Arene-bridged salicylaldimine-based binuclear neutral nickel(II) complexes; synthesis and ethylene polymerization activities

Article abstract of DOI:10.1021/om060778e

A series of novel m-arene-bridged salicylaldimine-based binuclear neutral nickel(II) complexes (2,4,6-(R²)₃C₆H-1,3-[N=CH- 4-X-6-R¹C₆H₂ONi(Ph)(PPh₃)] ² (3a-i: R¹, R², X = Me, Me, H (3a), ^tBu, Me, H (3b), Me, Et, H (3c), ^tBu, Et, H (3d), H, ⁱPr, H (3e), Me, ⁱPr, H (31), ⁱBu, ⁱPr, H (3g), Ph, ⁱPr, H (3h), NO₂, ⁱPr, NO₂ (3i), H, ⁱPr, NO₂ (3j)) are synthesized. The structure of complex 3h is further confirmed by an X-ray diffraction study showing that the two Ni centers adopt an unsymmetrical, distorted square planar geometry. In the presence or absence of the phosphine scavenger Ni(COD)₂, complexes 3a-j show high catalytic activities for ethylene polymerization. The effect of substituents on ethylene polymerization is significant. The introduction of an electron-withdrawing group to the ligand framework improves the catalytic activity significantly. The influence of polymerization temperature, polymerization time, and catalyst concentration on the activities of ethylene polymerization is also investigated. Highly branched polyethylenes (46-127 branches per 1000 carbon atoms) with moderate molecular weights (M_η, = (1.0-169) × 10⁴) and narrow molecular weight distributions (M_w/M_n = 2.3-2.4) are obtained by using complexes 3a-j as catalysts with or without a phosphine scavenger. In the presence of a polar solvent such as THF or Et₂O, complex 3h polymerizes ethylene as a single-component catalyst. In comparison to the corresponding mononuclear Ni catalysts, the binuclear Ni catalysts generally show higher thermal stability, and complexes 3a, 3c, 3e, and 3f, which feature small R¹ substituents, are capable of acting as single-component ethylene polymerization catalysts.

Full text of DOI:10.1021/om060778e

Organometallics 2007, 26, 617-625
617
Arene-Bridged Salicylaldimine-Based Binuclear Neutral Nickel(II)
Complexes: Synthesis and Ethylene Polymerization Activities
Qihui Chen, Jing Yu, and Jiling Huang*
Laboratory of Organometallic Chemistry, East China UniVersity of Science and Technology,
130 Meilong Road, Shanghai 200237, People’s Republic of China
ReceiVed August 26, 2006
A series of novel m-arene-bridged salicylaldimine-based binuclear neutral nickel(II) complexes (2,4,6-
t
(R2)3C6H-1,3-[NdCH-4-X-6-R1C6H2ONi(Ph)(PPh3)]2 (3a-i: R1, R2, X ) Me, Me, H (3a), Bu, Me, H
t
i
i
t
i
i
(3b), Me, Et, H (3c), Bu, Et, H (3d), H, Pr, H (3e), Me, Pr, H (3f), Bu, Pr, H (3g), Ph, Pr, H (3h),
i
i
NO2, Pr, NO2 (3i), H, Pr, NO2 (3j)) are synthesized. The structure of complex 3h is further confirmed
by an X-ray diffraction study showing that the two Ni centers adopt an unsymmetrical, distorted square
planar geometry. In the presence or absence of the phosphine scavenger Ni(COD)2, complexes 3a-j
show high catalytic activities for ethylene polymerization. The effect of substituents on ethylene
polymerization is significant. The introduction of an electron-withdrawing group to the ligand framework
improves the catalytic activity significantly. The influence of polymerization temperature, polymerization
time, and catalyst concentration on the activities of ethylene polymerization is also investigated. Highly
branched polyethylenes (46-127 branches per 1000 carbon atoms) with moderate molecular weights
(Mη ) (1.0-169) × 104) and narrow molecular weight distributions (Mw/Mn ) 2.3-2.4) are obtained by
using complexes 3a-j as catalysts with or without a phosphine scavenger. In the presence of a polar
solvent such as THF or Et2O, complex 3h polymerizes ethylene as a single-component catalyst. In
comparison to the corresponding mononuclear Ni catalysts, the binuclear Ni catalysts generally show
higher thermal stability, and complexes 3a, 3c, 3e, and 3f, which feature small R1 substituents, are capable
of acting as single-component ethylene polymerization catalysts.
Chart 1
Introduction
Due to their tolerance toward polar substrates, late-transition
metal catalysts for R-olefin polymerization or oligomerization
have received much attention.1 In 1995, nickel and palladium
complexes containing R-diimine ligands as olefin polymerization
catalysts were reported by Brookhart and co-workers.2 These
complexes could not only polymerize ethylene to highly
branched polymers but also copolymerize ethylene with polar-
functionalized R-olefins.3 In 1998, Brookhart’s4 and Gibson’s5
groups independently reported highly active cationic iron and
cobalt olefin polymerization catalysts with bulky pyridinyldi-
imine ligands, and their catalytic activities were up to 107 g
PE/(mol Fe‚h). Among the numerous late-transition metal
catalysts, neutral nickel complexes are considered to be very
promising catalysts for R-olefin polymerization. As a highlight
from the well-known Shell Higher Olefin Process (SHOP)
catalysts,6 Grubbs’ group reported that neutral nickel(II) catalysts
containing salicylaldimine ligands (Chart 1) exhibit high activi-
ties and efficiency for olefin polymerization in the presence of
polar comonomers.7 Recently, novel neutral nickel(II) complexes
reported by Brookhart’s group, based upon anilinotropone
ligands, have been shown to be highly active ethylene polym-
erization catalysts.8 As expected, these single-component cata-
lysts can produce high molecular weight polyethylenes. Jin’s
group reported the self-immobilized neutral nickel(II) catalysts
with an allyl functional group that can be used as a comonomer
in the polymerization process.9 More recently, Li’s group
reported that neutral nickel(II) complexes bearing â-ketoiminato
chelate ligands copolymerize ethylene with methyl methacry-
late.10 In addition, such neutral nickel complexes can polymerize
ethylene in an aqueous emulsion, affording stable polymer
lattices with high molecular mass.11
* Corresponding author. Tel/Fax: +86-21-54282375. E-mail: qianling@
online.sh.cn.
(1) (a) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479. (b) Ittel,
S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100, 1169. (c)
Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 534. (d) Gibson, V. C;
Spitzmesser, S. K. Chem. ReV. 2003, 103, 283.
(2) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414.
(3) Fernandes, S.; Marques, M. M.; Correia, S. G.; Mano, J.; Chien, J.
C. W. Macromol. Chem. Phys. 2000, 201, 2566.
(4) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc.
1998, 120, 4049.
(5) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.;
McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem. Comm.
1998, 849.
(7) (a) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R.
H.;. Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149. (b)
Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs,
R. H.; Bansleben, D. A. Science 2000, 287, 460.
(8) (a) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217. (b)
Jenkins, J. C.; Brookhart, M. Organometallis 2003, 22, 250. (c) Hicks, F.
A.; Jenkins, J. C.; Brookhart, M. Organometallis 2003, 22, 3533.
(9) (a) Zhang, D.; Jin, G. X.; Hu, N. H. Chem. Commun. 2002, 574. (b)
Zhang, D.; Jin, G. X.; Hu, N. H. Eur. J. Inorg. Chem. 2003, 1570.
(10) Li, X. F.; Li, Y. G.; Li, Y. S.; Chen, Y. X.; Hu, N. H.
Organometallics 2005, 24, 2502.
(6) Keim, W.; Kowaldt, F. H.; Goddard, R.; Krueger, C. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 466.
10.1021/om060778e CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/04/2007

618 Organometallics, Vol. 26, No. 3, 2007
Chen et al.
Scheme 1
Considerable attention has lately been focused on binuclear
organometallic compounds, based on expectations that their
catalytic behavior may significantly differ from that of analogous
mononuclear species.12 Interactions between closely adjacent
metal centers could potentially modify catalytic performance
or provide alternative means for substrate activation. For
example, Guo and Marks13 have reported that binuclear ti-
tanocene complexes promote the copolymerization of ethylene
with styrene. Although binuclear metallocenes for olefin po-
lymerization have attracted much attention,14 the binuclear
neutral nickel catalysts received only a little attention.15 We
designed binuclear neutral nickel complexes that are connected
via the conjugated π system of the bisalicylaldimine ligands
and could provide attractive candidates to investigate the
potential for cooperative effects during the ethylene polymer-
ization reactions, which is a reaction of considerable interest in
both academic and industrial sectors. The very rigid bisalicyl-
aldimine ligands are now readily accessible and whose steric
and electronic properties can be fine-tuned. In this contribution,
we describe the synthesis and characterization of binuclear
neutral nickel(II) complexes 3a-j, (2,4,6-(R2)3C6H-1,3-[NCH-
4-X-6-R1C6H2ONi(Ph)(PPh3)]2, R1 ) H, Me, tBu, Ph, NO2; R2
) Me, Et, iPr; X ) H, NO2), based on the rigid m-arene-bridged
bisalicylaldimine ligands 1a-j and their catalytic behavior of
ethylene polymerization. Complexes 3a-j are available as
precursors to activator-free catalysts. The introduction of an
electron-withdrawing group to the ligand framework improves
the catalytic activity significantly, and very high molecular
weight polyethylenes can be obtained.
