Organocobaloximes with mixed dioxime equatorial ligands: A convenient one-pot synthesis. X-ray crystal structures of BnCoIII(dmgH)(dpgH)Py and BnCOIII(chgH)(dpgH)py

Article abstract of DOI:10.1016/S0022-328X(01)00731-8

A simple and general route to the synthesis of organocobaloxime with mixed dioxime ligands, RCo(dmgH)(dpgH)Py and RCo(chgH)(dpgH)Py, has been described. The ¹³C-NMR chemical shifts have been analysed to see whether one dioxime wing has any effect on the other dioxime wing. The first crystal structure of an organocobaloxime with mixed dioxime ligand in the same complex, BnCo(dmgH)(dpgH)Py and BnCo(chgH)(dpgH)Py, is reported.

Full text of DOI:10.1016/S0022-328X(01)00731-8

Journal of Organometallic Chemistry 627 (2001) 80–92
www.elsevier.nl/locate/jorganchem
Organocobaloximes with mixed dioxime equatorial ligands: a
convenient one-pot synthesis. X-ray crystal structures of
BnCoIII(dmgH)(dpgH)Py and BnCOIII(chgH)(dpgH)pyꢀ
B.D. Gupta a,*, R. Yamuna a, Veena Singh a, Usha Tiwari a, T. Barclay b, W. Cordes b
a Chemistry Department, Indian Institute of Technology, Kanpur 208016, India
b Department of Chemistry and Biochemistry, Uni6ersity of Arkansas, Fayette6ille, AR, USA
Received 4 December 2000; accepted 15 February 2001
Abstract
A simple and general route to the synthesis of organocobaloxime with mixed dioxime ligands, RCo(dmgH)(dpgH)Py and
RCo(chgH)(dpgH)Py, has been described. The 13C-NMR chemical shifts have been analysed to see whether one dioxime wing has
any effect on the other dioxime wing. The first crystal structure of an organocobaloxime with mixed dioxime ligand in the same
complex, BnCo(dmgH)(dpgH)Py and BnCo(chgH)(dpgH)Py, is reported. © 2001 Published by Elsevier Science B.V.
Keywords: Cobalt; Cobaloxime; Dioxime; Organocobaloxime
organocobaloximes. The studies involving other oximes
with varying steric and electronic properties such as gH
1. Introduction
Organocobaloximes,1 originally proposed as models
of Vitamin B12 nearly three decades ago, have been
studied extensively and reviewed [1]. This was
prompted by the need to understand the factors behind
the cleavage of the CoꢀC bond in B12-dependent enzy-
matic reactions [1f]. In particular, a lot of study on the
steric factors that lead to the weakening of the CoꢀC
bond in vitamin B12 model compounds has been made
[1d]. This has been done in order to evaluate whether a
conformational change in the B12-coenzyme-enzyme
complex is responsible for the CoꢀC bond cleavage step
in catalysis by B12-dependent enzymes [2]. Most of these
studies have involved dmgH as the dioxime ligand in
[2,3], chgH [4,22] and dpgH [5] have been few. Recently
we have shown that the variation in the equatorial
dioxime ligand field has a pronounced cis influence on
the axial ligands [6].
The recent work on organocobaloximes shows that it
has outgrown its initial relevance of B12 model and it
has acquired an independent research field because of
its rich chemistry. The use of organocobaloximes has
been exploited in free-radical chemistry [7] and these
find numerous applications in organic reactions [8–13].
It is also observed that a slight variation in the equato-
rial ligand brings out profound changes in the CoꢀC
bond reactivity, for example in Diels–Alder reaction
[11], alkyl–alkenyl cross-coupling reaction [14] and in
the oxygen insertion reaction into the CoꢀC bond [15].
The key feature of these reactions is the fragility of the
CoꢀC bond [6,16,17] and hence a fine-tuning of its
strength has been a continuing challenge. Approaches
to this problem have mainly been via changes in the
steric and electronic properties of axial ligands [1d].
Therefore, there has been a sustained interest in the
synthesis of new organocobaloximes with new or
modified equatorial ligands [5,11,18–22].
ꢀ The preliminary account of this work has been published (B.D.
Gupta, V. Singli, K. Qanungo, V. Vijaikanth, R. Yamuna, T. Bar-
clay, W. Cordes, J. Organomet. Chem. 1 (2000) 602)
* Corresponding author. Tel.: +91-512-597730; fax: +91-512-
597436.
E-mail address: bdg@iitk.ac.in (B.D. Gupta).
1 General formula RCo(L)2B where R, an organic group s bonded
to cobalt; B, axial base trans to the organic group; L, dioxime ligand,
e.g. gH, glyoxime; dmgH, dimethylglyoxime; chgH, 1,2 cyclohexane-
dione dioxime; dpgH, diphenylglyoxime (all monoanions).
0022-328X/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII: S0022-328X(01)00731-8

B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
81
Fig. 1.
Keeping the above in view, we report here simple and
general route to the synthesis of organocobaloximes of
the type ArCH2CoIII(L)(L%)B with mixed equatorial
dioxime ligands. The synthesis is confirmed by the
crystal structure of BnCo(dmgH)(dpgH)Py and Bn-
Co(chgH)(dpgH)Py. These become the first structures
of an organocobaloxime with two different dioximes in
the same complex. After having synthesised these new
complexes, we have analysed the 13C-NMR resonance
to see whether one equatorial wing has any effect on
the other equatorial wing in the same plane (Fig. 1).
have used Schrauzer’s method, modified Schrauzer’s
method and oxidative alkylation of cobaloxime(I) gen-
erated from chlorocobaloxime for the synthesis
2. Results and discussion
2.1. Synthesis
A thorough literature survey reveals that such
organocobaloximes with mixed dioxime ligands have
never been isolated before.2 In the light of the lack of
preparative procedures we initially attempted synthetic
procedures that had been successful for the analogous
bis(dimethylglyoximato)cobalt(III) complexes. Organo-
cobaloximes, though, have been synthesised by several
methods [1e], but Schrauzer’s disproportionation
method [23] and the oxidative alkylation of cobal-
oxime(I) [24] find a much wider use in the synthesis. We
2 Johnson et al. have mentioned the formation of similar complexes
in solution [5a].
Scheme 1.

