One-pot sequences of reactions with sol-gel entrapped opposing reagents: An enzyme and metal-complex catalysts

Article abstract of DOI:10.1021/ja020799+

We extend our sol-gel methodology of one-pot sequences of reactions with opposing reagents to an enzyme/metal-complex pair. Sol-gel entrapped lipase and sol-gel entrapped RhCl[P(C₆H₅)₃]₃ or Rh₂Co₂(CO)₁₂ were used for one-pot esterification and C-C double bond hydrogenation reactions, leading to saturated esters in good yields. When only the enzyme is entrapped, the homogeneous catalysts quench its activity and poison it. Thus, when 10-undecenoic acid and 1-pentanol were subjected in one pot to the entrapped lipase and to homogeneously dissolved RhCl[P(C₆H₅)₃]₃ under hydrogen pressure, only 7% of the saturated 1-pentyl undecanoate was obtained. The yield jumped 6.5-fold when both the enzyme and the catalyst were immobilized separately in silica sol-gel matrixes. Similar one-pot esterifications and hydrogenations by sol-gel entrapped lipase and heterogenized rhodium complexes were carried out successfully with the saturated nonoic, undecanoic, and lauric acids together with several saturated and unsaturated alcohols. The use of (S)-(-)-2-methylbutanol afforded an optically pure ester. The heterogenized lipase is capable of inducing asymmetry during esterification with a prochiral alcohol. Both the entrapped lipase and the immobilized rhodium catalysts can be recovered simply by filtration and recycled in further runs without loss of catalytic activity.

Full text of DOI:10.1021/ja020799+

Published on Web 11/12/2002
One-Pot Sequences of Reactions with Sol-Gel Entrapped
Opposing Reagents: An Enzyme and Metal-Complex
Catalysts
Faina Gelman, Jochanan Blum,* and David Avnir*
Contribution from the Institute of Chemistry, The Hebrew UniVersity of Jerusalem,
Jerusalem 91904, Israel
Received June 5, 2002
Abstract: We extend our sol-gel methodology of one-pot sequences of reactions with opposing reagents
to an enzyme/metal-complex pair. Sol-gel entrapped lipase and sol-gel entrapped RhCl[P(C6H5)3]3 or
Rh2Co2(CO)12 were used for one-pot esterification and C-C double bond hydrogenation reactions, leading
to saturated esters in good yields. When only the enzyme is entrapped, the homogeneous catalysts quench
its activity and poison it. Thus, when 10-undecenoic acid and 1-pentanol were subjected in one pot to the
entrapped lipase and to homogeneously dissolved RhCl[P(C6H5)3]3 under hydrogen pressure, only 7% of
the saturated 1-pentyl undecanoate was obtained. The yield jumped 6.5-fold when both the enzyme and
the catalyst were immobilized separately in silica sol-gel matrixes. Similar one-pot esterifications and
hydrogenations by sol-gel entrapped lipase and heterogenized rhodium complexes were carried out
successfully with the saturated nonoic, undecanoic, and lauric acids together with several saturated and
unsaturated alcohols. The use of (S)-(-)-2-methylbutanol afforded an optically pure ester. The heterogenized
lipase is capable of inducing asymmetry during esterification with a prochiral alcohol. Both the entrapped
lipase and the immobilized rhodium catalysts can be recovered simply by filtration and recycled in further
runs without loss of catalytic activity.
teins5 and cells.6 The fast growth of these applications is mainly
due to a remarkable property of these functional doped materials,
Background
Heterogenization of reagents and catalysts by their direct or
physical entrapment in sol-gel inorganic matrixes has become
a widespread method.1 Many useful families of reactions have
been explored in this context, some major ones being reactions
for analytical and sensing purposes,1,2 catalytic reactions,1,3
electrochemical reactions,4 and reactions with entrapped pro-
namely that, on one hand, the dopant is well isolated and
protected within the porous matrix and yet, on the other hand,
it is accessible to substrate molecules which enter the matrix
from the environment by a diffusion process through the pore
network, reach the entrapped reagent, interact with it, and release
a product back to the environment through the same pore
network. This property can be rationalized, in the case of silica
sol-gel matrixes, by assuming the molecules to be entangled in
cyclic cage-like SimOn fragments which are known to be formed
during the early stages of the sol-gel process7 in such a way
that, while being tightly held, their active moieties are still open
to the pore network of the ceramic matrix.
