Studies on ferrocene derivatives. XV. Hydrolysis of diesters containing a ferrocene nucleus

Article abstract of DOI:10.1081/SIM-120015085

The hydrolysis of 1,1′-bis[ω-(methoxycarbonyl)alkanoyl]ferrocenes was carried out. In the compounds which have the same 1- and 1′-substituents, the values of k₁ and k₂ were different. This may be caused by the electrostatic interaction between the two carbonyl groups.

Full text of DOI:10.1081/SIM-120015085

This article was downloaded by: [York University Libraries]
On: 19 November 2014, At: 23:39
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt19
STUDIES ON FERROCENE DERIVATIVES. XV. HYDROLYSIS
OF DIESTERS CONTAINING A FERROCENE NUCLEUS
Yutaka Okada a , Hiroshi Kunitomo a , Shin Ikariya a & Takatoshi Hayashi a
a Department of Applied Chemistry , Ritsumeikan University , 1-1-1 Nojihigashi, Kusatsu-shi,
525-8577, Japan
Published online: 15 Feb 2007.
To cite this article: Yutaka Okada , Hiroshi Kunitomo , Shin Ikariya & Takatoshi Hayashi (2002) STUDIES ON FERROCENE
DERIVATIVES. XV. HYDROLYSIS OF DIESTERS CONTAINING A FERROCENE NUCLEUS, Synthesis and Reactivity in Inorganic and
Metal-Organic Chemistry, 32:9, 1649-1660
To link to this article: http://dx.doi.org/10.1081/SIM-120015085
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 32, No. 9, pp. 1649–1660, 2002
STUDIES ON FERROCENE DERIVATIVES.
XV. HYDROLYSIS OF DIESTERS
CONTAINING A FERROCENE NUCLEUS*
Yutaka Okada,{ Hiroshi Kunitomo, Shin Ikariya, and
Takatoshi Hayashi
Department of Applied Chemistry, Faculty of Science
and Engineering, Ritsumeikan University,
1-1-1 Nojihigashi, Kusatsu-shi, 525-8577, Japan
ABSTRACT
The hydrolysis of 1,10-bis[o-(methoxycarbonyl)alkanoyl]ferro-
cenes was carried out. In the compounds which have the same 1-
and 10-substituents, the values of k1 and k2 were different. This
may be caused by the electrostatic interaction between the two
carbonyl groups.
INTRODUCTION
As part of the broad program investigating ferrocene derivatives, the
present authors have investigated the rotation of the cyclopentadienyl (Cp)
rings. The two Cp rings of an unsubstituted ferrocene freely rotate around
the Cp–Fe–Cp bond axis in solution.[2] When a substituent is introduced
*The previous part of this series can be found in Ref. [1].
{Corresponding author. E-mail: ygvictor@se.ritsumei.ac.jp
1649
DOI: 10.1081=SIM-120015085
Copyright # 2002 by Marcel Dekker, Inc.
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com

1650
OKADA ET AL.
on a Cp ring, it is interesting to speculate as to what happens to the rotation
movement. Investigations of the ring rotation have been done by measuring
the dipole moment. For example, in 1,10-diacetyl- or dibenzoylferrocene, the
free rotation of the Cp rings was reported.[3] However, for the 1,10-dihalo-
ferrocenes, the rotation is restricted; the conformation in which two halogen
atoms are adjacent to each other becomes unstable.[4] Very few papers have
been published on the influence of the ring rotation on the reaction of a
substituent on the ferrocenyl group. In this work, the hydrolysis of 1,10-bis[o-
(methoxycarbonyl)alkanoyl]ferrocenes (Fig. 1) was carried out. The results
were discussed based on the specific structure of the ferrocene molecule on
compared with an aliphatic dicarboxylic ester. Electrostatic interaction
between the two carbonyl groups on the two Cp rings is proposed.
RESULTS AND DISCUSSION
Hydrolysis
The rate constants for the hydrolysis of the ferrocene derivatives and
dimethyl sebacate are shown in Table I.
Fc-½CO-ðCH2Þm-COOCH3ꢀ½CO-ðCH2Þn-COOCH3ꢀ
k1
! Fc-½CO-ðCH2Þm-COOHꢀ½CO-ðCH2Þn-COOCH3ꢀ
k2
! Fc-½CO-ðCH2Þm-COOHꢀ½CO-ðCH2Þn-COOHꢀ
ðEq:1Þ
Figure 1. Compounds (1)–(4) and dimethyl sebacate.

