Synthesis, characterization and structure-property relationship studies of cobaloximes with dithienylglyoxime as the equatorial ligand

Article abstract of DOI:10.1016/j.jorganchem.2011.08.035

The synthesis of cobaloximes, X/RCo(dThgH)₂Py (X = Cl, R = Me, Et, n-Pr, n-Bu and Bn) has been described. All the complexes have been characterized by elemental analyses and NMR spectral studies. The molecular structures of ClCo(dThgH)₂

Full text of DOI:10.1016/j.jorganchem.2011.08.035

Journal of Organometallic Chemistry 696 (2011) 3785e3791
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and structureeproperty relationship studies
of cobaloximes with dithienylglyoxime as the equatorial ligand
1
*
Kamlesh Kumar , Bhagwan D. Gupta
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of cobaloximes, X/RCo(dThgH)2Py (X ¼ Cl, R ¼ Me, Et, n-Pr, n-Bu and Bn) has been
described. All the complexes have been characterized by elemental analyses and NMR spectral studies.
The molecular structures of ClCo(dThgH)2Py, MeCo(dThgH)2Py, EtCo(dThgH)2Py and BnCo(dThgH)2Py
complexes are determined by X-ray crystallography. The electron withdrawing nature of 2-thienyl ring
affects the NMR as well as electrochemical behavior of these complexes. The electrochemical reduction
from Co(III) to Co(II) and from Co(II) to Co(I) are much easier in ClCo(dThgH)2Py as compared to
chlorocobaloximes with the other dioximes (gH, dmgH, dpgH, dmestgH). The molecular oxygen insertion
in the CoꢀC bond of benzyl complex (6) has been examined and a comparison of its reaction rate with
other similar cobaloximes is discussed. The structural features of a dioxy complex Bn(O2)Co(dThgH)2Py
(7) have also been reported.
Received 30 July 2011
Received in revised form
24 August 2011
Accepted 25 August 2011
Keywords:
Dithienylglyoxime
Cobaloxime
Cisetrans influence
Oxygen insertion
Electrochemistry
Structure elucidation
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
The recent works on organocobaloximes with different diox-
imes have shown that the effect of dioxime on the CoꢀC bond (cis
The spectral and structural properties of organocobaloximes2
have been extensively studied and reviewed [1e5] over the past
four decades ever since these have been proposed as structural and
functional model of vitamin B12 by G. N. Schrauzer [6e8]. These
complexes have established an independent research field by itself
due to their use as catalysts in chemical reactions [9,10] and as
templates in organic syntheses [11e19]. However, the main interest
remains in their role as models of vitamin B12 coenzyme because
the studies with cobaloximes have helped to understand the
chemistry and biochemistry of B12 coenzyme [20e22].
It is well known that cleavage of CoꢀC bond is a necessary step
in B12-dependent enzymatic as well as cobaloxime-mediated
reactions [1,3,11e19]. The weakening of CoꢀC bond in organo-
cobaloximes has been interpreted as a function of steric as well as
electronic properties of R, L, and B ligands [1e3,23,24].
influence) far exceeds the trans influence of the axial base [25e32].
A slight variation in equatorial ligand results in significant change
in CoꢀC bond stability/reactivity as well as NMR chemical shifts.
Hence, there has been considerable interest in the synthesis and
structural characterization of organocobaloximes with modified
equatorial dioxime and also study the structureeproperty rela-
tionship in these complexes.
Keeping the above in view, we have synthesized and charac-
terized a series of X/RCo(dThgH)2Py (X ¼ Cl, R ¼ Me, Et, n-Pr, n-Bu
and Bn, 1e6) with dithienylglyoxime (dThgH) as an equatorial
ligand (Scheme 1). All these complexes are new and have been
reported for the first time. The molecular structures of 1, 2, 3 and 6
have been determined by X-ray crystallography. In addition, we
have also studied CoꢀC bond reactivity in benzyl complex (6) with
molecular oxygen under photolytic condition. The insertion of
molecular oxygen in CoꢀC bond of complex 6 has resulted in the
dioxy complex, Bn(O2)Co(dThgH)2Py (7). The structural features of
oxygen inserted cobaloxime (7) are also reported.
* Corresponding author. Tel.: þ91 512 2597730; fax: þ91 512 2597436.
E-mail address: kamlesh@iitk.ac.in (K. Kumar).
1
2. Results and discussion
Prof. Bhagwan D. Gupta deceased on 31 March 2011.
Organocobaloximes have the general formula RCo(L)2B, where R is an organic
2
group
s-bonded to cobalt. B is an axial base trans to the organic group and L is
2.1. Synthesis of dithienylglyoxime and cobaloximes (1e7)
a
monoanionic dioxime e.g. glyoxime (gH), dimethylglyoxime (dmgH), 1,2-
cyclohexanedione dioxime (chgH), diphenylglyoxime (dpgH), dimesitylglyoxime
(dmestgH), bis(thiophenyl)glyoxime (dSPhgH) and bis(phenylselanyl)glyoxime
(dSePhgH).
Dithienylglyoxime (dThgH2) was synthesized from (2-thienyl)
MgBr and dichloroglyoxime following the procedure developed for
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.035

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K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3785e3791
complexes with other dioximes and follows the order
dThgH > dmestgH > dpgH > dmgH (Table S2).
Cl
Cl
N
N
N
N
CoCl2•6H2O
THF(dry)
N2
OH
OH
S
S
OH
OH
ClCo(dThgH)2Py
+
MgBr
S
Py, O2
EtOH
The chemical shift of Pya protons is affected not only by the trans
effect of the R/X group but also by the ring current in the metallabi-
cycle. The Pya shows adownfield shiftof0.07e0.14 ppm in2e6 and an
upfield shift of 0.14 ppm in 1 as compared to the unligated pyridine
(Table S3). This is due to the trans effect that works differently in
inorganic and organic cobaloximes as shown recently [38]. The cis
influence of the dioxime ligand on pyridine is observed by comparing
the coordination shift of pyridine protons (Dd1H), keeping the same R/
X but changing the equatorial ligand. A comparison of the Dd1H(Pya)
values in 1e6 with the values in other cobaloximes, RCo(dioxime)2Py,
gives the order dmestgH > dpgH > dThgH > gH z dmgH z chgH
(Table S3).
