Synthesis, reactivity and structural studies of (η5-methylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt and its derivatives

Article abstract of DOI:10.1016/j.jorganchem.2008.09.030

(η⁵-methylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt (1) and its derivatives, [(1-acetyl-2-methyl)η⁵-cyclopentadienyl](η⁴-tetraphenylcyclobutadiene)cobalt (2) [(1-acetyl-3-methyl)η⁵-cyclope

Full text of DOI:10.1016/j.jorganchem.2008.09.030

Journal of Organometallic Chemistry 693 (2008) 3780–3786
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Journal of Organometallic Chemistry
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Synthesis, reactivity and structural studies of (
g
5-methylcyclopentadienyl)
(g
4-tetraphenylcyclobutadiene)cobalt and its derivatives
*
Rajkumar Jana, M. Senthil Kumar, Nem Singh, Anil J. Elias
Department of Chemistry, Indian Institute of Technology, Delhi Hauz Khas, New Delhi 110 016, India
a r t i c l e i n f o
a b s t r a c t
5-methylcyclopentadienyl)(
methyl)
5-cyclopentadienyl](
pentadienyl](
enyl](
4-tetraphenylcyclobutadiene)cobalt (4) and [(1-carbomethoxy-3-methyl)
4-tetraphenylcyclobutadiene) cobalt (5) have been prepared in yields varying from 11% to 28% by
introducing the substituents on the cyclopentadienyl ring of methylcyclopentadienyl sodium and then
reacting with diphenylacetylene and CoCl(PPh3)3. The carboxylic acids [(1-carboxy-2-methyl)
5-cyclo-
pentadienyl](
4-tetraphenylcyclobutadiene)cobalt (6), [(1-carboxy-3-methyl) 5-cyclopentadienyl](g4
tetraphenylcyclobutadiene)cobalt (7) have been prepared after ester hydrolysis of compounds 4 and 5
using KOH/ethanol. [(1-dimethylaminomethyl-3-methyl)
5-cyclopentadienyl]( 4-tetraphenylcyclobut-
adiene) cobalt (8), was prepared selectively by direct substitution on the cyclopentadienyl ring of (g5
methylcyclopentadienyl)(
4-tetraphenylcyclobutadiene)cobalt in 65% yield. The 1,2-isomer was formed
only in traces in this reaction. Reactivity of (
5-methylcyclopentadienyl)( 4-tetraphenylcyclobutadi-
5-cyclopentadienyl)( 4-tetra-
g
g
4-tetraphenylcyclobutadiene)cobalt (1) and its derivatives, [(1-acetyl-2-
4-tetraphenylcyclobutadiene)cobalt (2) [(1-acetyl-3-methyl) 5-cyclo-
5-cyclopentadi-
5-cyclopentadienyl]
Article history:
(
g
Received 15 July 2008
Received in revised form 12 September
2008
Accepted 19 September 2008
Available online 27 September 2008
g
g
g
4-tetraphenylcyclobutadiene)cobalt (3) [(1-carbomethoxy-2-methyl)
g
g
g
(
g
g
Keywords:
g
g
-
Methylcyclopentadienyl
Tetraphenylcyclobutadiene
Acetyl
Carbomethoxy
Dimethylaminomethyl
Carboxylic acid
g
g
-
g
g
g
ene)cobalt and its carbomethoxy derivative have been compared with (
g
g
phenylcyclobutadiene)cobalt. All new compounds were characterized by 1H and 13C NMR, FT-IR, mass
spectra and CHN analysis. Compounds 2, 4, 6 and 8 have also been structurally characterized by single
crystal X-ray structural analysis.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
catalysis such as palladium catalyzed allylic substitutions and rear-
rangements of allylic trichloroacetimidates and N-(4-methoxy-
Planar chirality, a unique property of metal sandwich com-
pounds and particularly of ferrocene has been utilized in realizing
a variety of chiral ferrocene based chelating ligands such as Josi-
phos, bppfa, Walphos and Mandyphos which are used even in
industrial organic catalysis [1]. Such compounds are obtained
mostly by introducing two different substituents at 1,2 or 1,3 posi-
tions of a cyclopentadienyl ring of ferrocene and many synthetic
strategies have been evolved for the same [2]. The promise shown
by ferrocene in realizing such chiral molecules have evoked inter-
est in extending such studies to other chemically robust metal
sandwich compounds as well. The cobalt based sandwich com-
phenyl) trifluoroacetimidates [4–7].
The major impediment in developing substitution reactions of
(g g
5-Cp)Co( 4-C4Ph4) has been the poor reactivity of the cyclopen-
tadienyl ring of this compound and conventional electrophilic sub-
stitution reactions which work readily on the cyclopentadienyl
ring of ferrocene often do not proceed or occur with poor yields
on the cyclopentadienyl ring of this molecule [8,9]. Disubstitution
on the cyclopentadienyl ring of (g g
5-Cp)Co( 4-C4Ph4) has been re-
stricted to only a few examples of 1,2 and one 1,3 substituted com-
pound prepared by complex multistep methods [9–11]. With a
view to explore the possibility of synthesizing 1,2 and 1,3
pound, (
g
5-Cp)Co(
g
4-C4Ph4), show similarity to ferrocene in many
cyclopentadienyl substituted derivatives of the type
[ -
g5
ways [3]. The high air and moisture stability of this compound
which often surpass ferrocene and the relative ease of its synthesis
makes this molecule a potential alternative to ferrocene in many
(R1)(R2)C5H3]Co(
g
4-C4Ph4), where R1 is methyl and R2 is a well
utilized and functionally modifiable group such as –C(O)CH3,
–C(O)OMe, –COOH and –CH2NMe2 and also to determine if any
selectivity is possible in such disubstitution reactions, we have car-
ried out the preparation of a series of disubstituted derivatives of
reactions. A few examples of planar chiral derivatives of (g5
-
Cp)Co(g
4-C4Ph4) have already shown promise in enantioselective
(g g
5-Cp)Co( 4-C4Ph4). Herein we report the results obtained from
this study and compare the same with analogous reactions of
ferrocene.