Results and Discussion
Synthesis and Structure of Binuclear Neutral Nickel
Complexes. In this study, we utilized nickel complexes that
possess m-arene-bridged bisalicylaldimine chelate ligands. A
general synthetic route for these complexes is shown in Scheme
1. 2,4,6-Trialkyl-m-phenylenediamines were obtained by per-
forming the nitration of 1,3,5-trialkylbenzenes and sequential
reduction.16 The substituted salicylaldehyde was obtained by
treatment of a phenol derivative with paraformaldehyde in the
presence of anhydrous tin(IV) chloride in moderate yield.17
However, phenols containing an electron-withdrawing group
barely reacted. 5-Nitrosalicylaldehyde was isolated from a
mixture of 5-nitrosalicylaldehyde and 3-nitrosalicylaldehyde.18
3,5-Dinitrosalicylaldehyde was obtained by performing the
nitration of salicylaldehyde twice.19
All the bridged bisalicylaldimine ligands 1 were synthesized
in moderate yields by condensation of m-phenylenediamine with
2 equiv of salicylaldehyde in ethanol with a catalytic amount
of formic acid in order to minimize the amount of the mono-
salicylaldimine formed. It is clear that the excessive amount of
amine would otherwise result in more mono-salicylaldimine
ligand in our case.20
(11) (a) Bauers, F. M; Mecking, S. Macromolecules 2001, 34, 1165. (b)
Bauers, F. M.; Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 3020. (c)
Zuideveld, M. A.; Wehrmann, P.; Ro¨hr, C.; Mecking, S. Angew. Chem.,
Int. Ed. 2004, 43, 869.
(12) (a) Muetterties, E. L.; Krause, M. J. Angew. Chem., Int. Ed. Engl.
1983, 22, 135. (b) Beck, W.; Niemer, B.; Wieser, M. Angew. Chem., Int.
Ed. Engl. 1993, 32, 923. (c) van den Beuken, E. K.; Feringa, B. L.
Tetrahedron 1998, 54, 12985. (d) Barlow, S.; O’Hare, D. Chem. ReV. 1997,
97, 637. (e) Li, H.; Li, L.; Marks, T. J. Angew. Chem., Int. Ed. 2004, 43,
4937.
(13) Guo, N.; Li, L.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 6542.
(14) (a) Reddy, K. P.; Petersen, J. L. Organometallics 1989, 8, 2107.
(b) Juling, S.; Mullhaupt, R.; Plenio, H. J. Organomet. Chem. 1993, 460,
191. (c) Larkin, S. A.; Golden, J. T.; Shapiro, P. J.; Yap, G. P. A.; Foo, D.
M. J.; Rheingold, A. L. Organometallics 1996, 15, 2393. (d) Segerer, U.;
Blaurock, S.; Sieler, J.; Hey-Hawkins, E. Organometallics 1999, 18, 2838.
(15) (a) Zhang, D.; Jin, G. X. Organometallics 2003, 22, 2851. (b) Hu,
T.; Tang, L. M; Li, X. F.; Li, Y. S.; Hu, N. H. Organometallics 2005, 24,
2628. (c) Taquet, J.-p.; Siri, O.; Braunstein, P.; Welter, R. Inorg. Chem.
2006, 45, 4668.
The general synthetic route for binuclear neutral nickel(II)
complexes 3 is shown in Scheme 1. The deprotonation of free
bisalicylaldimine ligands 1 proceeded readily with excess
sodium hydride in dry THF at room temperature. Most sodium
(16) (a) Newton, A. J. Am. Chem. Soc. 1943, 65, 2434. (b) Myhre, P.
C.; Edmonds, J. W.; Kruger, J. D. J. Am. Chem. Soc. 1966, 88, 2459. (c)
Kiiater Stallberg. Ann. Chem. 1893, 478, 213. (d) Adams, R.; Chase, R. G.
J. Am. Chem. Soc. 1948, 70, 4202.
(17) Casiraghi, G.; Casnati, G.; Puglia, G.; Sartori, G.; Terenghi, G. J.
Chem. Soc. Perkin Trans. 1 1980, 1862.
(18) Lovert, R. J. Chem. Soc. 1928, 1978.
(19) Everett, G. W., Jr.; Finney, K. S. Inorg. Chem. 1970, 9, 2540.

Arene-Bridged Binuclear Neutral Nickel(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 619
Scheme 2
salts of 1 are quite soluble in THF and are easily separated from
residual NaH by filtration. After removal of the solvent, the
sodium salts were treated with 2 equiv of trans-NiCl(Ph)(PPh3)2
in toluene to afford binuclear neutral nickel(II) complexes as
analytically pure crystals after recrystallization from hydrocarbon
solvents. However, the sodium salt of 1j does not dissolve in
THF, and the residual NaH is difficult to separate from the
reaction system. In view of the acidity of the hydroxyl proton,
ligand 1j was reacted directly with trans-NiCl(Ph)(PPh3)2 in
the presence of NEt3 to afford the target complex 3j in moderate
yield (Scheme 2). The shift of the νC)N stretching absorption
band to lower frequency is a consequence of the coordination
through the nitrogen atom. For example, the IR spectrum of
ligand 1h shows a very strong absorption band at 1621 cm-1
attributed to νC)N, while the νC)N band of complex 3h is at
Table 1. Crystal Data and Structure Refinement Details for
Complex 3h
empirical formula
fw
C89H80N2Ni2O2P2‚4C6H6
1701.34
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
293(2)
0.71073
triclinic
P1h
11.3718(12)
20.898(2)
21.720(2)
66.805(2)
88.652(2)
83.274(2)
4710.4(8)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
calcd density (Mg/m3)
1.200
0.485
1796
absorp coeff (mm-1
F(000)
)
1597 cm-1. The strong absorption bands at about 1435 (νP-C
)
and 693 (νNi-P) cm-1 confirm the existence of PPh3.21
cryst size (mm)
θ range for data
collection (deg)
limiting indices
0.510 × 0.490 × 0.139
A single crystal of binuclear neutral nickel(II) complex 3h
suitable for X-ray diffraction analysis was obtained by slow
diffusion of n-hexane into a benzene solution of complex 3h at
room temperature. Crystallographic data together with the
collection and the refinement parameters are summarized in
Table 1. Selected bond lengths and angles are listed in Table 2.
As depicted in Figure 1, complex 3h possesses two unsymmetric
nickel centers and exhibits C1 symmetry in the solid state. The
coordination geometry around each Ni atom is a distorted square
plane with the triphenylphosphine ligand in the trans-position
to the nitrogen donor of the bulky 2,4,6-triisopropylbenzimine
moiety, as indicated by the very wide P(1)-Ni(1)-N(1) and
P(2)-Ni(2)-N(1) angles of 162.84(12)° and 161.81(11)°,
respectively. The phenyl ligand is located trans to the oxygen
donor with O(1)-Ni(1)-C(29) and O(2)-Ni(2)-C(66) angles
of 158.1(2)° and 157.49(17)°, respectively. The P-Ni-N and
O-Ni-C bond angles in complex 3h are somewhat smaller
than those found in the mononuclear Grubbs’ nickel complex
(172.16(12)° and 166.2(2)°).7 The bond distances of Ni(1)-
O(1) (1.888(3) Å) and Ni(1)-N(1) (1.910(4) Å) are shorter than
Ni(2)-O(2) (1.903(3) Å) and Ni(2)-N(2) (1.925(4) Å), re-
spectively, which fall within the range observed for the related
neutral nickel complexes (Ni-O, 1.885(3)-1.912(2) Å; Ni-
N, 1.883(14)-1.937(4) Å).7,9,10,20a In contrast, the bond distance
of Ni(1)-C(29) (1.902(4) Å) is longer than Ni(2)-C(66) (1.869-
(5) Å). Although the two segments in complex 3h have
seemingly identical chemical environments, the rigidity of the
m-arene bridge and the steric hindrance among ligands and
substituents most likely forces the unsymmetric orientation of
the two moieties.
1.74 to 26.00
-14 e h e 13,
-18 e k e 25,
-25 e l e 26
no. of reflns collected/unique
25 971/18 124
[R(int) ) 0.1426]
completeness to θ ) 26.00
absorp corr
98.1%
empirical
max. and min. transmn
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.00000 and 0.64310
full-matrix least-squares on F2
18 124/26/1108
0.841
R1 ) 0.0742, wR2 ) 0.1630
R1 ) 0.1305, wR2 ) 0.1845
1.045 and -0.663
largest diff peak and
hole (e Å-3
)
Table 2. Selected Bond Distances (Å) and Bond Angles (deg)
for Complex 3h
Ni(1)-O(1)
Ni(1)-C(29)
Ni(1)-N(1)
Ni(1)-P(1)
O(1)-C(22)
N(1)-C(16)
N(1)-C(1)
C(21)-C(23)
1.888(3)
1.902(4)
1.910(4)
2.1709(13)
1.274(5)
1.279(5)
1.486(5)
1.492(7)
Ni(2)-O(2)
Ni(2)-C(66)
Ni(2)-N(2)
Ni(2)-P(2)
O(2)-C(59)
N(2)-C(53)
N(2)-C(5)
C(58)-C(60)
1.903(3)
1.869(5)
1.925(4)
2.1868(14)
1.300(5)
1.283(5)
1.459(5)
1.466(7)
O(1)-Ni(1)-C(29)
O(1)-Ni(1)-N(1)
C(29)-Ni(1)-N(1)
O(1)-Ni(1)-P(1)
C(29)-Ni(1)-P(1)
N(1)-Ni(1)-P(1)
158.1(2)
C(66)-Ni(2)-O(2)
O(2)-Ni(2)-N(2)
C(66)-Ni(2)-N(2)
O(2)-Ni(2)-P(2)
C(66)-Ni(2)-P(2)
N(2)-Ni(2)-P(2)
157.49(17)
93.01(15)
96.22(17)
88.75(11)
88.82(13)
161.81(11)
92.44(14)
98.07(16)
89.05(10)
86.51(13)
162.84(12)
Ethylene Polymerizations Catalyzed by Binuclear Neutral
Complexes 3a-j. Binuclear complexes are interesting candi-
dates for catalytic reactions because they possess two potentially
reactive sites susceptible to showing cooperative effects. One
of our objectives was to determine whether cooperative effects
resulting from electronic communication between the metal
centers would lead to improved catalytic activity and/or broaden
the molecular weight distribution.
First, complexes 3a-j were tested as catalysts for ethylene
polymerization in the presence of a phosphine scavenger, Ni-
(COD)2. The results are summarized in Table 3. It was revealed
(20) (a) Sun, J.; Shan, Y.; Xu, Y.; Cui, Y.; Schumann, H.; Hummert,
M. J. Polym. Sci. Part A: Polym. Chem. 2004, 42, 6071. (b) Mitani, M.;
Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao, H.; Nakano, T.; Tanaka,
H.; Fujita, T. J. Am. Chem. Soc. 2003, 125, 4293. (c) Matsui, S.; Mitani,
M.; Saito, J.; Tohi, Y.; Makio, H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.;
Nitabaru, M.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem.
