Cobaloximes with mixed dioximes having C and S side chains: Synthesis, structure and reactivity

Article abstract of DOI:10.1016/j.jorganchem.2011.02.033

Ten mixed dioxime complexes RCo(L)(dmgH)Py [R = Cl, Me, Et, Bu, Benzyl] [L = dSPhgH (1-5) and dSEtgH (6-10)] have been synthesized and characterized by NMR. Formation of 1 and 6 is very fast and takes only 5 and 15 min in ethanol. Molecular oxygen insertion in 5 and 10 is monitored and forms mixture of products within 5 min. The crystal structure of 1, 4, 5, 6, 8 and 10 is reported. Benzyl ring is oriented over dmgH wing in both 5 and 10 and has a weak C-H...π interaction (3.33 and 3.22 ) and this causes high upfield shift of the dmgH protons. Electrochemical study on 1, 4, 5, 6, 8 and 10 is also reported. Because of increased electron donation by SEt group, 6 is more difficult to reduce than 1.

Full text of DOI:10.1016/j.jorganchem.2011.02.033

Journal of Organometallic Chemistry 696 (2011) 2693e2701
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cobaloximes with mixed dioximes having C and S side chains: Synthesis,
structure and reactivity
,b,
Gargi Dutta a, B.D. Gupta a
*
a Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
b Bahra University, Waknaghat, Shimla Hills 173215, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Ten mixed dioxime complexes RCo(L)(dmgH)Py [R ¼ Cl, Me, Et, Bu, Benzyl] [L ¼ dSPhgH (1e5) and
dSEtgH (6e10)] have been synthesized and characterized by NMR. Formation of 1 and 6 is very fast and
takes only 5 and 15 min in ethanol. Molecular oxygen insertion in 5 and 10 is monitored and forms
mixture of products within 5 min. The crystal structure of 1, 4, 5, 6, 8 and 10 is reported. Benzyl ring is
Received 17 January 2011
Received in revised form
25 February 2011
Accepted 28 February 2011
oriented over dmgH wing in both 5 and 10 and has a weak CeH.
p interaction (3.33 Å and 3.22 Å) and
this causes high upfield shift of the dmgH protons. Electrochemical study on 1, 4, 5, 6, 8 and 10 is also
reported. Because of increased electron donation by SEt group, 6 is more difficult to reduce than 1.
Ó 2011 Published by Elsevier B.V.
Keywords:
Mixed dioximes
Equilibration
Reaction monitoring
1. Introduction
RCo(dmgH) (chgH)B in solution but did not isolate this interme-
diate. Only solution NMR values of the mixtures were reported.
Organocobaloximes1 have been known for more than four
decades [1e12] and have extensively been used to mimic the B12
coenzyme [13e18] and the studies have continued to compliment
those on the more complex cobalamin and B12 based protein [19].
However, organocobaloximes with mixed dioximes have virtually
been unknown until recently. The first mention of these complexes
was made by Schrauzer and Windgassen in 1966 who proposed
that the following ligand exchange reaction undoubtedly pro-
ceeded by stepwise displacement of the dmgH2 ligand and the
The synthesis of RCo(L)(L0)Py complexes [L
¼
dpgH and
L0 ¼ dmgH, gH, chgH; R ¼ Cl, alkyl, benzyl] using different methods
has recently been published from our group [22e26]. A mixture of
three products, RCo(L)2Py, RCo(L0)2Py, and RCo(L)(L0)Py was always
formed and an equilibration between these products occurred in
solution and was time dependent. Both the dioximes in all the
reported complexes have carbon side chain. Since the nature of
dioximes and solvent affect the equilibration process we have
extended the study to mixed dioxime complexes having two
dissimilar dioximes, one with C side chain(dmgH) and the other
with S side chain (SPh or SEt). The study will allow us to make direct
comparison with the previously reported mixed dioxime complexes
in terms of synthesis, spectroscopy, structure and reactivity.
reaction did not involve an ionic intermediate like CH3eCo2þ
However, they failed to isolate the intermediate mixed ligand
complex, MeCo(dmgH)(chgH)B (B ¼ Py or H2O) [20].
.
