Synthesis and reactivity in ethylene oligomerization by heteroscorpionate dibromonickel(II) complexes

Article abstract of DOI:10.1016/j.ica.2016.12.026

Novel heteroscorpionate ligands were synthesized by a Peterson rearrangement during the reaction of 2-pyridinecarboxaldehyde (or 2-quinolinecarboxaldehyde) and 1,1-carbonyl-bis(pyrazoles). Nickel(II) dibromide reacts with these ligands in THF to give the heteroscorpionate dibromo complexes of general formula LNiBr₂. Crystal structures of two full-sandwich heteroscorpionate Ni(II) complexes were determined. Preliminary studies of catalytic activity in ethylene oligomerization using different organoaluminum cocatalysts were performed. The addition of one equivalent of triphenylphosphine resulted in increased catalytic activity for most examples. The catalyst system of (2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel(II) dibromide/Et₂AlCl/PPh₃dimerized ethylene with an activity of 650?g oligomer mol^?1?Ni?h^?1while the share of 1-butene in the mixture has reached 75%. Tris(3,5-dimethylpyrazol-1-yl)methyl nickel(II) dibromide, activated by Et₂AlCl/PPh₃produced isobutylene (75% of the butene fraction).

Full text of DOI:10.1016/j.ica.2016.12.026

Accepted Manuscript
Research paper
Synthesis and Reactivity in Ethylene Oligomerization by Heteroscorpionate
Dibromonickel (II) Complexes
Sergei V. Zubkevich, Svetlana Ch. Gagieva, Vladislav A. Tuskaev, Pavel V.
Dorovatovskii, Victor N. Khrustalev, Alexandr I. Sizov, Boris M. Bulychev
PII:
S0020-1693(16)30819-2
http://dx.doi.org/10.1016/j.ica.2016.12.026
ICA 17388
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
6 November 2016
18 December 2016
19 December 2016
Please cite this article as: S.V. Zubkevich, S.C. Gagieva, V.A. Tuskaev, P.V. Dorovatovskii, V.N. Khrustalev, A.I.
Sizov, B.M. Bulychev, Synthesis and Reactivity in Ethylene Oligomerization by Heteroscorpionate Dibromonickel
(II) Complexes, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.12.026
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Synthesis and Reactivity in Ethylene Oligomerization
by Heteroscorpionate Dibromonickel (II) Complexes
Zubkevich Sergei V.a, Gagieva Svetlana Ch.a, Tuskaev Vladislav A.a,b*, Dorovatovskii
Pavel V. c, Khrustalev Viсtor N b,d, Sizov Alexandr I. a, Bulychev Boris M.a
a Moscow State University, Chemical Department, Leninskie Gory 11, Moscow 119991, Russia
b Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul.
Vavilova 28, Moscow 119991, Russia
c National Research Center “Kurchatov Institute”, Moscow, Russia
d Peoples’ Friendship University of Russia (RUDN), Moscow, Russia
Abstract
Novel heteroscorpionate ligands were synthesized by a Peterson rearrangement during the
reaction of 2-pyridinecarboxaldehyde (or 2-quinolinecarboxaldehyde) and 1,1-carbonyl-
bis(pyrazoles). Nickel (II) dibromide reacts with these ligands in THF to give the
heteroscorpionate dibromo complexes of general formula LNiBr2. Crystal structures of two full-
sandwich heteroscorpionate Ni(II) complexes were determined. Preliminary studies of catalytic
activity in ethylene oligomerization using different organoaluminum cocatalysts were performed.
The addition of one equivalent of triphenylphosphine resulted in increased catalytic activity for
most examples. The catalyst system of (2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel
(II) dibromide / Et2AlCl / PPh3 dimerized ethylene with an activity of 650 g oligomer mol-1 Ni h-1
while the share of 1-butene in the mixture has reached 75%. Tris(3,5-dimethylpyrazol-1-
yl)methyl nickel (II) dibromide, activated by Et2AlCl / PPh3 produced isobutylene (75% of the
butene fraction).
Keywords: ethylene; oligomerization; heteroscorpionate nickel (II) complexes, selectivity
* Corresponding author.
Fax: +7 (495) 932 8846. E-mail: sgagieva@yandex.ru (Gagieva S.Ch.)
1. Introduction
Scorpionate ligands have been demonstrated as attractive ancillary ligands for the synthesis
of transition metal complexes [1-2]. These classes of tridentante ligands whose steric
environment and electronic structure can be easily modified can coordinate to a wide variety of
elements, e.g. from early to late transition metals.
1

A broad range of transition metal complexes bearing these ligands revealed they behave as
catalysts for ethylene oligo- or polymerization [3-4]. The vast majority of such catalysts are
formed on the basis of chromium complexes. Despite the fact that the nickel compounds are also
active in the oligomerization [5], only a few examples of tris(pyrazolyl)borate Ni complexes
have been employed as catalysts in the olefin oligomerization [6] and copolymerization of
ethylene and carbon monoxide [7].
The electronic and steric properties of an ancillary ligand can dramatically influence the
reactivity of a metal ion to which it is bound. As such, extensive efforts have been focused on the
development of ligand systems whose steric environment and electronic structure can be easily
modified, with the ultimate goal being the ability to ‘‘fine-tune’’ a metal complex to produce a
desired type of chemical reactivity.
Herein we report the synthesis and the structural research of the novel nickel (II) dibromide
complexes and their reactivity toward ethylene. Additionally, the influence of the additive of
triphenylphosphine on the catalytic activity and selectivity was investigated.
2. Experimental
Materials and Methods. All manipulations with air-sensitive materials were performed with
rigorous exclusion of oxygen and moisture in oven-dried Schlenk glassware on a dual manifold
Schlenk line, interfaced to a high-vacuum line. Argon and ethylene of special-purity grade
(Linde gas) were dried by purging through a Super Clean™ Gas Filters. Toluene, diethyl ether,
and tetrahydrofuran were distilled over Na/benzophenone ketyl. Dichloromethane was distilled
over calcium hydride. The water contents in these solvents were periodically controlled by Karl-
Fischer coulometry by using a Methrom 756 KF. CDCl3 and CD2Cl2 were degassed and stored
over 4 Å sieves. Diethylaluminumcloride and aluminium sesquichloride (Aldrich) were used as
1.0 M solution in heptane. Unless otherwise noted, all reagents were purchased from Sigma-
Aldrich. 4-Bromo-2,5-dimethylpyrazole [8], 3-tert-butyl-pentan-2,4-dione [9], 3,5-dimethyl-4-
tert-butilpirazol [10], bis(pyrazol-1-yl)methanone [11], bis(3,5-dimethylpyrazol-1-yl) methanone
[11] and tris(3,5-dimethylpyrazol-1-yl)methane 19 [12] were prepared by following literature
procedures; their 1H and 13C NMR spectra were found to match the published data.
Physical and Analytical Measurements.
NMR spectra were recorded on Bruker AMX-400. Chemical shifts are reported in ppm
vs. SiMe4 and were determined by reference to the residual solvent peaks. All coupling constants
are given in Hertz.
2

