Inorganic and organometallic cobaloximes with dioxime containing Se side chain: Synthesis, characterization and comparison with related B12 model compounds

Article abstract of DOI:10.1016/j.jorganchem.2011.07.012

New series of cobaloximes, RCo(dSePhgH)₂Py (R = Cl, Me, Et, n-Pr, n-Bu, Bn, 4-ClC₆H₄CH₂) have been synthesized and characterized by NMR and elemental analysis. Molecular oxygen insertion in the benzyl complexes

Full text of DOI:10.1016/j.jorganchem.2011.07.012

Journal of Organometallic Chemistry 696 (2011) 3343e3350
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Inorganic and organometallic cobaloximes with dioxime containing Se side chain:
Synthesis, characterization and comparison with related B12 model compounds
y
*
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:
New series of cobaloximes, RCo(dSePhgH)2Py (R ¼ Cl, Me, Et, n-Pr, n-Bu, Bn, 4eClC6H4CH2) have been
synthesized and characterized by NMR and elemental analysis. Molecular oxygen insertion in the benzyl
complexes under photochemical conditions has been carried out and a comparison of its reaction rate
with other similar cobaloximes gives the order dmestgH > dSePhgH > dpgH > dSPhgH ꢀ dmgH > gH.
Received 29 April 2011
Received in revised form
9 July 2011
Accepted 11 July 2011
The
molecular
structures
of
ClCo(dSePhgH)2Py,
MeCo(dSePhgH)2Py,
BnCo(dSePhgH)2Py,
4eClC6H4CH2Co(dSePhgH)2Py and a dioxy complex Bn(O2)Co(dSePhgH)2Py have been determined by
X-ray crystallography. The SePh groups in these complexes adopt either up-down, up-down or down-
down, down-down conformations in the solid state depending upon the steric bulk and steric interac-
tions with the axial ligand and also their orientation affects the NMR chemical shifts.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Bis(phenylselanyl)glyoxime
Cobaloxime
Reactivity
X-ray structure
1. Introduction
electronic and steric bulk properties of the dioxime are altered. Our
recent work on cobaloximes with dSPhgH [24] has shown that the S
In the past four decades a significant effort has been devoted to
the synthesis and characterization of simple cobalt complexes con-
side chain in the dioxime also plays an important role in the CoꢁC
bond stability/reactivity. With these objectives in mind we have
synthesized and characterized cobaloximes (1e7) with dioximes
having SePh side chain i.e. bis(phenylselanyl)glyoxime (Scheme 1).
All complexes are new and are reported for the first time. The
molecular structures of 1, 2, 6 and 7 have been determined by
single-crystal X-ray diffraction. The molecular oxygen insertion and
their rate in the benzyl complexes 6 and 7 have also been carried
out. The structural features of the dioxy complex (8) are described.
taining a stable CoꢁC
s bond [1e3] and systematic investigations
have been made to understand the strength of the CoꢁC bond as
a function of steric and electronic factors with a wide range of axial
ligands in cobaloximes [3]. The studies have helped to understand
the chemistry and biochemistry of B12 coenzymes [4e6]. The
influence of equatorial ligands (cis influence) in the Schiff base
compounds like Co(saloph)R (saloph ¼ dianion of disalicylidene-o-
phenylenediamine) [7,8], LCo(acacen)R [acacen ¼ dianion of ethyl-
enebis(acetylacetone imine)] [1], LCo(salen)R [salen ¼ dianion of
2. Experimental section
N,N0-ethylenebis(salicylideneamine)] [9] and Costa’s model [10,11]
0
such as [LCo{(DO)(DOH)pn}R]X [(DO)(DOH)pn, N2,N2 -propane-
2.1. Materials and physical measurements
diylbis(2,3-butanedione-2-imine-3-oxime)] has also been reported.
The most extensively studied cobaloximes have dmgH as
equatorial ligand and studies with other dioximes such as gH
[12e15], chgH [16e18], dpgH [19e21], dmestgH [22,23], and
dSPhgH [24] are few. The studies strongly suggest that the CoꢁC
bond stability/reactivity is significantly affected by the equatorial
dioximes (cis effect and cis influence). Hence, there has been
a sustained interest to synthesize cobaloximes in which the
CoCl2$6H2O (SD Fine, India), diphenyl diselenide, iodomethane,
iodoethane,1-bromobutane,1-bromopropane, benzyl chloride, and
4-chlorobenzyl chloride (all SigmaeAldrich, USA) were used as
received without further purifications. Dichloroglyoxime was
prepared and purified by reported literature procedure [24]. Silica
gel (100e200 mesh) and distilled solvents were used in all reac-
tions and in chromatographic separations. A Julabo UC-20 low-
temperature refrigerated circulator was used to maintain the
desired temperature. 1H and 13C spectra were recorded on a JEOL
ECX-500 FT NMR Spectrometer (500 MHz for 1H and 125 MHz for
13C) in CDCl3 with TMS as internal standard. Elemental analyses for
C, H and N were performed on CE-440 Elemental Analyzer. The
* Corresponding author. Tel.: þ91 512 2597730; fax:þ91 512 2597436.
E-mail address: kamlesh@iitk.ac.in (K. Kumar).
y
Prof. Bhagwan D. Gupta deceased on 31 March 2011.
