Conformational Effects of [Ni2(μ-ArS)2] Cores on Their Electrocatalytic Activity

Article abstract of DOI:10.1002/asia.201901037

Two nickel complexes supported by tridentate NS₂ ligands, [Ni₂(κ-N,S,S,S′-N^Ph{CH₂(MeC₆H₂R′)S}₂)₂] (1; R′=3,5-(CF₃)₂C₆H₃) and [Ni₂(κ-N,S,S,S′-N^iBu{CH₂C₆H₄S}₂)₂] (2), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid-state structure of 1 reveals that the [Ni₂(μ-ArS)₂] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF₃COOH at ?1.93 (overpotential of 1.04 V, with i_cat/i_p≈21.8) and ?1.47 V (overpotential of 580 mV, with i_cat/i_p≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni₂(μ-ArS)₂] core, which allows proximity of the two Ni???Ni centers at 2.730(8) ?; thus possibly favoring H⁺ reduction. In contrast, the planar [Ni₂(μ-ArS)₂] core of 2 results in a Ni???Ni distance of 3.364(4) ? and is unstable in the presence of acid.

Full text of DOI:10.1002/asia.201901037

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Conformational effects of [Ni2(ꢀꢀ-SAr)2] cores on their
electrocatalytic activity
Authors: alexander mondragon diaz, Elvis Robles-Marin, Brenda
Angelica Murueta-Cruz, Juan Camilo Aquite, Paulina Raquel
Martínez-Alanis, Marcos Flores-Alamo, Gabriel Aullón, Luis
Norberto Benítez, and Ivan Castillo Perez
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µ
Conformational effects of [Ni2( -SAr)2] cores on their
electrocatalytic activity
Alexander Mondragón-Díaz,*[a] Elvis Robles-Marín,[b] Brenda A. Murueta-Cruz,[a] Juan C. Aquite,[a]
Paulina R. Martínez-Alanis,[c] Marcos Flores-Alamo,[d] Gabriel Aullón,[c] Luis Norberto Benítez,[a] and Ivan
Castillo*[b]
Abstract: Two nickel complexes supported by tridentate NS2 ligands
[Ni2(ꢀ-N,S,S,S’-NPh{CH2(MeC6H2R’)S}2)2] (R’ = 3,5-(CF3)2C6H3) (1)
and [Ni2(ꢀ-N,S,S,S’-NiBu{CH2C6H4S}2)2] (2) were prepared as
bioinspired models of the active site of [NiFe] hydrogenases. The
solid-state structure of 1 reveals that the [Ni2(ꢁ-ArS)2] core is bent,
with the planes of the Ni centers at a hinge angle of 81.3(5)°, while 2
shows a coplanar arrangement between both Ni(II) ions in the dimeric
structure. 1 electrocatalyzes proton reduction from CF3COOH at –
1.93 V (overpotential of 1.04 V with ꢂcat/ꢂp ≈ 21.8) and –1.47 V
of protons and electrons with dihydrogen.[2] [NiFe]-hydrogenase
has interesting structural features in its heterobimetallic active site
that include a {Ni(ꢁ-CysS)2Fe}-butterfly arrangement formed by
the bridging cysteinyl ligands and a distorted square-planar
geometry about the Ni center; this butterfly conformation leads to
Ni···Fe distances from 2.9 to 2.5 Å that can accommodate a
bridging hydride when the active site is reduced.[2f] In such
systems, it has been observed that nickel is a crucial element that
participates in this redox process, as it is believed to be the
primary dihydrogen binding site due to its position at the end of
the H2 transfer channel in the enzyme, and its biochemical activity
is favored by the sulfur rich environment provided by cysteine
residues.[2] Thus, understanding how these sulfur donors tune the
redox potential at the metal center is key for the development of
hydrogenase-inspired metal complexes. Considerable attention
(overpotential of 580 mV with
ꢂcat/ꢂp ≈ . The
5.9) vs Fc+/0
electrochemical behavior of 1 relative to 2 may be related to the bent
[Ni2(ꢁ-ArS)2] core that allows proximity of the two Ni···Ni centers at
2.730(8) Å, possibly favoring H+ reduction. In contrast, the planar
[Ni2(ꢁ-ArS)2] core of 2 results in a Ni···Ni distance of 3.364(4) Å, and
is unstable in the presence of acid.
has been devoted to the development of discrete inorganic
[3],[4]
models with such electronic and structural features,
and
several types of chelating ligands featuring sulfur donor atoms
have been reported. Nonetheless, the spectrum of tridentate NS2
ligands is composed primarily of thioethers and thioamides, likely
due to their ease of preparation.[5] In the case of multidentate thiol-
based scaffolds, those reported to date are generally
characterized by limited steric protection, which leads to
aggregation and high sensitivity towards air oxidation.[6] In this
context, we have explored synthetic routes that lead to
Introduction
Important efforts are currently underway to develop artificial
systems for efficient hydrogen evolution reaction (HER), either by
light- or electric-driven methods.[1] In nature, some bacteria are
provided with extremely efficient metalloenzymes named
hydrogenases known to catalyze the reversible interconversion
thiophenol-based
multidentate
ligands
featuring
bulky
substituents in the ortho-position relative to sulfur, starting from
commercial salicylaldehydes (Scheme 1).[7]
[a]
Dr. A. Mondragón-Díaz, B. Sc. B. A. Murueta-Cruz, B.Sc. J. C.
Aquite, Dr. L. N. Benitez Departamento de Química, Facultad de
Ciencias
In the present work, we evaluate some of the steric and electronic
factors that determine the conformation of [Ni2(ꢁ-ArS)2]-type
complexes with aminodithiophenolate ligands, and its relationship
with the redox properties of the system. The steric effect
evaluated is that of the substituent in the ortho-position of the
thiophenolate ring (R1 in Scheme 1). Furthermore, the electronic
influence evaluated is that exerted by the substituent on the N-
atom of the central amine, by comparing the properties of
aromatic vs aliphatic groups (R3 in Scheme 1). We have thus
developed suitable ligands for the exploration of the properties of
the corresponding earth-abundant metal complexes as hydrogen
evolution electrocatalysts.[8] With these considerations, we herein
report the synthesis and characterization of Ni(II) complexes with
Universidad del Valle
Ciudad Universitaria Meléndez, Calle 13 #100-00
E-mail: mondragon.alexander@correounivalle.edu.co
Prof. Dr. I. Castillo, Dr. E. Robles-Marín
Instituto de Química
Universidad Nacional Autónoma de México
Ciudad Universitaria, México, 04510, México
E-mail: : joseivan@unam.mx
Dr. P. R. Martínez-Alanis, Prof. Dr. G. Aullón
Departament de Química Inorgánica i Orgànica, Institut de Química
Teòrica i Computacional
Universitat de Barcelona
Martí i Franquès 1-11, 08028 Barcelona, Spain
Dr. M. Flores-Alamo
Facultad de Química, División de Estudios de Posgrado
Universidad Nacional Autónoma de México
Ciudad Universitaria, México, 04510, México
[b]
[c]
[d]
Stioc
the novel dianionic (NS2)2- polytopic ligands obtained from Ln
(n = 1 o 2) precursors (Scheme 1), all of which provide geometric
flexibility due to the methylene connectors between the central
amine and the thiophenolate groups.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under https://doi.org/
10.1002/asia.201901037
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N
N
R1
R1
R1
S
O
O
S
R1
R1
S
N
S
N
ii
iii
i
S
N
N
O
O
R2
R2
R3
O
R2
R2
R2
O
OH
Cl
Stioc
a
c
b
Ln
∗
∗
∗
∗
R2 = -CH3 and R3 =
Stioc
=
L1
:
R1
F3C
CF3
∗
R2 = H and R3 =
Stioc
=
H
L2
:
R1
Scheme 2. Synthetic strategy for bis(S-arylthiocarbamate)amine ligand precursors from building group o-formyl-S-arylthiocarbamates: i) NaHB(OAc)3, thf, 6 d,
60oC, ii) SOCl2, CH2Cl2 r.t., 8 h, iii) primary amine (aniline or isobutylamine), K2CO3, NaI, thf, 8 d, 60oC.
R2
R2
R1
R1
N
N
S
Ni
N
S
R3
S
O
O
S
SNa
R2
SNa
R2
R1
R1
S
N
Ni
R1
R1
ii
i
R3
N
N
S
R1
R3
R3
R2
R2
R1
R2
R2
∗
∗
Stioc
∗
Ln
R2 = -CH3 and R3
=
=
R1
1:
2:
F3C
CF3
∗
∗
R2 = H and R3
=
=
H
R1
Scheme 1. Synthesis of Ni(II) complex with (NS2)2- ligands: i) MeONa, thf, 6 d, 65°C; ii) NiCl2·6H2O, r.t., overnight.
