Synthesis, crystal structures and use in ethylene oligomerization catalysis of novel mono- and dinuclear nickel complexes supported by (E)-N′-(1- (thiophen-2-yl)ethylidene)benzohydrazide ligand

Article abstract of DOI:10.1016/j.ica.2011.11.009

The coordination chemistry of Ni^II supported by (E)-N′-(1-(thiophen-2-yl)ethylidene)benzohydrazide ligand (HL) is reported and discussed. The crystal structure of ligand HL has been determined as well as those of three new Ni^II complexes (Ni(HL)₂Br ₂, NiL₂ and μ-aquo-Ni₂L₄). The pseudo-octahedral bis(chelate) Ni(II) complex 2 (NiL₂), in which unexpected and singular Ni...S interaction is observed, was evaluated as catalyst for the oligomerization of ethylene and found to provide ethylene dimers and trimers as primary products with a turnover frequency (TOF) of 31 200 mol of C₂H₄ per mol. of Ni and per hour.

Full text of DOI:10.1016/j.ica.2011.11.009

Inorganica Chimica Acta 383 (2012) 213–219
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Synthesis, crystal structures and use in ethylene oligomerization catalysis
of novel mono- and dinuclear nickel complexes supported by
(E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide ligand
Weiwei Zuo a, Clarisse Tourbillon a, Vitor Rosa a, Khaled Cheaib a, Marta M. Andrade b, Samuel Dagorne a,
Richard Welter a,
⇑
a Laboratoire DECOMET, UMR 7177 CNRS, Université Louis Pasteur, 4, rue Blaise Pascal, 67070 Strasbourg Cedex, France
b Requimte, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
a r t i c l e i n f o
a b s t r a c t
The coordination chemistry of NiII supported by (E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide
ligand (HL) is reported and discussed. The crystal structure of ligand HL has been determined as well
Article history:
Received 31 August 2011
Received in revised form 2 November 2011
Accepted 3 November 2011
Available online 13 November 2011
as those of three new NiII complexes (Ni(HL)2Br2, NiL2 and
l-aquo-Ni2L4). The pseudo-octahedral bis(che-
late) Ni(II) complex 2 (NiL2), in which unexpected and singular Niꢀ ꢀ ꢀS interaction is observed, was eval-
uated as catalyst for the oligomerization of ethylene and found to provide ethylene dimers and trimers as
primary products with a turnover frequency (TOF) of 31200 mol of C2H4 per mol. of Ni and per hour.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Coordination chemistry
Nickel complexes
Crystal structure
Ethylene oligomerization catalysis
1. Introduction
of dinuclear complexes [2,7] in the crystalline state (with possible
impact on their magnetic behaviour) and also due the spontaneous
We earlier reported interesting magnetic properties of
transition metal complexes supported by 2-salicyloylhydrazono-
1,3-dithiolane (H2L⁄) and its derivatives [1–7]. For instance, the
reduction of FeIII to FeII observed in iron mononuclear species, the
original ligand was modified at specific positions (see Scheme 1).
We have also become interested in studying the coordination
chemistry of this type of hydrazine ligands with other transition
metals, along with their possible applications as catalysts. In the
present article, we report the synthesis and structural characterisa-
tion of novel NiII complexes supported by the (E)-N0-(1-(thiophen-
2-yl)ethylidene)benzohydrazide ligand (Scheme 1) and their
subsequent use in ethylene oligomerization catalysis.
dinuclear complex Mn2(HL⁄)4(
l-OCH3)2 was found to exhibit the
largest J value (J = +19.7 cmꢁ1) reported so far for a MnIII–MnIII
ferromagnetic interaction [2]. On this basis, we have been working
on slight modifications of the organic peripheral backbone as well
as on using other metal centres, such as chromium [5], iron [3,7]
and cobalt [6].
When exploring the iron chemistry with such hydrazine deriv-
ative ligands, we also observed an unusual spontaneous reduction
from FeIII to FeII of the mononuclear complexes [3]. This possible
photo-induced redox reaction was subsequently fully investigated
by electrochemistry, EPR studies, magnetic measurements, as well
as solid-state molecular structure determinations. Such a phenom-
enon opens up new research opportunities, as recently pointed out
by Wernsdorfer and co-worker [8] and demonstrated by our patent
[9].