82
B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
Table 1
Product distribution with BnCl using methods (A-F)
a
Method
Molar distribution (%)
1a
1b
1c
A
B
C
D
E
F
83
73
62
35
94
84
17
10
15
42
6
–
17
22
23
–
7
9
a Reaction time is 3 h in all cases.
Scheme 2.
the BnCo(dmgH)2Py (1c) is consumed in the former
(Scheme 2).
of mixed-ligand complexes. In all, six different methods
(A–F) have been used (Scheme 1). A mixture of three
products (la–1c) is formed in every case, however,
the method D gives the best yield of the mixed-
ligand complex (1b) (Table 1). The yield of 1a is always
more than 1b and 1c in every case.
In order to know more about the synthesis, the
reaction pathway and to maximise the yield of 1b using
method D, a series of reactions with varying reaction
conditions have been carried out. An examination of
the product distribution in Table 2 points to the follow-
ing observations:
1. The formation of the mixed-ligand complex (1b) is a
function of time. The yield reaches a maximum
(entry 6) and then declines (entries 7–9).
2. The yield of 1b is low at the initial stages of the
reaction (entries 1–3) and is practically independent
of the residence time of cobalt(I) (entries 1–3). This
indicates that the following reaction is either very
slow or does not occur in the reaction time scale
otherwise we would have seen the formation of 1b in
the beginning of the reaction itself (entries 1–3).
4. It is noticed that in all these reactions the yield of
BnCo(dpgH)2Py (1a) is always more as compared to
BnCo(dmgH)2Py (1c). This suggests that processes
other than simple alkylation of CoI(dpgH)2Py are
also responsible for its formation, for example the
independent reactions (see Section 3) show that: (i)
BnCo(dpgH)2Py (1a) is formed by trans-alkylation
reaction of BnCo(dmgH)2Py (1c) with CoI(dpgH)2-
Py (path h); (ii) BnCo(dmgH)(dpgH)Py (1b) on
reaction with CoI(dpgH)2Py forms BnCoIII(dpgH)2-
Py (1a) in high yield (path e) while the reaction with
CoI(dmgH)2Py produces BnCo(dmgH)2Py (1c) in
low yield (path f) in the same reaction. This also
explains the depletion of the mixed dioxime complex
(1b) in the later stages of the reaction (Table 2).
We have synthesised seven new mixed-ligand com-
plexes, RCo(dmgH)(dpgH)Py (1b–7b) following
method D. A mixture of three products is formed in
each case. The molar distribution ratio is shown in
Table 3. The general features of these reactions are
similar to benzyl case as described above.
CoI(dmgH)2Py+CoI(dpgH)2Py
“2CoI(dmgH)(dpgH)Py
Since the yield of the mixed ligand complex (1b–7b)
is poor in all cases, the next aim was to improve its
yield. We have been able to achieve this via oxidative
alkylation of CoI(dmgH)(dpgH)Py, generated in situ,
by sodium borohydride reduction of ClCo(dmgH)-
(dpgH)Py (15b) (see Section 3 for its synthesis). The
desired mixed-ligand complex (1b–7b) is formed as the
major product in high yield (32–51%). The correspond-
ing side products (1a–7a) and (1c–7c) are formed in
less than 10% yield. Following this procedure we have
extended the studies to other mixed-ligand combina-
tions and have synthesised seven new complexes of the
type RCo(chgH)(dpgH)Py (8b–14b) (55–80%) (Table
4). However, when the studies are extended to the
dmgH/chgH combination, we find that three products
Thus 1b is not formed by direct alkylation of
CoI(dmgH)(dpgH)Py.3
3. BnCo(dpgH)2Py (1a) or BnCo(dmgH)2Py (1c), once
formed in solution by direct alkylation of
CoI(dpgH)2Py or CoI(dmgH)2Py (path a and b,
Scheme 2), reacts further with CoI(dmgH)2Py or
CoI(dpgH)2Py, respectively, (path c and d) to yield
the mixed dioxime complex (1b). This has been
confirmed by independent experiments using
equimolar quantities of each reactant (see Section
3). It is observed that path d is more facile than
path c. Nearly all of the BnCo(dpgH)2Py (1a) is
recovered back in the latter reaction while most of
1
are formed, as inferred from H-NMR, but all efforts
to separate these products by column chromatography,
crystallisation, failed. This observation is similar to the
earlier observation by Johnson et al. [5a].
3 In the absence of rates, it is assumed that the rates of oxidative
alkylation of Co
(dpgH)Py are similar.
I
(dmgH)2Py, CoI(dpgH)2Py and Co(dmgH)-

