Co-C bond cleavage in the reactions of alkyl, benzyl and heteroaromaticmethyl cobaloximes with arene sulfenyl chloride: Homolytic and heterolytic pathways

Article abstract of DOI:10.1016/S0022-328X(98)00689-5

The reactions of arene sulfenyl chlorides, ArSCl, (Ar=Ph, C₆Cl₅, 2,4 (NO₂)₂C₆H₃) with organocobaloximes, RCo(dmgH)₂Py, (R=alkyl, benzyl and heteroaromaticmethyl) were carried out under thermal and photochemical conditions. A variety of organic and organometallic products are formed depending upon the substrate cobaloxime. For 3-methoxybenzyl and heteroaromaticmethyl cobaloximes the results suggest that they represent a unique class of cobaloximes whereby both the aromatic ring as well as the Co-C bond are highly activated towards attack by the arene sulfenyl chloride. Both homolytic as well as heterolytic pathways are operative.

Full text of DOI:10.1016/S0022-328X(98)00689-5

Journal of Organometallic Chemistry 572 (1999) 49–58
CoꢀC bond cleavage in the reactions of alkyl, benzyl and
heteroaromaticmethyl cobaloximes with arene sulfenyl chloride:
Homolytic and heterolytic pathways1
B.D. Gupta *, Vandana Dixit, Indira Das 2
Chemistry Department, I.I.T., Kanpur, UP 208016, India
Received 27 March 1998
Abstract
The reactions of arene sulfenyl chlorides, ArSCl, (Ar=Ph, C6Cl5, 2,4 (NO2)2C6H3) with organocobaloximes, RCo(dmgH)2Py,
(R=alkyl, benzyl and heteroaromaticmethyl) were carried out under thermal and photochemical conditions. A variety of organic
and organometallic products are formed depending upon the substrate cobaloxime. For 3-methoxybenzyl and heteroaromat-
icmethyl cobaloximes the results suggest that they represent a unique class of cobaloximes whereby both the aromatic ring as well
as the CoꢀC bond are highly activated towards attack by the arene sulfenyl chloride. Both homolytic as well as heterolytic
pathways are operative. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Organocobaloximes; Homolytic; Heterolytic cleavage
1. Introduction
additional reagents, cleavage by light or heat, and
finally by the steric interaction between macrocycle
and the R group [5–12]. The actual cleavage process
depends on the nature of the R group and is often
governed by a combination of parameters. For exam-
ple, in the electrophilic displacement reactions
([10](a–d), [12]), the organocobaloximes are suscepti-
ble to oxidation by some of the electrophiles, there-
fore a direct heterolytic cleavage of the CoꢀC bond
competes with the electron transfer process.
Organocobaloximes are also prone to homolysis and
frequently contain traces of cobaloxime(II) which
may initiate chain reaction [8,10,11] even when the
heterolytic process might otherwise be dominant. Be-
cause of these competing reactions, a mixture of
products is often formed. Since CoꢀC cleavage is a
very facile process, any transformation of the organic
group without affecting the CoꢀC bond becomes a
challenging task. In the preliminary communication
[1] we have shown that an exclusive ring substitution
Organocobaloximes, RCo(dmgH)2Py (R=alkyl,
benzyl and heteroaromaticmethyl), have been exten-
sively studied [2] ever since Schrauzer first highlighted
their importance as models of coenzyme B12 [3]. Since
then they have outgrown their initial relevance and
have gained significance in their own right, mainly
because of their rich chemistry [2,4,10]. The CoꢀC
bond is weak and its cleavage has been achieved in
many ways. This includes electrophilic, nucleophilic,
or free radical attack at the R group, reduction/oxi-
dation of RCoIII, modification of the R group,
charge transfer interaction of the macrocycle with
* Corresponding author. Fax: +91 512 597436; e-mail:
bdg@iitk.ernet.in
1 A preliminary account of this work has been published (B.D.
Gupta, V. Dixit, J. Organometal. Chem. 533 (1997) 261).
2 Present address: IPC division, IICT, Hyderabad 500007, India.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00689-5