* Corresponding author. Tel.: +91 11 26591504.
E-mail address: eliasanil@gmail.com (Anil J. Elias).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.030

R. Jana et al. / Journal of Organometallic Chemistry 693 (2008) 3780–3786
3781
K-BuOt or acetylation of the Cp ring using Ac2O and H3PO4 were
found to be unsuccessful. The steric hindrance of the tetraphenyl-
cyclobutadiene moiety in coming in the way of the reactivity of the
Cp ring as indicated in the attempted lithiation of the non-methyl-
ated analogue of 1 [13]. The preparation of the acetyl derivative
was therefore carried out by introducing the acetyl group on the
sodium salt of methylcyclopentadienyl [14–16] and then reacting
it with CoCl(PPh3)3 and diphenylacetylene (Scheme 2).
Two positional isomers (1,2 and 1,3) of the acetyl derivative (2
and 3) of 1 were found to form in 11% and 28% yield, respectively.
The 1,3-isomer has been found to form in higher yields indicating
selectivity towards the formation of a particular isomer to avoid
steric hindrance, a trend which has also been observed for other
Cp disubstituted derivatives prepared in this study. The isomers
were separated on an alumina column. The overall yield of the
acetylated products is slightly higher compared to the yields re-
ported for the non-methylated analogue (26% and 33%) [14,16].
Compounds 2 and 3 show significant differences in their IR and
NMR spectra which have been discussed later. Attempted reduc-
tion of the acetyl derivatives 2 and 3, with sodium borohydride
was not found to proceed. Identity of compound 2 was further con-
firmed by single crystal X-ray diffraction studies.
2. Results and discussion
Reaction of sodium salt of methylcyclopentadienyl, CoCl(PPh3)3
and diphenylacetylene in refluxing toluene/THF mixture resulted
in the formation of (
relatively simple method to realize the methylated
Cp)Co(
4-C4Ph4) also indicated a higher yield of the cobalt sand-
wich compound 1 (64% isolated yield) compared to the synthesis
of (
5-Cp)Co( 4-C4Ph4) by the same method which gave only a
g g
5-MeCp)Co( 4-C4Ph4) (1) (Scheme 1). This
(
g5
-
g
g
g
maximum of 40% isolated yield [12]. The possible reason for the
higher yield is the increased reactivity of sodium salt of methylcy-
clopentadienyl compared to that of sodium cyclopentadienyl. A
different approach was also made to prepare compound 1 by
exhaustive reduction of the methoxyester derivative of (g5
-
Cp)Co(g
4-C4Ph4) using lithium aluminium hydride in THF. The
reaction ended in a mixture of products and hence the method
was abandoned.
The formation of compound 1 in good yield enabled us to ex-
plore the chemistry on its methyl functionalized cyclopentadienyl
unit. Our attempts to lithiate the Cp ring using n-BuLi or n-BuLi/
The carbomethoxy derivatives of the compound 1 were pre-
pared following a similar strategy to the acetylation reaction using
dimethyl carbonate instead of ethylacetate. These compounds are
good precursors for the synthesis of many other derivatives such
as carboxylic acids, alcohols, aldehyde etc. [15]. The yields of the
compounds were found to be 11% for 1,2-isomer (4) and 19% for
1,3-isomer (5) (Scheme 3). The main reason for the low yields of
these compounds is due to the fact that RCpCo(PPh3)2 is made
in situ and utilized and the formation of this compound is only in
moderate yields in the one pot reaction. Both compounds were
Na
Me
Me
Me
130-140˚C
+
Na
Me
Ph
Ph
Ph
Na
Ph
Ph
Me
+ 2
Co
THF, Toluene
reflux
CoCl(PPh3)3
Ph
1
Scheme 1.
C(O)Me
Na
Me
THF, Reflux
-EtOH
Me
C(O)Me
C(O)Me
Me
Me
Me
C
O
+
EtO
C(O)Me
Me
C(O)Me
Toluene, CoCl(PPh3)3
Ph
Ph
Co
Me
C(O)Me
Ph
Ph
Me
Co
-NaCl, -PPh3
Reflux
+
+
2
Ph
Ph
Ph
Ph
Ph
3
Ph
2
Scheme 2.
C(O)OMe
C(O)OMe
MeO
Na
THF, Reflux
-MeOH
Me
Me
Me
C(O)OMe
Me
C
O
+
MeO
C(O)OMe
Ph
Me
Ph
C(O)OMe
Me
Toluene, CoCl(PPh3)3
Ph
Ph
Co
Co
C(O)OMe
Me
-NaCl, -PPh3
Reflux
+
+
Ph
Ph
Ph
Ph
Ph
Ph
2
4
5
Scheme 3.

