Reactions of [η5-carboxycyclopentadiene][η4-tetraphenylcyclo butadiene] cobalt with alkyl and aryl tin oxides: Synthesis, structural studies and electrochemistry of novel monomeric and dimeric [η5-carboxycyclopentadiene][η4-tetraphenylcyclobutadiene]cobalt based stannoxanes

Article abstract of DOI:10.1016/j.jorganchem.2006.07.015

Reactions of [η⁵-carboxycyclopentadienyl][η⁴-tetraphenylcyclobutadiene] cobalt, Ph₄C₄CoC₅H₄COOH (1), with (Ph₃Sn)₂O, [(n-Bu)₂SnO]_n and (Ph₂SnO)_n in refluxing toluene resulted in the formation of the monomeric compound Ph₃SnOC(O)C₅H₄CoC₄Ph₄ (2) and dimeric compounds n-Bu₂Sn[OC(O)C₅H₄CoC₄Ph₄]₂ (3) and Ph₂Sn[OC(O)C₅H₄CoC₄Ph₄]₂ (4), respectively. Reactions carried out in the solid state by mechanical grinding also yielded same results. Crystal structure determination and cyclic voltammetric studies of compounds 1, 2, 3 and 4 have been carried out and compared with similar ferrocene carboxylic acid derivatives. The structures and electrochemistry of these compounds are compared with analogous organotin ferrocene carboxylates. The results obtained from the reaction of 1 with alkyl and aryl tin oxides suggest that the formation of stannoxanes assemblies having more than two carboxylate units are not favored indicating that 1 is a highly sterically hindered metallocene carboxylic acid.

Full text of DOI:10.1016/j.jorganchem.2006.07.015

Journal of Organometallic Chemistry 691 (2006) 4708–4716
www.elsevier.com/locate/jorganchem
Reactions of [g5-carboxycyclopentadiene][g4-tetraphenylcyclo
butadiene] cobalt with alkyl and aryl tin oxides: Synthesis, structural
studies and electrochemistry of novel monomeric and dimeric
[g5-carboxycyclopentadiene][g4-tetraphenylcyclobutadiene]cobalt
based stannoxanes
*
Muthiah Senthil Kumar, Shailesh Upreti, Hanuman P. Gupta, Anil J. Elias
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India
Received 31 May 2006; received in revised form 11 July 2006; accepted 13 July 2006
Available online 27 July 2006
Abstract
Reactions of [g5-carboxycyclopentadienyl][g4-tetraphenylcyclobutadiene] cobalt, Ph4C4CoC5H4COOH (1), with (Ph3Sn)2O, [(n-
Bu)2SnO]n and (Ph2SnO)n in refluxing toluene resulted in the formation of the monomeric compound Ph3SnOC(O)C5H4CoC4Ph4 (2)
and dimeric compounds n-Bu2Sn[OC(O)C5H4CoC4Ph4]2 (3) and Ph2Sn[OC(O)C5H4CoC4Ph4]2 (4), respectively. Reactions carried out
in the solid state by mechanical grinding also yielded same results. Crystal structure determination and cyclic voltammetric studies of
compounds 1, 2, 3 and 4 have been carried out and compared with similar ferrocene carboxylic acid derivatives. The structures and elec-
trochemistry of these compounds are compared with analogous organotin ferrocene carboxylates. The results obtained from the reaction
of 1 with alkyl and aryl tin oxides suggest that the formation of stannoxanes assemblies having more than two carboxylate units are not
favored indicating that 1 is a highly sterically hindered metallocene carboxylic acid.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: [g5-Carboxycyclopentadiene][g4-tetraphenylcyclobutadiene]cobalt; Alkyl; Aryl; Stannoxanes; Monomer; Dimer
1. Introduction
adopt these structures stems from a combination of steric
and electronic factors. Stannoxanes having multiferrocenyl
assemblies mimicking dendrimers have resulted when fer-
rocene based carboxylic acids are used in these reactions
[6]. The robustness and redox inactivity of the stannoxane
framework coupled with the control on the number and
orientation of ferrocenyl groups and potential use as elect-
roactive materials were reasons for introducing ferrocene
units on organostannoxanes [6,7]. It is of interest to note
that although a host of carboxylic acids have been reacted
with tin oxides and other organotin compounds, the only
carboxylic acid containing an organometallic unit among
them is still that which contains a ferrocene moiety [6–8].