B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
83
Table 2
Molar distribution at various reaction times
ClCo(dmgH)2Py Clco(dpgH)2- BnCl
Residence time
of CoI (min) a
Reaction time
(min) b
% molar distribution (after column)
Py one equivalent each
(equivalents)
BnCo(dpgH)2Py BnCo(dmgH)-
(dpgH)Py
BnCo(dmgH)2Py
Entry 1
Entry 2
Entry 3
Entry 4
Entry 5
Entry 6
Entry 7
Entry 8
Entry 9
3
3
3
3
3
3
3
3
3
30
5
5
5
5
10
5
5
15
15
30
73
63
63
61
45
35
44
55
63
3
0.4
0.8
23
36
36
21
24
23
26
25
36
60
17
120
180
240
300
400
31
42
30
20
10
0.8
a The time before the addition of benzyl chloride to Co(I).
b Refers to the time between the addition of benzyl chloride and the work up. The Julabo refrigerated circulator was turned off after the
addition of the halide.
Table 3
Method D molar distribution a
Reactants ClCo(dmgH)2Py
ClCo(dpgH)2Py (1:1)
Compound
number
RX (three equivalents)
Molar distribution (%) (after column)
RCo (dpgH)2Py
RCo(dmgH)-
(dpgH)Py
RCo (dmgH)2Py
Entry 1
Entry 2
Entry 3
Entry 4
Entry 5
Entry 6
Entry 7
1
2
3
4
5
6
7
PhCH2Cl
4-Cl-C6-CH2Cl
35
35
54
59
61
43
54
42
29
16
31
10
42
11
23
35
44
10
29
–
4-CN-C6H4CH2Br
4-OMe-C6H4CH2Cl
3-OMe-C6H4CH2C1
2-Thiophene CH2Cl
2-NaphthylCH2Br
34
a Reaction time is 3 h in all cases. The Julabo refrigerator circulator was switched off after the addition of the halide.
Table 4
Molar distribution a (after column): reaction time 3 h a
Reactant ClCo(chgH)(dpgH)Py RX (three equivalents)
Compound number % molar distribution
RCo(dpgH)2Py RCo(chgH)(dpgH)Py
RCo(chgH)2Py
8
Entry 1
Entry 2
Entry 3
Entry 4
Entry 5
Entry 6
Entry 7
PhCH2Cl
8
9
3
4
8
8
5
5
4
89
92
84
87
95
90
96
4Cl-C6H4CH2Cl
4-CN-C6H4CH2Br
4-OMe-C6H4CH2Cl
3-OMe-C6H4CH2Cl
2-thiophene CH2C1
2-naphthylCH2Br
10
11
12
13
14
8
5
–
5
–
a 8a–14a are the same as 1a–7a.
The spectral characteristics of compounds 1b–14b
and 1a–7a are given in Tables 5 and 6. The details of
compounds 1a–7a and 1c–14c have been described
earlier by us [15]. All the compounds give satisfactory
elemental analysis.
In light of the lack of preparative procedures for the
synthesis of ClCo(dmgH)(dpgH)Py (15b) and ClCo-
(chgH)(dpgH)Py (16b), we initially attempted synthetic
procedures that had been successful for the synthesis of
analogous ClCo(L)2Py (L=dmgH, dpgH, chgH) com-

Table 5
1H-NMR and umax values of 1b–14b a
b
Compound
number
OꢀHO (s)
Pyridine
Aromatic
dmgH (s)/chgH
dpgH (m)
CoꢀCH2 (s)
umax (log m)
(methanol)
h (d)
8.72
8.68
i (t)
7.37
7.34
k (t)
7.75
7.73
1b
2b
18.47
18.44
6.87–6.99 (m)
2.02
2.03
2.09
7.05–7.29
7.05–7.23
3.16
3.06
470.7 (3.15), 242
(4.50)
473 (3.27), 239 (4.62)
/
6.88–6.94 (m), 6.98–7.03
(m)
6.88 (d) [7.4]
c
3b
18.41
18.48
8.69
8.71
7.77
7.74
7.18–7.49 c
6.88–6.96,
7.14–7.22
6.91–6.99,
7.14–7.23
6.92–7.02,
3.02
3.17
469 (3.49), 239 (4.60)
238 (4.59)
4b d
7.34
6.63 (d) [1.6], 7.10 (d) [1.6] 2.00
5b d
6b
18.48
18.41
18.52
8.71
8.73
8.70
7.35
7.75
7.76
7.74
6.72–6.77 (m)
6.78–6.90 (m)
2.00
2.08
1.93
3.18
3.33
3.31
460 (3.16), 239 (4.55)
7.34
239 (4.51)
7.10–7.27
c
c
7b
6.79 (d) [6.8], 7.05–7.70
(m)
–
8b
9b
10b
11b d
12b d
18.17
–
18.15
18.23
18.19
8.72
8.70
8.65
8.71
8.72
7.36
7.36
7.36
7.35
7.36
7.76
7.76
7.78
7.75
7.76
6.95–6.7 (m)
6.93–6.95 (m)
6.92 (d)
6.64 (d) [8.4], 6.96 (d) [8.0] 2.48 (s),
6.73–6.79 (m)
2.46 (d) [2.8] 1.45 (s)
2.50 (s), 1.49 (s)
2.42 (s), 1.51 (s)
7.05–7.30
7.02–7.22
7.20–7.29
7.01–7.22
6.96–6.98,
7.18–7.23
3.16
3.06
3.02
3.17
3.18
472 (3.22), 244 (4.49)
471 (3.22), 244 (4.48)
472 (3.12)
239 (4.15)
475 (3.20), 244 (4.43)
627
(
2.47 (s), 1.45 (s)
8
13b
14b
18.14
18.26
8.71
8.72
7.36
7.76
7.75
6.78–7.01 (m)
6.88–7.41 (m)
2.50–2.63 (m), 1.53–1.55 (m)
2.33–2.39 (m), 1.27 (t) [6.4], 1.08 (t) [6.4]
7.16–7.21
3.37
3.36
244 (3.83)
–
9
c
c
a Rf 0.374–0.54 (EtOAc–CHCl3) (1:9); all the compounds give satisfactory elemental analyses. The coupling constants (J) in pyridine are h=4.8–5.6 Hz, i=6.0–7.5 Hz and k=6.9–7.6 Hz.
b Free Py appears as h=8.57; i=7.05; k=7.43.
c Merge with aromatic.
d OMe appears at 3.73.