140ꢁC
We herein report the synthesis and spectroscopic study of RCo(L)
(dmgH)Py [R ¼ Cl, Me, Et, Bu, Bn] [L ¼ dSPhgH (1e5); dSEtgH (6e10)]
complexes (Chart 1). The formation of 1 and 6 in different solvents
has also beenmonitoredwith time. Molecularoxygeninsertionin the
benzyl complexes, 5 and 10 is carried out and carefully monitored.
The X-ray structure of 1, 4, 5, 6, 8 and 10 is reported for the first time.
Electrochemical study of some complexes is also reported.
MeCoðdmgHÞ2H2O þ chgH2 toꢀul!ene;Py MeCoðchgHÞ2Py
Subsequently, Johnson et al. in 1977 reported the kinetics and
mechanistic details of the apparent alkyl transfer from alkylcoba-
loximes to cobaloxime (I), cobaloxime (II) and cobaloxime (III)
reagents [21]. They proposed the formation of mixed ligand species,
* Corresponding author. Bahra University, Waknaghat, Shimla Hills 173215, India.
Tel.: þ91 512 2597046; fax: þ91 512 2597436.
2. Experimental section
E-mail address: bdg@iitk.ac.in (B.D. Gupta).
1
Organocobaloximes have the general formula RCo(L)2B, where R is an organic
2.1. Materials and physical measurements
group s-bonded to cobalt. B is an axial base trans to the organic group, and L is
a monoanionic dioxime ligand (e.g. glyoxime (gH), dimethylglyoxime (dmgH), 1,2-
cyclohexanedione dioxime (chgH), diphenylglyoxime (dpgH), dimesitylglyoxime
(dmestgH), dithiophenylglyoxime (dSPhgH) and dithioethylglyoxime (dSEtgH).
Cobalt chloride hexahydrate (SD fine, India), glyoxime (Caution!
it is highly flammable and explosive when dry) (Alfa Aesar,
0022-328X/$ e see front matter Ó 2011 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2011.02.033

2694
G. Dutta, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 2693e2701
Chart 1. Cobaloximes under consideration.
Fig. 3. Monitoring of oxygen insertion of 5 in dichloromethane at 0 ꢁC under oxygen.
1H and 13C Spectra were recorded on a JEOL JNM LAMBDA 400 FT
NMR Spectrometer (400 MHz for 1H and 100 MHz for 13C) in CDCl3
solution with TMS as internal standard. NMR data are reported in
ppm. Elemental analysis was carried out at IIT Kanpur.
The molar percentage of the species in Figs. 1 and 2 has been
calculated from the integration of 1H NMR signals of Pya whereas in
Figs. 3 and 4 it is calculated from the integration of 1H NMR signals
of CH2 group bound to CoO2. 1a, 1b, 6a, 2ae5a, 7ae10a, 7be10b, 5c,
5d, 10c, 10d are characterized by 1H NMR (Table S1).
2.2. X-ray crystal structure determination and refinements
A slow evaporation of solvent from the solution of complexes 1,
4, 5, 6, 8, 10 (CH2Cl2/MeOH for 4, 5, 8 and 10 and CH2Cl2/MeOH/
Hexane for 1 and 6) in the refrigerator resulted in the formation of
orange crystals. Single-crystal X-ray data were collected using
Fig. 1. Equilibration of 1, 1a and 1b in ethanol.
Lancaster), iodomethane, ethyl, butyl and benzyl bromide
(Aldrich chemical company) were purchased and used as received.
Bis(thiophenyl)glyoxime and Bis(thioethyl)glyoxime were prepared
from dichloroglyoxime following the reported procedure [10]. Silica
gel (100e200 mesh) and distilled solvents were used in all reactions
and chromatographic separations. A julabo UC-20 low temperature
refrigerated circulator was used to maintain the desired tempera-
ture. Cyclic voltammetry measurements were carried out using
a BAS Epsilon electrochemical work stationwith a platinumworking
electrode, Ag/AgCl reference electrode (3 M KCl) and a platinum-
wire counter electrode. All the measurements were performed in
0.1 M nBu4NPF6 in dichloromethane (dry) at a concentration of 1 mM
of each complex.
graphite-monochromated Mo K
a
radiation (
l
¼ 0.71073 Å) at 100 K
for 1, 4, 5, 6 and 10; at 273 K for 8. The linear absorption coefficients,
scattering factors for the atoms, and the anomalous dispersion
corrections were taken from the International Tables for X-ray
Crystallography [27]. The data integration and reduction were
processed with SAINT Software [28]. An empirical absorption
correction was applied to the collected reflections with SADABS
[29] using XPREP [30]. The structure was solved by direct methods
Fig. 2. Equilibration of 1, 1a and 1b in acetone.