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.012

3344
K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3343e3350
Scheme 1. Synthesis of cobaloximes [1e7] and oxygen insertion reaction in complex 6.
kinetic studies were performed on an Ocean Optics USB4000 (BASi,
USA) UVevis spectrometer in dry CH2Cl2. Cyclic voltammetry
measurements were carried out using a BAS Epsilon electro-
chemical work station with a platinum working electrode, a Ag/
AgCl reference electrode (3 M NaCl) and a platinum–wire counter
electrode. All measurements were performed in 0.1 M nBu4NPF6 in
CH2Cl2 (dry) at a concentration of 1 mM of each complex.
solution of dichloroglyoxime (0.157 g, 1 mmol) in 10 mL dry ethanol
was added to the colorless solution with constant stirring and the
reaction mixture was stirred further for 12 h. Filtration was done to
remove any precipitate and the filtrate was kept aside for slow
evaporation of solvent. The solid crystalline compound so obtained
was washed with CH2Cl2 and dried under vacuum. Yield: 0.318 g
(w79%). The same yield was obtained when the reaction was scaled
up five times. 1H NMR (500 MHz, CDCl3þDMSO-d6,
d ppm): 7.53
(4H, d, J ¼ 6.8 Hz), 7.39e7.28 (6H, m), NꢁO∙∙∙H ¼ 11.84 (s). 13C
2.2. X-ray crystal structure determination and refinements
NMR (125 MHz, CDCl3þDMSO-d6,
d ppm): 143.78, 137.06, 128.94,
128.79, 125.49. Anal. Calcd for C14H12N2O2Se2: C, 42.23; H, 3.04; N,
7.04. Found: C, 42.39; H, 2.99; N, 7.10.
X-ray crystallographic data were collected using graphite-
monochromated Mo-K
a
radiation (
l
¼ 0.71073 Å) on “Bruker
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 [25]. The program SMART [26] was used for
collecting frames of data, indexing reflections, and determining
lattice parameters. The data integration and reduction were pro-
cessed with SAINT software [26]. An empirical absorption correc-
tion was applied to the collected reflections with SADABS [27] using
XPREP [28]. All the structures were solved by the direct method
using the program SHELXS-97 [29] and were refined on F2 by the
full-matrix least-squares technique using the SHELXL-97 [29]
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
‘SQUEEZE’ option in PLATON was used to remove disordered
solvent molecule from the overall intensity data in complex 8. The
pertinent crystal data and refinement parameters for compounds 1,
2, 6, 7 and 8 are compiled in Table 1.
2.3.2. Synthesis of ClCo(dSePhgH)2Py (1)
In a typical reaction, a solution of CoCl2$6H2O (0.100 g,
0.420 mmol) in 10 mL ethanol was added to a stirred solution of
bis(phenylselanyl)glyoxime (0.398 g, 0.840 mmol) in 15 mL ethanol
followed by the addition of pyridine 0.160 mL (2.0 mmol). The
stirring was continued further for 30 min and air was passed
through the solution for 2 h with occasional swirling. The solid
crude product was filtered, washed with water and dried over P2O5
and purified on a silica gel column using CH2Cl2 as eluent. Yield:
0.220 g (w54%). 1H NMR (500 MHz, CDCl3,
d
ppm): Pya ¼ 7.85 (2H,
d, J ¼ 5.6 Hz), Pyg ¼ 7.76 (1H, t, J ¼ 7.7 Hz), 7.26e7.21 (12H, m),
7.15e7.08 (10H, m), 18.04 (2H, s, OꢁH∙∙∙O). 13C NMR (125 MHz,
CDCl3, d ppm): 150.93 (Pya), 143.26 (C]N, Cq), 138.95 (Pyg), 132.72,
129.38, 128.42, 128.13, 125.99. Anal. Calcd for C33H27ClCoN5O4Se4:
C, 40.95; H, 2.81; N, 7.24. Found: C, 41.06; H, 2.77; N, 7.21.
2.3.3. Synthesis of RCo(dSePhgH)2Py (2e7): General procedure
A few drops of aqueous NaOH were added to the suspension of
ClCo(dSePhgH)2Py (0.100 g, 0.103 mmol) in 25 mL CH3OH and N2
gas was bubbled through the solution with stirring for 20 min.
Addition of pyridine (0.016 g, 0.206 mmol) followed by aqueous
NaBH4 (0.020 g, 0.529 mmol) at 0 ꢂC turned the solution blue.1 The
solution turned reddish-orange on addition of alkyl/benzyl halide
2.3. Syntheses
2.3.1. Synthesis of bis(phenylselanyl)glyoxime (dSePhgH2)
A degassed solution of NaBH4 (0.076 g, 2 mmol) in 1 mL water
was added drop wise to the solution of diphenyl diselenide (0.321 g,
1 mmol) in 20 mL dry ethanol under nitrogen atmosphere. On
completion of the addition, a degassed saturated solution of Na2CO3
was added drop wise until the reaction mixture became colorless. A
1
Pyridine must be added prior to the addition of NaBH4, otherwise the precip-
itation occurs.