Table 6
13C values of 1b–14b and 1a–7a
Compound
number
CꢁN a
Pyridine b
Aromatic+dpgH
dmgH or chgH c CoꢀCH2
h
i
k
lb
2b
150.78, 149.71
150.83, 149.79
151.13, 150.15
150.60, 149.53
150.82, 149.78
150.88, 149.87
150.81, 149.76
150.84, 150.48
150.87, 150.51
151.21, 150.88
150.69, 150.24
150.84, 150.54
150.94, 150.68
150.89, 150.51
151.03
150.24 125.35 137.68
150.15 125.39 137.80
150.19 125.51 138.00
150.21 125.32 137.62
150.23 125.35 137.70
150.29 125.35 137.71
150.24 125.36 137.69
150.29 125.35 137.68
150.18 125.39 137.80
150.19 125.53 138.01
150.24 125.33 137.63
150.25 125.35 137.68
150.30 125.35 137.71
150.27 125.37 .137.70
150.14 125.52 137.96
150.14 125.59 138.05
150.08 125.70 138.28
150.14 125.50 137.89
150.15 125.53 137.98
150.16 125.53 137.98
150.12 125.53 137.97
130.21, 129.73, 129.59, 128.92, 128.67, 127.75, 127.69, 127.64
130.09, 130.04, 130.00, 127.71, 129.68, 129.49, 128.75, 127.70
131.44, 130.06, 129.79, 129.41, 129.19, 129.08, 128.96, 128.78
130.24, 129.99, 129.94, 129.58, 128.61, 127.69, 127.62, 113.48
130.23, 129.60, 129.52, 128.64, 128.56, 127.64, 127.56, 121.66, 113.53, 111.03
130.24, 129.62, 128.72, 128.66, 128.59, 127.75, 127.55, 122.21
131.37,130.10,129.56, 129.50, 128.84, 128.65, 127.78, 127.58, 126.84, 124.28
130.31, 129.59, 128.97, 128.65, 127.91, 127.74, 127.70
12.05
12.12
12.23
12.02
12.07
12.13
11.99
25.26, 21.24
25.31, 21.11
25.43,21.19
25.24, 21.21
25.28, 21.08
25.34 21.28
25.16, 20.90
–
–
–
–
–
–
–
–
31.02
–
32.37
29.70
24.12
–
3b d
4b e
5b e
6b
/
7b
8b
9b
–
130.09, 130.04, 130.00, 127.71, 129.68, 129.49, 128.75, 127.70
131.48, 129.90, 129.50, 129.45, 129.21, 128.99, 127.84
130.32, 129.96, 129.59, 128.61, 127.68, 113.54
10b d
11b e
12b e
13b
14b
1a
–
32.28
–
130.29, 129.56, 128.59, 127.66, 121.68, 113.57, 110.87
130.24, 129.62, 128.72, 128.66, 128.59, 127.75, 127.55, 122.21
131.35, 130.23, 129.62, 129.54, 128.89, 128.63, 127.78, 127.67, 126.89, 126.79
147.35, 129.96, 129.66, 129.13, 128.89, 128.29, 127.66, 124.71
146.02, 130.23, 130.12, 129.81, 129.59, 129.03, 128.24, 127.76
131.81, 129.56, 129.50, 129.35, 129.25, 127.84, 120.26, 107.23
139.27, 130.15, 129.98, 129.67, 128.86, 127.64, 113.92
148.85, 129.96, 129.68, 129.04, 128.89, 127.64, 121.94, 113.85
130.07, 129.99, 129.80, 129.71, 129.30, 128.86, 128.06, 127.78
145.32, 134.06, 131.64, 129.82, 129.57, 128.99, 128.84, 127.81, 127.59, 127.32, 127.04, 125.85,
125.78, 124.41
32.71
34.11
32.66
31.70
34.11
33.72
26.42
34.50
2a
151.13
151.40
150.86
151.09
151.16
151.08
3a d
4a e
5a e
6a
627
(
7a
8
9
a The first value is CꢁN (dpgH) and the second value is CꢁN (dmgH) or (chgH).
b Free Py h=149.82; i=123.73; k=135.89.
c The first value corresponds to C1 and the second to C2 carbons in cyclohexane (for numbering see Fig. 1).
d CN appears at (154.61, 154.79, 154.41 ppm) for 3b, 10b and 3a, respectively.
e OMe appears at 55.32, 55.12, 55.29,55.16, 55.30, 55.10 for 4b, 5b, 11b, 12b, 4a and 5a, respectively.