3782
R. Jana et al. / Journal of Organometallic Chemistry 693 (2008) 3780–3786
characterized by a host of spectral and analytical techniques and
the crystal structure of 4 has also been determined.
by direct methods and crystal structure of 6 was solved by Patter-
son method. The program SAINT (version 6.22) was used for integra-
tion of the intensity of reflections and scaling. The program SADABS
was used for absorption correction [18]. The crystal structures
were solved and refined using the SHELXTL (version 6.12) package
[19]. All hydrogen atoms were included in idealized positions,
and a riding model was used. Non-hydrogen atoms were refined
with anisotropic displacement parameters. In order to bring down
the value of residual factor, we have omitted the higher 2h reflec-
tions in case of compound 8. Tables 1–4 lists the selected bond
lengths and angles of compounds 2, 4, 6 and 8.
In compound 2 the cobalt atom is at a distance of 1.680(1) Å
from the centroid of the Cp ring and makes a distance of
1.693(1) Å with the centroid of the cyclobutadiene ring. The mean
planes containing the four phenyl rings make angles of 24.81°,
28.08°, 37.03° and 54.03° with the cyclobutadiene ring. The cobalt
to ring-carbon distances of compound 2 average 2.071(4) Å with
As stable metallocene carboxylic acids are excellent precursors
for a host of organometallic molecules with a wide range of poten-
tial applications, preparation of the acid derivatives starting from
carbomethoxy derivatives were attempted by the reaction with
KOtBu in dry DMSO which has been the procedure reported for pre-
paring [g g
5-C5H4(COOH)]Co( 4-C4Ph4). However, the reaction was
not successful in this case. An ester hydrolysis method using
KOH/ethanol was found to proceed readily giving the acid deriva-
tives 6 and 7 of both 1,2 and 1,3 carbomethoxy esters (Scheme 4).
The two derivatives have been characterized by 1H NMR, 13C NMR,
mass spectra and FT-IR. The crystal structure of the 1,2-derivative 6
has also been determined.
The dimethylaminomethyl derivatives of compound 1 were
prepared by using bis(dimethylamino)methane and phosphoric
acid [3] (Scheme 5). In this reaction the 1,3-isomer was formed al-
most exclusively (65% isolated yield) and only a trace amount of
1,2-isomer was formed whose identity was confirmed by mass
spectrometry. The steric effect of the tetraphenylcyclobutadiene
moiety has possibly played a major role towards the exclusive for-
mation of the 1,3-isomer. It is interesting to note that the analo-
gous reaction reported on monomethyl ferrocene yielded the 1,2
and 1,3-isomers in 14% and 25%, respectively [17].
Table 1
Selected bond lengths and angles of compound 2
Bonds
Bond length (Å)
Bonds
Bond angles (°)
C2–O1
C7–C8
1.209(11)
1.505(11)
2.082(8)
2.083(7)
1.994(7)
1.983(7)
1.496(13)
O1–C2–C1
C8–C7-C3
C3–Co1–C12
C5–Co1–C11
C9–C12–C31
C2–C3–C4
123(10)
127.2(8)
125.3(3)
122.4(3)
136.1(6)
126.2(9)
90.1(6)
Co1–C3
Co1–C7
Co1–C12
Co1–C11
C1–C2
2.1. Molecular structures of compounds 2, 4, 6 and 8
Suitable crystals of compounds 2, 4, 6 and 8 for single crystal X-
ray study were obtained by slow evaporation of their respective
solutions in a mixture of hexane/ethylacetate. All the four com-
pounds were found to crystallize in the monoclinic system. Sin-
C9–C10–C11
Table 2
gle-crystal diffraction studies were carried out on
SMART APEX CCD diffractometer with a Mo K (k = 0.71073 Å)
sealed tube. Crystal structures of compound 2, 4 and 8 were solved
a Bruker
Selected bond lengths and angles of compound 4
a
Bonds
Bond length (Å)
Bonds
Bond angles (°)
Co1–C7
Co1–C3
Co1–C9
Co1–C12
C2–O1
2.062(4)
2.055(4)
2.018(4)
1.985(4)
1.348(7)
1.21(7)
C4–Co1–C9
O1–C2–O2
C8–C7–C3
C10–C19–C20
C11–C25–C26
C11–C12–C9
O2–C2–O1
133.47(17)
123.1(5)
128.5(5)
122.7(4)
120.57(39)
89.7(3)
Me
Me
O
C
OH
CO2Me
Ph
C2–O2
C9–C13
1.458(6)
123.1(5)
Ph
Ph
Ph
Ph
Ph
Co
Co
KOH/EtOH
Reflux
Table 3
6
4
Ph
Selected bond lengths and angles of compound 6
Ph
Bonds
Bond lengths (Å)
Bonds
Bond angles (°)
O
C
Co1–C2
Co1–C8
C8–C11
C1–C2
2.086(4)
1.998(3)
1.453(4)
1.450(6)
1.453(6)
1.270(5)
1.266(5)
0.819(5)
1.461(5)
C10–Co1–C9
C8–C11–C30
C11–C10–C9
C3–C4–C5
C2–C3–Co1
C7–C6–C2
C6–C2–C1
C2–C1–O1
O1–C1–O2
43.31(13)
134.3(3)
89.7(2)
108.1(4)
70.6(2)
128.4(4)
127.4(4)
116.3(4)
122.7(4)
Me
Ph
OH
Me
Ph
CO2Me
Ph
Ph
Co
Co
KOH/EtOH
Reflux
C2–C3
O1–C1
O2–C1
O1–H1
C11–C30
5
7
Ph
Ph
Ph
Ph
Scheme 4.