With this picture in mind, it becomes clear that, when in the
neighborhood of a chemical which is entrapped within a sol-
gel matrix, there is another sol-gel matrix doped with another
reagent, these two chemicals cannot interact with each other
when dispersed in a solvent, and these entrapped chemicals are
still accessible to react with substrate molecules which are
dissolved in that solution. Therefore, in principle, even an acid
* Correspondence: david@chem.ch.huji.ac.il, jblum@chem.ch.huji.ac.il.
(1) (a) Some representative 2001/2 publications in this journal on applications
of sol-gel materials: Moreau, J. J. E.; Vellutini, L.; Man, M. W. C.; Bied,
C. J. Am. Chem. Soc. 2001, 123, 1509. Moreau, J. J. E.; Vellutini, L.;
Man, M. W. C.; Bied, C.; Bantignies, J. L.; Dieudonne, P.; Sauvajol, J. L.
J. Am. Chem. Soc. 2001, 123, 7957. Hernandez, R.; Franville, A. C.;
Minoofar, P.; Dunn, B.; Zink, J. I. J. Am. Chem. Soc. 2001, 123, 1248.
Nablo, B. J.; Chen, T. Y.; Schoenfisch, M. H. J. Am. Chem. Soc. 2001,
123, 9712. Jung, J. H.; Kobayashi, H.; Masuda, M.; Shimizu, T.; Shinkai,
S. J. Am. Chem. Soc. 2001, 123, 8785. Sandee, A. J.; Reek, J. N. H.; Kamer,
P. C. J.; van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2001, 123, 8468.
Smith, K.; Silvernail, N. J.; Rodgers K. R.; Elgren, T. E.; Castro, M.; Parker
R. M. J. Am. Chem. Soc. 2002, 124, 4247. Rudzinski, C. M.; Young, A.
M.; Nocera, D. G. J. Am. Chem. Soc. 2002, 124, 1723. Hunter, G. W.;
Thomas, D. D.; Hoffman, B. M. J. Am. Chem. Soc. 2002, 124, 9404. (b)
Some additional representative recent 2002 references: Nocek, J. M.; Hatch,
S. L.; Seifert, J. L.; Stalikas, C.; Knopp, D.; Niessner, R. EnViron. Sci.
Technol. 2002, 36, 3372. Boury, B.; Corriu, R. J. P.; Muramatsu, H. New
J. Chem. 2002, 26, 981. Liang, C. D.; Weaver, M. J.; Dai, S. Chem.
Commun. 2002, 15, 1620. Cetinkaya, B.; Gurbuz, N.; Seckin, T.; Ozdemir,
I. J. Mol. Catal. A.: Chem. 2002, 184, 31. Nava, R.; Halachev, T.;
Rodriguez, R.; Castano, V. M. Appl. Catal., A 2002, 231, 131.
(5) Gill, I. Chem. Mater. 2001, 13, 3404. Yu, J. H.; Ju, H. X. Anal. Chem.
2002, 74, 3579.
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Solids 2002, 306, 138. Jimenez-Morales, A.; Galvan, J. C.; Aranda, P.
Electrochim. Acta 2002, 47, 2281.
(3) Ciriminna, R.; Bolm, C.; Fey, T.; Pagliaro, M. AdV. Synth., & Catal. 2002,
344, 159. Lindner, E.; Al-Gharabli, S.; Mayer, H. A. Inorg. Chim. Acta
2002, 334, 113.
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G. B.; Dong, S. J. Electroanalysis 2002, 14, 853.
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462, 11. Muraca, M.; Vilei, M. T.; Zanusso, G. E.; Ferraresso, C.;
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9
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J. AM. CHEM. SOC. 2002, 124, 14460-14463
10.1021/ja020799+ CCC: $22.00 © 2002 American Chemical Society

One-Pot Reactions with Sol-Gel Reagents
A R T I C L E S
Scheme 1. Reaction Routes of the Saturated and Unsaturated
and a base can be put in the same pot without mutual
annihilation, if properly protected by the sol-gel matrix. Where
can this property be put to use?