86
B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
plexes [5b,22,23]. The compounds were synthesised and
purified as detailed in Section 3. Interestingly, their
synthesis is always accompanied by the formation of
ClCo(dmgH)2Py/ClCo(dpgH)2Py and ClCo(chgH)2Py/
ClCo(dpgH)2Py, respectively. The crystal structure of
BnCo(dmgH)(dpgH)Py (1b) and BnCo(chgH)(dpgH)Py
(8b) have been determined and the details are given
later.
The exact mechanism of the reaction can be deci-
phered by detailed kinetic experiments. However, in the
absence of kinetic data our preliminary studies showed
that the randomisation of the dioxime ligand along
with alkyl transfer in the presence of cobalt(I) is taking
place.
The major concern with the cobaloxime(I) promoted
alkyl exchange reactions is to establish whether cobal-
oxime(I) or traces of cobaloxime(II) is the reactive
species. Usually, excess sodium borohydride is used in
the reaction and it reduces cobaloxime(II) to cobal-
oxime(I). Also, we did not get any ESR signal of the
blue cobaloxime(I) solution. We, therefore, believe that
there is no cobaloxime(II) impurity present in cobal-
oxime(I). The latter has a very labile fifth ligand, Py or
the solvent methanol, and exists in equilibrium with
significant proportion of the four-coordinate species.
The randomization might occur by any/all of the fol-
lowing pathways.
The exchange of equatorial ligand: (a) may take place
directly between 1a and 1c and free ligand; (b) may
occur via Co(I)(dmgH)(dpgH)Py as mentioned before;
(c) may occur by routes outlined in Scheme 2. We have
ruled out certain of these possibilities by independent
reactions as outlined above. The experiments have
shown further that 1b is formed albeit in low yield
when ClCo(dmgH)2Py/dpgH2 [1:10] or ClCo(dpgH)2Py/
dmgH2 [1:10] is reduced with borohydride in presence
of benzyl chloride (see methods E and F, Scheme 1). It
is very difficult to comment on whether the dissociation
of the equatorial ligand, i.e. randomization occur be-
fore or after the alkyl transfer.
intensity peak is assigned to Pya. The other two peaks
having lower intensity belong to CꢁN. Their intensity is
expectedly low because these are quaternary carbons.
The peak with higher ppm (l) is assigned to CꢁN
(dpgH) and the other with lower ppm (l) value is
assigned to CꢁN (dmgH or chgH). Pya lies in between
CꢁN (dmgH) and CꢁN (dpgH) in 1b–7b whereas it
occurs upfield as compared to CꢁN (chgH) and CꢁN
(dpgH) in 8b–14b.
1H and 13C-NMR spectra of the complexes (1b–14b)
(Tables 5 and 6) show some general trends that are
discussed below.
We have recently shown that organocobaloximes, in
general, are good systems for the study of cis and trans
influence [6,25]. It was observed, based on spectral
studies, that the cis influencing ability in alkylcobal-
oximes followed the order dpgH\chgH\dmgH and
1H and 13C-NMR studies indicated further that OHꢀO
and Pyg were the most affected followed by Pyg. The cis
influence studies in the present systems having mixed
ligands throw further light on the phenomenon. The
following observations are noteworthy.
1
1. The H-NMR values for Pya and CoꢀCH2 are af-
fected by the equatorial plane. For example, if we
compare the values in 1b–7b and 8b–14b with the
values in parent cobaloximes, RCo(L2)Py (L=
dmgH, chgH, dpgH) [15] then they lie in between
the 1a–7a and 1c–7c and 1a–7a and 8c–14c, re-
spectively. This indicates that the cis influence by
the equatorial plane on Pya and CoꢀCH2 depends
on both the equatorial wings around the cobalt
1
centre. The H-NMR values for Pya and CoꢀCH2 in
complexes 1b–7b are almost same as in 8b–14b
which further means that the cis effect of (dmgH/
dpgH) is similar to the (chgH/dpgH). This supports
our earlier findings in which the cis influence of
dmgH was found to be similar to chgH in
RCo(L2)Py (L=dmgH, chgH) complexes [22].
2. The OꢀHO values in 1b–7b and 8b–14b lie in
between the values for parent cobaloximes and the
values in 1b–7b are consistently down field as com-
pared to the values in 8b–14b.
2.2. Spectroscopy
3. The 13C resonance of pyridine on coordination to
the cobaloxime moiety shifts downfield and this
coordination shift (D13C=lcomplex−lfree pyridine) fol-
lows the order D13C Pyg\D13C Pyb\D13C Pya
(Table 7). However, the order observed based on the
coordination shift in 1H-NMR values is
D1Pyg$D1H Pyb\D1H Pya (Table 7)
1
1
Assignment of H and 13C resonance. The H-NMR
spectra of these complexes are easy to assign and the
assignment is similar to the RCo(dmgH)2Py and
RCo(dpgH)2Py complexes that have been reported ear-
lier by us [15]. However, the 13C values have been
assigned for only a few organocobaloximes in the liter-
ature [26] and therefore further comments are war-
ranted on its assignment.
4. We have considered whether one equatorial wing
has any effect on the other equatorial wing, i.e. the
1
The 13C resonance of dmgH (Me), chgH (C1 and
C2), CoꢀCH2, Pyb and Pyg are easily assigned based on
their chemical shifts. The difficult part has been the
assignment of CꢁN (dmgH or chgH), CꢁN (dpgH) and
Pya as these occur very close to each other. The highest
effect of dmgH or chgH wing on dpgH wing. H-
NMR data does not give any information. For
example, dmgH (Me) in RCo(dmgH)2Py and in
RCo(dmgH)(dpgH)Py have the same chemical shift.
However, the comparison of the 13C values of the

B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
87
Table 7
Coordination shift from 13C- and 1H-NMR values
Compound
D
13C Pya
D
13C Pyb
D
13C Pyg
D1H Pya
D1H Pyb
D1H Pyb
1b
2b
3b
4b
5b
6b
7b
8b
0.40
0.33
0.37
0.39
0.41
0.47
0.42
0.47
0.36
0.37
0.42
0.43
0.48
0.45
1.62
1.66
1.78
1.59
1.62
1.62
1.63
1.62
1.66
1.90
1.60
1.62
1.62
1.64
1.79
1.91
2.11
1.73
1.81
1.82
1.80
1.79
1.91
2.12
1.74
1.79
1.82
1.81
0.15
0.11
0.12
0.14
0.14
0.16
0.13
0.15
0.13
0.08
0.14
0.15
0.14
0.15
0.32
0.29
–
0.29
0.30
0.29
–
0.31
0.31
0.31
0.30
0.31
0.31
–
0.32
0.30
0.34
0.31
0.32
0.33
0.31
0.33
0.33
0.35
0.32
0.33
0.33
0.32
9b
10b
11b
12b
13b
14b
Table 8
Effect of one wing on the other wing (13C-NMR)
a
b
Compound
lCꢁN (dpgH)
lCꢁN (dpgH wing)
DdmgH
Compound
lCꢁN (dpgH wing)
DchgH
1
2
3
4
5
6
7
151.03
151.13
151.40
150.86
151.09
151.16
151.08
150.78
150.83
151.13
150.60
150.82
150.88
150.81
−0.25
−0.30
−0.27
−0.26
−0.27
−0.28
−0.27
8
9
150.84
150.87
151.21
150.69
150.84
150.94
150.89
−0.19
−0.26
−0.19
−0.17
−0.25
−0.22
−0.19
10
11
12
13
14
a DdmgH
b DchgH
=
=
13C l1b–7b
13C l8b–14b
−
−
13C l1a–7a
13C l1a–7a
.
.
13C of CꢁNoximinic.4 However, no correlation is ob-
served for a carbon. l13C (CꢁN)la–7a=0.72 (13)
D13C Pyg −107.23 (1911) (r=0.93, e.s.d=0.05
ppm). l13C (CꢁN)la–7a=0.38 (9) D13C Pyb
−55.24(1313) (r=0.89, e.s.d=0.03 ppm). l13C
(CꢁN)8b–14b=0.74(14) D13C Pyg −110.34 (2154)
(r=0.92, e.s.d=0.06 ppm). l13C (CꢁN)8b–14b=0.60
(12) D13C Pyb −89.42 (1871) (r=0.91, e.s.d=0.05
ppm).
phenyl carbons of dpgH ligand in both wings in
1b–14b might render some information. We cannot
test this viewpoint in the present series of complexes
since we are unable to make the precise assignment
as these are very close to the phenyl carbons. How-
ever, the comparison of 13C values for CꢁN (dpgH)
in 1b–14b with 13C (CꢁN) in 1a–7a shows that the
13C value shifts upfield by about 0.2 ppm in all cases
indicating that one wing has some effect on the
other wing (Table 8). This further means that there
is a higher charge density on CꢁN (dpgH) in the
mixed-ligand complexes, 1b–14b, as compared to
the pure complexes, RCo(dpgH)2Py (1a–7a). This
might be a general phenomenon, however, it re-
quires confirmation by extending it to more systems
with mixed ligands having both steric and electronic
differences. The studies are in progress in this direc-
tion. We, however, cannot comment on the origin of
this shift but it might be due to the electronic effect
of one wing on the other.
2.3. UV–6is spectra
Organocobaloximes generally show a CoꢀC CT band
between 440 and 470 nm and a CoDioxH CT band
between 230 and 250 nm [15,25]. We are not able to
observe the CoꢀC CT band in certain cases in the
mixed-dioxime complexes (1b–14b). 2-Naphthylmethyl
cobaloximes (7b and 14b) do not give any band at all
(Table 5).
5. The coordination shift of the g and b carbon of
pyridine, D13CPyg and D13CPyb, in (1a–7a and 8b–
14b) correlate well and show a linear trend with the
4 The least-square method and the programme ‘origin’ have been
used.

