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. 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- teins 5 and cells. 6 The fast growth of these applications is mainly due to a remarkable property of these functional doped materials, 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 Si m O n fragments which are known to be formed during the early stages of the sol-gel process 7 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. 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