1
Dithienylglyoxime (dThgH2)
R
Cl
O
H
O
N
O
N
H
O
S
S
S
S
S
NaBH4
N
N
Co
Co
N
O
N
O
N
N
O
RX
S
S
S
O
H
H
Py
Py
2-6
1
R = Me (2), Et (3), n-Pr (4), n-Bu (5), Bn (6)
Scheme 1. Synthesis of dithienylglyoxime (dThgH2) and cobaloximes (1e6).
Since the chemical shift of the axial CoꢀCa protons (CoCH3
protons in 2 and CoCH2 protons in 3e6) depends on the cis influ-
ence of the dioxime moiety and the ring current in the dioxime
moiety, the CoꢀCa protons in complexes 2e6 appear downfield
from the corresponding dmgH complexes and this downfield shift
is comparable with the dpgH and dmestgH complexes (Table S4).
The chemical shift values of CH2, Pya and the dioxime (C¼N) are
further affected in the dioxy complex 7. The signal for CH2O2 is
shifted downfield by 0.97 ppm in 1H NMR and 43.67 ppm in 13C NMR
as compared to precursor complex 6. The Pya protons are shifted
upfield (0.19 ppm) whereas 13C(Pya) and 13CC¼N signals are appeared
downfield by 0.88 and 2.0 ppm, respectively as compared to 6.
dmestgH2 [33]. The synthetic route is shown in Scheme 1. The 2-
thienyl group displaced the chloride of dichloroglyoxime and
gave the desired dithienylglyoxime product. The synthesis of
ClCo(dThgH)2Py (1) was accomplished by refluxing a stoichio-
metric mixture of CoCl2$6H2O, dThgH2 and pyridine in ethanol/THF
solvent mixture followed by the aerial oxidation. We found that the
synthesis of 1 in ethanol/THF solvent mixture (1:1) gave better
yield (70%) than in ethanol only (30%). The complexes 2e6 were
prepared by oxidative alkylation of cobaloxime(I) anion generated
in situ by NaBH4 reduction of ClCo(dThgH)2Py in CH3OH. The
reaction of molecular oxygen with benzyl cobaloxime (6) in CH2Cl2
at 0 ꢁC under visible light proceeds smoothly and the dioxy coba-
loxime (7) is formed in good yield within 1 h.
2.3. Electrochemical studies (cyclic voltammetry)
The electrochemical behavior of 1, 3 and 6 has been studied to
understand the effect of dioxime (dThgH) on the redox potentials of
the cobalt center. The cyclic voltammograms are shown in Figs. 1
and 2, and the CV data are given in Table 1. Three types of redox
couple; Co(III)/Co(II), Co(II)/Co(I) and Co(IV)/Co(III) in the cyclic
voltammogram are expected in any cobaloxime but complexes that
describe entire redox processes are very few [39e42].
The cyclic voltammogram of 1 (Fig. 1) shows one irreversible
peak at ꢀ0.239 V and one quasi-reversible peak (E1/2 ¼ ꢀ0.643 V) in
the reductive half corresponding to Co(III)/Co(II) and Co(II)/Co(I),
respectively. In the oxidation half only one quasi-reversible wave
corresponding to Co(IV)/Co(III) (E1/2 ¼ 1.368 V) is observed. The
2.2. NMR spectral studies (1H and 13C)
1H and 13C NMR data for all complexes (1e7) and dThgH2 are
summarized in experimental section. The solubility of free ligand
dThgH2 is poor in CDCl3 and hence a few drops of DMSO-d6 are
necessary to record the NMR. The 1H NMR spectra of the complexes
are easily assigned on the basis of the chemical shifts, their relative
intensities and also assignments are consistent with the previously
described complexes [25,26,29].
The CoꢀC bond stability in organocobaloximes depends on both
the cis and trans influences. The cis influence study has gained
importance only recently [25e32,34e36]. Usually, to study the cis
influence, either the axial ligands R/X or base B is varied, keeping
the same dioxime, or the dioxime is varied, keeping the axial
ligands constant and changes are monitored spectroscopically. The
NMR studies of cobaloximes with different dioximes have shown
that the chemical shifts of Pya, C¼N and the
a-carbon bound to
cobalt are most affected.
The extent of electron density on the metallabicycle for different
dioximes (keeping R/X and Py constant) can be understood by
13
comparing the coordination shift, Dd
(
C
) values [37]. In
C¼N
13
general,
to cobalt. We find that the
d
C
in free dioxime is shifted upfield on coordination
C¼N
13
d
C
C¼N
signals in dThgH complexes
(1e6) appeared significantly downfield as compared to the values
in cobaloximes with other dioximes. The order based on the upfield
shift value is gH > dmgH > dpgH > chgH > dmestgH > dThgH
(Table S1). This suggests the charge density on C¼N is much lower
in dThgH complexes than the other dioxime complexes. The elec-
trochemical study also shows up this effect (see later). The charge
density on C¼N should also affect the chemical shifts for OꢀH/O
proton signals. The lower the charge density on C¼N, weaker the
hydrogen bond and hence a more downfield shift of OꢀH/O
resonance would be expected. Indeed a considerable downfield
shift of OꢀH/O signals is observed in 1e6 as compared to the
Fig. 1. Cyclic voltammogram of 1 in CH2Cl2 with 0.1 M nBu4NPF6 as supporting elec-
trolyte at 0.1 V/s at 25 ꢁC.