88
B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
Table 9
2.4. Crystal structure determination and refinements
Crystal data collection and refinement parameters
Orange crystals were obtained by slow evaporation
of solutions of the complexes in methanol. A small
crystal size (Table 9) was selected and mounted on a
Enraf-Nonius CAD-4 diffractometer equipped with a
graphite monochromator. The unit cell parameters were
determined from 25 reflections (2q range 18–20) and
the cell parameters were refined by least-squares. Inten-
sities were collected with Mo–Ka radiation, using the
q–2q and multi-scan techniques. For compound 1b,
5179 intensities were measured in the range (4–50°) and
2877 were considered as observed applying the condi-
tion I\2.0|(I), while 7647 reflections were measured
for compound 8b in the range (2.27–30.17), from which
7646 were considered as observed. Empirical absorp-
tion corrections based on „-scan data were applied to
the reflection intensities for these two compounds.
The structures were isotropically refined by full-ma-
trix least-squares method, using the NRC386 and the
SHELXL-97 computer programs. The function min-
imised was [ꢀ[wꢁFoꢁ−ꢁFcꢁ2]0.5], where w=[|2(Fo2)+
(0.05Fo2)2]. The hydrogen atoms of the OH groups were
located on difference maps and were constrained to
these difference map positions. The orientations of the
methyl H atoms were also determined from difference
maps and refined with an overall isotropic temperature
factor. The perspective views of the molecular struc-
tures together with the atom numbering schemes are
shown in Figs. 2 and 3.
Compound
1b
8b
Formula
CoO4N5C30H30 CoC32H32N5O4
583.53
293
0.20×0.38×0.46 0.50×0.30×0.10
orange
Formula weight
Tempearture (K)
Crystal size (mm)
Crystal colour
Unit cell dimensions
609.56
293(2)
orange
,
a (A)
17.1950(19)
9.5165(13)
18.170(4)
–
107.050(14)
–
17.9648(5)
32.0298(8)
10.2559(9)
90.00
90.00
90.00
,
b (A)
,
c (A)
h (°)
i (°)
g (°)
3
)
,
V (A
2842.6(8)
25
5901.31(6)
25
Cell determination
reflections
Cell determination, 2q
range (°)
18–20
18–20
Dcalc (g cm−3
Space group
Z
1.36
P21/c
4
1217.7
Mo–Ka,
graphite
monochromated
0.7107
0.64
1.372
Pnca
8
2544
Mo–Ka, graphite
monochromated
)
F(000)
Radiation
,
u (A)
0.7107
0.627
Linear absorption
coefficient (mm−1
Diffractometer
)
Enraf-Nonius
CAD-4
q–2q
Enraf-Nonius CAD-4
Scan technique
2q range (°)
Index ranges (h, k, l)
Multi-scan
2.27–30.17
−24, 24; 44, 44;
−14, 13
4–50
−20, 20; −11,
0; −21, 0
2.5
Drift of standard
deviation (%)
2.5. Description of the structures
Absorption correction
Absorption range
Reflections measured
Unique reflections
R for merge
analytical
0.78–0.89
5179
5002
0.016
empirical
1.00–0.85
7647
7646
0.038
The cobalt atom is linked to four nitrogen atoms
belonging to the equatorial plane. Out of this, two
nitrogen atoms belong to diphenylglyoximato (dpgH)
ligand and the other two to dimethylglyoximato
(dmgH) or 1,2-cyclohexanedionedioximato (chgH) lig-
and. The Co atom displays an approximately octahe-
dral coordination. The Co atom in compound 1b is
Reflections in refinement, 2877
I\2.0|(I)
7646
Parameters refined
R(F) a, Rw(F) b
R for I\3.0|(I)
Goodness-of-fit on F2
p
331
0.054, 0.072
0.047
1.26
0.04
507
0.0668, 0.1655
0.1142
1.144
–
,
0.024(2) A out of the mean plane of the four nitrogen
(w−1=[|2(I)+pI2]
,
atoms, while it is 0.044(2) A in compound 8b. The
/4F2)
Largest D/|
Extinction correction
displacement is towards pyridine in both cases. These
0.00
None
−0.32(7),
+0.64(7)
NRC386 c
idealised
0.857
None
−0.563
deviations from planarity are well within the range
,
found in similar dmgh complex (0.05 A) [27]. Pyridine
Final difference map
ring is practically planar and parallel to the glyoxime
CꢀC bonds, its conformation being defined by a twist
of 80.3(5) and 79.0(3)° for the compounds 1b and 8b,
respectively. The CoꢀC24 and CoꢀNax bonds arc per-
pendicular (90°) to the equatorial plane as seen in the
NeqꢀCoꢀC24, NeqꢀCoꢀNax and C24ꢀCoꢀNax bond an-
gles. CoꢀN5 bond distance in 1b and 8b are some what
longer than the corresponding value in ClCo(L2)Py,
where L=dmgH, dpgH [5d,27]. The phenyl group of
the benzyl unit in 1b has disorder with 50–50 occu-
pancy in the model with both phenyl rings refined as
−3
,
(e A
)
Programs
SHELXL-97 d
idealised
H atom treatment
,
,
(C−H=0.95 A) (C−H=0.95 A)
a R=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
b The value is for Rw(F2) and wR=[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)]]0.5
,
w=[|2(Fo2)+(0.05Fo2)].
c
NRCVAX — An Interactive Program System for Structure Analy-
sis, E.J. Gabe, Y. Lepage, J.P. Charland, F.L. Lee, P.S. White, J.
Appl. Crystallogr. 22 (1989) 383.
d Sheldrick, G.M. (1993). SHELXL-97. Program for the Refinement
of Crystal Structures. University of Go¨ttingen, Germany.

