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V.A. Tuskaev et al. / Inorganica Chimica Acta 442 (2016) 167–171
was obtained from SIA ‘‘P&M-Invest” Ltd. Diethylaluminum chlo-
ride solution (Aldrich), polymethylaluminoxane (Witco) were used
as a 10% solutions in toluene.
NMR spectra were recorded on Bruker AMX-400 instrument.
Chemical shifts are reported in ppm vs. SiMe4 and were deter-
mined by reference to the residual solvent peaks. All coupling con-
stants are given in Hertz. IR spectra were recorded on a Magna-IR
750 spectrophotometer. Elemental analysis was performed by the
microanalytical laboratory at A.N. Nesmeyanov Institute of Orga-
noelement compounds.
independent reflections (Rint = 0.0576) out of 26641 collected were
used in structure solution and refinement. The structure was
solved by direct methods and refined by the full-matrix least-
squares technique against F2 in anisotropic approximation. The
positions of hydrogen atoms were calculated. Hydrogen atoms
were refined in riding model with U(H) equal to 1.5 U(C) and
1.2 U(C) of the connected methyl and other carbon atoms. The
refinement converged to R1 = 0.0442 (calculated for 8544 observed
reflections with I > 2r(I)), wR2 = 0.0829 and GOF = 1.011. All calcu-
lations were performed with SHELX software package [11]. Atomic
coordinates, bond lengths and angles and thermal parameters have
been deposited at the Cambridge Crystallographic Data Center
(CCDC), reference number 1061549.
Samples (1.0 lL of 3–5% solutions in toluene) were injected into
the chromatograph Trace GC ultra, connected to the mass
spectrometer Finnigan Polaris Q (Ion Trap, EI, 70 eV, mass range
33–1000 aem). Separation was performed on a capillary column
RTX-5 ms (5% Phenyl Polysilphenylene-siloxane; an inner diameter
2.4. Procedure for ethylene oligomerization
– 0.25 mm, thickness of the film phase – 0.25 lm, length 30 m).
Injector temperature – 270 °C; reset 1:200; initial column temper-
ature À90 °C; isotherm – 4 min; continue heating at a rate of 10
degrees per minute up to 320 °C, and holding at 320 °C – 3 min.
Ethylene oligomerizations at 3 atm ethylene pressures were
carried out in a 100 mL stainless steel autoclave equipped with
mechanical stirrer and temperature controller. Toluene, specified
amount of cocatalyst, and toluene solution of the catalytic
precursor (total volume was 50 mL) were added to the reactor in
this specific order under the ethylene atmosphere. Once the
desired reaction temperature was reached, ethylene pressure was
increased to 3 atm, and maintained at this level by constant
ethylene feed. After defined time, reaction was stopped by cooling
of the reactor on an ice bath followed by the excess pressure
release. A small sample of the reaction solution was preserved
and the rest of the reaction volume was terminated by the addition
of HCl-acidified ethanol (5%), and then this mixture was analyzed
by gas chromatography (GC) to determine the distribution of
oligomers obtained.
2.1. Synthesis of 2,3-bis[N,N-(2,3,5,6-tetrafluorophenyl)imino]butane,
(1)
In a 250 mL Schlenk flask 2.2 equiv. of 2,3,5,6-tetrafluoroanilin
were dissolved in toluene (150 mL), and catalytic amount of
p-toluenesulfonic acid monohydrate (0.06 equiv.) was added. 1
equiv. of 2,3-butanedione was added dropwise by a syringe. After
that the flask was connected to a water separator and a reflux
condenser. After refluxing the mixture for 40 h, the solvent was
evaporated in vacuo. Crude product was dissolved in methylene
chloride followed by addition of methanol. The resulting yellow
precipitate was filtered off and dried in vacuo. Anal. Calc. for
C
16H8F8N2 (380.06): C, 50.54; H 2.12; N 7.37; F 39.97. Found: C,
50.37, H, 2.04, N, 7.32, F. 39.81%. 1H NMR (400 MHz, CDCl3) d
6.88 (tt, J = 9.9, 7.2 Hz, 2H, ArH,), 2.25 (s, 7H, 2CH3).