Unlike ferrocene based carboxylic acids, which has
revealed a wide-ranging chemistry [9], very little has been
In recent years there has been considerable interest in
organotin cages and clusters due to their stability and
structural diversity as well as for their importance in catal-
ysis and other applications [1,2]. Among several such
organostannoxane compounds, the most versatile are com-
pounds prepared by the reaction of organotin oxides and
stannonic acids with a variety of carboxylic acids [3,4].
The structural diversity of these stannoxanes ranges from
drums, ladders, tetramers and dimers to monomers [1,3–
5]. The preference of a particular organostannoxane to
*
Corresponding author. Tel.: + 91 11 26591504.
E-mail address: eliasanil@gmail.com (A.J. Elias).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.07.015

M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
4709
explored on the synthesis and reactions of other metalloce-
nyl carboxylic acids. In this regard, the chemistry of
[g5-carboxycyclopentadienyl][g4-tetraphenylcyclobutadiene]
cobalt, Ph4C4CoC5H4COOH, a highly stable and neutral
cobalt(I) carboxylic acid becomes significant. First pre-
pared in 1996 by Mabrouk and Rausch [10], this com-
pound has recently been used in making novel
oxazolidine based chiral metallocenyl ligands and in asym-
metric catalysis [11]. In this paper we report the reactions
of this sterically hindered organometallic carboxylic acid
with alkyl and aryl tin oxides and compare the products
obtained and their electrochemistry with products from
similar reactions of ferrocene carboxylic acid.
ratio of di-n-butyltin oxide and ferrocene carboxylic acid
gave exclusively the mononuclear dicarboxylate n-Bu2
Sn[OC(O)Fc]2 which had both cis and trans forms in the
same unit cell [7]. A reaction in 1:1 molar ratio of ferrocene
carboxylic acid with di-n-butyltin oxide had resulted in a
tetranuclear tin derivative {[n-Bu2SnOC(O)Fc]2O}2 [8,12].
However, under identical reaction conditions in 1:1 molar
ratio, reaction of 1 with di-n-butyltin oxide gave exclusively
the mononuclear dicarboxylate 3. An attempt to make the
tetrameric compound by carrying out the reaction in
refluxing xylene also was not successful.
It is of interest to note that reactions of even moderately
sterically bulky carboxylic acids such as 2,4,6-tris(trifluo-
romethyl)benzoic acid and 2,6-dimethylbenzoic acid with
di-n-butyltin oxide in 1:1 molar ratio gave the tetranuclear
tetracarboxylate {[n-Bu2SnOC(O)-2,4,6-(CF3)3C6H2]2O}2
and {[n-Bu2SnOC(O)CH(CH3)2]2O}2 [14], respectively. In
addition, the reaction of 3,5-diisopropylsalicylic acid with
di-n-butyltin oxide in 1:1 ratio resulted in a hexameric com-
pound [n-Bu2Sn-3,5-i-Pr2C6H2(O)(COO)]6 [5a].
The reaction of 1 when carried out with diphenyltin
oxide in both 1:1 and 2:1 molar ratios afforded exclusively
the trans mononuclear dicarboxylate compound 4 in
almost quantitative yields similar to the reaction of 1 with
di-n-butyltin oxide. Under similar reaction conditions, the
reaction of ferrocene carboxylic acid with diphenyltin oxide
in 1:1 and 2:1 molar ratios did not yield the mononuclear
dicarboxylate, but resulted only in the dinuclear tetracarb-
oxylate compound {Ph2Sn[OC(O)Fc]2}2 (Scheme 2). The
formation of both 3 and 4 only in the trans forms and also
only as dicarboxylates from 1:1 and 1:2 molar ratio reac-
tions indicates that the steric effect of the four phenyl
groups present in the cyclobutadiene ring significantly
influence the nature of the products formed, suggesting 1
as a highly sterically hindered carboxylic acid. The results
also clearly indicate that reactivity of 1 with alkyl and aryl
tin oxides differ considerably with that of ferrocene carbox-
ylic acid and other moderately sterically bulky carboxylic
acids [15]. The 119Sn NMR spectra of compounds 3 exhibit
a single resonance peak at ꢀ140.34 ppm, which confirms a
five coordinate geometry of the tin atom in solution (ꢀ90
to ꢀ190 ppm) [13]. Compound 4 gave a single 119Sn
NMR peak at ꢀ280.80 ppm. This chemical shift value is
consistent with the hexacoordinate environment around
tin (2C, 4O) [7].