2. Experimental
2.1. General procedures
All manipulations were performed under aerobic conditions
unless specified otherwise. Reagents and solvents were commer-
cially purchased and used as received. NMR spectra were recorded
at room temperature on a Bruker AVANCE 300 spectrometer (1H,
300 MHz; 13C, 75.47 MHz). Assignments were based on 1H, 1H-
COSY, 1H, 13C-HMQC and 1H, 13C-HMBC experiments. IR spectra
were recorded in the region 4000–100 cmꢁ1 on a Nicolet 6700
FT-IR spectrometer (ATR mode, diamond crystal). Elemental analy-
ses were performed by the ‘‘Service de microanalyses’’, Université
de Strasbourg.
With the purpose of acquiring more insight into the structural
factors controlling and influencing the formation and stabilization
⇑
Corresponding author. Tel.: +33 90 24 15 93; fax: +33 90 24 12 29.
E-mail address: welter@unistra.fr (R. Welter).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.009

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W. Zuo et al. / Inorganica Chimica Acta 383 (2012) 213–219
Scheme 1. Structural relationship between HL ((E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide) and H2L⁄ (2-salicyloylhydrazono-1,3-dithiolane). The ligands HL0, and
HL00 have been previously described [4,7].
2.2. Synthesis of (E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide
(HL)
1438m, 1367w, 1309w, 1274w, 1189s, 1120s, 1024w, 720s, 696s.
Anal. Calc. for C26H22N4NiO2S2: C, 57.27; H, 4.07; N, 10.27. Found:
C, 57.25; H, 4.13; N, 10.44%.
Benzhydrazide (5.00 g, 36.7 mmol) and 2-acetylthiophene
(4.63 g, 36.7 mmol) were placed in a quartz tube in a QV-50S reac-
tor equipped with temperature and pressure probes, which was
introduced in the microwave oven (Milestone Micro-SYNTH appa-
ratus). The reaction proceeded under stirring for 4.5 min at 200 W,
with a final temperature of 247 °C and final pressure of 8.0 bar. The
system was then allowed to cool down to room temperature, lead-
ing to crystallization of the hydrazone. Ethyl ether was added to
the quartz tube to wash the product which was filtrated under re-
duced pressure and further washed with diethyl ether to afford
8.30 g (93%) of yellowish needles (m.p. 188–189 °C). 1H NMR (d6-
DMSO): d 2.39 (s, 3H, CH3), 7.11 (s, 1H, Thio-H), 7.69-7.38 (m,
4H, 2 ꢂ Thio-H and 2 ꢂ Ar–H), 7.87 (s, 2H, Ar–H), 10.79 (br s, 1H,
N–H). 13C{1H} NMR (d6-DMSO): d 14.9 (CH3), 127.5 (C-Thio),
127.7 (C-Thio), 128.2 (C-Thio), 129.0 (C-Thio), 131.4 (C–Ar),
143.1(C–Ar), 152.6 (C@N), 163.4 (C@O). IR (pure, orbit diamond):
1652 (C@O), 1637 (N–H), 1541(C@N). Anal. Calc. for C13H12N2OS:
C, 63.91; H, 4.95; N, 11.47. Found: C, 63.95; H, 4.94; N, 11.54%.
2.5. Synthesis of complex 3 [Ni2(l-H2O)(l-L)2(L)2]
To a well stirred solution of (E)-N0-(1-(thiophen-2-yl)ethyli-
dene)benzohydrazide (0.1 g, 0.41 mmol) in THF (12.5 mL), NiCl2
(0.026 g, 0.2 mmol) was added. An excess of Et3N (0.56 mL,
4.0 mmol) was added to the solution until the formation of a white
precipitate. The solution was left under stirring overnight at room
temperature and then the white precipitate (Et3NꢀHBr) was filtered
off. A green powder of the titled complex was obtained by solvent
evaporation and then dried under vacuum. Green monocrystals
suitable for X-ray crystal structure determination were collected
by slow diffusion of diethyl ether into a dichloromethane solution
of the titled complex (yield: 0.10 g, 25%). IR (pure, orbit diamond):
2363m, 1645w, 1575w, 1509m, 1423w, 1270w. Anal. Calc. for
C
60H62N8Ni2O7S4 (3ꢀ2THF): C, 57.52; H, 4.99; N, 8.94. Found: C,
57.66; H, 4.76; N, 8.87%.
