Facile Hydrolysis of Nickel(II) Complexes with N-Heterocyclic Carbene Ligands

Article abstract of DOI:10.1021/acs.organomet.5b00856

Metal complexes with N-heterocyclic carbene ligands (NHC) are ubiquitously used in catalysis, where the stability of the metal-ligand framework is a key issue. Our study shows that Ni-NHC complexes may undergo facile decomposition due to the presence of water in organic solvents (hydrolysis). The ability to hydrolyze Ni(NHC)₂X₂ complexes decreases in the order of NHC = 1,2,4-triazolium > benzimidazolium ≈ imidazolium. Depending on the ligand and substituents, the half reaction time of the complex decomposition may change from several minutes to hours. The nature of the halogen is also an important factor, and the ability for decomposition of the studied complexes decreases in the order of Cl > Br > I. NMR and MS monitoring revealed that Ni-NHC complexes in the presence of water undergo hydrolysis with Ni-C_carbene bond cleavage, affording the corresponding N,N′-dialkylated azolium salts and nickel(II) hydroxide. These findings are of great importance for designing efficient and recyclable catalytic systems, because trace water is a common contaminant in routine synthetic applications.

Full text of DOI:10.1021/acs.organomet.5b00856

Article
pubs.acs.org/Organometallics
Facile Hydrolysis of Nickel(II) Complexes with N‑Heterocyclic
Carbene Ligands
Alexander V. Astakhov,† Oleg V. Khazipov,† Evgeniya S. Degtyareva,‡ Victor N. Khrustalev,§
Victor M. Chernyshev,† and Valentine P. Ananikov*,†,‡
†Platov South-Russian State Polytechnic University (NPI), Prosveschenya 132, Novocherkassk 346428, Russia
‡Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, Moscow 119991, Russia
§A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str., 28, Moscow 119991, Russia
S
* Supporting Information
ABSTRACT: Metal complexes with N-heterocyclic carbene
ligands (NHC) are ubiquitously used in catalysis, where the
stability of the metal−ligand framework is a key issue. Our study
shows that Ni-NHC complexes may undergo facile decom-
position due to the presence of water in organic solvents
(hydrolysis). The ability to hydrolyze Ni(NHC)2X2 complexes
decreases in the order of NHC = 1,2,4-triazolium >
benzimidazolium ≈ imidazolium. Depending on the ligand and
substituents, the half reaction time of the complex decomposition
may change from several minutes to hours. The nature of the
halogen is also an important factor, and the ability for
decomposition of the studied complexes decreases in the order of Cl > Br > I. NMR and MS monitoring revealed that Ni-
NHC complexes in the presence of water undergo hydrolysis with Ni−Ccarbene bond cleavage, affording the corresponding N,N′-
dialkylated azolium salts and nickel(II) hydroxide. These findings are of great importance for designing efficient and recyclable
catalytic systems, because trace water is a common contaminant in routine synthetic applications.
Over the past few years, a growing number of environ-
mentally friendly synthetic methodologies propose water or
aqueous organic solvents for the implementation of metal-
catalyzed organic reactions.7 In this regard, hydrolytic stability
becomes an essential requirement for organometallic catalysts.
It is commonly accepted that the majority of metal complexes
with NHC ligands are highly stable and quite resistant to
hydrolysis, which is an important advantage of NHC ligands
over phosphine ligands for metal catalysts in aqueous media.7e,8
However, the question of the hydrolytic stability of Ni(II)-
NHC complexes has not been considered in detail. When
reproducing a number of procedures published in the literature
for the preparation of Ni(II) complexes with NHC ligands
generated from N,N′-dialkyl-1,2,4-triazolium salts, we discov-
ered that the yields of the target products highly depended on
the degree of dryness of the solvents and reagents. Moreover, in
many cases, we were unable to obtain the target products when
isolating the Ni(II) triazolium NHC complexes by dilution of
reaction mixtures with water, as can be carried out in the
synthesis of Ni(II) complexes with imidazolium and
benzimidazolium NHCs.9 Thus, we were puzzled by the
problem of the hydrolytic stability of Ni(II) complexes with
NHC ligands.
INTRODUCTION
■
Ni-catalyzed reactions have underwent outstanding growth in
recent years and have had a paramount impact on the
development of organic synthesis.1−6 In many cases, Ni-
catalyzed transformations have achieved high performance and
demonstrated efficient practical applications in industry and
fine organic synthesis. Moreover, in several cases, Ni was an
inexpensive replacement for demanding and expensive catalysts.
Ni complexes have shown unique reactivity and facilitated the
development of novel catalytic transformations. Ni-mediated
cross-coupling reactions, especially those involving alkyl halides,
and atom-economic addition reactions are parts of an
established toolbox of contemporary organic synthesis.1−4
Excellent recent developments have been made in C−H
bond functionalization reactions,5a carbonyl reduction to
alcohols,5b and the synthesis of biologically active heterocyclic
compounds.5c Particularly useful are nickel complexes with N-
heterocyclic carbene ligands (NHC ligands), which are easy to
prepare and are now widely used for C−C bond forma-
tion.1,3,4b,5a,d Ni-NHC complexes have also mediated regiose-
lective reductive coupling6 and stereospecific alkyl−alkyl cross-
coupling reactions, employing an enantioselective nickel
catalyst.4b Ni-NHC catalysts have been successfully applied to
reduce carbon dioxide over water under electrocatalytic
conditions.2d
Received: October 12, 2015
© XXXX American Chemical Society
A
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In this work, we investigate the hydrolytic stability of Ni(II)
complexes with NHC ligands generated from N,N′-dialkylated
salts of 1,2,4-triazole, benzimidazole, and imidazole, three
classes of heterocyclic systems used for the preparation of metal
NHC catalysts.
of NaH in THF, with the pyridine complex of NiCl2 (Scheme
2, Method C). The yields of compounds 4−6 decreased
significantly when the solvents or reagents were insufficiently
dried. Furthermore, we were unable to obtain imidazolium
complexes 6 containing Cl− or Br− as ligands by fusion of the
corresponding N,N-dialkylimidazolium chlorides or bromides
with nickel acetate. In these cases, only starting compounds
were isolated from the reaction mixtures. However, reaction of
the same reagents in the presence of I− anions resulted in the
successful formation of NHC complexes containing iodide
ligands. Thus, melting 1-butyl-3-methyl-1H-imidazol-3-ium
chloride, nickel(II) acetate, and an excess of tetrabutylammo-
nium iodide afforded complex 6b in 55% yield. These results
allowed us to assume that Ni(II) imidazolium carbene
complexes with iodine ligands are more thermodynamically
stable than analogous complexes with chlorine or bromine
ligands. Possibly, in the reactions of imidazolium salts with
nickel acetate, the equilibrium is shifted to the right in the case
of complexes with iodine ligands and to the left in the case of
complexes with chlorine or bromine ligands (Scheme S1 in the
Supporting Information).