K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3785e3791
3787
and is toward the base, pyridine. Since bending angle (
a) is
a measure of interaction between the axial and equatorial ligand,
a high
a
value for 6 (ꢀ7.57ꢁ) as compared to 1, 2 and 3 (1.08, 2.84, and
1.68ꢁ, respectively) is quite justified because of CꢀH/
p interaction.
The CoꢀCl or CoꢀC bond distances [2.222(1), 1.992(1), 2.025(1),
2.062(3) Å] and CoꢀNpy bond distances [1.955(3), 2.065(1),
2.048(1), 2.063(3) Å] in 1, 2, 3 and 6 do not differ significantly from
the reported values for the corresponding X/RCo(dioxime)2Py
complexes (Tables S6 and S7). However, the CoꢀC bond distance
increases from 1.992(1) Å in 2 to 2.025(1) Å in 3 and 2.062(3) Å in 6
with increasing bulk of axial alkyl/benzyl group. The benzyl group in
complex 6 is located over the dioxime wing and shows
CꢀH/ interactions with the dioxime moiety. The distances of
pdioxime
p/p and
p
/
pbenzyl and C8ꢀH8/pbenzyl are 3.586(1) and 3.702(1) Å,
respectively (Fig. 6).
2.5. Molecular structure of Bn(O2)Co(dThgH)2Py (7)
Fig. 2. Cyclic voltammograms of 3 and 6 in CH2Cl2 with 0.1 M nBu4NPF6 as supporting
electrolyte at 0.1 V/s at 25 ꢁC.
A slow evaporation of solvent from the solution of 7 (CH3OH/
CHCl3) has resulted in the formation of brown crystals. The X-ray
data analysis of 7 shows two molecules in its asymmetric unit and
they are numbered as 7A and 7B. The molecular structure with
selected numbering scheme is shown in Fig. 7 and the selected
bond lengths, bond angles and other structural parameters are
given in Table 3. The CoꢀOax, CoꢀNpy and OꢀO mean bond
distances; 1.878(1), 1.992(2) and 1.451(2) Å respectively, are similar
to those in the reported peroxo cobaloximes [32,43e46]. In both
molecules the displacement of Co atom (d) from N4 plane is toward
values show that 1 is the most easily reduced of the chlor-
ocobaloximes with dioxime having carbon side chain (Table S5). It
points to the electron withdrawing effect imparted by the 2-thienyl
ring which results in lower electron density on the cobalt center of
complex 1. The NMR studies also gave the same information.
The cyclic voltammograms of the organocobaloximes 3 and 6
(Fig. 2) show only one irreversible reduction response corre-
sponding to Co(III)/Co(II) at ꢀ1.341 and ꢀ1.302 V, respectively. In
the oxidative half a quasi-reversible one-electron oxidation wave
corresponding to Co(IV)/Co(III) is observed. The E1/2 value for this
process is 1.069 and 1.079 V in complexes 3 and 6, respectively. Due
pyridine and bending of dioxime units (a) is toward the BnO2. It is
interesting to note that the bending of dioxime units in oxygen
inserted complex, Bn(O2)Co(dThgH)2Py is opposite to the precursor
benzyl cobaloxime (6) which indicates the steric interaction of axial
benzyl with equatorial dioxime decreased after oxygen insertion.
The orientation of benzyl groups in both molecules of 7 in asym-
metric unit is different and angles of pyridine plane with benzyl
ring plane are 55.7ꢁ and 78.6ꢁ, respectively in 7A and 7B. In the
crystal packing diagram, molecules of 7 exhibit weak intermolec-
ular CꢀH/O interactions (C22AꢀH22A/O6A ¼ 2.585(2) Å in 7A
and C24BꢀH24B/O6B ¼ 2.485(2) Å in 7B) leading to one-
dimensional polymeric chains of 7A and 7B. Such 1-D chains of
to the higher s donation ability of the alkyl groups, the Co(III)/Co(II)
redox process in 3 and 6 is considerably cathodically shifted and
hence the Co(II)/Co(I) response is further cathodically shifted and is
not observed even down to ꢀ1.6 V.
2.4. Molecular structures of 1, 2, 3 and 6
Molecular structures of the complexes 1, 2, 3 and 6 have been
determined by X-ray crystallography. Selected bond lengths and
bond angles are given in Table 2 and molecular structures with
selected numbering schemes are depicted in Figs. 3e6. In all the
structures, cobalt atom has a distorted octahedral geometry with
four N atoms of the dioxime (dThgH) in the equatorial plane and
the axial positions are occupied by R/X and pyridine.
7A and 7B are interconnected through p/p interactions between
the 2-thienyl rings of dioximes with a distance of 3.714(1) Å
between the centroids of stacked rings; resulting 1-D double-chain
polymeric network (Fig. S1).
The Co(dThgH)2 unit in cobaloximes undergoes geometrical
deformations, due to flexibility, which is roughly represented by the
displacement of cobalt out of 4-nitrogen plane (d) and by the
2.6. Kinetic study of oxygen insertion in the CoꢀC bond of complex
6
butterfly bending angle between two dioxime units (
a
). The positive
The molecular oxygen insertion into the CoꢀC bond has
extensively been used to test the reactivity of organocobaloximes
[26,32,43e53]. Since the homolysis of CoꢀC bond is the key step in
this reaction and the effect of equatorial dioxime (cis influence) is
felt most on the CoꢀC bond, both are related to each other and
value of and d indicates bending toward R/X and displacement
a
toward base and vice versa. The deviations of cobalt atom from mean
equatorial N4 plane (d) are þ0.0444(5), þ0.0385(3), þ0.0436(3)
and þ0.0107(5) Å in 1, 2, 3 and 6, respectively. The deviation is small
Table 1
CV Data for complexes 1, 3 and 6 in CH2Cl2 and nBu4NPF6 at 0.1 V/s at 25 ꢁC.