B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
89
precipitation of the cobaloxime did not occur on pour-
ing the reaction mixture into water; instead an orange-
red emulsion formed. In those cases the emulsion was
extracted with dichloromethane, the solvent layer was
washed several times with brine, dried over anhydrous
sodium sulfate and the volume concentrated to a few
ml. The precipitation was then achieved by pouring it
dropwise into light petroleum with constant stirring.
The solid was filtered and then dried in vacuum.
1H and 13C spectra were recorded on a JEOL JNM
1
LA 400 PT NMR spectrometer (at 400 MHz for H
and at 100 MHz for 13C) in CHCl3-d solution with
Me4Si as internal standard. UV–vis spectra were
recorded on a Shimadzu 160A spectrometer. The de-
gassed solvent was used for recording spectra as these
compounds undergo oxygen insertion very readily. The
elemental analysis was carried out at the Regional
Sophisticated Instrumentation Center, Lucknow.
Fig. 2. ORTEP plot of structure benzylCo(dmgH)(dpgH)Py (1b).
3.1. Synthesis of BnCo(dmgH)(dpgH)Py (1b) (method
D): general procedure
NaOH (1 pellet dissolved in 1.0 ml water) was added
to a suspension of ClCoIII(dmgH)2Py (0.201 g, 0.5
mmol) and ClCoIII(dpgH)2Py (0.326 g, 0.5 mmol) in
methanol (10 ml) and the reaction mixture was thor-
oughly purged with argon for 15 min. The temperature
was brought down to 0°C by Julabo refrigerator circu-
lator. The reaction mixture turned deep blue after the
addition of NaBH4 (0.048 g, 1.27 mmol, dissolved in 1
Fig. 3. ORTEP plot of structure benzylCo(chgH)(dpgH)Py (8b).
Table 10
rigid groups (CꢀC=1.395). The N1ꢀN2 and N3ꢀN4
equatorial bond distances are shorter than the N2ꢀN3
and N1ꢀN4 bonds. This allows the location of the
oxime bridge hydrogen. The butterfly bending angle5
(h) for 1b is higher (4.90°) than in 8b (3.8°). The
selected bond lengths and bond angles are given in
Table 10.
Selected bond lengths and bond angles
Bond distances and angles
Compound 1b
Compound 8b
CoꢀC24
CꢀN5
CꢀN1
CoꢀN3
C1ꢀC8
C21ꢀC20
N1ꢀO1
N5ꢀCoꢀC24
N1ꢀCoꢀN5
N2ꢀCoꢀC24
N1ꢀCoꢀN2
O1ꢀO4
2.045(60
2.086(4)
1,882(4)
1.885(4)
1.471(7)
1.456(10)
1.334(6)
175.56(22)
89.83(17)
88.25(23)
81.96(19)
2.481(5)
2.479(5)
2.466(6)
2.853(6)
2.450(7)
2.848(6)
2.063(4) a
2.070(3)
1.876(3)
1.893(3)
1.473(4)
1.465(5)
1.336(3)
177.63(15) a
91.27(13)
93.65(14) a
81.91(12)
2.496(4)
2.488(4)
2.457(4)
2.867(4)
2.457(4)
2.859(4)
3. Experimental
Chlorocobaloxime, ClCoIII(L)2Py [L=dmgH, dpgH,
chgH], were synthesised according to the literature pro-
cedure [5b,22,23]. The cobaloxime(I) was generated in
situ by the sodium borohydride reduction of chloro-
cobaloxime under inert conditions at 0°C. Organocobal-
oximes have been synthesised by the reaction of
CoI(L)2Py with the corresponding benzyl halide under
strict anaerobic conditions at 0°C. The general work-up
procedure is similar to the organocobaloximes as de-
tailed earlier. It was observed that in certain cases the
O2ꢀO3
N1ꢀN2
N1ꢀN4
N3ꢀN4
N2ꢀN3
b
h
4.9(5)
80.3(5)
3.8(3)
79.0(3)
c
~
a Corresponds to CoꢀC26 in 8b.
b Butterfly bending angle.
c Twist angle of pyridine with respect to the line joining the
5 For definition and other details see Refs. [1c,6]
midpoints of C1ꢀC8 and C20ꢀC21.