K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3343e3350
3345
Table 1
Crystal data and structure refinement details for 1, 2, 6, 7 and 8.
parameters
1
2
6
7
8
Empirical formula
Formula weight
Temp (K)
C33H27ClCoN5O4Se4
967.82
100(2)
C34H30CoN5O4Se4
947.40
100(2)
C40H34CoN5O4Se4
1023.49
100(2)
C40H33ClCoN5O4Se4
1057.93
100(2)
C40H34CoN5O6Se4
1055.49
100(2)
Crystal system
Space group
Unit cell dimension
a (Å)
b (Å)
c (Å)
Orthorhombic
Pbcm
Orthorhombic
Pbcm
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
10.824(4)
13.179(5)
24.050(8)
90.00
90.00
90.00
3431(2)
4
1.874
4.868
10.907(3)
13.048(4)
24.257(7)
90.00
90.00
90.00
3452.2(18)
4
1.823
18.664(5)
12.647(5)
17.696(5)
90.000(5)
113.024(5)
90.000(5)
3844(2)
18.316(5)
13.942(4)
16.629(5)
90.00
113.927(5)
90.00
3881.7(18)
4
1.810
11.9113(17)
22.160(3)
15.508(2)
90.00
104.356(3)
90.00
3965.7(10)
4
1.768
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z
r
4
(calc), g/cm3
(Mo-K
) (mmꢁ1
1.768
4.283
m
a
)
4.761
4.311
4.158
F (000)
1888
1856
2016
2080
2080
Crystal size (mm3)
Index ranges
0.43 ꢃ 0.32 ꢃ 0.18
ꢁ13 ꢄ h ꢄ 13
ꢁ16 ꢄ k ꢄ 16
ꢁ15 ꢄ l ꢄ 29
18 222
0.37 ꢃ 0.23 ꢃ 0.17
ꢁ13 ꢄ h ꢄ 10
ꢁ15 ꢄ k ꢄ 15
ꢁ28 ꢄ l ꢄ 29
17 422
0.43 ꢃ 0.31 ꢃ 0.22
ꢁ22 ꢄ h ꢄ 20
ꢁ11 ꢄ k ꢄ 15
ꢁ21 ꢄ l ꢄ 20
20 199
0.32 ꢃ 0.22 ꢃ 0.18
ꢁ24 ꢄ h ꢄ 17
ꢁ17 ꢄ k ꢄ 18
ꢁ19 ꢄ l ꢄ 22
24 896
0.42 ꢃ 0.31 ꢃ 0.19
ꢁ14 ꢄ h ꢄ 14
ꢁ26 ꢄ k ꢄ 26
ꢁ18 ꢄ l ꢄ 12
21 027
No. of rflns collected
No. of indep rflns
GOOF on F2
3447
1.058
3278
1.048
7108
1.005
9500
1.059
7331
1.009
Final R indices (I > 2
s
(I))
R1 ¼ 0.0492
wR2 ¼ 0.1118
R1 ¼ 0.0747
wR2 ¼ 0.1498
3447/3/235
R1 ¼ 0.0404
wR2 ¼ 0.0900
R1 ¼ 0.0620
wR2 ¼ 0.1010
3278/8/236
R1 ¼ 0.0462
wR2 ¼ 0.0956
R1 ¼ 0.0763
wR2 ¼ 0.1092
7108/0/473
R1 ¼ 0.0598
wR2 ¼ 0.1300
R1 ¼ 0.1139
wR2 ¼ 0.1901
9500/1/504
R1 ¼ 0.0486
wR2 ¼ 0.1115
R1 ¼ 0.0784
wR2 ¼ 0.1290
7331/22/513
R indices (all data)
Data/restraints/param
(0.206 mmol). The stirring was continued at 0 ꢂC for 1 h. The
reaction mixture was slowly brought to room temperature and was
poured in ice cold water (20 mL). The resulting reddish-orange
precipitate was filtered, washed with ice-cold water and dried.
The crude product was purified by column chromatography using
CH2Cl2 as eluent.
1.19e1.15 (2H, m), 0.93e0.88 (2H, m), 0.79 (3H, t, J ¼ 7.4 Hz), 18.20
(2H, s, OꢁH∙∙∙O). 13C NMR (125 MHz, CDCl3, d ppm): 149.95 (Py
a),
139.77 (C]N, Cq), 137.71 (Pyg), 133.12, 129.18, 128.97, 127.92,
125.63, 35.15 (CoCH2), 32.94 (CH2), 23.67 (CH2), 13.89 (CH3). Anal.
Calcd for C37H36CoN5O4Se4: C, 44.91; H, 3.67; N, 7.08. Found: C,
45.07; H, 3.62; N, 7.04.
2.3.3.1. MeCo(dSePhgH)2Py (2). Yield: 0.055 g (w56%). 1H NMR
2.3.3.5. BnCo(dSePhgH)2Py (6). Yield: 0.060 g (w57%). 1H NMR
(500 MHz, CDCl3,
d
ppm): Pya ¼ 8.22 (2H, d, J ¼ 5.2 Hz), Pyg ¼ 7.83
(500 MHz, CDCl3,
d
ppm): Pya ¼ 8.09 (2H, d, J ¼ 4.6 Hz), Pyg ¼ 7.80
(1H, t, J ¼ 7.1 Hz), 7.23e7.07 (22H, m), 1.06 (3H, s, CoCH3), 18.28 (2H,
(1H, t, J ¼ 7.5 Hz), 7.17e7.12 (6H, m), 7.05e6.99 (19H, m), 6.94 (2H, d,
s, OꢁH∙∙∙O). 13C NMR (125 MHz, CDCl3,
d ppm): 149.83 (Pya),
J ¼ 7.5 Hz), 3.08 (2H, s, CoCH2), 18.25 (2H, s, OꢁH∙∙∙O). 13C NMR
139.85 (C]N, Cq), 137.74 (Py
g), 132.69, 129.12, 128.89, 127.77,
(125 MHz, CDCl3,
d ppm): 150.08 (Pya), 140.02 (C]N, Cq), 137.59
125.54, 12.26 (CH3). Anal. Calcd for C34H30CoN5O4Se4: C, 43.10; H,
3.19; N, 7.39. Found: C, 42.97; H, 3.17; N, 7.44.
