C-S Bond Cleavage, Redox Reactions, and Dioxygen Activation by Nonheme Dicobalt(II) Complexes

Article abstract of DOI:10.1021/acs.inorgchem.7b02432

Synthesis and reactivity of a series of thiolate/thiocarboxylate bridged dicobalt(II) complexes were investigated in comparison with their carboxylate bridged analogues bearing free thiol/hydroxyl groups. Upon one-electron oxidation, complexes [Co₂(N-Et-HPTB)(μ-SR¹)](BF₄)₂ (R¹ = Ph, 1a; Et, 1b; Py, 1c) and [Co₂(N-Et-HPTB)(μ-SCOR²)](BF₄)₂ (R² = Ph, 2a; Me, 2b) yielded [Co₂(N-Et-HPTB)(DMF)₂](BF₄)₃ (6) (DMF = dimethylformamide) along with the corresponding disulfides (where N-Et-HPTB is the anion of N,N,N′,N′-tetrakis[2-(1-ethylbenzimidazolyl)]-2-hydroxy-1,3-diaminopropane). Unlike the inertness of carboxylate bridged complexes [Co₂(N-Et-HPTB)(μ-O₂C-R³-SH)](BF₄)₂ (R³ = Ph, 3a; CH₂CH₂, 3b) and [Co₂(N-Et-HPTB)(μ-O₂CR⁴)](BF₄)₂ (R⁴ = Ph, 4a; Me, 4b; CH₂CH₂CH₂OH, 5) toward O₂, the bridging ethanethiolate in 1b was oxidized to yield a sulfinate bridged complex, [Co₂(N-Et-HPTB)(μ-O₂SEt)](BF₄)₂ (10). Detailed investigation of the synthetic aspects of 1a-1c led to the discovery of a C-S bond cleavage reaction and yielded the dicobalt(II) complexes [Co₂(N-Et-HPTB)(SH)(H₂O)](BF₄)₂ (8a), [Co₂(N-CH₂Py-HPTB)(SH)(H₂O)](BF₄)₂ (8b) (where N-CH₂Py-HPTB is the anion of N,N,N′,N′-tetrakis[2-(1-picolylbenzimidazolyl)]-2-hydroxy-1,3-diaminopropane)), and [Co₂(N-Et-HPTB)(μ-S)](BF₄) (9). Both 8a and 8b feature nonheme dinuclear Co(II) units containing a terminal hydrosulfide. The present study thus reports comparative redox reactions for a rare class of 16 dicobalt(II) complexes and introduces a selective synthetic strategy for the synthesis of unprecedented dicobalt(II) complexes featuring only one terminal hydrosulfide.

Full text of DOI:10.1021/acs.inorgchem.7b02432

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
C−S Bond Cleavage, Redox Reactions, and Dioxygen Activation by
Nonheme Dicobalt(II) Complexes
Manish Jana and Amit Majumdar*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur,
Kolkata 700032, India
*
S Supporting Information
ABSTRACT: Synthesis and reactivity of a series of thiolate/
thiocarboxylate bridged dicobalt(II) complexes were inves-
tigated in comparison with their carboxylate bridged analogues
bearing free thiol/hydroxyl groups. Upon one-electron
1
1
oxidation, complexes [Co (N-Et-HPTB)(μ-SR )](BF ) (R =
2
4 2
2
Ph, 1a; Et, 1b; Py, 1c) and [Co (N-Et-HPTB)(μ-SCOR )]-
2
2
(
(
BF ) (R = Ph, 2a; Me, 2b) yielded [Co (N-Et-HPTB)-
4
2
2
DMF) ](BF ) (6) (DMF = dimethylformamide) along with
2
4 3
the corresponding disulfides (where N-Et-HPTB is the anion of
N,N,N′,N′-tetrakis[2-(1-ethylbenzimidazolyl)]-2-hydroxy-1,3-
diaminopropane). Unlike the inertness of carboxylate bridged
3
3
complexes [Co (N-Et-HPTB)(μ-O C-R -SH)](BF ) (R = Ph,
3
2
2
4 2
4
4
a; CH CH , 3b) and [Co (N-Et-HPTB)(μ-O CR )](BF ) (R = Ph, 4a; Me, 4b; CH CH CH OH, 5) toward O , the
2 2 2 2 4 2 2 2 2 2
bridging ethanethiolate in 1b was oxidized to yield a sulfinate bridged complex, [Co (N-Et-HPTB)(μ-O SEt)](BF ) (10).
2
2
4 2
Detailed investigation of the synthetic aspects of 1a−1c led to the discovery of a C−S bond cleavage reaction and yielded the
dicobalt(II) complexes [Co (N-Et-HPTB)(SH)(H O)](BF ) (8a), [Co (N-CH Py-HPTB)(SH)(H O)](BF ) (8b) (where
2
2
4 2
2
2
2
4 2
N-CH Py-HPTB is the anion of N,N,N′,N′-tetrakis[2-(1-picolylbenzimidazolyl)]-2-hydroxy-1,3-diaminopropane)), and
2
[
Co (N-Et-HPTB)(μ-S)](BF ) (9). Both 8a and 8b feature nonheme dinuclear Co(II) units containing a terminal
2
4
hydrosulfide. The present study thus reports comparative redox reactions for a rare class of 16 dicobalt(II) complexes and
introduces a selective synthetic strategy for the synthesis of unprecedented dicobalt(II) complexes featuring only one terminal
hydrosulfide.
INTRODUCTION
occurring dioxygen carrier, cobalt-substituted hemoglobin
■
5
(
coboglobin) has been shown to bind oxygen reversibly.
Nonheme mono- and dinuclear cobalt(II) complexes have
been studied since long ago due to their presence in the active
The oxygen binding affinity of coboglobin is, however, lower
than the native iron proteins, and oxycoboglobin has been5
formulated as a Co(III) center with a coordinated superoxide.
Bioinorganic chemistry of cobalt mainly involves synthesis of
model mono- and dinuclear cobalt(II) complexes and
investigation of their reactivity to mimic the functional aspects
of the corresponding active sites. In model chemistry, a special
emphasis has always been on the oxygen binding capability of
sites of noncorrin cobalt-containing enzymes. To date, at leas1t
eight noncorrin cobalt-containing enzymes have been isolated,
namely, methionine aminopeptidase, proline dipeptidase,
nitrile hydratase, glucose isomerase, methylmalonyl-CoA
carboxytransferase, aldehyde decarbonylase, lysine-2,3-amino-
mutase, and bromoperoxidase. These enzymes contain either
mono or dinuclear Co(II) centers in a form that is quite
different from that found in the corrin ring of vitamin B . Two
of the above-mentioned enzymes that contain dinuclear Co(II)
units are methionine aminopeptidase from Escherichia coli
6
the Co(II) complexes. Mononuclear cobalt complexes with
1
2
7
8
salen and corrole ligands have been shown to achieve
reversible O2 binding. Oxygenation study of dicobalt(II)
complexes and characterization of the corresponding binuclear
2
,3
4
and proline dipeptidase from Pyrococcus furiosus. Methionine
aminopeptidase cleaves the N-terminal methionine of the
newly translated peptide chains in both eukaryotes and
9
−12
cobalt dioxygen complexes have been reported.
A
comparative thermodynamic study on the reactivity of
diiron(II) and dicobalt(II) complexes containing different
dinucleating ligands toward molecular oxygen is available in
3
prokaryotes, while proline dipeptidase mediates the specific
4
cleavage of proline-containing dipeptides at the C-terminus.
13
the literature. Recently it has also been reported that
dicobalt(II) complexes can be tuned with respect to their
Another interesting aspect of cobalt(II) complexes is their
oxygen binding capability. Reversible oxygen binding for
respiring organism is performed by hemoglobin, hemerythrin,
and hemocyanin, of which the latter two contain dimetallic
active sites. While cobalt has not been found in any naturally
Received: September 22, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02432
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Scheme 1. Deprotonated Forms of Some Representative Dinucleating N,O-Donor Ligands
a
Chart 1. Abbreviations and Designations
a
30,39
HN-Et-HPTB, N,N,N′,N′-tetrakis(2-(l-ethylbenzimidazolyI))-2-hydroxy-1,3-diaminopropane,
HN-CH Py-HPTB, N,N,N′,N′-tetrakis(2-(1-
2
picolylbenzimidazolyl))-2-hydroxy-1,3-diaminipropane.
dioxygen affinity and reversible chemisorption by varying the
electronic properties of the bridging carboxylate ligand.
substituted benzimidazole-based ligands definitely offer a
viable alternative option. For example, benzimidazole-based
ligands have been successfully used in the oxygenation
chemistry of diiron(II) complexes and related reactivity
14
However, none of these studies included X-ray structural
characterization of the dicobalt(II) complexes. Dicobalt(II)
complexes using ligands other than typical dinucleating ligands
27−29
studies.
Selected dinucleating ligands that have been
15−20
used in the above-mentioned studies are also known.
used for the synthesis and reactivity study of dinculear Co(II)
and/or Fe(II) complexes are collected in Scheme 1. Inspired
by the successful use of a particular benzimidazole-based
dinucleating ligand, HN-Et-HPTB (where N-Et-HPTB is the
anion of N,N,N′,N′-tetrakis[2-(1-ethylbenzimidazolyl)]-2-hy-
Synthesis, molecular structures, magnetic properties, and
spectroscopic properties for a large number of dicobalt(II)
and mixed-valence dicobalt(II, III) complexes with various
21−25
types of dinucleating ligands have been reported recently.