Fig. 4. Monitoring of oxygen insertion of 10 in dichloromethane at 0 ꢁC under oxygen.

G. Dutta, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 2693e2701
2695
Table 1
Crystal data and structure refinement details for compounds 1, 4 and 5.
Parameters
1
4
5
Empirical formula
Formula weight
Temp (K)
C23H23ClCoN5O4S2
591.98
100(2)
C27H32CoN5O4S2
613.65
100(2)
C30H30CoN5O4S2
647.64
100(2)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
Orthorhombic
P 21 21 21
Monoclinic
C2/c
Monoclinic
P 21/n
12.205(5)
12.599(5)
16.347(5)
90.000(5)
90.000(5)
90.000(5)
2513.7(16)
4
38.662(5)
11.222(5)
13.434(5)
90.000(5)
91.521(5)
90.000(5)
5826(3)
10.629(5)
14.453(5)
19.109(5)
90.000(5)
103.404(5)
90.000(5)
2855.6(18)
4
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z
r
8
(calc), mg/m3
(Mo-K
) (mmꢀ1
1.564
0.996
1.399
0.773
1.506
0.794
m
a
)
F (000)
1216
2560
1344
0.32 ꢂ 0.27 ꢂ 0.22
Crystal size (mm3)
Index ranges
0.40 ꢂ 0.35
0.47 ꢂ 0.34
ꢂ 0.30
ꢂ 0.22
ꢀ15 ꢃ h ꢃ 16
ꢀ10 ꢃ k ꢃ 16
ꢀ21 ꢃ l ꢃ 21
16389
ꢀ33 ꢃ h ꢃ 46
ꢀ12 ꢃ k ꢃ 13
ꢀ16 ꢃ l ꢃ 16
15323
ꢀ12 ꢃ h ꢃ 11
ꢀ15 ꢃ k ꢃ 17
ꢀ19 ꢃ l ꢃ 23
15084
5301
0.998
No. of rflns collected
No. of indep rflns
GOOF on F2
6244
1.112
5413
0.985
Final R indices
(I > 2s(I))
R indices (all data)
R1 ¼ 0.0578
WR2 ¼ 0.1283
R1 ¼ 0.0806
WR2 ¼ 0.1693
6244/0/325
R1 ¼ 0.0603
WR2 ¼ 0.1432
R1 ¼ 0.0919
WR2 ¼ 0.1662
5413/0/352
R1 ¼ 0.0552
WR2 ¼ 0.1388
R1 ¼ 0.0719
WR2 ¼ 0.1572
5301/0/379
Data/restraints/param
using SIR-97 [31] and were refined on F2 by the full-matrix least
squares technique using the SHELXL-97 [32] program package. All
non-hydrogen atoms were refined with anisotropic displacement
parameters. The hydrogen atom positions or thermal parameters
were not refined but were included in the structure factor calcu-
lations. The equatorial SEt groups in complex 8 were found to be
disordered and were modelled satisfactorily. The pertinent crystal
data and refinement parameters are compiled in Tables 1 and 2.
Table 2
Crystal data and structure refinement details for compounds 6, 8 and 10.