(Pyg), 132.84, 129.02, 128.94, 128.07, 127.64, 125.38, 125.32, 33.92
(CH2). Anal. Calcd for C40H34CoN5O4Se4: C, 46.94; H, 3.35; N, 6.84.
Found: C, 47.03; H, 3.33; N, 6.81.
2.3.3.2. EtCo(dSePhgH)2Py (3). Yield: 0.053 g (w53%). 1H NMR
(500 MHz, CDCl3,
d
ppm): Pya ¼ 8.19 (2H, d, J ¼ 5.2 Hz), Pyg ¼ 7.83
2.3.3.6. 4-ClC6H4CH2Co(dSePhgH)2Py (7). Yield: 0.069 g (w63%). 1H
(1H, t, J ¼ 7.1 Hz), 7.24e7.05 (22H, m), 1.97 (2H, q, J ¼ 7.8 Hz, CoCH2),
NMR (500 MHz, CDCl3,
d
ppm): Pya ¼ 8.08 (2H, d, J ¼ 5.2 Hz),
0.35 (3H, t, J ¼ 7.8 Hz), 18.20 (2H, s, OꢁH∙∙∙O). 13C NMR (125 MHz,
Pyg ¼ 7.81 (1H, t, J ¼ 7.8 Hz), 7.20e7.02 (22H, m), 6.95 (2H, d,
CDCl3, d ppm): 149.87 (Pya), 139.57 (C]N, Cq), 137.57 (Pyg), 132.95,
J ¼ 8.4 Hz), 6.79 (2H, d, J ¼ 8.4 Hz), 2.96 (2H, s, CoCH2), 18.14 (2H, s,
129.04, 128.84, 127.78, 125.48, 29.09 (CH2), 16.19 (CH3). Anal. Calcd
for C35H32CoN5O4Se4: C, 43.72; H, 3.35; N, 7.28. Found: C, 43.89; H,
3.39; N, 7.34.
OꢁH∙∙∙O). 13C NMR (125 MHz, CDCl3, d ppm): 150.06 (Py
a), 140.11
(C]N, Cq), 137.69 (Pyg), 133.00, 132.78, 129.96, 129.09, 128.98,
128.87,128.12,127.78,125.44. Anal. Calcd for C40H33CoN5O4Se4Cl: C,
45.41; H, 3.14; N, 6.62. Found: C, 45.30; H, 3.17; N, 6.65.
2.3.3.3. n-PrCo(dSePhgH)2Py (4). Yield: 0.041 g (w41%). 1H NMR
(500 MHz, CDCl3,
d
ppm): Pya ¼ 8.21 (2H, d, J ¼ 4.6 Hz), Pyg ¼ 7.82
2.3.4. Molecular oxygen insertion in 6: synthesis of
BnO2Co(dSePhgH)2Py (8)
(1H, t, J ¼ 7.5 Hz), 7.23e7.05 (22H, m), 1.79 (2H, t, J ¼ 8.7 Hz, CoCH2),
0.94e0.86 (2H, m), 0.73 (3H, t, J ¼ 7.1 Hz), 18.20 (2H, s, OꢁH∙∙∙O).
A solution of 6 (0.050 g) in 15 mL dry CH2Cl2 was irradiated at 0 ꢂC
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.
The evaporation of solvent under reduced pressure afforded the
crude product which was further purified on the silica gel column
using 5% EtOAc/CH2Cl2 mixture solvent as eluent. Yield: 0.041 g
13C NMR (125 MHz, CDCl3, d ppm): 149.97 (Py
a), 139.82 (C]N, Cq),
137.71 (Pyg), 133.12, 129.17, 128.93, 127.93, 125.62, 37.65 (CoCH2),
24.12 (CH2), 14.49 (CH3). Anal. Calcd for C36H34CoN5O4Se4: C, 44.33;
H, 3.51; N, 7.18. Found: C, 44.18; H, 3.48; N, 7.22.
