part A: Polym. Chem. 2002,
40, 2680. (c) Yang, H.; Li, Z.; Sun, W.-H. J . Mol. Catal A: Chem. 2003,
206, 23. (d) Mast, C.; Krieger, M.; Dehnicke, K.; Greiner, A. Macromol.
Rapid Commun. 1999, 20, 232. (e) Berchtold, B.; Lozan, V.; Lassahn,
P. G.; J aniak, C. J . Polym. Sci., Part A: Polym. Chem. 2002, 40, 3604.
(f) Sun, W.-H.; Yang, H.; Li, Z.; Li, Y. Organometallics 2003, 22, 3678.
(g) Yang, H.; Sun, W.-H.; Chang, F.; Li, Y. Applied Catal. A 2003, 252,
261. (h) Chang, F.; Zhang, D.; Xu, G.; Yang, H.; Li, J .; Song, H.; Sun,
W.-H. J . Organomet. Chem. 2003, 58, 1152. (i) Lozan, V.; Lassahn,
P.-G.; Zhang, C.; Wu, B.; J aniak, C.; Rheinwald, G.; Lang, Z. Natur-
forsch. B 2003, 58, 1152. (j) Lassahn, P.-G.; Lozan, V.; Timco, G. A.;
Christian, P.; J iniak, C.; Winpenny, R. E. P. J . Catal. 2004, 222, 260.
(k) Benedikt, G. M.; Elce, E.; Goodall, B. L.; Kalamarides, H. A.;
McIntosh, L. H.; Rhodes, L. F.; Selvy, K. T.; Andes, C.; Oyler, K.; Sen,
A.; Macromolecules 2002, 35, 8979. (l) Barnes, D. A.; Benedikt, G. M.;
Goodall, B. L.; Huang, S. S.; Kalamarides, H.A.; Lenhard, S.; Mclntosh,
L. H., III; Selvy, K. T.; Shick, R. A.; Rhodes, L. F. Macromolecules 2003,
36, 2623. (m) Mi, X.; Ma, Z.; Cui, N.; Wang, L.; Ke, Y.; Hu, Y. J . Appl.
Polym. Sci. 2003, 88, 3273.
(9) (a) Parks J , E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408. (b)
Evertt, G. W.; Holm, R. H. J . Am. Chem Soc. 1965, 87, 2117. (c) Evertt,
G W.; Holm, R. H. J . Am. Chem Soc. 1966, 88, 2442.
(10) (a) Feldman, J .; McLain, S. J .; Parthasarathy, A.; Marshall,
W. J .; Calabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(b) Clegg, W.; Cope, E. K.; Edwards, A. J .; Mair, F. S. Inorg. Chem.
1998, 37, 2317.
(7) (a) Zhang, D.; J in, G.-X.; Hu, N. Chem. Commun. 2002, 6, 574.
(b) Zhang, D.; J in, G.-X.; Hu, Ning-Hai. Eur. J . Inorg. Chem. 2003, 8,
1570. (c) Zhang, D.; J in, G.-X. J . Polym. Sci., Part A: Polym. Chem.
2004, 42, 1018.
(8) Zhang, D.; J in, G.-X. Organometallics 2003, 22, 2851.

3272 Organometallics, Vol. 23, No. 13, 2004
Zhang et al.