CH2NMe2
Me
Ph
CH2NMe2
Ph
Me
Ph
Me
Ph
Ph
Ph
Co
Co
Ph
Ph
Me2N-CH2-NMe2
H3PO4
Co
+
9
Ph
Ph
Ph
8
Ph
1
Scheme 5.

R. Jana et al. / Journal of Organometallic Chemistry 693 (2008) 3780–3786
3783
Table 4
distances between C2–O1, C2–O2 and O1–C1 are 1.349(7),
0
Selected bond lengths and angles of compound 8
1.210(7) and 1.461(7) ÅA, respectively, whereas the same distances
for the methoxyester derivative of
(g g
5-Cp)Co( 4-C4Ph4) are
Bonds
Bond length (Å)
Bonds
Bond angles (°)
0
1.343(4), 1.195(4) and 1.446(5) ÅA.
Co1–C4
Co1–C7
C3–N1
C9–C13
C7–C37
Co1–C9
C3–C4
N1–C1
C12–C31
C11–C25
2.068(6)
2.060(7)
1.445(7)
1.471(8)
1.474(17)
1.988(5)
1.459(8)
1.437(9)
1.458(7)
1.463(8)
C4–Co1–C9
C4–C3–N1
122.5(2)
112.7(5)
124.6(4)
112.5(3)
120.7(6)
90.3(4)
110.5(6)
124.4(15)
127.6(6)
107.1(9)
It is interesting to note that compound 6 exists as a dimer with
two molecules linked through symmetrical hydrogen bonding
interaction between the carboxylic groups. The carboxylic groups
C6–Co1–C12
C7–Co1–C12
C11–C25–C26
C9–C10–C11
C1–N1–C2
C37–C7–C8
C3–C4–C8
C5–C6–C7
have formed a six membered ring through hydrogen bonding
0
where the length of hydrogen bond is 1.852 (9) ÅA. The hydrogen
bonds are formed in such a way that the two metal sandwich moi-
eties orient themselves in trans orientation to avoid steric repul-
sion between the phenyl rings and the two cyclopentadienyl
rings of the dimer are almost in the same plane (angle between
the Cp planes is 1.01°). The closely related structure observed for
the non-methylated system shows that it exists as a dimer and
the carboxylic acid group is hydrogen bonded unsymmetrically
cyclopentadienyl ring and 1.984(7) Å with cyclobutadiene ring.
These values are in good agreement with the values reported for
0
0
the acetyl derivative of (g g
5-Cp)Co( 4-C4Ph4), where the Co–C dis-
where the hydrogen bond lengths are 1.844(7) ÅA and 1.861(7) ÅA
[21]. In the crystal structure of 6, the cobalt atom is at a distance
of 1.686(1) Å with the centroid of the Cp ring and is at a distance
tance average 2.070(2) Å to the cyclopentadienyl ring and
1.982(2) Å to the cyclobutadiene ring. The results indicate that
the introduction of one methyl group does not have any influence
on the distances between the Co atom and two rings. The phenyl
groups adopt a propeller like orientation with dihedral angles
ranging from 21° to 42°, and are bent in an exo fashion out of
the plane of the cyclobutadiene ring by 7.5 Å [14] (see Fig. 1).
In compound 4 (Fig. 2) the cobalt atom makes a distance of
1.680(1) Å with the centroid of the Cp ring and is at a distance of
1.700(1) Å from the centroid of cyclobutadiene ring which is simi-
of 1.696(1) Å with the centroid of cyclobutadiene ring whereas
0
the distances for the non-methylated case are 1.694(15) ÅA and
0
1.706(16) ÅA, respectively. The four phenyl rings of the tetraphenyl
cyclobutadiene rings of 6 are displaced at angles of 29.07°, 30.36°,
38.75° and 40.96° with respect to the cyclobutadiene ring (see
Fig. 3).
To the best of our knowledge no crystal structures of dimethyl-
aminomethyl derivatives of (
ported yet and we have carried out the single crystal X-ray
g g
5-Cp)Co( 4-C4Ph4) have been re-
lar to the distances for the0 carbomethoxy 0 derivative of (g5
Cp)Co(
The four phenyl rings of compound 4 make angles of 25.29°,
32.23°, 38.84° and 44.84° with the cyclobutadiene ring. The
-
g
4-C4Ph4) of 1.679(1) ÅA and 1.689(1) ÅA, respectively [20].
structure
methyl)
determination
of
g
[(1-dimethylaminomethyl-3-
g
5-cyclopentadienyl]( 4-tetraphenylcyclobutadiene) co-
balt (8). Suitable crystals of 8 for X-ray study were obtained by slow
evaporation of its solution in hexane/ethyl acetate mixture. In the
structure of compound 8, the cobalt atom is at a distance of
1.691(1) Å from the centroid of the Cp ring and is at a distance of
1.695(1) Å from the centroid of cyclobutadiene ring. The four phe-
nyl rings of the tetraphenyl cyclobutadiene rings of 8 are displaced
at angles of 42.50°, 32.47°, 30.80° and 40.87° with respect to the
cyclobutadiene ring. Some selected bond lengths and bond angles
are given in Table 4. To decrease steric hindrance, the –NMe2 group
of the compound 8 is oriented in such a way that the methyl groups
attached to N atom are projected above the average plane of the five
carbon atoms of the cyclopentadienyl ring and the N atom bound to
the –CH2 group is also above the same plane. The N atom of the
–CH2NMe2 group makes a deviation of 1.449 Å from the plane of
the five carbon atoms of cyclopentadienyl ring (see Fig. 4).
2.2. Spectral studies
Fig. 1. X-ray crystal structure of compound 2.