RESULTS AND DISCUSSION
Synthesis of the Complexes. An overview of the ligand
precursors used in this study is shown in Table 1. The 1,2,4-
■
Table 1. Overview of the Ligand Precursors Used in This
Study
R
R′
X
R
R′
X
1a
1b
1c
1d
1e
Me
Bu
Bn
Bu
Bn
Me
Bu
Me
Bn
Bn
I
2a
2b
2c
2d
3a
3b
Me
Bu
Et
I
All of the obtained complexes were fully characterized by 1H
and 13C NMR and elemental analysis. According to the spectral
data, the complexes were obtained in the form of trans isomers.
Similar to what was previously observed for trans-NHC
complexes with unsymmetrical ligands,9b,10,11 two sets of
NMR signals were obtained for all of the complexes, except
for 5d and 6a due to syn/anti isomerization. Specific shifts in
the 13C NMR resonances at δ 171−189 ppm of metal-bonded
C atoms were observed for all of these compounds.
Br
I
Me
Bu
Bu
Me
Bu
I
Bn
Bu
Br
Br
I
Br
CI
Me
Me
CI
triazolium and (benz)imidazolium salts were prepared by the
direct alkylation of a number of N-substituted 1,2,4-triazoles,
imidazoles, and benzimidazoles. These quaternization reactions
are commonly performed in refluxing acetone or acetonitrile.
The salts were obtained in good yields as white to yellowish
solids, and most of them were hygroscopic. These carbene
The structures of complexes 4e and 5c,d were confirmed by
single-crystal X-ray diffraction analyses (Figures 1−3).
In the crystal structure, the molecule of 4e is located in a
special position with C2h symmetry and is consequently
disordered over two sites. Unlike the case for 4e, the molecules
of 5c,d in the crystal lie on an inversion center. In all
compounds, the coordination geometry around the nickel(II)
center is nearly perfectly square planar, with the coordination of
two NHC ligands and two halogenides in trans positions. Due
to the virtual symmetry, the bond angles at the Ni atom in 4e
are strictly equal to 90°, whereas they are very close to this
value in 5c,d. The Ni−Hal and Ni−C bond distances are within
the range reported for other nickel NHC complexes, but those
of Ni−Ccarbene for 5c,d are expectedly shorter than that found in
4e. The triazole (for 4e) or benzimidazole (for 5c,d) rings are
oriented nearly perpendicular to the coordination plane of the
Ni atom with dihedral angles of 71.6(6)° (in the case of 4e)
and 76.79(5) and 82.42(5)° (in the case of 5c,d), which is a
1
precursors were characterized by H and 13C NMR spectros-
copy and high-resolution mass spectrometry (HRMS).
Nickel complexes 4a−e with 1,2,4-triazole carbenes were
synthesized by heating triazolium salts 1a−e with anhydrous
NiCl2 in dry acetonitrile (Scheme 1).10 The highest yields (65−
75%) were observed for the well-crystallized iodine-containing
complexes 4a,c, while the yields of highly soluble chlorine- and
bromine-containing complexes were in the range of 39−58%.
Complexes with benzimidazole (5a−d) and imidazole ligands
(6a,b) were prepared by the fusion of salts 2a−d and 3a,b with
anhydrous nickel(II) acetate in molten tetrabutylammonium
bromide or iodide at 130−160 °C under vacuum, according to
the known procedure (Scheme 2, Methods A,B).9 Alternatively,
complexes 5b,d were obtained by the reaction of NHC species,
generated from the corresponding azolium salts in the presence
Scheme 1. Synthesis of Compounds 4a−e
B
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Scheme 2. Synthesis of Compounds 5a−d and 6a,b
Figure 1. Molecular structure of the solvate of compound 4e with 1,2-
dichloroethane. Thermal ellipsoids are shown at the 50% probability
level. Dashed lines indicate the alternative positions of the disordered
fragments. Selected bond lengths (Å) and angles (deg): Ni1−Cl1
2.1922(17), Ni1−C2 1.919(8), N1−C2 1.349(7); Cl1−Ni1−C2 90.0,
N1−C2−N1B 103.1(7).
Figure 2. Molecular structure of compound 5c. Thermal ellipsoids are
shown at the 50% probability level. Selected bond lengths (Å) and
angles (deg): Ni1−Br1 2.3082(3), Ni1−C2 1.899(2), N1−C2
1.355(3), C2−N3 1.358(3); Br1−Ni1−C2 89.57(7), N1−C2−N3
106.16(19).
characteristic feature of carbene complexes that relieves steric
strain.
For all NHC ligands in 4e and 5c,d, the N-substituent
wingtips dangle anti to each other. All molecules in the crystals
are arranged at van der Waals distances.
Benzimidazolium and imidazolium complexes of Ni(II) also
underwent hydrolysis (Scheme 3); however, their hydrolytic
resistance is appreciably higher. For example, the starting
complexes were isolated in 12−30% yields in addition to the
formed proligands 2a,b,d after heating complexes 5a,b,d at 70
°C in 90% v/v aqueous acetonitrile for 24 h (Table 2). The
hydrolytic resistance of complexes 6c,d with bulky substituted
imidazolium ligands (Chart 1) is even higher. For these
complexes no decomposition was observed in aqueous THF at
room temperature within 24 h, which is consistent with the
published data for compound 6d.11b Heating of these
compounds at 70 °C in 90% v/v aqueous THF (10% water
and 90% THF) for 24 h initiated slow hydrolysis (compounds
6c,d are insoluble in acetonitrile).
Stability of Ni-NHC Complexes in the Presence of
Water. We established that Ni(II) complexes with triazolium
carbenes are unstable in the presence of water (aqueous
acetonitrile, THF, ethanol, acetone) and decompose even at
room temperature. Solutions of compounds 4a−e in aqueous
acetonitrile discolored almost completely within a few minutes
after heating at 70 °C. Figure 4 shows the influence of water
addition to the solution of compound 4b in acetonitrile. A
bluish green nickel(II) hydroxide, the structure of which was
confirmed by XRF and XRD analyses, precipitated from the
solutions. Proligands 1a−e were isolated in high yields (Table
2) from these solutions after precipitation of nickel hydroxide
1
(the structures were confirmed by H and 13C NMR and
We performed kinetic experiments to estimate the hydrolytic
ability of complexes 4−6 in aqueous acetonitrile. The progress
HRMS experiments). Therefore, hydrolysis of these Ni(II)-
NHC complexes readily took place according to the reaction
shown in Scheme 3.