Parameters
6
8
10
Empirical formula
Formula weight
Temp (K)
C15H23ClCoN5O4S2
495.90
100(2)
C17H28CoN5O4S2
489.49
273(2)
C22H30Co N5O4S2
551.58
100(2)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
Monoclinic
C c
Monoclinic
P21/n
Orthorhombic
P 21 21 21
14.527(4)
8.554(4)
17.152(6)
90.000
109.441(9)
90.000
2009.8(12)
4
1.639
16.150(5)
9.423(5)
8.357(5)
9.274(5)
31.861(5)
90.000(5)
90.000(5)
90.000(5)
2469(2)
16.573(5)
90.000(5)
113.722(5)
90.000(5)
2309.0(16)
4
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z
r
4
(calc), mg/m3
(Mo-K
) (mmꢀ1
1.408
0.955
1.484
0.903
m
a
)
1.227
F (000)
1088
1024
1128
Crystal size (mm3)
Index ranges
0.46 ꢂ 0.35
0.32 ꢂ 0.24
0.42 ꢂ 0.36
ꢂ 0.21
ꢂ 0.18
ꢂ 0.22
ꢀ19 ꢃ h ꢃ 18
ꢀ11 ꢃ k ꢃ 9
ꢀ18 ꢃ l ꢃ 22
6346
ꢀ19 ꢃ h ꢃ 15
ꢀ11 ꢃ k ꢃ 11
ꢀ18 ꢃ l ꢃ 20
11820
ꢀ10 ꢃ h ꢃ 10
ꢀ11 ꢃ k ꢃ 7
ꢀ38 ꢃ l ꢃ 38
13092
No. of rflns collected
No. of indep rflns
GOOF on F2
3755
1.135
4254
0.978
4580
0.979
Final R indices
(I > 2s(I))
R indices (all data)
R1 ¼ 0.0617
wR2 ¼ 0.1414
R1 ¼ 0.0803
wR2 ¼ 0.1833
3755/2/253
R1 ¼ 0.0585
wR2 ¼ 0.1535
R1 ¼ 0.0974
wR2 ¼ 0.1995
4254/4/289
R1 ¼ 0.0525
wR2 ¼ 0.1383
R1 ¼ 0.0556
wR2 ¼ 0.1416
4580/0/307
Data/restraints/param

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G. Dutta, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 2693e2701
Scheme 1.
Scheme 2.
2.3. Synthesis
(6e8%) and RCo(dSEtgH)2Py (4e7%), were formed in the reaction
with (6).
2.3.1. Synthesis of ClCo(dmgH)(dSPhgH)Py (1)
Pyridine (0.265 ml, 0.0032 mol) was added with constant stir-
ring to a refluxing solution of CoCl2$6H2O (0.391 gm, 0.0016 mol),
dmgH2 (0.190 gm, 0.0016 mol), dSPhgH2 (0.500 gm, 0.0016 mol) in
95% ethanol. The solution was allowed to cool to room temperature
and air was bubbled through the reaction mixture for 5 min. The
residue obtained after evaporation of solvent was extracted with
dichloromethane and the organic layer was dried over anhydrous
sodium sulphate. The solid product obtained after evaporation of
dichloromethane was chromatographed on silica gel column
(100e200 mesh). ClCo(dSPhgH)2Py (1a) (0.037 gm, 3%) eluted out
first with dichloromethane, ClCo(dmgH)(dSPhgH)Py (1) (0.757 gm,
80%) came out with 10e15% ethyl acetateedichloromethane
mixture and finally ClCo(dmgH)2Py (1b) (0.0645 gm, 10%) came out
with 100% ethyl acetate.
2.3.4. Reaction monitoring: formation of (1) and (6)
Pyridine was added with constant stirring to a refluxing solution
of CoCl2$6H2O, dmgH2, dSPhgH2 (or dSEtgH2) in 95% ethanol or
acetone. The solution was allowed to cool to room temperature and
the air was bubbled through the reaction mixture. Aliquots from
reaction mixture were taken out at time intervals of 5 min, 15 min,
30 min and 45 min and 60 min for 1 and 15 min, 30 min and 60 min
for 6. Water was added to each aliquot followed by extraction with
dicholoromethane. Three products were formed in each case
(Scheme 1) and their molar ratio was calculated from the integra-
tion of the 1H NMR signals of Pya for 1 and from the isolated
products after column chromatography for 6. The molar ratios are
given in Tables 3 and 4.
2.3.5. Oxygen insertion reaction monitoring of 5 and 10
2.3.2. Synthesis of ClCo(dmgH)(dSEtgH)Py (6)
Oxygen gas was bubbled through a solution of PhCH2Co(dmgH)
(dSPhgH)Py (5) or PhCH2Co(dmgH)(dSEtgH)Py (10) (100 mg) in
10 ml of dichloromethane at 0 ꢁC while the solution was irradiated
with a 200 W tungsten lamp. The aliquots from the reaction
mixture were taken out at time intervals of 5 min, 30 min, 60 min,
120 min and 150 min for 5 and 5 min, 15 min, 30 min, 45 min and
60 min for 10. The aliquot solution was evaporated to dryness and
its NMR was recorded in CDCl3. Oxygen insertion in 5 results in
formation of two products; whereas it gives three products in case
of 10 (Scheme 3) and their molar ratio was calculated from the
integration of the 1H NMR signals of CH2 group bound to CoO2
(Tables 5 and 6).