2. Results and discussion
Recent reports on the preparation of organostannoxane
clusters using carboxylic acids indicate two different syn-
thetic approaches. The traditional method involves reac-
tions carried out in a solvent such as benzene or toluene
with the azeotropic removal of water, while a more recent
approach involves mechanical grinding of the two reac-
tants at room temperature, followed by solvent extraction
[8]. As our interest was to explore the reactions of 1 with
organotin oxides and compare the chemistry to ferrocene
carboxylic acid, we have carried out reactions under both
these conditions. We have observed that for compounds
2, 3 and 4, the results obtained under both these reaction
conditions are the same with slight variations in the yield
of products.
The reaction of bis(triphenyltin) oxide with 1 in 1:2
molar ratio afforded the compound [Ph3SnOC(O)C5H4-
CoC4Ph4] (2) (Scheme 1) in 70% yield. Compound 2 is
very stable and was recrystallized from a chloroform/hex-
ane mixture. Under analogous reaction conditions, ferro-
cene carboxylic acid yielded
a similar monomeric
compound [7,12]. The 119Sn NMR spectrum of compound
2 in CDCl3 solution exhibit a single resonance peak at
ꢀ117.82 ppm, which is observed in the range for four
coordination of triphenyltin compounds in solution
(ꢀ40 to ꢀ120 ppm) [13].
The reaction of di-n-butyltin oxide with 1 in 1:2 molar
ratio gave exclusively the mononuclear dicarboxylate 3
(Scheme 2). In compound 3, the two metallocenyl moieties
are trans to each other. In contrast, a reaction of 1:2 molar
O
O
O
Ph
Sn Ph
Ph
OH
Ph
Ph
Ph
Ph
Co
Ph
Ph
Ph
Ph
Co
Toluene, Reflux, 6h
-H2O
+ Ph3SnOSnPh3
2
Scheme 1. Reaction of 1 with bis(triphenyltin) oxide forming monomeric organostannoxane 2.

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M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
O
R
C
O
n-Bu
n-Bu
R
O
n-Bu
n-Bu
Sn
C
Ph
Ph
O
O
O
Sn
O
O
C
O
O
R
R
(or) R
C
Sn
R
Sn
O
O
O
O
Sn
O
Ph
O
n-Bu
n-Bu
C
Ph
n-Bu Sn
n-Bu
R
O
C
R
O
Ph
Ph
1:1Ratio
2:1Ratio
(RI2SnO)n
RCOOH
+
Co
Ph
Ph
RI
RI
O
O
Sn
O
O
Ph
Ph
Ph
Ph
Co
Ph
R=
Ph
Ph
Ph
Co
; RI = n-Bu (3) or Ph (4)
Scheme 2. Reactions of 1 with di-n-butyltin oxide and diphenyltin oxide.
˚
2.1. Molecular structures of 1, 2, 3 and 4
boxylic acid group is hydrogen bonded [Oꢁ ꢁ ꢁH 1.844(7) A
˚
and 1.861(7) A, Fig. 1], similar to ferrocene carboxylic
Since the crystal structure of the parent carboxylic acid
has not been reported so far, we have carried out its crys-
tal structure to compare its structural features to that of
its organostannoxane complexes. Red colored crystals of
1, suitable for X-ray crystallography were obtained by
slow evaporation of its chloroform solution. The crystal
structure of 1 shows that it exists as a dimer and the car-
acid. Further, one of the phenyl groups present on the
cyclobutadiene ring makes weak C–Hꢁ ꢁ ꢁp interaction with
the centroid of the cyclopentadienyl ring of the neigh-
˚
bouring molecule [2.983(1) A]. The combination of com-
paratively stronger H-bonding and weak C–Hꢁ ꢁ ꢁp
interaction in 1 leads to a three-dimensional supramolec-
ular architecture.
Fig. 1. Thermal ellipsoid view of 1 showing O–Hꢁ ꢁ ꢁO hydrogen bonding (with 30% probability factor).