1
of the reactions was monitored by NMR H spectroscopy (see
Figure 5). The kinetics of the hydrolytic reactions were
C
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Table 2. Decomposition of the Ni-NHC Complexes in the
Presence of Water
complex decomposed
proligand formed
b
a
complex
t, h
(complex remaining),
%
(proligand isolated), %
4a
4b
4c
4d
4e
5a
5b
5c
5d
5d
6a
6b
10
3
99 (trace)
99 (trace)
99 (trace)
99 (trace)
99 (trace)
99 (84)
99 (91)
99 (88)
99 (79)
99 (81)
70 (61)
72 (63)
99 (83)
88 (67)
99 (82)
99 (88)
10
3
0.5
24
24
24
24
60
48
48
c
70 (30)
c
72 (28)
99 (trace)
c
88 (12)
99 (trace)
99 (trace)
99 (trace)
d
99 (86)
a
The amount of decomposed Ni-NHC complex as determined by
NMR (the amount of remaining complex is shown in parentheses).
b
The amount of free proligand formed after hydrolysis of the Ni-NHC
Figure 3. Molecular structure of compound 5d. Thermal ellipsoids are
shown at the 50% probability level. Selected bond lengths (Å) and
angles (deg): Ni1−Br1 2.3005(4), Ni1−C2 1.903(3), N1−C2
1.354(4), C2−N3 1.359(3); Br1−Ni1−C2 89.08(8), N1−C2−N3
105.9(2).
complex (the isolated yield of the proligand is given in parentheses).
Isolated yield. Yield of 3-butyl-1-methyl-1H-imidazol-3-ium iodide
(3c).
c
d
Scheme 3. Hydrolysis of Ni(II)-NHC Complexes
Chart 1. Structures of Ni(II)-NHC Complexes 6c,d
Figure 4. Photos of solutions of complex 4b (1.3 × 10−2 M) in dry
acetonitrile (a), in 90% v/v aqueous acetonitrile (10% water and 90%
acetonitrile) after 10 min at 25 °C (b), and in 90% v/v aqueous
acetonitrile after 10 min at 70 °C (c). Metal complex decomposition
and precipitation of nickel hydroxide readily took place.
monitored by following the signals of the α protons of N-alkyl
groups in the starting complexes 4−6 (or methyl groups in
compound 6c) and the proligands 1−3 formed during
hydrolysis. Due to the large excess of water in the reaction
mixtures, all of the studied reactions were first order with
respect to the concentration of the complex. Pseudo-first-order
rate constants (k), half reaction times (t50), and times for 99%
conversion (t99) of the Ni(II)-NHC complexes are presented in
Table 3.
The kinetic data obtained show that the hydrolytic resistance
of benzimidazolium and imidazolium complexes 5 and 6 is
sufficiently higher than that of triazolium complexes 4. It is also
important to mention that the nature of the coordinated
halogen has an appreciable effect on the hydrolytic stability,
which increases in the order Cl < Br < I. For example, the rate
constant for the hydrolysis of compound 4e (X = Cl) is ∼30
times higher than that of 4a,c (X = I). The hydrolysis of
bromide complexes is several times faster than that of
analogous iodide complexes. The hydrolytic stability of
imidazole complexes with N-aryl-substituted ligands 6c,d is
sufficiently higher than that with the N-alkyl-substituted
complexes 6a,b. The reason for this higher stability is unclear
but is likely due to a combination of steric and electronic
factors.
It should be noted that hydrolysis with cleavage of the
metal−Ccarbene bond is considered an atypical reaction for the
majority of NHC metal complexes.1,7e,8,10−12 An analogous
reaction was described for Ag(I)-NHC complexes, for which
the metal−carbon bond energy is relatively small.13 However,
to the best of our knowledge, such a hydrolysis reaction of
Ni(II)-NHC complexes has not been described in the
literature.
CONCLUSIONS
■
To summarize, the ability of Ni(II) complexes with NHC
ligands to hydrolyze under mild conditions with Ni−Ccarbene
bond cleavage was demonstrated for the first time. The
D
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the catalysts, where decomposition during the reaction and
workup is a critical factor.
EXPERIMENTAL SECTION
■
General Information. Melting points were determined in open
capillary tubes in a Thiele apparatus and are uncorrected. H and 13C
1
NMR spectra were recorded on a Bruker DRX 500 instrument at 500
and 125 MHz, respectively, in DMSO-d6, CD3CN, or CDCl3 and
using TMS as an internal standard. High-resolution mass spectra
(HRMS) were obtained on a TOF MS instrument using electrospray
ionization (ESI) in positive ion mode (interface capillary voltage 4500
V). Powder XRD measurements were taken on an ARL X’TRA
instrument using monochromatic Cu Kα radiation as the incident
beam, operating at 40 kV/40 mA. XRD diffraction patterns were
obtained by continuous scanning in a 2θ range of 15−80° with a 2θ
step size of 0.01° and a scan step time of 1 s. Elemental analyses were
performed using a PerkinElmer 2400 elemental analyzer.
1-Butyl-1,2,4-triazole, 1-benzyl-1,2,4-triazole, 1-methylbenzimida-
zole, 1-butylbenzimidazole, and compounds 6c,d were obtained by
known methods.14,15
General Procedure for the Preparation of 1,4-Dialkyl-1,2,4-
triazolium Halides 1a−e. A mixture of 1-substituted 1,2,4-triazole
(0.01 mol), alkyl halide (0.02 mol), and acetonitrile (15 mL) was
heated under reflux for 36 h (5 h in case of MeI or BnBr); the volatiles
were then removed under reduced pressure, and the crude product
was washed with anhydrous diethyl ether (10 mL) or recrystallized
and dried in vacuo.
1
1,4-Dimethyl-4H-1,2,4-triazol-1-ium Iodide (1a). Yield: 1.664 g
(74%) of colorless hygroscopic crystals. Mp: 121−123 °C (lit. mp
121−123 °C).16a 1H NMR (CD3CN, 500 MHz): δ 3.98 (s, 3H, CH3),
4.10 (s, 3H, CH3), 8.78 (s, 1H, 3-H), 9.88 (s, 1H, 5-H). 13C{1H}
NMR (CD3CN, 125 MHz): δ 34.5, 39.1, 143.0, 145.0. HRMS (ESI):
Figure 5. Time-dependent H NMR spectral changes of the reaction
mixture during hydrolysis of 4b in CD3CN diluted with D2O (10% v/
v) at 70 °C. The CH signals of 1b marked by asterisks disappear
gradually due to a known process of H/D exchange.
+
calcd for C4H8N3 [M − I−]+ 98.0713, found 98.0713.