Synthesis of complexes
Results and Discussion
Stioc
Preparation of the nickel complexes derived from L1Stioc and L2
namely [Ni2(ꢀ-N,S,S,S’-NPh{CH2(MeC6H2R’)S}2)2] (R’ = 3,5-
,
CF3)2C6H3) (1) and [Ni2(ꢀ-N,S,S,S’-NiBu{CH2C6H4S}2)2] (2),
Synthetic procedures
Stioc
followed the same protocols; in both cases, treatment of Ln
To access (NS2)2- ligands, their preparation involves a Newman-
Kwart thermal rearrangement (NKR) as the key step to obtain o-
formyl-S-arylthiocarbamates from the corresponding O-
arylthiocarbamates using N-methylpyrrolidinone (NMP) as
solvent.[7b] Treatment of the products through the route outlined in
with sodium methoxide (4 equiv.) in tetrahydrofuran (thf) under an
inert atmosphere was required (Scheme 2). Complete
Stioc
deprotection of Ln
was determined by monitoring the
disappearance of the peak arising from the carbamate group at
m/z 72 by Electron Impact Mass Spectrometry (EI MS, Figure
S16). After this time, slow addition of solid NiCl2·6H2O to a thf
suspension of the in situ generated bis(thiophenolate)amines
immediately change the color of the solution from yellow to brown
and dark red, indicating the formation of the corresponding Ni(II)
complexes 1 and 2, respectively (Scheme 2). Removal of sodium
chloride and insoluble byproducts by filtration, followed by
crystallization from saturated CHCl3/CH3CN solutions, afforded
the analytically pure complexes.
Scheme
1 produces the building blocks 2-chloromethyl-S-
arylthiocarbamates c for the subsequent reaction with one equiv.
of aniline or isobutylamine (Scheme 1, see full characterization in
Figures S1-S8),[7] affording the bis(S-aryltiocarbamate) amine
Stioc
Stioc
ligand precursors L1
and L2
in 83% and 81% yields,
respectively (see Figures S9-S20 for spectroscopic data).
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Characterization of 1. Complex 1 was isolated as a black
crystalline material in 45% yield by crystallization from a 9:1
CHCl3/CH3CN mixture. 1 was formulated as a dimeric species
based on Fast Atom Bombardment Mass Spectrometry
measurements (FAB MS, Figure S21), with the molecular ion [M]+
giving rise to a peak at m/z 1692; the assignment was further
confirmed through NMR spectroscopy, and structural
stable for extended periods of time in the solid state and in CHCl3,
CH2Cl2, ethyl acetate and diethyl ether solutions. 3, which was
formulated as C29H28N2NiS2 by combustion analysis, was
obtained in 67% yield and characterized by 1H and 13C❴1H❵ NMR,
IR, FAB MS (Figures S28-S32) and XRD (Figure S33), all this
corresponding to the formation of the monomeric complex [Ni(ꢀ-
N,S,S’-NiBu{CH2C6H4S}2)(C≡NC10H7)] (3) with a 1:1 metal/ligand
stoichiometry.
1
determination by X-ray diffraction (XRD). The H NMR spectrum
and additional characterization allowed to establish the identity of
1 (Figures S22-25). This complex is stable under air and moisture
both in the solid state, and in CH2Cl2, CHCl3, ethyl acetate, or
diethyl ether solutions.
S
N Ni
S
Ni N
S
S
N Ni
i
N
S
S
Characterization of 2. The reaction of in situ generated
aminodithiolate ligand derived from L2Stioc (see FAB MS in Figure
S26) and NiCl2·6H2O afforded the analytically pure red
microcrystalline complex 2 in 52% yield. This complex is an air
stable species that is insoluble in most common organic solvents,
including hot DMF, toluene, or DMSO, so that informative NMR
spectra could not be recorded. The infrared spectroscopic
analysis allowed us to confirm the presence of the ligand through
the characteristic stretches of the organic fragment in the complex,
(such as aromatic C-H stretch 3051 and 3008 cm-1, Figure S27).
Combustion and XRD analysis confirmed that 2 is a dimer of the
form [Ni2(ꢀ-N,S,S,S’-NiBu{CH2C6H4S}2)2]. Additionally, indirect
characterization of 2 by derivatization to a more soluble species
was envisioned. Thus, suspensions of 2 in CH2Cl2 were treated
with 2-naphthylisocyanide, which resulted in the dark green
product 3 (Scheme 3); this new complex is soluble in common
organic solvents except for hexane or toluene, and is also air
3
2
Scheme 3. Reaction of 2 with 2-naphthylisocyanide: i) 2-naphthylisocyanide,
CH2Cl2, r.t., overnight.
Solid-state structures
Slow evaporation of a solution of 1 in CHCl3/CH3CN (9:1) yielded
black single crystals, red crystals of 2 were obtained by slow
cooling of a hot CHCl3 solution (70oC) in a sealed vial, while slow
evaporation of CH2Cl2/MeOH (1:1) solution of complex 3 leads to
formation of dark green microcrystals. All of the above crystals
were suitable for structural elucidation by XRD (Figures 1, S33,
Figure 1. Top: Mercury diagrams of 1 and 2 at the 50 % probability level showing the coordination environments defined by the N and S donors around the Ni(II)
ions; H and minor-occupancy atoms are omitted for clarity; colour code: C, grey; F, lime; S, yellow; N, blue; Ni, green. Bottom: hinge angles of 1 and 2.
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Tables S1 and S2). Both complexes 1 and 2 crystallize in the
monoclinic space group P21/c (Table 1 lists selected bond
distances and angles). In the dimeric structures, each Ni center is
tetracoordinated by the tridentate ligand via the N-atom of the
central amine and the thiophenolate sulfur donors; the
coordination environment of the Ni(II) ions is completed by a
bridging sulfur donor of a second monomeric unit, resulting in the
observed dinuclear structure (Figure 1). For each Ni center in 1
the average S-Ni-Sbridge trans angle is 164.82(5)°, whereas the
corresponding N−Ni−Sbridge angle is 171.31(11)°; for 2 the
corresponding angles are 168.04(3)° and 171.13(5)° respectively.
Thus, the coordination geometry of Ni(II) in compounds 1 and 2
can be described as distorted square planar. Those planes
around the Ni centers in 1, defined by N1, S1, S2, and S4 (N1,
S1, S2, and S1bridge for 2) are joined along one edge by means of
S1 and S2 (S1 and S1bridge for 2, see Table 1 and Figure 1);
therefore, for both complexes each monomeric unit has a terminal
thiophenolate ligand that may be considered electron-rich (S4 and
S3 atoms for 1 and S2 for 2 in Figure 1).[9] Additionally, the two
coordination planes around the Ni centers in 1 define a dihedral
angle (ꢃ) of 81.3(5)° (hinge angle) leading to a Ni···Ni distance of
2.7295(8) Å, comparable with previously reported [Ni2(ꢀ-N,S,S,S’-
NiBu{CH2(MeC6H2R’)S}2)2] (R’ = 3,5-(CF3)2C6H3, 4, with Ni···Ni
distance of 2.702(8) Å, and (ꢃ) = 85.5(4)°).[7c] On the other hand,
in 2 the hinge angle is ꢃ = 180(2)o (Table 1 and Figure 1), resulting
in a coplanar arrangement with considerably longer Ni···Ni
distance of 3.364(4) Å.
nickel ion.[10a] This may stabilize these conformations relative to
the coplanar ones, where such overlap is much less effective,
resulting in no possibility for a cooperative effect of electron
delocalization between the two metal centers. To establish the
factors that determine whether the structure will be bent or
coplanar, the influence of the terminal and bridging ligands on the
Ni···Ni interactions in the bent molecules can be analyzed. Thus,
ligands capable of accepting metal charge transfer on their ꢄ*-
orbitals (ꢄ-acidic ligands) tend to strengthen the Ni···Ni interaction,
while ꢄ-basic ligands tend to weaken it.[10a] In both 1 and 2, the
same type of bridging and terminal donor atoms are present
(except for the N-phenyl or N-isobutyl substituents), but the main
difference is a steric one: the choice of bulky 3,5-(CF3)2C6H3
substituents at the thiophenolate moieties and steric repulsion
between these terminal ligands at the two metal atoms may be
the governing factor for the large degree of bending observed,
highlighting the importance of the substituents in the ortho-
position relative to the sulfur donor to stabilize a particular
conformation.[10]
Optical Spectroscopy
The electronic absorption spectrum of 1 (Figure 2, blue trace) in
CH2Cl2 solution exhibits intense bands at 360 (2.66 x 104 M-1cm-
1) and 443 nm (9.18 x 103 M-1cm-1), assigned as LMCT bands
according to previous reports.[1g],[11],[12] The other bands observed
for 1 were assigned to an intraligand transition at 289 nm
(shoulder, 2.92 x 104 M-1cm-1, L⟶L), and a Sbridge⟶Ni transition
at 533 nm (3.09 x 103 M-1 cm-1). On the other hand, for 2 all
electronic transitions are shifted to higher energies (Figure 2, red
trace). The absorption maxima were observed at 263 nm (3.45 x
104 M-1cm-1) for L⟶L transitions, together with LMCT at 301 nm
(3.90 x 104 M-1cm-1, Sꢅ⟶Ni), 369 nm (1.48 x 104 M-1cm-1,
Sꢄ⟶Ni) and 416 nm (shoulder, 1.05 x 104 M-1 cm-1, Sbridge⟶Ni).
Finally, the monomeric complex 3 featuring a naphthylisocyanide
ligand, [13] displays only the L⟶L transition at 235 nm (6.4 x 104
M-1cm-1), and a Sꢅ ⟶Ni transition at 313 nm (3.90 x 104 M-1cm-1)
without evidence of a Sbridge⟶Ni band, as expected (Figure 2,
green trace).