M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
4711
The molecular structure of 2 shows that the triorganotin
carboxylate adopts a discrete monomeric structure which
resembled structures of few other triphenyltin aryl carb-
oxylates [1,7]. The two oxygen atoms present in the carbox-
ylate group attached to the tin were in an anisobidentate
chelating [Sn1–O1 2.750(3) A and Sn1–O2 2.057(3) A]
coordination mode (Fig. 2). Similar anisobidentate bond-
ing distances for the analogous ferrocenecarboxylate were
Three different C–Hꢁ ꢁ ꢁp interactions were observed in
˚ ˚
between the phenyl groups (2.658(6) A and 3.201(1) A,
Fig. 3) and between the cyclopentadienyl and phenyl
groups. It is of interest to note that the novel CO2–p weak
interaction reported in the ferrocene analogue was absent
in this molecule [7].
˚
˚
The mononuclear tin dicarboxylate 3 crystallizes as a
chloroform solvate. Unlike the ferrocene analogue, which
crystallizes in cis and trans forms in the same unit cell, 3
crystallizes only in trans form, which can be attributed to
the steric bulkiness of the tetraphenyl cyclobutadiene moi-
ety [7]. The tin atom is hexacoordinate and the geometry
around the tin can be described as a skewed trapezoidal
bipyramid [16]. The two carboxylate ligands are coordi-
nated to the tin atom in an anisobidendate mode [Sn1–
˚
˚
Sn1–O1 2.080(2) A and Sn1–O2 2.598(2) A, respectively
[7]. The presence of seven phenyl groups and cyclopenta-
dienyl group lead to an unusual supramolecular assembly.
˚
˚
˚
O1 2.650(6) A, Sn1–O2 2.096(5) A, Sn1–O3 2.115(5) A
˚
and Sn1–O4 2.439(7) A (Fig. 4)]. The angle subtended by
the butyl carbon atoms on the tin atom (C69–Sn1–C73)
is 132.52(34)ꢁ, whereas in the trans ferrocene analogue it
was 145.0(3)ꢁ and 146.6(2)ꢁ in the case of the cis isomer
[7]. Similar to compound 1, compound 2 is rich in weak
interactions. For example, the cyclopentadienyl ring of
one molecule makes weak C–Hꢁ ꢁ ꢁp parallel displaced
˚
stacking (3.812(1) A) interaction with the cyclopentadienyl
ring of the neighbouring molecule.
The mononuclear tin dicarboxylate 4 crystallizes as a
dichloromethane solvate. The unit cell contains two inde-
pendent molecules in the asymmetric unit. Similar to com-
pound 3, here also the tin atom is six-coordinate with a
C2O4 coordination environment with skewed trapezoidal
bipyramidal geometry. The two cobalt sandwich moieties
are trans to each other. The two carboxylate ligands are coor-
dinated to the tin atom in an anisobidendate coordination
Fig. 2. Thermal ellipsoid view of compound 2 (with 30% probability
factor).
Fig. 3. Thermal ellipsoid view of compound 2 showing weak intermolecular C–Hꢁ ꢁ ꢁp interaction (with 30% probability factor).

4712
M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
Fig. 4. Thermal ellipsoid view of compound 3 with chloroform as a solvate (with 30% probability factor).
mode. However, unlike compound 3, which has four differ-
ent Sn–O bond distances for two carboxylate ligands, com-
pound 4 has only two different values of Sn–O bond
862.5 mV. Compound 2 shows one irreversible process
with anodic potential EAp value at 1287 mV, indicating that
for compound 2, oxidation process is more facile than the
reduction process. This observation is not unusual as we
have observed that although the tetraphenylcyclobutadi-
enyl carboxylicacid 1 gives a reversible voltammogram,
related carboxylic acids having other substituents on the
cyclcopentadienyl ring gives quasi-reversible cyclic voltam-
mograms under identical conditions of measurement with a
dominant oxidation peak [17]. Cyclic voltammogram of
compound 3 shows no electron transfer processes indicat-
ing its electrochemical stability under the given conditions.
In contrast, compound 4 shows one reversible redox couple
at an E1/2 value of 806 mV (Fig. 7). The occurrence of a sin-
gle reversible peak indicates that, the electrochemical
behaviour of two metallocenyl units in 4 are same and this
˚
distances for two carboxylate ligands [Sn1–O1 2.521(5) A
˚
and Sn1–O2 2.087(5) A]. The two independent asymmetric
units differ from each other from the angles between the
mean planes containing O–Sn–O atoms [O10–Sn1–O1
21.04ꢁ and O30–Sn1–O3 14.67ꢁ] (Fig. 5). The tin atom is
flanked by the two phenyl groups (C75–Sn1–C750) by an
angle of 122.56(37)ꢁ (see Tables 1 and 2).