Table 3. Pseudo-First-Order Rate Constants (k), Half-
Reaction Times (t50), and Times for 99% Conversion (t99) of
Ni(II)-NHC Complexes in 90% v/v Aqueous Acetonitrile at
70 1 °C
1,4-Dibutyl-4H-1,2,4-triazol-1-ium Bromide (1b). Yield: 1.919 g
(73%) of yellowish hygroscopic crystals. Mp: 63−65 °C (oil).16b 1H
NMR (CDCl3, 500 MHz): δ 0.97−1.00 (m, 6H, 2CH3), 1.37−1.48
(m, 4H, 2CH2), 1.97−2.06 (m, 4H, 2CH2), 4.54 (t, J = 7.5 Hz, 2H,
CH2), 4.62 (t, J = 7.2 Hz, 2H, CH2), 9.50 (s, 1H, CH), 11.62 (s, 1H,
complex
k, 103 min−1
t50
t99
1
CH). H NMR (CD3CN, 500 MHz): δ 0.95−0.98 (m, 6H, 2CH3),
4a
4b
4c
4d
4e
5a
5b
5c
5d
6a
6b
11.2 0.9
48.1 1.0
1 h
6 h 50 min
1 h 40 min
9 h
1.36−1.43 (m, 4H, 2CH2), 1.91−1.98 (m, 4H, 2CH2), 4.39 (t, J = 7.4
Hz, 2H, CH2), 4.45 (t, J = 7.2 Hz, 2H, CH2), 9.08 (s, 1H, CH), 10.83
(s, 1H, CH). 13C{1H} NMR (CDCl3, 125 MHz): δ 13.3, 13.4, 19.3,
30.7, 32.0, 48.4, 52.5, 142.5, 144.5 (2 signals are overlapped). 13C{1H}
NMR (CD3CN, 125 MHz): δ 12.70, 12.71, 18.98, 19.00, 30.3, 31.2,
14 min
8.5 0.7
1 h 20 min
6 min
122.1 21.5
271.3 41.9
0.78 0.07
0.81 0.08
3.49 0.23
1.44 0.11
3.29 0.08
1.94 0.01
0.27 0.03
35 min
3 min
20 min
+
47.8, 52.0, 142.4, 144.3. HRMS (ESI): calcd for C10H20N3 [M −
14 h 45 min
14 h 20 min
3 h 20 min
8 h
98 h
Br−]+ 182.1652, found 182.1655.
95 h
1-Benzyl-4-methyl-4H-1,2,4-triazol-1-ium Iodide (1c). Yield: 2.078
g (69%) of colorless hygroscopic crystals. Mp: 123−125 °C (lit. mp
122−124 °C).16a 1H NMR (CDCl3, 500 MHz): δ 4.21 (s, 3H, CH3),
5.69 (s, 2H, CH2), 7.41−7.42 (m, 3H, Ph), 7.58−7.59 (m, 2H, Ph),
8.86 (s, 1H, CH), 11.20 (s, 1H, CH). 1H NMR (CD3CN, 500 MHz):
δ 3.96 (s, 3H, CH3), 5.65 (s, 2H, CH2), 7.45−7.46 (m, 3H, Ph), 7.53−
7.55 (m, 2H, Ph), 8.77 (s, 1H, CH), 10.06 (s, 1H, CH). 13C{1H}
NMR (CDCl3, 125 MHz): δ 35.8, 56.6, 129.4, 129.6, 129.8, 131.4,
143.1, 144.6. 13C{1H} NMR (CD3CN, 125 MHz): δ 34.6, 55.6, 129.1,
129.3, 132.5, 142.7, 145.4 (2 signals are overlapped). HRMS (ESI):
22 h
53 h
3 h 30 min
6 h
23 h 20 min
39 h 30 min
288 h 30 min
a
6c
43 h
a
The experiment was performed in 90% v/v aqueous THF (10% water
and 90% THF), since the complex was insoluble in acetonitrile.
+
calcd for C10H12N3 [M − I−]+ 174.1026, found 174.1030.
hydrolytic ability depends on the nature of the NHC ligand and
is enhanced with an increase in the π deficiency of heterocyclic
ligands: NHC = 1,2,4-triazolium > benzimidazolium ≈
imidazolium. Furthermore, the hydrolytic ability is influenced
by the nature of the coordinated halogen: Cl > Br > I.
The stability of Ni(II)-NHC complexes and their ability to
hydrolyze should be kept in mind for the synthesis of these
complexes as well as their applications in catalytic reactions.
Decomposition of Ni-NHC complexes due to the presence of
water may affect the activity and selectivity of catalytic
reactions. The key issue concerns the recovery and reuse of
4-Benzyl-1-butyl-4H-1,2,4-triazol-1-ium Bromide (1d). Yield:
2.310 g (78%) of colorless hygroscopic crystals. Mp: 125−127 °C.
1H and 13C{1H} NMR spectra (CDCl3, 500 and 125 MHz,
correspondingly) are analogous to those published in the literature.16c
1H NMR (CD3CN, 500 MHz): δ 0.93 (t, J = 7.4 Hz, 3H, CH3), 1.31−
1.39 (m, 2H, CH2), 1.86−1.92 (m, 2H, CH2), 4.36 (t, J = 7.2 Hz, 2H,
CH2), 5.50 (s, 2H, CH2Ph), 7.46−7.52 (m, 5H, Ph), 8.79 (s, 1H, CH),
9.81 (s, 1H, CH). 13C{1H} NMR (CD3CN, 125 MHz): δ 12.7, 19.0,
30.2, 51.4, 52.3, 129.2, 129.4, 129.5, 132.6, 144.1 (2 signals are
overlapped). HRMS (ESI): calcd for C13H18N3+ [M − Br−]+ 216.1495,
found 216.1498.
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1,4-Dibenzyl-4H-1,2,4-triazol-1-ium Chloride (1e). Yield: 2.373 g
(83%) of colorless hygroscopic crystals. Mp: 178−181 °C (lit. mp
178−181 °C).16a 1H NMR (CDCl3, 500 MHz): δ 5.63 (s, 2H, CH2),
5.79 (s, 2H, CH2), 7.30−7.33 (m, 6H, Ph), 7.49−7.51 (m, 2H, Ph),
overlapped). HRMS (ESI): calcd for C18H21N2+ [M − Br−]+ 265.1699,
found 265.1700.
1,3-Dibutyl-1H-benzo[d]imidazol-3-ium Bromide (2d). Yield:
2.680 g (86%) of colorless crystals. Mp: 144−145 °C (lit. mp 140−
142 °C).16g 1H NMR (CDCl3, 500 MHz): δ 1.00 (t, J = 7.4 Hz, 6H,
2CH3), 1.44−1.51 (m, 4H, 2CH2), 2.03−2.09 (m, 4H, 2CH2), 4.65 (t,
J = 7.4 Hz, 4H, 2CH2), 7.66−7.69 (m, 2H, Ar), 7.72−7.74 (m, 2H,
Ar), 11.54 (s, 1H, NCH). 1H NMR (CD3CN, 500 MHz): δ 0.97−1.00
(m, 6H, 2CH3), 1.40−1.48 (m, 4H, 2CH2), 1.98−2.04 (m, 4H,
2CH2), 4.54−4.57 (m, 4H, 2CH2), 7.68−7.70 (m, 2H, Ar), 7.94−7.96
(m, 2H, Ar), 10.35 (s, 1H, NCH). 1H NMR (DMSO-d6, 500 MHz): δ
0.94 (t, J = 7.4 Hz, 6H, 2CH3), 1.32−1.40 (m, 4H, 2CH2), 1.89−1.95
(m, 4H, 2CH2), 4.52−4.55 (m, 4H, 2CH2), 7.70−7.72 (m, 2H, Ar),
8.12−8.14 (m, 2H, Ar), 10.00 (br. s, 1H, NCH). 13C{1H} NMR
(CD3CN, 125 MHz): δ 12.8, 19.3, 30.8, 47.0, 113.5, 126.7, 131.6,
141.8. 13C{1H} NMR (DMSO-d6, 125 MHz): δ 13.9, 19.6, 31.0, 46.9,
1
7.63−7.64 (m, 2H, Ph), 9.32 (s, 1H, CH), 12.20 (s, 1H, CH). H
NMR (CD3CN, 500 MHz): δ 5.49 (s, 2H, CH2), 5.56 (s, 2H, CH2),
1
7.43−7.51 (m, 10H, Ph), 8.78 (s, 1H, CH), 9.96 (s, 1H, CH). H
NMR (DMSO-d6, 500 MHz): δ 5.62 (s, 2H, CH2), 5.68 (s, 2H, CH2),
7.39−7.49 (m, 8H, Ph), 7.56−7.58 (m, 2H, Ph), 9.52 (s, 1H, CH),
10.78 (s, 1H, CH). 13C{1H} NMR (CDCl3, 125 MHz): δ 51.9, 56.1,
129.2, 129.3, 129.4, 129.6, 129.8, 131.9, 132.4, 143.0, 144.2 (2 signals
are overlapped). 13C{1H} NMR (CD3CN, 125 MHz): δ 51.6, 55.8,
129.1, 129.26, 129.27, 129.35, 129.38, 129.6, 132.4, 132.5, 142.2,
144.5. 13C{1H} NMR (DMSO-d6, 125 MHz): δ 51.0, 55.3, 129.3,
129.36, 129.39, 129.5, 133.7, 134.2, 143.4, 145.5 (signals are partially
overlapped). HRMS (ESI): calcd for C16H16N3+ [M − Cl−]+ 250.1339,
found 250.1339.