No
Co(III)/Co(II)
Co(II)/Co(I)
Co(IV)/Co(III)
E1/2(V)a
E1/2
(V)
ipc
A)
3.45
ipa
A)
2.91
E1/2(V)a
Ep, mV)
E1/2
ipc
ipa
a
b
b
b
Epc
Epc
ipc
A)
(V)
(V)
(
m
(
DEp, mV)
(
m
(
m
(
D
(V)
1
3
6
ꢀ0.239
ꢀ1.341
ꢀ1.302
ꢀ0.666
ꢀ1.768
ꢀ1.729
2.01
6.71
7.38
ꢀ0.643(95)
ꢀ1.069
1.368 (128)
1.069 (95)
1.079 (106)
0.941
0.642
0.652
2.68
4.02
3.32
7.11
7.22
6.62
a
Vs. Ag/AgCl.
b
Vs. Fc/Fcþ (E1/2 ¼ 0.4269 V).

3788
K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3785e3791
Table 2
Selected bond lengths and bond angles for 1, 2, 3 and 6.
Parameters
1
2
3
6
CoeC/Cl (Å)
CoeNpy (Å)
a
2.222(1)
1.955(3)
1.992(1)
2.065(1)
2.025(1)
2.048(1)
2.062(3)
2.063(3)
(ꢁ)
d (Å)
(ꢁ)
þ1.08
ꢀ2.84
ꢀ1.68
ꢀ7.57
þ0.0444(5)
85.73(10)
þ0.0385(3)
68.14(32)
þ0.0436(3)
87.44(10)
þ0.0107(5)
89.06(35)
s
follow the same order in benzyl complexes [26,30e32,43]. There-
fore, we have undertaken the study of CoꢀC bond reactivity in
complex 6. The inherently weak CoꢀC bond and also the weak
interaction of benzyl group with the equatorial dioxime in benzyl
complex (6) make it an ideal system for such study. The rate study is
carried out following the procedure reported in earlier studies
under pseudo-first-order conditions at 0 ꢁC [31,32]. The lmax for the
CoeC CT band in benzyl cobaloxime (6) is 454 nm. The rate
constant (kobs) is calculated from the slope of the linear plot of
ln(AtꢀAN) versus time, where At is the absorbance at time t and AN
is the final absorbance, and is given in Fig. 8. The rate data in Table 4
shows that the oxygen insertion depends upon the dioxime and
follows the order dmestgH > dThgH > dpgH > dmgH. Interestingly,
the rate of oxygen insertion in dThgH complex (6) is faster than that
of the dpgH complex although the cis influence in dpgH and dThgH
complexes is quite similar on the basis of the chemical shift value
for CoꢀCH2 protons and also the CoeC bond distances are similar in
both complexes (Table S7). The larger puckering of the Co(diox-
Fig. 4. Molecular structure of MeCo(dThgH)2Py (2). Most of the hydrogen atoms have
been omitted for clarity.
4. Experimental section
4.1. Materials and physical measurements
CoCl2$6H2O (SD Fine, India), 2-bromothiophene, iodomethane,
iodoethane, 1-bromopropane, 1-bromobutane and benzyl chloride
(all from Sigma-Aldrich, USA) were used as received without
further purifications. Dichloroglyoxime was prepared and purified
according to reported literature procedure [30]. The solvents were
purified rigorously by standard procedures prior to their use and
THF was dried over sodium/benzophenone. A Julabo UC-20 low-
temperature refrigerated circulator was used to maintain the
desired temperature. Cyclic voltammetry measurements were
carried out using a BAS Epsilon electrochemical work station with
a platinum working electrode, a Ag/AgCl reference electrode (3 M
NaCl) and a platinumewire counter electrode. All measurements
were performed in 0.1 M nBu4NPF6 in CH2Cl2 (dry) at a concentra-
tion of 1 mM of each complex. 1H NMR spectra were recorded on
JEOL JNM LAMBDA-400 model operating at 400 MHz and 13C NMR
spectra were recorded on JEOL ECX-500 model operating at
125 MHz in CDCl3 with TMS as internal standard. Elemental anal-
yses for C, H and N were performed on CE-440 Elemental Analyzer.
ime)2 unit in complex 6 (
compared to the BnCo(dpgH)2Py (
might be the driving force for the higher rate constant in
BnCo(dThgH)2Py.
a
¼ ꢀ7.57ꢁ and d ¼ þ0.0107 Å) as
a
¼ 1.75ꢁ and d ¼ ꢀ0.0275 Å) [54]
3. Conclusion
In this work we have described synthesis and characterization of
cobaloximes with dithienylglyoxime as the equatorial ligand. The
electron withdrawing nature of 2-thienyl ring affects the NMR as
well as the electrochemical behavior of these complexes. The
13
C
C¼N
signals in dThgH complexes appear significantly downfield
as compared to cobaloximes with other dioxime systems. Among
all the reported chlorocobaloximes, ClCo(dThgH)2Py (1) is most
easy to reduce electrochemically from Co(III) to Co(II) and Co(II) to
Co(I). The reactivity of benzyl complex with molecular oxygen
under photolytic condition has been examined and a comparison of
its reaction rate with the other similar cobaloximes gives the order
of equatorial dioximes, dmestgH > dThgH > dpgH > dmgH.
4.2. X-ray crystal structure determination and refinements
Single crystals suitable for X-ray crystallographic analyses were
obtained by the slow evaporation of the solvent from the solutions
of complexes [CH3OH/CH2Cl2 for 1 and CH3OH/CHCl3 for 2, 3, 6 and
Fig. 3. Molecular structure of ClCo(dThgH)2Py (1). Solvent molecule and most of the
Fig. 5. Molecular structure of EtCo(dThgH)2Py (3). Most of the hydrogen atoms have
hydrogen atoms have been omitted for clarity.
been omitted for clarity.

K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3785e3791
3789
Table 3
Selected bond lengths and bond angles for 7.