Soc. 2001, 123, 6847.
(21) Kla¨ui, W.; Bongards, J.; Reiss, G. J. Angew. Chem., Int. Ed. 2000,
39, 3894.

620 Organometallics, Vol. 26, No. 3, 2007
Chen et al.
Figure 1. ORTEP diagram of complex 3h. (Four benzene solvent molecules are present in the unit cell and all hydrogen atoms are omitted
for clarity.)
that these complexes exhibited high catalytic activities for
ethylene polymerization, and the highest activity, 314 kg PE/
(mol Ni‚h), was observed for the 3j/Ni(COD)2 (R1 ) H, X )
catalysts. The polymerization temperature has a remarkable
effect on the catalytic behavior, as demonstrated in Table 3.
When the polymerization temperature is elevated from 25 to
70 °C, the activity of complex 3a rises from 32.8 to 203 kg
PE/(mol Ni‚h) (entries 1-3, Table 3). For complexes 3d and
3i, it is found that the catalytic activities decrease gradually
with elevating the temperature from 25 to 90 °C. A higher
temperature is favorable for the abstraction of PPh3, which
decreases the induction period and generates the active “Ni-
H” species faster. At the same time, the deactivation of active
species and the â-hydride elimination reaction also become more
significant at high temperature. The optimal polymerization
temperature for individual systems depends on the balance
between the propagation rate and the thermal stability. In
comparison to the analogous mononuclear nickel catalysts,
which usually are deactivated above 80 °C under polymerization
conditions, our binuclear nickel catalysts are more stable and
still show moderate catalytic activities even at 90 °C.7,9
i
NO2, R2 ) Pr) catalytic system (entry 38). In general, these
binuclear neutral nickel complexes show similar catalytic
activities to Grubbs’ analogous mononuclear nickel complexes.7
Binuclear nickel complexes 3a-j were synthesized in an effort
to explore the effects of varying the ortho-substituents on phenol
and N-aryl moieties of ligands 1a-j on ethylene polymerization.
Complexes 3a, 3c, 3e, and 3f (R1 ) H or Me), with small
substituents at the ortho-position of the phenolic ring, are less
active at low temperature (25 °C). The phosphine scavenger
Ni(COD)2 binds PPh3 more strongly than the nickel(II) complex
and removes phosphine from the nickel complex. Less sterically
hindered ortho-substituents disfavor the dissociation of PPh3
to form a vacant coordination site at low temperature and
therefore extend the induction period of generating the active
“Ni-H” species. It has been proposed for the SHOP system
that the induction period is due to the slow coordination and
insertion of ethylene into the Ni-Ph bond, followed by
â-hydride elimination to generate the active “Ni-H” species.22
Increasing the polymerization temperature to 70 °C accelerates
the abstraction of PPh3 from the Ni center. Due to the same
effect, the complexes containing bulky ortho-substituents (tBu
or Ph) reach optimal activities at relatively lower temperatures
(25 or 50 °C) than those with smaller ortho-substituents.
Complexes 3i and 3j, containing the electron-withdrawing nitro
groups, show enhanced catalytic activities and produce poly-
ethylenes with higher molecular weights. Compared with
complex 3j, complex 3i, bearing 4-nitro groups, shows lower
catalytic activity. It was observed that the polymer was rapidly
precipitated at the beginning of the polymerization in the case
of complex 3i, which would lead to the occlusion of the catalytic
active center in the precipitated polymer and disfavor the mass
transport of ethylene.
Highly branched polyethylenes were obtained by using
complexes 3a-j/Ni(COD)2 systems. The degree of branching,
1
determined by H NMR spectroscopy, varies from 46 to 127
branches per 1000 carbon atoms. Complexes with small
substituents at the ortho-position of the phenolic ring produce
polyethylene with a low number of branches, which is in contrast
to the mononuclear nickel catalytic system. A branch in the
polymer is introduced by â-hydride elimination of a growing
polymer chain followed by olefin rotation and reinsertion with
opposite regiochemistry. The high-temperature 13C NMR spec-
trum of the polymer (entry 18, Table 3) shows there are few
ethyl and longer branches besides methyl ones in the resulting
PE chains. Analysis of the more highly branched polymer (entry
26, Table 3) shows that no other types of short branches are
observed besides methyl branches. The polyethylenes obtained
using complex 3g display a relatively narrow molecular weight
distribution (Mw/Mn ) 2.43); a possible reason is that binuclear
nickel complexes may possess a symmetric structure in solution
(entry 26, Table 3). Increasing the polymerization temperature,
the molecular weights of the obtained polymer are decreased,
which could be attributed to the much faster â-hydride elimina-
tion and chain transfer rate caused by raising the polymerization
The polymerization runs were carried out at different tem-
peratures (25-90 °C) to study the thermal stability of all
(22) (a) Klabunde, U.; Ittel. S. D. J. Mol. Catal. 1987, 41, 123. (b)
Klabunde, U.; Mulhaupt, R.; Herskovitz, T.; Janowicz, A. H.; Calabrese,
J.; Ittel, S. D. J. Polym. Sci. Part A: Polym. Chem. 1987, 25, 1989.

Arene-Bridged Binuclear Neutral Nickel(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 621
Table 3. Ethylene Polymerization by Binuclear Nickel
Table 4. Ethylene Polymerization by Binuclear Nickel
Complex 3g with Scavenger Ni(COD)2 under Different
Catalyst Concentrationsa
a
Complexes 3a-j with Scavenger Ni(COD)2
c
complex temp yield PE
Mη
branchese/
1000C
activityb (104 g mol-1
)
c
entry (µmol) (°C)
(g)
complex
(µmol)
temp
(°C)
yield
PE (g)
Mη
entry
activityb
(104 g mol-1
)
1
2
3
4
5
6
7
8
9
3a (2.0)
3a (2.0)
3a (2.0)
3a (2.0)
3b (2.0)
3b (2.0)
3b (2.0)
3b (2.0)
3c (2.0)
3c (2.0)
3c (2.0)
3c (2.0)
3d (2.0)
3d (2.0)
3d (2.0)
3d (2.0)
3e (2.0)
3e (2.0)
3e (2.0)
3e (2.0)
3f (2.0)
3f (2.0)
3f (2.0)
3f (2.0)
3g (2.0)
3g (2.0)
3g (2.0)
3g (2.0)
3h (2.0)
3h (2.0)
3h (2.0)
3h (2.0)
3i (2.0)
3i (2.0)
3i (2.0)
3i (2.0)
3j (2.0)
3j (2.0)
3j (2.0)
3j (2.0)
25
50
70
90
0
0.0875
0.2105
0.5425
0.2824
0.1147
0.5272
0.3020
0.1524
0.0539
0.1595
0.3662
0.2790
0.5910
0.4532
0.2179
0.1280
0.1668
0.2340
0.3769
0.2724
0.1089
0.1184
0.3144
0.1824
0.3877
0.4624
0.2367
0.1772
0.5035
0.3350
0.2735
0.2232
0.5965
0.5086
0.4434
0.2730
0.6751
0.8360
0.4925
0.2847
32.8
78.9
203
106
43.0
198
113
57.2
20.2
59.8
137
105
221
170
15.4
5.70
65
1
2
3
4
3g (1.0)
3g (2.0)
3g (4.0)
3g (6.0)
50
50
50
50
0.2373
0.4624
0.8428
0.9360
178
173
158
117
3.96
3.11
4.56
2.83
1.95
1.80
3.05
1.96
1.78
1.23
25
50
70
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
a Conditions: solvent, toluene 25 mL; pressure, 10 atm; polymerization
b
c
time, 40 min; Ni(COD)2/3g ) 2. kg PE/(mol Ni‚h). Molecular weights
were determined by intrinsic viscosity.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
5.94
2.88
2.81
3.19
6.11
5.17
Table 5. Ethylene Polymerization by Binuclear Nickel
Complex 3g with Scavenger Ni(COD)2 under Different
Polymerization Timesa
complex
(µmol)
temp
(°C)
time
(min)
yield PE
(g)
entry
activityb
81.7
48.6
62.6
87.8
1
2
3
4
5
3g (2.0)
3g (2.0)
3g (2.0)
3g (2.0)
3g (2.0)
50
50
50
50
50
10
20
40
60
80
0.1853
0.2961
0.4624
0.6240
0.6773
278
222
173
156
127
15.3
6.71
4.12
1.08
46
141
102
40.8
44.4
117
68.4
145
173
88.8
66.3
189
16.7
8.61
5.46
3.44
4.56
3.11
2.07
1.89
15.7
20.9
5.30
2.43
a Conditions: solvent, toluene 25 mL; pressure, 10 atm; Ni(COD)2/3g
b
) 2. kg PE/(mol Ni‚h).
The catalytic performance of binuclear neutral nickel com-
plexes 3a-j is also evaluated as single-component catalysts for
ethylene polymerization. The results are summarized in Table
6. In the absence of Ni(COD)2 as a phosphine scavenger, these
complexes still exhibit high catalytic activities for ethylene
polymerization. Although a decrease of the catalytic activity is
observed for most complexes when compared with complexes
3a-j/Ni(COD)2 catalytic systems. It is worth noting that 3i
shows greater activity as a single-component catalyst and
exhibits the highest activity, 298 kg PE/(mol Ni‚h) (entry 33).
Obviously, complex 3i is much more suitable for use as a single-
component catalyst for ethylene polymerization. As can be seen
in Table 6, when the catalyst concentration and polymerization
time decrease at the same time, the catalytic activity of 3i rises
from 271 to 710 kg PE/(mol Ni‚h) (entries 34 and 35). The
strong electron-withdrawing substituent and bulky ortho-sub-
stituents essentially promote the dissociation of PPh3 from the
nickel center under the polymerization conditions.