+
114.2, 127.0, 131.6, 142.6. HRMS (ESI): calcd for C15H23N2 [M −
Br−]+ 231.1856, found 231.1854.
General Procedure for the Preparation of 1,3-Dialkylimida-
zolium and 1,3-Dialkylbenzimidazolium Halides 2a−d and 3a.
A mixture of 1-alkylimidazole or 1-alkylbenzimidazole (0.01 mol), the
appropriate alkyl halide (0.02 mol), and acetone (20 mL) was heated
under reflux for 5 h. Then, volatiles were removed under reduced
pressure, and the residue obtained was washed with diethyl ether (10
mL) and dried under vacuum.
1,3-Dimethyl-1H-imidazol-3-ium Iodide (3a). Yield: 1.880 g
(84%) of yellowish hygroscopic crystals. Mp: 78−80 °C (lit. mp
81−83 °C).16h 1H NMR (CDCl3, 500 MHz): δ 3.50 (s, 6H, 2CH3),
7.15 (s, 2H, 2CH), 9.00 (s, 1H, NCH). 13C{1H} NMR (CDCl3, 500
+
MHz): δ 36.8, 123.4, 136.2. HRMS (ESI): calcd for C5H9N2 [M −
I−]+ 97.0760, found 97.0759.
1-Ethyl-3-methyl-1H-benzo[d]imidazol-3-ium Iodide (2a). Yield:
2.650 g (92%) of colorless crystals. Mp: 191−193 °C (lit. mp 191−
194 °C).16d 1H NMR (CDCl3, 500 MHz): δ 1.79 (t, J = 7.3 Hz, 3H,
CH3), 4.31 (s, 3H, CH3), 4.66 (q, J = 7.3 Hz, 2H, CH2), 7.68−7.70
General Procedure for the Synthesis of Compounds 4a−e. A
mixture of compound 1a−e (8 mmol), 0.520 g (4 mmol) of
anhydrous NiCl2, and 2.024 g (20 mmol) of Et3N in dry acetonitrile
(100 mL) was heated under reflux for 5 h. Then, the solvent and Et3N
were removed under reduced pressure, and the residue obtained was
chromatographed on a silica gel column, with neat CHCl3 as eluent.
Bis(2,4-dimethyl-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)-
1
(m, 2H, Ar), 7.75−7.77 (m, 2H, Ar), 11.05 (s, 1H, NCH). H NMR
(CD3CN, 500 MHz): δ 1.63 (t, J = 7.3 Hz, 3H, CH3), 4.12 (s, 3H,
CH3), 4.56 (q, J = 7.3 Hz, 2H, CH2), 7.70−7.74 (m, 2H, Ar), 7.89−
1
1
7.94 (m, 2H, Ar), 9.60 (s, 1H, NCH). H NMR (DMSO-d6, 500
diiodonickel(II) (4a). Yield: 1.321 g (65%) of red-brown crystals. H
MHz): δ 1.56 (t, J = 7.2 Hz, 3H, CH3), 4.10 (s, 3H, CH3), 4.54 (q, J =
7.2 Hz, 2H, CH2), 7.70−7.72 (m, 2H, Ar), 8.03−8.11 (m, 2H, Ar),
9.77 (br. s, 1H, NCH). 13C{1H} NMR (CD3CN, 125 MHz): δ 13.8,
33.5, 42.6, 113.3, 113.4, 126.8, 126.9, 131.2, 132.3, 141.5. 13C{1H}
NMR (DMSO-d6, 125 MHz): δ 14.7, 33.8, 42.5, 113.96, 114.04, 126.9,
131.2, 132.3, 142.8 (2 signals are overlapped). HRMS (ESI): calcd for
NMR (CDCl3, 500 MHz) (mixture of syn and anti isomers): δ 4.20
and 4.24 (both s, 6H, 2CH3), 4.34 and 4.38 (both s, 6H, 2CH3), 7.76
and 7.77 (both s, 2H, 2CH). 1H NMR (CD3CN, 500 MHz) (mixture
of syn and anti isomers): δ 4.19 and 4.20 (both s, 6H, 2CH3), 4.30 and
4.32 (both s, 6H, 2CH3), 8.04 and 8.05 (both s, 2H, 2CH). 13C{1H}
NMR (CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 35.10,
35.15, 39.74, 39.79, 143.07, 143.09, 179.28, 179.31. Anal. Calcd for
C8H14N6I2Ni: C, 18.96; H, 2.78; N, 16.58. Found: C, 18.72; H, 2.75;
N, 16.76.
+
C10H13N2 [M − I−]+ 161.1073, found 161.1074.