Ta ble 1. Cr ysta l Da ta a n d Su m m a r y of Da ta Collection a n d Refin em en t Deta il for 1, 4, a n d 5
1
4
5
formula
cryst size (mm)
fw
C44 H44NNiOP
0.40 × 0.30 × 0.30
692.48
C41H44NNiOP
0.45 × 0.25 × 0.20
656.45
C47H56N2NiP
0.20 × 0.15 × 0.10
738.62
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
triclinic
P1h
triclinic
P1h
monoclinic
P2(1)/n
11.9854(15)
20.481(3)
18.536(2)
90
108.381(2)
90
4318.0(10)
4
8.7839(16)
9.7859(18)
22.642(4)
98.765(2)
97.512(3)
103.571(2
1841.5(6)
2
9.252(2)
9.611(2)
21.215(5)
84.184(3)
80.258(3)
69.734(3)
1742.2(7)
2
Z
D
calcd, Mg/m3
1.249
1.251
1.136
radition (λ), Å
2θ range, deg
µ, mm-1
Μï ΚR (0.71073)
1.84 to 50.02
0.604
Μï ΚR (0.71073)
3.90 to 52.02
0.635
Μï ΚR (0.71073)
3.06 to 54.02
0.518
F(000)
732
696
1580
no. of obsd reflns
no. of params refnd
goodness of fit
R1[I > 2σ(I)]
wR2(all data)
6396
439
0.946
0.0416
6667
412
0.882
0.0538
9351
470
0.801
0.0566
0.0955
0.0975
0.1006
F igu r e 2. Molecular structure of complex 4. Selected bond
lengths [Å] and angles [deg]: Ni(1)-C(1) ) 1.881(4), Ni-
(1)-O(1) ) 1.881(3), Ni(1)-N(1) ) 1.951(3), Ni(1)-P(1) )
2.1868(12), C(7)-C(8) ) 1.356(5), C(8)-C(9) ) 1.400(5),
C(7)-C(10) ) 1.506(5), C(9)-C(11) ) 1.513(5), C(1)-Ni-
(1)-O(1) ) 170.69(15), C(1)-Ni(1)-N(1) ) 95.82(14), O(1)-
Ni(1)-N(1) ) 92.78(12), C(1)-Ni(1)-P(1) ) 87.24(12),
O(1)-Ni(1)-P(1) ) 84.12(9), N(1)-Ni(1)-P(1) ) 176.81-
(10).
F igu r e 1. Molecular structure of complex 1. Selected bond
lengths [Å] and angles [deg]: Ni(1)-C(1) ) 1.887(3), Ni-
(1)-O(1) ) 1.9126(18), Ni(1)-N(1) ) 1.920(2), Ni(1)-P(4)
) 2.1731(8), C(1)-Ni(1)-O(1) ) 171.43(10), C(1)-Ni(1)-
N(1) ) 92.62(10), O(1)-Ni(1)-N(1) ) 92.25(8), C(1)-Ni-
(1)-P(4) 85.24(8), O(1)-Ni(1)-P(4) ) 89.75(6).
O(1)-Ni(1)-C(1) angle of 171.43(10)°. The cis angles at
nickel are in the range 85.24-92.62°. Thus the four-
coordinate atoms [P(4), O(1), N(1), and C(1)] have an
almost exactly square-planar geometry with the Ni(1)
approximately 0.03 Å from the plane in complex 1.
Bond length distances in complexes 1 and 4 are not
significant, although they have different steric conges-
tions due to the replacement of tert-butyl and methyl
of the phenyliminophenolato ligand L1 by the methyl
and isopropyl groups of the â-enaminoketonato ligand
L4. The Ni(1)-C(1) and Ni(1)-O(1) bond distances
[1.887(3) and 1.9126(18) Å] in complex 1 are similar to
those found in complex 4 [1.881(4) and 1.881(3) Å,
respectively], and Ni(1)-N(1) and Ni(1)-P(4) bond
lengths [1.920(2), 2.1731(8) Å] are slightly shorter than
those in complex 4 [Ni(1)-N(1) 1.951(3) Å; Ni(1)-P(1)
2.1868(12) Å].
As given in the Experimental Section, after the
ligands L3-L5 were treated with 1 equiv of BuLi in
toluene the mixture was not isolated but continuously
reacted with trans-[chloro(phenyl)bis(triphenylphos-
phine)nickel(II)]. However, the obtained complex 5 no
longer contains a phenyl group like complex 4 described
above under the same reaction conditions. The crystal-
Because of the obvious structural similarity between
â-ketoamine and salicylaldimine, particularly with re-
spect to steric disposition, complex 4 has a molecular
structure (Figure 2) similar to complex 1, although
seemingly there are many differences between the two
kinds of ligands. The four-coordinate atoms [N(1), O(1),
P(1), and C(1)] and the central Ni atom are also almost
in the same planar. The trans N(1)-Ni(1)-P(1) [C(1)-
Ni(1)-O(1)] angle and cis C(1)-Ni(1)-N(1) [C(1)-Ni-
(1)-P(1)] angle are 176.81(10) [170.69(15)]° and 95.82-
(14) [87.24(14)]°. Moreover, the bond lengths of C(7)-
C(8) [1.356(5) Å] and C(8)-C(9) [1.400(5) Å] are shorter
than that of a normal C-C single bond, which suggests
the significant delocalization within the π-system of the
â-enaminoketonato ligand.