FERROCENE DERIVATIVES. XV
1651

1652
OKADA ET AL.
Acid or Alkaline Catalyzed Hydrolysis of 1,10-bis[3-(Methoxycarbonyl)-
propanoyl]ferrocene (1) in Methanol
No difference was recognized in the rate constants of the first and
second step hydrolysis under acidic conditions (Table I, entry 1). Namely,
the two methoxycarbonyl groups could be independently hydrolyzed under
acidic conditions. In contrast, under alkaline conditions, the rate constant of
the first step, k1, was greater than that of the second step, k2; the first step
reaction proceeded faster than the second step (Table I, entry 2).
To confirm whether or not this result is applicable to a compound not
containing a ferrocene nucleus, the following experiments were performed.
Considering that one ferrocenyl group corresponds to three methylene
groups in length, an aliphatic dicarboxylic acid having a length equal to
compound (1) is sebacic acid. The hydrolysis of dimethyl sebacate was then
carried out under alkaline conditions.
Alkaline Catalyzed Hydrolysis of Dimethyl Sebacate
The rate constants, k1 and k2, were approximately equal for the
alkaline catalyzed hydrolysis of dimethyl sebacate that contains no ferro-
cene nucleus (Table I, entry 8). In general, the difference between the rate
constants, k1 and k2, of an aliphatic diester becomes smaller with increasing
number of methylene groups between both ester groups.[5] The hydrolysis by
sodium hydroxide converts one ester group to COOꢁ. The COOꢁ group
electrostatically interacts with another ester group, so that the hydrolysis of
this group is inhibited. However, for the higher members of diesters that
have a longer methylene chain, for example, dimethyl sebacate, such an
interaction is not possible. Thus, the two ester groups would be indepen-
dently hydrolyzed, so that k1 and k2 were approximately equal.
Alkaline Catalyzed Hydrolysis of 1,10-bis[5-(Methoxycarbonyl)pentanoyl]-
(2) and 1,10-bis[9-(Methoxycarbonyl)nonanoyl]ferrocene (3) in Methanol
The hydrolysis of compounds (2) and (3), which have longer methy-
lene chains (n ¼ 4 and 8), was carried out under alkaline conditions. A
difference between k1 and k2 was recognized in compounds (2) and (3) as
well as in compound (1) (Table I, entries 4 and 5). This was not noted for
aliphatic dimethyl sebacate which has a shorter molecular length. The dif-
ferences that lead to different rate constants may be caused by the structure
of the diesters containing the ferrocene nucleus.

FERROCENE DERIVATIVES. XV
1653
To ascertain whether or not a difference between the rate constants is
found for unsymmetrically substituted ferrocenes, the hydrolysis was carried
out with a ferrocene derivative which has different 1 and 10 substitutents.
Alkaline Catalyzed Hydrolysis of 1-[9-(Methoxycarbonyl)nonanoyl]-10-[3-
(methoxycarbonyl)propanoyl]ferrocene (4) in Methanol
The k1 and k2 values were approximately equal for the hydrolysis of
compound (4) (Table I, entry 7). Thus, the hydrolysis of the two ester groups
proceeded independently.
Interaction Between the 1- and 10-Substituents of the 1,10-bis[o-
(Methoxycarbonyl)alkanoyl]ferrocenes Comparison of
Acid and Alkaline Catalyzed Hydrolysis
In general, under alkaline conditions, a methoxycarbonyl group is
hydrolyzed to a carboxylate ion.[5] In 1,10-bis[o-(methoxycarbonyl)alkanoyl]-
ferrocenes, the formed carboxylate ion possibly can interact electrostatically
with the remaining methoxycarbonyl group which has not been yet hydro-
lyzed (Fig. 2).
The alkaline catalyzed hydrolysis is initiated by the attack of a
hydroxide ion to a carbonyl carbon. The attack would be inhibited by the
interaction shown in Fig. 2. In the second step of the hydrolysis of the
ferrocenes containing two ester groups, the attack of the hydroxide ion on
another carbonyl carbon is sterically protected, so that the rate constant is
lower than that of the first step. In contrast, under acidic conditions, the
carboxyl group exists as the free acid form. Such an interaction found under
alkaline conditions is impossible, so that both rate constants, the first- and
the second steps, are approximately equal.
Figure 2. The interaction between methoxycarbonyl group and carboxylate ion.