IR spectra were recorded on a Magna-IR 750 spectrophotometer. Elemental analysis was
performed by the microanalytical laboratory at A. N. Nesmeyanov Institute of Organoelement
Compounds. Mass spectra under atmospheric pressure electrospray (ESI) were recorded in the
full scan mass of positive and negative ions on the dynamic tandem mass spectrometer Finnigan
LCQ Advantage (USA), equipped with a mass analyzer oktapol ion trap pump MS Surveyor,
Surveyor autosampler, nitrogen generator Schmidlin-Lab (Germany) and a system for collecting
and processing the data using the X Calibur program (version 1.3, Finnigan). Transfer capillary
temperature of 150 °C, voltage field between the needle and counter electrode 4.5 kV. Samples
were introduced into the ion source with the input syringe acetonitrile at a 50 ml/min flow rate
through the 5 mL Reodyne injector loop.
Bis(4-tert-butyl-3,5-dimethylpyrazol-1-yl)methanone
(7).
4-tert-butyl-3,5-
dimethylpyrazole 3 (2.37 g, 15.6 mmol) was dissolved in THF (20 mL) and NEt3 (2.13 mL) was
added afterwards. Triphosgene, Cl3COCOOCCl3 (0.772 g, 2.60 mmol), was dissolved in THF
(20 mL) and the resulting solution was added as quickly as possible to the initial one. After 16 h
of stirring at room temperature, the white solid formed was filtered off and washed twice with
THF. The THF fractions were combined and the solvent evaporated. The product was obtained
as an orange-brown oil in a yield of 1.055 g (69.3%).1H NMR (400 MHz, CDCl3) δ 2.50 (s,
6H), 2.36 (s, 6H), 1.36 (s, 18H). Anal. Calcd for C19H30N4O (330.48): C, 69.06; H, 9.15; N,
16.95; O, 4.84. Found: C, 68.95; H, 9.01; N, 16.88.
Bis(4-bromo-3,5-dimethylpyrazol-1-yl)methanone (8). The method was similar to that
used for 7. The obtained solid was recrystallised from toluene/hexane obtaining white crystals.
Yield: 1.88 g (64.2 %). 1H NMR (400 MHz, CDCl3) δ 2.49 (s, 6H), 2.29 (s, 6H). Anal. Calcd for
C11H12Br2N4O (376,05): C, 35.13; H, 3.22; Br, 42.50; N, 14.90; O, 4.25. Found: C, 35.07; H,
3.16; Br, 42.38; N, 14.81.
2-[Di(pyrazol-1-yl)methyl]pyridine (9). A mixture of bis(pyrazol-1-yl)methanone 5
(0.74 g, 4.59 mmol), 2-formylpyridine (0.492 g, 4.59 mmol) and CoCl2·6H2O (0.011 g, 0.046
mmol) was heated with vigorous stirring at 100 °C during 4 h. Resulting solid was dissolved in
CH2Cl2, washed with water three times and dried over Na2SO4. Then, solvent was removed by
rotary evaporation and the resulting black product was dissolved in CH2Cl2 and filtered through
a short pad of silica gel, and then the solvent was removed by rotary evaporation and the
resulting viscous burgundy oil was crystallized from toluene / petroleum ether 1: 3, to give
oranges brown crystals. Yield - 0.444 g (31.8%).1H NMR (400 MHz, CDCl3) δ 8.65 (d, J = 4.5
Hz, 1H), 7.77 – 7.69 (m, 2H), 7.67 – 7.61 (m, 4H), 7.30 (dd, J = 7.5, 4.9 Hz, 1H), 7.04 (d, J = 7.9
3

Hz, 1H), 6.35 (s, 2H). Anal. Calcd for C12H11N5 (225.25): C, 63.99; H, 4.92; N, 31.09. Found: C,
63.78; H, 4.88; N, 30.98.
2-[Bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine (10). The method was similar to that
used for 9. Amounts were as follows: bis(3,5-dimethylpyrazol-1-yl)methanone (1.0 g, 4.59
mmol), 2-formylpyridine (0.492 g, 4.59 mmol) and CoCl2·6H2O (0.011 g, 0.046 mmol).
Resulting brown solid was washed with minimal Et2O and was recrystallized by cooling a hot
hexane solution to room temperature to give 0.886 g (68.7%) of 10 .1H NMR (400 MHz, CDCl3)
δ 8.64 (d, J = 4.5 Hz, 1H), 7.68 (t, J = 7.7 Hz, 1H), 7.56 (s, 1H), 7.24 (d, J = 7.5 Hz, 1H), 6.93
(d, J = 7.8 Hz, 1H), 5.85 (s, 2H), 2.20 (s, 6H), 2.18 (s, 6H). Anal. Calcd for C16H19N5 (281.36):
C, 68.30; H, 6.81; N, 24.89. Found: C, 68.26; H, 6.80; N, 24.80.
2-[Bis(4-tert-buthyl-3,5-dimethylpyrazol-1-yl)methyl]pyridine (11). The method was
similar to that used for 10. Amounts were as follows: bis(4-tert-buthyl-3,5-dimethylpyrazol-1-
yl)methanone (1.0 g, 4.59 mmol), 2-formylpyridine (0.492 g, 4.59 mmol) and CoCl2·6H2O
(0.011 g, 0.046 mmol). Brown oil was triturated with petroleum ether and the precipitate formed
is filtered off. Evaporation of the filtrate gave a brownish yellow oil which was dried under
о
vacuum and identified as 11. Yield - 0.812 g (85.9%). M.p.=145-147 С.1H NMR (400 MHz,
CDCl3) δ 8.60 (d, J = 4.2 Hz, 1H), 7.65 (td, J = 7.8, 1.6 Hz, 1H), 7.55 (s, 1H), 7.21 (dd, J = 7.3,
13
5.0 Hz, 1H), 6.77 (d, J = 7.8 Hz, 1H), 2.28 (s, 6H), 2.22 (s, 6H), 1.32 (s, 18H). C NMR (75
MHz, CDCl3) δ 156.35 (Py, C2), 149.38 (Py, C6), 146.05 (Pz, C5), 137.06 (Pz, C3), 136.50 (Py,
C4), 124.64 (Pz, C4), 123.05 (Py, C3), 122.33 (Py, C5), 74.96 (Cα), 31.80 (t-Bu, Me), 31.54 (t-Bu,
C), 16.96 (Me5), 12.58 (Me3). Масс-спектр 393 (M-1, 4.05); 241 (66,75). Anal. Calcd for
C24H35N5 (393.58): C, 73.24; H, 8.96; N, 17.79. Found: C, 73.19; H, 8.91; N, 17.70.
2-[Bis(4-bromo-3,5-dimethylpyrazol-1-yl)methyl]pyridine (12). The method was
similar to that used for 10. Amounts were as follows: bis(4-bromo-3,5-dimethylpyrazol-1-
yl)methanone (1.0 g, 4.59 mmol), 2-formylpyridine (0.492 g, 4.59 mmol) and CoCl2·6H2O
(0.011 g, 0.046 mmol). Obtained solid was dissolved in toluene and filtered through a short pad
of silica gel, and then the solvent was removed by rotary evaporation to give beige crystals.
о
Yield – 0.178 g (32.4%). M.p. =171-172 С.1H NMR (400 MHz, CDCl3) δ 8.64 (d, J = 4.0 Hz,
1H), 7.71 (t, J = 7.7 Hz, 1H), 7.58 (s, 1H), 7.33 – 7.28 (m, 1H), 6.98 (d, J = 8.0 Hz, 1H), 2.20 (d,
13
J = 1.1 Hz, 12H). C NMR (75 MHz, CDCl3) δ 154.30 (Py, C2), 149.83 (Py, C6), 147.74 (Pz,
C5), 139.06 (Pz, C3), 137.22 (Py, C4), 123.75 (Py, C3), 122.48 (Py, C5), 96.71 (Pz, C4), 76.11
(Cα), 12.77 (Me5), 11.01 (Me3). Mass-spectrum (E.I., 70 eV, m/z, %): 439 (4.99); 264 (100).
4