87d
126
102
88.7
127
224
191
166
102
253
314
185
109
169
60.5
82.3
66.1
13.6
6.56
a Conditions: solvent, toluene 25 mL; pressure, 10 atm; polymerization
b
c
time, 40 min; Ni(COD)2/3 ) 2. kg PE/(mol Ni‚h). Molecular weights were
determined by intrinsic viscosity. Mw ) 2.93 × 104, Mw/Mn ) 2.43, Mw
d
e
1
and Mw/Mn were determined by GPC. Determinted by H NMR.
temperature. The polyethylenes produced by complexes 3i and
3j containing the nitro groups show very high molecular
weights; an Mη value as high as 169 × 104 g/mol is detected
(entry 34, Table 3). The electron-withdrawing nitro groups
decrease the ethylene insertion barrier.23 The acceleration of
chain propagation results in an increase in molecular weights.
The effect of the catalyst concentration on polymerization
by complex 3g was investigated (Table 4). High catalyst
concentration results in the decrease of catalytic activity, which
could be interpreted as a mass-transport effect. More polymer
is produced at higher catalyst concentration, and the viscosity
of the reaction mixture is increased. In particular, the reaction
mixture becomes a paste at high catalyst concentration, which
inhibits ethylene from reaching the active center.
We further investigated the effect of polymerization time on
the ethylene polymerization. The data in Table 5 show that the
activity decreases gradually when the polymerization time is
prolonged from 10 to 80 min. The slight reduction of activity
may be attributed to the deactivation of the active centers or
the occlusion of part of the catalyst in the precipitated polymer.
It has been reported that the structure analogous Grubbs’
catalysts a and b (Chart 1) were not active for ethylene
polymerization as single-component catalysts, because the
deactivation of catalysts easily occurs via ligand dimerization.
Computational work by Ziegler and co-workers supports the
proposal that the bulky ortho-substituent is primarily responsible
for the high catalytic activity by promoting PPh3 dissociation.23
In our case, complexes containing less bulky substituents, such
as hydrogen or methyl, can still polymerize ethylene as single-
component catalysts. The two metal centers in these binuclear
nickel complexes are connected through the m-arene bridge and
are located in trans-position. The interaction between two Ni
centers seems weak, and the m-arene bridge may play an
important role in raising the activity and thermal stability by
the unique steric bulkiness and electronic effect.
Polymerization temperature has a dramatic effect on the
catalytic activities of complexes 3a-j employed as single-
component catalysts for ethylene polymerization trials. When
the polymerization temperature is elevated from 25 to 70 °C,
the activity of complex 3a increases more than 6-fold. For
complexes 3i and 3j, the catalytic activities decrease gradually
with increasing temperature from 25 to 90 °C. The polymeri-
zation behavior is similar to that using Ni(COD)2 as a scavenger
(23) Chan, M. S. W.; Deng, L.; Ziegler, T. Organometallis 2000, 19,
2741.

622 Organometallics, Vol. 26, No. 3, 2007
Chen et al.
Table 7. Ethylene Polymerization by Binuclear Nickel
Table 6. Ethylene Polymerization by Binuclear Nickel
Complexes 3a-j as Single-Component Catalysts
Complex 3h as a Single-Component Catalyst in the Presence
of Polar Additivesa
c
complex
(µmol)
temp
(°C)
yield PE
(g)
Mη
entry
activityb
(104 g mol-1
)
complex temp
yield
PE (g)
entry
(µmol)
(°C)
polar additiveb
no additive
tetrahydrofuran
activityc
1
2
3
4
5
6
7
8
9
3a (4.0)
3a (4.0)
3a (4.0)
3a (4.0)
3b (4.0)
3b (4.0)
3b (4.0)
3b (4.0)
3c (4.0)
3c (4.0)
3c (4.0)
3c (4.0)
3d (4.0)
3d (4.0)
3d (4.0)
3d (4.0)
3e (4.0)
3e (4.0)
3e (4.0)
3e (4.0)
3f (4.0)
3f (4.0)
3f (4.0)
3f (4.0)
3g (4.0)
3g (4.0)
3g (4.0)
3g (4.0)
3h (4.0)
3h (4.0)
3h (4.0)
3h (4.0)
3i (4.0)
3i (4.0)
3i (1.0)e
3i (4.0)
3i (4.0)
3j (4.0)
3j (4.0)
3j (4.0)
3j (4.0)
25
50
70
90
0
0.0754
0.2259
0.4744
0.2395
0.1936
0.5362
0.2216
0.1454
trace
14.2
42.4
89.0
44.7
36.3
101
6.21
1.98
1.72
1.21
4.22
2.45
1.92
1.40
1
2
3
4
5
3h (4.0)
3h (4.0)
3h (4.0)
3h (4.0)
3h (4.0)
50
50
50
50
50
0.6631
0.1598
124
29.9
31.3
95.7
79.9
1,2-dimethoxyethane 0.1674
diethyl ether
dichloromethane
0.5182
0.4274
25
50
70
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
70
90
25
50
50
70
90
25
50
70
90
41.2
27.3
a Conditions: solvent, toluene 25 mL; pressure, 10 atm; polymerization
b
time, 40 min. Quantity of additive, 0.5 mL. c kg PE/(mol Ni‚h).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
0.1081
0.1942
0.0856
0.1244
0.2190
0.2050
0.0698
0.1344
0.1459
0.1673
0.1956
0.0996
0.1143
0.1775
0.1620
0.6513
0.3875
0.1570
0.0833
0.5264
0.6631
0.2591
0.2170
1.591
20.3
36.4
16.0
23.3
82.1
76.9
13.1
25.2
27.4
31.4
36.6
18.7
21.4
33.3
30.4
122
72.7
29.4
15.6
98.7
124
48.6
40.7
298
9.72
2.38
1.47
9.78
6.56
2.59
DME > CH2Cl2 > Et2O. The binuclear neutral nickel complex
can tolerate polar functional groups, so complexes 3g-j were
tested as catalysts for ethylene/MMA copolymerization in the
presence of a phosphine scavenger, Ni(COD)2. To our disap-
pointment, complexes 3g-j do not exhibit MMA incorporation
ability from the analysis of the high-temperature 13C NMR
spectrum of the resultant polymer.
25.1
6.52
4.15
2.63
15.4
10.5
7.71
6.91
6.17
2.15d
1.58
1.16
19.7
16.3
1.74
1.60
40.5
29.7
25.8
27.5
11.0
56.6
47.2
27.0
12.4
Conclusions
Ten new binuclear neutral Ni(II) complexes bearing a
chelating bisalicylaldimine ligand have been synthesized. The
binuclear molecular structure of complex 3h was confirmed by
X-ray diffraction analysis. In the presence of the phosphine
scavenger Ni(COD)2, complexes 3a-j prove to be efficient
catalytic systems for the polymerization of ethylene. In addition,
when employed as single-component ethylene polymerization
catalysts, these complexes show high catalytic activities and
yield polyethylene products with moderate molecular weights
(Mη ) (1.0-169) × 104), narrow molecular weight distributions
(Mw/Mn ) 2.3-2.4), and a high degree branching (ca. 46-127
branches per 1000 carbon atoms). The variation of substituents
on the ortho-positions of the phenyl rings and arene bridge of
the ligand dramatically influences the polymerization behavior
of these binuclear nickel complexes. The introduction of an
electron-withdrawing group to the ligand framework improves
the catalytic activity significantly, and very high molecular
weight polyethylenes can be obtained by complexes 3i and 3j
with nitro groups. The binuclear neutral nickel complexes show
much higher thermal stability and can tolerate polar functional
groups.
1.448
271
710
156
125
139
115
75.9
58.1
0.2365
0.8299
0.6646
0.7412
0.6126
0.4050
0.3106
a Conditions: solvent, toluene 25 mL; pressure, 10 atm; polymerization
b
c
time, 40 min. kg PE/(mol Ni‚h). Molecular weights were determined by
intrinsic viscosity. Mw ) 1.84 × 104, Mw/Mn ) 2.36, the number of
d
e
branches ) 111 per 1000 C. Polymerization time, 10 min.
at different polymerization temperatures for all complexes 3a-
j. The resultant polymer obtained by using complex 3g as a
single-component catalyst has a moderate molecular weight (Mw
) 1.84 × 104) with a relatively narrow molecular weight
distribution (Mw/Mn ) 2.36), which is similar to that using Ni-
(COD)2 as a scavenger. The number of branches is 111 per 1000
carbon atoms, which is higher than that produced in the presence
of Ni(COD)2 as a scavenger. The Mη value of the resultant
polymer increases with increasing steric hindrance on the N-aryl
ligands. The steric hindrance on the axial site is important in
controlling the molecular weight of polyethylenes by increasing
the chain termination barrier.23
As mentioned previously, late-transition metal catalysts are
tolerant toward functional groups. Therefore, complex 3h was
selected as an example to investigate the tolerance of these
binuclear Ni catalysts to functional group as a single-component
catalyst for ethylene polymerization. The results are listed in
Table 7. These results demonstrate that the polymerizations can
still be carried out successfully in the presence of polar
substances, but the impact varies significantly across the various
polar species. Binuclear neutral catalysts show similar tolerance
for functional groups to Grubbs’ mononuclear Ni catalysts. The
degree of the impact decreases in the following order: THF >
Experimental Section
General Remarks. All operations were carried out under an
argon atmosphere using standard Schlenk techniques. All solvents
were distilled from sodium wire prior to use, and chemicals were
obtained from commercial suppliers. Methylene dichloride was
1
distilled from drying CaH2 under argon. H NMR and 31P NMR
spectra were recorded on a Bruker Avance-500 spectrometer with
CDCl3 or C6D6 as the solvent. 13C NMR spectra were recorded on
a Bruker Avance-300 spectrometer with CDCl3 or C6D6 as the
solvent. Chemical shifts were referenced internally using the residual
solvent resonances or reported relative to tetramethylsilane. El-
emental analysis data were obtained with an EA-1106 spectrometer.