3-Butyl-1-methyl-1H-benzo[d]imidazol-3-ium Iodide (2b). Yield:
2.815 g (89%) of colorless crystals. Mp: 161−162 °C.16e 1H NMR
(CDCl3, 500 MHz): δ 1.00 (t, J = 7.4 Hz, 3H, CH3), 1.45−1.53 (m,
2H, CH2), 2.05−2.11 (m, 2H, CH2), 4.32 (s, 3H, CH3), 4.61 (t, J =
7.4 Hz, 2H, CH2), 7.68−7.71 (m, 2H, Ar), 7.78−7.85 (m, 2H, Ar),
10.90 (s, 1H, NCH). 1H NMR (CD3CN, 500 MHz): δ 0.99 (t, J = 7.4
Hz, 3H, CH3), 1.41−1.49 (m, 2H, CH2), 1.98−2.02 (m, 2H, CH2),
4.12 (s, 3H, CH3), 4.52 (t, J = 7.3 Hz, 2H, CH2), 7.69−7.73 (m, 2H,
Ar), 7.89−7.97 (m, 2H, Ar), 9.64 (s, 1H, NCH). 13C{1H} NMR
(CD3CN, 125 MHz): δ 12.8, 19.3, 30.8, 33.6, 47.0, 113.37, 113.43,
Dibromo[bis(2,4-dibutyl-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)]-
1
nickel(II) (4b). Yield: 0.911 g (39%) of red-brown crystals. H NMR
(CDCl3, 500 MHz) (mixture of syn and anti isomers): δ 1.07−1.09
(m, 12H, 4CH3), 1.56−1.58 (m, 8H, 4CH2), 2.29−2.38 (m, 8H,
1
4CH2), 4.81−5.03 (m, 8H, four CH2), 7.76 (s, 2H, 2CH). H NMR
(CD3CN, 500 MHz) (mixture of syn and anti isomers): δ 1.07−1.09
(m, 12H, 4CH3), 1.54−1.56 (m, 8H, 4CH2), 2.25−2.35 and 2.35−
2.50 (both m, 8H, 4CH2), 4.82−4.84 and 4.99−5.01 (both m, 8H,
4CH2), 8.07 (s, 2H, 2CH). 13C{1H} NMR (CDCl3, 125 MHz)
(mixture of syn and anti isomers): δ 13.7, 13.8, 20.1, 20.2, 31.65, 31.68,
32.25, 32.29, 48.45, 48.53, 52.7, 52.8, 141.65, 141.68, 172.41, 172.44
(signals are partially overlapped). Anal. Calcd for C20H38Br2N6Ni: C,
41.34; H, 6.59; N, 14.46. Found: C, 41.19; H, 6.68; N, 14.59.
Bis(2-benzyl-4-methyl-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)-
+
126.8, 126.9, 131.4, 132.3, 141.7. HRMS (ESI): calcd for C12H17N2
[M − I−]+ 189.1386, found 189.1388.
1-Benzyl-3-butyl-1H-benzo[d]imidazol-3-ium Bromide (2c).
Yield: 2.830 g (82%) of colorless crystals. Mp: 162−164 °C.16f 1H
NMR (CDCl3, 500 MHz): δ 0.99 (t, J = 7.4 Hz, 3H, CH3), 1.44−1.51
(m, 2H, CH2), 2.04−2.10 (m, 2H, CH2), 4.63 (t, J = 7.4 Hz, 2H,
CH2), 5.93 (s, 2H, CH2), 7.31−7.37 (m, 3H, Ar), 7.53−7.74 (m, 6H,
Ar), 11.58 (s, 1H, NCH). 1H NMR (CD3CN, 500 MHz): δ 1.00 (t, J
= 7.4 Hz, 3H, CH3), 1.42−1.49 (m, 2H, CH2), 1.99−2.05 (m, 2H,
CH2), 4.53 (t, J = 7.4 Hz, 2H, CH2), 5.84 (s, 2H, CH2), 7.39−7.45 (m,
3H, Ar), 7.56−7.57 (m, 2H, Ar), 7.64−7.67 (m, 2H, Ar), 7.81−7.82
1
diiodonickel(II) (4c). Yield: 1.979 g (75%) of red-brown crystals. H
NMR (CDCl3, 500 MHz) (mixture of syn and anti isomers): δ 4.20
and 4.24 (both s, 6H, 2CH3), 5.95 and 6.01 (both s, 4H, 2CH2), 7.31−
7.61 (m, 10H, 2Ph), 7.771 and 7.773 (both s, 2H, two CH). 1H NMR
(CD3CN, 500 MHz) (mixture of syn and anti isomers): δ 4.23 and
4.26 (both s, 6H, two CH3), 6.00 and 6.03 (both s, 4H, two CH2),
7.34−7.66 (m, 10H, 2Ph), 8.08 and 8.09 (both s, 2H, 2CH). 13C{1H}
NMR (CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 35.41,
35.44, 56.6, 128.3, 128.4, 128.6, 128.7, 129.2, 129.3, 134.7, 134.8,
143.7, 143.8, 179.9, 180.0 (signals are partially overlapped). Anal.
Calcd for C20H22I2N6Ni: C, 36.46; H, 3.37; N, 12.75. Found: C, 36.63;
H, 3.19; N, 13.00.
1
(m, 1H, Ar), 7.93−7.94 (m, 1H, Ar), 10.38 (s, 1H, NCH). H NMR
(DMSO-d6, 500 MHz): δ 0.95 (t, J = 7.4 Hz, 3H, CH3), 1.34−1.42
(m, 2H, CH2), 1.91−1.97 (m, 2H, CH2), 4.54−4.57 (m, 2H, CH2),
5.82 (s, 2H, CH2), 7.37−7.44 (m, 3H, Ar), 7.54−7.57 (m, 2H, Ar),
7.64−7.70 (m, 2H, Ar), 7.98−8.00 (m, 1H, Ar), 8.13−8.15 (m, 1H,
Ar), 10.12 (br. s, 1H, NCH). 13C{1H} NMR (CD3CN, 125 MHz): δ
12.8, 19.4, 30.6, 47.2, 50.5, 113.7, 113.8, 126.9, 128.5, 129.0, 129.1,
131.4, 131.8, 133.6, 141.9 (2 signals are overlapped). 13C{1H} NMR
(DMSO-d6, 125 MHz): δ 13.9, 19.6, 30.9, 47.1, 50.4, 114.4, 127.1,
127.2, 128.7, 129.2, 129.4, 131.3, 131.8, 134.5, 142.9 (2 signals are
Bis(4-benzyl-2-butyl-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)-
dibromonickel(II) (4d). Yield: 1.146 g (44%) of red-brown crystals. 1H
NMR (CDCl3, 500 MHz) (mixture of syn and anti isomers): δ 0.96
F
DOI: 10.1021/acs.organomet.5b00856
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and 1.10 (both t, J = 7.2 Hz and J = 7.1 Hz, 6H, 2CH3), 1.42−1.49 and
1.57−1.65 (both m, 4H, 2CH2), 2.23−2.29 and 2.31−2.37 (both m,
4H, 2CH2), 4.91 and 5.03 (both t, J = 7.3 Hz and J = 7.3 Hz, 4H,
2CH2), 6.01 and 6.23 (both s, 4H, 2CH2), 7.35−7.58 (m, 12H, 2Ph
14.0, 20.76, 20.78, 30.7, 31.0, 34.6, 34.8, 48.6, 48.7, 109.15, 109.23,
109.60, 109.63, 121.9, 122.0, 135.5, 136.3, 189.0, 189.1 (signals are
partially overlapped). HRMS (ESI): calcd for C24H32IN4Ni+ [M − I−]+
561.1020, found 561.1005. Anal. Calcd for C24H32N4I2Ni: C, 41.83; H,
4.68; N, 8.13. Found: C, 41.88; H, 4.76; N, 8.32.