The 1H NMR spectrum of compound 1 shows two peaks (4.44
and 4.51 ppm) indicating the presence of two unequal sets of pro-
tons on the cyclopentadienyl ring, ortho and meta with respect to
methyl group. In contrast, the protons of the methylcyclopentadie-
nyl ring of methylferrocene have been reported to appear as a sin-
glet at 4.12 ppm [22]. 1,2 and 1,3-isomers of the functionalized
derivatives of 1 show significant differences both in their 1H
NMR chemical shifts and splitting pattern in all the cases. The
chemical shifts of cyclopentadienyl protons of the disubstituted
derivatives are complex and vary from 4.37 to 5.16 ppm depending
on the type of substituent on the cyclopentadienyl ring. The 1H
NMR chemical shift differences are only marginal when compared
to the mono substituted non-methylated analogues except for the
1,2 acetyl derivative (2) [8,14,15]. The protons of the acetyl group
of
g g
5-CpC(O)CH3]Co( 4-C4Ph4) appear at 1.65 ppm [14] whereas
in compounds 2 and 3 it appears at 1.66 and 1.87 ppm, respec-
tively. The methyl protons of all the derivatives appear in the range
of 1.45–1.90 ppm. The positional isomers of the derivatives show
Fig. 2. X-ray crystal structure of compound 4.

3784
R. Jana et al. / Journal of Organometallic Chemistry 693 (2008) 3780–3786
Fig. 3. X-ray crystal structure of compound 6 showing symmetrical hydrogen bonding.
atives (acetyl, carbomethoxy, carboxylic acid and aminomethyl)
are described. The study critically evaluates the scope and utility
of disubstitution on the cyclopentadienyl ring of (
5-Cp)Co(g4
C4Ph4). Two different positional isomers (1,2 and 1,3) of the deriv-
atives of (
5-MeCp)Co( 4-C4Ph4) were found to form. In all the
g
-
g
g
reactions, the relative yields of the 1,3-isomer was higher than that
of the 1,2-isomer and in the case of dimethylaminomethyl deriva-
tive, 8 the 1,3-isomer was formed almost exclusively. It was
observed that both 1,2 and 1,3 carbomethoxy derivatives of (g5
-
MeCp)Co(g
4-C4Ph4) gave the corresponding acid derivatives after
ester hydrolysis reaction with KOH/ethanol. X-ray crystal structure
of compounds 2, 4, 6 and 8 have been determined and the orienta-
tion of four phenyl rings with respect to the cyclopentadienyl ring
are also reported. The increase in yield of the 1,3-isomer on going
from carbomethoxy to acetyl to aminomethyl derivative, possibly
indicates a substituent effect in controlling the formation of a par-
ticular positional isomer. All the new compounds reported are
highly stable to air and moisture, are high melting and are impor-
tant precursors for the synthesis of a host of useful derivatives of
Fig. 4. X-ray crystal structure of compound 8.
(g g
5-MeCp)Co( 4-C4Ph4).
differences not only in the 1H NMR spectra but also in other spec-
tral studies. Compounds 4 and 5 show a difference of ꢀ4 cmꢁ1 in
their carbonyl stretching frequency whereas compounds 2 and 3
4. Experimental
differs by only ꢀ2 cmꢁ1
.
13C NMR studies also help to identify sub-
4.1. General procedures
stitution especially from the chemical shifts of the ipso carbon
atoms of the Cp ring. The ipso carbon atom of MeC5H4 unit of 1 ap-
pears at 94.57 ppm while the rest of the ring-carbon atoms appear
at 82.74 and 83.56 ppm. This shift is similar to the trends shown by
monoacetyl (93.80 ppm) and monocarboxylic acid (92.90 ppm)
All manipulations were carried out using standard Schlenk tech-
niques under a nitrogen atmosphere. THF and toluene were freshly
distilled from sodium benzophenone ketyl and hexane was distilled
and dried over sodium and used. Tris(triphenylphosphine)cobalt
chloride was prepared according to reported procedure [23].
Diphenylacetylene, triphenylphosphine and methylcyclopentadi-
ene dimer procured from Aldrich were used as such. 1H and
13C{1H} spectra were recorded on a Bruker Spectrospin DPX-300
NMR spectrometer at 300 and 75.47 MHz, respectively. IR spectra
in the range 4000–250 cmꢁ1 were recorded on a Nicolet Protége
460 FT-IR spectrometer as KBr pellets. Elemental analyses were car-
ried out on a Carlo Erba CHNSO 1108 elemental analyzer. Mass
spectra were recorded in the EI and TOF mode using a JEOL SX
102/DA-6000 and MALDI-TOF Q-Star Micromass.
derivatives of (g g
5-Cp)Co( 4-C4Ph4) [14,21]. Moving from 1,2 to
1,3 derivative, significant changes in the 13C NMR chemical shift
values of the ipso carbon atoms are observed. For example, in acet-
yl derivatives of 1, the chemical shifts of the ipso carbon atoms are
99.44 and 93.03 ppm for the 1,2-isomer (compound 2) and 96.58
and 90.55 ppm for the 1,3-isomer (compound 3). Similarly, differ-
ences are also shown by carbomethoxy and carboxylic acid deriv-
atives. The positions of the substituents in the new derivatives
have been further confirmed by X-ray crystallography.