Carboxylic Acids and Alcoholsa
Synthetic chemistry is governed traditionally by linear,
consecutive sequences of reactions linking starting materials to
products through intermediate molecules. Tedious as this route
may be, there is not much choice, because each synthetic step
is carried out with a different reagent or catalyst, which quite
often quenches each other if put in one pot. Efforts to address
this one-pot problem by anchoring reactive species to polymeric
supports are known,8 but this approach never gained popularity,
apparently because of a host of problems such as the noninert-
ness of the polymeric support, destructive exposure of anchored
opposing moieties to each other, and complicated synthetic
routes for the preparation of derivatized polymers, all of which
make the saving of steps in a one-pot procedure not worthwhile.
Experience gained with the porous, high surface area, inert sol-
gel matrixes and the ease of their functionalization, simple one-
step direct physical or covalent entrapment, have made this
approach an attractive alternative as a heterogenizing support
for multiple reagent one-pot procedures.
a Ru (acid): CH2dCH(CH2)8 (1). Rs (acid): CH3(CH2)9 (2), CH3(CH2)7
(3), CH3(CH2)10 (4). Ru (alcohol): CHdCHCH2 (5), CHdCHCH(CH3)CH2
(6). Rs (alcohol): CH3(CH2)2 (7), CH3(CH2)4 (8), (S)-(-)-CH3CH2CH-
(CH3)CH2 (9).
enzyme and entrapped metal-complex catalysts in one-pot
reaction pairs, despite the fact that the free catalyst in solution
inhibits the action of the enzyme.
In a recent series of publications, we have shown the
versatility of this sol-gel approach to one-pot sequences of
reactions with several reaction pairs.9 These include (i) indeed
reaction sequences in which one step requires an acid while
the other requires a base, an example being the acid-catalyzed
pinacol-pinacolone rearrangement followed by a base-promoted
condensation of the ketone with malononitrile;9a (ii) one-pot
oxidation/reduction sequences, with an example being the
conversion of 1-(4-nitrophenylethanol) into 4-aminoacetophe-
none, where the oxidant was SiO2-sol-gel entrapped pyridinium
dichromate and the reductant H2 activated by entrapped RhCl-
[P(C6H5)3]3;9b and (iii) one-pot sequences requiring metallic
catalysts in the presence of catalyst inhibitors, with an example
being the base-catalyzed dehydrohalogenation of phenethylbro-
mide by an immobilized diamine, followed by RhCl[P(C6H5)3]3-
catalyzed hydrogenation of the resulitng styrene.9c,d
Results and Discussion
The system we selected in order to study the feasibility of
the one-pot Enzyme@s-g + Catalyst@s-g approach (we use
the entrapment notation compound@s-g) consists of lipase and
a hydrogenation catalyst. Sol-gel entrapped lipases, particularly
those which were immobilized in hydrophobic sol-gel matrixes
(as used here),11 are among the most successful examples of
this enzyme-heterogenization methodology.5 We mention here
also that some enzyme/catalyst couples have already been used
for chiral syntheses and enantiomeric resolutions, either with
soluble catalysts12 or with Pd,13 where the catalyst did not
interfere with the activity of the enzyme.