Infrared spectra using KBr pellets were collected on a Nicolet
Magna-IR 550 spectrophotometer. ESI-MS spectra were recorded
on a Micromass LCT mass instrument. Polymer grade ethylene was
directly used for polymerization without further purification. The
starting materials 2,4,6-trialkyl-m-phenylenediamine,16 3-methyl-
salicylaldehyde, 3-tert-butylsalicylaldehyde, 3-phenylsalicylalde-
hyde,17 3,5-dinitrosalicylaldehyde,18 5-nitrosalicylaldehyde,19 trans-
NiCl(Ph)(PPh3)2,24 and bis(1,5-cyclooctadiene)nickel (Ni(COD)2)25
were prepared according to the literature procedures.

Arene-Bridged Binuclear Neutral Nickel(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 623
1H NMR and 13C NMR spectra of polyethylenes were recorded
on a Bruker Avance-500 spectrometer with C6D4Cl2 at 110 °C. The
formula used to calculate branching was [CH3/3]/[(CH + CH2 +
CH3)/2] × 1000 ) branches per 1000 carbons.8b CH3, CH2, and
CH refer to the integration obtained for the methyl, methylene, and
methane resonances, respectively. The intrinsic viscosities [η] of
polyethylenes (PE) in decahydronaphthrene were measured with a
(yield, 74%) of yellow needle crystals. 1H NMR (CDCl3, 500
MHz): δ 8.34 (s, 2H, CHdN), 7.43 (m, 2H, ArH), 7.20 (d, J )
7.5 Hz, 2H, ArH), 7.02 (s, 1H, ArH), 6.90 (t, J ) 7.5 Hz, 2H,
ArH), 2.20 (s, 6H, Me), 2.08 (s, 3H, Me), 1.49 (d, J ) 7.6 Hz,
t
18H, Bu). 13C NMR (CDCl3, 300 MHz): 167.8, 160.7, 147.0,
137.8, 130.6, 130.4, 130.0, 124.9, 119.6, 118.7, 118.2, 35.0, 29.4,
18.4, 14.2.
Ubbelohde viscometer at 135 °C. The viscosity average molecular
Complex 3b was prepared using the same procedure for complex
3a. A 0.060 g (0.20 mmol) amount of sodium hydride, 0.353 g
(0.750 mmol) of ligand 1b, and 1.00 g (1.44 mmol) of trans-NiCl-
(Ph)(PPh3)2 were used to give 0.557 g (yield, 59%) of yellow
0.67
weights (Mη) were calculated as follows: [η] ) 6.77 × 10-4 Mη
.
The gel permeation chromatography (GPC) performed on a Waters
150 ALC/GPC system in a 1,2,4-trichlorobenzene solution at 135
°C was used to determine the weight-average molecular weights
(Mw) and the molecular weight distributions (Mw/Mn) of the
polymer.
1
crystals. H NMR (C6D6, 500 MHz): δ 7.94 (d, J ) 8.8 Hz, 2H,
CHdN), 7.77 (d, J ) 8.8 Hz, 12H, ArH), 7.58 (d, J ) 9.1 Hz, 3H,
ArH), 7.42 (d, J ) 7.3 Hz, 2H, ArH), 7.24 (d, J ) 7.6 Hz, 2H,
ArH), 7.02-6.90 (m, 17H, ArH), 6.62 (t, J ) 7.6 Hz, 2H, ArH),
6.44 (s, 1H, ArH), 6.35 (t, J ) 7.1 Hz, 2H, ArH), 6.29-6.24 (m,
4H, ArH), 6.00 (t, J ) 7.1 Hz, 2H, Ar), 2.67 (s, 5H, Me), 2.11 (s,
Synthesis of Binuclear Nickel Complex 3a. The ligand 1a was
prepared by the following procedure. To an ethanol (25 mL)
solution of 3-methylsalicylaldehyde (1.36 g, 10.0 mmol) were added
formic acid (0.5 mL) and 2,4,6-trimethyl-m-phenylenediamine (0.75
g, 5.0 mmol). The resulting mixture was refluxed for 4 h and then
cooled to room temperature. A precipitate was formed, which was
recrystallized from ethyl acetate to afford yellow crystals in 64%
yield (1.23 g). 1H NMR (CDCl3, 500 MHz): δ 8.32 (s, 2H, CHd
N), 7.28 (d, J ) 7.4 Hz, 2H, ArH), 7.20 (d, J ) 7.4 Hz, 2H, ArH),
7.02 (s, 1H, ArH), 6.87 (t, J ) 7.4 Hz, 2H, ArH), 2.34 (s, 6H,
Me), 2.18 (s, 6H, Me), 2.05 (s, 3H, Me). 13C NMR (CDCl3, 300
MHz): δ 167.5, 159.6, 146.7, 134.6, 130.1, 126.5, 125.1, 119.7,
118.7, 117.9, 18.3, 15.6, 14.1. IR (cm-1, KBr) ν: 3052w, 3002m,
2958m, 2915w, 1619vs, 1583s, 1490m, 1461s, 1435s, 1376m,
1354w, 1319w, 1302w, 1268s, 1251m, 1235m, 1210s, 1162w,
1090s, 1074m, 1031s, 1010m, 984w, 963w, 861w, 829m, 808s,
773s, 746vs, 683w.
t
2H, Me), 2.01 (s, 2H, Me), 0.91 (s, 18H, Bu). 13C NMR (C6D6,
300 MHz): 166.7, 166.1, 150.0, 141.9, 138.3, 136.8, 136.3, 135.1,
134.9, 133.4, 132.4, 131.9, 131.2, 129.7, 127.8, 127.5, 126.9, 125.2,
123.6, 121.8, 121.0, 115.8, 34.6, 29.8, 19.5, 15.5. IR (cm-1, KBr):
3045m, 3004w, 2949m, 2855m, 1596vs, 1561m, 1535vs, 1481m,
1466m, 1435s, 1416vs, 1387m, 1142m, 1096s, 1083m, 1055w,
1018w, 998w, 981w, 863w, 749s, 730s, 694vs, 646w, 618w, 606w,
531s, 511s, 493m, 449w. Anal. Calcd for C79H76N2Ni2O2P2: C,
75.02; H, 6.06; N, 2.21. Found: C, 75.00; H, 6.24; N, 2.10.
Synthesis of Binuclear Nickel Complex 3c. Ligand 1c was
prepared using the same procedure for ligand 1a. A 1.36 g (10.0
mmol) sample of 3-methylsalicylaldehyde and 0.96 g (5.0 mmol)
of 2,4,6-triethyl-m-phenylenediamine were used to give 1.47 g
1
(yield, 68%) of yellow crystals. H NMR (CDCl3, 500 MHz): δ
8.36 (s, 2H, CHdN), 7.29 (d, J ) 7.5 Hz, 2H, ArH), 7.21 (d, J )
7.5 Hz, 2H, ArH), 7.04 (s, 1H, ArH), 6.88 (t, J ) 7.5 Hz, 2H,
ArH), 2.51 (m, 6H, CH2), 2.34 (s, 6H, Me), 1.17 (t, J ) 7.5 Hz,
6H, Me), 0.99 (t, J ) 7.5 Hz, 3H, Me). 13C NMR (CDCl3, 300
MHz): 167.4, 160.8, 146.1, 137.8, 131.0, 130.6, 130.4, 126.9,
125.7, 118.6, 118.2, 35.0, 29.4. 24.7, 20.6. 15.0, 14.6.
To a suspension of sodium hydride (0.060 g, 0.20 mmol) in THF
(10 mL) was added a solution of ligand 1a (0.290 g, 0.750 mmol)
in THF (20 mL). The resulting mixture was stirred for 4 h at
ambient temperature. After filtration, the solvent of the filtrate was
removed under vacuum. The solid residue was washed with
n-hexane (10 mL) and dried under vacuum. The sodium salt of
ligand 1a was immediately used in the next step without further
purification. The sodium salt obtained above and trans-NiCl(Ph)-
(PPh3)2 (1.00 g, 1.44 mmol) were dissolved in toluene (30 mL)
and stirred for 14 h at room temperature. After filtration to remove
the formed sodium chloride, the clear solution was concentrated to
ca. 10 mL under vacuum, and n-hexane (20 mL) was added to the
solution. A yellow solid precipitated from solution was isolated by
filtration. The crude product was recrystallized from toluene and
n-hexane to give yellow needle crystals as complex 3a in 65% yield
based on ligand 1a. 1H NMR (C6D6, 500 MHz): δ 7.67-7.63 (m,
14H, CHdN and ArH), 7.36 (d, J ) 7.5 Hz, 2H, ArH), 7.20 (d, J
) 8.0 Hz, 3H, ArH), 6.98-6.95 (m, 6H, ArH), 6.90-6.86 (m, 13H,
ArH), 6.67 (d, J ) 7.5 Hz, 2H, ArH), 6.55 (t, J ) 7.4 Hz, 2H,
ArH), 6.40 (t, J ) 7.1 Hz, 3H, ArH), 6.25 (t, J ) 6.3 Hz, 2H,
ArH), 6.17 (t, J ) 7.4 Hz, 2H, ArH), 2.48 (s, 5H, Me), 2.21 (s,
2H, Me), 1.55 (s, 2H, Me), 1.44 (s, 6H, Me). 13C NMR (C6D6, 300
MHz): 166.2, 164.6, 150.1, 149.1, 148.4, 138.0, 137.2, 134.7,
134.5, 133.8, 132.3, 131.9, 131.7, 130.9, 129.6, 127.8, 127.7, 127.5,
126.4, 125.3, 121.1, 119.0, 113.9, 19.2, 16.3, 15.8. 31P NMR (C6D6,
202.5 MHz): δ 30.1 (s). IR (cm-1, KBr): 3048m, 3019w, 3003w,
2986w, 2942w, 1606vs, 1586s, 1560s, 1544vs, 1478m, 1449vs,
1433vs, 1377s, 1330s, 1286w, 1238s 1216s, 1198m, 1185w, 1160w,
1121w, 1096vs, 1075s, 1053w, 1017w, 997w, 973w, 890w, 866w,
748s, 734s, 694vs, 649w, 614w, 530vs, 510s, 498m, 469w. Anal.