2.6. Oligomerization of ethylene
2.3. Synthesis of complex 1 [Ni(HL)2(Br)2]
4 ꢂ 10ꢁ5 mmol of Ni complex 2 was dissolved in 15 mL toluene
and injected into the reactor under an ethylene flux. Then a 5 mL
toluene solution of AlEtCl2 (8 ꢂ 10ꢁ5 mol/L) was added to obtain
a total volume of 20 mL. The reactor was pressurised to 10 bars
and a rise in temperature was observed as a result of the reaction
exothermicity. The 10 bar working pressure was maintained dur-
ing the experiments through a continuous feed of ethylene from
a reserve bottle placed on a balance to allow continuous monitor-
ing of the ethylene uptake. At the end of the test (35 min), a dry ice
bath was used to rapidly cool down the reactor, thus stopping the
reaction. An ice bath was then used and when the inner tempera-
ture reached 0 °C, the ice bath was removed allowing the temper-
ature to slowly rise to 10 °C. The gaseous phase was then
transferred into a 10 L polyethylene tank filled with water. An ali-
quot of this gaseous phase was transferred into a Schlenk flask for
GC analysis. The products in the reactor were alcoholyzed in situ by
the addition of ethanol (10 mL), transferred into a Schlenk flask,
and separated from the metal complexes by trap-to-trap evapora-
tion (20 °C, 0.8 mbar) into a second Schlenk flask previously
immersed in liquid nitrogen, in order to avoid any loss of product.
To a solution of Ni(Br)2(PPh3)2 (0.15 g, 0.20 mmol) in THF
(20 mL), (E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide (0.1 g,
0.41 mmol) was added. The green solution was left under stirring
overnight at room temperature and then filtered. Green powder of
the titled complex was obtained after solvent evaporation and then
dried under vacuum. Green monocrystals suitable for X-ray crystal
structure determination were obtained by slow diffusion of diethyl
ether into an acetonitrile solution of the complex (yield: 0.15 g,
52.5%). IR (pure, orbit diamond): 3310s, 2316m, 2289w, 1619m,
1571w. Anal. Calc. for C26H24Br2N4NiO2S2: C, 44.16; H, 3.42; N, 7.92.
Found: C, 44.27; H, 3.56; N, 7.87%.
2.4. Synthesis of complex 2 [Ni(L)2]
Excess of Et3N (0.56 mL, 4.0 mmol) was added to a solution of
Ni(Br)2(PPh3)2 (0.15 g, 0.20 mmol) in THF (20 mL) until the
formation of a white precipitate. (E)-N0-(1-(thiophen-2-yl)ethyli-
dene)benzohydrazide (0.1 g, 0.41 mmol) was added to the mixture
and the solution was left under stirring overnight at room temper-
ature. The white precipitate of Et3NꢀHBr was filtered off and a yel-
low powder of the titled complex was obtained by solvent
evaporation and then dried under vacuum. Dark monocrystals suit-
able for X-ray analysis were collected upon slow diffusion of
diethyl ether into a THF solution of the titled complex (yield:
0.13 g, 60%). IR (pure, orbit diamond): 1648m, 1577w, 1486m,
2.7. Crystal structure determinations
Suitable crystals for the X-ray analysis of all compounds were
obtained as described above. Single crystals of the ligand and com-
plexes 1–3 (two different cif files are given for complex 3, as will be

W. Zuo et al. / Inorganica Chimica Acta 383 (2012) 213–219
215
explained in the text) were mounted on a Nonius Kappa-CCD area
detector diffractometer (Mo K k = 0.71073 Å). The complete con-
0.980/2.380/3.241(4) Å/146.3°, (ꢃ = ꢁ1/2 ꢁ x, ꢁ1/2 + y, z). A selected
a
packing diagram in the (a and c) sheet is provided in Fig. 1.
ditions of data collection (DENZO software [10]) and structure refine-
ments are given in supporting material. The cell parameters were
determined from reflections taken from one set of 10 frames
(1.0° steps in phi angle), each at 20s exposure. The structures were
solved using direct methods (SHELXS97) and refined against F2 using
the SHELXL97 and CRYSTALBUILDER software [11,12]. The absorption was
not corrected. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were generated according to stereochemis-
try and refined using a riding model in SHELXL97. Crystallographic
data (excluding structure factors) have been deposited in the
Cambridge Crystallographic Data Centre as Supplementary
publication No. CCDC 835284–835288. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: (+44)1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk)
3.2. Synthesis and structures of the derived Ni complexes (1–3)
3.2.1. Synthesis and crystal structure of Ni(HL)2(Br)2 (complex 1)
The reaction of NiBr2(PPh3)2 with 2 eq. of the ligand HL (THF,
room temperature, 12 h) afforded complex 1 [Ni(HL)2(Br)2] as a
green powder with reasonable yield (Scheme 2). Green crystals
of complex 1 suitable for single X-ray crystal structure determina-
tion were obtained by a slow Et2O diffusion (at room temperature)
into a CH3CN solution of pure 1. The molecular structure of com-
plex 1 along with a selected packing diagram is illustrated in Fig. 2.