Table 1. Selected bond distances (Å) and angles (°) for 1 and 2
Bonds
1
Bonds
Ni1···Ni1*
Ni1-S1
2
Ni1···Ni2
Ni1-S1
2.7295(8)
2.2251(1)
2.1803(1)
2.2062(1)
1.997(4)
164.82(5)
171.31(11)
96.63(1)
97.96(1)
90.48(5)
74.80(5)
76.12(4)
3.364(4)
2.2136(6)
2.1697(6)
2.1969(5)
1.9928(2)
168.04(3)
171.13(5)
95.53(5)
96.43(5)
87.54(2)
80.57(2)
99.43(2)
Ni1-S4
Ni1-S2
Ni1-S2
Ni1-S1*
Ni1-N1
Ni1-N1
S1-Ni1-S4
N1-Ni1-S2
N1-Ni1-S1
N1-Ni1-S4
S4-Ni1-S2
S2-Ni1-S1
Ni1-S1-Ni2
S1-Ni1-S2
N1-Ni1-S1*
N1-Ni1-S1
N1-Ni1-S2
S2-Ni1- S1*
S1*-Ni1-S1
Ni1-S1-Ni1*
Structural analysis of these dimers reveals a bent-endo 1 and
planar-anti 2 conformations of the [Ni2(ꢁ-ArS)2] frameworks. In
this context, Aullón and co-workers have reported that in
molecules with a strongly bent (ꢃ < 150o) [L2M(ꢁ-SR)2ML2]
fragment, the shorter Ni···Ni distances observed reflect a high
degree of intermetallic overlap between 3dz2-4pz orbitals of each
Figure 2. UV−vis spectrum of 1 (blue trace), 2 (red trace), and 3 (green trace)
in CH2Cl2 solution ca. 0.04 mM.
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Electrochemical Studies
product Z may occur. In contrast, oxidation of 3 is most likely a
ligand-centered redox process (Figure 3, green trace).[14b, c]
Electrochemical analysis for complexes 1, 2, and 3 in 0.1 M
NBu4PF6/CH2Cl2 was performed under a N2 atmosphere. Cyclic
voltammograms of 1 [1 mM] are characterized by a reversible
Electrocatalytic dihydrogen generation
redox couple attributed to reduction processes of one of the two
The most common method to evaluate the catalytic activity of
artificial hydrogenases is through cyclic voltammetry in the
presence of increasing concentration of a proton source.[15]
Previous studies have evaluated the activity of this type of
catalysts using acids of varying strength: perchloric,[16a]
(II,II)/(II,I)
nickel centers, Ni2
at E1/2 = -1.65 V versus the
ferrocenium/ferrocene couple (Fc+/0) as internal standard (scan
rate 100 mV s-1, ΔEp = 100 mV, see Figure 3, blue trace). This
peak separation is comparable to the maximum separation
observed for the Fc+/0 couple under the same conditions (Figure
S34).[14a]
tetrafluoroboric,[16b]
p-toluenesulfonic,[16c]
acetic,[16d]
and
trifluoroacetic (TFA) acids.[16e] The catalytic activity is thus gauged
by changes in the reduction peak (ꢆcat) in the presence of acids,
with the best catalysts producing a larger increase in current.[15]
Figure 4 shows the CV of 1 after successive additions of TFA.
Noticeably, the catalytic wave does not grow directly at the same
potential as the reversible couple for Ni2(II,II)/(II,I) but is observed at
Ecat/2 = −1.93 V, a value that is displaced cathodically by 280 mV
relative to the reversible couple; this behavior has been observed
in the presence of strong acids.[1g],[17] In addition, at concentrations
greater than 4.0 mM of TFA, a new wave at Ecat = −1.47 V
/2
emerges; this suggests that an intermediate that can be reduced
more easily than 1 may be formed.[1g] A protonated species
proposed as 1-H, from protonation at the electron-rich terminal
sulfur, arising in a CE mechanism (with C corresponding to a
chemical step, in this case protonation, follow by E representing
an electron transfer process) in which the reduction of the
protonated species 1-H occurs at a less cathodic potential than
the direct reduction of 1 (see Figure 9 and DFT studies below).
Although this proposal is tentative until more evidence can be
obtained to support this mechanism, it seems a reasonable
hypothesis to explain the dependence of HER processes on the
nature of the acid. Additionally, following the method of Barton
and Rauchfuss,[17d] overpotential (ꢇ) values for 1 were determined
at 1.04 V (-1.93) and 580 mV (- 1.47 vs. Fc+/0, see Figure 5 for
indication of Ecat/2 and the overpotential).
Figure 3. Cathodic CV of complexes 1 (blue trace), 2 (red trace), and 3 (green
trace) at a scan rate of 100 mV s−1 (1 mM in 0.1 M Bu4NPF6-CH2Cl2, glassy
carbon electrode).
Surprisingly, neither the substituent on the nitrogen atom of the
central amine (compare CVs of 1 with related systems 4),[7c] nor
the conformation of the [Ni2(ꢁ-ArS)2] framework seem to have an
effect on the potentials values for the cathodic processes. Thus,
(II,II)/(II,I)
for the previously reported complex 4,[7c] the Ni2
redox
couple was determined at E1/2 = -1.65 V versus Fc+/0, for 2 the
same process is characterized by a reversible redox couple at E1/2
= -1.67 V (ΔEp = 118 mV, Figure 3, red trace), while an irreversible
wave at -1.75 V is observed for monomeric complex 3 (Figure 3,
green trace). When the scanning direction is reversed, 1 reveals
two reversible redox processes; the first one is assigned to
Ni2(II,II)/(II,III) at E1/2 = 0.32 V vs Fc+/0, (Figure 3 blue trace and Figure
S35), a feature that is analogous to that observed for the iso-
butylamine-based analogue 4, but 150 mV less positive.[7c] The
second redox process, attributed to Ni2(II,III)/(III,III), is observed at E1/2
= 0.91 V (ΔEp = 100 mV, Figure 3, blue trace). In contrast, the
planar 2 revealed irreversible processes at E1a = 0.20, and E2a
=
0.90 V (the anodic CV and inversion potentials allowed us to
assign the reduction of these species, Figures S36 and S37). One
possible explanation for this difference is that in the anodic
(II,II)/(II,III)
couple could be stabilized by Ni(d7)-
Figure 4. CVs of 1 in CH2Cl2 with increasing trifluoroacetic acid [TFA].
Experimental conditions: 1.0 mM 1 with 0.1 M NBu4PF6 collected at scan rate of
0.1 V s-1 with 0.0, 0.1, 0.5, 1.0, 2.0, 4.0, 8.0, 12.0, 20.0 and 30.0 mM (bottom)
TFA concentrations; Fc as internal standard. Inset: ꢆcat/ꢆp dependence with
increasing [TFA] at 100 mVs-1 near to cathodic processes at -1.93 V (purple
triangles) and -1.47 V (blue squares).
processes, the Ni2
Ni(d8) electronic delocalization, which is favored in bent molecules
(see DFT studies below). In this context, the oxidations at 0.20
and 0.90 V in 2 correspond to an electron transfer followed by a
chemical reaction EiCi.[14],[15] Thus, fast conversion from the
electrochemically generated Ni(III) complex to an oxidation
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Figure 5 Experimental CVs for proton reduction. Ecat/2 denotes the half-peak
potential of the catalytic wave. Conditions: 1 mM 1 in a 0.1 M NBu4PF6 solution
in CH2Cl2, 100 mV s-1 scan rate, glassy carbon electrode. The red trace was run
in the absence of acid, then blue trace with 30 mM TFA.
Figure 6 CVs of 2 in CH2Cl2 with increasing [TFA]. Experimental conditions: 1.0
mM 1 with 0.1 M NBu4PF6 collected at scan rate of 0.1 V s-1 with 0.0, 0.1, 0.2,
0.4, 0.8, 1.6, 2.4, 3.2, 4.0, 5.0, 6.0, 7.0 and 8.0 mM (bottom) TFA concentrations;
Fc as internal standard. Inset: ꢆcat/ꢆp dependence with increasing [TFA] at 100
mV s-1 near to cathodic process at -1.67 V.
In contrast, successive additions of TFA during electrochemical
experiments to solutions of 2 resulted in the appearance of
several reduction waves with different current responses, as
Kinetic Studies
shown in Figure 6. Only a very small current increase is observed
(II,II)/(II,I)
at -1.67 V (ꢇ = 780 mV) related to the Ni2
redox couple, a
Analysis of the three redox processes observed for 1 (Figure 3,
S45 and S46), and 2 (the process centered at E1/2 = -1.67 V in
Figure 3, red trace and S47) at different scan rates determined
process attributed to the direct reduction of 2 at lower TFA
concentrations. However, significant current enhancement is
observed at -1.53 V (ꢇ = 640 mV) and -1.08 V (ꢇ = 190 mV) upon
increasing the amount TFA. These irreversible processes are
associated with ligand protonation in different binding sites and
subsequent dissociation (see Figure 10 and DFT studies below).