The procedure is exactly the same as that of 1 except that the air
was passed through the solution for 15 min to maximize yield and
three products were isolated after chromatography, ClCo(dmgH)
(dSEtgH)Py (6) (65%), ClCo(dSEtgH)2Py (6a) (5%) and
ClCo(dmgH)2Py (1b) (21%).
2.3.3. Preparation of RCo(dmgH)(dSPhgH)Py and RCo(dmgH)
(dSEtgH)Py (2e5, 7e10)
The same procedure, as described earlier for the preparation of
mixed dioxime complexes, RCo(dpgH) (dioxime)Py, was used [25].
In this study 1 and 6 have been used as the starting material. The
reaction took 15 min for completion and a mixture of products was
formed in each case and the ratio of these products remained
constant up to reaction time of 1 h (Scheme 2). Two products,
RCo(dmgH)(dSPhgH)Py (2e5) (76e80%) and RCo(dSPhgH)2Py
(2e5%) were formed in the reaction with (1) whereas three prod-
ucts, RCo(dmgH) (dSEtgH)Py (7e10) (65e68%), RCo(dmgH)2Py
3. Results and discussion
3.1. Synthesis
The mixed dioxime cobalt complexes, RCo(dpgH)(dioxime)Py
(dioxime ¼ gH, dmgH, chgH) were first reported from our
Table 3
Molar distribution (%) of 1, 1a and 1b in ethanol and acetone.
Table 4
Time (min)
1/1a/1b
Molar distribution (%) of 6, 6a and 1b in ethanol and acetone.
Ethanol
Acetone
Time (min)
6/6a/1b
5
83/5/12
71/2/27
56/1/43
55/2/43
57/1/42
19/2/79
44/1/55
51/2/47
53/3/44
55/2/43
Ethanol
Acetone
15
30
45
60
15
30
60
69/7/24
67/7/26
54/6/40
38/9/53
24/13/63
49/11/40

G. Dutta, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 2693e2701
2697
Scheme 3.
Table 5
Table 8
1H NMR data (ppm) for 6e10.
Molar distribution (%) of 5c and 5d in DCM.
Time (min)
5c
5d
Compd Py
no
a
Py
b
Py
g
H-1 dSEtgH
dmgH OeH.O Other
proton
5
30
60
120
150
31
32
34
70
87
1
3
4
17
11
6
8.26 7.24 7.71
3.52(m),3.12(m), 2.41
1.22(t)
18.17
7
8.59 7.37 7.73 0.94 3.19(m),3.04(m), 2.14
1.06(t)
18.31
8
9
8.57 7.32 7.71 1.86 3.11(m), 1.05(t) 2.13
8.57 7.31 7.72 1.75 3.11(m), 1.05(t) 2.13
18.21
18.21
0.39
0.81,
0.96,1.22
10
8.51 7.29 7.69 2.98 3.14(m), 1.07(t) 1.75
18.17
6.97e7.14
Table 6
Molar distribution (%) of 10c, 10d and 5d in DCM.
Time
10c
10d
5d
5 min
15 min
30 min
45 min
1 h
52
61
84
91
95
2
2
2
2
2
3
3
3
3
3
2. The product ratios in (6) cannot be monitored from the
chemical shift of Pya since the values are almost identical for (6)
and (1b) [8.25 & 8.26 ppm]. So the product ratios are based on
the isolated products after the column chromatography.
However, the information is similar, as described for (1).
The organo complexes (2e5) and (7e10) are formed by the
reaction of CoI(dmgH)(dSPhgH)Py or CoI(dmgH)(dSEtgH)Py, gener-
ated in situ by the sodium borohydride reduction of the corre-
sponding chlorocobaloxime (1) and (6), with alkyl halides. A mixture
of two or three products is formed in each case depending upon the
dioxime side chain. The scrambling of products occurs by a process
similar to the previously described RCo(dpgH)(L)Py [L ¼ dmgH, gH,
chgH] complexes [25,26]. However, the process is much faster in the
laboratory and a reaction scheme was proposed based on many
independent reactions. The formation of ClCo(dpgH) (dioxime)Py
was slow and took 2 he2days depending upon the nature of the
dioxime and the yields varied between 25% and 58% [25,26]. In
contrast, in the present systems it takes only 5 and 15 min to form 1
and 6 in very high yield. The monitoring of the formation of 1 and 6
in ethanol and acetone gives the following useful information.