30
Examples include cobalt(II) centers containing mostly
carboxylate bridges, although in some cases phosphodiester
droxy-1,3-diaminopropane; Scheme 1), in different aspects of
28,29,31−36
various model diiron(II) complexes,
we started using
21
groups as auxiliary bridges are also reported.
the ligand for the synthesis and reactivity study of Fe(II) and
Co(II) complexes. While in general, a large number of Fe(II)/
Co(II)−thiolate complexes are available in the literature,
nonheme diiron(II)/dicobalt(II) complexes with bridging or
Dinuclear Co(II) complexes are mostly synthesized using
N,O-donor dinucleating ligands along with carboxylates as
ancillary coligands. Compartmental ligands of the “end-off”
type containing phenolic or alcoholic oxygen as endogenous
bridge have often been the choice of supporting dinucleating
37,38
free thiolates/thiocarboxylates are relatively less explored
and thus offer an opportunity to explore the synthetic aspects
and reactivity of the later complexes in detail. In this line, we
recently reported the reactivity study of carboxylate bridged
2
6
ligands. While the majority of the ligands used in the
chemistry of dicobalt(II) complexes are pyridine-based,
B
DOI: 10.1021/acs.inorgchem.7b02432
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Article
a
Scheme 2. Schematic Representation for the Synthesis of 1a−10
a
Complex 8b was synthesized using procedure analogous to that shown for 8a but using HN-CH Py-HPTB ligand.
2
diiron(II) complexes (using HN-Et-HPTB) in comparison
Py) in 2:1:2:1 ratio in either DMF (1a, 1c) or MeCN (1b).
Addition of RCOSH (R = Ph, Me) into a solution of 1b
yielded 2a and 2b, respectively. Alternatively, 2a and 2b may
be synthesized directly in a procedure analogous to the
synthesis of 1a and 1b in 54−60% yield. Complexes 4a, 4b,
and 5 could be obtained in 60−70% yield by following a
procedure analogous to that described for 1a and 1b. Direct
synthesis of 3a and 3b, however, may create a selectivity
problem due to the possibility that both the thiolate and the
carboxylate in 4-mercaptobenzoic acid and 3-mercaptopro-
pionic acid, in principle, may bind to the Co(II) centers. This
situation may create the possibility for the formation of three
different species, namely, (i) 3a/3b, (ii) thiolate bridged
dicobalt(II) complex bearing free carboxylic acid, and (iii)
another species where two dicobalt(II) units may be bridged
together by a 4-mercaptobenzoate/3-mercaptopropionate
using both the thiolate and carboxylate functionality as
bridging sites (Figure S1). It is therefore not surprising that
attempted synthesis of 3a/3b following a procedure analogous
to that described for 1a and 1b could not provide 3a/3b as
pure crystalline samples. A similar situation was encountered
39
with their thiolate bridged analogues. In a more recent work,
a thioacetate bridged diiron(II) complex in the HN-Et-HPTB
ligand platform was used by us to synthesize the first example
of a mononitrosyl diiron(II) complex that could mediate the
reduction of NO to N O in relation with flavodiiron nitric
2
4
0
oxide reductases. With these results, we planned to explore
the synthetic aspects for various types of thiolate/thiocarbox-
ylate bridged dicobalt(II) complexes using the HN-Et-HPTB
ligand and study their reactivity in comparison with analogous
carboxylate bridged dicobalt(II) complexes.
Here we report the synthesis and characterization of five
different types of dicobalt(II) complexes (Chart 1) that
contain bridging thiolates (1a, 1b, 1c), bridging thiocarbox-
ylates (2a, 2b), bridging carboxylates (4a, 4b), and bridging
carboxylates with free hydroxy (5) and free thiol groups (3a,
3
b). Solution stability and reactivity of these complexes with
one-electron oxidants and O were explored, which yielded the
2
complexes [Co (N-Et-HPTB)(DMF) ](BF ) (6) (where
2
2
4 3
DMF = dimethylformamide), [Co (N-Et-HPTB)(μ-
2
HNCOCH )](BF ) (7), and [Co (N-Et-HPTB)(μ-O SEt)]-
3
4 2
2
2
(
BF ) (10). Most importantly, detailed investigation of the
4 2
39
by us during the synthesis of analogous diiron(II) complexes,
synthetic strategy for thiolate bridged dicobalt(II) complexes
led to the discovery of a C−S bond cleavage reaction to yield
two unprecedented dicobalt(II) complexes with only one
terminal hydrosulfide, [Co (L)(SH)(H O)](BF ) (L = N-Et-
and the synthetic problem was solved by introducing a
selective proton exchange strategy. Successful synthesis of 3a
and 3b (Scheme 2) thus relied on the possibility that during
the reaction of the thiolate bridged dicobalt(II) complexes
2
2
4 2
1−
1−
HPTB , 8a; N-CH Py-HPTB , 8b), and a related sulfide
2
bridged complex, [Co (N-Et-HPTB)(μ-S)](BF ) (9). The C−
(1a−1c) with a mercaptocarboxylic acid reagent, the μ -SR (R
2
2
4
S bond cleavage reaction was demonstrated by using different
= Ph, Et, Py) group may preferentially accept one proton from
the more acidic carboxylic acid groups rather than from
comparatively less acidic aromatic/aliphatic thiol groups.
Moreover, it is quite likely that a three atom bridge offered
by a carboxylate group may be more stable than a single atom
thiolate bridge. Thus, the proton exchange reaction selectively
afforded 3a and 3b in 63−69% yields. Importance of the
proton exchange reaction was also indicated by the reaction of
the acetate bridged dicobalt(II) complex (4b) with PhCOSH,
t
aliphatic thiolates (NaSR; R = Bu, Et) and dinucleating
3
0
ligands (HN-Et-HPTB and HN-CH Py-HPTB), and a
2
plausible mechanism has been proposed. All of the 16 new
complexes and a new ligand, HN-CH Py-HPTB, were
2
characterized by a combination of single-crystal X-ray structure
determination and/or elemental analysis.
RESULTS AND DISCUSSION
■
General Synthesis. Complexes 1a−1c were synthesized
directly in ∼60% yield (Scheme 2) by the addition of
Co(BF ) ·6H O into a mixture of the dinucleating ligand HN-
which yielded the thiobenzoate bridged dicobalt(II) complex
−
(2a). In this reaction both CH
COO and PhCOS− can
3
potentially offer three atom bridges to the dicobalt(II) unit,
and hence the driving force for the reaction may be related
4
2
2
3
0,39
Et-HPTB,
Et N, and the corresponding NaSR (R = Ph, Et,
3
C
DOI: 10.1021/acs.inorgchem.7b02432
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Article
Figure 1. Molecular structures of selected complexes with 30% probability thermal ellipsoids and partial atom labeling schemes. Hydrogen atoms
are omitted for clarity.
with the lower pK of PhCOSH (pK = 3.61) compared with
the desired complex [Co (N-Et-HPTB)(DMF) ](BF ) (6)
2 2 4 3
a
a
that for CH COOH (pK = 4.76).
(minor product), a major product obtained in this synthetic
3
a
Synthesis of a dicobalt(II) complex without any bridging
procedure was found to be [Co (N-Et-HPTB)(μ-
2
ligand, [Co (N-Et-HPTB)(DMF) ](BF ) (n = 1−4), was
HNCOCH )](BF ) (7). Formation of 7 was also observed
2
n
4 3
3
4 2
initially attempted by addition of Co(BF ) ·6H O into a
during the synthesis of 1a−1c in MeCN. This situation was,
however, avoided by using a slight excess of NaSPh/NaSEt/
NaSPy. To confirm the source of the bridging acetamido
4
2
2
solution of HN-Et-HPTB and Et N with 2:1:2 ratio in MeCN
3
followed by recrystallization from DMF. However, other than
D
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Figure 2. Molecular structures of 8a−10 with 30% probability thermal ellipsoids and partial atom labeling scheme. Except for hydrogen bonds in
a−8b, hydrogen atoms are omitted for clarity.
8
group, isotope labeling experiments by using MeCN and
discussed later in this manuscript. Molecular structures of
selected complexes (1b, 2a, 3a, 4a, 5, and 6) are shown in
Figure 1, while those for 1a, 1c, 2b, 3b, 4b, and 7 are provided
in Figure S3.
CD CN in two independent syntheses of 7 were performed
3
followed by mass spectrometry of the reaction products in each
case. The observed molecular ion peaks with m/z = 448.65 and
4
50.17 corresponding to [Co (N-Et-HPTB)(μ-
C−S Bond Cleavage of Aliphatic Thiolates by
2
2
+
HNCOCH )] (expected m/z = 448.65) and [Co (N-Et-
HPTB)(μ-HNCOCD )] (expected m/z = 450.16), respec-
Dicobalt(II) Complexes. Synthesis and reactivity of thiolate
3
2
2+
−
t
(RS ) bridged diiron(II) complexes with R = Me, Et, Bu, Ph
3
tively, confirmed that the bridging acetamide is indeed
generated from MeCN (Figure S2). Base-catalyzed hydrolysis
of MeCN in the presence of transition metals is well-
documented and has also been reported previously for
in HN-Et-HPTB ligand platform were recently reported by
3
9
us.
However, no account of analogous dicobalt(II)
complexes is known in the literature. Synthesis of a series of
dicobalt(II) complexes analogous to 1a was therefore
attempted with various other bridging thiolates. In the present
3
1,41
iron.
Hydrolysis of nitriles and related species by model
−
cobalt and iron complexes in relevance to nitrile hydratase and
study, on the one hand, use of MeS could not produce
mechanistic studies of such nitrile hydrolysis reaction are
diffraction-quality single crystals. On the other hand, use of
BuS in the synthesis of 1a−1c in MeCN resulted into the
4
2−46
t
−
available in the literature.