2.2. Electrochemical studies
Electrochemical studies on compounds 1–4 were carried
out using cyclic voltammetry. The cyclic voltammogram of
1 (Fig. 6) shows only one reversible peak with E1/2 at
Fig. 5. Thermal ellipsoid view of compound 4 (with 50% probability factor).

M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
4713
Table 1
Crystallographic data of compounds 1–4
Compound
1
2
3
4
Empirical formula
Formula weight
Temperature (K)
C35H27CoO2.CHCl3
655.00
298(2)
C52H39CoO2Sn
873.47
150(2)
C76H66Co2O4Sn Æ 2CHCl3C80H54
1518.60
298(2)
Co2O4Sn.3CH2Cl2
1570.58
298(2)
˚
Wavelength (A)
0.71073
0.71073
0.71073
0.71073
Crystal system
Space group
a (A)
Monoclinic
P21
11.4656(16)
17.134(2)
15.774(2)
90
103.489(3)
90
3013.3(7)
1.418
Orthorhombic
P212121
14.310(3)
15.527(4)
18.308(4)
90
Monoclinic
P21/n
27.880(3)
9.3487(9)
28.443(3)
Monoclinic
C2/c
24.3056(16)
26.1679(17)
22.0854(14)
90
91.158(2)
90
14044.0(16)
1.486
˚
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
90
112.213(2)
90
6863.4(12)
1.470
3
˚
V (A )
4067.8(16)
1.426
Dcalc (Mg/m3)
Minimum and maximum transmission
0.901 and 0.933
0.867
1318
0.733 and 0.875
1.063
1776
0.759 and 0.887
1.123
2978
0.839 and 0.889
1.101
6368
Absorption coefficient (mmꢀ1
F(000)
)
Crystal habit, color
Crystal size (mm)
h Range for data collection (ꢁ)
Rod, Red
0.219 · 0.098· 0.082
1.33–25.08
ꢀ13 6 h 6 13,
ꢀ20 6 k 6 20,
ꢀ18 6 l 6 18
28946
5553 (0.0661)
0.0943
0.2045
Block, Red
0.371 · 0.247 · 0.129
2.22–25.00
ꢀ17 6 h 6 17,
ꢀ18 6 k 6 18,
ꢀ21 6 l 6 21
37981
4029 (0.0477)
0.0288
0.0760
Block, Red
0.327 · 0.203 · 0.109
1.30–25.50
ꢀ33 6 h 6 33,
ꢀ11 6 k 6 11,
ꢀ34 6l 6 34
66204
12726 (0.5783)
0.0966
0.2039
Block, Red
0.218 · 0.130 · 0.110
1.46–25.23
ꢀ29 6 h 6 29,
ꢀ31 6 k 6 31,
ꢀ26 6 l 6 26
66517
12698 (0.0845)
0.0993
0.2076
Index ranges
Number of reflections collected
Number of independent reflections (Rint
R1 [I > 2r(I)]a
)
wR2 [I > 2r(I)]b
S (all data)c
1.166
0.721 and ꢀ0.865
1.236
0.854 and ꢀ0.517
1.385
2.005 and ꢀ1.518
1.128
0.973 and ꢀ1.843
ꢀ3
˚
Largest difference in peak and hole (e A
)
.
P
P
a
R1 = (iFoj ꢀ jFci)/ jFoj.