1. There is an equilibration between (1) and (1b), for example, the
amount of (1) is highest at 5 min and gradually decreases up to
15 min and then becomes almost constant. On the other hand
the amount of (1b) gradually increases up to 15 min and
becomes constant (Fig. 1). A different scene emerges when the
reaction is monitored in acetone, instead of ethanol. Now (1b)
forms first and its amount is highest at 5 min which slowly
decreases and becomes constant at 30 min. At the same time
the formation of (1) is slow in the beginning but it gradually
increases with time and becomes constant at 30 min (Fig. 2).
The amount of (1a) is slight (1e5%) and does not change much
with time, in ethanol or acetone. The product ratios are
calculated from the chemical shift ratio of Pya in (1), (1a)
and (1b).
Table 7
1H NMR data (ppm) for 1e5.
Compd no. Py
a
Pyb
Pyg
Aromatic H-1 dmgH OeH.O Other
proton
proton
1
2
3
4
8.17 7.24 7.76 7.12e7.24
2.42
17.70
17.95
17.92
17.93
8.45 7.27 7.74 6.85e7.19 0.97 2.08
8.48 7.31 7.80 6.89e7.10 1.95 2.13
8.48 7.32 7.79 6.91e7.10 1.83 2.13
0.39
1.22, 0.95,
0.80
5
8.44 7.29 7.78 6.94e7.28 3.09 1.73
17.76
Fig. 5. Molecular structure of 1.

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Fig. 8. Molecular structure of 6.
Two compounds 5c and 5d are formed within 5 min. The
amount of 5d remains constant up to 1 h and then increases and
becomes constant again after 2 h. The amount of 5c continuously
increases with time (Fig. 3).
Fig. 6. Molecular structure of 4.
The insertion in 10 is faster compared to 5 and three products
10c, 10d and 5d are formed during the course of the reaction. The
amount of 10c increases with time and becomes constant after
45 min. However the amount of 10d and 5d is very small and
remains constant during the course of the reaction (Fig. 4).
present systems and takes only 15 min for completionwhich is much
less compared to the time needed for RCo(dpgH)(L)Py complexes.
3.2. Oxygen insertion
Oxygen insertion in ArCH2Co(L)(L0)Py where L and L0 are diox-
imes with carbon side chain, has been described from our group
and it shows the formation of three products, ArCH2(O2)Co(L)2Py,
ArCH2(O2)Co(L)(L0)Py and ArCH2(O2)Co(L0)2Py [33]. The ratios
depend upon the nature of the dioxime. In the present study the
4. Spectroscopy
All the complexes 1e10 have been characterized by 1H (Tables 7
and 8) and 13C NMR and in addition 1, 4, 5, 6, 8 and 10 have also
been characterized by X-ray. The NMR assignments are consistent
with the previously described cobaloxime complexes. Bis(thio-
phenyl)glyoxime (dSPhgH2) and bis(thioethyl)glyoxime (dSEtgH2)
are not completely soluble in CDCl3 and a drop of DMSO-d6 is
necessary to dissolve it.
oxygen insertion reaction in
information.
5 and 10 gives the following
Fig. 7. Molecular structure of 5.
Fig. 9. Molecular structure of 8.

G. Dutta, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 2693e2701
2699
Fig. 11. Cyclic voltammograms of 1 and 6 in CH2Cl2 with 0.1 M (nBu4NPF6) as sup-
porting electrolyte at 0.1 V sꢀ1at 25 ꢁC.
interaction in the latter, as revealed by X-ray, since the benzyl
centroid lies over dpgH and not over dmgH wing.
Fig. 10. Molecular structure of 10.
In general, the chemical shifts of dmgH (Me), Pya and OH.O in
2e5 and 7e10 are upfield shifted as compared to the values in
RCo(dmgH) (dpgH)Py and the upfield shift is much larger in 2e5.
A quartet for eCH2 and a triplet for eCH3 group is observed, as
expected, in free dSEtgH2 but CH2 appears as two sets of multiplets in
1:1 ratio in 6e10 and their separation depends upon the axial R
group, for example it is largest in 6 whereas these merge in 8, 9 and
10. This can happen only if the CH2 protons become non-equivalent
and have interaction with the methyl group. Interestingly, the
chemical shift of the methyl group remains almost the same in all
complexes.