Calcd for C73H64N2Ni2O2P2: C, 74.26; H, 5.46; N, 2.37. Found:
C, 74.49; H, 5.63; N, 2.22.
Complex 3c was prepared using the same procedure for complex
3a. A 0.060 g (0.20 mmol) amount of sodium hydride, 0.321 g
(0.750 mmol) of ligand 1c, and 1.00 g (1.44 mmol) of trans-NiCl-
(Ph)(PPh3)2 were used to give 0.664 g (yield, 72%) of yellow
1
crystals. H NMR (C6D6, 500 MHz): δ 7.96 (d, J ) 9.1 Hz, 2H,
CHdN), 7.65 (t, J ) 8.6 Hz, 12H, ArH), 7.02 (d, J ) 6.7 Hz, 4H,
ArH), 6.97-6.90 (m, 27H, ArH), 6.52 (t, J ) 7.4 Hz, 2H, ArH),
6.41 (t, J ) 7.1 Hz, 2H, ArH), 6.28-6.24 (m, 4H, ArH), 6.13 (s,
1H, ArH), 3.42 (m, 1H, CH2), 3.03 (m, 2H, CH2), 2.57 (m, 1H,
CH2), 2.40 (m, 5H, CH2 and Me), 2.10 (s, 3H, Me), 1.44 (s, 6H,
Me), 1.00 (t, J ) 7.5 Hz, 6H, Me). 13C NMR (C6D6, 300 MHz):
166.2, 164.8, 148.8, 148.7, 137.9, 137.8, 134.7, 134.5, 134.0, 133.0,
132.2, 131.7, 131.0, 130.2, 129.6, 127.7, 124.7, 123.6, 123.2, 121.0,
118.4, 114.0, 25.8, 22.7, 16.3, 15.5, 15.2. IR (cm-1, KBr): 3045m,
3018m, 2960s, 2926m, 2864m, 1605vs, 1583s, 1563s, 1543vs,
1449s, 1431vs, 1375m, 1331s, 1236m, 1214s, 1189m, 1160m,
1095s, 1078s, 1053m, 1020m, 996m, 970m, 872s, 746s, 728s,
692vs, 529s, 509s, 493s, 441m, 419m. Anal. Calcd for C76H70N2-
Ni2O2P2‚C6H5CH3: C, 75.82; H, 5.98; N, 2.13. Found: C, 75.69;
H, 5.86; N, 2.19.
Synthesis of Binuclear Nickel Complex 3d. Ligand 1d was
prepared using the same procedure for ligand 1a. A 1.78 g (10.0
mmol) portion of 3-tert-butylsalicylaldehyde and 0.96 g (5.0 mmol)
of 2,4,6-triethyl-m-phenylenediamine were used to give 1.80 g
1
(yield, 70%) of yellow crystals. H NMR (CDCl3, 500 MHz): δ
8.37 (s, 2H, CHdN), 7.43 (dd, J ) 7.6 Hz, J ) 0.9 Hz, 2H, ArH),
7.21 (dd, J ) 7.6 Hz, J ) 0.9 Hz, 2H, ArH), 7.04 (s, 1H, ArH),
Synthesis of Binuclear Nickel Complex 3b. Ligand 1b was
prepared using the same procedure for ligand 1a. A 1.78 g (10.0
mmol) sample of 3-tert-butylsalicylaldehyde and 0.75 g (5.0 mmol)
of 2,4,6-trimethyl-m-phenylenediamine were used to give 1.43 g
(24) (a) Sehun, P. A. Inorg. Synth. 1972, 13, 124. (b) Hidai, M.;
Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet. Chem. 1971, 30, 279.
(25) Wilke, G. Angew. Chem. 1960, 72, 581.

624 Organometallics, Vol. 26, No. 3, 2007
Chen et al.
6.89 (t, J ) 7.6 Hz, 2H, ArH), 2.51 (m, 6H, CH2), 1.48 (s, 18H,
tBu), 1.18 (t, J ) 7.5 Hz, 6H, Me), 1.00 (t, J ) 7.5 Hz, 3H, Me).
13C NMR (CDCl3, 300 MHz): δ 167.4, 160.7, 146.0, 137.8, 131.0,
130.6, 130.5, 126.8, 125.8, 118.6, 118.2, 35.0, 29.4, 24.8, 20.6,
15.1, 14.6. Anal. Calcd for C34H44N2O2: C, 79.65; H, 8.65; N, 5.46.
Found: C, 79.34; H, 8.65; N, 5.34.
7.5 Hz, 2H, ArH), 7.17 (s, 1H, ArH), 6.88 (t, J ) 7.5 Hz, 2H,
ArH), 3.20 (m, 1H, CH), 2.95 (m, 2H, CH), 2.35 (s, 6H, Me), 1.19
(d, J ) 6.8 Hz, 12H, Me), 1.16 (d, J ) 7.2 Hz, 6H, Me). 13C NMR
(CDCl3, 300 MHz): 167.2, 159.5, 145.8, 135.7, 134.4, 130.0, 128.5,
126.4, 120.9, 118.7, 117.9, 28.2, 28.0, 23.8, 22.3, 14.3. Anal. Calcd
for C31H38N2O2: C, 79.11; H, 8.14; N, 5.95. Found: C, 78.93; H,
8.17; N, 5.86.
Complex 3d was prepared using the same procedure for complex
3a. A 0.060 g (0.20 mmol) sample of sodium hydride, 0.385 g
(0.75o mmol) of ligand 1d, and 1.00 g (1.44 mmol) of trans-NiCl-
(Ph)(PPh3)2 were used to give 0.811 g (yield, 83%) of yellow-brown
Complex 3f was prepared using the same procedure for complex
3a. A 0.060 g (0.20 mmol) portion of sodium hydride, 0.353 g
(0.750 mmol) of ligand 1f, and 1.00 g (1.44 mmol) of trans-NiCl-
(Ph)(PPh3)2 were used to give 0.624 g (yield, 66%) of yellow
1
crystals. H NMR (C6D6, 500 MHz): δ 7.98 (d, J ) 9.2 Hz, 2H,
1
CHdN), 7.78 (t, J ) 8.7 Hz, 12H, ArH), 7.43 (d, J ) 7.4 Hz, 2H,
ArH), 7.10 (d, J ) 7.6 Hz, 2H, ArH), 7.05-6.91 (m, 21H, ArH),
6.77 (d, J ) 7.6 Hz, 2H, ArH), 6.61 (t, J ) 7.4 Hz, 2H, ArH), 6.32
(t, J ) 7.0 Hz, 2H, ArH), 6.18 (t, J ) 7.4 Hz, 2H, ArH), 6.12 (t,
J ) 7.0 Hz, 2H, ArH), 3.51 (m, 1H, CH2), 3.08 (m, 2H, CH2),
2.68 (m, 1H, CH2), 2.51 (t, J ) 7.5 Hz, 3H, Me), 2.42 (m, 2H,
crystals. H NMR (C6D6, 500 MHz): δ 8.06 (d, J ) 9.1 Hz, 2H,
CHdN), 7.66 (m, 12H, ArH), 6.97-6.78 (m, 26H, ArH), 6.52-
6.34 (m, 9H, ArH), 4.13 (m, 1H, CH), 3.64 (m, 2H, CH), 1.50 (s,
6H, Me), 1.02-0.87 (m, 18H, Me). IR (cm-1, KBr): 3049m, 2956s,
2926m, 2865m, 1605vs, 1583s, 1561m, 1542vs, 1481m, 1466m,
1448s, 1433vs, 1376s, 1360m, 1329s, 1240m, 1217s, 1191m,
1163m, 1095s, 1083m, 1052m, 1018m, 998w, 969w, 868m, 747s,
729s, 693vs, 640w, 529s, 511s, 492m, 453w, 420w. Anal. Calcd
for C79H76N2Ni2O2P2: C, 75.02; H, 6.06; N, 2.21. Found: C, 75.26;
H, 6.32; N, 1.82.
t
CH2), 1.00 (t, J ) 7.5 Hz, 6H, Me), 0.92(s, 18H, Bu). 13C NMR
(C6D6, 300 MHz): 167.1, 166.4, 148.9,147.5, 146.3, 141.9, 137.4,
137.2, 135.1, 134.9, 133.6, 133.3, 132.4, 131.8, 131.4, 129.7, 126.1,
124.7, 124.2, 120.9, 120.4, 113.9, 34.6, 29.8, 25.8, 22.8, 15.7, 15.5.
IR (cm-1, KBr): 3046m, 3004w, 2961s, 2867m, 1601vs, 1587vs,
1563s, 1536vs, 1481m, 1461s, 1435s, 1417s, 1386s, 1337s, 1317s,
1222w, 1187s, 1144s, 1092s, 1056w, 1018w, 996w, 965w, 871m,
859w, 749s, 729s, 693vs, 530s, 511s, 490s, 450w, 438w, 421w.
Anal. Calcd for C82H82N2Ni2O2P2: C, 75.36; H, 6.32; N, 2.14.
Found: C, 75.12; H, 6.50; N, 1.98.
Synthesis of Binuclear Nickel Complex 3g. Ligand 1g was
prepared using the same procedure for ligand 1a. A 1.78 g (10.0
mmol) amount of 3-tert-butylsalicylaldehyde and 1.17 g (5.00
mmol) of 2,4,6-triisopropyl-m-phenylenediamine were used to give
2.09 g (yield, 71%) of yellow crystals. 1H NMR (CDCl3, 500
MHz): δ 8.32 (s, 2H, CHdN), 7.44 (d, J ) 7.5 Hz, 2H, ArH),
7.20 (d, J ) 7.5 Hz, 2H, ArH), 7.17 (s, 1H, ArH), 6.90 (t, J ) 7.5
Hz, 2H, ArH), 3.21 (m, 1H, CH), 2.96 (m, 2H, CH), 1.49 (s, 18H,
tBu), 1.20 (d, J ) 6.7 Hz, 12H, Me), 1.17 (d, J ) 6.9 Hz, 6H, Me).