1654
OKADA ET AL.
To confirm the above discussion, the following experiment was done.
In the presence of a crown ether, an alkaline hydrolysis was carried out in
benzene solution. No differences were found between k1 and k2 for both
compounds (1) and (3) (Table I, entries 3 and 6). Under these conditions, the
hydroxide ion is not solvated, that is to say, it exists as a naked anion. The
naked ion is sterically small,[6] so that no steric hindrance to the attack of a
carbonyl carbon appears, even under alkaline conditions, which results in
the interaction shown in Fig. 2. As a result, no difference between the k1 and
k2 rate constants would be recognized.
Chain-Length Effect
In compounds (1), (2) and (3), in which the 1- and 10-substituents
are the same, the values of k1 and k2 are different. This would be caused by
the electrostatic interaction between the two carbonyl groups because these
groups are adjacent to each other. In contrast, in compound (4)
having different substituents, the two ester groups are sterically separated,
so that no interaction occurs. Thus, each substituent will be independently
hydrolyzed.
The values of k1=k2 for compounds (1), (2) and (3) were obtained. For
compound (1), which has a shorter methylene chain (n ¼ 2), this value was 2.8.
For the higher members (n ¼ 4 and 8), compounds (2) and (3), the values
were 1.8–1.9. For the conformations in which the 1- and 10-substituents are
adjacent (Figs. 3a and 3a0), the two carbonyl groups are able to approach
more easily than for the lower member compound (1). As a result, the
interaction mentioned above easily occurs. Thus, compound (1) forces a
stronger interaction between the two carbonyl groups.
Figure 3. The five antiprismatic conformers of 1,10-disubstituted ferrocene.

FERROCENE DERIVATIVES. XV
1655
On the other hand, in dimethyl sebacate, which is considered to have the
same molecular length, no difference between k1 and k2 was found. There-
fore, the interaction found in the ferrocene derivatives is not present in the
aliphatic diester, which has no ferrocene nucleus but only a methylene chain.
Conclusion
In 1,10-bis[o-(methoxycarbonyl)alkanoyl]ferrocenes (1)–(3), the values
of k1 and k2 were different. This would be caused by the electrostatic
interaction between the two carbonyl groups. The result means that the two
Cp rings of these ferrocenes are restricted to rotate around the Cp–Fe–Cp
bond axis. Thus, the electrostatic interaction between the two carbonyl
groups would suppress the rotation movement.
EXPERIMENTAL
Synthesis
The [o-(methoxycarbonyl)alkanoyl]ferrocenes [compounds (1)–(4)]
were prepared by known method.[7,8] The compounds were identified by
1
1H NMR, IR, and mass spectra. H NMR was measured at room tem-
perature using a JEOL A-400 spectrometer. IR spectra were recorded on a
Shimadzu FTIR 8400 spectrometer. Mass spectra were obtained by a Shi-
madzu LCMS-QP8000 mass spectrometer. The ionization mode was that of
the Atmospheric Pressure Chemical Ionization (APCI) method. The nega-
tive ion mode was used for the half esters and dicarboxylic acid and the
positive mode for diesters. The data are shown in Tables II and III.
Hydrolysis
Acid Catalyzed Hydrolysis in Methanol
In a screw-capped test tube, 1.5 mL methanol, 1.5 mL H2O and
10.5 mL of 0.12 N HCl were added. The tube was kept at 40 ꢃC. A quantity
of 0.12 mmol of a ferrocene derivative was dissolved in 10 mL methanol, and
the solution was added to the test tube. When the materials were added, the
rate measurement was initiated. Sampling of the reaction mixture was car-
ried out at regular intervals. The amounts of the substrate and products
were determined by HPLC.