5. Structural studies
The diamond diagram of complexes 1, 4, 5, 6, 8 and 10 are shown
in Figs. 5e10.
Selected bond angles and bond distances are presented in
Table 9. The Cobalt atom is linked to four nitrogen atoms belonging
to the equatorial plane. Out of this, two nitrogen atoms belong to
dmgH ligand and the other two belong to dSPhgH or dSEtgH. The
CoeCl or CoeC bond distances [2.2368(16), 2.012(3), 2.056(3),
2.226(2), 2.040(6), 2.065(4) Å] and CoeNPy bond distances
[1.965(5), 2.083(3), 2.065(3), 2.002(7), 2.078(4), 2.058(4) Å] in 1, 4,
5, 6, 8 and 10 do not differ significantly from the reported value of
mixed cobaloxime complexes. Cobalt atom deviates, 0.0225, 0.0029
and 0.0173 Å from mean equatorial CoN4 plane [34] towards neutral
pyridine in 4, 6 and 8 respectively whereas the deviation is 0.0446,
0.0012 and 0.0314 Å towards R group in 1, 5 and 10. Pyridine
dPya is upfield shifted in 1e5 as compared to the unligated Py
and its value lies in-between the parent complexes, RCo(dmgH)2Py
and RCo(dSPhgH)2Py as observed earlier in RCo(dpgH)(L)Py
[L ¼ dmgH chgH, gH] [10,11]. It is possible that the upfield shift in
1e5 may be the result of the close proximity of Pya to the phenyl
ring of the dioxime (see X-ray). Little or no upfield shift in Pya value
in 6e10 supports this view.
The dmgH (Me) is significantly upfield shifted in the benzyl
complexes 5 and 10 when compared with the corresponding alkyl
complexes 2e4 and 7e9. Two factors may be responsible for this (a)
enhanced ring current in the metallabicycle when alkyl is replaced
by the benzyl (b) CeH.
and dmgH protons. Since
the alkyl and benzyl complexes, this rules out the first factor
(Tables S2 and S3). X-ray structures of 5 and 10 also support the
second factor; the benzyl group is oriented over the dmgH wing
p
interaction between the benzyl centroid
attached to cobalt has a twist angle (s) [35] of 85.755, 84.563,
d
13C (Pya) and 13C(CeH) are similar in
d
83.905, 82.723, 87.045 and 83.412 in 1, 4, 5, 6, 8 and 10 respectively.
The orientation of SPh groups with respect to dioxime plane
remains same in 1, 4 and 5 but varies with change in R in
RCo(dSPhgH)2Py. The orientation of SEt group in 6 and 10 is same but
different in 8.
and has a weak CeH.
comparison of
1H dmgH (Me) in 5 and 10 with PhCH2Co(dmgH)
(dpgH)Py also supports the second factor;
1H dmgH (Me) is 0.29
and 0.27 ppm upfield shifted in 5 and 10 as compared to
p interaction (3.33 Å and 3.22 Å). A
d
Although the distance between phenyl centroid and Pya proton
(4.014, 5.259 and 5.212 Å in 1, 4 and 5 respectively) is relatively
d
large to have any CeH.p interaction, it is the close proximity of
PhCH2Co(dmgH)(dpgH)Py (Table S4). There is no CeH.
p
the phenyl ring which causes upfield shift of Pya in 1e5.
Table 9
Selected bond lengths (Å), bond angles (deg) and structural data for 1, 4, 5, 6, 8 and 10.
1
4
5
6
8
10
CoeCl/CoeC
CoeN
CleCoeN/CeCoeN
d (Å)
2.2368(16)
1.965(5)
176.85(15)
ꢀ0.0446(8)
ꢀ5.354(168)
85.755(156)
2.012(3)
2.083(3)
176.46(14)
þ0.0225(5)
þ3.191(110)
84.563(87)
2.056(3)
2.065(3)
175.55(12)
ꢀ0.0012(6)
ꢀ8.146(109)
83.905(89)
2.226(2)
2.002(7)
179.2(2)
þ0.0029(11)
þ4.576(301)
82.723(191)
2.040(6)
2.078(4)
178.9(2)
þ0.0173(7)
þ8.316(150)
87.045(124)
2.065(4)
2.058(4)
176.89(17)
ꢀ0.0314(6)
ꢀ2.717(101)
83.412(117)
a
(deg)
(deg)
s
For definition of d,
a
and
s
see Refs. [34] and [35].