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B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
2. Results
into the aromatic ring can be achieved without affect-
ing the CoꢀC bond leading to the synthesis of
modified organocobaloximes.
Alkyl cobaloximes (1–9) react with arene sulfenyl
chlorides, ArSCl, [Ar=Ph, C6Cl5, 2,4, (NO2)2C6H3 A,
B, and C, respectively] in 1:1 molar ratio under pho-
tolytic conditions (P1, irradiation by 2×200 W tung-
sten lamp at 0°C) to give exclusively the corresponding
alkyl phenyl sulfides (10–30) in 50–90% yield. The
reaction takes 4–20 h depending upon the substrate
cobaloxime (Scheme 1). The inorganic product is
chlorocobaloxime in all cases.
Benzyl cobaloximes (31–37) react under similar P1
conditions to form the corresponding sulfides (38–51)
with (A and B). However with (C), some side products,
e.g. bibenzyls (59–65) and benzyl ether of dimethylgly-
In the present study, we describe the reactions of
arene sulfenyl chlorides, ArSCl, with organocoba-
loximes under thermal and photochemical conditions.
The reason for choosing arene sulfenyl chlorides as
the reactive substrate is simply because these can act
both as free radicals and/or as electrophiles depending
upon the reaction conditions and the substituents on
the arene ring [13]. The present study, therefore, has
been aimed: (i) at understanding the CoꢀC cleavage
mechanism; and ii) to study the phenomenon of CoꢀC
cleavage vs ring substitution in benzyl and heteroaro-
maticmethyl cobaloximes.
Scheme 1. Reactions of RCoIII (dmgH)2Py (1–9) with ArSCl under P1 conditions.
Scheme 2. Reaction of 4RꢀC6H4CH2CoIII (dmgH)2Py (31–37, 73 and 76) with ArSCl.

B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
51
Scheme 3.
oxime (66–72) are also formed in addition to the arene
sulfides (52–58). Thermal reactions are slow in general,
for example, the reaction of benzyl cobaloxime (31) with
(B) at room temperature in the dark remains incomplete
even after 40 h. The only organic product isolated is the
corresponding sulfide (45). 3-Methoxybenzyl coba-
loxime (73), on the other hand, forms the ring substi-
tuted organometallic product (75) with (A) in the dark
whereas under P1 it forms 3-methoxybenzyl sulfide (74)
(Scheme 2). Similarly PhSCH2Co(dmgH)2Py (76) forms
the corresponding sulfide (77) with B in 62% yield.
The reactions of heteroaromaticmethyl cobaloximes
(78, 84 and 89) with (A, B or C) are relatively fast and
finish within 1.5 h under all conditions, whether thermal
or photochemical. Both organic and organometallic
products are formed in each reaction (Schemes 3–5).
The yield and nature of the product depend upon the
substrate cobaloxime and the reaction conditions
(Scheme 6). The change in solvent from
dichloromethane to acetic acid does not make any
Scheme 4.
Scheme 5.

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B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
III
Scheme 6. Reaction products of RCo
(78, 84, 89) with ArSCl.
significant difference in the nature of the products,
though the ratio is changed in certain cases.
The characteristics of all the products are given in
Tables 1–5 [24].
centre [16] may lead to products from reductive elimi-
nation and from the nucleophilic displacement of the h
carbon; (c) attack may take place at the ligand leading
to a variety of products including those from insertion
process [17,18] (ligand migration); and (d) attack may
also occur at the h carbon (on the C–M bond orbital
[19]b. Reactions of each of these types is known and the
path followed is certainly a function of the particular
electrophile, its interaction with the HOMO of the
complex, and the nature of the reaction medium. In all
cases a certain degree of electron transfer occurs [7,19].
3. Discussion
Arene sulfenyl chlorides can act both as sources of
free radicals and/or as electrophiles depending upon the
reaction conditions and the substituents on the arene
ring [13].
If ArSCl reacts with organocobaloximes in a free
radical manner, it may do so in a number of ways [7,8]
(i) CoꢀC bond homolysis and subsequent reactions of
the generated R; and (ii) SH2 reactions at the carbon
centre displacing cobaloxime(II); (iii) electron transfer
from RCo(III) complex to ArSCl followed by attack of
ArS. on the intermediate organocobalt (IV) species.
However, if ArSCl acts as an electrophile, then in
principle, it may attack the organometallic complex at a
number of sites: (a) attack may take place at the
aromatic ring (benzyl and heteroaromaticmethyl coba-
loximes) leading to substitution [1,14] and/or to metal
carbon bond cleavage [15]; (b) attack at the metal
3.1. Alkyl cobaloximes
The experimental observations point to the free radi-
cal nature of these reactions. The alkyl sulfides are
formed by a direct displacement of cobaloxime(II) by
attack of the ArS. radical on the h carbon of the alkyl
group. A trace of cobaloxime(II) present as impurity in
all organocobaloximes is sufficient to generate ArS.
radical by the abstraction of Cl. from the ArSCl. We do
not prefer the alternative route where R., formed by the
unimolecular homolysis of RCoIII, attacks the sulfur
centre of ArSCl to form ArSR. As the alkyl radicals are
known to dimerise fast and have the tendency to ab-