Parameters
7
A
B
CoeOax (Å)
CoeNpy (Å)
OeO (Å)
1.879 (1)
1.990 (2)
1.454 (2)
1.876 (1)
1.994 (2)
1.447 (2)
1.444 (3)
116.98 (9)
OeC (Å)
1.436 (3)
CoeOeO (ꢁ)
OeOeC (ꢁ)
CoeOeOeC (ꢁ)
OeCeC (ꢁ)
OeOeCeC (ꢁ)
113.92 (9)
105.87 (11)
102.79 (13)
107.65 (15)
107.27 (13)
ꢀ105.53 (14)
106.02 (17)
ꢀ163.30 (13)
173.90 (5)
þ0.0438 (4)
þ7.43
ꢀ179.71 (15)
170.44 (6)
þ0.0196 (4)
þ3.01
N
pyeCoeOax (ꢁ)
d (Å)
a
(ꢁ)
(ꢁ)
s
70.44 (34)
75.78 (13)
data and refinement parameters for compounds 1, 2, 3, 6 and 7 are
compiled in Table 5.
Fig. 6. Molecular structure of BnCo(dThgH)2Py (6). Most of the hydrogen atoms have
been omitted for clarity.
4.3. Syntheses
7]. X-ray crystallographic data were collected using graphite-
4.3.1. Synthesis of dithienylglyoxime (dThgH2)
monochromated Mo K
a
radiation (
l
¼ 0.71073 Å) on “Bruker
A solution of dichloroglyoxime (1.0 g, 6.36 mmol) in 10 mL dry
THF was added slowly with stirring to a solution of (2-thienyl)MgBr
at 0 ꢁC under nitrogen atmosphere. The (2-thienyl)MgBr was
prepared in dry THF (25 mL) from 2-bromothiophene (5.198 g,
31.83 mmol), Mg (0.851 g, 35.01 mmol) and one crystal of I2 under
nitrogen atmosphere. After the addition of dichloroglyoxime, the
solution was allowed to warm to room temperature and stirred
further for 5 h before quenching with saturated aqueous NH4Cl
(20 mL). The content was stirred vigorously for 10 min. The two
layers were separated and the aqueous layer was extracted with
THF (3 ꢂ 7 mL). The combined organic solution washed with brine
solution and dried over anhydrous Na2SO4. The solvent was evap-
orated off under reduced pressure on a rotary evaporator to result
in a brown colored solid which was washed with petroleum ether.
Yield: 1.437 g (w89%). 1H NMR (400 MHz, CDCl3 þ DMSO-d6,
SMART APEX CCD diffractometer” at 100 K. The linear absorption
coefficients, scattering factors for the atoms and the anomalous
dispersion corrections were taken from the International Tables for
X-ray Crystallography [55]. The program SMART [56] was used for
collecting frames of data, indexing reflections, and determining
lattice parameters. The data integration and reduction were pro-
cessed with SAINT software [56]. An empirical absorption correc-
tion was applied to the collected reflections with SADABS [57] using
XPREP [58]. All the structures were solved by the direct method
using the program SHELXS-97 [59] and were refined on F2 by the
full-matrix least-squares technique using the SHELXL-97 [59]
program package. All non-hydrogen atoms were refined with
anisotropic displacement parameters in all the structures. The
hydrogen atom positions or thermal parameters were not refined
but were included in the structure factor calculations. The 2-thienyl
rings in all complexes were found to be disordered and were
modeled satisfactorily using part instructions. The pertinent crystal
d
ppm): thienyl protons ¼ 7.38 (2H, d, J ¼ 5.2 Hz), 7.14 (2H, d,
J ¼ 3.8 Hz), 6.86e6.84 (2H, m), NꢀO/H ¼ 11.70 (s). 13C NMR
(125 MHz, CDCl3 þ DMSO-d6, ppm): 146.04 (C¼N), 131.89, 130.93,
d
130.50, 125.63. Anal. Calcd. for C10H8N2O2S2: C, 47.60; H, 3.20; N,
11.10. Found: C, 47.86; H, 3.11; N, 11.27.
Fig. 7. Molecular structure of BnO2Co(dThgH)2Py (7). One molecule of 7 present in the
asymmetric unit, solvent molecules and most of the hydrogen atoms have been
omitted for clarity.
Fig. 8. Plot of ln(At e AN) versus time (sec) for BnCo(dThgH)2Py (6).

3790
K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3785e3791
Table 4
orangeered on the addition of organic halide (0.3 mmol). The
reaction was stirred 1 h at 0 ꢁC then poured into 20 mL chilled water
containing few drops of pyridine. The resulting orangeered
precipitate was filtered, washed with water, and dried. The crude
product was purified on the silica gel column using CH2Cl2 as eluent.
Pseudo-first-order rate constant (kobs) for oxygen insertion in BnCo(dioxime)2Py.
BnCo(dioxime)2Py
kobs (sꢀ1
)
Ref.
BnCo(dmgH)2Py
BnCo(dpgH)2Py
BnCo(dmestgH)2Py
BnCo(dThgH)2Py
1.2 ꢂ 10ꢀ3
4.8 ꢂ 10ꢀ3
5.0 ꢂ 10ꢀ2
8.05 ꢂ 10ꢀ3
[32]
[32]
[32]
this work
4.3.3.1. MeCo(dThgH)2Py (2). Yield: 0.052 g (w54%). 1H NMR
(400 MHz, CDCl3,
d
ppm): Pya ¼ 8.71 (2H, d, J ¼ 5.2 Hz), Pyb ¼ 7.37
(2H, t, J ¼ 7.0 Hz), Pyg ¼ 7.76 (1H, t, J ¼ 8.0 Hz), thienyl protons ¼ 7.49
(4H, d, J ¼ 5.2 Hz), 6.98 (4H, t, J ¼ 4.4 Hz), 6.86 (4H, d, J ¼ 3.6 Hz),1.32
(3H, s, CoCH3), 18.94 (2H, s, OꢀH/O). 13C NMR (125 MHz, CDCl3,
4.3.2. Synthesis of ClCo(dThgH)2Py (1)
In a typical reaction, pyridine (0.2 mL, 2.5 mmol) was added to
a hot solution of dithienylglyoxime (0.252 g, 1.0 mmol) and
CoCl2$6H2O (0.118 g, 0.5 mmol) in 30 mL of 1:1 ethanol/THF solvent
mixture and the resulting solution was refluxed for 1 h. The solu-
tion was cooled to room temperature and air was passed vigorously
for 3 h with occasional swirling to get desired crude product. The
solid crude product was filtered, washed with water and dried over
P2O5 overnight and purified on a silica gel column using CH2Cl2.