Moreover, reactions of
II
II
pyrazolate bridged Co -μ−OH-Co dimers with acetonitrile
isolation of 7. To avoid the formation of 7, the latter reaction
was therefore attempted in DMF. Interestingly enough, the
latter reaction yielded an unexpected dicobalt(II) complex,
[Co (N-Et-HPTB)(SH)(H O)](BF ) (8a), in 57% yield.
to generate bridging acetamidato complexes have been studied
4
7
extensively. These previous reports and the present
observations thus strongly indicate that the bridging acetamido
ligand in 7 might have been generated in situ by the base-
catalyzed partial hydrolysis of MeCN in the presence of
Co(II). Complex 7 was identified only by molecular structure
determination, and no attempt was made to prepare this
compound in pure form. Complex 6 may also be obtained,
although not as an analytically pure sample, by addition of
Co(BF ) ·6H O into a solution of HN-Et-HPTB and Et N in
2
2
4 2
Complex 8a was again isolated in 55% yield when the
synthesis of 1b was attempted in DMF instead of in MeCN.
Formation of 8a, which features a terminal hydrosulfide group
coordinated to one Co(II) center of the dicobalt(II) unit
t
−
(Figure 2), presumably indicates C−S bond cleavage of BuS /
−
EtS . To reproduce this exciting synthetic procedure, a
modified ligand system, HN-CH Py-HPTB, was synthesized
4
2
2
3
2
tetrahydrofuran (THF) (instead of MeCN) with 2:1:2 ratio,
followed by recrystallization from DMF. Complex 6 was finally
obtained as an analytically pure crystalline sample by a
different procedure using (Cp Fe)(BF ) and has been
and characterized (Figure S4). Replacement of HN-Et-HPTB
by HN-CH Py-HPTB in the synthesis of 8a again yielded a
2
dicobalt(II) complex containing one terminal hydrosulfide,
[Co (N-CH Py-HPTB)(SH)(H O)](BF ) (8b) (Figure 2).
2
4
2
2
2
4 2
E
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a
Scheme 3. Set of Reactions Performed to Identify the Roles of a Preformed Dicobalt(II) Unit Identical to 6, Et N and H O in
3
2
the Formation of 8a via C−S Bond Cleavage of NaSEt
a
Or at least very similar.
4
8−53
The cleavage of C−S bonds mediated by cobalt
and other
the importance of H O in the reaction. Reaction of 6 with
2
4
9−51,53−57
transition metals
has been reported in the literature,
NaSEt in the presence of only 5 equiv of H O (and no Et N),
2
3
and in most of the cases the C−S bond of a coordinated ligand
is involved. However, demonstration of C−S bond cleavage of
simple aliphatic thiolates at room temperature (RT) and
utilization of the reaction to synthesize unsymmetrical
dinuclear transition metal complexes with only one terminal
hydrosulfide have never been reported. Isolation of 8a was
initially a fortunate stroke of serendipity during our attempt to
extend the series of thiolate bridged dicobalt(II) complexes.
However, the unique structural motif observed in 8a and 8b
and its facile synthesis successfully established using two
however, could not produce any crystalline material that may
be identified by a single-crystal X-ray structure determination,
thus indicating the importance of Et N in the reaction
3
(Scheme 3, eqn (vii)). In the absence of both Et N and
3
H O, 6 reacts with NaSEt (1:1) in DMF to yield 1b, which,
2
upon further treatment with H O, yielded uncharacterized
2
products (Scheme 3, eqn (iv)). Therefore, considering all of
the above-mentioned experiments (Scheme 3), it may be
concluded that a dinuclear Co(II) complex, identical or at least
very similar to 6, is surely capable of mediating the C−S bond
t
−
−
different thiolates ( BuS , EtS ) in two different ligand systems
cleavage of aliphatic thiolates to yield 8a and that both Et N
3
3
0
(
HN-Et-HPTB and HN-CH Py-HPTB) prompted us to
and H O play major roles in triggering the reaction.
2
2
study the synthetic rationale for the formation of 8a and 8b in
more detail.
Furthermore, it was also observed that 1b itself could not
yield 8a upon treatment with H O and Et N, thus indicating
2
3
The formation of 8a may either have been triggered by
Co(II) salt, such as Co(BF ) ·6H O, in the presence of Et N
that, once bridged, the thiolates may not undergo C−S bond
cleavage reaction anymore.
4
2
2
3
in DMF (without the ligand) or by a preformed dicobalt(II)
unit (similar to 6). To examine these two possibilities, a set of
reactions in different conditions was performed (Scheme 3),
while keeping the crystallization procedures identical to that
Attempted synthesis of 8a in anhydrous conditions using
anhydrous CoCl (along with NaBF ) yielded [Co (N-Et-
2
4
2
HPTB)(μ-S)](BF ) (9) (Scheme 2) in 52% yield. The striking
4
difference between the structural motifs in 8a (one terminal
t
used for 8a. A mixture of Co(BF ) ·6H O, Et N, and NaS Bu
−SH and one H O) compared with 9 (one bridging sulfide)
4
2
2
3
2
in 2:2:1 ratio could not produce any crystalline material that
may be identified by single-crystal X-ray structure determi-
nation (Scheme 3, eqn (ii)). However, addition of a DMF
may be due to the absence of H O in the synthesis of 9.
2
Addition of H O into a solution of 9 in DMF, however, could
2
not yield 8a. This situation indicates that, once bridged, the
solution of HN-Et-HPTB and Et N into a stirred solution of
sulfide cannot be protonated by H O, and hence protonation
of S may precede binding with dicobalt(II) unit. Addition of
3
2
t
2−
Co(BF ) ·6H O, NaS Bu, and Et N in DMF in 1:1:2:1:1 ratio
4
2
2
3
yielded 8a in 60% yield (Scheme 3, eqn (iii)). While these two
a 48% aqueous solution of HBF into a purple colored solution
4
reactions indicate a major role of a preformed dicobalt(II) unit
of 9 in DMF in 1.1:1 ratio resulted into a blue colored solution
instead of the expected pink color of 8a. The absorption
spectroscopic data (Figure S5) obtained for a mixture of 9 in
(
similar to 6) in the reaction under discussion, it cannot rule
out the possible role of Co(II) salts alone to cleave the C−S
bond. Reaction of 6 with NaSEt in the presence of Et N (not
DMF and 48% aqueous HBF in different ratios (1:0.8/1/1.2/
3
4
dried before reaction) in 1:1:1 ratio yielded 8a, although in
1.4) also could not confirm the formation of 8a. However, pink
colored crystals were obtained along with a blue colored oily
mass upon crystallization of the reaction product over 2 d.
Unit-cell determination of the pink crystals confirmed the
formation of 8a. No attempt was made to characterize the blue
oily mass. Therefore, we may conclude that, while 8a may be
obtained upon treatment of 9 with aqueous solution of HBF4,
∼
30% yield (Scheme 3, eqn (v)) compared with 57% yield in
the original synthesis of 8a (Scheme 3, eqn (i)). Use of EtSH
instead of NaSEt in the same reaction allowed the isolation of
8
a in 35% yield. Upon addition of 5 equiv of H O during the
2
reaction with NaSEt (Scheme 3, eqn (vi)), 8a was again
obtained, and the yield was increased to 55%, thus indicating
F
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a
Scheme 4. A Plausible Working Mechanism for the Formation of 8a via C−S Bond Cleavage of Aliphatic Thiolates in the
Presence of H O and Et N
2
3
a
t
−
Shown for BuS .
it may not be the only product formed in this reaction. The
molecular structures of 8a, 8b, and 9 are shown in Figure 2.
To investigate the fate of the alkyl groups of the thiolates
after C−S bond cleavage, diethyl ether was added to a reaction
mixture containing HN-Et-HPTB, Et N, Co(BF ) ·6H O, and
rather than occupying terminal positions at any or both of the
metal centers.
Reaction with One-Electron Oxidants and Intercon-
versions of Selected Complexes. Redox properties of
selected complexes were studied by cyclic voltammetry in
MeCN, and the corresponding cyclic voltammetric traces are
shown in Figures S7−S9. Investigation of the redox properties
of 1a−9 indicates that the oxidations of the Co(II) centers in
all the complexes are irreversible processes and in all the cases
(except for 1c) take place at much higher potentials (>1 V vs
3
4 2
2
t
NaS Bu in DMF to precipitate out the metal-containing
species, and after filtration the filtrate was examined by gas
t
chromatography (GC). Presence of BuOH in the filtrate was
identified by the GC experiments (see Figure S6). It was
further observed that 8a may also be synthesized in
+
comparable yields by using bases other than Et N, such as
Fc/Fc ). Oxidation of the bridging thiolates/thiocarboxylates,
3
t
BuNH (yield of 8a = 58%). The fact that 8a could not be
however, could not be observed. Similar situation was
encountered in the electrochemical behavior of the analogous
2
obtained from 6 in the absence of 1 equiv of a base
t
39
(
Et N/ BuNH ) strongly indicates the important and neces-
diiron(II) complexes, where the oxidation of the bridging
3
2
sary role of Et N as a base in the synthesis of 8a−8b.
thiolates could not be observed as well. However, the bridging
thiolates in the analogous diiron(II) complexes could be
3
Combining these results, a plausible working mechanism for
the formation of 8a may be proposed (Scheme 4). A species
identical (or at least very similar) to “A” may form initially,
oxidized by (Cp
Fe)(BF
) to yield a solvent-coordinated
diiron(II) complex analogous to 6. In a similar way, the
Fe)(BF ) to
2
4
3
9
followed by attack of the coordinated H O to the tertiary
bridging thiolates in 1a−1c were oxidized by (Cp
2
4
2
t
carbon atom (in case of S Bu, shown in Scheme 4) of the
the corresponding disulfides (Figures S10 and S11) along with
thiolate coordinated to the adjacent Co(II) center to yield “B”,
which subsequently may yield BuOH and 8a. Presence of
the formation of presumably a MeCN-coordinated dicobalt(II)
t
3+
complex, [Co
(N-Et-HPTB)(MeCN)
] , which, when crystal-
2
2
Et N may promote activation of the coordinated H O and thus
lized from DMF, yielded 6. In the same line, 2b was found to
yield 6 and (CH COS) (Figure S12) upon treatment with
3
2
may facilitate the attack on the thiolate carbon atom. While
a−8b can only be synthesized in DMF and not in MeCN, the
3
2
1
−
1
8
(Cp Fe)(BF ). The bridging thiolates (R S , R = Ph, Et, Py)
2 4
exact role of DMF in the above transformations cannot be
defined at this stage. However, the failure of the reaction in
MeCN to yield 8a may be due to the fast base-catalyzed partial
hydrolysis of MeCN in the presence of Co(II) to form a
potential bidentate ligand, acetamide, which eventually yields
in 1a−1c may also react with (NO)(BF ) (E = 0.87 V vs
+ 1
4
1/2
Fc/Fc ) in 1:1 ratio to form R SNO in solution, which will
eventually form NO, corresponding disulfides, and 6. Complex
6 may then react with the in situ generated NO (available ratio
= 1:1) to yield nitrosylated products. However, the reaction of
7.