B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
53
Table 1
Characteristics of alkyl sulphides (16–30)
Comp. No 1H-NMR chemical shift l, CDCl3 (ppm)
MP (°C)
lmax
Anal. found (calc.) (%)
CH3OH
(nm)
CH2S
(CH2)n (m) Me
Aromatica
7.31–8.78
7.32–8.78
7.32–8.80
7.4–8.85
C
H
N
S
(16)
(17)
(18)
(19)
(20)
(21)
2.35 (s)
3.0 (q)
2.8 (t)
—
—
126
88
80
95
65
74
335, 270,
210
335, 270,
211
335, 272,
210
336, 271,
211
335, 272,
210
336, 270,
221
28.19 28.33 0.95 1.01
31.12 30.91 1.56 1.61
33.17 33.28 2.14 2.16
33.20 33.28 2.01 2.16
35.18 35.45 2.60 2.66
39.21 39.29 3.47 3.55
—
—
—
—
—
—
10.71 10.79
10.38 10.30
9.80 9.86
9.82 9.86
9.39 9.45
8.68 8.73
—
2.36 (t)
1.16 (t)
1.5 (d)
0.82 (bm)
0.8 (bm)
1.7
—
3.56 (m)
2.8 (t)
1.55
1.6
7.25–8.78
7.26–8.78
2.85 (t)
(22)
(23)
(24)
(25)
(26)
(27)
(28)
(29)
2.33 (s)
2.9 (q)
2.83 (t)
3.46 (m)
2.9 (t)
2.8 (t)
2.6–3.3 (m) 2.6–3.3
2.5—3.0
(m)
—
—
1.5
—
1.5
1.5
—
—
—
—
—
—
—
7.03
65
66
59
55
72
76
64
65
295,214
296, 214
297, 213
298, 213
296,213
300, 213
297, 220
290, 222
39.39 39.25 2.77 2.80
42.01 42.10 3.49 3.51
44.62 44.63 4.12 4.13
44.58 44.63 4.07 4.13
46.93 46.88 4.60 4.69
50.78 50.70 5.58 5.63
55.21 55.26 3.81 3.95
56.74 56.60 4.36 4.40
12.98 13.08 14.90 14.95
12.30 12.28 14.01 14.03
11.52 11.57 13.19 13.22
11.51 11.57 13.16 13.22
10.87 10.94 12.57 12.50
2.33 (t)
1.0 (t)
1.23 (d)
0.97 (bm)
0.86 (bm)
—
9.89 9.86
9.25 9.21
8.69 8.80
11.25 11.27
10.63 10.53
10.01 10.06
1.6–2.1
2.5–2.9 (m) 6.5–7.4
(30)
3.0–3.3 (t) 1.8–2.2
3.6–4.3 (m) 6.5–7.2
60
284, 219
53.83 53.89 4.12 4.19
8.18 8.28
9.61 9.58
a Multiplet.
that the ring is highly activated. Its chemistry resembles
with the heteroaromaticmethyl cobaloximes and is dis-
cussed later.
stract halogen from ArSCl, a complete absence of both
the products, i.e. R–R and RCl supports the above
viewpoint. Evidence for both these processes has been
provided in the literature ([13]d, [25]).
3.3. Heteroaromaticmethyl cobaloximes
3.2. Benzyl cobaloximes
The reactions, in general, are complicated and a
mixture of products, both organic and organometallic,
are formed in each reaction. The product distribution
suggests that these reactions proceed by a mixture of
mechanisms. In general, the following useful informa-
tion emerges out of the study.
A similar argument as above is extended for the
results for (A) and (B) and the benzyl sulfides are
formed by the direct displacement of cobaloxime(II) by
the attack of ArS. radical on the h carbon of the benzyl
group.
The product distribution in case of (C), however,
suggests that the mechanism is different under thermal
and photochemical conditions. For example, the forma-
tion of bibenzyl (59–65) under P1 conditions is indica-
tive of the presence of benzyl radicals as intermediates
whereas the formation of benzyl ethers of dimethylgly-
oximes (66–72) under thermal conditions points to the
existence of RCoIV as an intermediate in solution.
Recently, such similar ether products have been ob-
served as side products in many electrophilic, free radi-
cal and oxidation reactions of organocobaloximes
([7,8]a, [10,20]) and RCoIV species is shown to be
present as an intermediate in such reactions.
(a)In the reactions of (78, 84, 89) with (A) or (B), all
the products formed, organic or organometallic, are the
ring substituted products. This suggests that the ring
substitution is the primary process followed by CoꢀC
bond cleavage [10]a. The exclusive formation of the
ring substituted product in the dark lends support to
this viewpoint. It looks as if we are dealing with a
unique class of organocobaloximes having a highly
activated aromatic ring. This may be justified consider-
ing
the
highly
activating
nature
of
the
CH2Co(dmgH)2Py group [10]a. The formation of the
dimer (81, 86 and 91) and the heteroaromaticmethyl
ether of dimethylglyoxime (82, 87 and 92) can be
explained by the electron transfer process as discussed
above for benzyl case. The disulfides (80, 85 and 90)
Interestingly, 3-methoxybenzyl cobaloxime (73) un-
dergoes a facile ring substitution with (A) suggesting