90
B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
ml water). Benzyl chloride (0.189 g, 1.5 mmol) in
methanol (5 ml) was added dropwise. The reaction
mixture was stirred for 3 h in dark during which the
reaction mixture was brought to ambient temperature
and then the contents were poured into water. The
orange-red solid was filtered, dried and chro-
matographed on a silica gel column with ethylacetate–
chloroform as eluent yielding three cobaloximes 1a
(0.142 g), 1b (0.145 g) and 1c (0.063 g). The products 1a
and 1c were compared with the authentic samples from
this laboratory [22].
Note: the general procedure used for the preparation
of ClCoIII(dpgH)2Py does not yield any product.
3.5. Synthesis of ClCoIII(chgH)(dpgH)Py (16b)
This has been synthesised by two methods.
(a) Solid cobalt(II) chloride hexahydrate (2.02 g, 5
mmol) was added to a suspension of diphenylglyoxime
(2.02 g, 8.4 mmol) and Nioxime (1.20 g, 8.4 mmol) in
acetone (100 ml). The mixture was stirred for 48 h at
room temperature (r.t.) during which the reaction mix-
ture gradually changed from deep blue to green. Pyri-
dine (1.58 g, 16.80 mmol) was added dropwise and the
solution slowly turned brownish-green. It was stirred
for additional 1 h and the solvent was evaporated on
the rotavap. The crude product so obtained was sepa-
rated and purified on the column. The solvent system
was similar to as outlined above for ClCoIII(dmgH)-
(dpgH)Py complex. Three products were isolated
ClCoIII(dpgH)2Py (0.184 g), ClCoIII(chgH)(dpgH)Py
(1.149 g), ClCoIII(chgH)2Py (0.630 g).
3.2. Synthesis of BnCo(chgH)(dpgH)Py (8b) (method
D): general procedure
The same procedure as outlined above for the prepa-
ration of BnCo(dmgH))(dpgH)Py was used. The only
difference is that now a mixture of ClCoIII(chgH)2Py
(0.230 g, 0.5 mmol) and ClCoIII(dpgH)2Py (0.326 g, 0.5
mmol) was used. Three products were formed, which
were separated by column chromatography: 8a (0.280
g), 8b (0.060 g) and 8c (0. 120 g).
(b) Pyridine (1.58 g, 16.80 mmol) was added with
constant stirring to a refluxing solution of cobalt(II)
chloride hexahydrate (2.02 g, 5 mmol), Nioxime (1.20 g,
8.4 mmol) and diphenylglyoxime (2.02 g, 8.4 mmol) in
95% ethanol (50 ml). The solution was allowed to cool
to r.t. and air was passed through the reaction mixture
for 6 h. The crude product obtained after evaporation
of the solvent was separated and purified on the
column. Three products were isolated ClCoIII(dpgH)2Py
3.3. Synthesis of
BnCo(dmgH)(dpgH)Py/BnCo(chgH)(dpgH)Py from
ClCoIII(dmgH)(dpgH)Py/ClCoIII(chgH)(dpgH)Py:
general procedure
The general procedure and work-up was similar to
method D except that ClCoIII(dmgH)(dpgH)Py or
ClCoIII(chgH)(dpgH)Py was used as the starting mate-
rial. The yields (after column) of the products (lb–7b)
and (8b–14b) are in the range 32–51 and 55–80%,
respectively.
(0.740
g),
ClCOIII(chgH)(dpgH)Py
(1.782
g),
ClCoIII(chgH)2Py (0.275 g).
3.4. Synthesis of ClCoIII(dmgH)(dpgH)Py (15b)
3.6. Separation of products: column details
Pyridine (0.79 g, 10 mmol) was added with constant
stirring to a refluxing solution of cobalt(II) chloride
hexahydrate (1.20 g, 5 mmol), dimethylglyoxime (0.58
g, 5 mmol) and diphenylglyoxime (1.20 g, 5 mmol) in
95% ethanol (25 ml). The solution was allowed to cool
to RT and air was bubbled through the reaction mix-
ture for 6 h. The solid residue obtained after the
evaporation of the solvent on the rotavap was purified
on the column. The residue, dissolved in a minimal
amount of chloroform, was loaded on a silica gel
column (100–200 mesh) pre-eluted with chloroform.
Three distinct bands were visible with 10% ethylacetate.
The first band corresponding to the ClCoIII(dpgH)2Py
complex (1.02 g) came out completely with 10% ethyl-
acetate in chloroform. The mixed-ligand complex,
ClCoIII(dmgH)(dpgH)Py (1.12 g) came out with 10–
50% ethyl acetate–chloroform mixture and finally the
ClCoIII(dmgH)2Py complex (0.208 g) came out with
100% ethylacetate mixture. Any deviation in these ra-
tios gives the contaminated products.
The separation of the products has posed a lot of
problems. Various adsorbents (silica gel, basic alu-
mina), solvent systems (carbon tetrachloride–ethylac-
etate,
petroleum
ether–chloroform–ethylacetate),
column dimensions and flash chromatography were
tried. The best separation could be achieved by the
following procedure.
The orange–red powder containing the mixture of
cobaloximes, dissolved in minimum amount of chloro-
form, was loaded on a silica gel (100–200 mesh)
column pre-eluted with chloroform. The polarity was
increased carefully with ethylacetate. Three distinct
bands were visible with 1% ethylacetate in chloroform.
The first band corresponding to the dpgH complex
came out completely with 1% ethylacetate. The mixed-
ligand complex came out with 1–10% ethyl acetate–
chloroform mixture and the dmgH complex finally
came out with 50–100% ethylacetate–chloroform mix-
ture. Any deviation in these ratios gives the contami-
nated products.

B.D. Gupta et al. / Journal of Organometallic Chemistry 627 (2001) 80–92
91
3.7. Reaction of BnCoIII(dpgH)2Py with CoI(dmgH)2Py
336033; email: deposit@ccdc.com.ac.uk or www:http://
www.ccdc.cam.ac.uk)
In this reaction a suspension of BnCoIII(dpgH)2Py
(0.350 g, 0.50 mmol in 10 ml methanol) is added to a
blue solution of CoI(dmgH)2Py [generated by the reduc-
tion of ClCo(dmgH)2Py, 0.50 mmol in 10 ml methanol]
at 0°C under nitrogen atmosphere and the mixture is
stirred for 3 h. After the usual work-up, most of the
BnCoIII(dpgH)2Py was recovered back (0.195 g). A
small amount of 1b (0.063 g) and 1c (0.026 g) was
formed.
Acknowledgements
We thank the Department of Science and Technol-
ogy (DST), New Delhi for funding this project (project
No. SP/SI/F20/99).
3.8. Reaction of BnCoIII(dmgH)2Py with CoI(dpgH)2Py
References
The same procedure as stated above was used. Al-
most all the BnCoIII(dmgH)2Py was consumed and was
transformed into 1a and lb.
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3.9. Reaction of BnCoIII(dmgH)(dpgH)Py with
CoI(dmgH)2Py
Cobaloxime(I), CoI(dmgH)2Py, (generated in situ by
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form after pouring the reaction mixture into water.
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4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 135131 and 149630 for 1b
and 8b, respectively. Copies of the data can be obtained
free of charge from The Director, CCDC, 12 Union
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