1
and 2CH). H NMR (CD3CN, 500 MHz) (mixture of syn and anti
isomers): δ 0.95 and 1.10 (both t, J = 7.3 Hz and J = 7.3 Hz, 6H,
2CH3), 1.40−147 and 1.56−1.63 (both m, 4H, 2CH2), 2.20−2.26 and
2.31−2.37 (both m, 4H, 2CH2), 4.91 and 5.03 (both t, J = 7.3 Hz and
J = 7.3 Hz, 4H, 2CH2), 6.04 and 6.24 (both s, 4H, 2CH2), 7.36−7.66
(m, 10H, 2Ph), 7.93 and 7.95 (both s, 2H, 2CH). 13C{1H} NMR
(CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 13.7, 13.8,
20.1, 20.2, 31.7, 31.8, 52.3, 52.4, 52.8, 52.9, 128.8, 128.9, 129.0, 129.2,
129.3, 134.38, 134.41, 141.5, 141.6, 172.8, 172.9 (signals are partially
overlapped). Anal. Calcd for C26H34Br2N6Ni: C, 48.11; H, 5.28; N,
12.95. Found: C, 47.95; H, 5.35; N, 12.85.
Dichlorobis(2,4-dibenzyl-2,4-dihydro-3H-1,2,4-triazol-3-ylidene)-
nickel(II) (4e). Yield: 1.459 g (58%) of orange crystals. 1H NMR
(CDCl3, 500 MHz) (mixture of syn and anti isomers): δ 5.99 and 6.03
(both s, 4H, 2CH2), 6.09 and 6.13 (both s, 4H, 2CH2), 7.31−7.35 (m,
20H, 4Ph), 7.44 and 7.54 (both s, 2H, 2CH). 1H NMR (CD3CN, 500
MHz) (mixture of syn and anti isomers): δ 6.05−6.22 (m, 8H, 4CH2),
7.35−7.56 (m, 20H, 4Ph), 8.02 (br s, 2H, 2CH). 13C{1H} NMR
(CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 52.1, 56.3,
128.2, 128.66, 128.71, 129.2, 134.7, 135.6, 142.0, 170.6 (signals are
partially overlapped). HRMS (ESI): calcd for C32H30ClN6Ni+ [M −
Cl−]+ 591.1578, found 591.1568. Anal. Calcd for C32H30Cl2N6Ni: C,
61.18; H, 4.81; N, 13.38. Found: C, 61.38; H, 4.98; N, 13.49.
General Procedure for the Synthesis of Compounds 5a−d
and 6a,b. Method A. A mixture of compound 2a−d (8 mmol),
anhydrous Ni(OAc)2 (0.708 g, 4 mmol), and tetrabutylammonium
bromide or iodide (4 g) was dried under vacuum at 80 °C for 1 h and
then slowly heated to 130 °C (bromide salts) or 160 °C (iodide salts);
the molten mixture that formed was stirred at this temperature for 5 h
under vacuum. Then, the solid mixture was cooled to 20 °C and
triturated with water (∼30 mL). The insoluble reddish product was
collected by filtration, washed with water, recrystallized from
acetonitrile, and dried under vacuum.
Method B. A mixture of 8 mmol of compound 3a,b, anhydrous
Ni(OAc)2 (0.708 g, 4 mmol), and tetrabutylammonium iodide (12 g)
was dried under vacuum at 80 °C for 1 h and then heated slowly to
160 °C; the molten mixture that formed was stirred at this
temperature for 5 h under vacuum. Then, the solid mixture was
cooled to 20 °C and triturated with water (∼30 mL). The insoluble
reddish product was collected by filtration, washed with water, and
dried under vacuum.
Method C. A mixture of compound 2b,d (4 mmol) and NaH (60%
dispersion in paraffin oil, 0.176 g, 4.4 mmol) in dry THF (30 mL) was
magnetically stirred for 30 min at 25 °C. Then, a solution of
[NiCl2Py2] (0.576 g, 2 mmol) in pyridine (3.0 mL) was added to the
reaction mixture. The mixture was stirred at room temperature for 24
h, and then the solvent was removed under vacuum. The residue
obtained was treated with water (20 mL), and an insoluble reddish
product was collected by filtration, washed with water, recrystallized
from acetonitrile, and dried under vacuum.
Bis(1-benzyl-3-butyl-1,3-dihydro-2H-benzimidazol-2-ylidene)-
dibromonickel(II) (5c). Yield: 1.713 g (57%, Method A) of red-brown
crystals. 1H NMR (CDCl3, 500 MHz) (mixture of syn and anti
isomers): δ 0.87−0.90 and 1.15−1.18 (both m, 6H, 2CH3), 1.39−1.45
and 1.71−1.77 (both m, 4H, 2CH2), 2.32−2.37 and 2.45−2.50 (both
m, 4H, 2CH2), 5.15−5.18 and 5.26−5.28 (both m, 4H, 2CH2), 6.46
and 6.69 (both s, 4H, 2CH2), 6.94−7.68 (m, 18H, Ar). 13C{1H} NMR
(CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 13.7, 14.1,
20.6, 20.9, 31.7, 31.8, 48.4, 52.8, 53.3, 109.7, 109.8, 110.8, 111.0,
122.15, 122.24, 127.7, 127.8, 127.9, 128.0, 128.6, 128.8, 134.7, 135.0,
135.2, 135.3, 135.4, 135.7, 184.4, 184.5 (signals are partially
overlapped). Anal. Calcd for C36H40N4Br2Ni: C, 57.87; H, 5.40; N,
7.50. Found: C, 58.15; H, 5.31; N, 7.36.
Dibromobis(1,3-dibutyl-1,3-dihydro-2H-benzimidazol-2-ylidene)-
nickel(II) (5d). Yield: 1.734 g (64%, Method A), 0.703 g (52%, Method
C) of red-brown crystals. 1H NMR (CDCl3, 500 MHz) (mixture of syn
and anti isomers): δ 1.12 (t, J = 7.4 Hz, 12H, 4CH3), 1.67−1.74 (m,
8H, 4CH2), 2.38−2.44 (m, 8H, 4CH2), 5.29 (t, J = 7.4 Hz, 8H, 4CH2),
7.17−7.19 (m, 4H, Ar), 7.31−7.33 (m, 4H, Ar). 13C{1H} NMR
(CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 14.1, 20.9,
31.7, 48.4, 109.9, 122.0, 135.0, 183.4. HRMS (ESI): calcd for
C30H44BrN4Ni+ [M − Br−]+ 597.2097, found 597.2088. Anal. Calcd
for C30H44N4Br2Ni: C, 53.05; H, 6.53; N, 8.25. Found: C, 53.24; H,
6.42; N, 8.34.