Thus, while 1 shows chemical stability under these conditions
(Figures S38 and S39), complexes 2 and 3 (Figures. S40 and
S41) appear to be degraded at concentrations above 8 mM TFA,
since fast extinction of the S⟶Ni charge transfer bands is evident
as the concentration of TFA is increased. The choice of acid is
related to its reduction potential at the glassy carbon (GC)
electrode, since a larger potential window where TFA is not
reduced is available compared with other acids. This leads to
that the electrochemically reversible electron transfer processes
[18]
involve freely diffusing species.
Kinetic studies have been
carried out for HER catalyzed by 1, directly from CVs by
comparing the ratio of catalytic current in the presence of TFA (icat)
to the peak current for the reduction of 1 in the absence of acid
(ip), with the linear relationship between ꢆcat/ꢆp and [TFA] indicating
a second-order dependence on proton concentration (see eq. 1
and Figure 4).[20] Although eq. 1 is typically applicable to catalysts
that employ simple first-order ErCi (Reversible electron transfer
followed by an irreversible chemical reaction) mechanisms, there
are several reports in which it has been used in the analysis of
more complex systems for comparative purposes.[1g],[17] Therefore,
linear plots of (ꢆcat/ꢆp) vs [TFA] are observed in a wide range of TFA
concentrations (0.1 to 30 mM) and for scan rates between 0.10
and 0.30 V s-1 for 1 (Figure S48). By contrast, in the case of 2,
decomposition of the catalyst occurs at a lower acid concentration,
leading to deviation from linearity (Figure 6 inset).
proton reduction catalyzed by the complex, and not directly at the
[16e]
electrode surface.
This was experimentally verified by
measuring the CV of TFA in supporting electrolyte solution,
effectively demonstrating that in the working potential window for
the nickel complexes there are no redox processes at the glassy
carbon electrode (Figure S42). On the other hand, the catalytic
current obtained with TFA as the proton source is higher when
compared with trichloroacetic (TCA) and acetic (HOAc) acids,
indicating that the catalytic reaction depends on the nature of the
acid (Figures S43 and S44), a characteristic that reinforces the
proposed CE mechanism. [17b]
⁄
ꢗ ꢓ
ꢆꢈꢉꢊ
ꢌ
ꢎꢏꢐ[ꢑꢒ]ꢓ
ꢔꢕ
=
ꢍ
ꢖ
(1)
ꢆꢋ
0.4463
On the other hand, at higher concentrations of TFA, the ratio ꢆcat/ꢆp
tends to plateau at a maximum value. Since the current reaches
saturation at high concentrations of TFA, in 1 the maximum value
of ꢆcat/ꢆp was found at 21.8 (at -1.93 V). Thus, using the relation in
eq. 1, a value of kobs (TOF) = 45.6 s-1 can be derived. For 2
degradation occurs at lower acid concentrations (Figure 6); this is
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true for all the scan speeds at which the study was conducted, so
that TOF and ꢆcat/ꢆp values cannot be extracted due to the unknown
nature of the active species under these conditions. This contrasts
with the observations for 1, where the metal is supported by an
auxiliary ligand with bulky substituents ortho to sulfur that confer
steric protection and a bent conformation to the bimetallic
complex. Therefore, the poor catalytic behavior of 2 compared to
that of 1 can be related to its planar conformation and instability
in acidic medium, both features attributed to the lack of steric
hindrance in L2Stioc. Thus, 1 is active with ꢆcat/ꢆp = 21.8 in CH2Cl2,
which is among the highest values reported for these types of
systems, ranging from ꢆcat/ꢆp = 7.8,[19a] through ꢆcat/ꢆp = 4.0,[21b] to
Electronic population analysis provides valuable information
about the electronic structure of the complexes: the low charges
calculated for the atoms in the [Ni2(ꢁ-ArS)2] core shows a higher
degree of covalency in these Ni-S bonds than for those involved
in the terminal Ni-S interactions, see Table S4. Negligible charge
changes are calculated for the N-aromatic vs N-aliphatic
substituents, despite the difference of 150 mV in the
electrochemical properties observed for 1 vs 4. However, the
different Ni-N distances obtained, larger for N-Ar than for N-iBu,
suggests inferior donor ability of the N-atom in the aniline-based
1, destabilizing the oxidized Ni(III) complex. A time-dependent
DFT study was performed to calculate the electronic transitions of
the complexes in dichloromethane solution, see Figures S49 and
S50. In most cases the spectra are dominated by intense bands
between 250 nm and 450 nm. Complex 1 shows a strong
electronic transition at 357 nm that is mainly attributed to S⟶Ni
ligand-to-metal charge transfer (LMCT); according to the
experimental results and previous reports at 446 nm a LMCT
band is observed. [1g], [11] For 2, three main bands were calculated
at 274, 316, and 407 nm assigned to S⟶L, and S⟶Ni transitions.
For the bent analogue 2B, the corresponding S⟶L and S⟶Ni
transitions were calculated at 264 and 368 nm. The similar shape
of the UV-vis bands observed for the coplanar 2, and for the
folded 2B may be rationalized by the vibrational modes allowed
by the geometry of the compounds, which have small energetic
differences and may interconvert in solution. Only one Ar⟶Ar*
(Ar* = antibonding orbital in the aromatic group) excitation is
predicted for 3 at 268 nm. These results agree with the
experimental data, where the general observation are high
intensity electronic absorptions (typical for charge transfer
transitions), with relatively low energies that reflect good orbital
overlap between the sulfur donors and the Ni(II) ions, while also
attesting to the high degree of covalency of the Ni-S bonds. In
addition, it is confirmed that the conformations of the [Ni2(ꢁ-ArS)2]
frameworks significantly affect the electronic structure of the
complexes, leading to high intensity and low energy S⟶Ni charge
transfer transitions for the bent complexes relative to the planar
ones, presumably because the interaction of the nickel centers in
bent complexes leads to greater orbital delocalization.
ꢆ
cat/ꢆp = 2.0.[21] Nonetheless, this value corresponds to a modest
TOF of 45.6 s−1 at a TFA concentration of 30 mM, which is
compatible with a 1.0 mM catalyst concentration in terms of
stability.
Computational Studies
The electronic properties of dimeric complexes 1, 2, and
monomeric 3 were analyzed computationally by density functional
theory (DFT). Complex 2B was also considered, corresponding to
optimization of 2 with a bent geometry between the two Ni
coordination planes; all attempts to achieve a planar geometry for
1 failed. Figure 7 shows the optimized geometries of dimeric 1 (a),
2 (b), the hypothetical 2B (c) and monomeric 3 (d). For 2B the
energy calculated with an angle of 102o between the coordination
planes is 2.3 kcal mol-1 higher than that of planar 2. The small
energetic difference allows us to postulate the possibility of
interconversion of planar and bent conformations in solution.
Moreover, the predicted geometry of 2B agrees with a previous
[10b]
report by Alvarez et al.,
where the ligands generate six
membered rings that can favor the Ni coordination planes to adopt
an endo conformation. Square planar geometry was observed
around the metals centers, with a Ni···Ni distance calculated at
3.45 Å for 2, in contrast with the weak metal-metal interaction that
may be present in bent 1 and 2B, characterized by distances of
2.90 Å.[20] This configuration may be aided by H-bonds from the
N-Ph moiety to the CF3 groups at C-H…F distances of 2.602 and
2.739 Å at 119.9° and 130.3° respectively.
Figure 8 shows the HOMO and LUMO orbitals for the calculated
Ni(II) complexes. The ligand- vs metal-centered redox processes
can be analyzed from the calculated frontier molecular orbitals of
the complexes and specifically for the highest-occupied molecular
orbital (HOMO), which presumably loses an electron upon
oxidation. Likewise, the LUMO level must be involved during
reduction. For complex 3, the LUMO is predicted to be too high in
energy to allow a reversible reduction process, as determined
experimentally. The energetic proximity of the orbitals close to
HOMO (HOMO-2 at ca. -0.220 a.u.) in complexes 1 and 2, with
contributions of more than 62% of Ni atom could be the involved
in the generation of the proposed Ni(III) species generated
electrochemically.
Figure
7 DFT-optimized structures of dimeric complexes 1 (a), 2 (b),
hypothetical 2B (c), and monomeric 3 (d). H-atoms are omitted for clarity.
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Figure
9
Calculated protonation free energies of 1. The values in red
correspond to the free energy difference between the most stable protonation
site and the other two options in the gas phase; blue values correspond to the
free energy change estimated in dichloromethane as PCM.
Figure 8 Simplified diagrams of the frontier HOMO and LUMO of the Ni(II)
complexes 1, 2, 2B, and 3.
Finally, in an effort to explain the electrocatalytic results and the
different chemical stabilities between 1 and 2, DFT calculations
were performed to explore the possible protonation step prior to
electrochemical H2 formation process. Calculations indicate that
the terminal sulfur in 1 (see b-sulfur in Figure 9) is the
energetically favorable site for protonation in the gas phase and
in CH2Cl2 as Polarization Continuum Model (PCM), whereas for
a-S and g-N the relatively high barriers of 17.0 and 16.0 kcal mol-
1 respectively, render the protonation at such positions less likely.
Additionally, the Ni-Ni distance is not affected during b-sulfur
protonation and 1 does not undergo major structural changes. On
the other hand, two possible protonation sites are energetically
accessible for 2: at the terminal sulfur atom (see b-sulfur in Figure
10), where no significant structural changes are observed. The
second possibility is at the tertiary amine (g-nitrogen in Figure 10),
where drastic geometric changes occur, including the loss of the
Ni-N bond upon protonation.