3. Conclusions
4.2. Preparation of methylcyclopentadienyl sodium
A simple synthetic method for the preparation of methylcyclo-
pentadienyl derived cobalt sandwich compound, (
C4Ph4), and preparation and characterization of a host of its deriv-
g
5-MeCp)Co(g4
-
Freshly cut sodium 0.50 g (21.74 mmol) was added to 16.5 mL
of methylcyclopentadiene dimer at room temperature. On slow

R. Jana et al. / Journal of Organometallic Chemistry 693 (2008) 3780–3786
3785
heating, the solution turned blue (ꢀ35–40 °C) then to deep orange
and later to brown (ꢀ75–80 °C). The mixture was heated to re-
fluxed at 140 °C until all the sodium got dissolved. During heating,
a light yellow solid was found to precipitate out. After the hydro-
gen evolution stopped, the reaction mixture was further refluxed
for 2 h. The mixture was allowed to cool to room temperature un-
der nitrogen atmosphere. The excess methylcyclopentadiene di-
mer was partially removed using a syringe. The wet solid was
washed with dry hexane (3 ꢂ 60 mL) under nitrogen atmosphere.
The air and moisture sensitive solid obtained was dried and kept
under nitrogen at 0 °C. The compound was directly used for further
reactions. Yield: 1.85 g (84%).
1H NMR (300 MHz CDCl3): d = 1.58 (s, 3H), 1.66(s, 3H), 4.64(brs,
1H), 5.09 (t, 2H, J1 = 1.8 Hz, J2 = 9.6 Hz), 7.25(bs, 12H, m, m+p-Ph-
H), 7.42 (bs, 8H, m+o-Ph-H) ppm. 13C NMR (75 MHz CDCl3):
d = 12.49, 28.14, 75.75, 84.73, 85.4, 89.77, 90.55, 96.58, 126.71,
128.14, 128.67, 135.04, 198.9 ppm IR (KBr
m
/cmꢁ1): 1662(C@O,
vs), 1597(m), 1493(s), 1436(s), 1354(m), 1298(m), 1185(m),
1067(w), 1024(w), 776(m), 743(s), 698(vs), 559(m). MS (ES+) m/e
(fragment): 537 (M+1), 538 (M+2). Anal. Calc.: C, 80.59; H, 5.45.
Found: C, 79.00; H, 5.35%.
4.5. Preparation of {
g
5-1-[(MeOC(O)}, 2-MeC5H3}Co(
g
4-C4Ph4) (4)
and {
g
5-1-[(MeOC(O)}, 3-MeC5H3)]Co(
g
4-C4Ph4) (5)
4.3. Preparation of (
g
5-MeCp)Co(
g
4-C4Ph4) (1)
0.62 g (6.08 mmol) of the sodium salt was taken in a two necked
R.B flask under nitrogen. 30 mL of dry THF was added and the
resulting solution was stirred for 15 min. Then dimethylcarbonate
(1.00 mL, 9.78 mmol) was added to the reaction mixture and the
mixture was stirred at reflux for 5–6 h. During this time a red color
developed. After bringing the solution to room temperature, 5.35 g
(6.08 mmol) of chlorotris(triphenylphosphine)cobalt, 1.50 g
(8.43 mmol) of diphenylacetylene and 50 mL of dry toluene were
added to the reaction mixture. The resulting solution was refluxed
overnight was then allowed to cool to room temperature. The reac-
tion mixture was filtered using a Büchner funnel and washed with
hexane–ethylacetate mixture (50%). The colored solution obtained
was concentrated and the residue was chromatographed on a neu-
tral alumina column. After removal of triphenyl phosphine with
hexane, compound 4 was eluted as first fraction with 2–3% (v/v)
ethyl acetate/hexane mixture and compound 5 with 3–4% (v/v)
A solution of 0.62 g (6.08 mmol) of methylcyclopentadienyl so-
dium in 30 mL of dry THF was stirred at room temperature for
15 min.
5.35 g
(6.08 mmol)
of
chlorotris(triphenylphos-
phine)cobalt(I), 1.50 g (8.43 mmol) of diphenylacetylene and
50 mL of dry toluene were added to the THF solution of the sodium
salt. The resulting solution was refluxed for 24 h and then allowed
to cool to room temperature. The reaction mixture was filtered
using a Büchner funnel and washed with hexane–ethylacetate mix-
ture (50%). The colored solution obtained was concentrated and a
slurry was made with silica gel and this was chromatographed with
hexane–ethylacetate (98:2) mixture to get red crystals of
(
(
g
g
5-methylcyclopentadienyl)(
g
4-tetraphenylcyclobutadiene)cobalt,
5-MeCp)Co(
g
4-C4Ph4) (1) Yield: 1.33 g (64%). m.p: 160–162 °C.
1H NMR (300 MHz, CDCl3): d = 1.53 (s, 3H), 4.43 (s, 2H), 4.50 (s,
2H), 7.22 (t, 12H, m, m+p-Ph-H, J1 = 3.6 Hz, J2 = 1.5), 7.43 (t, 8H,
m+o-Ph-H, J1 = 3.6 Hz, J2 = 3.6 Hz) ppm. 13C NMR (75 MHz CDCl3):
d = 11.47, 74.50, 82.74, 83.58, 94.57, 125.99, 127.89, 128.81,
ethyl acetate/hexane mixture.