1a−1c with (NO)(BF ) yielded 6 (confirmed by unit-cell
4
Further treatment of 8a with NaSPh and NaSEt, however,
determination). Moreover, no reaction could be observed
could not afford the attempted monothiolato, monohydrosu-
fido dicobalt(II) complex. The products obtained in these
reactions were instead identified as 1a and 1b, respectively.
Such results are not surprising, since, in the case of both
diiron(II) and dicobalt(II) systems (this work), thiolates,
even when used in excess, were always found to form bridges,
upon treatment of 6 with up to 4 equiv of Ph CSNO in DMF.
3
Direct reaction of 6 with excess NO gas was therefore
investigated. In two separate experiments, NO gas was bubbled
in solutions of 6 in MeCN and in CH Cl for 5 min at RT. IR
2
2
3
9
spectroscopic data for the reaction solutions in comparison
with control experiments (Figure S13) indicated nitrosylation
G
DOI: 10.1021/acs.inorgchem.7b02432
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Inorganic Chemistry
Article
−
1
of 6 (νNO = 1712 cm ). Upon crystallization under NO
atmosphere, the product was isolated within 3 d as pink
colored crystalline solid, which, however, upon IR spectro-
scopic measurements (both as KBR pellet and in CH Cl
reports of dioxygen activity for other dicobalt(II) complexes
9
,12,13
are known since long ago.
The dioxygen affinity of
dicobalt(II) complexes is known to be influenced by the ligand
nitrogen atoms and the chelate rings associated with the
2
2
11,63
solution) could not show the presence of any coordinated NO
bridging oxygen.
Nature of the dinucleating ligands is also
(
Figure S14).
known to influence the thermal stability of the μ-peroxo
complexes against irreversible oxidation. An account of
different dioxygen affinity of dicobalt(II) complexes with
various “end-off” compartmental ligands is available in the
Considering the synthesis and one-electron oxidation
reactions of the complexes it becomes apparent that many of
these complexes may undergo interconversions among
themselves. The chemical interconversions of some selected
dicobalt(II) complexes are summarized in Scheme 5. Results of
26
literature. Representative examples of previously reported
dicobalt(II) complexes with less or no dioxygen affinity
2
+
includes [Co (bpmp)(O CCH ) ] , which does not react
2
2
3 2
2
+
Scheme 5. Interconversions of Selected Dicobalt(II)
Complexes Using Substitution and One-Electron Redox
Reactions
with O in MeCN, and [Co (bpep)(O CCH )] (see Scheme
2 2 2 3
1 for bpmp and bpep ligands), which shows no reactivity
2
6
toward O even at −40 °C. The major difference between N-
2
−
Et-HPTB and other ligands in Scheme 1 is the combination
of benzimidazolyl N donors and bridging alkoxide O donor,
−
which are present in N-Et-HPTB , while the rest of the ligand
systems contain different combinations of pyridyl N-donor and
bridging phenolate/alkoxide O-donor sites. These differences in
the ligand systems may therefore be responsible for the
unusual stability of Co(II) centers in dicobalt(II) complexes
(
in the present study) toward molecular oxygen compared
with the highly reactive nature of the dicobalt(II) complexes
reported in the literature.
9
,12−14,26
Thiols are known to be prone toward oxidation by molecular
oxygen to yield the corresponding disulfides, and very often
this reaction can be catalyzed by transition metals.
Representative examples include the oxidation of both
aromatic and aliphatic thiols mediated by Co(II) phthalocya-
6
4
65
VI
nines in ionic liquid, FeCl /NaI in MeCN, [Mo O (O -
3
2
2
2
−
CC(S)Ph ) ] in a Zn(II)−Al(III) layered double hydroxide
2
2
6
6
67
the reactions in each case were confirmed by unit-cell
determination of diffraction-quality single crystals obtained
from the reaction products. These facile interconversions may
indicate synthetic control over a wide variety of new
dicobalt(II) complexes.
host, RhH(PPh ) /1,4-bis(diphenylphosphino)butane,
3 4
68
2− 69
VOCl
[Co(PyPepRS)
bis(triphenylphosphoranylidene)),
,
[Fe
S
2
(SR)
] , (Et ] and Na-
], [PPN][(NO)Fe(S,S−C H ) ] (PPN =
6 4 2
N)[Co(PyPepS)
4 2
3
4
4
4
7
0
7
1
72
cis-Ru(bpy)
[DPPBT = 2-diphenylphosphinoben-
Cl ,
2
2
7
3
[PPN][Ru(DPPBT)
zene thiolate], and a N7 S(thiolate) iron(II) cysteine
4
4
]
3
Reaction with Molecular Oxygen. The oxidation events
70−74
for the Co(II) centers in 1a−5 take place at much higher
dioxygenase model complex. While some of the studies
6
4−69
+
potentials (>1 V vs Fc/Fc ), which indicate their possible
reported the formation of sulfinates, other studies
did not
inertness toward reaction with molecular oxygen at RT. While
all the complexes were initially synthesized under argon
atmosphere, the carboxylate bridged dicobalt(II) complexes,
involve the formation of sulfinic acids/sulfinates as a product.
Moreover, a separate study on the oxidation of thiols by
molecular oxygen reported that the ability of transition metals
to catalyze oxidation of thiols to disulfide in aqueous solutions
4
a, 4b, and 5, as well as the DMF-coordinated dicobalt(II)
75
complex 6 are perfectly stable in air at RT. No change in the
absorption spectroscopic signatures of 6 in DMF could be
changes in the order Co ≪ Ni < Fe < Mn < Cu. Oxidation of
thiols by hydrogen peroxide, however, leads to the formations
76−78
observed upon purging of O at RT. However, there are
of sulfenic, sulfinic, and sulfonic acids.
Other methods for
2
literature reports of air-stable Co(II) complexes that rapidly
the conversion of thiols to sulfinic and sulfonic acids include
7
9
80
react with O at low temperatures to form Co(III)-superoxo
the use of HOF·MeCN complex and Me SO. Oxidation of
2
2
8
,58−62
species.
Therefore, possible reactions of 6 with O at low
n-octyl mercaptan and thiophenol in tert-butanol containing
varying amounts of KO Bu to generate disulfide and/or acids
(sulfinic and sulfonic) is also reported.
2
t
temperatures in different solvents were also investigated using
absorption spectroscopic measurements (Figure S15). A DMF
81
solution of 6 did not react with O at −50 °C upon bubbling of
2
The thiolate bridged complexes 1a and 1b are stable in
solution under inert atmosphere, and no dissociation of the
bridging thiolates could be observed within 2 d. Interestingly,
attempted synthesis of 1b in open air at RT yielded a sulfinate
bridged dicobalt(II) complex, [Co (N-Et-HPTB)(EtSO )]-
2
O for 15 min. No reaction could be observed either when a
solution of 6 in MeCN was allowed to react with O at −35
2
°
C. Similar situations prevailed when in two separate
experiments solutions of 6 in CH Cl and in acetone were
2
2
2
2
allowed to react with O at −80 °C. On the contrary, a recent
(BF ) (10) (Scheme 2) in 33% yield. Cyclic voltammetric
2
4 2
report on reversible O binding in dicobalt(II) complexes
traces of 1b (Figure S7) show that the oxidation events for the
Co(II) centers are irreversible events and take place at
potentials higher than 1 V. Absorption spectroscopic measure-
ments indicated that 1b did not react with oxygen (Figure
S16) either at RT (in DMF) or at low temperatures (in DMF,
2
containing 2,6-bis(N,N-bis(2-pyridylmethyl)-aminomethyl)-4-
tert-butylphenolate ligand (bpdp in Scheme1) has described
the dicobalt(II) complexes as “very air-sensitive pink powders”
14
which “turn brown rapidly on exposure to air”. Similar
H
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Inorganic Chemistry
Article
Table 1. Selected Bond Distances (Å) and Angles (deg) for 1a−4a
complexes
parameters
1a
1b
1c
2a
2b
3a
3b
4a
a
Co−OL
1.923(2)
1.930(2)
1.924(2)
2.410(1)
2.426(1)
1.909(2)
1.913(2)
2.452(1)
2.454(1)
1.962(4)
1.939(4)
2.371(1)
1.986(5)
1.956(5)
2.369(3)
1.950(3)
1.943(3)
1.964(4)
1.960(5)
1.931(3)
1.943(3)
1
.919(2)
2.466(1)
.426(1)
Co−S
2
b
Co−O
1.989(4)
2.018(6)
2.012(4)
2.020(5)
2.004(5)
2.033(5)
2.035(6)
2.279(6)
2.024(6)
2.013(6)
2.298(6)
3.510
2.018(4)
2.026(3)
2.027(5)
2.014(4)
2.250(4)
2.037(4)
2.009(4)
2.277(4)
3.405
2
.012(4)
Co−NL
2.024(3)
2.017(2)
2.027(2)
2.305(2)
2.015(3)
2.030(2)
2.281(2)
3.131
108.6(1)
80.7(1)
83.5 (1)
84.0(1)
2.012(3)
2.012(3)
2.254(3)
2.013(3)
2.009(3)
2.253(3)
3.112
108.9(1)
78.7(1)
84.4(1)
84.5(1)
2.059(5)
2.040(4)
2.274(5)
2.039(4)
2.021(5)
2.228(4)
3.496
2.035(6)
2.036(8)
2.277(7)
2.048(7)
2.036(6)
2.245(7)
3.569
2.051(4)
2.034(4)
2.264(4)
2.034(4)
2.030(4)
2.259(4)
3.406
2
2
2
2
2
.012(3)
.283(3)
.023(3)
.029(3)
.276(3)
Co−Co
3.114
a
Co−OL −Co
108.3(1)
79.1(1)
84.5(1)
127.3(1)
129.7(3)
122.1(1)
126.9(1)
123.1(1)
Co−S−Co
S−Co−OL
a
103.1(1)
104.2(1)
101.0(1)
102.7(2)
8
5.7 (1)
b
a
O −Co−O
100.0(1)
98.2(1)
98.1(1)
100.5(1)
100.0(1)
L
1
01.5(1)
a
b
Deprotonated hydroxyl group from ligand. O atom of thiocarboxylate (2a and 2b) or carboxylate (3a−4a).