Anal. Calcd for C16H17Br2N5 (439.16): C, 43.76; H, 3.90; Br; 36.39; N, 15.95. Found: C, 43.88;
H, 3.92; Br, 36.32; N, 15.70.
2-[Bis(3,5-dimethylpyrazol-1-yl)methyl]quinoline (13). The method was similar to that
used for 10. Amounts were as follows: bis(3,5-dimethylpyrazol-1-yl)methanone (0.62 g, 2,85
mmol), 2-formylquinoline (0.447 г, 2,85 mmol) and CoCl2·6H2O (0.010 g, 0,028 mmol).
Orange-brown crystals, yield 0.672 g (71.3%).1H NMR (400 MHz, CDCl3) δ 8.14 (d, J = 8.6 Hz,
1H), 8.05 (d, J = 8.5 Hz, 1H), 7.81 (d, J = 8.0 Hz, 1H), 7.72 – 7.65 (m, 2H), 7.54 (t, J = 7.4 Hz,
13
1H), 7.26 (t, J = 4.2 Hz, 2H), 5.89 (s, 2H), 2.19 (s, 12H). C NMR (101 MHz, CDCl3) δ 155.57
a
(Quin., C2), 148.61 (Pz, C5), 147.51 (Quin., C8 ), 140.95 (Pz, C3), 136.81 (Quin., C4), 129.83
a
(Quin., C7), 129.60 (Quin., C8), 127.78 (Quin., C5), 127.59 (Quin., C4 ), 127.04 (Quin., C6),
120.46 (Quin., C3), 106.97 (Pz, C4), 75.54 (Cα), 13.94 (Me5), 11.52 (Me3). Mass-spectrum (E.I.,
70 eV, m/z, %): 331 (7.5); 236 (100). Anal. Calcd for C20H21N5 (331.42): C, 72.48; H, 6.39; N,
21.13. Found: C, 72.42; H, 6.31; N, 21.01.
Synthesis of Nickel(II) complexes
[N,N,N-(2-[bis(pyrazol-1-yl)methyl]pyridine nickel (II) dibromide (14). A solution of
2-[bis(pyrazol-1-yl)methyl]pyridine 9 (0.342 g, 1.52 mmol) in THF (10 mL) was slowly added
to a stirred solution of [NiBr2 DME] (0.470 g, 1.52 mmol) in THF (15 mL). After brief stirring at
r.t., the beige precipitate was separated out by filtration, washed with THF and dried in vacuum.
Yield: 0.384 g (57%). Anal. Calcd for C12H14Br2N5Ni.2C4H8O (590.98): C 40.65; H 5.12; N
11.85; O 5.41; Br 27.04; Ni 9.93. Found: C 40.23; H 4.69; N 11.32; Ni 9.58. IR, cm-1: ν(Ni-N)
489, 420. Mass spectrum (E.I., 70 eV, m/z, %): 366 [M+-Br]. ESI-MS: m/z (%) 366 [(M − Br)+,
100%].
[N,N,N-(2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel (II) dibromide (15).
The method was similar to that used for 14. Amounts were as follows: [NiBr2 DME] (0.179 g,
0.58 mmol), 2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine 10 (0.163 g, 0,58 mmol). Bluish-
green solid. Yield: 0.241 g (83%). Anal. Calcd for C16H22Br2N5Ni.C4H8O (572,02): C 41.78; H
5.2l; N 12.18; O 2.78; Br 27.79; Ni 10.21. Found: C, 41.45; H 5.08; N 12.04; Ni 9.97. IR, cm-1:
ν(Ni-N) 447. Mass spectrum (E.I., 70 eV, m/z, %): 423 (M-Br, 100%). ESI-MS: m/z (%) 423
[(M − Br)+, 100%].
[N,N,N-(2-[bis(4-tert-buthyl-3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel (II)
dibromide (16). The method was similar to that used for 14. Amounts were as follows: [NiBr2
5

DME] (0.636 g, 2.06 mmol), 2-[bis(4-tert-buthyl-3,5-dimethylpyrazol-1-yl)methyl]pyridine
(0.812 g, 2,06 mmol). Yield: 0.847 g (67,1%). Anal. Calcd for C24H20Br2N5Ni C4H8O (687.20):
C 48.94; H 6.75; N 10.19; O 2.33; Br 23.25; Ni 8.54. Found: C 47.99; H 6.43; N 10.20; Ni 8.20.
IR, cm-1: ν(Ni-N) 531, 412. Mass spectrum (E.I., 70 eV, m/z, %): 535 [(M-Br)+, 100%].
[N,N,N-(2-[bis(4-bromo-3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel (II)
dibromide (17). The method was similar to that used for 14. Amounts were as follows: [NiBr2
DME] (0.155 g, 0.50 mmol), 2-[bis(4-bromo-3,5-dimethylpyrazol-1-yl)methyl]pyridine (0.220 g,
0.50 mmol). Yield: 0.290 g (72%). Anal. Calcd for C16H20Br4N5Ni.2C4H8O (804.88): C 35.8; H
4.51; N 8.70; O 3.98; Br 39.71; Ni 7.29. Found: C 35.20; H 4.12; N 8.20; Ni 7.00. IR, cm-1:
ν(Ni-N) 497, 435. ESI-MS: m/z (%) 501 [(M-Br)+, 100%].
[N,N,N-(2-[bis(3,5-dimethylpyrazol-1-yl)methyl]quinoline nickel (II) dibromide (18).
The method was similar to that used for 14. Amounts were as follows: [NiBr2 DME] (0.327 g,
1.06 mmol), 2-[bis(3,5-dimethylpyrazol-1-yl)methyl]quinoline (0.351 g, 1,06 mmol). Yield:
0.489 g (83,9%). Anal. Calcd for C20H24Br2N5Ni.C4H8O (625.04): C 46.12; H 5.16; N 11.20; O
2.56; Br 25.57; Ni 9.39. Found: C 45.20; H 4.96; N 10.32; Ni 8.75. IR, cm-1: ν(Ni-N) 597, 418.
Mass spectrum (E.I., 70 eV, m/z, %): 545 [(M-Br)+, 100%].
N,N,N-tris(3,5-dimethylpyrazol-1-yl)methyl nickel (II) dibromide (20). The method
was similar to that used for 14. Amounts were as follows: [NiBr2 DME] (0.519 g, 1,68 mmol),
tris(3,5-dimethylpyrazol-1-yl)methane (0.500 g, 1.68 mmol). Yield: 0.847 g (67,1%). Anal.
Calcd for C20H35Br2N6Ni.C4H8O (594.03): C 40.44; H 5.94; N 14.15; O 2.69; Br 26.90; Ni 9.88.
Found: C 40.23; H 4.92; N 14.05; Ni 8.77. IR, cm-1: ν(Ni-N) 520, 440. MALDI-TOF-MS (m/z):
calcd for C20H35BrN6Ni.C4H8O: 515.0315; found: 515.0279 [M-Br]+.
Bis- [tris(3,5-dimethylpyrazol-1-yl)methane] nickel (II) tetrabromine nickelate (21).
Anhydrous NiBr2 (0.219 g, 1.00 mmol) was added to a CH3CN solution (20 mL) of tris(3,5-
dimethylpyrazol-1-yl)methane 19 (0.298 g, 1.00 mmol). The resulting solution was refluxed for
48 h. The brown-green precipitate was separated out by filtration, washed with CH3CN and dried
in vacuo. Yield: 0.425 g (79%). Anal. Calcd for C32H50Br4N12Ni2 2CH3CN: C 38.54; H 5.03; N
17.48; Br 28.49; Ni 10.46. Found: C, 38.42; H 4.86; N 17.37; Br 28.37; Ni 10.27. IR, cm-1: ν(Ni-
N) 423, 499. ESI-MS, m/z (%):1039.82 [(M)+, 97%].
Bis-2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel (II) tetrabromine
nickelate (22).
6