{g
5-1-[(MeOC(O)}, 2-MeC5H3}-
Co(g
4-C4Ph4) (4). Yield: 0.18 g (12%). m.p: 171–173 °C. 1H NMR
(300 MHz, CDCl3): d = 1.88(s, 3H), 3.28 (s, 3H), 4.65 (brs, 2H),
5.13 (brs, 1H), 7.29 (brs,12H, m, m+p-Ph-H), 7.45 (brs, 8H, m+o-
Ph-H) ppm. 13C NMR (75 MHz CDCl3): d = 11.58, 50.86, 75.71,
83.91, 84.83, 85.21, 88.13, 97.08, 126.55, 128.04, 128.83, 135.09,
136.48 ppm. IR(KBr,
m
/cmꢁ1): 3053(m), 2920(w), 2362(w),
1598(vs), 1497(vs), 1445(s), 699(vs), 564(s), 408(s). Mass (ES+)
m/e (fragment): 494(M+), 495(M+1), 496(M+3), 415(MꢁMeCp).
Anal. Calc.: C, 82.58; H, 5.50. Found: C, 82.47; H, 5.53%.
167.13 ppm. IR(KBr m
/cmꢁ1): 1708 (vs, C@O), 1597 (w), 1497 (s),
1444 (w), 1283 (s) 1218 (w), 1161(vw), 1089 (w), 1029 (w), 819
(w), 778 (w), 746 (w), 700 (s), 618 (vw), 589 (vw), 562 (vw). MS
(ES+) m/e (fragment): 553 (M+1), 415 [MꢁMeO(O)C5H3Me]+. Anal.
4.4. Preparation of {
g
5-1-[(MeC(O)], 2-MeC5H3}Co(
g
4-C4Ph4) (2) and
{
g
5-1-[MeC(O)], 3-MeC5H3}Co(
g
4-C4Ph4) (3)
Calc.: C, 78.25; H, 5.29. Found: C, 77.00; H, 5.36%. {g
5-1-[(MeO-
0.62 g (6.08 mmol) of the sodium salt of 1 was taken in a two
C(O)}, 3-MeC5H3)]Co(g
4-C4Ph4) (5). Yield: 0.30 g (19%). m.p:
necked R.B flask under nitrogen. 30 mL of dry THF was added
and the resulting solution was stirred for 15 min. Dry ethylacetate
(1.5 mL, 15.03 mmol) was then added to the reaction mixture and
it was stirred at reflux for 5–6 h. During this time a red color devel-
oped. After cooling the solution to room temperature, CoCl(PPh3)3
(5.35 g, 6.08 mmol) was added followed by dry toluene (50 mL).
Diphenylacetylene (1.00 g, 5.62 mmol) was then added and the
resulting mixture was heated at reflux overnight. The mixture
was cooled to room temperature, filtered, concentrated and chro-
matographed on neutral alumina column. After removal of tri-
phenylphosphine and its oxide from the column, compound 2
was eluted out with 96:5 hexane–ethylacetate mixture as the first
216–218 °C. 1H NMR (300 MHz, CDCl3): d = 1.90 (s, 3H), 3.29 (s,
3H), 4.67 (d, 2H, J = 8.1 Hz), 5.15 (brs, 1H), 7.29 (d,12H, J = 6.3 Hz,
m, m+p-Ph-H), 7.47 (d, 8H, J = 6.3 Hz, m+o-Ph-H) ppm. 13C NMR
(75 MHz CDCl3): d = 11.67, 51.14, 83.99, 84.49, 86.34, 86.86,
98.16, 126.66, 128.03, 128.82, 135.18, 166.57 ppm. IR (KBr
m
/cmꢁ1): 1712(vs, C@O), 1596(m), 1494(s), 1446(s), 1299(s),
1207(w), 777(m), 741(m), 698(vs), 558(s) MS (ES+) m/e (frag-
ment): 553 (M+1), 415 [MꢁMeO(O)C5H3Me]+. Anal. Calc.: C,
78.25; H, 5.29. Found: C, 78.54; H, 5.39%.
4.6. Preparation of [g g
5-1-(COOH), 2-MeC5H3]Co( 4-C4Ph4) (6)
fraction followed by compound 3 (93:7 hexane–ethylacetate). {g5
-
Compound 4 (0.18 g, 0.32 mmol) was taken in a 100 ml two
necked round bottom flask followed by 50 mL of distilled ethanol.
Potassium hydroxide (0.40 g, 7.12 mmol) dissolved in 5 mL of dis-
tilled water was added to the mixture and it was heated at reflux
for 36 h. The orange red solution was poured into a beaker contain-
ing 100 ml of distilled water. Concentrated hydrochloric acid was
added dropwise to neutralize the solution. A bright yellow precip-
itate formed immediately. The solution was extracted with dichlo-
romethane. The organic extracts were washed twice with distilled
water and concentrated. The solid obtained was purified on a silica
gel column (60–120 mesh) using hexane and ethylacetate mixture
(93:7) as eluent to get an yellow colored product 6. Yield: 0.13 g
(76%), 1H NMR (300 MHz, CDCl3): d = 1.84 (s, 3H), 4.685 (brs, 2H),
1-[(MeC(O)], 2-MeC5H3}Co(g
4-C4Ph4) (2). Yield: 0.17 g (11%). m.p:
181–184 °C. 1H NMR (300 MHz, CDCl3): d = 1.69 (s, 3H), 1.87 (s,
3H), 4.54 (brs, 1H), 4.69 (t, 1H, J1 = 2.7 Hz, J2 = 2.7 Hz), 4.99 (q,
1H, J1 = 1.8 Hz, J2 = 1.2 Hz, J3 = 1.5 Hz), 7.263 (brs, 12H, m, m+p-
Ph-H), 7.38 (brs, 8H,m+o-Ph-H) ppm. 13C NMR (75 MHz CDCl3):
d = 11.40, 26.86, 76.29, 82.86, 83.32, 87.99, 93.03, 99.44, 126.77,
128.21, 128.68, 135.13, 198.3 ppm. IR (KBr
m
/cmꢁ1): 1659(vs,
C@O), 1597(m), 1495(m), 1419(m), 1350(m), 1271(m), 1213(w),
1176(w),1069(w),1024(w), 926(w), 775(s), 744(s), 699(vs),
561(m). MS (TOF MS ES+) m/e (fragment): 536(M+). Anal. Calc.: C,
80.59; H, 5.45. Found: C, 79.87, H, 5.62%. {
g
5-1-[MeC(O)], 3-
MeC5H3}Co(
g
4-C4Ph4) (3). Yield: 0.42 g (28%). m.p: 151–153 °C.