P
P
2
1=2
b
wR2 ¼ f ½wðF 2o ꢀ F c2Þꢂ= ½wðF 2oÞ ꢂg
Table 2
Selected bond lengths (A) and bond angles (ꢁ) of compounds 1–4
˚
˚
Compounds
Bond lengths (A)
Bond angles (ꢁ)
Ph4C4CoC5H4COOH (1)
Co1–C2
Co1–C7
2.068(8)
1.994(7)
O1–C1–O2
124.33(90)
[Ph3SnOC(O)CpCoCbPh4] (2)
Sn1–O2
Sn1–O1
2.057(3)
2.750(3)
C41–Sn1–C35
C35–Sn1–O2
C35–Sn1–C47
C41–Sn1–C47
C41–Sn1–O2
112.37(15)
92.44(12)
112.37(15)
114.92(13)
115.47(13)
[n-Bu2Sn{OC(O)C5H4CoPh4}2] (3)
[Ph2Sn{OC(O)C5H4CoC4Ph4}2] (4)
Sn1–O1
Sn1–O2
Sn1–O3
Sn1–O4
2.650(6)
2.096(5)
2.115(5)
2.439(7)
C69–Sn1–C73
O2–Sn1–O3
O1–Sn1–O4
132.52(34)
81.35(19)
167.97(18)
Sn1–O1
Sn1–O2
Sn2–O4
Sn2–O3
2.521(5)
2.087(5)
2.493(7)
2.077(5)
C75–Sn2–C750
O3–C41–O1
O3–Sn2–O4
O1–Sn1–O2
122.56(37)
118.89(71)
56.40(19)
55.60(17)
is in accordance with the results obtained from the molec-
ular structure of 4. The E1/2 values obtained for 1, 2 and 4
are within the range of values reported by Gleiter et al. for
similar cobalt metallocenyl systems [18]. It is very interest-
ing to note that, while compound 1 shows slow electro-
chemical decomposition after second cycle, compounds 2
and 4 are very stable even after five electrochemical cycles.
The difference observed between the cyclic voltammograms
of 2, 3 and 4 compared to the free acid 1, suggests that the
stannoxane framework affects the electrochemical behav-
iour of compounds 2, 3 and 4. These results are in contrast
with the results obtained from the ferrocene carboxylic acid

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M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
800
The results obtained from the reaction of 1 with alkyl
and aryl tin oxides seems to suggest that the formation of
stannoxane assemblies having more than two carboxylate
units are not favored in these reactions indicating that 1
is a highly sterically hindered metallocene carboxylic acid.
Also we wish to report that our preliminary attempts of the
reaction of 1 with n-butylstannonic acid in both solution
phase and solvent-free methods, which is expected to give
hexameric drum cluster failed to give any isolable product,
further conforming the above findings. Electrochemical
studies on compounds 1 to 4 show that unlike ferrocene
derived stannoxanes which in almost all cases showed
redox inactivity [10] the stannoxane cores seems to influ-
ence the electrochemical behaviour of the metallocenyl
units in these compounds.
600
400
200
0
1600 1400 1200 1000 800
600
400
200
0
-200
-400
potential
4. Experimental
Fig. 6. Cyclic voltammogram of 1 in CH2Cl2 with 0.1 M Bu4NClO4 as
supporting electrolyte at 0.1 V sꢀ1 at 25 ꢁC using Ag/AgCl electrode as a
reference.
4.1. General procedure
All manipulations of the complexes were carried out
using standard Schlenk techniques under nitrogen atmo-
sphere. All reactions were carried out by two different
methods namely using toluene as solvent with azeotropic
removal of water and by the solvent free method involving
mechanical grinding. Toluene was freshly distilled from
sodium benzophenone ketyl under nitrogen atmosphere
and used. [(n-Bu)2SnO]n, (Ph3Sn)2O and (Ph2SnO)n were
procured from Aldrich and used as such. Ph4C4CoC5H4-
COOH (1) was prepared following the reported procedure
600
400
200
0
2500
2000
1500
1000
500
0
1
[11]. H, 13C {1H} NMR and spectra were recorded on a
-200
-400
-600
Bruker Spectrospin DPX-300 NMR spectrometer at
300.13 and 75.47 MHz, respectively. 119Sn NMR was
recorded on a JEOL GSX 400 NB FT-NMR spectrometer.
IR spectra in the range 4000–250 cmꢀ1 were recorded on a
´
Nicolet Protege 460 FT-IR spectrometer as KBr pellets.
potential
Elemental analyses were carried out on a Carlo Erba
CHNSO 1108 elemental analyzer.
Fig. 7. Cyclic voltammogram of 4 in CH2Cl2 with 0.1 M Bu4NClO4 as
supporting electrolyte at 0.15 V sꢀ1 at 25 ꢁC using Ag/AgCl electrode as a
reference.
4.2. Crystal structure studies
Single-crystal diffraction studies were carried out on a
based stannoxanes, which showed an almost complete
redox-inactivity of stannoxane cores [8]. However, a
detailed electrochemical study on more examples of similar
type of compounds is required to ascertain these
observations.