3. Result and discussion
The synthesis of the a-diimine ligand 1 proceeds via a conden-
2.2. Synthesis of {2,3-bis[N,N-(2,3,5,6-tetrafluoro phenyl)imino]
butane}dibromonickel, ([L2Ni2Br3(H2O)2][Br, 3THF]), 2
sation reaction of 2 equiv. of a 2,3,5,6-tetrafluoroaniline with 1
equiv. of a 2,3-butanedione according to Fig. 1. Due to poor solubil-
ity of anhydrous nickel dibromide, complex 2 was obtained in
methanol.
Anhydrous NiBr2 (0.22 g, 1.00 mmol) and 2,3-bis[N,N-(2,3,5,6-
tetrafluorophenyl)imino]butane (0.38 g, 1.00 mmol) were com-
bined in a Schlenk flask under argon atmosphere. CH3OH (20 mL)
was added, and reaction mixture was refluxed at room tempera-
ture for 24 h. Resulting suspension was filtered and recrystallized
from the methanol:THF = 1:1 to yield a complex 2 (0.54 g, 79%).
Anal. Calc. for C44H44Br4F16N4Ni2O5 (1450): C, 36.45; H, 3.06; N,
3.86; Ni, 8.10. Found: C, 36.40; H, 2.94; N, 3.81; Ni, 8.07%. 1H
NMR (400 MHz, THF) d = 7.31–7.27 (t, 2H, ArH), 3.58 (8H,
THF), 2.26 (12H, CH3), 1.73 (4H, H2O). 19F NMR (400 MHz,
THF) d = À82.48, À82.54, À82.57, À94.61, À94.67, À94.70. 13C
NMR (400 MHz, THF) d = 174.13, 147.54, 145.27, 137.92, 135.65,
The ligand was characterized by FT-IR, 1H and 13C NMR spectro-
scopic measurements as well as by elemental analysis. Due to low
solubility and the paramagnetic nature of this type of complexes
they were not subjects for NMR spectroscopy. The FT-IR spectrum
of complex 2 has demonstrated a C@N stretching frequencies
of the nickel complex shifted to lower values (1600–1620 cmÀ1
)
with weaker intensity compared to those of the corresponding
frequencies for free ligand. Molecular structure of complex 2 was
confirmed by single-crystal X-ray diffraction (Fig. 2).
According to X-ray data, complex 2 in a crystalline state has a
composition [L2Ni2Br3]+[Br, (H2O)2]À, i.e. it is an ionic compound,
and contains two molecules of crystallization water in the external
sphere in addition to the bromine anion. The complex is binuclear,
with three bromine atoms bridging between two nickel centers,
and one remaining bromine atom is outer-sphere anion. Both
metal centers adopt a distorted octahedral geometry, each with
three Br atoms, two nitrogen atoms of the ligands and one oxygen
atom of the coordinated water molecule (Fig. 2). The Br–Ni bond
lengths vary from 2.5116(6) to 2.5723(6) Å; Ni–N distances vary
from 2.087(3) to 2.107(3) Å; finally, Ni1–O1 and Ni2–O2 distances
are approximately equal (2.057(3) and 2.044(3) Å). The bite
angles N–Ni–N of two ligands are very close and equal to 76.55
(12) and 77.25(12)° for atoms Ni1 and Ni2. Hydrogen atoms of
the coordinated water molecules participate in hydrogen bonds
with anionic BrÀ moiety and three solvating THF molecules.
129.85, 101.40, 101.26, 100.79, 16.38. FT-IR (KBr): 3150 cmÀ1
(H2O), 1660 cmÀ1 d(H2O), 1627 cmÀ1
(C@N). Single crystals of
m
m
complex, suitable for X-ray analysis were obtained at room tem-
perature by dissolving the nickel complex in THF, following by
slow layering of the resulting solution with n-hexane.
2.3. X-ray diffraction data for 2
Were collected on a Bruker APEX DUO diffractometer (k(Mo
Ka) = 0.71073 Å, x-scans with 0.55° step and 20 s per frame expo-
sure, 2h < 56.18°). Brownish crystals of C44H44Br4F16N4Ni2O5 at
ꢀ
120 K are triclinic, space group P1, a = 11.4337(3), b = 12.0720(3),
c = 20.0749(5) Å,
a = 105.652(2), b = 98.778(2), c = 100.992(2)°,
V = 2557.44(11) Å3, Z = 2, d = 1.883 g cmÀ3. Intensities of 12416