Complex 1 crystallizes in the monoclinic space group P21/c. Its
solid-state molecular structure (Fig. 2) features a Ni2+ metal centre
located on a crystallographic inversion centre ꢁ1. The Ni2+ ions are
surrounded by two neutral HL ligands and two trans-located bro-
mide ligands to complete the octahedral coordination geometry
(Fig. 2). The packing diagram shown in Fig. 2 also points out
the position of the intermolecular N–Hꢀ ꢀ ꢀBr hydrogen bonds. The
parameters for intra- and inter-molecular hydrogen bonds for
complex 1 are summarised in Table 1.
Our group has recently reported similar coordination modes to
that observed in complex 1 with Fe2+ ion coordinated by closely
related ligands [3,4]. To the best of our knowledge, complex 1 is
the first example of transition metal complex supported by the
(E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide ligand. Exam-
ples of complexes featuring similar coordination modes have been
reported, where the metal centres are coordinated to two trans-
located bromides and two N^O chelating ligands [15–18].
3. Results and discussion
3.1. Synthesis and structural characterisation of (E)-N0-(1-(thiophen-
2-yl)ethylidene)benzohydrazide (HL)
The initial task of the present work dealt with the synthesis and
characterisation of (E)-N0-(1-(thiophen-2-yl)ethylidene)benzohyd-
razide ligand. Following a literature procedure [13], (E)-N0-(1-
(thiophen-2-yl)ethylidene)benzohydrazide was synthesized in
4.5 min, in high yield and on a 5-g scale under microwave irradia-
tion, starting from benzhydrazide and 2-acetylthiophene. Crystals
suitable for single X-ray diffraction studies were extracted directly
from this sample. The solid-state structure of (E)-N0-(1-(thiophen-
2-yl)ethylidene)benzohydrazide is depicted in Fig. 1.
The ligand HL crystallizes in the orthorhombic space group Pbca
with eight HL molecules in the unit cell. In the solid state, the HL
molecules are not planar (52° between thiophene group and phe-
nyl ring), which contrasts with our previous observations for re-
lated ligands (i.e. quite planar in the solid state); this is probably
due to the absence of an OH group on the phenyl ring [1]. Three
classical intermolecular hydrogen bonds (N–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀO)
were detected [14]. The bond lengths and angles for these interac-
tions are as follows: N1–H1ꢀ ꢀ ꢀO1⁄: 0.879(3)/2.463(3)/3.323(3) Å/
165.8°; C1–H1AꢀꢀꢀO1⁄: 0.949/2.387/3.234(4) Å/148.4°; C9–H9CꢀꢀꢀO1⁄:
3.2.2. Synthesis and crystal structure of Ni(L)2 (complex 2)
When the reaction of NiBr2(PPh3)2 with 2 eq. of the ligand HL is
carried out in the presence of an excess of Et3N (20 eq. to metal),
the formation of complex 2, in which the nickel centre is chelated
by two anionic Lꢁ ligands, is observed as deduced from X-ray crys-
tallographic data (Scheme 3). The role of triethylamine is to cap-
ture the halide from the metal precursor, with the deposition of
Et3NꢀHBr (triethylamine hydrobromide) as a white solid. Dark crys-
tals of complex 2 suitable for single crystal X-ray analysis were col-
lected upon slow diffusion of Et2O into a THF solution of species 2.
Fig. 3 shows the ORTEP view of complex 2 along with selected
bond lengths and angles.
Fig. 1. ORTEP view (left) and selected packing diagram (right) of the ligand HL with partial labelling scheme. The ellipsoids enclose 50% of the electronic density. On the
packing diagram, the H atoms have been omitted for clarity.

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W. Zuo et al. / Inorganica Chimica Acta 383 (2012) 213–219
2
3 2
Scheme 2. Synthesis of Ni(HL)2(Br)2.