2700
G. Dutta, B.D. Gupta / Journal of Organometallic Chemistry 696 (2011) 2693e2701
reversible wave at ꢀ0.734 V corresponding to CoII/CoI. In compar-
ison 6 is difficult to reduce with values ꢀ0.522 V and ꢀ0.930 V
respectively. One quasi-reversible wave at þ1.34 V and þ1.25 V is
observed in 1 and 6 respectively. This may simply be due to the
increased electron donation by SEt group in 6 which puts more
negative charge on the cobalt.
In contrast 4, 5, 8 and 10 show a different behaviour. Only one
completely irreversible reductive half corresponding to CoIII/CoII
at ꢀ1.44 V, ꢀ1.45 V, ꢀ1.51 V and ꢀ1.42 V is obtained. Due to
enhanced
s
donation by the R- group the CoIII state in 4, 5, 8, and 10
is substantially stabilized. In other words, the CoIII/CoII redox
process in these complexes is considerably cathodically shifted.
Due to this, the CoII/CoI response is further cathodically shifted and
therefore is not observed even down to ꢀ1.6 V.
7. Conclusion
This is the first study of mixed dioxime complexes with two
dissimilar dioximes with C and S side chain. Their formation is
much faster compared to similar complexes having both dioximes
with C side chain. Molecular oxygen insertion in the benzyl
complexes is fast and forms mixture of products within 5 min. The
upfield shift of Pya in the alkyl complexes occurs due to its close
proximity to the phenyl ring of the dioxime and the high upfield
Fig. 12. Cyclic voltammograms of 4 and 8 in CH2Cl2 with 0.1 M (nBu4NPF6) as sup-
porting electrolyte at 0.1 V sꢀ1at 25 ꢁC.
Since bending angle [34] is a measure of interaction between
the axial and equatorial ligand, a high
to 1 and 4 (5.35 and 3.19 respectively) is quite justified (because of
CeH. interaction). This is the highest value observed among all
the reported mixed benzyl cobaloxime structures so far. In spite of
having similar type of CeH. interaction in 10, bending angle
a value for 5 (8.14) compared
p
a
shift of dmgH proton in the benzyl complexes is due to the CeH.
p
interaction between the benzyl centroid and dmgH protons. This
has been confirmed by the X-ray studies.
p
decreases as we go from 8 to 10, which is quite surprising. We
cannot offer any explanation right now for this.
Acknowledgement
The structure of 1 and 6 show some interesting properties. The
crystal packing of 1 shows one-dimensional chain due to one
CeH.Cl intermolecular hydrogen bond [C11(Py, CeH) acts as
donor and the metal bound Cl1 acts as acceptor] (Figure S1).
Compound 6 forms a two dimensional lamellar network involving
two intermolecular CeH.Cl contacts. One-dimensional polymeric
network is formed by CeH.Cl hydrogen bonds [C8 (Py, CeH) acts
as donor and metal bound Cl1 acts as acceptor]. Two such poly-
meric networks are interconnected through one more CeH.Cl
hydrogen bond [C15 (CH3, CeH) acts as donor and Cl1 acts as
acceptor] (Figure S2).
This work has been supported by a grant from DST, New Delhi,
India.
Appendix. Supplementary material
CCDC 806944, 806946, 806947, 806948, 806949 and 806945
contains the supplementary crystallographic data for 1, 4, 5, 6, 8
and 10 respectively. Copies of the 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.
6. Cyclic voltammetry
CV study in cobaloximes is not very well defined because of the
possibility of change in coordination number of cobalt during
reduction/oxidation process [36e38]. Inorganic cobaloximes, in
general, give a better cyclic voltammogram as compared to organo
derivatives and three types of redox couples CoIII/CoII, CoII/CoI, and
CoIV/CoIII are expected. The cyclic voltammograms of 1, 4, 6 and 8
are shown in Figs. 11 and 12 and CV data are given in Table 10.
The cyclic voltammogram of 1 shows an irreversible wave in the
reductive half at ꢀ0.457 V, corresponding to CoIII/CoII and a quasi-
Appendix. Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.02.033.
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