Figure 10 Calculated protonation free energies of 2. The values in red
correspond to the free energy difference between the most stable protonation
site and the other two in the gas phase; blue values correspond to the free
energy change estimated in dichloromethane as PCM.
Conclusions
Among the three nickel complexes with sulfur-rich environments
reported herein, the dimeric complex [Ni2(ꢀ-N,S,S,S’-
NPh{CH2(MeC6H2R’)S}2)2]
1
was found to be active for
electrocatalytic proton reduction; in contrast, the related [Ni2(ꢀ-
N,S,S,S’-NiBu{CH2C6H4S}2)2] 2 shows poor stability under catalytic
conditions. 1 reduces protons at Ecat/2 = −1.93 V (vs Fc+/0) with
ꢆ
cat/ꢆp = 21.8 and at Ecat = −1.47 V with ꢆcat/ꢆp = 5.9, making it a
/2
better catalyst than 2, which undergoes degradation at low acid
concentrations. The good activity of 1 is likely a result of the bulky
nature of the ligand due to the presence of the
bis(trifluromethyl)aromatic substituent group ortho to the S-atom,
which not only protects the metal centers in [Ni2(ꢁ-ArS)2], but also
provides a hinge angle that allows the nickel ions to approach and
stabilize the different oxidation states necessary for HER. In
contrast, the poor catalytic activity of 2 can be attributed to the
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Cambridge Crystallographic Data Center as supplementary material
number CCDC 1862077 (1), 1862079 (2), 1862078 (3). Copies of the data
can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK. E-mail:deposit@ccdc.cam.ac.uk.
negligible steric protection provided by the ligand, and to the
planar conformation of the [Ni2(ꢁ -ArS)2] core. In both cases, a
significant degree of covalency of the Ni-S bonds is predicted by
DFT calculations. The theoretical studies also establish that the
proximity of the Ni(II) ions in the bent complexes (1, the calculated
2B, and the previously reported 4) favor a weak interaction
between the metal centers, which appears to be crucial for
electrocatalytic proton reduction.
Computational details
Unrestricted calculations were carried out using the Gaussian09
package.[28] The hybrid density functional method known as B3LYP was
applied.[29] Effective core potentials (ECP) were used to represent the
innermost electrons of the transition atoms and the basis set of valence
double-ꢙ quality for associated with the pseudopotentials known as
LANL2DZ.[30] The basis set for the light elements as S, C, N, and H was 6-
Experimental Section
31G*.[31] Energies in solution were taken into account by PCM calculations
General remarks
[32]
(dichloromethane, ε = 8.93),
keeping the geometry optimized for gas
phase (single-point calculations).
Unless otherwise indicated, all manipulations were carried out without
taking precautions to exclude air and moisture. Specific synthetic
operations were performed under a dry dinitrogen atmosphere by Schlenk
techniques. Et2O, thf, and dimethoxyethane (DME) were obtained oxygen-
and moisture free by distilling from sodium benzophenone under N2.
MeOH was obtained free of oxygen and moisture by distillation on sodium
and under N2 atmosphere using standard Schlenk techniques. N-methyl-
2-pyrrolidone (NMP) was distilled at reduced pressure and used
immediately. All chemicals and solvents were used as received without
further purification unless mentioned otherwise. Unsubstituted O- and S-
Electrochemical details
Cyclic voltammetry measurements were made under N2 in anhydrous
CH2Cl2 with a potentiostat–galvanostat, CH Instruments 600E, with a
glassy carbon working electrode and a platinum wire auxiliary electrode.
Potentials were recorded versus
a pseudo-reference electrode of
AgBr(s)/Ag(wire) immersed in a 0.1 M NBu4Br CH2Cl2 solution. All
voltammograms were started from open circuit potential (OCP) and were
scanned in both directions, positive and negative, and obtained at a scan
rate from 0.050 to 0.400 V s−1. In agreement with IUPAC convention, the
voltammogram of the ferrocenium–ferrocene (Fc+/0) system was obtained
to establish the values of half wave potentials (E1/2) from the expression
E1/2 = (Ea + Ec)/2.
(2-formylphenyl)-N,N-dimethylthiocarbamates (a, R1 = H, R2 =H) are easily
[21]
accessible from the corresponding phenol.
The synthesis of the
precursors 2,4- disubstituted N,N-dimethylthiocarbamates (a, R1 = C6H4-
(CF3)2, R2 = CH3) has been reported in previous work.
1H (400 MHz)
[7d]
and 13C{1H} (100 MHz) NMR spectra were recorded on a Bruker 400 MHz
Ultrashield™ NMR spectrometer using the residual protiated solvent signal
or tetramethylsilane (TMS) as internal references (TMS ꢘ = 0.00, CHCl3
ꢘ
Synthesis of ligands precursors
= 7.26 ppm) at room temperature; subsequently they were processed
through the MestReNova software of Mestrelab Research. Electron Impact
mass spectrometry (EI MS) experiments were performed a Shimadzu
GCMS-QP2010 spectrometer. Positive ion FAB+ MS were acquired with a
JEOL JMS-SX-102A mass spectrometer operated at an accelerating
voltage of 10 kV from a nitrobenzyl alcohol matrix by using xenon atoms
at 6 keV.
S-2-(Hydroxymethyl)phenyl-N,N-dimethylthiocarbamate
(b).
Unsubstituted salicylaldehyde (R1 = H, R2 = H in scheme 1), (1.24 g, 5.93
mmol) was dissolved in dry thf (50 mL) under nitrogen at room temperature.
NaBH(OAc)3 (3.77, 17.79 mmol) was added to the stirring solution,
generating a white suspension; this mixture was refluxed for 24 hours.
After this time, the resulting suspension was cooling down to room
temperature, so disappearance of starting material was confirmed by thin
layer chromatography (hexane/EtOAc 9:1) together with conversion to one
major product. The solution was evaporated to dryness under reduced
pressure, and the resulting white solid residue was collected by filtration
and dissolved in CHCl3 (25 mL). The organic layer was washed with water
(3 x 15 mL), dried with Na2SO4 and concentrated under reduced pressure.
The product was purified by column chromatography (SiO2 70:230,
hexane:EtOAc 8:2 to 60:40). Light yellow oil 1.02 g, (81%). Rf = 0.12 in
70:30 hexane/ethyl acetate. 1H NMR (400 MHz, CDCl3, r. t.): δ 7.63 (d, 1H,
J = 7.6, Hz, Ar), 7.53 (d, 1H, J = 7.6 Hz, Ar), 7.49 (t, 1H, J = 7.6 Hz, Ar),
7.33 (t, 1H, J = 7.6, Ar), 4.69 (s, 2H, Ar-CH2-OH), 3.25 (br, 1H, ArCH2-OH),
3.11 (s, 3H, ArS(CO)N(CH3)2), 3.03 (s, 3H, ArS(CO)N(CH3)2) ppm. 13C
{1H} NMR (100 MHz, CDCl3, room temperature): δ 168.02 (1C), 145.46
(1C, Ar), 137.09 (1C, Ar), 130.76 (1C, Ar), 130.51 (1C, Ar), 128.44 (1C,
Ar), 127.25 (1C, Ar), 64.23 (1C), 37.22 (2C) ppm. m/z (rel. Int.): 212 (30)
[M+]. IR (ATR, cm-1): 3404 (ꢚC-OH), 1256 (ꢚC-O). Anal. Calcd (%) for
C10H13NO2S: C, 56.85; H, 6.20; N, 6.63; S, 15.17. Found: C, 56.54; H,
6.11; N, 6.35; S, 14.05.
X-ray crystallography
Suitable single crystals of 1-3 mounted on a glass fiber were studied with
Oxford Diffraction Gemini "A" diffractometer with a CCD area detector
(lMoka = 0.71073 Å, monochromator: graphite) source equipped with a
sealed tube X-ray source at 130 K. Unit cell constants were determined
with a set of 15/3 narrow frame/runs with1° in w scans. The double pass
method of scanning was used to exclude any noise. The collected frames
were integrated by using an orientation matrix determined from the narrow
frame scans [22] were used for data collection and data integration. Analysis
of the integrated data did not reveal any decay. Final cell constants were
determined by a global refinement of 6758 for 1, 4150 for 2 and 2956
reflections for 3 with 4.0390 < q < 29.6612°. Collected data were corrected
[23]
for absorbance by using analytical numeric absorption correction
.
Structure solution and refinement were carried out with the SHELXS-2014
[24]
[26]
and SHELXL-2014 [25]; wingx v2014.1
and Mercury CSD 4.1.0
software [27] was used to prepare material for publication. Full-matrix least-
squares refinement was carried out by minimizing (Fo2–Fc2)2. All non-
hydrogen atoms were refined anisotropically. H atoms attached to C atoms
were placed in geometrically idealized positions and refined as riding on
their parent atoms, with C–H = 0.95– 1.0 Å and with Uiso(H) = 1.2Ueq(C)
for aromatic, methine and methylene groups and Uiso(H) = 1.5Ueq(C) for
methyl groups. Crystallographic data have been deposited at the
S-2-(Chloromethyl)phenyl-N,N-dimethylthiocarbamate (c). To
a
solution of S-2-(hydroxymethyl)phenyl-N,N dimethylthiocarbamate (b)
(2.12 g, 10.02 mmol) in 60 mL of CH2Cl2, 2.19 mL of thionyl chloride was
added. The resulting Light-yellow solution was stirred at room temperature
for 5 h. after this time volatile materials were evaporated under vacuum.