Neutral Nickel Catalysts
Organometallics, Vol. 23, No. 13, 2004 3273
Ta ble 2. Ad d ition P olym er iza tion of Nor bor n en e
w ith Nick el Com p lexes 1-5 Activa ted by Mod ified
Meth yla lu m in oxa n e (MMAO)a
c
c
run complex T (°C) yield (%) activityb
Mw
Mw/Mn
1
1
2
2
2
2
2
2
3
4
4
4
4
4
4
5
5
5
5
5
5
5
5
-
30
30
30
0
60
30
30
30
30
30
30
0
60
30
30
30
30
30
30
0
59
49
48
45
50
59
0
54
59
46
37
38
50
53
0
42
35
62
55
52
56
0
3.35
2.75
2.74
2.53
2.84
1.66
0
3.02
1.67
2.60
2.11
2.13
2.80
1.49
0
2.36
1.97
1.75
1.54
2.93
3.16
0
13.56
11.42
15.18
12.66
9.32
2.48
2.39
2.14
2.26
2.58
2.33
2
3d
4
5
6e
12.12
f
7
8
14.23
13.24
12.48
14.99
17.50
10.95
13.40
2.40
2.29
2.32
2.53
2.31
2.90
2.59
9g
10
11d
12
13
14e
f
15
16
F igu r e 3. Molecular structure of complex 5. Selected bond
lengths [Å] and angles [deg]: Ni(2)-N(1) ) 1.889(3), Ni-
(2)-N(2) ) 1.911(3), Ni(2)-P(1) ) 2.2044(12), C(1)-N(1)
) 1.324(5), C(3)-N(2) ) 1.331(5), C(1)-C(2) ) 1.392(5),
C(2)-C(3) ) 1.397(5), C(1)-C(4) ) 1.514(5), C(3)-C(5) )
1.520(5); N(1)-Ni(2)-N(2) ) 96.77(14), N(1)-Ni(2)-P(1)
) 142.53(11), N(2)-Ni(2)-P(1) ) 120.60(10).
13.16
13.46
15.22
12.73
18.91
12.54
2.63
3.45
2.32
2.61
2.39
2.67
17d
18g
19e
20
21
60
30
30
22f
23h
0
0
a
lographic analysis shows clearly that reduction occurred
to give a nickel(I) complex with PPh3 as the second
ligand. The X-ray structure of 5 (Figure 3) contains only
a chelating â-diketiminato ligand and a triphenylphos-
phine ligand and reveals rare trigonal-planar coordina-
tion at nickel. The Ni(2)-P(1) distance [2.2044(12) Å]
is slightly longer than that in either complex 1 [2.1731(8)
Å] or 4 [2.1868(12) Å]. Consistent with a lower coordi-
nation number at nickel(I) just reported, the â-diketimi-
nate Ni-N distances (1.889(3)-1.911(3) Å) in 5 are
slightly longer than those in the three-coordinate com-
plexes [2,4,6-Me3NN]NiI(NO)] [1.883(2) and 1.885(2)Å]
{2,4,6-Me3NN ) (2,4,6-Me3(C6H2)NdC(CH3))2CH}11 and
[LNiI(THF)] [1.876(1) and 1.882(1) Å] {L ) (2,6-i-
Pr2(C6H3)NdC(t-Bu))2CH},12 while the N-Ni-N
angle of complex 5 [96.77(14)°] lies in the range of
95.79(10)° of [2,4,6-Me3NN]NiI(NO)]11 and 100.46(6)° of
[[LNiI(THF)].12 However, compared with other three-
coordinate nickel(II) complexes, the Ni-N distances of
complex 5 are much longer than that in [LNiIICl]
[1.81(5) Å] {L ) (2,6-i-Pr2(C6H3)NdC(t-Bu))2CH}12 but
shorter than those in [LMeNiIIN(SiMe3)2] [1.911(2) and
1.953(2) Å] {LMe ) (2,6-i-Pr2(C6H3)NdC(CH3))2CH}.13
It has been reported that attempted alkylation gives
reduction of the Ni(II) complex to Ni(I).12 Another
support for the nickel(I) oxidation state comes from the
ESR spectra of the nickel complex 5 both in toluene and
in the solid state. An investigation to understand the
mechanism of reduction is still in progress.