−
50 °C; in MeCN, −35 °C; in CH Cl , −80 °C; in acetone,
ethanethiolate to the corresponding sulfinate via the formation
of peroxo dicobalt(III) or related species may possibly be ruled
out. Therefore, it may be concluded that the coordination of
the thiolates with the Co(II) centers must have activated the
2
2
−
80 °C). Synthesis of 10 at −50 °C in open air (yield = 27%)
or use of excess NaSEt (yield = 31%) in the synthesis did not
have any significant effect on the yield of 10. Bubbling of O2
into the reaction mixture during the synthesis of 10 at RT also
could not increase the yield significantly (35%). Addition of
bridged thiolates to undergo a direct reaction with O in the
2
presence of Et N to yield sulfinates at RT.
3
excess Et N increased the yield from 33% to 40%, which may
Molecular Structures. All of the 16 dicobalt(II)
3
be considered only as a nominal increase. Considering the
observations and the inertness of 6 toward dioxygen, the
involvement of Co(II) centers in the oxidation of the bridged
complexes and HN-CH Py-HPTB were characterized by
single-crystal X-ray structure determinations. The molecular
structures for selected dicobalt(II) complexes are shown in
2
Table 2. Selected Bond Distances (Å) and Angles (deg) for 4b−10
complexes
parameters
4b
5
6
7
8a
8b
9
10
a
Co−OL
1.955(4)
1.977(5)
1.978(5)
2.021(5)
2.032(5)
1.983 (4)
1.987(4)
1.977(4)
1.980(4)
2.007(5)
2.020(5)
2.000(5)
2.029(5)
2.000(4)
1.991(4)
2.024(5)
1.908(5)
1.897(4)
1.986(4)
1.990(4)
2.035(5)
2.022(5)
1
.949(4)
1.991(4)
.013(5)
b
c
Co−O
2.033(5)
c
2
2.043(5)
Co−μ-S
HS−OH2
Co−SH
Co−NL
2.456(1)2.455(2)
2.843
2.800
2.318(3)
2.034(6)
2.061(7)
2.263(6)
2.032(7)
2.017(6)
2.248(6)
3.706
2.232(3)
2.060(5)
2.059(5)
2.301(5)
2.031(5)
2.045(5)
2.248(5)
3.648
2.028(5)
2.022(6)
2.042(6)
2.321(6)
2.064(7)
2.044(6)
2.301(6)
3.531
2.041(6)
2.056(6)
2.214(6)
2.012(6)
2.028(5)
2.300(6)
3.637
2.033(5)
2.044(5)
2.306(5)
2.016(6)
2.024(5)
2.286(6)
3.555
2.002(5)
2.005(6)
2.245(5)
1.999(6)
2.009(6)
2.228(6)
3.173
113.0(2)
80.6(1)
82.1(1)
2.028(5)
2.049(6)
2.295(5)
2.058(5)
2.042(5)
2.275(5)
3.607
2
2
2
2
2
.038(5)
.273(5)
.016(5)
.013(5)
.304(5)
Co−Co
3.479
126.0(1)
a
Co−OL −Co
126.4(2)
132.7(2)
127.9(2)
134.4(2)
132.1(2)
130.3(2)
Co−S−Co
S−Co−OL
a
103.9(1)
97.6(2)
104.2(1)
96.8(1)
8
2.4(1)
b
a
c
O −Co−O
99.0(1)
97.8(2)
98.5(2)
108.4(1)
101.1(1)
98.1(1)
99.0(1)
L
c
9
8.0(1)
99.8(1)
a
b
Deprotonated hydroxyl group from ligand. O atom of carboxylate (4b and 5), acetamide (7, Co1−N1 = 2.014(5)), H O (8a, 8b), or sulfinate
2
c
(10). O atom of coordinated DMF.
I
DOI: 10.1021/acs.inorgchem.7b02432
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Inorganic Chemistry
Article
8
4
Figures 1 and 2, while those for the rest of the complexes are
2.383(8) Å ([Co (μ -S) (μ-SH) (μ-PEt )(PHEt ) ]) re-
3 3 2 2 2 2 6
−
II
provided in Figure S3. Molecular structure of H-N-CH Py-
ported for complexes containing bridging HS . The Co −
OH distances of 2.029(5) and 2.024(5) Å in 8a and 8b are
also comparable with previously reported Co −OH bond
distances of 2.073(2), 2.072(1), 2.081(2), and 2.095 (2)
2
HPTB is provided in Figure S3. Selected bond distances and
angles for all the 16 complexes are collected in Tables 1 and 2.
In all the dinuclear complexes, Co(II) centers are five-
coordinate. On the basis of the molecular structures, the
dicobalt(II) complexes may be divided into seven different
types: (i) thiolate bridged complexes (1a−1c), (ii) thiocarbox-
ylate bridged complexes (2a, 2b), (iii) carboxylate bridged
complexes with or without free hydroxyl/thiol groups (3a−5)
and ethanesulfinate bridged complex (10), (iv) DMF-
coordinated complex without any bridging ligand (6), (v)
acetamido bridged complex (7), (vi) complexes featuring one
2
II
2
85
86
87
88
Å. The terminal −SH and H O are engaged in hydrogen
2
bonding (Figure 2) to make a H−S−H−O−H bridge similar
to the few known H−O−H−O−H bridges in aquo-hydroxy
89−93
bridged complexes,
and the corresponding HS···HOH
distances are 1.953(3) (8a) and 1.893(2) Å (8b). The S −
HS
O
distances in 8a and 8b are 2.843 and 2.800 Å,
H2O
respectively, which are smaller than the corresponding van
der Waals distance of 3.32 Å and much larger than the S−O
distances in the thiocarboxylate bridged complexes 2a (2.623
Å) and 2b (2.590 Å). In 8b, the second hydrogen atom of the
terminal water molecule is also engaged in hydrogen bonding
with a DMF molecule, where the HOH···ODMF distance is
1.892(6) Å (Figure 2). It is the hydrogen bonding interaction
terminal hydrosulfide and one terminal H O (8a, 8b) and (vii)
2
sulfide bridged complex (9). In general, two different sets of
Co−N
distances are observed in all the complexes
Tables 1 and 2), of which the Co−benzimidazole nitrogen
N‑Et‑HPTB
(
distances (2.009(3)−2.064(7) Å) are much smaller than the
Co−tertiary amine nitrogen distances (2.214(6)−2.321(6) Å).
The Co−Co distance varies a lot (3.112−3.706 Å) among the
complexes (1a−10) due to the presence (or absence) of
different bridging ligands in different types of dicobalt(II)
complexes. As expected for comparatively more strained
structures, the Co−Co distances in the thiolate bridged
complexes 1a−1c range from 3.112 to 3.131 Å, while for the
sulfide bridged complex 9, the distance is 3.173 Å. These
distances are much smaller than any of the dicobalt(II)
complexes with bidentate bridging ligands presented in this
manuscript. The Co−Co distance increases upon going from
between the −SH and H O that presumably favors the nearly
2
coplanar arrangement of these two terminal ligands in contrast
to the bent arrangement of the coordinated DMF molecules in
6. The two Co(II) centers in 9 are bridged by a sulfide ligand
with Co−μ-S distances of 2.456 (1) and 2.455(2) Å, while the
Co−S−Co angle was found to be 80.6(1)°.
SUMMARY AND CONCLUSIONS
■
Synthesis, molecular structures, and comparative reactivity for
seven different types of nonheme dicobalt(II) complexes have
been investigated using two benzimidazole-based dinucleating
ligands. While analogous nonheme carboxylate bridged
dicobalt(II) complexes are known in the literature, there are
no precedents for the dicobalt(II) complexes that feature
bridging carboxylates containing free thiol/hydroxyl functional
4a (benzoate bridged, 3.405 Å) to 4b (acetate bridged, 3.479
Å) to 5 (γ-hydroxy butyrate bridged, Co−Co 3.531 Å), while
for 7 and 10 the distances are 3.555 and 3.607 Å, respectively.
Complexes 2a, 2b, 3a, and 3b follow a similar trend, where 2a
(
thiobenzoate bridged, Co−Co = 3.496 Å) and 3a (4-
39
groups. Unlike their diiron(II) analogues and other air-
mercaptobenzoate bridged, Co−Co = 3.406 Å) exhibit smaller
Co−Co distances compared with that observed in 2b
9,12−14,26
sensitive dicobalt(II) complexes,
all of the 16
dicobalt(II) complexes presented here are stable in air and
show irreversible oxidation processes at potentials greater than
V. Depending upon the reaction conditions, selected five-
(
thioacetate bridged, Co−Co = 3.569 Å) and 3b (3-
mercaptopropionate bridged, Co−Co = 3.510 Å), respectively.