2.3.3.4. n-BuCo(dSePhgH)2Py (5). Yield: 0.046 g (w45%). 1H NMR
(500 MHz, CDCl3,
(1H, t, J ¼ 7.7 Hz), 7.23e7.05 (22H, m), 1.83 (2H, t, J ¼ 8.8 Hz, CoCH2),
(w79%). 1H NMR (500 MHz, CDCl3,
J ¼ 5.2 Hz), Pyg ¼ 7.75 (1H, t, J ¼ 7.8 Hz), 7.32e7.27 (5H, m), 7.16e7.10
(14H, m), 6.99 (8H, t, J ¼ 7.8 Hz), 4.30 (2H, s, O2CH2), 18.29 (2H, s,
d
ppm): Pya ¼ 7.98 (2H, d,
d
ppm): Pya ¼ 8.22 (2H, d, J ¼ 5.2 Hz), Pyg ¼ 7.81

3346
K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3343e3350
13
OꢁH∙∙∙O). 13C NMR (125 MHz, CDCl3, d ppm): 150.90 (Py
a
), 142.29
understood by comparing the Dd
(
C
C]N
) [30] values of the diox-
13
(C]N, Cq),138.35 (Py
g
),136.81,132.88,132.76,129.47,129.14,128.17,
ime in R/XCo(dioxime)2Py. The upfield shift Dd
(
C
C]N
) is smaller in
127.91, 125.69, 125.59, 78.47 (OCH2). Anal. Calcd for C40H34Co-
N5O6Se4: C, 45.52; H, 3.25; N, 6.64. Found: C, 45.69; H, 3.28; N, 6.75.
2e7 as compared to the corresponding gH, dmgH and dpgH
complexes but is larger than the dSPhgH and dmestgH analogues
(Table S3) and follows the order gH
> dmgH > dpgH >
2.4. Kinetic study
dSePhgH > chgH > dSPhgH > dmestgH. This means that the charge
density on Co(dioxime)2 in 2e7 is higher than the dSPhgH and
dmestgH complexes.
The kinetics of oxygen insertion in the CoꢁC bond of complexes
6 and 7 under photochemical conditions were monitored spectro-
photometrically at
The chemical shifts of RCH2 and Pya are further affected in the
0
ꢂC under pseudo-first-order conditions.
dioxy complex 8. CH2eO2 is shifted downfield by 1.22 ppm in 1H
Oxygen was bubbled through the solution and hence used in large
excess. The progress of the reaction was monitored following the
changes (decreases) in absorbance (the absorbance due to the CoꢁC
CT band around 460 nm) at regular intervals. Ocean Optics software
in the UVevis machine allows continuous scan for the change in
absorbance at a particular wavelength with time. The kobs rate
constants were obtained from the slope of the linear plots of
ln(AtꢁAN), versus time, where At is the absorbance at time t and AN
is the final absorbance. Kinetic data were analyzed with ORIGIN 8.
NMR and 44.55 ppm in 13C NMR as compared to 6. 1H Py
a
reso-
13
nance appears upfield (0.11 ppm) and
C
signal appears
C]N
downfield by 2.27 ppm as compared to 6. The data points to the
higher cobalt anisotropy in the dioxy complex 8 than 6.
3.3. X-ray crystallographic studies. Description of the molecular
structures of 1, 2, 6 and 7
Single-crystals suitable for X-ray crystallographic analyses were
obtained by slow evaporation of solvent from the solution of
complexes 1, 2, 6 and 7 (CH2Cl2/CH3OH). Molecular structures along
with selected numbering scheme are shown in Figs. 1e4 and
selected bond lengths, bond angles and structural parameters are
given in Table 2. It can be seen from Figs.1e4 that all complexes have
distorted octahedral geometry around the central cobalt atom with
four nitrogen atoms of the dioxime (dSePhgH) in the equatorial
plane and, pyridine and Cl (Me or Bn) are axially coordinated.
Complexes 1 and 2 have a symmetry plane, and the molecular
building blocks are formed by a symmetric operation on one
asymmetric unit. The benzyl group in complexes 6 and 7 is located
over the dioxime wing and shows some interaction with the diox-
ime ring current similar to the reported benzyl cobaloximes [31,32].
The CoꢁCl or CoꢁC bond distances [2.224(2), 1.992(5) Å] and
CoꢁNpy bond distances [1.971(6), 2.064(5) Å] in 1 and 2 are almost
identical with the reported values in the corresponding Cl/
MeCo(dioxime)2Py complexes (Table S4). The CoꢁC [2.077(5),
2.073(6) Å] and CoꢁNpy bond distances [2.070(4), 2.061(5) Å] in the
benzyl complexes 6 and 7 do not differ significantly and also they
are comparable with the reported values in BnCo(dSPhgH)2Py
(Table S5). As expected, the data in Table 2 show that the CoꢁC
3. Results and discussion
3.1. Synthesis
Bis(phenylselanyl)glyoxime(dSePhgH2) was prepared from sodium
benzeneselenolate and dichloroglyoxime in ethanol solvent (Scheme
1). Aerial oxidation of the stoichiometric mixture of CoCl2$6H2O,
dSePhgH2 and pyridine in ethanol formed ClCo(dSePhgH)2Py, similar
to the known chlorocobaloximes with other dioximes. The oxidative
alkylation of CoI(dSePhgH)2Py with alkyl/benzyl halide in CH3OH
under an inert atmosphere formed organocobaloximes 2-7. The
preparation, unlike the other reported organocobaloximes, required
the addition of pyridine before the addition of NaBH4 otherwise the
precipitation occurred which led to very low yield of the product.
Molecular oxygen insertion in 6 under photolytic conditions at 0 ꢂC
formed the dioxy compound (8) within 1 h in good yield.