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The resulting yellow solid residue was collected by filtration and dissolved
in CHCl3 (30 mL). The organic layer was washed with water (3 x 20 mL),
dried with Na2SO4 and concentrated under reduced pressure. The product
was purified by recrystallization (toluene/CHCl3 8:2). Colorless crystals
1.94 g, (84%). Rf = 0.45 in 71:29 hexane/ethyl acetate. melting point: 85-
87°C. 1H NMR (400 MHz, CDCl3, r. t.): δ 7.60 (dd, 1H, J = 7.7, 1.5 Hz, Ar),
7.58 (dd, 1H, J = 7.7, 1.4 Hz, Ar), 7.47 (td, 1H, J = 7.5, 1.5 Hz, Ar), 7.38
(td, 1H, J = 7.6, 1.6 Hz, Ar), 4.80 (s, 2H, Ar-CH2-Cl), 3.18 (s, 3H,
ArS(CO)N(CH3)2), 3.05 (s, 3H, ArS(CO)N(CH3)2) ppm. RMN 13C {1H} NMR
(100 MHz, CDCl3, room temperature): δ 165.06 (1C), 140.95 (1C, Ar),
137.20 (1C, Ar), 129.82 (1C, Ar), 129.77 (1C, Ar), 128.47 (1C, Ar), 127.81
(1C, Ar), 45.06 (1C), 37.38 (2C, ArS(CO)N(CH3)2) ppm. EI MS m/z = 229
[M+]. IR (ATR, cm-1): 766 (ꢚC-Cl). Anal. Calcd (%) for C10H12ClNOS: C,
52.28; H, 5.27; N, 6.10. Found: C, 52.07; H, 5.18; N, 6.01.
constant stirring, then a NaOMe/MeOH (25 % 0.25 mL, 1.08 mmol)
solution was transferred to this mixture; immediately after this addition, the
solution turned yellow. This mixture was kept at 65 °C under constant
stirring for 6 days (monitoring the progress by mass spectrometry), once
confirmed complete deprotection of all the precursor, NiCl2∙6 H2O (0.07 g,
0.27 mmol), is added, immediately the dispersion changed to a dark brown
color; This mixture was left overnight to ensure complete reaction. Finally,
the solution was evaporated and an extraction was carried out in diethyl
ether/water. The product was crystallized in ether (slow evaporation),
obtaining crystals in the shape of black needles. Yield: 45%; black crystals;
melting point: 278 °C; 1H NMR (400 MHz, CDCl3, room temperature): δ
1.95 (s, 6H, CH3), 2.19 (s, 6H, CH3*), 3.81 (d, 2H, CH2), 4.56 (d, 2H, CH2),
5.15 (d, 2H, CH2), 6.15 (s, 2H, CH2), 6.51-7.66 (30 H, Ar) ppm. 13C{1H}
NMR (100 MHz, CDCl3, room temperature): δ 20.60, 21.18, 67.26, 72.84,
119.80, 121.28, 122.47, 122.94, 127.74, 128.26, 129.93, 131.29, 132.31,
134.26, 135.53, 135.71, 137.82, 138.41, 140.14, 141.80, 142.85, 144.39
ppm. UV-vis ꢛ nm (ꢜ M-1cm-1) 238 (7.3 x 104), 289 (3.0 x 104), 360 (2.66 x
104), 443 (9.18 x 103), 533 (3.09 x 103), 775 (7.7 x102). IR (ATR, cm-1):
2914 (ꢚC-H), 1584 (ꢚC=C), 1124 (ꢚC-F). Anal. Calcd (%) for C76H50F24N2Ni2S4:
C, 53.92; H, 2.98; N, 1.65; S, 7.58; found: C, 52.03; H, 3.02; N, 1.70; S,
7.53; FAB-MS m/z 1692 [M]+.
Proligand L1Stioc. In a 100 mL Schlenk flask, approximately 50 mL of DME
were transferred under N2 atmosphere, then (1.00 g, 2.19 mmol) of 2-
(chloromethyl)-4-methyl-6-[3,5-bis(trifluoromethyl)phenyl]-S-
phenylthiocarbamate (c in Scheme 1) [7d] was added, followed by NaI (0.33
g, 2.19 mmol); after 1 hour of stirring at room temperature, anilinium
chloride (0.13 g, 0.10 mmol) and K2CO3 (0.55 g, 3.99 mmol) were added;
the solution was stirred at 80°C for 7 days (monitoring by thin-layer
chromatography). After the reaction was complete, DME was evaporated
and an extraction was carried out in diethyl ether/water. Finally, the product
obtained was crystallized in a methanol/CHCl3 mixture as a colorless solid,
yield: 83%; melting point: 157°C. 1H NMR (400 MHz, CDCl3, room
temperature): δ 7.91 (s, 2H, CF3Ar), 7.86 (s, 4H, CF3Ar), 7.31 (s, 2H, SAr*),
7.29 (t, 2H, m-NAr), 7.20 (s, 2H, SAr*), 6.79 (3H, o and p (NAr)), 4.90 (s,
4H, PhN-CH2), 3.02 (s, 6H, NCH3*), 2.97 (s, 6H, ArS(CO)N(CH3)2), 2.43 (s,
6H, ArS(CO)N(CH3)2) ppm. 13C{1H} NMR (100 MHz, CDCl3, room
temperature): δ 24.43 (s), 39.50 (s), 39.61 (s), 56.68 (s), 114. 26 (s),
118.61 (s), 122.64 (q, 3JC-F = 3.4 Hz ArCF3), 124.21 (s), 125.25 (q, 1J =
268.6 Hz CF3), 129.97 (s), 131.07 (s), 131.4 (s), 132.51 (q, 2JC-F = 32.7 Hz
ArCF3), 138.06 (s), 142.44 (s), 145.23 (s), 145.76 (s), 147.22 (s), 149.97
(s), 167.04 (s) ppm. IR (ATR, cm-1): 1656 (ꢚC=O), 1122 (ꢚC-F), 1276 y 1375
(ꢚC-N). Anal. Calcd (%) for C44H37F12N3O2S2 : C, 56.27; H, 3.84; N, 4.58; S;
found: C, 55.12; H, 3.78; N, 4.32.
[Ni2(
ꢀ
-N,S,S,S’-NiBu{CH2C6H4S}2)2] (2). In a 100 mL Schlenk flask under
N2 atmosphere (L2Stioc) (0.265 g, 0.56 mmol) was dissolved in anhydrous
thf, then solution of NaOMe/ MeOH was added and this mixture was stirred
8 days at 65oC. Then, solid NiCl2.6H2O (0.13 g, 0.56 mmol) was added,
this mixture was stirred 6 hours at room temperature. The solvent was
evaporated to dryness, the solid was washed with ethyl acetate, diethyl
ether and water. The red, sparingly soluble microcrystals were added
CH2Cl2 and placed in a sealed vial and warmed up, allowing for slow
cooling to room temperature. The solid obtained was insoluble in most
solvents and very sparingly soluble in CHCl3 and CH2Cl2, 0.11 g, 51 %
yield. Rf = 0.44 in 3:1 hexane/ ethyl acetate M.p. > 250 (dec. 140°C). EI
MS m/z 746 [M+]. UV-vis ꢛ nm (ꢜ M-1cm-1) 263 (3.4 x 104), 301 (3.90 x 104),
369 (1.48 x 104), 416 (1.05 x 104), 524 (2.9 x 103), 775 (3.2 x102); IR (ATR,
cm-1): 3443 (ꢚO-H), 2958 (ꢚC-H), 1586 (ꢚC=C). Anal. Calcd (%) for
C36H42N2Ni2S4(CHCl3): C, 51.21; H, 5.00; N, 3.23; S, 14.78. Found: C,
51.63; H, 5.18; N, 3.65; S, 14.53.
Proligand L2Stioc. In a 250 mL round bottom Schlenk flask under N2
atmosphere the S-2-(chloromethyl)phenyl-N,N-dimethylthiocarbamate (c)
(0.80 g, 3.48 mmol) was added followed by NaI (0.58 g, 3.87 mmol),
isobutylamine (174 ꢁL, 1.73 mmol) and K2CO3 (0.97 g, 7.02 mmol); this
mixture was stirred 4 days at 65oC and the solvent evaporated to dryness,
the solid residue was dissolved in CH2Cl2. The organic layer was washed
with (3 x 25 mL) sodium thiosulfate aqueous solution, dried with Na2SO4
and concentrated under reduced pressure. The product was purified by
crystallization for slow evaporation (CH2Cl2/MeOH 1:1). Colorless crystals,
0.65 g, 81% yield. melting point: 137°C. Rf = 0.21 in 2:1 hexane/ethyl
acetate. 1H NMR (400 MHz, CDCl3): δ 7.64 (d, 2H, J = 7.5 Hz, Ar), 7.45 (d,
2H, J = 7.5 Hz, Ar), 7.35 (t, 2H, J = 7.5 Hz, Ar), 7.22 (t, 2H, J = 7.2 Hz, Ar),
3.68 (s, 4H, iBuN(CH2)Ar), 3.04 (d, 12H, J = 7.1 Hz, ArS(CO)N(CH3)2, 2.15
(d, 2H, J = 7.2 Hz, iBuN), 1.84 (m, 1H, J = 6.7 Hz, iBuN) , 0.85 (d, 6H, J =
7.2 Hz, iBuN) ppm. 13C {1H} NMR (100 MHz, CDCl3, room temperature): δ
166.70 (2C), 143.88 (2C), 137.12 (1C), 130.53 (2C), 129.36 (2C), 128.43
(2C), 127.04 (2C), 63.06 (2C), 57.44 (2C), 36.96 (2C), 26.23 (1C), 21.04
(2C) ppm. EI MS m/z 459 [M+]. IR (ATR, cm-1): 1281 (ꢚC-O), 1186 (ꢚC-O-C).
