Aldehyde Decarbonylation Catalysis under Mild Conditions

Reaction of [RhCl(NBD)](2) with 2.0 equiv of triphos (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine; NBD = bicyclo[2.2.1]hepta-2,5-diene) in THF solution at room temperature affords [Rh(NBD)(triphos)][Cl] (4a), which was isolated as [Rh(NBD)(triphos)][SbF6] (4b) in 67% yield. Treatment of 4b with aqueous formaldehyde in THF solution; at 80 degrees C forms [Rh(CO)(triphos)][SbF6] (2a), which reversibly binds a second equivalent of CO(g) to give [Rh(CO)(2)(triphos)][SbF6] (2b). The complex [Rh(CO)(triphos)][SbF6] has been found to be an effective aldehyde decarbonylation catalyst for primary and aryl aldehydes at temperatures as low as that of refluxing dioxane, with little or no undesirable side products resulting from beta elimination or radical rearrangement.