Bruker Smart Apex CCD diffractometer with a Mo Ka
(k = 0.71073 A) sealed tube. All crystal structures were
˚
solved by direct methods and refined using the SHELXTL
package [19]. All hydrogen atoms were included in ideal-
ized positions, and a riding model was used. Non-hydrogen
atoms were refined with anisotropic displacement
parameters.
3. Conclusions
We have carried out the first reactions of [g5-carboxycy-
clopentadienyl][g4-tetraphenylcyclobutadiene]cobalt, Ph4-
C4CoC5H4COOH with alkyl and aryl tin oxides. New
organometallic cobalt based stannoxanes 2, 3 and 4 have
been prepared and structurally characterized. The struc-
tures and electrochemistry of these compounds are com-
pared with analogous organotin ferrocene carboxylates.
4.3. Electrochemical studies
All electrochemical measurements were taken in basic
electrochemistry system ECDA-001, using a three-elec-
trode configuration of a Pt working electrode (0.1 mm
diameter), commercially available Ag/AgCl electrode as
the reference electrode and a Pt mesh electrode as a counter

M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
4715
1
electrode. Half-way potentials were measured as the aver-
age of the cathodic and anodic peak potentials. The vol-
tammograms were recorded in CH2Cl2 containing 0.1 M
tetrabutylammonium perchlorate as the supporting electro-
lyte, and the potential was scanned from 0 to +2 V at var-
ious scan rates. Ferrocene gave a reversible single redox
couple with E1/2 at 664 mV under the same experimental
condition.
M.p.: 168 ꢁC; H NMR (CDCl3, ppm): d 0.87 (t, 12H,
butyl methyl); 1.16–1.26 (m, 4H, butyl-CH2); 1.42 (m,
4H, butyl-CH2), 1.56 (t, 4H, butyl-CH2), 4.76 (d, 4H, Cp-
H), 5.31 (d, 4H, Cp-H), 7.20–7.22 (m, 24H, Ar-H); 7.43-
7.46 (m, 16H, Ar-H); 13C NMR (CDCl3, ppm): d 13.62
(–CH3 C), 24.78 (–CH2C), 26.46 (–CH2 C), 26.80 (–CH2
C), 84.26 (Cb C), 87.88 (Cp C), 126.69 (Ar C), 128.06
(Ar C), 128.90 (Ar C), 135.03 (Ar C); 119Sn NMR (CDCl3,
ppm): d ꢀ140.34; IR (KBr disk, m/cmꢀ1): 3428m, 3054m,
3026m, 2954s, 2923s, 2854m, 2361w, 1599vs (masymOCO),
1577vs (masymOCO), 1498vs, 1463vs,1400w, 1371s (msymOCO),
1352s (msymOCO), 1175s, 1070m, 1024s, 918w, 816s, 780s,
619w, 698vs, 586s, 562vs, 490s (mSnO). Anal. Calc. for
C76H66Co2O4Sn Æ 2CHCl3: C, 61.64; H, 4.48. Found: C,
61.10; H, 4.41%.
4.4. General synthetic procedure for the preparation
of 2, 3 and 4
A stoichiometric mixture of the organotin oxide and 1 in
toluene (100 mL) was heated under reflux for 6 h. The
water formed in the reaction was removed by using a
Dean-Stark apparatus. Solvent was evaporated from the
mixture and dried in vacuo for 2 h. The resulting solid
material was dissolved in dichloromethane, filtered using
a G3 frit and recrystallized from corresponding solvents.
Crystals of 1, 2, 3 and 4 suitable for X-ray analysis were
obtained by slow evaporation of their saturated solutions
in chloroform/hexane mixture for compounds 1, 2 and 3
and in dichloromethane/hexane mixture for compound 4.
All the above compounds are stable at room temperature
and to air.
Compounds 2, 3, and 4 were also prepared by a solvent-
free method. In this method, similar to the procedure
reported by Chandrasekhar and co-workers [8], a stoichi-
ometric mixture of the organotin precursor and 1 were
ground to a fine powder for 45 min using a mortar and pes-
tle. At the completion of the grinding period, the product
was extracted in dichloromethane, filtered and
recrystallized.