d
ppm): 149.87 (Pya), 144.57 (C¼N, Cq), 138.01 (Pyg), 130.34, 129.62,
128.51, 126.06, 125.76. Anal. Calcd. for C26H22CoN5O4S4: C, 47.63; H,
3.38; N, 10.68. Found: C, 47.74; H, 3.45; N, 10.53.
4.3.3.2. EtCo(dThgH)2Py (3). Yield: 0.057
(400 MHz, CDCl3,
g
(w57%). 1H NMR
ppm): Pya ¼ 8.69 (2H, d, J ¼ 5.2 Hz), Pyb ¼ 7.35
d
(2H, t, J ¼ 7.0 Hz), Pyg ¼ 7.74 (1H, t, J ¼ 8.0 Hz), thienyl
protons ¼ 7.49 (4H, d, J ¼ 5.2 Hz), 6.98e6.96 (4H, m), 6.86 (4H, d,
J ¼ 3.2 Hz), 2.25 (2H, q, J ¼ 7.6 Hz, CoCH2), 0.59 (3H, t, J ¼ 7.6 Hz),
Yield: 0. 237 g (w70%). 1H NMR (400 MHz, CDCl3,
d ppm):
Pya ¼ 8.43 (2H, d, J ¼ 5.6 Hz), Pyb ¼ 7.29 (2H, t, J ¼ 7.2 Hz), Pyg ¼ 7.74
(1H, t, J ¼ 7.4 Hz), thienyl protons ¼ 7.56 (4H, d, J ¼ 3.6 Hz),
7.03e7.00 (8H, m), 18.90 (2H, s, OꢀH/O). 13C NMR (125 MHz,
CDCl3, d ppm): 150.86 (Pya), 147.09 (C¼N, Cq), 139.27 (Pyg), 130.94,
129.96, 129.40, 126.16, 126.03. Anal. Calcd. for C25H19ClCoN5O4S4: C,
44.41; H, 2.83; N, 10.36. Found: C, 44.26; H, 2.71; N, 10.51.
18.87 (2H, s, OꢀH/O). 13C NMR (125 MHz, CDCl3,
d ppm): 149.90
(Pya), 144.58 (C¼N, Cq), 137.90 (Pyg), 130.43, 129.49, 128.45, 126.09,
125.71, 29.79 (CH2), 16.40 (CH3). Anal. Calcd. for C27H24CoN5O4S4: C,
48.42; H, 3.61; N, 10.46. Found: C, 48.24; H, 3.48; N, 10.62.
4.3.3.3. n-PrCo(dThgH)2Py (4). Yield: 0.059 g (w58%). 1H NMR
4.3.3. Synthesis of RCo(dThgH)2Py (2e6): general procedure
(400 MHz, CDCl3,
d
ppm): Pya ¼ 8.68 (2H, d, J ¼ 5.2 Hz), Pyb ¼ 7.34
These complexes were synthesized by following the general
procedure described earlier for the synthesis of RCo(dioxime)2Py
and involved the reaction of cobaloxime(I) with organic halide. In
typical procedure, a solution of 1 (0.100 g, 0.147 mmol) in 10 mL of
CH3OH was purged thoroughly with N2 for 20 min and was cooled to
0 ꢁC with stirring. The solution turned deep blue after the addition of
few drops of aqueous NaOH followed by NaBH4 (0.012 g,
0.320 mmol in 0.5 mL of water). The color of the solution turned
(2H, t, J ¼ 6.8 Hz), Pyg ¼ 7.73 (1H, t, J ¼ 8.0 Hz), thienyl
protons ¼ 7.49 (4H, d, J ¼ 4.8 Hz), 6.97 (4H, t, J ¼ 4.4 Hz), 6.86 (4H, d,
J ¼ 3.2 Hz), 2.12 (2H, t, J ¼ 8.8 Hz, CoCH2), 1.25e1.21 (2H, m), 0.84
(3H, t, J ¼ 7.0 Hz), 18.88 (2H, s, OꢀH/O). 13C NMR (125 MHz, CDCl3,
d
ppm): 149.83 (Pya), 144.62 (C¼N, Cq), 137.88 (Pyg), 130.45, 129.47,
128.42, 126.07, 125.67, 37.43 (CoCH2), 24.17 (CH2), 14.85 (CH3). Anal.
Calcd. for C28H26CoN5O4S4: C, 49.19; H, 3.83; N, 10.24. Found: C,
48.96; H, 3.64; N, 10.38.
Table 5
Crystal data and structure refinement details for 1, 2, 3, 6 and 7.