Fig. 2. Left: ORTEP view of complex 1 with a partial labelling scheme. Hydrogen bonds (intra molecular) are represented in dashed lines. The ellipsoids enclose 50% of the
electronic density. Symmetry code for 0 = ꢁx, ꢁy, ꢁz. Selected distances (Å): Br–Ni 2.5502(5), Ni–O 2.036(4), Ni–N2 2.120(5), O–C7 1.233(6), N1–C7 1.352(7), N1–N2 1.404(7).
Right: packing view showing N–Hꢀ ꢀ ꢀBr hydrogen bonds (dashed lines).
Table 1
from the two extra bromide ligands, complex 2 lacks both the NH
moiety and bromides due to deprotonation of the ligand by the
addition of Et3N. The absence of the bromide ligands together with
the rotation ability of the five-member ring about the exocyclic
C–C bond may facilitate the coordination of the two sulfur atoms
to the nickel centre.
Yet, the Ni–S interaction appears to be rather weak, as deduced
from the values of the Ni–S bond distances (2.92(1) and 2.78(1) Å
for Ni–S1 and Ni–S2, respectively, in comparison with the average
distance value of 2.39(2) Å founded for classical Ni–S bond – about
100 references into the CCDC data base). In a comparable example
of nickel complex bearing two tridentate S^N^O ligands [19], the
analogue Ni–S distances were found to be about 0.3–0.4 Å shorter
than those found in complex 2. No classical hydrogen bonds were
Bond lengths and angles of intramolecular and intermolecular hydrogen bonds in
complex 1.
Type
Donor–
Hꢀ ꢀ ꢀacceptor
dH–A
(Å)
dD–A (Å) D–H–A angle
(°)
Intramolecular N(1)–H(1 N)ꢀ ꢀ ꢀS
Intermolecular N(1)–H(1 N)ꢀ ꢀ ꢀBr00
Intramolecular C(9)– H(9C)ꢀ ꢀ ꢀO0
2.328
2.643
2.163
2.879(5) 120.7
3.332(4) 135.9
3.080(9) 155.1
0
00
Symmetry codes: = ꢁx, ꢁy, ꢁz; = ꢁx, ꢁ1/2 + y, 1/2 ꢁ z.
S
H
O
detected in the crystal structure of complex 2 but specific CHꢀ ꢀ ꢀ
p
NEt3, NiBr2(PPh3)2
THF
N
N
N
N
interactions were observed between one hydrogen atom of the
methyl group and the thiophene ring (Fig. 3, on the right). To our
knowledge, species 2 constitute the first example of a Ni complex
in which the Ni2+ metals bears two (O^N^S) tridentate ligands
coordinated in mer-configuration. The use of complex 2 as a cata-
lyst precursor for ethylene oligomerisation was also studied (vide
infra).
Ni
N
N
O
S
O
S
Scheme 3. Synthesis of Ni(L)2.
ꢀ
Complex 2 crystallizes in a triclinic space group P1 with two
molecules in the unit cell. Its solid-state molecular structure exhib-
its a Ni2+ metal centre that may be seen as effectively chelated by
two tridentate N,O,S L2X-type anionic Lꢁ ligands, both of which
coordinating in a mer-fashion. This is rather an unusual coordina-
tion mode for this type of ligand, which classically behaves as a
N,O bidendate ligand. X-ray data contain no residual peak in the
Fourier map differences, unambiguously indicating the absence
of hydrogen on the N1 and N3 atoms and establishing the mono-
anionic nature of each chelating ligand (same conclusions have
been made with close related ligands published by our group re-
cently – see for examples Refs. [3–7]). In contrast to the situation
in complex 1, where the sulfur external orientation is stabilized
by the N–Hꢀ ꢀ ꢀS hydrogen bonding and further stabilization derives
3.2.3. Synthesis and crystal structure of Ni2(l-H2O)(l-L)2(L)2
(complex 3)
Changing the nickel metal precursor from NiBr2(PPh3)2 to NiCl2
(under near identical reaction conditions to those used for the syn-
thesis of species 2) led to the formation of a new dinuclear complex
3, whose identity and molecular structure was determined by X-
ray crystallographic studies (Scheme 4, Fig. 4). The detailed reason
for the formation of different complex structures by only changing
the starting metal precursor is unknown at the moment. Green
monocrystals of complex 3 were obtained after slow diffusion of
diethyl ether into a dichloromethane solution. Suitable single crys-
tals can also be obtained by slow diffusion of THF into dichloro-
methane solution of the complex. Structure determination
studies were conducted for both crystalline samples (see corre-

W. Zuo et al. / Inorganica Chimica Acta 383 (2012) 213–219
217
Fig. 3. Left: ORTEP view of compound 2 with partial labelling scheme. The ellipsoids enclose 50% of the electronic density. Selected distances (Å) and angles (°): Ni–O1
1.949(1), Ni–O2 1.949(1), Ni–N2 1.986(5), Ni–N4 1.990(1), Ni–S1 2.921(1), Ni–S2 2.781(1), O1–Ni–O2 107.85(5), N2–Ni–N4 165.58(6), O2–Ni–N4 81.27(5). Framed: selected
0
view of the coordination sphere. Right: packing view. Arrows indicate CHꢀ ꢀ ꢀ
p
bonds. Hydrogen atoms have been omitted for clarity. Symmetry code for = ꢁx, 1ꢁy, 1 ꢁ z.
