Selective catalytic hydrogenations in a microfluidics-based high throughput flow reactor on ion-exchange supported transition metal complexes: A modular approach to the heterogenization of soluble complex catalysts Henrietta H. Horva ´th a , Ga ´bor Papp b , Csaba Csaja ´gi c , Ferenc Joo ´ a,b, * a Institute of Physical Chemistry, University of Debrecen, Debrecen H-4010, Hungary b Research Group of Homogeneous Catalysis, Hungarian Academy of Sciences, P.O. Box 7, Debrecen H-4010, Hungary c Thales Nanotechnology, Za ´ hony u. 7, Budapest, H-1031, Hungary Received 1 February 2006; received in revised form 17 July 2006; accepted 18 July 2006 Available online 1 August 2006 Abstract Water-soluble ruthenium(II) and rhodium(I) complexes containing monosulfonated triphenylphosphine (mtppms) ligands were immobilized on commercially available anion-exchangers. The resulting solid catalysts were suitable for use in a microfluidics-based flow reactor (H-Cubee) of high throughput capability. With the heterogenized [{RuCl 2 (mtppms) 2 } 2 ] disubstituted alkynes were hydrogenated to cis-alkenes with up to 85% selectivity, while the use of the immobilized [RhCl(mtppms) 3 ] yielded 1,2-diphenylethane as the major prod- uct. The ruthenium catalyst also reduced trans-cinnamaldehyde to 3-phenylpropanal selectively and catalyzed the isomerization of 1- octen-3-ol to octan-3-one. This simple and versatile method of the immobilization of water-soluble complexes yields active and durable molecularly dispersed yet solid catalysts. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Alkynes; Hydrogenation; Ruthenium; Immobilization; Flow reactor 1. Introduction The rapid development of high throughput and combi- natorial synthesis led to increased demand for fast methods of analysis and of further synthetic transformations. Obvi- ously, these methods are more valuable if they can be quickly adapted to a wide range of possible substrates and can be performed both with the generally small amounts of compounds generated by combinatorial synthesis and with the millimolar or larger quantities of usual laboratory syntheses. The recently developed microfluidics-based hydrogenation reactor proved to be a versatile equipment for fast reduction of a wide range of compounds on well- known catalysts (Pd/C, Raney-Ni, etc.) [1–3], however, there is still a need for efficient catalysts of stability and selectivity superior to these traditional heterogeneous cata- lysts. Many soluble transition metal complexes show extre- mely high catalytic activity and chemo- and stereoselectivity in various catalytic reactions [4] including hydrogenation [5–7], however, if suitable heterogeneous catalysts are avail- able they are preferred for the ease of handling and separa- tion from the reaction mixture [8]. Recently, the heterogenization of soluble complexes has entered a new phase of development [9]. Many ingenious methods have been used to immobilize such catalysts on the surface or within the interior structure of solid supports resulting in so-called heterogenized homogeneous catalysts showing the advantages of both the homogeneous and het- erogeneous ones. The catalytically active complex can be 1566-7367/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2006.07.016 * Corresponding author. Address: Institute of Physical Chemistry, University of Debrecen, Debrecen H-4010, Hungary. Tel.: +36 52 512915x22382; fax: +36 52 512900. E-mail address: fjoo@delfin.unideb.hu (F. Joo ´). www.elsevier.com/locate/catcom Catalysis Communications 8 (2007) 442–446