The specific reaction pairs represent two simultaneous
catalytic reactions: hydrogenation of a C-C double bond
catalyzed either by entrapped RhCl[P(C6H5)3]3 (Cat1@s-g)14 or
by the immobilized efficient bimetallic hydrogenation catalyst,
Rh2Co2(CO)12 (Cat2@s-g)15 and an esterification reaction
catalyzed by the entrapped lipase (Lipase@s-g).16 The resulting
saturation of the final ester can be achieved through various
possible routes, depending on which of the starting materials
carries the unsaturation. All of the three main possible routes
were tested in this study, and these are as follows (Scheme 1
and Table 1): (I) interaction between an unsaturated carboxylic
acid and a saturated alcohol (two parallel routes may lead to
the same saturated ester (Scheme 1, top left) by esterification
followed by reduction of the double bond of the resulting
unsaturated ester or by saturation of the acid followed by its
esterification); (II) reaction of a saturated acid with an unsatur-
ated alcohol (Scheme 1, top right), with two possible routes
Here, we report the further generalization of the one-pot sol-
gel methodology to the important, versatile class of enzymati-
cally functionalized sol-gel materials. The past decade has
witnessed a very rapid growth in the preparation and utilization
of these bioactive materials,5,10,11 a growth which has been
mainly due to the synthetic ease of enzyme entrapment proce-
dures and to the significantly enhanced stability of the entrapped
enzyme. As such, this class of reactive sol-gel materials seemed
to be suitable for one-pot reaction sequences in the presence of
entrapped chemicals which otherwise quench the enzymatic
activity. In particular, we report the coexistence of an entrapped
(8) Cohen, B. J.; Kraus, M. A.; Patchornik, A. J. Am. Chem. Soc. 1977, 99,
4165. Cainelli, G.; Contento, M.; Manescalchi, F.; Regnoly, R. J. Chem.
Soc., Perkin Trans. 1 1980, 2516.
(9) (a) Gelman, F.; Blum, J.; Avnir, D. Angew. Chem., Int. Ed. 2001, 40, 3647.
(b) Gelman, F.; Blum, J.; Avnir, D. New J. Chem., in press. (c) Gelman,
F.; Blum, J.; Avnir, D. J. Am. Chem. Soc. 2000, 122, 11999. (d) Gelman,
F.; Blum, J.; Schumann, H.; Avnir, D. J. Sol.-Gel Sci. Technol. 2003, 26,
43.
(12) Kim, M. J.; Choi, Y. K.; Choi, M. Y.; Kim, M. J.; Park, J. J. Org. Chem.
2001, 66, 4736. Choi, Y. K.; Kim, M. J.; Ahn, Y.; Kim, M. J. Org. Lett.
2001, 3, 4099.
(10) Reetz, M. T.; Zonta, A.; Simpelkamp, J.; Konen, W. Chem. Commun. 1996,
11, 1397. Reetz, M. T. AdV. Mater. 1997, 9, 943. Reetz, M. T.; Zonta, A.;
Reetz, M. T.; Wenkel, R.; Avnir, D. Synthesis 2000, 781.
(11) Vijayakrishnen, V.; Schimessek, K. J. Mol. Catal. A: Chem. 1998, 134,
251. Pires, E. L.; Miranda, E. A.; Valenca, G. P. Appl. Biochem. Biotechnol.
2002, 98, 963. Ikeda, Y.; Kurokawa, Y. J. Biosci. Bioeng. 2002, 93, 98.
Sharma, R.; Chisti, Y.; Banerjee, U. C. Biotechnol. AdV. 2001, 19, 627.
Ikeda, Y.; Nozaki, R.; Kurokawa, Y. J. Chem. Technol. Biotechnol. 2002,
77, 86.
(13) Persson, B. A.; Larsson, A. L. E.; Ray, M. L.; Backvall, J. E. J. Am. Chem.
Soc. 1999, 121, 1645. Reetz, M. T.; Schimossek, K. Chimia 1996, 668.
Allen, J. V.; Williams, J. M. J. Tetrahedron Lett. 1996, 37, 1859.
(14) Sertchook, H.; Avnir, D.; Blum, J.; Joo´, F.; Ka´tho, A.; Schumann, H.;
Weimann, R.; Wernik, S. J. Mol. Catal. A: Chem. 1996, 108, 153.
(15) Gelman, F.; Avnir, D.; Schumann, H.; Blum, J. J. Mol. Catal. A: Chem.
2001, 171, 191.
(16) Sol-gel immobilized lipase from Mucor miehei, coated on SIRAN, Fluka
(Catalog # 622274).
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A R T I C L E S
Gelman et al.
Table 1. One-Pot Reactions of Saturated and Unsaturated Carboxylic Acids and Alcohols in the Presence of Immobilized Lipase and
Homogeneous or Heterogenized Rhodium Catalysts
entry
alcohol
acid
catalyst
H pressure, atm
2
reaction time, h
products (yield,%)a
1
2
3
4
5
6
7
8
9
1-pentanol (8)
1-pentanol (8)
1-propanol (7)
1-propanol (7)
1-propanol (7)
2-propenol (5)
2-methyl-3-butenol (6)
(S)-(-)-2-methyl-butanol (9)
2-propenol (5)
1
1
1
1
1
1
1
1
3
4
Cat1@s-g
RhCl[P(C6H5)3]3
Cat2@s-g
Rh2Co2(CO)12
Cat2@s-g
Cat2@s-g
Cat2@s-g
Cat2@s-g
Cat2@s-g
Cat2@s-g
14
14
7
7
7
7
7
7
7
24
24
4
4
1
4
6
6
4
2-8 (46), 2 (54)
2-8 (7), 2 (93)
2-7 (71), 2 (29)
2-7 (19), 1-7 (4), 2 (50)
2-7 (30),b 2 (70)
2-7 (58), 2-5 (5), 2 (37)
2-9 (82, ee ) 19%), 2 (18)
2-9 (91, optically pure), 2 (9)
3-7 (67)
10
2-propenol (5)
7
4
4-7 (60)c
a The missing percentage reflects on the unreacted starting acid. b Under the same reaction conditions, the yield of 2-7 in the following five runs were
29, 30, 29, 28, and 27%, respectively. c Both of the catalysts were used after recycling.