3.2. Spectroscopy
All complexes (1e8) and dSePhgH2 have primarily been char-
acterized by 1H and 13C NMR spectroscopy and the spectral data are
summarized in Experimental Section. The dioxime dSePhgH2 is
partially soluble in CDCl3 and a drop of DMSO-d6 is necessary to
dissolve it. The 1H NMR spectra of these complexes are easily
assigned on the basis of the chemical shifts. The signals are assigned
according to their relative intensities and are consistent with the
related alkyl and benzyl cobaloximes with gH, dmgH, dpgH and
dSPhgH. The 1H Pyb resonance is obscured in all the complexes.
The cis and trans influence study includes the investigation of all
possible steric and electronic effects of the dioxime on the axial
ligands and vice versa. The NMR studies of cobaloximes have
shown that Py
affected by the variation in equatorial dioxime [22,24]. Py
a
and the
a
-carbon bonded to cobalt are most
protons
a
in 2-7 show considerable upfield shift as compared to the corre-
sponding gH, dmgH, chgH, dpgH and dmestgH complexes and this
upfield shift is similar to the dSPhgH complexes. Overall, (Δd a)
1Hpy
follows the upfield shift order dmestgH < dpgH < gH z dmgH z
chgH < dSPhgH z dSePhgH (Table S1). This high upfield shift
occurs by the shielding of Pya protons by the magnetic anisotropy
of the phenyl ring of SePh groups.
The effect of cis influence on the chemical shift of CoꢁCH2 protons
in complexes 2e7 is similar to dSPhgH and follows the order
dmgH < gH < dSePhgH z dSPhgH < dpgH < dmestgH (Table S2).
The extent of electron density on the Co(dioxime)2 chelate ring
for different dioximes (keeping R/X and Py constant) can be
Fig. 1. Molecular structure of 1.

K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3343e3350
3347
Table 2
Selected bond lengths, bond angles and other relevant structural parameters for 1, 2,
6, and 7.
parameters
1
2
6
7
CoꢁC/X (Å)
2.224(2)
1.971(6)
177.9(2)
þ3.98(28)
90.0
1.992(5)
2.064(5)
175.7(3)
þ6.84(19)
90.0
2.077(5)
2.070(4)
174.7(2)
ꢁ0.78(15)
68.2(4)
2.073(6)
2.061(5)
175.1(3)
þ1.96(14)
89.9(7)
CoꢁNpy (Å)
X/CꢁCoꢁNpy (ꢂ)
a
s
(ꢂ)
(ꢂ)
d (Å)
∙∙∙
þ0.0314(11)
þ0.0530(8)
þ0.0431(7)
þ0.0479(9)
p
p
(Å)
3.525(1)
3.5204(9)
bond length increases from 1.992(5) Å in 2 to 2.077(5) Å in 6 with
increasing bulk of alkyl group.
Due to flexibility, the Co(dSePhgH)2 unit undergoes geometrical
deformation which is roughly represented by the displacement of
cobalt atom from mean equatorial N4 plane (d) [33] and by the
butterfly bending angle between two dioxime units (a) [33]. The
deviations of the central cobalt atom from equatorial N4 plane
are þ0.0314(11), þ0.0530(8), þ0.0431(7) and þ0.0479(9) Å in 1, 2, 6
and 7 respectively. The deviation is small and is toward the axial
pyridine in all cases. The butterfly bending angle in 2 is þ6.84ꢂ and
is much larger than the reported value in MeCo(dioxime)2Py
complexes (dpgH, 4.7ꢂ; dmgH, 3.2ꢂ; gH, 2.0ꢂ), but slightly smaller
than MeCo(dmestgH)2Py complex [22]. The corresponding values
in 1, 6 and 7 are þ3.98, ꢁ0.78 and þ1.96ꢂ, respectively.
Fig. 2. Molecular structure of 2.
The pyridine ring is practically planar in all cases and is parallel
to the dioxime CꢁC bond bonds in 1, 2 and 7. Its conformation being
defined by the twist angles (torsion angle,s
)2 90.0, 90.0 and 89.9ꢂ in
1, 2, and 7. The complex 6 has very low twist angle (68.2ꢂ) and the
plane of pyridine lies below one of the NꢁO bonds of the dioxime.
Also, pyridine is inclined toward one dioxime wing (C31ꢁN5ꢁCo)
by 170.51ꢂ, which is unusual and unique for an organocobaloxime.
This may have resulted from the strong CꢁH∙∙∙
p interaction
[C21ꢁH21∙∙∙ (Py) ¼ 3.1849(7) Å, Fig. 3].
p
3.4. Orientation of SePh groups with respect to dioxime plane
In an extensive work on RCo(DBPh2)2L complexes with different
R and L axial ligands by NMR and X-ray, Randaccio and coworkers
have shown that the nature of the axial ligands determines the
conformation of the equatorial moiety (phenyl groups of BPh2)
[34e37]. They suggested that the steric bulk of the axial ligand and
its electronic interactions with the axial phenyls of the BPh2 groups
played an important role. Recently we showed that the SPh groups
in RCo(dSPhgH)2Py complexes adopted different conformations
depending of the steric bulk of R and also, the structure and NMR
were affected by the orientation of the SPh groups [24]. On the
similar lines, SePh groups in 1, 2, 6 and 7 adopt different confor-
mations in the solid state, for example, SePh groups exhibit up-
down, up-down conformation in 1 and 2, and down-down,
down-down conformation in 6 and 7. This occurs because the
benzyl group is more bulky than Cl or Me and its free rotation along
the CoꢁC bond leads to steric interactions with the equatorial SePh
groups (Scheme 2).