Anhydrous NiBr2 (0.127 g, 0.58 mmol) was added to a CH3OH solution (20 mL) of 2-[bis(3,5-
dimethylpyrazol-1-yl)methyl]pyridine 10 (0.163 g, 0.58 mmol). The resulting suspension was
refluxed for 48 h. The green precipitate was separated out by filtration, washed with CH3OH and
dried in vacuo. Yield: 0.269 g (85%). Anal. Calcd for C32H44N10Ni2Br4 CH3OH: C 38.19; H
4.66; N 13.50; Br 30.80; Ni 13.50. Found: C, 38.03; H 4.27; N 13.17; Br 30.15; Ni 11.15. IR,
cm-1: ν(Ni-N) 418, 497. ESI-MS, m/z (%): 1005.76 [(M)+, 95%].
X-ray diffraction studies.
The single-crystal X-ray diffraction data for 21 and 22 were collected on the ‘Belok’
beamline of the Kurchatov Synchrotron Radiation Source (National Research Center ‘Kurchatov
Institute’, Moscow, Russian Federation) using a Rayonix SX165 CCD detector at λ = 0.96990 Å.
A total of 720 images for two different orientations in the case of each crystal were collected
using an oscillation range of 1.0° and ϕ scan mode. The data were indexed and integrated using
the utility iMOSFLM from the CCP4 program suite [13] and then scaled and corrected for
absorption using the Scala program [14]. For details, see Table 2. The structures were
determined by direct methods and refined by full-matrix least square technique on F2 in
anisotropic approximation for non-hydrogen atoms. The independent parts of the unit cells of 21
and 22 contained two acetonitrile and one methanol solvate molecules, respectively. The
hydrogen atoms of the solvate molecules were objectively localized in the difference-Fourier
map and included in the refinement within the riding model with isotropic displacement
parameters [Uiso(H) = 1.5Ueq(O, N or C)]. The other hydrogen atoms in 21 and 22 were placed in
calculated positions and refined within the riding model with fixed isotropic displacement
parameters [Uiso(H) = 1.5Ueq(C) for the methyl groups and 1.2Ueq(C) for the other groups]. All
calculations were carried out using the SHELXTL program suite [15]. Crystallographic data for
21•2CH3CN and 22•CH3OH have been deposited with the Cambridge Crystallographic Data
Center, CCDC 1511204 (21) and CCDC 1511203 (22).
Table 1. Crystal data and structure refinements.
Compound
21 •2CH3CN
C36H50Br4N14Ni2
1115.88
22 • CH3OH
C33H42Br4N10Ni2O
1031.82
Empirical formula
Formula weight
Temperature, K
Crystal system
Space group
100.0(2)
100.0(2)
Monoclinic
P21/c
Monoclinic
P21/c
7

a, Å
10.300(2)
23.867(5)
18.967(4)
90
9.6801(19)
19.060(4)
21.750(4)
90
b, Å
c, Å
α, deg.
β, deg.
92.95(3)
90
93.68(3)
90
γ, deg.
V, Å3
4656.5(17)
4
4004.8(14)
4
Z
Dcalc, g·cm-3
1.592
1.711
3.065
3.547
Absorption coefficient, µ
F(000)
2240
2056
Crystal size, mm
0.02×0.10×0.15
3.35 – 38.41
0.08×0.10×0.12
3.39 – 39.79
Theta range for data collection
Index ranges
-13 < h < 13
-29 < k < 29
-22 < l < 18
-11 < h < 11
-23 < k < 23
-27 < l < 27
Reflections collected
Independent reflections, Rint
Reflections observed with I > 2σ(I)
Absorption correction
Data / restraints/ parameters
Goodness-of-fit on F2
R1 [I > 2σ(I)]
61005
36804
9485, 0.076
7057
8261, 0.071
6595
semi-empirical
9485 / 0 / 523
1.051
semi-empirical
8261 / 0/ 464
1.050
0.061
0.065
wR2 [all data]
0.177
0.190
Extinction coefficient
Tmin / Tmax
0.00183(19)
0.660 / 0.930
0.00184(19)
0.666 / 0.737
Oligomerization of Ethylene was performed in a 100-ml reactor (Parr Instrument Co.) equipped
with a magnetic stirrer and inlets for loading components of catalytic systems and ethylene at a
total ethylene and toluene vapors pressure of 3 atm. Toluene (50 ml) and the necessary amount
of a co-catalyst (Et2AlCl, Et3Al2Cl3) were loaded in the reactor. The reactor was heated to a
specified temperature, and reaction mixture was saturated with ethylene. Oligomerization was
initiated by addition of pre-catalyst to the reaction mixture and pressurization of 3 atm of
ethylene in the reactor. The pressure of ethylene was maintained constant during
8

oligomerization. After a desired time, the reaction solution was quickly cooled down and then
quenched with 5 ml isopropanol and 5 ml 5% dilute hydrochloric acid. After washed by water
and dried by Na2SO4, the organic compounds were characterized by gas chromatography and
GC–MS to determine the composition and molar mass distribution. Samples with desiccant were
stored in sealed flasks in the refrigerator. Samples (1.0 µl) 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). The separation was performed on a capillary column RTX-5ms (5%
Phenyl Polysilphenylene-siloxane; an inner diameter - 0.53 mm, length 50 m). Injector
temperature - 270 °C; reset 1: 200; initial column temperature -90 °C; isotherm – 4 min; further
heating at a rate of 10 degrees per minute up to 320 °C, and holding at 320°C – 3 min.
3. Results and Discussion
3.1. Synthesis and characterization.
The synthetic procedure for the heteroscorpionate ligands consisting of azine and
substituted pyrazole rings is shown in Scheme 1. The substituted pyrazoles 1-4 were treated with
bis(trichloromethyl)carbonate in THF solution in the presence of trimethylamine. The resulting
bis(pyrazolyl)methanones 5-8 was converted by Peterson rearrangement into the
heteroscorpionate ligands 9-13.
Structure of the ligands 9-13, 19 was confirmed by NMR and mass spectroscopy.
Reactions of the ligands with [NiBr2 DME] in THF at room temperature resulted in the
corresponding complexes 14-18, 20. These Ni(II) complexes were isolated in 57–84% yields and
characterized by elemental analysis, IR spectra and mass spectrometry. Their IR spectra in nujol
mull showed all the bands required by coordination of the scorpionate ligand; bands at 420-497
-1
→Ni).
cm were assigned to the stretching vibrations ν (N
Meaningful signals in the MS spectra
of the complexes 14-18, 20 were attributed to the loss of a bromine atom what is fairly well-
known in the chemistry of nickel halide complexes, e.g. [16].
9