(again saturation either prior or after esterification); and (III)
interaction of an unsaturated acid with an unsaturated alcohol,
where several possible routes can take place, two of which are
shown in Scheme 1.
enzymatic activity by H2/Rh2Co2(CO)12 involves not only metal
poisoning but also reductive destruction of the enzyme.
Route I may lead of course to chiral esters if a chiral alcohol
is used, and this has been demonstrated by using the pair of
acid 1 and (S)-(-)-2-methylbutanol, 9. The saturated chiral ester,
(S)-(-)-2-methylbutyl undecanoate (CH3(CH2)9COOCH2CH-
(CH3)CH2CH3, 2-9) was obtained in 91% yield (along with
9% of the saturated acid 2) by employing Cat2@s-g and
Lipase@s-g (hexane, 50°C, 7 atm of H2, 6 h). In fact, this chiral
ester could be obtained also through route III, namely where
both the acid and the alcohol are unsaturated. Thus, esterification
of 1 with the racemic 2-methyl-3-butenol, 6, afforded 2-9 in
an enantiomerically enriched racemic mixture (ee ) 19%), as
determined from synthesized (S)-2-9 ([R]D20 ) 2.4°, heptane,
c ) 0.6 (lit.17 1.9°)).
The feasibility of route II (unsaturation in the alcohol) was
demonstrated in a reaction between nonoic acid, 3, and
2-propenol, 5 (n-hexane, 50°C, 7 atm of H2, 4 h) resulting in
67% of 1-propyl nonanoate, 3-7. Here, yet another demonstra-
tion of the recyclability was performed, by using the same
recycled catalytic system (Cat2@s-g and Lipase@s-g) for a
different acid/alcohol pair, namely for the reaction with lauric
acid, 4, and 2-propenol, 5. Under the same reaction conditions
60% of 1-propyl laurate, 4-7, was obtained.
An example for route I (unsaturation in the acid) is provided
by the pair of 10-undecenoic acid (CH2dCH(CH2)8COOH, 1)
and 1-pentanol, 8. As the hydrogenation process proved to be
faster than the esterification, the reaction pair involved primarily
the sequence in which the H2/Cat1@s-g catalyzed hydrogenation
of the double bond of 1 (to yield the saturated 1-undecanoic
acid (CH3(CH2)9COOH, 2)) was followed by the Lipase@s-g
catalyzed esterification with 1-pentanol, 8. After 24 h (in
benzene at 60°C under 14 atm of H2), 46% of the reduced ester,
1-pentyl undecanoate (CH3(CH2)9COO(CH2)4CH3, 2-8 (the
ester notation is acid number-alcohol number)) was obtained.
In a blank experiment under the same conditions with entrapped
lipase but with nonentrapped RhCl[P(C6H5)3]3, all of the 10-
undecenoic acid, 1, was reduced to 1-undecanoic acid, 2, but
only 7% of it was esterified to 2-8 by the entrapped enzyme.
This experiment indicates that both the lipase and the metallic
catalyst must be entrapped in sol-gel matrixes, since nonen-
trapped RhCl[P(C6H5)3]3 acts as a lipase inhibitor, even if the
latter is entrapped.