S
S
N
N
N
H
N
NEt3
THF
N
O
2
N
NiCl2
O
Ni
Ni
O
O
S
N
N
O
O
N
N
S
S
Scheme 4. Synthesis of Ni2(l-H2O)(l-L)2(L)2.
sponding cif files given in Supporting material). The crystal struc-
ture obtained by THF diffusion is the one described here.
rable to that in related bis(chelate) Ni complexes [25,26]. Complex
2 exhibited a turnover frequency (TOF) of 31200 mol of C2H4 (mol
of Ni hꢁ1) in the oligomerization of ethylene with dimers (64.8% in
mass) and trimers (30.7%) as the major products. Traces of C8
(3.8%) and C10 (0.7%) olefins were also detected (Fig. 5). This prod-
uct distribution is in contrast to the results of the previously re-
ported cobalt [27] and titanium [28] complexes, where the
presence of thien-2-yl group in the ligand close to the metal centre
usually led to the generation of olefins or polymers with longer
carbon chains; this was ascribed to the coordination of the sulfur
atom to the metal centre in the presumed transition state, likely
to stabilize such an electron-deficient transition state for migratory
Complex 3 crystallizes in the monoclinic space group C2/c with
four molecules (each placed on the crystallographic 2-fold axis, the
oxygen O3 is on the axis) in the unit cell. Complex 3 is a Ni dinu-
clear specie, in which the Ni metal centres are linked to one an-
other via two bridging
-O water molecule. Thus, as shown in Fig. 4, each Ni2+ centre is
surrounded by four anionic bidendate ligands Lꢁ: two being coor-
dinated in a classical chelating
2-N,O mode and two bridging
g2 anionic Lꢁ moieties. Here again, the mono-anionic nature
l: ,
g1 g2 anionic Lꢁ ligands and a bridging
l
g
l: ,
g1
of the chelating data is supported by X-ray data: no residual peak is
detected in the Fourier map differences, indicating the absence of
the hydrogen atom on N1 (N10) and N3 (N30). The hydrogen atoms
of the water molecule are also clearly detected and form two clas-
sical hydrogen bonds with the oxygen atoms of the neighbouring
THF solvent molecules in the crystal packing. All these observa-
tions confirm the +2 charge of Ni. Five examples of similar coordi-
nation for Ni2+ dinuclear compounds can be found in the
Cambridge Data base [20–24]. The Ni–Ni distance of 2.91 Å lies
in the typical range for such dinuclear species. The presence of a
bridging water molecule in this compound can be explained by
the presence of water in the solvent used for these experiments.
insertion. The selectivity for
butene for ethylene dimers and 1.8% of
a
-olefins was relatively low (10% of 1-
-C6 for trimers), which is
a
probably due to the fast isomerization of the generated 1-butene
and 1-hexene. Theoretical and experimental investigations
reported in the literature indicate the real active site for olefin
oligomerization or polymerisation to be a cationic metal alkyl
species that would then allow for the binding of the monomer
and its subsequent insertion [29,30]. In our case, as reported for
other N,O bis(chelate) nickel(II) complexes with comparable ethyl-
ene oligomerization [26,31–33], it appears likely that the Lewis
acid Al co-catalyst AlEtCl2 abstracts one of the Ni-coordinated
chelating ligand to form a reactive and electron-deficient alkyl Ni
intermediate likely to be the catalytically active species [31,33].