Complexes 6, 8a, and 8b exhibit much larger Co−Co distances
(
1
coordinate dinuclear cobalt(II) units may take part in (i) C−S
bond cleavage of aliphatic thiolates, (ii) one-electron oxidation
of bridging thiolates to the corresponding disulfides, and (iii)
molecular oxygen mediated oxidation of thiolate to the
corresponding Co(II) bound sulfinate. Most importantly, the
C−S bond cleavage of aliphatic thiolates provides a unique
synthetic strategy for the preparation of unprecedented
dicobalt(II) complexes bearing only one terminal hydrosulfide.
The synthetic strategy has been investigated in detail, and a
plausible mechanism for the above transformation has been
proposed. This new synthetic strategy has been established
with two different thiolates using two different ligand systems
and may be further investigated in future to synthesize similar
complexes with other transition metals, especially iron.
3.637−3.706 Å) than the others due to the absence of any
bridging ligand between the two Co(II) centers in 6, 8a, and
b. These metric parameters are consistent with the Co−O −
8
L
Co angles (Table 1), which are smallest for 1a−1c (108.3(1)−
1
08.9(1)°) and largest for 8a (134.4(2)°). Unlike the
symmetrical carboxylate bridges with nearly equal bond
distances in 3a, 3b, 4a, 4b, and 5, the thiocarboxylate bridges
in 2a and 2b show different C−O (1.262(9) and 1.212(10) Å),
C−S (1.669(9) and 1.665(10) Å), Co−O (1.989(4) and
2
.018(6) Å), and Co−S (2.371(1) and 2.369(3) Å) bond
distances, where the bridging thiocarboxylates retain the C−O
double bond character. The structural motifs in 8a and 8b
exhibit unprecedented features, where one five-coordinate
Co(II) center is coordinated by a terminal hydrosulfide, while
the other five-coordinate Co(II) center is coordinated by a
water molecule. Two Co(II) centers in 8a and 8b are separated
by a distance of 3.706 and 3.648 Å, respectively, while the
EXPERIMENTAL SECTION
■
Preparation of Compounds. All the reactions and manipulations
described in this manuscript were performed under a pure argon
atmosphere using either standard Schlenk techniques or an inert
atmosphere glovebox, unless otherwise mentioned. Solvents were
corresponding Co1−O1−Co2 angles are 134.4(2) and
II
1
(
32.1(2)°, respectively. The Co −SH distances of 2.318(3)
8a) and 2.232 (3) Å (8b) are comparable with Co−SH
distance of 2.2398(13) Å reported for a mononuclear Co(II)
complex containing terminal SH, namely, [Co-
C H N) (SH) ], and Co−SH bond distances of 2.292−
.303 Å ([{Co(μ-SH)(cyclam)} ][SH]2 and 2.343(8)−
94
dried following literature procedures. All the filtrations were
performed through diatomaceous earth, and solvent removal steps
were performed in vacuo inside an inert atmosphere glovebox. Yields
reported in each case are for recrystallized compounds and are average
of individual yields obtained from multiple (at least three) batches of
82
(
2
9
7
2
2
83
2
J
DOI: 10.1021/acs.inorgchem.7b02432
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
reactions. All the yields are calculated using corresponding molecular
residue was extracted with 2 mL of DMF and filtered, and the filtrate
weights of the compounds shown in Tables S1−S3. HN-Et-
was diffused overnight with Et O at −35 °C and allowed to stand for
2
30,39
30
HPTB
was synthesized following a reported procedure. HN-
1 d at RT to afford the product as a pink crystalline solid (53 mg,
58%). Anal. Calcd for C H N B F Co S O (1b): C, 50.30; H,
CH Py-HPTB was synthesized by a procedure analogous to that used
2
45 54 10
2
8
2
1
1
t
for HN-Et-HPTB. Co(BF ) ·6H O (99%), NaSEt (90%), NaS Bu
5.07; N, 13.04. Found: C, 50.25; H, 4.94; N, 13.26%. UV−Vis (in
4
2
2
−1 −1
(
(
90%), 4-mercaptobenzoic acid (90%), 3-mercaptopropionic acid
99%), thioacetic acid (96%), thiobenzoic acid (90%), sodium
MeCN) λ nm (ε M cm ): 529 (330 ± 10), 770 (60 ± 4).
[Co (N-Et-HPTB)(μ-SPy)](BF ) (1c). To a mixture of HN-Et-HPTB
2
4 2
benzoate (99%), ferrocene (98%), ferrocenium tetrafluoroborate
technical grade), (NO)(BF ) (95%), and tetra-n-butylammonium
(0.08 mmol, 57.8 mg), Et N (0.16 mmol, 16.2 mg), and 4-
mercaptopyridine (0.085 mmol, 9.45 mg) in 2 mL of DMF was
3
(
4
hexafluorophosphate (98%) were obtained commercially and used
without further purifications. Identity of all the 16 compounds in
added Co(BF ) ·6H O (0.16 mmol, 54.5 mg) with stirring, and the
4
2
2
resultant slurry was stirred for 4 h. The reaction mixture was filtered,
Chart 1 along with HN-CH Py-HPTB was confirmed by molecular
and the dark red colored filtrate was diffused overnight with Et O at
2
2
structure determinations, and bulk purity was confirmed (except for
−35 °C and allowed to stand for 1 d at RT to afford the product as a
dark pink crystalline solid (50 mg, 55%). UV−Vis (in MeCN) λ nm
1
c and 9) by elemental analysis.
−
1
−1
N,N,N′,N′-Tetrakis(2-(1-picolylbenzimidazolyl))-2-hydroxy-1,3-
(ε M cm ): 349 (5650 ± 190), 520 (400 ± 20), 573 (170 ± 5),
780 (60 ± 4). Reasonable elemental analysis data could not be
obtained for this compound.
diaminipropane (HN-CH Py-HPTB). 1,2-Diaminobenzene (5.25 g,
2
0
2
.048 mol) was ground to a fine powder and thoroughly mixed with
-hydroxy-1,3-diaminopropanetetraacetic acid (2.5 g, 0.008 mol). The
[Co (N-Et-HPTB)(μ-SCOC H )](BF ) (2a). To a mixture of HN-Et-
2
6
5
4 2
solid mixture was heated at 170−180 °C for 1.5 h, at which stage
effervescence had ceased. After the mixture was cooled to RT, the
resulting red glass was taken up in 4 M HCl (total 150 mL) by using
small portions each time to yield a bluish-gray precipitate. After the
solution was filtered, the bluish-gray precipitate was washed by
slurrying in acetone multiple times. The precipitate was then dissolved
in water, and dilute ammonia was used to neutralize the solution. The
off-white precipitate thus formed was collected, recrystallized from
acetone, ground to a fine powder, and dried under vacuum to yield
the precipitate as off-white fine dust (4.5 g, 94%).
HPTB (0.08 mmol, 57.8 mg) and triethyl amine (0.16 mmol, 16.2
mg) in 4 mL of MeCN was added a solution of Co(BF ) ·6H O (0.16
4
2
2
mmol, 54.5 mg) in 2 mL of MeCN with stirring. After 15 min, a
suspension of C H COSH (0.085 mmol, 11.75 mg) in 2 mL of
6
5
MeCN was added, and the resultant slurry was stirred for 4 h. The
reaction mixture was filtered, and the reddish-pink colored filtrate was
evaporated to dryness. The residue was extracted with 2 mL of DMF
and filtered, and the filtrate was diffused overnight with Et O at −35
2
°C and allowed to stand for 1 d at RT to afford the product as a dark
pink crystalline solid (50 mg, 54%). Anal. Calcd for
C H B F Co N O S (2a): C, 52.19; H, 4.73; N, 12.17. Found:
A portion of this off-white solid (1.73 g, 0.0029 mol) was
suspended in dry tetrahydrofuran (30 mL) and stirred with NaOH
5
0
54
2
8
2
10
2 1
−
1
C, 51.86; H, 4.52; N, 12.16%. UV−Vis (in MeCN) λ nm (ε M
cm ): 533 (380 ± 8).
[Co (N-Et-HPTB)(μ-SCOCH )](BF ) (2b). To a mixture of HN-Et-
−
1
(0.93 g) overnight. 2-(Chloromethyl) pyridine hydrochloride (1.9 g)
was then added, and the resulting solution was stirred for 2 d. The
solvents were then stripped to dryness, and the resulting solid powder
was dissolved in chloroform. The chloroform solution was filtered to
remove insoluble NaCl, and the filtrate was stripped to a very small
volume. Acetone was added into the solution, and the resulting
solution was kept standing for 30 min to yield white powder of HN-
2
3
4 2
HPTB (0.08 mmol, 57.8 mg) and Et N (0.16 mmol, 16.2 mg) in 4
3
mL of MeCN was added a solution of Co(BF ) ·6H O (0.16 mmol,
4
2
2
54.5 mg) in 2 mL of MeCN with stirring. After 15 min, a suspension
of CH COSH (0.085 mmol, 6.46 mg) in 2 mL of MeCN was added,
3
and the resultant slurry was stirred for 4 h. The reaction mixture was
filtered, and the reddish-pink colored filtrate was evaporated to
dryness. The residue was extracted with 2 mL of DMF and filtered,
1
CH Py-HPTB (1.18 g, 42%). H NMR (300 MHz, CDCl ) δ 8.21−
2
3
8
.20 (d, J = 3 Hz, 4H), 7.63−7.60 (dd, J = 3 Hz, 4H), 7.24−7.08 (m,
6H), 6.95−6.91 (q, J = 6 Hz, 4H), 6.57−6.54 (d, J = 9 Hz, 4H), 6.41
1
(
and the filtrate was diffused overnight with Et O at −35 °C and
2
s, 1H) 5.36−5.21 (q, J = 15 Hz, 8H), 4.18−4.13 (d, J = 15 Hz, 4H),
allowed to stand for 1 d at RT to afford the product as a dark pink
crystalline solid (53 mg, 61%). Anal. Calcd for-
C H B F Co N O S (2b): C, 49.65; H, 4.81; N, 12.87. Found:
3
2
1
1
.98−3.93 (d, J = 15 Hz, 4H), 2.84−2.77 (q, J = 6 Hz, 2H), 2.57−
1
3
.52 (dd, J = 3 Hz, 2H). C NMR (75 MHz, CDCl ) 155.69, 151.96,
3
45 52
2
8
2
10
2 1
−
1
49.54, 142.33, 136.83, 135.68, 122.90, 122.54, 122.21, 120.86,
19.78, 110.05, 67.96, 59.87, 52.48, 48.54. Time-of-flight mass
spectrometry (TOF-MS) (+) m/z calcd for C H N O ([M +
C, 49.45; H, 5.01; N, 12.58%. UV−Vis (in MeCN) λ nm (ε M
−1
cm ): 537 (450 ± 12), 758 (80 ± 2).
