Catalysis Letters 56 (1998) 231–235 231 WGSR catalyzed by cis-[Rh(CO) 2 (amine) 2 ]PF 6 heterogenised on poly(4-vinylpyridine) Alvaro J. Pardey a,∗ , Marta Mediavilla a , Massimo Canestrari a , Caribay Urbina a , Delfin Moronta b , Eduardo Lujano c , Pablo Baricelli c,∗ , Clementina Longo d , Rub´ en Pastene e and Sergio A. Moya e,∗ a Escuela de Qu´ ımica, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela E-mail: apardey@strix.ciens.ucv.ve b Escuela de F´ ısica, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela c Centro de Investigaciones Qu´ ımicas, Facultad de Ingenier´ ıa, Universidad de Carabobo, Valencia, Venezuela d Facultad de Farmacia, Universidad Central de Venezuela, Caracas, Venezuela e Departamento de Qu´ ımica Aplicada, Facultad de Qu´ ımica y Biolog´ ıa, Universidad de Santiago de Chile, Santiago de Chile, Chile Received 29 June 1998; accepted 9 November 1998 This paper describes catalytic activation studies of the water–gas shift reaction by cis-[Rh(CO) 2 (amine) 2 ]PF 6 (amine = 4-picoline, 3-picoline, 2-picoline, pyridine, or 2,6-lutidine) heterogenised on poly(4-vinylpyridine) in aqueous 2-ethoxyethanol. The effect of varying the nature of the amine was investigated. The rhodium complexes bearing 4-picoline (4-pic) ligands proved to be most active among those surveyed, and displaying turnover frequencies for hydrogen production of 8.9 mol of H 2 per mole of Rh per day for 9.4 ×10 −5 mol cis-[Rh(CO) 2 (4-pic) 2 ]PF 6 /1.00 g poly(4-vinylpyridine), P (CO) = 0.9 atm at 100 ◦ C. Keywords: water–gas shift reaction, rhodium, poly(4-vinylpyridine), carbon monoxide 1. Introduction Catalysis of the water–gas shift reaction (WGSR) CO + H 2 O ⇋ CO 2 + H 2 (1) by transition metal complexes both in solution [1–12] or heterogenised on polymers [13–19] has been reported. Rhodium(I), cis-[Rh(CO) 2 (amine) 2 ]PF 6 , complexes dis- solved in aqueous pyridine and substituted pyridines so- lution (amine = 4-picoline, 2-picoline, pyridine, or 2,6- lutidine) have been used as catalysts for the WGSR [3] as well as for the catalytic nitrobenzene reduction to aniline under WGSR conditions [20]. The catalytic activity was shown to be sensitive to the nature of amines. Both elec- tronic and steric effects of the methyl groups apparently influence this trend. Our current interest in the reduction of nitro deriva- tives [20,21] as well as in the catalysis of the WGSR by transition metal complexes [7,8,11,12] led us to study the catalytic properties of cis-[Rh(CO) 2 (amine) 2 ]PF 6 /poly (4-vinylpyridine) in aqueous 2-ethoxyethanol in order to compare the catalytic behavior of this polymer-supported system to its homogeneous counterpart formed by cis-[Rh (CO) 2 (pyridine) 2 ]PF 6 /pyridine and other substituted pyri- dines previously studied by Pardey and Ford [3] and restud- ied by Fachinetti et al. [5]. ∗ To whom correspondence should be addressed. 2. Experimental 2.1. Materials Pyridine (py), 4-picoline, 3-picoline, 2-picoline (-pic) and 2,6-lutidine were obtained from Aldrich and dis- tilled from KOH before use. RhCl 3 ·3H 2 O was obtained from Aldrich. Water was doubly distilled. 2-ethoxyethanol (Aldrich) was distilled from anhydrous stannous chlo- ride. Poly(4-vinylpyridine) (P(4-VP), 2% cross-linked was used as provided by Reilly Industries. The gas mixture CO/CH 4 (95.8%/4.2%, v/v) was purchased from BOC Gases. The rhodium complexes cis-[Rh(CO) 2 (amine) 2 ]PF 6 (amine = 4-picoline, 3-picoline, 2-picoline, pyridine or 2,6-lutidine) were prepared as reported by Pannetier et al. [22]. 2.2. Catalyst preparation A 1.00 g sample of P(4-VP) and a known amount of the rhodium complex cis-[Rh(CO) 2 (amine) 2 ]PF 6 (ca. 1.0 × 10 −4 mol) were stirred for 72 h in 10 ml of 2-ethoxyethanol until almost all the rhodium was extracted by the poly- mer from the solution as marked by the presence of a col- orless clear solution above the polymer beads. The yel- low polymer was filtered, washed with 2-ethoxyethanol (15 ml) to remove the unabsorbed rhodium complex of which the concentration was determined by UV-visible spectroscopy.  J.C. Baltzer AG, Science Publishers