Bis(1,3-dimethyl-1,3-dihydro-2H-imidazol-2-ylidene)diiodonickel-
(II) (6a). Yield: 1.010 g (50%, Method B) of red crystals. The physical
and spectral characteristics of the product obtained are identical with
those described in the literature.17
Bis(1-butyl-3-methyl-1,3-dihydro-2H-imidazol-2-ylidene)-
diiodonickel(II) (6b). Yield: 1.298 g (55%, Method B) of reddish
brown crystals. The physical and spectral characteristics of the product
obtained are identical with those described in the literature.9a
General Procedure for the Hydrolysis of Nickel(II) Com-
plexes 4−6. A mixture of the compound 4−6 (0.1 mmol), water (2
mL), and CH3CN (18 mL) was heated to 70 °C (see Table 2). A
bluish green powder of Ni(OH)2 that precipitated during the synthesis
was filtered out, and the filtrate was evaporated under reduced
pressure to afford a white or yellowish solid of compound 1a−e, 2a−d,
3a or 1-butyl-3-methyl-1H-imidazol-3-ium iodide (3c). The physical
and spectral characteristics of the products obtained are identical with
those described above for 1a−e, 2a−d, and 3a. The characteristics of
compound 3c are identical with those described in the literature.9a
Hydrolysis Kinetics. Kinetic experiments on the hydrolysis of
compounds 4a−e were carried out in NMR tubes. D2O (70 μL) was
added to a solution of compound 4a−e (10.0 mg) in 600 μL of
CD3CN (THF-d8 for 6c). The resulting mixture was shaken and
thermostated at 70
centrifuged, and its H NMR spectrum was recorded.
1 °C. At certain intervals, the mixture was
1
Kinetic experiments on the hydrolysis of compounds 5a−d and 6a,b
were performed in 5 mL screw-top glass vials. A magnetically stirred
solution of the corresponding Ni complex (5 mg) in a mixture of
CH3CN (3 mL) and water (0.35 mL) was thermostated at 70 1 °C
for an appropriate amount of time. Then, the solvent was removed
quickly under reduced pressure, and the solid obtained was dissolved
Bis(1-ethyl-3-methyl-1,3-dihydro-2H-benzimidazol-2-ylidene)-
diiodonickel(II) (5a). Yield: 1.703 g (67%, Method A) of red-brown
crystals. 1H NMR (CDCl3, 500 MHz) (mixture of syn and anti
isomers): δ 1.85−1.88 (m, 6H, 2CH3), 4.49 and 4.50 (both s, 6H,
2CH3), 5.17−5.22 (m, 4H, 2CH2), 7.18−7.22 (m, 4H, Ar), 7.29−7.32
(m, 4H, Ar). The 13C NMR spectrum of 5a could not be obtained due
to low solubility. Anal. Calcd for C20H24N4I2Ni: C, 37.95; H, 3.82; N,
8.85. Found: C, 38.14; H, 3.94; N, 8.74.
Bis(1-butyl-3-methyl-1,3-dihydro-2H-benzimidazol-2-ylidene)-
diiodonickel(II) (5b). Yield: 1.252 g (45%, Method A), 0.317 g (23%,
Method C) of red-brown crystals. 1H NMR (CDCl3, 500 MHz)
(mixture of syn and anti isomers): δ 1.11 and 1.15 (both t, J = 7.3 Hz
and J = 7.3 Hz, 6H, 2CH3), 1.64−1.70 (m, 4H, 2CH2), 2.34−2.41 (m,
4H, 2CH2), 4.51 and 4.52 (both s, 6H, 2CH3), 5.03−5.08 (m, 4H,
2CH2), 7.18−7.19 (m, 4H, Ar), 7.27−7.29 (m, 4H, Ar). 13C{1H}
NMR (CDCl3, 125 MHz) (mixture of syn and anti isomers): δ 13.9,
1
in 600 μL of CDCl3. The solution was centrifuged, and its H NMR
spectrum was recorded.
The relative concentrations of starting complex 4−6 and the
corresponding proligands formed during hydrolysis were determined
from the integral intensities of the signals of α protons of N-alkyl
groups.
X-ray Crystal Structure Determination of 4e and 5c,d. Data
were collected on a Bruker SMART APEX-II CCD diffractometer
(λ(Mo Kα) radiation, graphite monochromator, ω and φ scan mode)
and corrected for absorption using the SADABS program.18 For
details, see the Supporting Information. The structures were solved by
G
DOI: 10.1021/acs.organomet.5b00856
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
direct methods and refined by the full-matrix least-squares technique
on F2 with anisotropic displacement parameters for non-hydrogen
atoms. The crystal of 4e contained a solvate dichloroethane molecule
occupying a special position on the mirror plane. The solvate molecule
was disordered over two sites with equal occupancies. All hydrogen
atoms were placed in calculated positions and refined within the riding
model with fixed isotropic displacement parameters (Uiso(H) =
1.5[Ueq(C)] for the CH3 groups and Uiso(H) = 1.2[Ueq(C)] for the
other groups). All calculations were carried out using the SHELXTL
program.19 Crystallographic data for 4e and 5c,d have been deposited
with the Cambridge Crystallographic Data Center. CCDC 1426180
(4e), CCDC 1426181 (5c), and CCDC 1426182 (5d) contain
supplementary crystallographic data for this paper. These data can be
obtained free of charge from the Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, + 44 1223 336033; e-mail, deposit@
ccdc.cam.ac.uk; web, www.ccdc.cam.ac.uk).
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00856.
NMR spectra for the synthesized compounds and details
of the X-ray structure determinations (PDF)
Crystallographic data for 4e (CIF)
Crystallographic data for 5c (CIF)
Crystallographic data for 5d (CIF)
(10) Dash, C.; Shaikh, M. M.; Butcher, R. J.; Ghosh, P. Dalton Trans.
2010, 39, 2515−2524.
(11) (a) Zhang, D.; Zhou, S.; Li, Zh.; Wang, Q.; Weng, L. Dalton
AUTHOR INFORMATION
Corresponding Author
*E-mail for V.P.A.: val@ioc.ac.ru.
■
́
Trans. 2013, 42, 12020−12030. (b) Hameury, S.; de Fremont, P.;
Breuil, P.-A. R.; Olivier-Bourbigou, H.; Braunstein, P. Organometallics
2015, 34, 2183−2201.
Notes
The authors declare no competing financial interest.
(12) Henrion, M.; Oertel, A. M.; Ritleng, V.; Chetcuti, M. J. Chem.
Commun. 2013, 49, 6424−6426.
ACKNOWLEDGMENTS
(13) Hindi, K. M.; Siciliano, T. J.; Durmus, S.; Panzner, M. J.;
Medvetz, D. A.; Reddy, D. V.; Hogue, L. A.; Hovis, C. E.; Hilliard, J.
K.; Mallet, R. J.; Tessier, C. A.; Cannon, C. L.; Youngs, W. J. J. Med.
Chem. 2008, 51, 1577−1583.
■
This work was financially supported by the Russian Science
Foundation (grant no. 14-23-00078). Technical assistance by
Dr. Chizhov A. O. and Mr. Fakhrutdinov A. N. is gratefully
acknowledged. The authors also thank the Shared Research
Center “Nanotechnologies” of the Platov South-Russian State
Polytechnic University and the Department of Structural
Studies of Zelinsky Institute of Organic Chemistry for analytical
services.
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DOI: 10.1021/acs.organomet.5b00856
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