[Co (N-Et-HPTB)(μ-O CC H SH)](BF ) (3a). To a pink colored
+
5
9
54 14
2
2
6
4
4 2
+
+
H] ) = 975.4678, ([M + Na] ) = 997.4498; found 975.1154,
97.1203. Identity of HN-CH Py-HPTB was further confirmed by a
solution of 1b (0.1 mmol, 107 mg) in 5 mL of MeCN was added a
suspension of 4-mercaptobenzoic acid (0.1 mmol, 17.1 mg) in 2 mL
of MeCN with stirring, and the reaction mixture was stirred for 4 h.
The resulting pink solution was evaporated to dryness. The residue
was extracted with 2 mL of DMF and filtered, and the filtrate was
9
2
single-crystal X-ray structure determination (Figure S3). Colorless
block-shaped crystals, suitable for single-crystal X-ray diffraction
study, were obtained by keeping a concentrated methanol solution of
HN-CH Py-HPTB at 0 °C for 2 d.
diffused overnight with Et O at −35 °C and allowed to stand for 1 d
2
2
[
Co (N-Et-HPTB)(μ-SPh)](BF ) (1a). To a mixture of HN-Et-HPTB
at RT to afford the product as a pink colored crystalline solid (80 mg,
69%). Anal. Calcd for C H N O B F S Co (3a·Et O): C, 52.28;
2
4 2
(
(
(
0.08 mmol, 57.8 mg), Et N (0.16 mmol, 16.2 mg), and NaSPh
0.085 mmol, 11.2 mg) in 2 mL of DMF was added Co(BF ) ·6H O
0.16 mmol, 54.5 mg) with stirring, and the resultant slurry was
3
50 54 10
3
2
8
1
2
2
H, 5.20; N, 11.29. Found: C, 52.26; H, 5.39; N, 11.60%. UV−Vis (in
4
2
2
−1 −1
MeCN) λ nm (ε M cm ): 535 (375 ± 35), 775 (50 ± 4).
[Co (N-Et-HPTB)(μ-O CC H SH)](BF ) (3b). To a pink colored
stirred for 4 h. The reaction mixture was filtered, and the dark pink
2
2
3
4
4 2
colored filtrate was diffused overnight with Et O at −35 °C and
solution of 1b (0.1 mmol, 107 mg) in 5 mL of MeCN was added a
suspension of 3-mercaptopropionic acid (0.1 mmol, 10.61 mg) in 2
mL of MeCN with stirring, and the reaction mixture was stirred for 4
h. The resulting pink solution was evaporated to dryness. The residue
was extracted with 2 mL of DMF and filtered, and the filtrate was
2
allowed to stand for 1 d at RT to afford the product as a dark pink
crystalline solid (58 mg, 60%). Anal. Calcd for
C H B F Co N O S (1a·H O): C, 51.60; H, 4.95; N, 12.28.
49
54
2
8
2
10
1
1
2
Found: C, 51.49; H, 5.09; N, 12.78%. UV−Vis (in MeCN) λ nm (ε
−
1
−1
M
cm ): 345 (360 ± 30), 527 (460 ± 20), 780 (90 ± 4).
Co (N-Et-HPTB)(μ-SEt)](BF ) (1b). To a mixture of HN-Et-HPTB
diffused overnight with Et O at −35 °C and allowed to stand for 1 d
2
[
at RT to afford the product as a pink colored crystalline solid (71 mg,
63%). Anal. Calcd for C H N O B F S Co (3b): C, 49.39; H,
2
4 2
(
0.08 mmol, 57.8 mg) and Et N (0.16 mmol, 16.2 mg) in 4 mL of
3
46 54 10
3
2
8
1
2
MeCN was added a solution of Co(BF ) ·6H O (0.16 mmol, 54.5
4.87; N, 12.52. Found: C, 49.49; H, 4.85; N, 12.18%. UV−Vis (in
4
2
2
−1 −1
mg) in 2 mL of MeCN with stirring. After 15 min, a suspension of
NaSEt (0.085 mmol, 7.9 mg) in 2 mL of MeCN was added, and the
resultant slurry was stirred for 4 h. The reaction mixture was filtered,
and the dark pink colored filtrate was evaporated to dryness. The
MeCN) λ nm (ε M cm ): 527 (380 ± 10), 760 (80 ± 5).
[Co (N-Et-HPTB)(μ-COOC H )](BF ) (4a). To a mixture of HN-Et-
2
6
5
4 2
HPTB (0.08 mmol, 57.8 mg) and triethylamine (0.16 mmol, 16.2
mg) in 4 mL of MeCN was added a solution of Co(BF ) ·6H O (0.16
4
2
2
K
DOI: 10.1021/acs.inorgchem.7b02432
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
mmol, 54.5 mg) in 2 mL of MeCN with stirring. After 15 min, a
suspension of C H COONa (0.085 mmol, 12.24 mg) in 2 mL of
MeCN was added, and the resultant slurry was stirred for 4 h. The
reaction mixture was filtered, and the pink colored filtrate was
evaporated to dryness. The residue was extracted with 2 mL of DMF
C H B F N S O Co ·2H O (8b·2H O): C, 52.38; H, 4.47; N,
5
9
56
2
8
14
1
2
2
2
2
14.5. Found: C, 52.47; H, 4.74; N, 14.28%. UV−Vis (in MeCN) λ nm
6
5
−
1
−1
(ε M cm ): 527 (322 ± 15), 775 (90 ± 3).
[Co (N-Et-HPTB)(μ-S)](BF ) (9). To a mixture of HN-Et-HPTB
2
4
(0.05 mmol, 36 mg), Et N (0.075 mmol, 7.6 mg), NaBF (0.10 mmol,
3
4
t
and filtered, and the filtrate was diffused overnight with Et O at −35
10.93 mg), and NaS Bu (0.075 mmol, 8.4 mg) in 2 mL of DMF was
2
°C and allowed to stand for 1 d at RT to afford the product as pale
added anhydrous CoCl (0.10 mmol, 12.9 mg) with stirring, and the
2
pink crystalline solid (55 mg, 60%). Anal. Calcd for
C H B Co F N O (4a): C, 52.93; H, 4.80; N, 12.35. Found: C,
resultant slurry was stirred for 4 h. The reaction mixture was filtered,
and the purple colored filtrate was allowed to diffuse overnight with
5
0
54
2
2
8
10
3
−
1
−1
5
5
2.42; H, 4.47; N, 12.17%. UV−Vis (in MeCN) λ nm (ε M cm ):
31 (385 ± 30), 770 (60 ± 2).
Et O at −35 °C and allowed to stand for 1 d at RT to afford the
2
product as purple crystalline solid (30 mg, 52%). UV−Vis (in MeCN)
[Co (N-Et-HPTB)(μ-COOCH )](BF ) (4b). To a mixture of HN-Et-
−1
−1
2
3
4 2
λ nm (ε M cm ): 537 (270 ± 15), 695 (46 ± 3), 820 (60 ± 2).
Reasonable elemental analysis data could not be obtained for this
compound.
HPTB (0.08 mmol, 57.8 mg) and triethylamine (0.16 mmol, 16.2
mg) in 4 mL of MeCN was added a solution of Co(BF ) ·6H O (0.16
4
2
2
mmol, 54.5 mg) in 2 mL of MeCN with stirring. After 15 min, a
[
Co (N-Et-HPTB)(μ-O SEt)](BF ) (10). To a mixture of HN-Et-
2 2 4 2
suspension of CH COONa (0.085 mmol, 6.97 mg) in 2 mL of MeCN
3
HPTB (0.08 mmol, 57.8 mg) and Et N (0.16 mmol, 16.2 mg) in 4
3
was added, and the resultant slurry was stirred for 4 h. The reaction
mixture was filtered, and the pink colored filtrate was evaporated to
dryness. The residue was extracted with 2 mL of DMF and filtered,
mL of MeCN was added a solution of Co(BF ) ·6H O (0.16 mmol,
4
2
2
54.5 mg) in 2 mL of MeCN with stirring in open air. After 15 min, a
suspension of NaSEt (0.085 mmol, 7.9 mg) in 2 mL of MeCN was
added, and the resultant slurry was stirred for 4 h. The reaction
mixture was filtered, and the dark pink colored filtrate was evaporated
to dryness. The residue was extracted with 2 mL of DMF and filtered.
and the filtrate was diffused overnight with Et O at −35 °C and
2
allowed to stand for 1 d at RT to afford the product as pale pink
crystalline solid (60 mg, 70%). Anal. Calcd for C H B Co F N O
4
5
52
2
2
8
10
3
(
5
±
4b·0.5 C H NO): C, 50.36; H, 5.04; N, 13.26. Found: C, 50.26; H,
3 7
1
−
−1
The filtrate was diffused overnight with Et O at 0 °C and allowed to
2
.32; N, 12.98%. UV−Vis (in MeCN) λ nm (ε M cm ): 525 (210
10), 770 (36 ± 2).