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B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
Table 2
Characteristics of benzyl sulphides (45–58 and 77)
Comp. No 1H-NMR chemical shift l, (ppm)
MP (°C)
umax CH3OH
Anal. found (calc.) (%)
(nm)
CH2S (s)
Aromatic
Others
C
H
N
S
(45)
(46)
(47)
(48)
(49)
(50)
(51)
(52)
(53)
(54)
(55)
(56)
(57)
(58)
(74)
(77)
4.05
4.06
4.06
4.05
4.08
4.15
4.03
4.30
4.20
4.20
4.15
4.60
4.68
4.30
3.90
4.30
7.13 (s)
7.03 (s)
7.03–7.36 (m)
7.13 (s)
75
76
73
237, 217
237, 216
258, 213
363, 217
221, 217
262, 215
225, 216
332, 269
334, 270, 230
335, 270, 230
332, 265, 221
334, 265, 233
335, 278, 211
335, 272, 230
338, 272, 228
217.5
41.80 41.88
43.40 43.46
47.62 47.61
38.21 38.33
42.29 42.32
37.28 37.36
41.71 41.74
53.71 53.79
55.21 55.26
58.79 58.96
48.10 48.07
53.29 53.33
46.43 46.57
52.39 52.50
73.00 73.04
38.50 38.57
1.84 1.88
2.29 2.33
3.46 3.50
1.44 1.47
1.45 1.51
1.38 1.44
2.19 2.24
3.34 3.44
3.87 3.95
5.12 5.20
2.71 2.77
2.76 2.86
2.66 2.69
3.69 3.75
6.01 6.09
1.69 1.73
—
—
—
—
3.49 3.53
3.31 3.35
—
9.61 9.66
9.12 9.21
8.12 8.09
8.61 8.63
13.35 13.33
12.39 12.54
8.62 8.75
—
8.55 8.59
8.22 8.28
7.42 7.47
7.74 7.86
8.00 8.06
7.60 7.66
7.90 7.95
11.10 11.03
10.43 10.53
9.12 9.25
9.78 9.86
10.00 10.16
9.51 9.55
9.98 10.00
13.84 13.91
15.78 15.82
2.25
1.27
—
—
—
114
145
135
152
130
121
122
124
128
138
125
120
88
7.20–7.44 (m)
7.29–8.04 (dd)
6.68–7.06 (dd)
7.4–9.10 (m)
7.2—9.10 (m)
7.0–9.10 (m)
7.1–8.9 (m)
7.74–9.12 (m)
7.65–9.15 (m)
6.9–9.10 (m)
3.66–7.18 (m)
7.28 (s)
3.73
2.30
1.32
1.26
—
—
3.80
3.60
—
—
(e) The reaction of (83b) with tosyl chloride under P1
forms the corresponding sulphone [1H-NMR (CDCl3),
4.16 (s), 2.36 (s), 6.33–6.50 (m)] and the dmgH ether
product (82b). In contrast the same reaction with (78)
forms the sulphone exclusively [8]a.
(f) All efforts to put the second group into the
aromatic ring have failed. It seems that a combined
effect of ꢀCH2Co(dmgH)2Py, (a conjugatively electron
releasing group) and ꢀSAr (an electron withdrawing
group) does not make the heteroaromatic ring activated
enough towards ring substitution.
may arise either by the direct SE2 or SH2 process at the
h carbon of the ring substituted product. It is however
very difficult to pin point the exact pathway at this
stage.
The reactivity of (C) however is different from (A)
and (B) since the ring substitution as well as the cleav-
age of the CoꢀC bond in the parent cobaloxime (78, 84
and 89) occur simultaneously.
(b) The formation of the ring substituted methyl
furan (79) is quite novel as it is rarely seen in such
studies. The following mechanism is proposed for its
formation. A similar mechanism was proposed by us to
explain the formation of the ring halogenated toluene
in the halogenation of 4-methoxybenzyl cobaloxime
[10]a.
(g) The mass spectral data has been collected only on
certain representative cases. The fragmentation does
not show any clear-cut pattern but the fragments like
SPh,
SC6Cl5,
SC6Cl4,
SC6Cl3,
SC6H3(NO2)2,
SC6H3(NO), furfurylmethyl, thienylmethyl, etc. are dis-
tinctly seen and the compounds are clearly identified.
The base peak in the dimers corresponds to the
monomer.
4. Conclusions
The present study clearly shows that both homolytic
as well as heterolytic pathways are equally important in
the cleavage of CoꢀC bond in organocobaloximes. Dif-
ferent reaction pathways have been observed with the
same reacting substrate-arene sulfenyl chloride. Bi-
molecular homolytic displacement, SH2, is the domi-
nant pathway for alkyl and benzyl cobaloximes with
the electron transfer process occurring in the latter as a
competitive process. The reaction of heteroaromat-
icmethyl cobaloximes are quite complex in nature be-
cause of the simultaneous participation of a number of
(c) The oxidation potentials of the ring substituted
organocobaloximes (83, 88 and 93) are comparable to
the parent cobaloximes and are reversible in nature.
(d) The ring substituted organocobaloximes undergo
very facile oxygen insertion into the cobalt carbon bond
under photochemical conditions, for example (83b)
forms the inserted product within 2 h at 0°C under
irradiation. [1H-NMR (CDCl3), 2.3 (s), 4.26 (s), 6.3–
6.70 (dd), 7.20, 7.56, 8.24 (m).