3.3. Ethylene oligomerization using complex 2 as catalyst precursor
We evaluated the bis(chelate) nickel complex 2 for ethylene
oligomerization catalytic activity in the presence of 10 eq. AlEtCl2
as co-catalyst. Under an ethylene pressure of 10 bar, the complex
2/AlEtCl2 catalytic mixture was found to feature an activity compa-
4. Concluding remarks – summary
The (E)-N0-(1-(thiophen-2-yl)ethylidene)benzohydrazide (HL),
readily synthesized in high yield and on 5 g-scale within a few

218
W. Zuo et al. / Inorganica Chimica Acta 383 (2012) 213–219
Fig. 4. ORTEP view of the complex 3 with partial labelling scheme. The ellipsoids enclose 50% of the electronic density. Selected distances (Å) and angles (°): Ni–O1 1.949(1),
Ni–O1 2.000(2), Ni–O2 2.039(2), Ni–N2 2.053(2), Ni–N4 2.053(2), Ni–O3 2.152(2), Ni–O2 2.1570(2), Ni–Ni 2.9101(6); Ni–O2–Ni 87.78(7), Ni–O3–Ni 85.09(10). Hydrogen
atoms as well as THF solvent molecules have been omitted for clarity. Symmetry code for 0 = ꢁx + 1, y, ꢁz + 1/2. Framed: view of the faces sharing of both deformed octahedral
surrounded Ni2+ ions.
molecule, is accessible by the reaction of ligand HL with NiCl2 in
the presence of excess Et3N. The solid-state structures of (E)-N0-
(1-(thiophen-2-yl)ethylidene)benzohydrazide (HL) and of all three
Ni complexes were all determined by single crystal X-ray diffrac-
tion studies. In the presence of 10 eq. AlEtCl2 as co-catalyst,
complex Ni(L)2 (2) was found to be active in ethylene oligomeriza-
tion with a TOF value of 31200 mol of C2H4 (mol Ni h)ꢁ1, which is
similar to those obtained with bis(chelate) Ni(II) complexes coordi-
nated by N,O chelates [25,31,32]. C4 and C6 olefins were the main
products of the latter polymerisation catalysis that occurs with low
a-olefin selectivity.
Acknowledgements
We thank the CNRS and the Ministère de la Recherche (Paris)
for recurrent funding and Fundação para a Ciência e Tecnologia,
(FCT), for a postdoctoral fellowship (SFRH/BPD/44262/2008) to
Vitor Rosa. We also thank Marc Mermillon-Fournier for his help
during the catalytic test and Dr. Pierre Braunstein for fruitful
discussions.
Fig. 5. Product distribution in the oligomerization of ethylene using 2/AlEtCl2
catalytic mixture.
Appendix A. Supplementary data
minutes under microwave irradiation, was found to be suitable
for coordination to Ni(II) and afford structurally diverse HL- and
L-supported Ni derivatives. Three types of nickel complexes,
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.11.009.
Ni(HL)2(Br)2, Ni(L)2 and Ni2(l-H2O)(l-L)2(L)2 were prepared by
reaction of HL with different nickel sources and/or under different
reaction conditions. Thus, while the reaction of NiBr2(PPh3)2 with
HL in the absence of base, yielded the Ni complex Ni(HL)2(Br)2
(1), the addition of excess Et3N in the reaction medium led to the
formation of species 2, Ni(L)2 with two unexpected and original
References
[1] C. Beghidja, M. Wesolek, R. Welter, Inorg. Chim. Acta 358 (2005) 3881.
[2] C. Beghidja, G. Rogez, J. Kortus, M. Wesolek, R. Welter, J. Am. Chem. Soc. 128
(2006) 3140.
[3] N. Bouslimani, N. Clément, G. Rogez, P. Turek, M. Bernard, S. Dagorne, D.
Martel, H.N. Cong, R. Welter, Inorg. Chem. 47 (2008) 7623.
Niꢀ ꢀ ꢀS interactions. The dinuclear complex
L)2(L)2], in which the two Ni(II) ions are connected through two
bridging -O water
g2 anionic Lꢁ ligands and a bridging
3 [Ni2(l-H2O)(l-
[4] N. Bouslimani, N. Clément, C. Toussaint, S. Hameury, P. Turek, S. Choua, S.
Dagorne, D. Martel, R. Welter, Eur. J. Inorg. Chem. (2009) 3734.
l:
g1
,
l

W. Zuo et al. / Inorganica Chimica Acta 383 (2012) 213–219
219
[5] N. Clément, C. Toussaint, G. Rogez, C. Loose, J. Kortus, L. Brelot, S. Choua, S.