Polymerization conditions: solvent, chlorobenzene; total vol-
ume, 10 mL; nickel complex, 0.20 µmol; 1.0 mL of MMAO (2.2 M)
[Al/Ni(molar) ) 11 000]; norbornene, 1.88 g [nornorene/Ni(molar)
) 136 000]; reaction time, 10 min. 107 g PNB mol-1 Ni h-1
.
c Mw
b
-5
d
(10
g mol-1) and Mw/Mn values were determined by GPC. 0.5
mL of MMAO (2.2 M). e Reaction time, 20 min. f Without cocatalyst
g
h
MMAO. Nickel complex, 0.40 µmol. Without nickel complex.
M
w (106 g mol-1), narrow molecular weight distribution
Mw/Mn (from 2.31 to 3.45), and high glass transition
temperature Tg (≈400 °C), while under the same condi-
tions, the complexes themselves and MMAO did not
produce polymer (runs 7, 15, 22, and 23). These values
of PNB productivity were below 59%, which is different
from other reported results.5,6
The norbornene polymerization results are collected
in Table 2. In general, the steric structure and bulky
group in nickel complexes slightly influence their cata-
lytic activities. For example, complexes 1 and 2, bearing
phenyliminophenolato, have higher activities than com-
plexes 3 and 4, bearing â-enaminoketonato, at same
polymerization conditions due to the unpliant frame-
work of the former ligands. Complex 5, having two big
steric groups [2,6-i-Pr2(C6H3)N], is the least active
among all five catalysts. Recently, the addition mech-
anism of norbornene using neutral nickel complexes was
hypothesized as the insertion of norbornene into the
Ni-C bond.6i,l If so, we can easily explain that the higher
activaties for complexes 1 and 2 than those for 3 and 4
is because the former have less rigid ligand frameworks
and norbornene inserts into the Ni-C bond more easily
after the precatalyst is activated with MMAO to afford
an empty site.
MMAO was essential for the polymerization of nor-
borene catalyzed by 1-5. Variation of the ratio of
MMAO:complex (1-5), which is expressed here as Al:
Ni ratio, showed considerable effects on molecular
weight but barely any effect on catalyst activity and
polymer yield (runs 2 and 3). Like other nickel catalytic
systems for norbornene polymerization,6 when the total
reaction volume was kept constant, an increase of
monomer concentration (the molar ratio of norbornene:
Ni) caused a dramatic increase of activity combined with
Preliminary experiments indicated that complexes
1-5 are not able to catalyze ethylene polymerization
with or without modified methylaluminuoxane (MMAO)
as cocatalyst at 1 atm pressure of ethylene. However,
after being activated with MMAO these catalytic pre-
cursors 1-5 could polymerize norbornene to afford
addition-type polynorbornene (PNB) with high activities
(107 g PNB mol-1 Ni h-1), high molecular weight
(11) Puiu, S. C.; Warren, T. H. Organometallics 2003, 22, 3974.
(12) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J . J . Am. Chem. Soc. 2002, 124, 14416.
(13) Eckert, N. A.; Bones, E. M.; Lachicotte, R. J .; Holland, P. L.
Inorg. Chem. 2003, 42, 1720.

3274 Organometallics, Vol. 23, No. 13, 2004
Zhang et al.
further purification. The starting materials 3-tert-butyl-5-
methylbenzaldehyde15 and trans-[Ni(PPh3)2(Ph)Cl]16 were pre-
pared according to literature procedures. Schiff-base [N, O]
ligands 3-t-Bu-5-Me-(2,6-Me2(C6H3)NdCH)C6H2OH (L1) and
3-t-Bu-5-Me-(2,6-i-Pr2(C6H3)NdCH)C6H2OH (L2) were synthe-
sized as we previously reported.7 â-Diketiminato [N, O] ligands
(2,6-Me2(C6H3)NdC(CH3)CHdC(CH3)OH (L3)9 and (2,6-i-
Pr2(C6H3)NdC(CH3)CHdC(CH3)OH (L4) and â-diketiminato
[N, N] ligand (2,6-i-Pr2(C6H3)NdC(CH3))2CH2 (L5)10 were
obtained according to literature methods or using analogous
methods reported. All five ligands were characterized by 1H
NMR spectra. Other commercially available reagents were
purchased and used without purification.
a slight decrease of molecular weight (runs 9 and 10).