3786
R. Jana et al. / Journal of Organometallic Chemistry 693 (2008) 3780–3786
5.16 (brs, 1H), 7.218 (t, 12H, m, m+p-Ph-H, J1 = 3.3 Hz, J2 = 2.4),
7.404 (t, 8H, m+o-Ph-H, J1 = 3.3 Hz, J2 = 3.6 Hz) ppm. 13C NMR
(75 MHz CDCl3): d = 11.78, 75.98, 83.298, 84.9, 86.04, 88.34,
Acknowledgements
The authors thank Department of Science and Technology (DST)
[SR/S1/IC-31/2007] and Council of Scientific and Industrial Re-
search (CSIR) India, [01(2054) 06/ EMR-II] for financial assistance
in the form of research grants. We acknowledge DST-FIST and IITD
for funding of the single crystal X-ray diffraction facility at IIT
Delhi. M.S.K. thanks CSIR India for a senior research fellowship.
R.J. thanks Associate Dean, IRD, IIT Delhi for a summer research
fellowship.
97.65, 126.58, 128, 128.68,134.85, 172.07 ppm. IR (KBr m
/cmꢁ1):
3053 (vw), 2923 (w), 2607(vw), 2361(vw), 1949(w), 1883(w),
1723(vw), 1761(vs), 1597(s), 1468(w), 1439(w), 1380(w),
1347(w), 1283(s), 1226(s), 1161(w), 1090(m), 1025(s), 819(w),
773(s), 697(vs), 556(s). MS (+TOF) m/e (fragment): 561 (M+Na+).
4.7. Preparation of [g g
5-1-(COOH), 3-MeC5H3]Co( 4-C4Ph4) (7)
Compound 5 (0.22 g, 0.39 mmol) was taken in a 100 mL two
necked round bottom flask followed by 50 mL of distilled ethanol.
Potassium hydroxide (0.40 g, 7.12 mmol) dissolved in 5 mL dis-
tilled water was added to the mixture and it was heated at reflux
for 36 h. The reaction mixture was worked up similar to the proce-
dure used for 6 to yield an yellow colored compound 7. Yield:
0.15 g (72%), 1H NMR (300 MHz, CDCl3): d = 1.554 (s, 3H), 4.632
(brs, 1H), 5.12 (d, 2H, J = 13.2 Hz), 7.214 (brs, 12H, m, m+p-Ph-H),
7.415 (brs, 8H, m+o-Ph-H) ppm. 13C NMR (75 MHz CDCl3):
d = 11.75, 60.37, 84.67, 84.74, 87.21, 87.27, 98.73, 126.66, 128.04,
Appendix A. Supplementary material
CCDC 693176, 693174, 693177 and 693175 contain the supple-
mentary crystallographic data for 2, 4, 6 and 8. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.jorganchem.2008.09.030
References
128.66, 134.93, 171.13 ppm. IR (KBr m
/cmꢁ1): 3053(vw), 2922(s),
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4.8. Preparation of [
g
5-1-(Me2NCH2), 3-MeC5H3]Co(
g
4-C4Ph4) (8) and
[g
5-1-(Me2NCH2), 2-MeC5H3]Co(
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4-C4Ph4) (9)
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(8.92 mmol) of ortho phosphoric acid followed by 2.3 mL of
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with 50 ml saturated NaHCO3 solution and then with water. The
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fraction study.
[g g
5-1-(Me2NCH2), 3-MeC5H3]Co( 4-C4Ph4) (8).
Yield: 0.16 g (65%). m.p: 121–123 °C. 1H NMR (300 MHz, CDCl3):
dH = 1.45 (s, 3H), 2.05 (s, 6H), 2.66 (d, 2H), 4.369 (s, 1H), 4.475 (t,
2H), 7.24 (bs, 12H, m, m+p-Ph-H), 7.43 (bs, 8H, m+o-Ph-H) ppm.
13C NMR (75 MHz CDCl3): d = 11.75, 44.81, 56.75, 82.39, 83.83,
84.26, 92.85, 94.79, 126–128.74, 136.34. MS (ES+) m/e (fragment)
552 (M+1), 553 (M+2), 554 (M+3), 555 (M+4), 507 (MꢁNMe2). IR
(KBr) cmꢁ1
:
1596(s), 1496(s), 1447(s), 1254(w), 1170(w),
1069(w), 1021(s), 844(w), 777(m), 744(m), 699(vs), 562(s). Anal.
Calc.: C, 80.56; H, 6.21; N, 2.54. Found: C, 79.79; H, 6.17; N,
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2.39%. {
g g
5-1-[Me2NCH2], 2-MeC5H3}Co( 4-C4Ph4) (9) MS (ES+)
m/e (fragment) 551(M+).