13C NMR (CDCl3, 300 MHz): δ 167.6, 160.7, 145.6, 137.9, 135.7,
130.6, 130.5, 128.7, 120.9, 118.5, 118.2, 35.0, 29.4, 28.2, 27.9,
23.8, 22.2. Anal. Calcd for C37H50N2O2: C, 80.10; H, 9.08; N, 5.05.
Found: C, 80.12; H, 8.64; N, 4.95.
Synthesis of Binuclear Nickel Complex 3e. Ligand 1e was
prepared using the same procedure for ligand 1a. A 1.22 g (10.0
mmol) amount of salicylaldehyde and 1.17 g (5.00 mmol) of 2,4,6-
triisopropyl-m-phenylenediamine were used to give 1.83 g (yield,
1
82%) of yellow crystals. H NMR (CDCl3, 500 MHz): δ 8.32 (s,
2H, CHdN), 7.43 (t, J ) 7.4 Hz, 2H, ArH), 7.36 (d, J ) 8.1 Hz,
2H, ArH), 7.18 (s, 1H, ArH), 7.08 (d, J ) 8.1 Hz, 2H, ArH), 6.97
(t, J ) 7.4 Hz, 2H, ArH), 3.19 (m, 1H, CH), 2.94 (m, 2H, CH),
Complex 3g was prepared using the same procedure for complex
3a. A 0.060 g (0.20 mmol) sample of sodium hydride, 0.416 g
(0.750 mmol) of ligand 1g, and 1.00 g (1.44 mmol) of trans-NiCl-
(Ph)(PPh3)2 were used to give 0.821 g (yield, 81%) of yellow-brown
1.20 (d, J ) 6.9 Hz, 12H, Me), 1.17 (d, J ) 7.1 Hz, 6H, Me). 13
C
NMR (CDCl3, 300 MHz): δ 167.2, 161.4, 144.9, 136.2, 133.9,
132.5, 128.8, 121.2, 119.3, 118.3, 117.5, 28.2, 28.0, 23.7, 22.2. IR
(cm-1, KBr) ν: 3061m, 2957s, 2927m, 2784m, 1626vs, 1576s,
1495s, 1463s, 1409m, 1383w, 1316m, 1327w, 1273vs, 1242w,
1224w, 1191s, 1152s, 1115w, 1090w, 1059w, 1033m, 1013m,
992w, 947w, 908s, 887m, 816s, 756vs, 736m, 708w. Anal. Calcd
for C29H34N2O2: C, 78.70; H, 7.74; N, 6.33. Found: C, 78.64; H,
7.54; N, 6.19.
1
crystals. H NMR (C6D6, 500 MHz): δ 8.07 (d, J ) 8.9 Hz, 2H,
CHdN), 7.76 (m, 12H, ArH), 7.44-7.39 (m, 4H, ArH), 7.02-
6.93 (m, 21H, ArH), 6.63-6.59 (m, 4H, ArH), 6.33-6.17 (m, 6H,
ArH), 4.31 (m, 1H, CH), 2.95 (m, 2H, CH), 1.31(d, J ) 5.3 Hz,
t
6H, Me), 1.03(d, J ) 5.3 Hz, 12H, Me), 0.95 (s, 18H, Bu). 13C
NMR (C6D6, 300 MHz): 167.6, 166.1, 148.6, 142.1, 138.8, 137.2,
135.0, 134.9, 133.5, 132.1, 131.5, 130.4, 129.7, 127.5, 125.4, 124.6,
120.9, 120.0, 119.2, 113.9, 34.6, 30.3, 29.9, 28.6, 26.2, 25.6, 24.9,
22.5. IR (cm-1, KBr): 3049m, 3003w, 2956s, 2906m, 2876m,
1600vs, 1562m, 1536vs, 1481w, 1466m, 1436s, 1417s, 1384m,
1360w, 1338m, 1319m, 1265w, 1246w, 1224w, 1187m, 1143m,
1098s, 1057w, 1020w, 997w, 869w, 748s, 729m, 693vs, 657w,
636w, 530s, 511m, 492m. ESI-MS (m/e): 1349 (M+). Anal. Calcd
for C85H88N2Ni2O2P2: C, 75.68; H, 6.58; N, 2.08. Found: C, 75.77;
H, 6.56; N, 1.82.
Complex 3e was prepared using the same procedure for complex
3a. A 0.060 g (0.20 mmol) amount of sodium hydride, 0.332 g
(0.750 mmol) of ligand 1e, and 1.00 g (1.44 mmol) of trans-NiCl-
(Ph)(PPh3)2 were used to give 0.818 g (yield, 88%) of yellow
1
crystals. H NMR (C6D6, 500 MHz): δ 8.02 (d, J ) 8.6 Hz, 2H,
CHdN), 7.64 (m, 12H, ArH), 7.42-6.93 (m, 26H, ArH), 6.51-
6.29 (m, 11H, ArH), 4.15 (m, 1H, CH), 2.73 (m, 2H, CH), 1.35 (d,
J ) 7.1 Hz, 3H, Me), 0.94 (d, J ) 7.2 Hz, 12H, Me), 0.84 (d, J )
7.1 Hz, 3H, Me). 13C NMR (C6D6, 300 MHz): 166.6, 160.0, 148.2,
146.8, 138.3, 138.0, 134.5, 134.4, 134.0, 131.9, 131.4, 129.9, 127.8,
127.5, 125.2, 124.7, 122.8, 121.1, 119.4, 114.3, 30.0, 28.5, 26.0,
25.2, 24.8, 22.2. IR (cm-1, KBr): 3047w, 2957m, 2869w, 1606vs,
1582s, 1561m, 1531s, 1465m, 1444vs, 1374w, 1358m, 1327m,
1251w, 1199w, 1146m, 1127w, 1095m, 1057w, 1018w, 925w,
743m, 731s, 694vs, 530s, 512s, 494m, 454w. Anal. Calcd for
C77H72N2Ni2O2P2: C, 74.78; H, 5.87; N, 2.27. Found: C, 75.08;
H, 6.14; N, 2.07.
Synthesis of Binuclear Nickel Complex 3h. Ligand 1h was
prepared using the same procedure for ligand 1a. 3-Phenylsalicyl-
aldehyde (1.98 g, 10.0 mmol) and 1.17 g (5.00 mmol) of 2,4,6-
triisopropyl-m-phenylenediamine were used to give 2.12 g (yield,
1
71%) of yellow crystals. H NMR (CDCl3, 500 MHz): δ 8.38 (s,
2H, CHdN), 7.70 (d, J ) 7.4 Hz, 4H, ArH), 7.52 (d, J ) 7.5 Hz,
2H, ArH), 7.47 (t, J ) 7.5 Hz, 4H, ArH), 7.37 (t, J ) 7.4 Hz, 4H,
ArH), 7.17 (s, 1H, ArH), 7.05 (t, J ) 7.5 Hz, 2H, ArH), 3.21 (m,
1H, CH), 2.96 (m, 2H, CH), 1.12-1.17 (m, 18H, Me). 13C NMR
(CDCl3, 300 MHz): δ 167.3, 158.3, 145.5, 137.4, 135.9, 134.4,
131.8, 130.1, 129.4, 128.6, 128.2, 127.3, 121.0, 119.1, 118.7, 28.3,
28.0, 23.8, 22.3. IR (cm-1, KBr) ν: 3051w, 2960s, 2925m, 2867m,
2786w, 2718w, 1621vs, 1585s, 1526w, 1492w, 1453s, 1432s,
1383w, 1362m, 1322m, 1280m, 1220w, 1204m, 1169w, 1099s,
Synthesis of Binuclear Nickel Complex 3f. Ligand 1f was
prepared using the same procedure for ligand 1a. A 1.36 g (10.0
mmol) amount of 3-methylsalicylaldehyde and 1.17 g (5.00 mmol)
of 2,4,6-triisopropyl-m-phenylenediamine were used to give 1.81
g (yield, 77%) of yellow crystals. 1H NMR (CDCl3, 500 MHz): δ
8.31 (s, 2H, CHdN), 7.30 (d, J ) 7.5 Hz, 2H, ArH), 7.20 (d, J )

Arene-Bridged Binuclear Neutral Nickel(II) Complexes
Organometallics, Vol. 26, No. 3, 2007 625
1071m, 1015m, 933m, 905w, 882w, 851w, 831m, 797w, 754s,
696s, 640w, 617w, 579w. Anal. Calcd for C41H40N2O2: C, 82.79;
H, 7.12; N, 4.71. Found: C, 82.82; H, 6.89; N, 4.57.
of 2,4,6-triisopropyl-m-phenylenediamine were used to give 2.34
g (yield, 88%) of yellow crystals. 1H NMR(CDCl3, 500 MHz): δ
8.40 (s, 2H, CHdN), 8.35 (m, 4H, ArH), 7.26 (s, 1H, ArH), 7.15
(d, J ) 8.8 Hz, 2H, ArH), 3.13 (m, 1H, CH-H), 2.88 (m, 2H,
CH), 1.22 (d, J ) 6.8 Hz, 12H, Me), 1.16 (d, J ) 7.0 Hz, 6H,
Me). 13C NMR (CDCl3, 300 MHz): 166.8, 165.9, 144.3, 140.1,
136.5, 128.8, 128.4, 121.6, 118.6, 117.4, 28.3, 28.1, 23.7, 22.3.
Anal. Calcd for C29H31N4O6: C, 65.40; H, 6.06; N, 10.52. Found:
C, 65.29; H, 5.61; N, 10.41.