4.4.3. {Ph2Sn[OC(O)C5H4CoC4Ph4]2} (4)
Diphenyltin oxide (0.05 g, 0.17 mmol),
1 (0.18 g,
0.34 mmol) (0.17 g), 4 (77% yield); solvent-free method,
grinding time is 45 min (70% yield); 1H NMR (CDCl3,
ppm): d 4.80 (4H, CpH); 5.37 (4H, CpH); 6.83 (4H,
ArH); 7.09–7.12 (12H, ArH); 7.23–7.25 (6H, ArH), 7.39–
7.41 (8H, ArH); 13C NMR (CDCl3, ppm): d 84.68 (Cb
C), 87.98 (Cp C), 125.15(Ar C), 126.70 (Ar C), 128.01
(Ar C), 128.77 (Ar C), 129.77 (Ar C), 131.39(Ar C),
134.83 (Ar C), 135.99 (Ar C), 136.94 (Ar C); 119Sn NMR
(CDCl3, ppm): d ꢀ280.80; IR (KBr disk, m/cmꢀ1): 2923w,
2800w, 1950w, 1597vs (masymOCO), 1566vs (masymOCO),
1464s, 1372s (msymOCO), 1324s (msymOCO), 1175s, 1069m,
916w, 785m, 822s, 736vs, 696vs, 588w, 563s, 493s (mSnO),
446m. Anal. Calc. for C83H60Co2O4Sn.3CH2Cl2: C,
63.42; H, 3.82. Found: C, 63.38; H 3.79%.
5. Supplementary data
4.4.1. Ph3SnOC(O)C5H4CoC4Ph4 (2)
Bis(triphenyltin)oxide (0.17 g, 0.20 mmol), 1 (0.25 g,
0.48 mmol), 0.14 g (70% yield); solvent-free method,
grinding time is 45 min (70% yield); m.p.: 175 ꢁC; 1H
NMR (CDCl3, ppm): d 4.69 (d, 2H, Cp-H), 5.28 (d,
2H, Cp-H), 7.00–7.05 (m, 9H, SnAr-H), 7.08–7.13 (m,
6H, SnAr-H), 7.34–7.40 (m, 12H, CbAr-H), 7.57–7.60
(m, 8H, CbAr-H); 13C NMR (CDCl3, ppm): d 76.40
(Cb C), 84.44 (Cp C), 86.09 (Cp C), 87.64 (Cp C),
126.53 (CbAr C), 127.91 (CbAr C), 128.60 (CbAr C),
128.70 (SnAr C), 129.01 (SnAr C), 135.03 (CbAr C),
136.91 (SnAr C), 138.78 (SnAr C); 119Sn NMR (CDCl3,
ppm): d ꢀ117.82; IR (KBr disk, m/cmꢀ1): 3427m, 3057
m, 2924vw, 1616vs (masymOCO), 1461s, 1498s, 1430m,
1369s (msymOCO), 1319m, 1172s, 1073m, 1024m, 996vw,
917vw, 814m, 736vs, 698vs, 614vw, 587s, 564m, 491s
(mSnO), 446m; Anal. Calc. for C54H45CoO2Sn: C, 71.78;
H, 5.02. Found: C, 71.93; H, 5.19%.
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 609310, 609311, 609312 and 609313
for compounds 1, 2, 3 and 4, respectively. Copies of this
information may be obtained free of charge from: The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ
UK (fax (int code): +44 1223 336 033 or e-mail: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgments
The authors thank Department of Science and Tech-
nology, India for financial assistance in the form of a re-
search grant and IIT Delhi for an equipment grant. We
acknowledge DST-FIST and IITD for funding of the sin-
gle crystal X-ray diffraction facility at IIT Delhi. We
thank Prof. P.S. Verma, Department of Chemistry, Uni-
versity of Rajasthan, Dr. J.K. Bera, and S.K. Patra,
Department of Chemistry, IIT Kanpur, Mr. N.K. Nauti-
yal and Mr. J.P. Singh of Department of Chemistry, IIT,
Delhi, for their assistance in electrochemical and spectral
measurements. We thank Dr. M.S. Moni, and the NMR
4.4.2. {n-Bu2Sn[OC(O)C5H4CoC4Ph4]2} (3)
Di-n-butyltin oxide (0.07 g, 0.2 mmol),
1 (0.07 g,
0.1 mmol), 3 (65% yield); solvent-free method, grinding
time is 45 min (45% yield).

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M.S. Kumar et al. / Journal of Organometallic Chemistry 691 (2006) 4708–4716
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