b
a
R1=R2=H; R3-pyridine-2-yl;
9.
R1=R2= H
. R1=Me, R2=H,
.R1=Me, R2 = tBu
R1=Me, R2 = Br
8.
5.
R1=R2=H
. R1=Me, R2=H,
.R1=Me, R2 = tBu
R1=Me, R2 = Br
1.
. R1=Me, R2=H; R3 - pyridine-2-yl;
.R1=Me, R2=tBu; R3- pyridine-2-yl;
. R1=Me, R2=Br; R3- pyridine-2-yl;
.R1=Me, R3- quinoline-2-yl;
10
11
12
13
6
2
3
4
7
c
R1=R2=H
14.
18
. R1=Me, R2=H,
.R1=Me, R2 = tBu
R1=Me, R2 = Br
15
16
17.
NEt3, THF, Cl3OC(O)OCl3;
a
b
c
2-formylpyridine/2-formylquinoline, CoCl 6H O;
2
2
NiBr DME, THF.
2
Scheme 1. Synthesis of heteroscorpionate ligands and their dibromonickel(+2) complexes.
To identify the impact of azine ring on the catalytic activity we used known ligand 19
containing only pyrazole rings – tris(3,5-dimethylpyrazole-1-yl)methane [12]. Reactions of
scorpionate ligands with Ni(II) salts can, in principle, give half-sandwich or full-sandwich
complexes through the tripodal coordination of one or two scorpionates via the pyrazolyl ring’s
nitrogen atom. Numerous examples of such cationic spiro-complexes are given in [17-21].
Indeed, the interaction of the ligand 19 with anhydrous NiBr2 in CH3CN medium results in the
formation of ionic complex [L2Ni]+[NiBr4]-·CH3CN (21). Complex 22 having a similar structure
was obtained under the same conditions starting from the ligand 10 in methanol medium
(scheme 2). Structures containing nickel both in the cation and in the anion fragments have been
previously known (for example, [(tpm)2NiII][(tpm)NiII(NCS)3]2·2CH3OH [21] ). Structurally
related to 20 - complex LNiCl2·H2O was obtained in methanol-dichloromethane medium [22].
10

c
d
19
20
21
e
10
NiBr , THF; NiBr , MeCN; NiBr , MeOH
c
d
e
2
2
2
22
Scheme 2. Synthesis of full- and half-sandwich heteroscorpionate Ni(II) complexes.
The structures of the products 21 and 22 were unambiguously established by X-ray
diffraction study and are shown in Figures 1 and 2 along with the atomic numbering scheme. The
selected bond lengths and angles are given in Table 2.
The both nickel complexes crystallize in the monoclinic space group P21/c with two
crystallographically independent dications occupying special positions on the inversion centers.
It is important to note that complex 21 is structurally similar to {Ni[HC(3,5-Me2pz)3]2}(BF4)2
(23) and {Ni[HC(3,5-Me2pz)3]2}Br2 (24) reported previously [23, 24]. However, there are three
main differences between them: (i) the counter-anion NiBr4 (in 21) instead of BF4 (in 23) and Br
(in 24), (ii) no any solvate molecules are found in the crystals of 23 and 24, and (iii) the cations
of 23 and 24 possess the intrinsic Ci (1, at 220 K) and C2h (2/m) symmetry, respectively, those
are absent within the cation of 21. Moreover, the crystal of 23 undergoes the low temperature
phase transition (from monoclinic to triclinic syngony) at 163 K, but no phase transition is
observed for 21 at lowering of temperature to 100 K. In the case of complexes 21 and 22 the bite
of the tripodal ligand and the geometry of the ligand result in an unsymmetrical orientation of the
11

azaheterocycles relative to each other. The tridentate ligands subtend the N─M─N angles to
85.80(16)-86.53(16) and 85.89(16)-87.24(16)° (for two independent dications of 22) and
85.41(16)-86.33(15) and 84.88(16)-87.28(16)° (for two independent dications of 21) resulting in
a trigonal distortion from octahedral co-ordination geometry. The interplane angles between the
azaheterocycles are 52.8(2), 60.2(2), 67.1(2) and 57.8(2), 60.2(2), 62.1(2)° (for two independent
dications of 22) and 57.3(2), 57.9(2), 64.8(2) and 52.4(2), 62.5(2), 65.3(2)° (for two independent
dications of 21). The nickel-pyrazole bond lengths in 21 and 22 are significantly longer than
those in complexes involving monodentate pyrazole ligands (Table 2) [25, 26]. For the pyrazole
rings, the M─N─N angles are substantially smaller than the M─N─C angles (Table 2). The
pyridine rings are more symmetrically disposed, exhibiting the endo-cyclic M─N─C angles
about 4° smaller than the exo-cyclic M─N─C angles (Table 2). The tetrabromo-nickel(II)
dianions in 21 and 22 have a typical distorted tetrahedral geometry (Table 2).
Fig. 1. Molecular structure of 21•2CH3CN.
12

Fig. 2. Molecular structure of 22•CH3OH.
In the crystal of 22, the solvate methanol molecule forms the strong
O1─H1O⋅⋅⋅π(C2─C3─C4) (H1O⋅⋅⋅C3 2.49 Å, O1⋅⋅⋅C3 3.377(7) Å, ∠O1─H1O⋅⋅⋅C3 170°)
hydrogen bond to dication. Crystal packing of 21 and 22 is stacking along the crystallographic a
axis (Figures 3 and 4). The dianions, dications and solvate molecules are linked by weak
C─H⋅⋅⋅Br and C─H⋅⋅⋅N hydrogen bonding interactions into three-dimensional framework.
A
B
Fig. 3. Crystal structures of 21•2CH3CN (A) and 22•CH3OH along the crystallographic a axis.
Table 2. Bond distances (Å) and angles (°) for Ni(II) and the bridgehead carbon in 21 and 22.
13

Compound
21
22
2.093(4)
2.134(4)
2.157(4)
2.110(4)
2.117(4)
2.132(4)
85.41(16)
85.82(15)
86.33(15)
84.88(16)
87.22(16)
87.28(16)
115.5(3)
116.3(3)
117.5(3)
116.0(3)
117.0(3)
119.7(4)
137.6(3)
138.1(3)
139.2(3)
138.1(3)
138.5(3)
138.9(3)
110.0(4)
111.6(4)
111.7(4)
110.3(4)
111.7(4)
111.7(4)
2.3675(12)
2.4340(9)
2.4389(9)
2.098(4)
2.116(4)
2.126(4)
2.085(4)
2.090(4)
2.105(4)
85.80(16)
86.28(17)
86.53(16)
85.89(16)
86.76(16)
87.24(16)
116.1(3)
116.5(3)
118.5(3)
116.0(3)
116.5(3)
119.0(3)
137.9(4)
137.8(3)
122.2(4)
138.6(4)
138.2(3)
122.9(3)
110.4(4)
111.6(4)
111.9(4)
110.8(4)
110.9(4)
111.6(4)
2.3905(10)
2.3959(10)
2.4117(11)
─N
Ni1
Ni2─N
─Ni1─N
N
N─Ni2─N
─N─X (endo)
─N─X (endo)
Ni1
Ni2
Ni1─N─C (exo)
─N─C (exo)
Ni2
N─C1─X
─C17─X
N
─Br
Ni3
14