Parameters
1
2
3
6
7
Empirical formula
Formula weight
Temp (K)
Crystal system
Space group
Unit cell dimension
a (Å)
C26H21Cl3CoN5O4S
761.00
100(2)
Orthorhombic
Pbca
C26H22CoN5O4S4
655.66
100(2)
Monoclinic
P21/c
C27H24CoN5O4S4
669.68
100(2)
Triclinic
P-1
C32H26CoN5O4S4
731.75
100(2)
Monoclinic
P21/n
C34H29.5Cl4.5CoN5O6.5S4
958.82
100(2)
Triclinic
P-1
17.500(5)
18.453(5)
19.250(5)
90.000
90.000
90.000
6216(3)
8
1.626
1.121
8.993(3)
9.382(3)
9.583(5)
9.733(3)
b (Å)
c (Å)
10.865(4)
27.480(9)
90.000
94.415(6)
90.000
2677.3(15)
4
1.627
12.291(4)
14.223(5)
115.377(5)
103.084(5)
95.893(6)
1406.2(8)
2
31.288(5)
10.255(5)
90.000(5)
90.820(5)
90.000(5)
3074(2)
19.078(5)
23.497(7)
111.042(5)
94.710(5)
102.981(5)
3903.8(18)
4
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
V (Å3)
Z
r
4
(calc), g/cm3
(mmꢀ1
1.582
0.952
1.581
0.878
1.631
1.015
m
)
0.998
F (000)
3088
1344
688
1504
1952
Crystal size (mm3)
Index ranges
0.35 ꢂ 0.26 ꢂ 0.18
ꢀ23 ꢃ h ꢃ 18
ꢀ17 ꢃ k ꢃ 24
ꢀ25 ꢃ l ꢃ 25
39296
0.32 ꢂ 0.21 ꢂ 0.16
ꢀ11 ꢃ h ꢃ 11
ꢀ10 ꢃ k ꢃ 14
ꢀ35 ꢃ l ꢃ 36
16976
0.53 ꢂ 0.34 ꢂ 0.22
ꢀ11 ꢃ h ꢃ 11
ꢀ14 ꢃ k ꢃ 14
ꢀ13 ꢃ l ꢃ 17
7543
0.41 ꢂ 0.33 ꢂ 0.22
ꢀ11 ꢃ h ꢃ 11
ꢀ37 ꢃ k ꢃ 35
ꢀ12 ꢃ l ꢃ 11
16372
0.51 ꢂ 0.36 ꢂ 0.23
ꢀ11 ꢃ h ꢃ 11
ꢀ15 ꢃ k ꢃ 22
ꢀ27 ꢃ l ꢃ 25
20272
No. of rflns collected
No. of indep rflns
GOOF on F2
7777
1.104
6598
1.085
5143
1.131
5706
1.055
13526
1.035
Final R indices
(I > 2s(I))
R indices (all data)
R1 ¼ 0.0587
wR2 ¼ 0.1392
R1 ¼ 0.0980
wR2 ¼ 0.1898
7777/46/412
R1 ¼ 0.0630
wR2 ¼ 0.1569
R1 ¼ 0.1073
wR2 ¼ 0.2262
6598/20/399
R1 ¼ 0.0539
wR2 ¼ 0.1414
R1 ¼ 0.0660
wR2 ¼ 0.1657
5143/10/386
R1 ¼ 0.0527
wR2 ¼ 0.1272
R1 ¼ 0.0734
wR2 ¼ 0.1424
5706/32/455
R1 ¼ 0.0634
wR2 ¼ 0.1602
R1 ¼ 0.0883
wR2 ¼ 0.1999
13526/52/1067
Data/restraints/param

K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3785e3791
3791
4.3.3.4. n-BuCo(dThgH)2Py (5). Yield: 0.061 g (w60%). 1H NMR
(400 MHz, CDCl3,
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[6] G.N. Schrauzer, J. Kohnle, Chem. Ber 97 (1964) 3056e3064.
[7] G.N. Schrauzer, Inorg. Synth. 11 (1968) 61e69.
[8] G.N. Schrauzer, Angew. Chem. Int. Ed. Engl. 15 (1976) 417e426.
[9] A. Rockenbaur, M. Eyor, M. Kwielinsci, S. Tyrlik, Inorg. Chim. Acta 58 (1982)
237e242.
[10] S. Nemeth, L. Simandi, J. Mol. Catal. 14 (1982) 87e93.
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Pergamon Press, Oxford, U.K, 1986.
[12] I. Das, S. Chowdhury, K. Ravikumar, S. Roy, B.D. Gupta, J. Organomet. Chem.
532 (1997) 101e107.
d
ppm): Pya ¼ 8.69 (2H, d, J ¼ 5.2 Hz), Pyb ¼ 7.34
(2H, t, J ¼ 6.8 Hz), Pyg ¼ 7.73 (1H, t, J ¼ 7.6 Hz), thienyl
protons ¼ 7.48 (4H, d, J ¼ 4.8 Hz), 6.98e6.96 (4H, m), 6.85 (4H, d,
J ¼ 3.2 Hz), 2.14 (2H, t, J ¼ 8.6 Hz, CoCH2), 1.30e1.24 (2H, m),
1.20e1.12 (2H, m), 0.80 (3H, t, J ¼ 7.2 Hz), 18.87 (2H, s, OꢀH/O). 13C
NMR (125 MHz, CDCl3,
d
ppm): 149.85 (Pya), 144.61 (C¼N, Cq),
137.88 (Pyg), 130.49, 129.44, 128.41, 126.09, 125.67, 34.87 (CoCH2),
33.30 (CH2), 23.56 (CH2), 14.01 (CH3). Anal. Calcd. for C29H28Co-
N5O4S4: C, 49.92; H, 4.04; N,10.04. Found: C, 50.03; H, 3.91; N,10.15.
[13] A.K. Ghosh, Y. Chen, Tetrahedron Lett. 36 (1995) 505e508.
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Chem. 582 (1999) 279e281 (and refs cited therein).
[16] T. Brown, A. Dronsfield, A. Jablonski, A.S. Wilkinson, Tetrahedron Lett. 37
(1996) 5413e5416.