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B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58

B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
57
sulfenyl chloride (A) was prepared [21] by the chlori-
nation of diphenyldisulfide with sulfuryl chloride at
ambient temperature (b.p. 46–48oC/4 mm), lit. 49oC/2
processes. The electrophilic substitution into the aro-
matic ring being the key feature of these reactions
and this is quite remarkable as the CoꢀC bond is
susceptible to cleavage by electrophiles and free radi-
cals. The preference of one process over the other is
guided by many factors like the nature of the sub-
strate cobaloxime, arene sulfenyl chloride and the re-
action conditions. We believe that it is very difficult
to assess precisely the relative contribution of each of
these process until a more detailed study is under-
taken.
1
mm [21], H-NMR (CCl4) 7.4 (s, Ar), Pentachloroben-
zene sulfenyl chloride was prepared [22] by the chlori-
nation of pentachlorobenzenethiol with chlorine gas
(m.p. 100oC), lit. 104oC [22]. The thiol was prepared
[23] from hexachlorobenzene, sodium sulfide and sul-
fur under refluxing condition.
5.1. Reaction of arene sulfenyl chloride with
organocobaloximes: general procedure
5.1.1. Photochemical reaction (P1)
5. Experimental
All reactions are carried out in a specially designed
glass apparatus with external water cooling system.
Organocobaloxime and arene sulfenyl chloride (1
mmol each) are added to deaerated dichloromethane
(25 ml). The solution is irradiated with 2×200 tung-
sten lamps placed at a distance of 10 cm from the
reaction vessel while the temperature was maintained
at 0oC by a Julabo refrigerated circulator. The pro-
gress of the reaction is monitored for cobaloxime by
silica gel using ethyl acetate as the solvent. On com-
pletion the reaction mixture is concentrated in vacuo
and flash chromatographed using dichloromethane as
the eluant. Once the organic product has eluted, the
solvent is changed to ethyl acetate when the ring sub-
stituted organometallic product elutes out. Finally the
inorganic product is taken out with acetone. The or-
ganic and the organometallic products are chro-
matographed further to obtain the pure products.
All the organocobaloximes and the organic precur-
sors used in this study were synthesised by the proce-
dures outlined in our earlier papers [10]. Benzene
Table 5
Mass spectra of the organic products from the reaction alkyl, benzyl
and heteroaromaticmethyl cobaloximes with ArSCl
Comp. no Mass (m/e) [% relative abundance]
(22)a
(23)a
(24)a
(25)a
(26)a
(27)a
(45)a
(46)b
(47)c
(48)a
(49)b
(50)b
(51)b
(79a)
(79b)
(79c)
(80a)
(80b)
(81a)
(81b)
(82a)
(85a)
(85b)
(86a)
(86c)
(87a)
(90a)
(90b)
(91a)
(91c)
(92a)
296 (2.86)
310 (3.05)
324 (4.36), 43 (100)