2.4680(9)
103.85(3)
104.64(3)
107.25(4)
108.39(4)
112.28(4)
119.88(3)
2.4190(11)
105.80(3)
106.05(4)
108.19(3)
109.82(4)
112.52(4)
114.35(4)
─Ni3─Br
Br
3.2. Oligomerization experiments
The performance of the nickel complexes 14-18, 20-22 in ethylene oligomerization was
investigated using diethylaluminum chloride and ethylaluminum sesquichloride as activators and
under standard experimental conditions: temperature: 30°С, constant ethylene pressure 3 atm.,
molar ratio Ni/Al = 1/75. The main results are summarized in Table 3.
Table 3. Ethylene oligomerization with 1/OAC a
Additive,
[PPh3],
equiv.
Oligomer distribution,%
Pre-
catalyst
[Ni], Co-catalyst,
Entry
Ab
mol
[Al]/[Ni]
С4
С6
Et2AlCl,
75/1
Et3Al2Cl3,
75/1
Et2AlCl,
75/1
Et3Al2Cl3,
75/1
1
2
3
4
4·10-5
4·10-5
1·10-5
1·10-5
-
-
55
n.d.c
n.d.c
n.d.c
n.d.c
n.d. c
n.d.c
n.d.c
n.d.c
14
14
14
14
63.5
120
100
1
1
95
((Z)-2-butene – 52;
(E)-2-butene – 32;
1-butene – 16)
Et2AlCl,
75/1
5
6
15
15
4·10-5
4·10-5
-
-
323
5
100
Et3Al2Cl3,
75/1
((Z)-2-butene – 35;
(E)-2-butene – 24;
1-butene – 41)
320.5
-
100
Et2AlCl,
75/1
((Z)-2-butene – 15;
(E)-2-butene – 10;
1-butene – 75)
7
8
1·10-5
1·10-5
1
1
650
408
15
15
97
Et3Al2Cl3,
75/1
((Z)-2-butene – 68;
(E)-2-butene – 22;
1-butene – 10)
3
15

94.7
((Z)-2-butene – 40;
(E)-2-butene – 27;
isobutene – 1;
5.3
(1-hexene – 55,
2-hexene – 45)
Et2AlCl,
75/1
9
4·10-5
-
270
16
1-butene – 32)
95
5
Et3Al2Cl3,
75/1
((Z)-2-butene – 29;
(E)-2-butene – 23;
1-butene – 48)
10
11
12
4·10-5
1·10-5
1·10-5
-
192.5
400
16
16
16
(1-hexene – 53.7,
2-hexene – 46.3)
96
Et2AlCl,
75/1
((Z)-2-butene – 19.3;
(E)-2-butene – 16.3;
1-butene – 64.4)
1
1
4
91
Et3Al2Cl3,
75/1
((Z)-2-butene – 25;
(E)-2-butene – 21.7;
1-butene – 53.3)
348
9
9
91
((Z)-2-butene – 20;
(E)-2-butene – 15.1; (1-hexene – 35,
Et2AlCl,
75/1
13
4·10-5
-
87
17
isobutene – 4.9;
2-hexene – 65)
1-butene – 60)
92
((Z)-2-butene – 16;
(E)-2-butene – 13;
isobutene – 1;
1-butene– 70)
8
Et3Al2Cl3,
75/1
14
15
16
17
18
4·10-5
1·10-5
1·10-5
4·10-5
4·10-5
-
1
1
-
65
370
(1-hexene – 67,
2-hexene – 33)
17
17
17
18
18
85
Et2AlCl,
75/1
((Z)-2-butene – 23;
(E)-2-butene – 15.6;
1-butene – 61.4)
15
10
90
Et3Al2Cl3,
75/1
((Z)-2-butene – 40;
(E)-2-butene – 20;
1-butene – 40)
312
90
Et2AlCl,
75/1
((Z)-2-butene – 17.5;;
(E)-2-butene – 12.8;
1-butene – 69.1)
133,5
408
10
92.6
Et3Al2Cl3,
75/1
((Z)-2-butene – 42.9;
(E)-2-butene – 28.5;
1-butene – 28.6)
-
7.4
97
((Z)-2-butene – 37.8;
(E)-2-butene – 31.4;
isobutene – 4;
Et2AlCl,
75/1
19
1·10-5
1
340
18
3
1-butene – 26.8)
16

100
((Z)-2-butene – 30;
(E)-2-butene – 27;
isobutene – 6;
Et3Al2Cl3,
75/1
20
1·10-5
1
348
-
18
1-butene – 37)
86
((Z)-2-butene – 9.7;
(E)-2-butene – 90.3)
Et2AlCl,
75/1
21
22
4·10-5
4·10-5
-
-
97
20
20
14
6
94
Et3Al2Cl3,
75/1
((Z)-2-butene – 10;
(E)-2-butene – 23;
1-butene – 81)
120
98
((Z)-2-butene – 8;
(E)-2-butene – 2;
isobutene – 75;
1-butene – 13)
Et2AlCl,
75/1
23
1·10-5
1
398
20
2
97
Et3Al2Cl3,
75/1
((Z)-2-butene – 3;
(E)-2-butene – 2;
1-butene – 95)
24
25
26
1·10-5
4·10-5
4·10-5
1
-
298
48
20
21
22
3
5
1
95
Et2AlCl,
75/1
((Z)-2-butene – 47;
(E)-2-butene – 13;
1-butene – 40)
99
Et2AlCl,
75/1
((Z)-2-butene – 36;
(E)-2-butene – 28;
1-butene – 36)
-
51
а) Oligomerization carried out in 50 mL of toluene at a constant ethylene pressure for 30 min, temperature
30oC, ethylene pressure 3 atm; b) kgoligomer mol−1 Ni h−1 (The activities were calculated from the total
consumption of ethylene (1.0 L ethylene = 1.2 g product); c) not determined.
The pre-catalyst 14 containing unsubstituted pyrazole rings showed lowest activity among all the
tested complexes (Table 3, entries 1-2), which is probably explained by its very low solubility in
toluene. Due to these results, further studies of its catalytic properties were not conducted.
Complex 15 containing methyl groups in positions 3 and 5 of the pyrazole ring is significantly
more active (Table 3, entries 5-6, Fig.4). Such increase of activity can be assigned to growth of
precatalyst solubility in toluene. The reaction products are mixtures of butene and hexene
isomers with predominance of internal olefins.
Introduction a tert-butyl group in position 4 of the pyrazole ring further increases the solubility
of the complex 16 in toluene, but in spite of this fact its catalytic activity with both co-catalysts is
17

