Metal Catalysis inside Polymer Frameworks: Evaluation of Catalyst Stability and Reusability Milan Kra ¬lik,* [a] Vieroslav Kratky, [a] Mirco De Rosso, [b] Massimo Tonelli, [c] Silvano Lora, [d] and Benedetto Corain* [b] Abstract: The polymer framework of a resin-based catalyst built up with Pd nanoclusters (ca. 3 nm) dispersed inside the nanoporous domains of a thermally stable gel-type polyacrylic resin exhibits a good chemical stability under 5 bar H 2 at 40 8C for reasonable contact times. Chemical and physico-chemical integrity of the polymer framework are checked with a variety of instrumental analytical methods. Catalyst reusability turns out to be quite good. Keywords: cluster compounds ¥ gel-type resins ¥ metal catalysis ¥ palladium ¥ polymers Introduction Metal catalysts built up with metal nanoclusters supported on functional resins are currently used in a few industrial processes, which originated from Bayer technology developed in the Eighties. [1±3] In spite of the scientific novelty and of potential further technological breakthroughs, the pertinent scientific and patent literature appeared to be almost nonexistent at the beginning of the Nineties. This observation prompted us to start a long-term project aimed at discovering the scientific bases of these most promising catalysts. [4±12] In conventional supported metal catalysts (Figure 1), the support is typically a ™microstone∫ with defined physical and Figure 1. Metal catalysis on inorganic supports (top) versus metal catalysis inside organic polymer frameworks (below). physico-chemical features, and its chemical ones are control- lable to some extent. In the case of resin-supported metal nanoclusters, the support particles are ™microsponges∫, the physical, physico-chemical, and chemical features of which can be designed and are controllable in nature. [13, 14] Thus, reagents involved in a given metal-catalyzed reaction must be able to enter the microreactor (size selectivity), in which they will meet a liquid medium (e.g. a mixture of two different solvents). The composition of the reagents and solvents may be quite different from that which they exhibit in the bulk of the reaction medium. Moreover, the kinetics and the thermodynamics of the catalyzed reaction might be quite different from those existing in the bulk medium itself, [15] and even the concentration of the reagents inside the micro- reactors may be quite different from that existing in the bulk medium. Consequently, functional resin-supported metal [a] Prof. M. Kra ¬lik, Dr. V. Kratky Department of Organic Technology Slovak University of Technology Radlinske ¬ho9, 81237 Bratislava1 (Slovak Republic) Fax: ( 421)-2-52493198 E-mail: kralik@chtf.stuba.sk [b] Prof. B. Corain, Dr. M. De Rosso Istituto di Scienze e Tecnologie Molecolari C.N.R., Sezione di Padova c/o Dipartimento di Chimica Inorganica Metallorganica Analitica Via Marzolo1, 35131 Padova (Italy) Fax : ( 39)049-8275223 E-mail: benedetto.corain@unipd.it [c] Prof. M. Tonelli C.I.G.S. Universita ¡ di Modena, 41100 Modena (Italy) Fax: ( 39)059-370551 E-mail: tonelli.massimo@unimo.it [d] Dr. S. Lora Istituto per la Sintesi Organica e la Fotoreattivita ¡ C.N.R., via Romea4, 35020 Legnaro (Italy) Fax: ( 39)049-641925 E-mail: lora@frae.bo.cnr.it FULL PAPER Chem. Eur. J. 2003, 9, No. 1 ¹ 2003 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim 0947-6539/03/0901-0209 $ 20.00+.50/0 209