The polymerization seems independent of temperature,
and the polymerization reaction showed a higher activ-
ity tendency with increasing reaction temperature from
0 to 60 °C (runs 4, 2, and 5). As shown in Table 2, the
yields of PNB increase and the molecular weights of the
polymer decrease slightly with longer reaction time
(runs 10 and 14).
The polymers obtained were characterized by 1H
1
NMR, IR, and GPC analyses. The H NMR spectra of
six PNB products are similar to each other. The
resonances of PNB appear at 2.6-0.9 (m, maxima at
1.2, 1.4, 1.6, 2.3 ppm), and the absence of bands at
1680-1620 cm-1 in the IR spectra indicated no double
bonds, which was different from the polymers of nor-
bornene ring-opening metathesis polymerization.14 The
GPC molecular weights Mw of five polymers were very
high, up to near 2 000 000, indicating that the normal
mode of chain transfer (â-hydride elimination) was not
possible in PNB given the geometry of the active
growing center. From XRD data of these polymers, only
very weak signals could be observed. The DSC study of
obtained PNB did not gave an endothermic signal upon
heating to the decomposition temperature (above 450
°C), and the TGA scans suggested these polymers are
very stable up to 400 °C.
All measurements were carried out at the Analysis Center
of Changchun Institute of Applied Chemistry, The Chinese
1
Academy of Sciences. H NMR spectra were recorded with a
Varian Unity-400 spectrometer. Elemental analyses were
performed with a Perkin-Elmer Series II CHN/O analyzer
2400. Average 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). Trichlo-
robenzene was employed as a solvent at a flow rate of 1.00
mL/min. IR spectra were measured with a Bio-Rad FTS 135
spectrometer.
P r ep a r a t ion of [3-t-Bu -5-Me-(2,6-Me2(C6H 3)NdCH )-
C6H2O](P P h 3)(P h )Ni](1). The suspension solution of sodium
hydride (0.2 g, 5 mmol) in THF (20 mL) was channeled into a
100 mL flask with a solution of the ligand L1 (0.596 g, 1.5
mmol) in THF (20 mL). After stirring at room temperature
for 2 h, the mixture was centrifuged and the upper clear
solution was transferred and concentrated in vacuo to afford
a pale yellow solid residue. The residue was washed with
hexane (20 mL), and the resulting sodium salt of L1 was used
for the next step without any other purification. A solution
containing the sodium salt of L1 (0.443 g, 1.5 mmol) and trans-
[Ni(PPh3)2(Ph)Cl] (1.0 g, 1.44 mmol) in benzene (50 mL) was
stirred at room temperature. After 6 h, the reaction mixture
was separated by centrifugaton to remove NaCl. The upper
clear solution was evaporated to about 5 mL in a vacuum, and
then hexane (30 mL) was slowly added. Complex 1 was
obtained as a yellow solid. Yield: 0.81 g (78%). Single crystals
were obtained from hexane/toluene. 1H NMR (400 MHz,
C6D6): δ 7.98 (d, 1 H, NdCH), 7.85-6.44 (m, 25 H, Ar-H),
2.50 (s, 6 H, CH3-Ar), 2.31 (s, 3 H, CH3-Ar), 1.01 (s, 9 H,
CH3 of t-Bu). Anal. Calcd for C44H44NNiOP (692.507): C 76.31,
H 6.40, N 2.02. Found: C 76.31, H 6.45, N 2.12.
Con clu sion
We have synthesized nickel complexes of bulky
monoanionic â-diketiminato, ketiminato, and Shiff-base
ligands and examined their catalytic behavior for the
addition polymerization of norbornene. â-Ketiminato
nickel complexes can be conveniently prepared by the
same synthetic method as Shiff-base phenyl nickel
complexes, and they all share the four-coordination
binding mode around nickel(II). The steric protection
of the â-diketiminato ligand can stabilize highly elec-
tronically unsaturated organometallic complexes, and
thus it has been possible to synthesize a rare three-
coordinate nickel(I) complex (5) in the presence of PPh3.
All these nickel complexes show extremely high activi-
ties for the addition polymerization of norbornene with
the MMAO as cocatalyst. A mechanistic study of the
formation of the nickel(I) from nickel(II) as well as the
steric effects of the substituents is our current investi-
gation.
