Catalytic properties of the bimetallic clusters PPN[PtRh 5(CO) 15] and (PPN) 2[PtRh 4(CO) 12] in carbon monoxide hydrogenation

Abstract

PPN[PtRh 5(CO) 15], 1, PPN[Rh 5(CO) 15], 2 and (PPN) 2[PtRh 4(CO) 12], 3, were used as catalysts for CO hydrogenation at 230 °C in the pressure range of 1400 – 2000 bar in the presence and absence of the promoter 2-hydroxypyridine. The results were compared with those obtained with composed Rh and Pt/Rh catalysts, using Rh(CO) 2acac and Pt(acac) 2 in the presence of PPN(OAc) in the same concentrations as with 1, 2 and 3. Ethylene glycol is in most cases the favoured product, and clusters 1 and 2 show much higher activities than cluster 3. If clusters 1 and 2 are used in the absence of 2-hydroxypyridine, methanol is the favoured product. Analysis of product yields with reference to catalysts composed from mononuclear rhodium and platinum compounds indicates that platinum acts not as a separate catalyst, but is rather present in mixed Pt/Rh cluster species. However, these results do not permit determination of the exact nature of the actual catalytic species.