Complex 3h was prepared using the same procedure for complex
3a. Sodium hydride (0.060 g, 0.20 mmol), 0.476 g (0.750 mmol)
of ligand 1h, and 1.00 g (1.44 mmol) of trans-NiCl(Ph)(PPh3)2 were
1
used to give 0.857 g (yield, 77%) of yellow-brown crystals. H
NMR (C6D6, 500 MHz): δ 7.95 (d, J ) 8.6 Hz, 2H, CHdN), 7.52
(m, 12H, ArH), 7.37 (dd, J ) 7.2 Hz, J ) 1.9 Hz, 2H, ArH), 7.09
(d, J ) 7.6 Hz, 1H, ArH), 7.02-6.91 (m, 16H, ArH), 6.82 (t, J )
7.0 Hz, 15H, ArH), 6.72 (t, J ) 7.3 Hz, 3H, ArH), 6.64 (t, J ) 7.5
Hz, 4H, ArH), 6.60 (s, 1H, Ar-H), 6.55 (t, J ) 7.5 Hz, 2H, ArH),
6.39 (t, J ) 7.0 Hz, 2H, ArH), 6.26 (t, J ) 7.2 Hz, 4H, ArH), 3.94
(m, 1H, CH), 2.68 (m, 2H, CH), 2.08 (s, 3H, Me), 1.00-0.79 (m,
18H, Me). 13C NMR (C6D6, 300 MHz): 167.2, 163.6, 148.3, 140.1,
139.2, 135.2, 134.7, 134.5, 134.1, 132.0, 131.5, 129.7, 128.1, 127.8,
127.5, 127.2, 125.4, 121.0, 119.6, 118.8, 114.4, 30.1, 28.6, 26.0,
25.2, 24.8, 22.3, 21.2. IR (cm-1, KBr): 3049m, 2958s, 2930m,
2867w, 1597vs, 1561m, 1540vs, 1466m, 1423vs, 1380m, 1361w,
1328s, 1282m, 1244w, 1217s, 1192m, 1162w, 1095s, 1072m,
1021m, 998w, 948w, 907w, 884w, 854m, 750s, 731s, 693vs, 616w,
599w, 575w, 529s, 512s, 494m, 453w, 418w. ESI-MS (m/e):
1389.3 [M + H]+. Anal. Calcd for C89H80N2Ni2O2P2‚C6H5CH3: C,
77.85; H, 5.99; N, 1.89. Found: C, 77.67; H, 6.02; N, 1.66.
Synthesis of Binuclear Nickel Complex 3i. Ligand 1i was
prepared using the same procedure for ligand 1a. 3,5-Dinitrosali-
cylaldehyde (2.12 g, 10.0 mmol) and 1.17 g (5.00 mmol) of 2,4,6-
triisopropyl-m-phenylenediamine were used to give 2.43 g (yield,
78%) of yellow crystals. 1H NMR (CDCl3, 500 MHz): δ 9.09 (d,
J ) 2.6 Hz, 2H, ArH), 8.61 (s, 2H, ArH), 8.42 (s, 2H, CHdN),
7.33 (s, 1H, ArH), 3.15 (m, 1H, CH), 2.88 (m, 2H, CH), 1.26 (d,
J ) 6.9 Hz, 12H, Me), 1.23 (d, J ) 7.0 Hz, 6H, Me). 13C NMR
(CDCl3, 300 MHz): 165.8, 164.6, 140.1, 136.7, 133.0, 131.5, 130.7,
126.6, 124.4, 122.7, 119.0, 28.5, 27.3, 23.7, 22.3. Anal. Calcd for
C29H30N6O10: C, 55.95; H, 4.86; N, 13.50. Found: C, 55.86; H,
4.47; N, 13.26.
To a suspension of trans-NiCl(Ph)(PPh3)2 (1.04 g, 1.50 mmol)
and NEt3 (0.175 g, 1.73 mmol) in toluene (15 mL) was added
dropwise a toluene solution (20 mL) of ligand 1j (0.400 g, 0.750
mmol). This reaction mixture was allowed to stir for 12 h at ambient
temperature. After filtration, the filtrate was concentrated to ca. 10
mL under vacuum, and n-hexane (20 mL) was added to the solution.
A yellow solid precipitated from solution was isolated by filtration.
The crude product was recrystallized from toluene and n-hexane
to give yellow crystals as complex 3j in 52% yield. 1H NMR (C6D6,
500 MHz): δ 8.25 (d, J ) 2.6 Hz, 2H, ArH), 7.94-7.89 (m, 4H,
CHdN and ArH), 7.50 (t, J ) 8.9 Hz, 12H, ArH), 7.05-6.93 (m,
26H, ArH), 6.60 (m, 1H, ArH), 6.47 (s, 1H, ArH), 6.38 (t, J ) 7.1
Hz, 2H, ArH), 6.23 (t, J ) 7.1 Hz, 2H, ArH), 6.18 (t, J ) 7.3 Hz,
2H, ArH), 5.98 (t, J ) 7.3 Hz, 2H, ArH), 3.95 (m, 1H, CH), 2.64
(m, 2H, CH), 2.10 (s, 3H, Me), 1.22 (d, J ) 7.0 Hz, 3H, Me), 0.93
(d, J ) 6.6 Hz, 6H, Me), 0.85 (d, J ) 6.6 Hz, 9H, Me). 13C NMR
(C6D6, 300 MHz): 170.2, 166.3, 147.3, 144.4, 138.5, 137.8, 137.3,
136.7, 134.3, 131.3, 131.0, 130.4, 130.0, 127.9, 125.7, 125.4, 125.0,
123.0, 121.7, 119.5, 118.2, 31.7, 30.0, 26.1, 25.2, 25.0, 22.1, 21.2.
IR (cm-1, KBr): 3049w, 2959m, 2918w, 2867w, 1606vs, 1561m,
1543s, 1468s, 1433s, 1379m, 1322vs, 1243w, 1186m, 1095s,
1019w, 996w, 950m, 834m, 730s, 693s, 649w, 528m, 510m, 458w.
Anal. Calcd for C77H70N4Ni2O6P2‚C6H5CH3: C, 71.11; H, 5.54;
N, 3.95. Found: C, 71.12; H, 5.68; N, 3.92.
Ethylene Polymerization Procedure. A 100 mL autoclave,
equipped with a magnetic stirrer bar, was heated at 100 °C under
vacuum for 30 min and then cooled to the required temperature.
Toluene was injected into the reactor and pressurized with ethylene
to 1 atm. After equilibrating for 3 min, an appropriate volume of
catalyst solution and Ni(COD)2 solution were injected to start the
reaction. The ethylene pressure was kept constant at 10 atm during
the polymerization. After the desired run time, the reactor was
vented and the reaction mixture was quenched with 3% HCl in
ethanol. The precipitated polymer was filtered, washed to neutral
with ethanol, and then dried overnight in a vacuum oven at 80 °C.
X-ray Crystallography of Complex 3h. A yellow-brown crystal
of complex 3h was sealed in a capillary under an argon atmosphere.
All measurements were made on a Bruker AXSD8 diffractometer
with graphite-monochromated Mo KR (λ ) 0.71073 Å) radiation.
All data were collected at 20 °C using the scan techniques. The
structure of 3h was solved by direct methods and refined using
Fourier techniques. An absorption correction based on SADABS
was applied.26 All non-hydrogen atoms were refined by full-matrix
least-squares on F2 using the SHELXTL program package.27
Hydrogen atoms were located and refined by the geometry method.
The cell refinement, data collection, and reduction were done by
Bruker SAINT.28 The structure solution and refinement were
performed by SHELXS-9729 and SHELXL-97,30 respectively. For
further crystal data and details of measurements see Table 1.
Complex 3i was prepared using the same procedure for complex
3a. Sodium hydride (0.060 g, 0.20 mmol), 0.467 g (0.750 mmol)
of ligand 1i, and 1.00 g (1.44 mmol) of trans-NiCl(Ph)(PPh3)2 were
1
used to give 0.586 g (yield, 52%) of yellow-brown crystals. H
NMR (C6D6, 500 MHz): δ 8.26 (d, J ) 2.8 Hz, 2H, ArH), 7.93
(d, J ) 2.8 Hz, 2H, ArH), 7.78 (d, J ) 7.9 Hz, 2H, CHdN), 7.49
(t, J ) 9.1 Hz, 12H, ArH), 7.13-7.01 (m, 27H, ArH), 6.59 (s, 1H,
ArH), 6.43 (t, J ) 7.1 Hz, 2H, ArH), 6.25-6.20 (m, 4H, ArH),
3.84 (m, 1H, CH), 2.56 (m, 2H, CH), 2.10 (s, 3H, Me), 1.11 (d, J
) 7.0 Hz, 3H, Me), 0.97 (d, J ) 6.8 Hz, 6H, Me), 0.90 (d, J ) 6.8
Hz, 9H, Me). 13C NMR (C6D6, 300 MHz): 165.5, 161.5, 147.0,
142.7, 138.9, 136.9, 134.2, 134.1, 133.9, 133.0, 130.4, 129.9, 128.1,
127.8, 127.5, 124.8, 122.0, 121.5, 120.0, 29.2, 27.8, 26.0, 25.1,
24.9, 22.1, 21.2. IR (cm-1, KBr): 3051w, 2958w, 2868w, 1612vs,
1557s, 1530m, 1507w, 1474m, 1434s, 1334vs, 1222w, 1185w,
1096s, 1018w, 1185w, 1096s, 1018w, 995w, 909w, 732m, 692s,
529m, 509m. Anal. Calcd for C77H68N6Ni2O10P2‚C6H5CH3: C,
66.86; H, 5.08; N, 5.57. Found: C, 66.62; H, 5.33; N, 5.18.
Synthesis of Binuclear Nickel Complex 3j. Ligand 1j was
prepared using the same procedure for ligand 1a. A 1.67 g (10.0
mmol) amount of 5-nitrosalicylaldehyde and 1.17 g (5.00 mmol)
(26) SADABS, Bruker Nonius area detector scaling and absorption
correction-V2.05; Bruker AXS Inc.: Madison, WI, 1996.
(27) Sheldrick, G. M. SHELXTL 5.10 for windows NT, Structure
Determination Software Programs; Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 1997.
(28) SAINT, Version 6.02; Bruker AXS Inc.: Madison, WI, 1999.
(29) Sheldrick, G. M. SHELXS-97, Program for the Solution of Crystal
Structures; University of Gottingen: Germany, 1990.
Acknowledgment. This work is subsidized by the National
Basic Research Program of China (2005CB623801) and the
National Natural Science Foundation of China (20372022).
Supporting Information Available: Data in CIF format. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(30) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
Structures; University of Gottingen: Germany, 1997.
OM060778E