Dagorne, P. Turek, R. Welter, Dalton Trans. 39 (2010) 4579.
[6] C. Toussaint, C. Beghidja, R. Welter, C.R. Chimie 13 (2010) 343.
[7] N. Bouslimani, N. Clément, G. Rogez, P. Turek, S. Choua, S. Dagorne, R. Welter,
Inorg. Chim. Acta 363 (2010) 213.
[8] L. Bogani, W. Wernsdorfer, Nature Mat. 7 (2008) 179.
[9] R. Welter, WO/2009/130562.
[10] B.V. Nonius, Kappa CCD Operation Manual, Delft, The Netherlands, 1997.
[11] G.M. Sheldrick, SHELXL97: Program for the Refinement of Crystal Structures,
University of Göttingen, Göttingen, Germany, 1997.
[12] R. Welter, Acta Crystallogr., Sect. A 62 (2006) s252.
[13] M.M. Andrade, M.T. Barros, J. Comb. Chem. 12 (2010) 245.
[14] A.L. Spek, PLATON software, J. Appl. Crystallogr. 36 (2003) 7–13.
[15] K.R. Adam, L.F. Lindoy, R.J. Smith, G. Anderegg, K. Henrick, M. McPartlin, P.A.
Tasker, J. Chem. Soc., Chem. Commun. 18 (1979) 812.
[20] K.E. Vostrikova, V.I. Ovcharenko, G.V. Romanenko, V.N. Ikorskii, N.V.
Podberezskaya, V.A. Reznikov, L.B. Volodarskii, Zh. Neorg. Khim. 37 (1992) 1755.
[21] E.D. McKenzie, F.S. Stephens, Inorg. Chim. Acta 32 (1979) 253.
[22] W. Luo, X. Wang, G. Cheng, S. Gao, Z. Ji, Inorg. Chem. Commun. 11 (2008) 769.
[23] L. Rodríguez, E. Labisbal, A. Sousa-Pedrares, J.A. García-Vázquez, J. Romero,
M.L. Durán, J.A. Real, A. Sousa, Inorg. Chem. 45 (2006) 7903.
[24] A. Berkessel, K. Roland, M. Schröder, J.M. Neudörfl, J. Lex, J. Org. Chem. 71
(2006) 9312.
[25] E. Nelkenbaum, M. Kapon, M.S. Eisen, Organometallics 24 (2005) 2645.
[26] A. Kermagoret, P. Braunstein, Dalton Trans. (2008) 1564.
[27] C. Bianchini, D. Gatteschi, G. Giambastiani, I.G. Rios, A. Ienco, F. Laschi, C.
Mealli, A. Meli, L. Sorace, A. Toti, F. Vizza, Organometallics 26 (2007) 726.
[28] J. Huang, T. Wu, Y. Qian, Chem. Commun. (2003) 2816.
[29] D.J. Tempel, L.K. Johnson, R.L. Huff, P.S. White, M. Brookhart, J. Am. Chem. Soc.
122 (2000) 6686.
[16] H.J. Goodwin, K. Henrick, L.F. Lindoy, M. McPartlin, P.A. Tasker, Inorg. Chem. 21
(1982) 3261.
[17] D.J. Macchia, W.F. Furey Jr., R.A. Lalancette, Acta Crystallogr., Sect. C 49 (1993)
1706.
[30] L.H. Shultz, D.J. Tempel, M. Brookhart, J. Am. Chem. Soc. 123 (2001) 11539.
[31] L. Wang, C. Zhang, Z. Wang, Eur. J. Inorg. Chem. (2007) 2477.
[32] C. Carlini, M. Isola, V. Liuzzo, A.M.R. Galletti, G. Sbrana, Appl. Catal., A 231
(2002) 307.
[18] L.K. Minacheva, N.B. Generalova, I.K. Kireeva, V.G. Sakharova, A.Y. Tsivadze,
M.A. Porai-Koshits, Zh. Neorg. Khim. 38 (1993) 1666.
[33] C. Carlini, M. Marchionna, A.M.R. Galletti, G. Sbrana, Appl. Catal., A 206 (2001)
1–12.
[19] S. Karmakar, S.B. Choudhury, D. Ray, A. Chakravorty, Polyhedron 12 (1993)
2325.