Fig. 3. Molecular structure of 6.
3.5. Reactivity studies
The inherently weak CoꢁC bond in the organocobaloximes
undergoes homolytic cleavage with visible light, similar to the
2
The torsion angle (s) is the angle between two virtual planes that bisect
cobaloxime plane. This shows dihedral angle between the plane of pyridine and the
Fig. 4. Molecular structure of 7.
plane bisecting the CeC bond of two dioxime units through the cobalt atom.

3348
K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3343e3350
Scheme 2. Schematic representation of orientation of SePh groups with respect to
dioxime plane in 1, 2, 6 and 7.
activation of vitamin B12 by apoenzyme [6,38e40] and the insertion
of molecular oxygen into the CoꢁC bond has extensively been used
to test the reactivity of these complexes [41e48]. Since the stability
of the CoꢁC bond is affected by the dioxime (cis-influence) [23], we
have studied the CoꢁC bond reactivity in complexes 6 and 7 by
measuring the rate of oxygen insertion under photolytic conditions.
The benzyl system has been particularly chosen since the CoꢁC
bond is inherently weak and also the weak interaction between the
benzyl group and the dioxime moiety might influence the CoꢁC
bond reactivity [31,49]. The reaction obeys a pseudo-first-order rate
law and the rates lie between the dmestgH and dpgH complexes
(Table 3). The overall rate follows the order dmestgH > dS
ePhgH > dpgH > dSPhgH ꢀ dmgH > gH. The variation of substit-
uent in the dioxime from carbon to SPh does not change the rate
much; however change with SePh has led to faster rate of oxygen
insertion.
Fig. 5. Molecular structure of 8.
A significant reactivity difference in oxygen insertion in 6 and 7
has been observed, although the CoꢁC bond length is similar in
both cases. Recently we have proposed that the puckering in the
complex 8 has the highest value of dihedral angle (124.5ꢂ) whereas
it is lowest in complex A (106.2ꢂ). The higher the dihedral angle the
greater the BPꢁLP interaction. The steric cis interaction of
[Co(dioxime)2] moiety with the axial ligand is much smaller in the
present complex than the reported dioxy complexes as it contains
the lowest CoeOeO bond angle (110ꢂ vs 116ꢂ).
Co(dioxime)2 (
[32]. This may be the case here also; the d values are similar but
values are different and changes from negative to positive in
complexes 6 and 7, respectively. The puckering of dioxime plane
towards the axial R group (positive value) might be the reason for
a
and d values) influences the CoꢁC bond reactivity
a
a
The orientation of the benzyl group in 8 is guided by strong
higher rate in 7 as compared to the complex 6.
CꢁH∙∙∙
p
interactions with the dioxime and this has led to OꢁO
and CꢁC(Ph) plane almost parallel (178ꢂ) to each other. This has
3.6. Description of the molecular structure of 8
partially resulted from the p∙∙∙p interaction (3.666 Å) between the
phenyl rings of benzyl groups in the crystal packing (Figure S3).
The data in Table 4 shows that the CoeO, CoeNpy, and OeO bond
distances in 8 do not differ significantly from the reported oxygen-
inserted complexes (A, B, and C), however, equatorial dioxime
plane is somewhat puckered in the former as it contains high
A slow evaporation of solvent from the solution of 8 (CH2Cl2/
CH3OH) resulted in the formation of brown crystals suitable for X-
ray studies. Details about data collection, refinement, and structure
solution are summarized in Table 1 and molecular structure with
selected numbering schemes is shown in Fig. 5. Selected geomet-
rical parameters are given in Table 4 and are compared with the
known dioxy complexes containing Co(O2) bound to a primary
carbon atom. The SePh groups in 8 exhibit up-down, up-down
conformation; similar to the confirmation in 1 and 2 and indicates
that the steric interaction of the axial benzyl group with the
equatorial SePh groups is decreased after the oxygen insertion.
A significant parameter for the peroxide compounds is the
ReOꢁOꢁR0 dihedral angle and it is governed by the bond pair-lone
pair (BPeLP) and LPꢁBP interactions around the OꢁO bond. The
a
value. The large a value may have resulted due to the CeH∙∙∙p
interactions and the crystal packing.
Table 4
Selected bond lengths, bond angles and structural parameters for 8 and comparison
with other dioxy complexes (A ¼ 4eCNC6H4CH2(O2)Co(dmestgH)2Py [23]; B ¼ 2-
naphthylCH2(O2)Co(dmestgH)2Py [23]; C ¼ Bn(O2)Co[dS(3,5-Me2C6H3)gH]2Py [32]).
parameters
8
A
B
C
CoeOax (Å)
CoeNpy (Å)
OeO (Å)
1.866(3)
2.004(4)
1.466(4)
1.411(7)
110.9(3)
106.0(4)
124.5(4)
106.3(4)
178.1(4)
174.21(17)
1.896(2)
1.995(3)
1.435(3)
1.421(4)
116.43(17)
107.5(2)
106.2(2)
115.4(3)
60.8(4)
1.875(4)
1.978(4)
1.399(5)
1.446(7)
116.5(3)
108.1(4)
ꢁ114.0(4)
105.3(5)
175.3(5)
171.8(2)
þ0.021
1.891(5)
1.991(5)
1.424(6)
1.433(7)
116.0(3)
103.8(4)
Table 3
OeC (Å)
Pseudo-first-order rate constant (kobs) for oxygen insertion in RCo(dioxime)2Py.