4.3.3.5. BnCo(dThgH)2Py (6). Yield: 0.078
(400 MHz, CDCl3,
g
(w72%). 1H NMR
ppm): Pya ¼ 8.64 (2H, d, J ¼ 5.2 Hz), Pyb ¼ 7.32
d
(2H, t, J ¼ 7.0 Hz), Pyg ¼ 7.71 (1H, t, J ¼ 7.8 Hz), thienyl/aromatic
protons ¼ 7.45 (4H, d, J ¼ 5.2 Hz), 7.12e7.07 (3H, m), 6.94e6.91 (6H,
m), 6.69 (4H, d, J ¼ 3.6 Hz), 3.35 (2H, s, CoCH2), 18.90 (2H, s,
[17] S. Roy, I. Das, K. Bhanuprakash, B.D. Gupta, Tetrahedron 50 (1994)
1847e1858.
OꢀH/O). 13C NMR (125 MHz, CDCl3,
d ppm): 150.03 (Pya), 144.75
[18] J.L. Gage, B.P. Branchaud, Tetrahedron Lett. 38 (1997) 7007e7010.
[19] K. Kumar, B.D. Gupta, J. Organomet. Chem. 696 (2011) 2280e2286.
[20] D. Dolphin (Ed.), B12, Wiley & Sons, New York, 1982.
[21] R. Banerjee, Chemistry and Biochemistry of B12. Wiley & Sons, Inc., N. Y.,
1999.
[22] K.L. Brown, Chem. Rev. 105 (2005) 2075e2149.
[23] L. Randaccio, S. Geremia, E. Zangrando, C. Ebert, Inorg. Chem. 33 (1994)
4641e4650.
(C¼N, Cq), 137.95 (Pyg), 130.37, 129.65, 129.00, 128.37, 128.24,
126.03, 125.71, 125.00, 34.61 (CH2). Anal. Calcd. for C32H26Co-
N5O4S4: C, 52.52; H, 3.58; N, 9.57. Found: C, 52.41; H, 3.55; N, 9.60.
4.3.4. Synthesis of BnO2Co(dThgH)2Py (7)
[24] P. Siega, L. Randaccio, P.A. Marzilli, L.G. Marzilli, Inorg. Chem. 45 (2006)
3359e3368.
[25] B.D. Gupta, K. Qanungo, Organomet. Chem. 543 (1997) 125e134.
[26] B.D. Gupta, V. Vijaikanth, V. Singh, J. Organomet. Chem. 570 (1998) 1e7.
[27] B.D. Gupta, K. Qanungo, T. Barclay, W. Cordes, J. Organomet. Chem. 560 (1998)
155e161.
A solution of complex 6 (0.030 g, 0.041 mmol) in CH2Cl2 (10 mL)
was irradiated with a 200 W tungsten lamp kept at a distance of
approximately 10 cm, and pure oxygen gas was bubbled into this
solution for 1 h at 0 ꢁC. The solvent was evaporated under reduced
pressure to obtain a crude product of complex 7. The crude product
was further purified on the silica gel column using 5% ethyl acetate/
[28] B.D. Gupta, R. Yamuna, V. Singh, U. Tiwari, Organometallics 22 (2003)
226e232.
CH2Cl2. Yield: 0.026 g (w81%). 1H NMR (400 MHz, CDCl3,
d ppm):
[29] D. Mandal, B.D. Gupta, Organometallics 24 (2005) 1501e1510.
[30] G. Dutta, K. Kumar, B.D. Gupta, Organometallics 28 (2009) 3485e3491.
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[32] M. Bhuyan, M. Laskar, D. Mandal, B.D. Gupta, Organometallics 26 (2007)
3559e3567.
[33] K.A. Lance, K.A. Goldsby, D.H. Busch, Inorg. Chem. 29 (1990) 4537e4544.
[34] C. López, S. Alvarez, M. Font-Bardia, X. Solans, J. Organomet. Chem. 414 (1991)
245e259.
Pya ¼ 8.45 (2H, d, J ¼ 5.2 Hz), Pyb ¼ 7.21 (2H, t, J ¼ 6.4 Hz), Pyg ¼ 7.63
(1H, t, J ¼ 7.6 Hz), thienyl/aromatic protons ¼ 7.44 (4H, d,
J ¼ 5.2 Hz), 7.03e6.96 (5H, m), 6.90e6.88 (4H, m), 6.79 (4H, d,
J ¼ 4.0 Hz), 4.32 (2H, s, O2CH2), 19.02 (2H, s, OꢀH/O). 13C NMR
(125 MHz, CDCl3,
d
ppm): 150.91 (Pya), 146.75 (C¼N, Cq), 138.72
(Pyg), 136.56, 130.63, 130.10, 129.49, 129.05, 127.79, 127.40, 126.03,
125.85, 78.28 (O2CH2). Anal. Calcd. for C32H26CoN5O6S4: C, 50.32; H,
3.43; N, 9.17. Found: C, 50.44, H, 3.48; N, 9.10.
[35] C. López, S. Alvarez, X. Solans, M. Font-Bardia, Polyhedron 11 (1992)
1637e1646.
[36] P.J. Toscano, L. Lettko, E.J. Schermerhorn, J. Waechter, K. Shufon, S. Liu,
E.V. Dikarev, J. Zubieta, Polyhedron 22 (2003) 2809e2820.
13
13
[37] Dd
(
C
C¼N
) value has been taken instead of
d(
C
). This is to avoid the
C¼N
direct effect of substituent on
d(C¼N) value.
Acknowledgments
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(1981) 5558e5566.
We are thankful to the Department of Science and Technology
(DST), Government of India and the Council of Scientific and
Industrial Research (CSIR), India for financial support. K. K. thanks
UGC, New Delhi, India for Senior Research Fellowship (SRF).
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Appendix A. Supplementary material
CCDC 832464-832468 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from the Director, CCDC,12 Union Road, Cambridge CB2 1EX,
UK (fax þ44-1223-336033; email: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk/). Supplementary data associ-
ated with this article can be found in the online version.
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Appendix. Supplementary material
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.08.035.
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X-ray Systems, Inc., Madison, WI, 2003.
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[1] N. Bresciani-Pahor, M. Forcolin, L.G. Marzilli, L. Randaccio, M.F. Summers,
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