P r ep a r a t ion of [3-t-Bu -5-Me-(2,6-i-P r 2(C6H3)NdCH)-
C6H2O](P P h 3)(P h )Ni](2). Complex 2 was obtained as a
1
yellow solid. Yield: 0.92 g (81%). H NMR (400 MHz, C6D6):
δ 8.07 (d, 1 H, NdCH), 7.90-6.51 (m, 25 H, Ar-H), 4.31 (m,
2 H, CH of i-Pr), 2.32 (s, 3 H, CH3-Ar), 1.24 (d, 6 H, CH3 of
i-Pr), 1.10 (d, 6 H, CH3 of i-Pr), 0.98 (s, 9 H, CH3 of t-Bu). Anal.
Calcd for C48H52NNiOP (748.614): C 77.01, H 7.00, N 1.87.
Found: C 77.90, H 7.03, N 1.88.
P r ep a r a t ion of [(2,6-Me2(C6H3)NC(CH3)dCHCOCH3)-
(P P h 3)(P h )Ni] (3). Ligand L3 was obtained as a white solid
in 61% yield by using the analogous method according to ref
9. 1H NMR (400 MHz, CDCl3): δ 12.03 (s, 1 H, NH), 7.30-
7.14 (m, 3 H, Ar-H), 5.19 (m, 1 H, CHbackbone), 2.33 (s, 6 H,
CH3-Ar), 2.13 (s, 3 H, CH3-Ar), 1.64 (d, 3 H, CH3).
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All experiments with metal
complexes and ligands were carried out under argon using
standard Schlenk and vacuum-line techniques. Solvents were
dried by refluxing with appropriate drying agents and distilled
under argon prior to use. 2,6-Dimethylaniline, 2,6-diisopro-
pylaniline, 2-tert-butyl-4-methylphenol, NaH (60%), and
n-BuLi (1.6 M) were obtained from Acros Chem. Co. Nor-
bornene (bicyclo[2.2.1]hept-2-ene, Fluka) was purified by
sublimation under reduced pressure and used as a solution
in chlorobenzene. Modified methylaluminoxane (MMAO)
[(AlMeO)n/(AliBuO)m ) 3:1] was purchased from Acros Organ-
ics as 10% weight of a toluene solution and used without
n-BuLi (0.95 mL, 1.6 M, 1.52 mmol) in a solution of toluene
and hexane was slowly added to a solution of the ligand L3
(0.305 g, 1.5 mmol) in toluene (20 mL) at -78 °C. The mixture
was warmed to room temperature by itself and stirred for
(14) (a) Yu, R.-C.; Hung, C.; Huang, J .-H.; Lee, H.-Y.; Chen, J .-T.
Inorg. Chem. 2002, 41, 6450. (b) Barnes, D. A.; Benedikt, G. M.;
Goodall, B. L.; Huang, S. S.; Kalamarides, H. A.; Lenhard, S.; McIntosh,
L. H., Selvy, K. T.; Shick, R. A.; Rhodes, L. F. Macromolecules 2003,
36, 2623.
(15) Gasiraghi, G.; Casnati, G.; Sartori G.; Terenghi, G. J . Chem
Soc., Perkin Trans. 1980, 1, 1862.
(16) (a) Sehun, P. A. Inorg. Synth. 1972, 13, 124. (b) Hidai, M.;
Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J . Organomet. Chem. 1971, 30,
279.

Neutral Nickel Catalysts
Organometallics, Vol. 23, No. 13, 2004 3275
another 2 h to afford the lithium salt of the ligand L3. The
solution containing the lithium salt of L3 was slowly channeled
into a 100 mL flask with 1.0 g of trans-[Ni(PPh3)2(Ph)Cl] (1.44
mmol) in toluene (20 mL) and continuously stirred overnight
at room temperature. The reaction mixture was separated by
centrifugation to remove LiCl. After the upper clear, dark red
solution was concentrated to about 5 mL, 30 mL of hexane
was added to the top of the solution. Complex 3 was obtained
as yellow-orange crystals. Yield: 0.95 g (83%). Anal. Calcd for
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-mono-
chromated Mo KR radiation (λ ) 0.71073 Å). All data were
collected at room temperature using the ω scan technique.
These structures were solved by direct methods, using Fourier
techniques, and refined on F2 by a full-matrix least-squares
method. All the non-hydrogen atoms were refined anisotropi-
cally, and all the hydrogen atoms were included but not
refined. Crystallographic data are summarized in Table 1.