reduced in comparison to 15 (entries 9-10). Since the bulky tert-butyl groups are at a
considerable distance from the metal center, one would assume that the observed effect is not
due to steric, but electronic factors leading to an increase in electron density at the metal center.
However, the introduction of electron-withdrawing substituents - bromine in the 4-position of the
pyrazole ring (complex 17, entries 13-14) also was accompanied by a reduction in catalytic
activity, although an increase in the acidity of the metal center might be accompanied by the
growth of activity. Nonetheless, the ratio of α-olefins in the reaction products greatly increased.
Thus, for system 17 / Et3Al2Cl3, the share of 1-butene in the C4 fraction amounted to 70%, and
in the C6 fraction was detected up to 67% of 1-hexene. In the case of 17 /Et2AlCl, reaction
product comprises about 5% of isobutene, which was not observed earlier in such systems.
Replacement of the pyridine ring by the quinoline (complex 18) leads not only to increased
lipophilicity, but also to an increase in steric hindrance of metal center. Activity of catalyst
systems involving compound 18 depends on the nature of the co-catalysts to the much more
extent, and reaches the maximum - 408 g / mmol Ni per hour while using Et3Al2Cl3 (entry 18).
However, the increased activity is accompanied by a decline in selectivity: the share of 1-butene
in the C4 fraction does not exceed 29%.
Complex 20, stabilized by tris(pyrazolyl)methane ligand, exhibits a rather low reactivity.
The nature of organoaluminum cocatalyst has a considerable but ambiguous effect on the activity
and selectivity of the catalytic systems. Thus, it has practically no influence on the activity of
complexes 14, 15, but in the case of complexes 18, 20 there is a some increase in activity while
using Et3Al2Cl3. With the exception of complex 18, the use of Et3Al2Cl3 increases the content of
1-butene and decreases the content of hexene isomers. For complexes 16, 17 activated by
Et3Al2Cl3, growth of activity is not observed but the selectivity of the process is similar to the
previously discussed.
The effect of the PPh3 additive (1 equiv.) on the activity and selectivity of the catalyst systems
was studied. According to the literature the addition of Ph3P can significantly increase the
activity of catalytic systems based on nickel [27-34] and other metals complexes [35]. The
addition of the PPh3 to catalyst systems involving complex 15 led to a significant increase in
activity, which made it impossible to use the flow meters correctly. Such high values of activity
determined the necessity to reduce the amount of catalyst: in all experiments involving
phosphine, pre-catalyst concentration was 4 times reduced. For pre-catalysts 14, 15 activated by
Et2AlCl, addition of 1 equiv. of triphenylphosphine was accompanied by increased activity by ≈
18

2 times. The ability of triphenylphosphine to increase the activity by almost 5 times was
discovered for compound 17 (entries 15-16, Fig.4).
Oligomers obtained on pre-catalyst 15 consisted of 95-100% of butene isomers. The content of
α-isomer in the butene fraction was low (16% for system 15 / Et2AlCl; 41% for 15 / Et3Al2Cl3).
Addition of triphenylphosphine to the catalyst system 15 / Et2AlCl improved selectivity to 1-
butene up to 75%.
The addition of PPh3 to the system 15 / Et3Al2Cl3 had the opposite effect: the content of 1-butene
in the C4-fraction droped to 10%, while at the same time a small increase (to 3%) of hexenes was
observed.
For pre-catalyst 17, the addition of triphenylphosphine led to a substantial increase both in
activity and in the content of hexenes fraction. However, when Et3Al2Cl3 was used as co-catalyst
simultaneous decrease in the ratio of 1-butene to 40% was observed.
The most exciting results were obtained while studying the effect of PPh3 on the selectivity of
the pre-catalyst 20. Thus, while using Et2AlCl, hexenes (14%) and 2-butene isomers (86%) were
obtained. In the presence of triphenylphosphine the share of butene isomers increased to 98%,
and 75% of this fraction falls on isobutylene. Addition of phosphine to 20 / Et3Al2Cl3 not only
increased the activity, but also gives a significant increase in selectivity to 1-butene – up to 95%
of the whole C4 fraction.
19

100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
2
3
3
10 10 4
3
3
2
4
5
5
1
5
6
6
9
7
8
1
9
9
4
14
8
15
10
15
19
15
35
24
16
36
28
36
27
9
23
30
18
14
47
38
20
13
37
36
12
40
50
12
15
62
66
74
20
48
22
46
27
37
hexenes
13
40
92
18
30
26
30
isobutene
(Z)-2-butene
(E)-2-butene
1-butene
26
27
78
76
75
64
62
30
15
55
52
41 21
10
8
2
36
26
13
Fig. 4. Composition of oligomer mixtures obtained with pre-catalysts 15-18, 20-22.
Thus, the system 20 / Et2AlCl / PPh3 is simultaneously "working" not only as ethylene
dimerization catalyst, but also is able to catalyze the isomerization of butane oligomers yielding
isobutene.
The coordinatively saturated complexes 21-22, as expected, showed a very moderate activity.
The general positive impact of PPh3 additive on catalytic activity was previously investigated
and can be attributed to several factors. First, it coordinates to the nickel core and further
dissociation and association of PPh3 molecule leads to activation and protection of metal center.
[30] Second, this additive can act as electron donor agent, while coordinated to metal core, and
thus enhances the oligomerization reaction. [35] But none of these factors can explain a sharp
increase of selectivity in some cases. So there may be another acting factor that is responsible for
these dramatic changes in catalytic behavior. In our view reversible coordination of PPh3 can
prevent formation of catalytically inactive structures with the formula L2Ni2+.
4. Conclusion
A series of new neutral tridentate N,N,N-heteroscorpionate ligands 9-13 and their Ni(II)
complexes 14-18, 20-22 have been prepared and characterized. Ligands were modified in an
attempt to change steric effects and the electronic density of the metal center and eventually to
improve the activity in oligomerization of ethylene and to control the oligomer structure. The
20

behavior of 14-18, 20-22 as ethylene oligomerization catalysts was preliminary explored after
activation with several co-catalysts.
The product distribution from oligomerization reactions, however, is frequently difficult to
control and optimize. In present paper it is shown that the addition of PPh3, in some cases, has a
significant influence on the selectivity. Thus, the phosphine role can be explained not only by the
reversible coordination with nickel atom that can facilitate the formation of vacant coordination
sites required for the realization of catalytic activity. Probably, the coordination of
triphenylphosphine molecule can prevent rearrangement of complexes to more
thermodynamically advantageous, but catalytically inactive structures with the formula L2Ni2+.
Further work will be focused on the design and optimization of the heteroscorpionate ligand and
the process condition to produce oligomers with high selectivity.
Acknowledgment This work was financially supported by the Russian Foundation for Basic
Research (Project Nos 16-33-80071, 16-03-00643, 14-43-01014).
Appendix A. Supplementary material
CCDC 1511204 and CCDC 1511203 contain the supplementary crystallographic data for 21 and
22. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
References
[1] C. Pettinari, R. Pettinari, Coord. Chem. Rev. 249 (2005) 663– 691,
doi:10.1016/j.ccr.2004.08.017.
[2] A. Otero, J. Fernández-Baeza, A. Antiñolo, J. Tejeda, A. Lara-Sánchez, Dalton Trans.
2004, 1499–1510, DOI: 10.1039/B401425A.
[3] A. Otero, J. Fernandez-Baeza, A. Lara-Sanchez, L. F. Sanchez-Barba, Coord. Chem.
Rev. 257 (2013) 1806– 1868, http://dx.doi.org/10.1016/j.ccr.2013.01.027.
[4] O. Ojwach, J. Darkwa, Inorg. Chim. Acta 363 (2010) 1947–1964,
doi:10.1016/j.ica.2010.02.014.
[5] S. Wang, W.-H. Sun, C. Redshaw, J. Organomet. Chem 751 (2014) 717-741,
http://dx.doi.org/10.1016/j.jorganchem.2013.08.021.
[6] F. A. Kunrath, R. F. de Souza, R. S. Mauler, O. L. Casagrande Jr., Organometallics 22
(2003) 4739–4743, DOI: 10.1021/om034035u.
[7] W. Klaui, B. Turkowski, G. Rheinwald, H. Lang, Eur. J. Inorg. Chem. 1 (2002) 205-209,
DOI: 10.1002/1099-0682(20021)2002:1<205::AID-EJIC205>3.0.CO;2-S.
21