324 (3), 43 (88)
338 (2.7), 57 (100)
366 (4.4), 85 (100)
372 (3.55), 91 (100)
385 (6.19), 281 (8.7), 105 (100)
428 (11.7), 147 (100)
407 (4.2), 126 (100)
396 (1.52), 117 (100)
416 (12.45), 136 (100)
401 (0.5), 117 (100)
190 (42.8), 109 (100), 218 (74)
366 (82.5), 298 (59), 114 (100)
280 (3.9), 183 (24), 152 (25), 113 (24)
298 (3.9), 189 (100), 109 (95.5)
643 (6.3), 362 (100), 281 (12.9), 246 (25.7)
378 (23.2), 189 (100), 109 (97.5)
279 (74.8), 183 (20.2), 125 (45.1)
304 (10.9), 218 (38.1), 204 (89), 189 (43.4), 109 (100)
314 (6.2), 205 (93.1), 171 (57.2)
659 (2.4), 378 (30.4), 342 (100), 246 (80.1), 177 (88)
410 (89.1), 301 (10.7), 205 (100)
296 (17), 183 (12), 109 (27.9)
320 (50.6), 220 (76.6), 205 (100)
314 (10.1), 205 (100), 109 (16.8), 128 (10.5)
378 (47.3), 342 (100), 246 (79.1), 177 (99.6)
320 (62), 205 (100)
5.1.2. Thermal reaction (P2)
A similar procedure as above is adopted except that
the reaction is carried out either under dark at 0°C or
under reflux in diffused light. The reaction vessel is
covered with Al foil or with a piece of cloth.
Physical measurements and instruments: 1H-NMR
spectra are recorded on Jeol JNM-PMX 60 and
Varian 400 spectrometers. The elemental analysis and
mass spectra are done at Regional sophisticated In-
strumentation Centre at Lucknow. The UV-VIS ab-
sorption spectra are recorded on Shimadzu 160A
model. The cyclic voltammetric studies are done on
BAS model CV-27 polarographic analyser utilizing the
three electrode configuration, glassy carbon (working
electode), platinum wire (auxillary electrode) and Ag/
AgCl (reference electrode). An omnigraphic 100 XY
recorder is used to record the current voltage output.
A scan rate of 100 mV s−1 is used in all cases and
dry dichloromethane is used as the solvent medium.
The measurements are also made with the scan rate
of 50 mV s−1 in certain cases.
296 (17.9), 201(22.1), 183 (13.1), 109 (21.2)
320 (40.5), 220 (56.6), 205 (100)
a Values refer to (M++2) and (M-SC6Cl5).
b Values refer to (M++H) and (M-SC6Cl5).
c Values refer to (M+) and (M-SC6Cl5).

58
B.D. Gupta et al. / Journal of Organometallic Chemistry 572 (1999) 49–58
[12] (a) P. Abley, E.R. Dockal, J. Halpern, J. Am. Chem. Soc. 95
Acknowledgements
(1975) 3166. (b) M.D. Johnson, The Nature and Cleavage of
Metal Carbon Bonds, vol. 2, Wiley Interscience, New York,
1985, p. 513. (c) R.D.W. Kemmit, D.R. Russel, in: G. Wilkinson
(Ed.), Comprehensive Organometallic Chemistry, vol. 5, Perga-
mon, Oxford, 1982, p. 80. (d) J.H. Espenson, W.R. Bushby,
M.E. Chmielewski, Inorg. Chem. 14 (1975) 1302. (e) J.H. Espen-
son, H.L. Fritz, R.A. Heckman, C. Nicolinin, Inorg. Chem. 15
(1976) 906.
We thank the department of science and technology,
New Delhi, for funding this project.
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