C
37H36NNiOP (600.366): C 74.02, H 6.04, N 2.33. Found: C
73.88, H 6.22, N 2.47.
P r ep a r a tion of [(2,6-i-P r 2(C6H3)NC(CH3)dCHCOCH3)-
(P P h 3)(P h )Ni] (4). Ligand L4 was obtained as a white solid
P olym er iza tion of Nor bor n en e. In a typical procedure
(run 4, Table 2), 0.2 µmol of nickel complex 4 in 2.0 mL of
chlorobenzene, 1.88 g of norbornene in 4.0 of mL chorobenzene,
and another 3.0 mL of fresh chlorobenzene were added into a
special polymerization bottle (20 mL) with a strong stirrer
under Ar atmosphere. After the mixture was kept at 30 °C for
10 min, 1.0 mL of MMAO (10%) was charged into the
polymerization system via syringe, and the reaction was
started. Ten minutes later, the acidic ethanol (Vmethanol:Vconcd.HCl
) 20:1) was added to terminate the reaction. The PNB was
isolated, washed with methanol, and dried at 80 °C for 48 h
under vacuum. For all the polymerization procedures, the total
reaction volume was 10.0 mL, which can be achieved by
variation of the amount of chlorobenzene when necessary. IR
(KBr): 2947, 2866, 1475, 1453, 1295, 1223, 1190, 1147, 1108,
1043, 942, 892 cm-1. 1H NMR (o-dichlorobenzene-d4, 400 Hz):
δ 0.9-2.6 (m, maxima at 1.2 1.4, 1.6 2.3).
1
by using a method similar to L3 in 65% yield. H NMR (400
MHz, CDCl3): δ 12.07 (s, 1 H, NH), 7.32-7.17 (m, 3 H,
Ar-H), 5.20 (m, 1 H, CHbackbone), 3.03 (m, 2 H, CH of i-Pr),
2.13 (s, 3 H, CH3), 1.64 (d, 3 H, CH3), 1.20 (d, 6 H, CH3 of
i-Pr), 1.15 (d, 6 H, CH3 of i-Pr). Complex 4 was synthesized as
a yellow-orange solid. Yield: 0.92 g (81%). Orange single
crystals were obtained from toluene at -30 °C. Anal. Calcd
for C41H44NNiOP (656.474): C 75.01, H 6.76, N 2.13. Found:
C 74.92, H 6.91, N 2.15.
P r epar ation of [((2,6-i-P r 2(C6H3)NdC(CH3))2CH)(P P h 3)-
Ni] (5). n-BuLi (0.95 mL, 1.6 M, 1.52 mmol) in a solution of
toluene and hexane was slowly added to a solution of the
ligand L5 (0.605 g, 1.5 mmol) in toluene (20 mL) at -78 °C.
The mixture was warmed to room temperature by itself and
stirred for another 2 h to afford the lithium salt of the ligand
L5. The solution containing the lithium salt of L5 was slowly
channeled into a 100 mL flask with 1.0 g of trans-[Ni(PPh3)2-
(Ph)Cl] (1.44 mmol) in toluene (20 mL) and continuously
stirred overnight at room temperature. The reaction mixture
was separated by centrifugation to remove LiCl. After the
upper clear, dark red solution was concentrated to about 5 mL,
30 mL of hexane was added. Complex 3 was obtained as a red-
orange solid. Yield: 0.56 g (53%). Red-orange single crystals
suitable for X-ray were recrystallized from toluene at -30 °C.
Anal. Calcd for C47H56N2NiOP (738.64): C 76.43, H 7.64, N
3.79. Found: C 76.60, H 7.53, N 3.88. EPR (9.4280 GHz, 298
K, toluene): g ) 2.0202.
Ack n ow led gm en t. Financial support by the Na-
tional Nature Science Foundation of China for Distin-
guished Young Scholars (29925101, 20274008) and by
the Key Project of Science and Technology of the
Education Ministry of China is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: CIF data of 1, 4,
and
5 are available free of charge via the Internet at
http://pubs.acs.org.
Str u ctu r e Solu tion a n d Refin em en t for Com p lexes 1,
4, a n d 5. For complexes 1, 4, and 5, a single crystal suitable
OM0499658