[8] M.K. Ehlert, A. Storr, R.C. Thompson, Can.J. Chem. 70 (1992) 1121-1128, DOI:
10.1139/v92-148.
[9] J. Christoffers, T. Kauf, T. Werner, M. Rössle, Eur. J. Org. Chem. 2006, 2601-2608,
DOI: 10.1002/ejoc.200600061.
[10]
[11]
J. Elguero, et al. Bull. Soc. Chim. Fr. (1968) 707.
G. Alesso, V. Tabernero, T. Cuenca, J. Organomet. Chem. 717 (2012) 202-210,
http://dx.doi.org/10.1016/j.jorganchem.2012.07.004 .
[12]
D. L. Reger, T. C. Grattan, K. J. Brown, C. A. Little, J.J.S. Lamba, A.L.
Rheingold, R.D. Sommer, J. Organomet. Chem. 607 (2000) 120-128,
http://dx.doi.org/10.1016/S0022-328X(00)00290-4.
[13]
T. G. G. Battye, L. Kontogiannis, O. Johnson, H. R. Powell, A. G. W. Leslie, Acta
Cryst., 2011, D67, 271-281, doi: 10.1107/S0907444910048675.
[14]
P. R. Evans, Acta Cryst., 2006, D62, 72-82,
https://doi.org/10.1107/S0907444905036693.
[15]
[16]
G. M. Sheldrick, Acta Cryst., 2015, C71, 3-8, DOI:10.1107/S2053229614026540.
M. Helldörfer, J. Backhaus, W. Milius, H. G. Alt, Journal of Molecular Catalysis
A: Chemical 193 (2003) 59–70, http://dx.doi.org/10.1016/S1381-1169(02)00468-5.
[17] S. Trofimenko, J. Am. Chem. Soc.1970, 92, 5118–5126, DOI:
10.1021/ja00720a021.
[18] T. Astley, J. M. Gulbis, M. A. Hitchman, E. R. T. Tiekink, J. Chem. Soc., Dalton
Trans. 1993, 509–515, DOI: 10.1039/DT9930000509.
[19]
G. Lyubartseva and S. Parkin, Acta Cryst. (2009). E65, m1530,
https://doi.org/10.1107/S1600536809046108.
[20]
R. Wanke, M. F. C. Guedes da Silva, S. Lancianesi, T. F. S. Silva, L. M. D. R. S.
Martins, C. P and A. J. L. Pombeiro, Inorg. Chem., 2010, 49 7941–7952, DOI:
10.1021/ic100966u.
[21]
G. Lyubartseva, S. Parkin and U. P. Mallik, Acta Cryst. (2011). E67, m1656-
m1657, DOI: 10.1107/S1600536811045144.
[22]
S. Liang, S. Chattopadhyay, J. L. Petersen, V. G. Young, M. P. Jensen,
Polyhedron 2013; 50:75–81, DOI: 10.1016/j.poly.2012.10.034.
[23]
10.1021/ic0112645.
[24] A. Michaud, F.-G. Fontaine, D. Zargarian, Acta Crystallogr. E61 (2005) m784-
m786, https://doi.org/10.1107/S1600536805009451.
D. L. Reger, A. L. Little, M. D. Smith, Inorg. Chem. 41 (2002) 4453-4460, DOI:
22

[25]
T. O. Denisova, G. G. Aleksandrov, O. P. Fialkovskii, S. E. Nefedov, Russ. J.
Inorg. Chem. 2003, 48, 1476.
[26]
S. Kannan, G. Venkatachalam, H.-J. Lee, B. K. Min, W. Kim, E. Koo, Y. R. Do,
S. Yoon, Polyhedron, 2011, 30, 340-346, DOI: 10.1016/j.poly.2010.10.019.
[27]
10.1002/anie.199002351.
[28] S. Song, T. Xiao, T. Liang, F. Wang, C. Redshaw, W.-H.Sun, Catal. Sci. Technol.
1 (2011) 69-75, DOI: 10.1039/C0CY00002G.
[29] X. Tang, Y. Cui, W.-H. Sun, Z. Miao, S.Yan, Polym. Int. 53 (2004) 2155-2161,
DOI: 10.1002/pi.1646.
[30] W.-H. Sun, W. Zhang, T. Gao, X. Tang, L. Chen, Y. Li, X. Jin, J. Organomet.
Chem. 689 (2004) 917-929, DOI: 10.1016/j.jorganchem.2003.12.022.
W. Keim, Angew Chem. Int. Ed. 29 (1990) 235-244, DOI:
[31]
X. Tang, D. Zhang, S. Jie, W.-H. Sun, J. Chen, J. Organomet. Chem. 690 (2005)
3918-3928, DOI: 10.1016/j.jorganchem.2005.05.026.
[32]
S. Al-Benna, M. J. Sarsfield, M. Thornton-Pett, D. L. Ormsby, P. J. Maddox, P.
Bres, M. Bochmann, J. Chem. Soc., Dalton Trans. (2000) 4247-4257, DOI:
10.1039/B006329K.
[33]
Froöhlich,
10.1016/j.jorganchem.2006.06.028
W.-H. Sun, S. Zhang, S. Jie, W. Zhang, Y. Li, H. Ma, J. Chen, K. Wedeking, R.
J.
Organomet.
Chem.
691
(2006)
4196-4203,
DOI:
[34]
J. C. Jenkins, M. Brookhart, Organometallics 22 (2003) 250-256, DOI:
10.1021/om020648f.
[35]
H. Liu, F. Wang, L. Liu, B. Dong, H. Zhang, C. Bai, Y. Hu, X. Zhang, Inorg.
Chim. Acta, 421 (2014) 284-291, DOI: 10.1016/j.ica.2014.06.010.
23

Fig. 1. Molecular structure of 21•2CH3CN.
olygomers,
R1 = H, Me
R2=H, tBu, Br
Et2AlCl or Et3Al2Cl3
24

Highlights
•
A series of heteroscorpionate dibromonickel (II) complexes have been synthesized and
characterized.
•
•
Their behavior as ethylene oligomerization catalysts was preliminary explored.
The addition of PPh3 has a significant influence on the selectivity.
25