Anal. Calcd (%) for C24H33N3O2S2: C, 62.71; H, 7.24; N, 9.14; S, 13.95.
Found: C, 62.88; H, 7.20; N, 8.82; S, 12.27.
[Ni(
ꢀ
-N,S,S-NiBu{CH2C6H4S}2)(C≡NC10H7)] (3). In a 100 mL Schlenk flask
under N2 atmosphere, complex 2 (37 mg, 0.07 mmol) was dissolved in
CH2Cl2 at 40 °C and 2-naphthylisocyanate was added (11 mg, 0.07 mmol),
this mixture was stirred 90 minutes at 40oC and concentrated under
reduced pressure. The product was purified by crystallization by slow
evaporation (CH2Cl2/MeOH 1:1). Dark green microcrystals (32 mg) were
obtained in 67 % yield. Rf = 0.55 in 3:1 hexane/ ethyl acetate. M.p. > 250
(dec. 132 oC). 1H NMR (400 MHz, CDCl3): δ 7.92 (s, 1H, Ar), 7.88 (t, 3H,
Ar), 7.62 (m, 4H, Ar), 7.48 (s, 1H, Ar), 7.30 (s, 1H, Ar), 7.20 (s,1 H, Ar),
7.06 (m, 4H, Ar), 4.69 (dd, 4H, iBuN(CH2)), 2.70 (m, 1H, J = 7.1 Hz, iBuN),
2.63 (d, 2H, iBuN), 1.39 (d, 6H, iBuN) ppm. 13C{1H} NMR (100 MHz, CDCl3,
room temperature): ꢘ 166.90 (1C), 165.58 (2C), 152.02 (1C), 141.67 (2C),
137.90 (2C), 131.38 (2C), 130.25 (2C), 127.58 (2C), 127.20 (2C), 126.86
(2C), 118.22 (1C), 111.51 (2C), 60.08 (1C), 53.50 (2C), 37.06 (4C), 14.48
(1C) ppm. EI MS m/z 552 [M+]. UV-vis ꢛ nm (ꢜ M-1cm-1) 235 (6.4 x 104),
313 (3.90 x 104), 366 (3.67 x 104), 775 (1.1 x102); IR (ATR, cm-1): 2958
(ꢚC-H), 2162 (ꢚC≡H), 1584 (ꢚC=C). Anal. Calcd (%) for C29H28N2NiS2: C,
66.05; H, 5.35; N, 5.31; S, 12.16. Found: C, 66.57; H, 5.11; N, 5.36; S,
11.15.
Synthesis of Complexes
Conflicts of interest
[Ni2(
ꢀ
-N,S,S,S’-NPh{CH2(MeC6H2R’)S}2)2] (R’ = 3,5-(CF3)2C6H3) (1). In a
There are no conflicts to declare
100 mL round bottom Schlenk flask, 50 mL of anhydrous thf were
transferred, subsequently (L1Stioc) (0.25 g, 0.27 mmol) was added under
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Heinemann, Eur. J. Inorg. Chem. 1999, 1715-1725; e) C.-M. Lee, T.-W.
Chiou, H.-H. Chen, C.-Y. Chiang, T.-S. Kuo, W.-F. Liaw, Inorg. Chem.
2007, 46, 8913−8923. f) D. Huang, L. Deng, J. Sun, R. H. Holm, Inorg.
Chem. 2009, 48, 6159−6166; g) D. S. Warner, C. Limberg, S. Z. Mebs,
Anorg. Allg. Chem. 2013, 639, 1577−1583; h) X. Wei, X. Kang, S. Wang,
M. Zhu, Dalton Trans. 2018, 47, 13766 -13770; i) S. Yang, J. Chai, H.
Chong, Y. Song, H. Yu, M. Zhu, Chem. Commun. 2018, 54, 4314-4316;
j) P. A. Mane, S. Dey, A. K. Pathak, M. Kumar, N. Bhuvanesh, Inorg.
Chem. 2019, 58, 2965–2978.
Acknowledgements
ERM and IC thank DGAPA-PAPIIT IN203317. PRMA and GA
thank IQTC-UB for computational resources. AMD and LNB thank
Colciencias and Universidad del Valle (convocatoria interna) for
financial support. The authors thank L. E. Hurtado Lloreda for EI
MS, C. A. Rodriguez Padilla for 1H and 13C RMN spectroscopy, M.
P. Orta for combustion analysis, and L. Velasco for FAB MS.
[7]
a) A. Mondragón, I. Monsalvo, I. Regla, I. Castillo, Tetrahedron Lett. 2010,
51, 767–770; b) A. Mondragón, I. Monsalvo, I. Regla, M. Flores-Alamo,
I. Castillo, Tetrahedron, 2013, 69, 9499–9506; c) A. Mondragón, M.
Flores-Alamo, P. R. Martínez-Alanis, G. Aullón, V. M. Ugalde-Saldívar,
Castillo, Inorg. Chem. 2015, 54, 619−627; d) E. Robles-Marín, A.
Mondragón, M. Flores-Alamo, I. Castillo, J. Braz. Chem. Soc. 2018, 29,
1751-1760.
Keywords: Nickel complexes • Hydrogenase • Biomimetic
Model • Hydrogen evolving reaction • Electrocatalyst
[1]
a) B. M. Hunter, H. B. Gray, A. M. Müller, Chem. Rev. 2016, 116, 14120–
14136; b) M. Kobashi, S. Masaoka, K. Sakai, Angew. Chem. Int. Ed.
2012, 51, 7431-7434; c) W. T. Eckenhoff, R. Eisenberg, Dalton Trans.
2012, 41, 13004-13021; d) H. N. Kagalwala, D. N. Chirdon, I. N. Mills, N.
Budwal, S. Bernhard, Inorg. Chem. 2017, 56, 10162–10171; e) Y. Chen,
L. Wang, Y. Zhai, H. Chen, Y. Dou, J. Li, H. Zheng, R. Cao, RSC Adv.
2017, 7, 32310-32315; f) X. Ma, J. Wang, D. Liu, R. Kong, S. Hao, G. Du,
A. M. Asiri, X. Sun, New J. Chem. 2017, 41, 4754-4757; g) G.-G. Luo,
Y.-H. Wang, J.-H. Wang, J.-H. Wu, R.-B. Wu, Chem. Commun. 2017, 53,
7007-7010.
[8]
[9]
J. R. McKone, S. C. Marinescu, B. S. Brunschwig, J. R. Winkler, H. B.
Gray, Chem. Sci. 2014, 5, 865−878.
a) M. Kumar, R. O. Day, G. J. Colpas, M. J. Maroney, J. Am. Chem. Soc.
1989, 111, 8323−8325; b) G. J. Colpas, M. Kumar, R. O. Day, M. J.
Maroney, Inorg. Chem. 1990, 29, 4779−4778.
[10] a) G. Aullón, G. Ujaque, A. Lledós, S. Alvarez, P. Alemany, Inorg. Chem.
1998, 37, 804-813; b) G. Aullón, G. Ujaque, A. Lledós, S. Alvarez, Chem.
Eur. J. 1999, 5, 1391−1410; c) G. Aullón, M. Hamidi, A. Lledós, S.
Alvarez. Inorg. Chem. 2004, 43, 3702-3714.
[2]
a) W. Lubitz, H. Ogata, O. Rüdiger, E. Reijerse, Chem. Rev. 2014, 114,
4081-4148; b) S. Frielingsdorf, T. Schubert, A. Pohlmann, O. Lenz, B.A.
Friedrich, Biochemistry 2011, 50, 10836-10843; c) P. E. M. Siegbahn, J.
W. Tye, M. B. Hall, Chem. Rev. 2007, 107, 4414-4435; d) J. C. Fontecilla-
Camps, A. Volbeda, C. Cavazza, Y. Nicolet, Chem. Rev. 2007, 107,
4273-4303; e) K. A. Vincent, A. Parking, F. A. Armstrong, Chem. Rev.
2007, 107, 4366-4413; f) C. Tard, C. J. Pickett, Chem. Rev. 2009, 109,
2245–2274
[11] E. I. Solomon, S. I. Gorelsky, A. J. Dey, Comput. Chem. 2006, 27,
1415−1428.
[12] S. A. Mirza, M. A. Pressler, M. Kumar, R. O. Day, M. J. Maroney, Inorg.
Chem. 1993, 32, 977–987
[13] a) F. A. Cotton, F. Zingales, J. Am. Chem. Soc. 1961, 83, 351−355; b) H.
