The cobalt-catalyzed hydroformylation of 1-octene using the complex bis{tri(3-fluorophenyl)phosphine}hexacarbonyldicobalt (1) and Co-2(CO)(8) as pre-catalysts in supercritical carbon dioxide (scCO(2)) as a reaction medium was investigated. The catalytic performance in scCO(2) was compared to the one in toluene as a conventional solvent. Similar activities and selectivities were obtained in both reaction media. In scCO(2), a substantial improvement of the selectivity for aldehydes was found by using (1) (P:Co = 1:1) in comparison to the unmodified catalyst Co-2(CO)(8) (P:Co = 0:1). Surprisingly, further addition of (m-FC6H4)(3)P (P:Co = 6:1 and 11:1, respectively) resulted in a little enhancement of the aldehydes selectivity only, whereas the conversion and, hence, the aldehydes yield were reduced. A concept for catalyst recycling by using scCO2 was introduced. It was found that (1) was insoluble in the cold reaction mixture and was completely soluble in the supercritical reaction medium. By cooling the reactor content after the olefin conversion, the catalyst was regenerated as a solid, separated by filtration and could be recycled several times. (c) 2006 Elsevier B.V. All rights reserved.