In another route I two-step sequence with acid 1, the
bimetallic Cat2@s-g was used along with 1-propanol, 7,
resulting under the conditions of Table 1 in 71% of the saturated
ester 1-propyl undecanoate [CH3(CH2)9COO(CH2)2CH3, 2-7]
(Scheme 1). The conditions in this process were even milder:
4 h at 50 °C and 7 atm of H2, in hexane. An important obser-
vation made with this system is the good recyclability of the
sol-gel materials: the immobilized lipase and the heterogenized
bimetallic catalyst could be used for six runs without any
significant reduction of their catalytic activities (footnote b of
Table 1). In a blank experiment that was performed under the
same conditions with Lipase@s-g and nonentrapped Rh2Co2-
(CO)12, the yield dropped from 71% to 19%, (along with 4%
of the corresponding unsaturated ester, CH2dCH(CH2)8COO-
(CH2)2CH3, 1-7, and 50% of the hydrogenated acid 2).
Although subjecting the enzyme to nonentrapped Rh2Co2(CO)12
in the absence of hydrogen has no synthetic rational, we did
perform this blank reaction as well and, interestingly, found
that nonentrapped Rh2Co2(CO)12 in the presence of H2 is a
stronger quencher of the enzymatic activity compared to its
absence: when the saturated undecanoic acid, 2, was taken as
a substrate for the enzyme (because it is the main substrate for
lipase in the presence of hydrogen), 35% of the saturated ester
2-7 was obtained. This suggests that the quenching of the
It should be noted that although the hydrogenation of the
C-C double bonds of both the acid and the alcohol is, under
our reaction conditions, faster than the esterification, the routes
of esterification prior to reduction (leading to the same product,
1
Scheme 1) were found, by H NMR monitoring, to take place
as well. Thus, esterification of 1 with 2-propen-1-ol, 5, (route
III, in hexane, 50°C, 7 atm of H2, 4 h) led not only to the fully
reduced ester 2-7 as a major product but also to 5% of
2-propen-1-yl undecanoate [CH3(CH2)9COOCH2CHdCH2, 2-5].
Likewise, when the reaction of 1 and saturated 1-propanol, 7,
in the presence of Lipase@s-g and Cat2@s-g was stopped after
1 h, a 5:1 mixture of the saturated 1-propyl undecanoate, 2-7,
and the unsaturated 1-propyl 10-undecenoate, 1-7, was ob-
tained.
In conclusion, we believe that the positive results of this
feasibility-of-concept study should be applicable to many other
enzyme-based one-pot reaction sequences as well.
Experimental Details
Typically, a suspension of 0.1 g of Lipase@s-g16 (12 U), 0.3 g of
Cat2@s-g15 (containing 0.01 mmol of Rh2Co2(CO)12), 0.12 g (0.6 mmol)
of acid, and 2.6 mmol of the carbinol in 3 mL hexane was placed in
(17) Guye, P. A.; Chavanne, L. Bull. Soc. Chim. Fr. 1896, 15(3), 275.
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One-Pot Reactions with Sol-Gel Reagents
A R T I C L E S
an autoclave. After the autoclave was purged with H2, it was charged
with 7 atm of H2 and heated at 50 °C for the desired length of time
(for time durations and other pressures, see Table 1). After the autoclave
was cooled to room temperature, the sol-gel materials were filtered
off and the solvent was evaporated. The resulting products were
identified by GC, GC-MS, and NMR. For recycling, the catalysts were
sonicated three times in 10 mL of hexane for 10 min. The reaction
pair with Cat1@s-g was performed with 0.6 g of ceramic material
containing 0.015 mmol of entrapped catalyst and 2.6 mmol carbinol at
60 °C, 14 atm of H2, in 3 mL of benzene. For the detection of the two
parallel sequences in the synthesis of 2-7, 0.6 mmol of 1 and 2.6 mmol
of 1-propanol, 7, were reacted at 50 °C, under 3.5 atm of H2 in the
presence of 0.08 g of Cat2@s-g (containing 0.003 mmol of Rh2Co2-
(CO)12) and 0.1 g of Lipase@s-g. The reaction was stopped prematurely
after 1 h revealing, along with unreacted starting materials, a mixture
of 11% of the fully saturated 1-propyl undecanoate, 2-7, and 2.2% of
the unsaturated 1-propyl 10-undecenoate, 1-7.
Acknowledgment. We gratefully acknowledge support from
the Ministry of Science, Art and Sport through the Tashtiot
project, as well as from the Israel Science Foundation through
Grant # 143/00-12.0.
JA020799+
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