Co (N-Et-HPTB)(μ-O CCH CH CH OH)](BF ) (5). To a mixture of
stand for 2 d at RT to afford the product as a pink crystalline solid (29
mg, 33%). Anal. Calcd for C H N B F Co S O (10·H O): C,
[
45 54 10
2
8
2
1
3
2
2
2
2
2
2
4 2
4
8.06; H, 5.02; N, 12.46. Found: C, 48.0; H, 4.97; N, 12.41%. UV−
HN-Et-HPTB (0.08 mmol, 57.8 mg) and Et N (0.16 mmol,16.2 mg)
3
−1 −1
Vis (in MeCN) λ nm (ε M cm ): 530 (360 ± 20), 778 (60 ± 2).
General Physical Methods. A PerkinElmer 2400 series II CHNS
analyzer was used for the elemental analysis. Electrochemical studies
in 4 mL of MeCN was added a solution of Co(BF ) ·6H O (0.16
4
2
2
mmol, 54.5 mg) in 2 mL of MeCN with stirring. After 15 min, a
suspension of sodium γ-hydroxybutyrate (0.085 mmol, 10.7 mg) in 2
mL of MeCN was added, and the resultant slurry was stirred for 4 h.
The reaction mixture was filtered, and the pink colored filtrate was
evaporated to dryness. The residue was extracted with 2 mL of DMF
−
3
of the dicobalt(II) complexes (1 × 10 M in MeCN) were
performed using a CHI620E electrochemical analyzer (CH Instru-
ments, USA). A three-electrode setup comprising a glassy carbon
working electrode, a platinum wire auxiliary electrode, and a silver
wire as the pseudo reference electrode was employed for the study.
Tetra-n-butylammonium hexafluorophosphate (0.1 M) was the
supporting electrolyte of choice. Electrochemical potentials for all
the complexes are referenced to the ferrocene/ferrocenium couple at
0.0 V. Gas chromatography Agilent 7890B equipped with a packed
column (Agilent J & W GC columns) and a 5977A MS detector was
used for identification of the disulfides.
and filtered, and the filtrate was diffused overnight with Et O at −35
2
°
C and allowed to stand for 1 d at RT to afford the product as pink
colored crystalline solid (53 mg, 59%). Anal. Calcd for
C H N O B F Co (5·H O): C, 49.76; H, 5.15; N, 12.35.
4
7
56 10
4
2
8
2
2
Found: C, 49.60; H, 5.34, N, 12.02%. UV−Vis (in MeCN) λ nm
−
1
−1
(
ε M cm ): 527 (365 ± 10), 775 (65 ± 2).
[
Co (N-Et-HPTB)(DMF) ](BF ) (6). To a pink colored solution of
2
2
4 3
1a (0.04 mmol, 44.9 mg) in 5 mL of MeCN was added ferrocenium
tetrafluoroborate (0.06 mmol, 16.4 mg) in 2 mL of MeCN with
stirring, and the reaction mixture was stirred for 4 h. The resulting
purple solution was evaporated to dryness. The residue was washed
several times with THF and dried. The residue was then extracted
with 2 mL of DMF and filtered, and the filtrate was allowed to diffuse
X-ray Structure Determinations. The molecular structures of all
the complexes 1a−10 in Chart 1 and HN-CH Py-HPTB were
2
determined. Diffraction-quality crystals were obtained as described in
the respective syntheses. Single crystals coated with mineral oil were
mounted under a 150 K nitrogen cold stream. Data were collected
either at 150 K on a Bruker SMART APEX-II diffractometer with
graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å)
controlled by the APEX 2 (v. 2010.1−2) software package (1a−7,
overnight with Et O at −35 °C followed by 1 d at RT to afford the
2
product as pink colored crystalline solid (30.5 mg, 65%). Anal. Calcd
for C H B F Co N O (6): C, 47.22; H, 5.09; N, 13.49. Found:
4
9
63
3
12
2
12
3
−
1
C, 47.11; H, 4.96; N, 13.04%. UV Vis (in MeCN) λ nm (ε M
1
0 and HN-CH Py-HPTB) or at 100 K (8b and 9) on a Bruker
−
1
2
cm ): 518 (300 ± 10), 742 (40 ± 2).
D8VENTURE Microfocus diffractometer equipped with PHOTON
II Detector, with Mo Kα radiation (λ = 0.710 73 Å), controlled by the
APEX3 (v2017.3−0) software package. Raw data were integrated and
corrected for Lorentz and polarization effects using the Bruker APEX
[
Co (N-Et-HPTB)(SH)(H O)](BF ) (8a). To a mixture of HN-Et-
2
2
4 2
HPTB (0.08 mmol, 57.8 mg), Et N (0.16 mmol, 16.2 mg), and
3
t
NaS Bu (0.085 mmol, 9.5 mg) in 2 mL of DMF was added Co(BF ) ·
H O (0.16 mmol, 54.5 mg) with stirring, and the resultant slurry was
4
2
6
2
95
II /APEX III program suite. Absorption corrections were performed
stirred for 4 h. The reaction mixture was filtered, and the pink colored
using SADABS. Space groups were assigned by analysis of metric
symmetry and systematic absences (determined by XPREP) and were
filtrate was allowed to diffuse overnight with Et O at −35 °C and
2
allowed to stand for 1 d at RT to afford the product as a pink
crystalline solid (49 mg, 57%). Anal. Calcd for
C H B F N S O Co (8a·C H NO): C, 48.57; H, 5.23; N, 13.54.
96,97
further checked by PLATON
for additional symmetry. All the
structures were solved by direct methods and were refined against all
43
52
2
8
10
1
2
2
3
7
2
data in the reported 2θ ranges by full-matrix least-squares on F with
Found: C, 48.70; H, 5.26; N, 13.54%. UV−Vis (in MeCN) λ nm (ε
9
8
99
−
1
−1
the SHELXL program suite using the OLEX 2 interface.
Hydrogen atoms at idealized positions were included during the
final refinements of each structure. The OLEX 2 interface was used
for structure visualization, analysis of bond distances and angles, and
M
cm ): 531 (270 ± 2), 800 (45 ± 2).
Co (N-CH Py-HPTB)(SH)(H O)](BF ) (8b). To a mixture of HN-
[
2
2
2
4 2
CH Py-HPTB (0.06 mmol, 60 mg), Et N (0.12 mmol, 12.5 mg), and
2
3
t
NaS Bu (0.085 mmol, 9.5 mg) in 2 mL of DMF was added Co(BF ) ·
4
2
100,101
6
H O (0.12 mmol, 40.8 mg) with stirring, and the resultant slurry was
drawing ORTEP
plots. Crystallographic data and final agree-
2
stirred for 4 h. The reaction mixture was filtered, and the pink colored
ment factors for the 17 compounds (CCDC Nos. 1556873−1556886,
1573986, 1573990, and 1573991) are provided in Tables S1−S3.
Refinement details and relevant explanations (wherever applicable)
are included in the individual CIFs.
filtrate was allowed to diffuse overnight with Et O at −35 °C and
2
allowed to stand for 1 d at RT to afford the product as pink colored
crystalline solid (45 mg, 57%). Anal. Calcd for
L
DOI: 10.1021/acs.inorgchem.7b02432
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Cobalt−Alkynyl Complexes. J. Am. Chem. Soc. 2004, 126, 2515−
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02432.
■
2525.
*
S
(9) Suzuki, M.; Kanatomi, H.; Murase, I. Synthesis and Properties of
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Pyridylmethyl)Aminomethyl −4-Methylphenol. Chem. Lett. 1981,
10, 1745−1748.
(10) Suzuki, M.; Kanatomi, H.; Murase, I. Dinuclear Cobalt(II)
Cyclic voltammetric traces, GCMS data, molecular
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data, and final agreement factors for the compounds
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CCDC 1556873−1556886, 1573986, and 1573990−1573991
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.ca-
m.ac.uk/data_request/cif, or by emailing data_request@ccdc.
cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
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(2,6-
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AUTHOR INFORMATION
14) Vad, M. S.; Johansson, F. B.; Seidler-Egdal, R. K.; McGrady, J.
■
E.; Novikov, S. M.; Bozhevolnyi, S. I.; Bond, A. D.; McKenzie, C. J.
Corresponding Author
E-mail: icam@iacs.res.in.
Tuning affinity and reversibility for O binding in dinuclear Co(II)
*
2
complexes. Dalton Trans. 2013, 42, 9921−9929.
ORCID
(15) Chaudhuri, P.; Querbach, J.; Wieghardt, K.; Nuber, B.; Weiss, J.
Amit Majumdar: 0000-0003-0522-8533
Notes
The authors declare no competing financial interest.
Synthesis, electrochemistry, and magnetic properties of binuclear
n+
cobalt complexes containing the Co (μ-X)(μ-carboxylato) core (X
2
2
II
=
OH, Cl, or Br; n= 1−3). The crystal structures of [Co (μ-
ClH CCO ) (μ-Cl)L ]PF and [Co Co (μ-MeCO ) (μ-OH)L ]-
2
II III
2
2
2
2
6
2
2
2
[
ClO ] ·0.5H O (L = N,N′,N″-trimethyl-1,4,7-triazacyclononane). J.
4
2
2
ACKNOWLEDGMENTS
This work was supported by Grant Nos. SB/S1/IC-43/2013
SERB, DST, India) and 01(2804)/14/EMR-II (CSIR, India).
M.J. acknowledges CSIR, India, for a senior research
fellowship. M.J. acknowledges Ms. M. Mukherjee and Md. E.
Ahmed of Dr. A. Dey research group at IACS for help with the
GC and solution IR experiments, respectively. The authors
sincerely thank the anonymous reviewers for their valuable
suggestions during the revision stage.
■
(
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