Hou, P. K. Gantzel, C. P. Kubiak, J. Am. Chem. Soc. 2003, 125,
9564−9565; c) H. Hou, P. K. Gantzel, C. P. Kubiak, Organometallics
2003, 22, 2817−2819.
[3]
a) J. Jiang, M. Maruani, J. Solaimanzadeh, W. Lo, S. A. Koch, M. Millar,
Inorg. Chem. 2009, 48, 6359−6361; b) K. Weber, T. Krämer, H. S.
Shafaat, T. Weyhermüller, E. Bill, M. V. Gastel, F. Neese, W. A. Lubitz,
J. Am. Chem. Soc. 2012, 134, 20745−20755; c) B. C. Manor, T. B.
Rauchfuss, J. Am. Chem. Soc. 2013, 135, 11895−11900; d) C. Greco,
Dalton Trans. 2013, 42, 13845-13854; e) H. Tai, Y. Higuchi and S. Hirota,
Dalton Trans. 2018, 47, 4408-4423; f) G. Dong, Q. M. Phung, K. Pierloot,
and U. Ryde, Inorg. Chem. 2018, 57, 15289–15298; g) R. Breglia, C.
Greco, P. Fantucci, L. De Gioia, M. Bruschi, Inorg. Chem. 2019, 58, 279–
293; h) S. Qiu, L. M. Azofra, D. R. Macfarlane, C. Sun, Inorg. Chem. 2019,
58, 2979–2986.
[14] a) R. R. Gagné, C. A. Koval, G. C. Lisensky, Inorg. Chem. 1980, 19,
2855-2857; b) G. A. Mabbott, J. Chem. Edu. 1983, 60, 697-702; c) D. J.
Martin, B. D. McCarthy, E. S. Rountree, J. L. Dempsey, Dalton Trans.
2016, 45, 9970-9976.
[15] G. A. N. Felton, R. S. Glass, D. L. Lichtenberger, D. H.; Evans, D. H.
Inorg. Chem. 2006, 45, 9181-9184.
[16] a) S. Jiang, J. Liu, L. Sun, Inorg. Chem.Commun. 2006, 9, 290-292; b)
J.-F. Capon, F. Gloaguen, P. Schollhammer, J. Talarmin, Coord. Chem.
Rev. 2005, 249, 1664-1676; c) S. J. Borg, T. Behrsing, S. P. Best, M.
Razavet, X. Liu, C. J. Pickett, J. Am. Chem. Soc. 2004, 126, 16988-
16999; d) L.-C. Song, C. Jea, J. Yan, H. T. Wang, X.-F. Liu, Q.-M. Hu,
Organometallics 2006, 25, 1544-1547; e) B. D. McCarthy, D. J. Martin,
E. S. Rountree, A. C. Ullman, J. L. Dempsey, Inorg. Chem., 2014, 53,
8350−8361.
[4]
a) C. Tard, C. J. Pickett, Chem. Rev. 2009, 109, 2245-2274; b) Y.
Yasuhiro, K. Tatsumi, Eur. J. Inorg. Chem. 2011, 973-985; c) T. R.
Simmons, G. Berggren, M. Bacchi, M. Fontecave, V. Artero, Coord.
Chem. Rev. 2014, 270−271, 127−150; d) K.-T. Lai, W.-C.Ho, T.-W.
Chiou, W.-F. Liaw, Inorg. Chem. 2013, 52, 4151−4153; e) D. Yang, Y. Li,
B. Wang, X. Zhao, L. Su, S. Chen, P. Tong, Y. Luo, J. Qu, Inorg. Chem.
2015, 54, 10243−10249; f) F. Koch, H. Schubert, P. Sirsch, A. Berkefeld,
Dalton Trans. 2015, 44, 13315-13324; g) F. Koch, A. Berkefeld, H.
Schubert, C. Grauer, Chem. Eur. J. 2016, 22, 14640 – 14647.
a) M. Asti, R. Cammi, D. Cauzzi, C. Graiff, R. Pattacini, G. Predieri, A.
Stercoli, A. Tiripicchio, Chem. Eur. J. 2005, 11, 3413−3419; b) S.-Q. Bai,
T. S. A. Hor, Chem. Commun. 2008, 0, 3172−3174; c) Y. Klerman, E.
Ben-Ari, Y. Diskin-Posner, G. Leitus, L. J. W. Shimon, Y. Ben-David, D.
Milstein, Dalton Trans. 2008, 0, 3226−3234; d) T. Teratani, T.-A. Koizumi,
T. Yamamoto, K. Tanaka, T. Kanbara, Dalton Trans., 2011, 40,
8879−8886; e) Q.-Q. Wang, R. A. Begum, V. W. Day, K. Bowman-James,
Inorg. Chem. 2012, 51, 760−762.
[17] a) W. R. McNamara, Z. Han, C.-J. Yin, W. W. Brennessel, P. L. Holland,
R. Eisenberg, Proc. Natl. Acad. Sci. 2012, 109, 15595-15599; b) S.
Ghosh, S. Basak-Modi, M. G. Richmond, E. Nordlander, G. Hogarth,
Inorganica Chim. Acta, 2018, 480, 47-53; c) B. E. Barton and T. B.
Rauchfuss, J. Am. Chem. Soc. 2010, 132, 14877-14885; d) A. D. Wilson,
R. H. Newell, M. J. McNevin, J. T. Muckerman, M. R. DuBois, D. L.
DuBois, J. Am. Chem. Soc. 2006, 128, 358-366.
[5]
[18] a) N. Elgrishi, K. J. Rountree, B. D. McCarthy, E. S. Rountree, T. T.
Eisenhart, J. L. Dempsey, J. Chem. Educ. 2018, 95, 197−206; b) D. H.
Evans, K. M. O'Connell, R. A. Petersen, M. J. Kelly, J. Chem. Educ.,
1983, 60, 290-293.
[19] a) G. P. Connor, K. J. Mayer, C. S. Tribble, W. R. McNamara, Inorg.
Chem. 2014, 53, 5408−5410; b) J. W. Tye, J. Lee, H.-W. Wang, R. Mejia-
Rodriguez, J. H. Reibenspies, M. B. Hall, M. Y. Darensbourg, Inorg.
Chem. 2005, 44, 5550-5552; c) M. T. Olsen, A. K. Justice, F. Gloaguen,
T. B. Rauchfuss, S. R. Wilson, Inorg. Chem. 2008, 47, 11816-11824.
[6]
a) H.-J. Kruger, R. H. Holm, Inorg. Chem. 1989, 28, 1148−1155; b) R.
Hahn, A. Nakamura, K. Tanaka, Y. Nakayama, Inorg. Chem. 1995, 34,
6562−6564; c) T. L. James, L. Cai, M. C. Muetterties, R. H. Holm, Inorg.
Chem. 1996, 35, 4148−4161; d) D. Sellmann, D. Häußinger, F. W.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

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FULL PAPER
[20] I. S. Ignatyev, H. F. Schaefer R. B. King, S. T. Brown, J. Am. Chem. Soc.,
2000, 122, 1989–1994.
Tomasi, M. Cossi, N. Rega, J. Millam, M. Klene, J. E. Knox, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O.
Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J.
Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J.
V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09 (Revision B.1); Gaussian,
Inc.: Wallingford, CT, 2010.
[21] B. Gjoka, F. Romano, C. Zonta, G. Licini, Eur. J. Org. Chem., 2011, 5636-
5640.
[22] CrysAlisPro and CrysAlis RED software packages Agilent Technologies,
Agilent 2013. Yarnton, England.
[23] R. C. Clark, J. S. Reid. Acta Cryst. 1995, A51, 887–897.
[24] G. M. Sheldrick. Acta Crystallogr. 2015, A71, 3−8.
[25] G. M. Sheldrick. Acta Crystallogr. 2015, C71, 3−8
[26] L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837-838..
[27] C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P. Shields, R.
Taylor, Towler and van der Streek, J. Appl. Crystallogr., 2006, 39, 453-
457.
[29] a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648−5652; b) C. Lee, W.
Yang, R. G. Parr, Phys. Rev. B, 1988, 37, 785−789.
[30] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299−310.
[31] a) P. C. Hariharan, J. A. Pople, Theor. Chim. Acta 1973, 28, 213−222; b)
M. M. Francl, W. J. Petro, W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J.
DeFrees, J. A. Pople, J. Chem. Phys. 1982, 77, 3654−3665.
[28] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino,
G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. A. Montgomery, J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
[32] a) J. Tomasi, M. Persico, M. Chem. Rev. 1994, 94, 2027−2094; b) C.
Amovilla, V. Barone, R. Cammi, E. Cancès, M. Cossi, B. Mennucci, C. S.
Pomelli, J. Tomasi, Adv. Quantum Chem. 1998, 32, 227−261.
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These studies demonstrate the
importance of controlling the
Author(s), Corresponding Author(s)*
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conformations of [Ni2(ꢁ-SAr)2] cores in
Ni(II) dimeric complexes to enhance
electrocatalytic properties.
Title
((Insert TOC Graphic here: max.
width: 5.5 cm; max. height: 5.0 cm))
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Title
These studies demonstrate the importance of controlling the conformations of
[Ni2(ꢁ-SAr)2] cores in Ni(II) dimeric complexes to enhance electrocatalytic
properties.
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