CoeOeO (ꢂ)
OeOeC (ꢂ)
CoeOeOeC (ꢂ)
OeCeC (ꢂ)
OeOeCeC (ꢂ)
RCo(dioxime)2Py
kobs (sꢁ1
)
Ref.
ꢁ114.4(5)
BnCo(gH)2Py
BnCo(dmgH)2Py
BnCo(dpgH)2Py
BnCo(dSPhgH)2Py
BnCo(dmestgH)2Py
BnCo(dSePhgH)2Py
4-ClBnCo(dSePhgH)2Py
7.1 ꢃ 10ꢁ4
1.2 ꢃ 10ꢁ3
4.8 ꢃ 10ꢁ3
1.29 ꢃ 10ꢁ3
5.0 ꢃ 10ꢁ2
6.95 ꢃ 10ꢁ3
1.13 ꢃ 10ꢁ2
[23]
[23]
[23]
[32]
[23]
this work
this work
108.4(5)
ꢁ165.6(5)
173.5(3)
þ0.007(9)
þ1.105(15)
68.77(14)
N
pyeCoeOax (ꢂ)
173.80(11)
þ0.011
d (Å)
þ0.0190(8)
þ6.09(17)
66.92(16)
a
s
(ꢂ)
(ꢂ)
3.24(11)
79.84(8)
3.079(1)
3.37(21)
88.60(10)
3.110(2)
CeH∙∙∙p (Å)

K. Kumar, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 3343e3350
3349
Table 5
CV Data for 1e3 in CH2Cl2 and nBu4NPF6 at 0.1 V/s at 25 ꢂC.
No
Co(III)/Co(II)
Co(II)/Co(I)
Co(IV)/Co(III)
E1/2(V)a
E1/2b (V)
E1/2(V)a
E1/2 (V)
a
b
b
Epc (V)
Epc (V)
(D
Ep (mV))
(DEp (mV))
1
2
3
ꢁ0.285
ꢁ1.155
ꢁ1.174
ꢁ0.711
ꢁ1.582
ꢁ1.601
ꢁ0.530(125)
ꢁ0.957
1.430 (124)
1.223 (89)
1.178 (99)
1.003
0.796
0.751
e
e
e
e
a
Vs. Ag/AgCl.
b
Vs. Fc/Fcþ (E1/2 ¼ 0.4269 V).
shifted and hence the Co(II)/Co(I) response is further cathodically
shifted and is not observed even down to ꢁ1.5 V. The values show
that the electrochemical reduction of
2 and 3 is easier as
compared to the alkyl cobaloxime with the dSPhgH equatorial
ligand (Table S6).
Fig. 6. Cyclic voltammogram of 1 in CH2Cl2 with 0.1 M nBu4NPF6 as supporting elec-
4. Conclusion
trolyte at 0.1 V/s at 25 ꢂC.
The synthesis and characterization of a new series of cobalox-
imes with bis(phenylselanyl)glyoxime as equatorial ligand has been
described. The reactivity of benzyl cobaloximes with molecular
oxygen has been examined and the rate of insertion depends on the
dioxime and follow the order dmestgH > dSePhgH > dpgH >
dSPhgH ꢀ dmgH > gH. The conformation of the SePh groups in the
benzyl cobaloxime and its dioxy product is different and indicates
that the steric interaction of the axial benzyl group with the
equatorial SePh groups is decreased after the oxygen-insertion.
3.7. Electrochemical studies (cyclic voltammetry)
The electrochemical behavior of 1e3 has been studied to
understand the effect of dioxime (dSePhgH) on the redox potentials
of the cobalt center. The cyclic voltammograms are shown in Figs. 6
and 7, and the CV data are given in Table 5. The cyclic voltammo-
gram of 1 (Fig. 6) shows one irreversible peak at ꢁ0.285 V and one
quasi-reversible peak (E1/2 ¼ ꢁ0.530 V) in the reductive half cor-
responding 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 1.430 V) is observed. A similar cyclic voltam-
mogram was shown by ClCo(dSPhgH)2Py [24]. However, on
comparison of these values with those for ClCo(dSPhgH)2Py,
complex 1 is more difficult to reduce from Co(III)/Co(II) and from
Co(II)/Co(I) (Table S6).
Acknowledgement
This work has been supported by the grants from DST and CSIR,
India. K. K. thanks UGC, New Delhi, India for Senior Research
Fellowship.
Appendix A. Supplementary material
The cyclic voltammograms of the organocobaloximes (2 and 3)
show only one irreversible reduction response corresponding to
Co(III)/Co(II) at ꢁ1.155 and ꢁ1.174 V, respectively (Fig. 7). 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 1.223 and 1.178 V in complex 2 and 3, respectively. Due
to the higher electron donation ability of the alkyl groups, the
Co(III)/Co(II) redox process in 2 and 3 is considerably cathodically
CCDC 819076ꢁ819080 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Appendix. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2011.07.012.
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