1656
OKADA ET AL.

FERROCENE DERIVATIVES. XV
1657

1658
OKADA ET AL.

FERROCENE DERIVATIVES. XV
1659
Alkaline Catalyzed Hydrolysis in Methanol
A quantity of 35 mL of methanol and 0.06 mmol of a ferrocene deri-
vative were mixed in a three-necked flask and stirred at 40 ꢃC. Five mL of
0.1 N NaOH were added to the flask. The same procedure as described
above was then followed.
Alkaline Catalyzed Hydrolysis in Benzene
A quantity of 35 mL benzene, 0.24 mmol of ferrocene derivative and
2 mmol (0.53 g) 18-crown-6 were mixed in a three-necked flask and stirred at
40 ꢃC. Five mL of 0.4 N NaOH were added to the flask. The same procedure
as mentioned above was followed.
Alkaline Catalyzed Hydrolysis of Dimethyl Sebacate in Methanol
A quantity of 135 mL of methanol and 5 mL of 1 N NaOH were mixed
in a three-necked flask, and stirred at 40 ꢃC. A 0.24 mmol (0.055 g) sample of
dimethyl sebacate was dissolved in 5 mL of methanol, and the solution was
added to the above flask. Titration with NaOH was carried out to determine
the amount of methyl sebacate and sebacic acid.
Calculation of Rate Constants
The measurement of the hydrolysis rate was carried out at least two
times. The values in Table I are the average of these results.
The concentration of acid or alkali was much higher than that of the
esters. The rate constants were then calculated for a pseudo-first order reac-
tion of the substrate. The first-step rate constant, k1, was calculated from the
decrease of the amount of the 1,10-bis derivative (diester). The second-step,
k2, was determined as follows: in compounds (1) and (4) for which the half
esters were synthesized, the hydrolysis of these half esters was carried out
under the same conditions. The amount of the half esters was determined,
and k2 was calculated from the decrease of the amount of the half esters. In
the other case, in which the corresponding half esters were not prepared, a
simulation method[9] was employed. The amount of the substrate and two
products (half ester and dicarboxylic acid) were calculated from the
experimental k1 and a hypothetical k2, and then compared with the
experimental values. The best-fitted values of k2 were employed as calcu-
lated values.

1660
OKADA ET AL.
REFERENCES
1. Part XIV: Okada, Y.; Nakagawa, T.; Hayashi, T. Studies on Ferrocene
Derivatives. XIV. Oxidation Reaction of (2,6-Disubstituted phe-
nyl)ferrocenes. Inorg. Chim. Acta 2001, 312, 197–200.
2. Richmond, H.H.; Freiser, H. The Electric Moments of Mono- and
Diacetylferrocene. J. Am. Chem. Soc. 1955, 77, 2022–2023.
3. Sorriso, S.; Lumbroso, H. Sur Les Conformations des Molecules de
Diacetyl-1,10 et de Dibenzoyl-1,10-ferrocenes. Tetrahedron 1970, 26,
2695–2701.
4. Sorriso, S. Energy Barrier to Internal Rotation in Some Ferrocene
Derivatives from Dielectric Measurements. J. Organomet. Chem. 1979,
179, 205–213.
5. Ritchie, M. Saponification of Diesters. J. Chem. Soc. 1931, 3112–3125.
6. Pedersen, C.J. Cyclic Polyethers and their Complexes with Metal Salts.
J. Am. Chem. Soc. 1967, 89, 2495–2496.
7. Rinehard, K.L.; Curby, R.J.; Scokol, P.E. Organic Chemistry of Fer-
rocene. II. The Preparation of o-Ferrocenyl Aliphatic Acids. J. Am.
Chem. Soc. 1957, 79, 3420–3424.
8. Dabard, R.; Patin, H. Contribution a l0Etude des Metallocenes. VII.
Synthese et Etudes Physicochimiques de Diacyl-1,10-ferrocenes et de
Diacyl-2,10 et 3,10-Alcoylferrocenes. Nouveaux Ferrocenophanes. Bull.
Soc. Chim. Fr. 1973, 2158–2164.
9. Noggle, J.H. Practical Curve Fitting and Data Analysis; PTR Prentice
Hall, Inc.: Englewood Cliffs, New Jersey, 1993; 146–158.
Received April 12, 2001
Accepted June 29, 2002
Referee I: D. L. Lichtenberger
Referee II: T. E. Bitterwolf