Rhodium-Catalyzed Hydrogenation of Alkenes by Rhodium/ Tris(fluoroalkoxy) phosphane Complexes in Fluorous Biphasic System

Article abstract of DOI:10.1002/adsc.200202122

The reaction of [Ir(μ-Cl)(COD)]₂ with various fluorous derivatives of triphenylphosphane containing a para-, meta-, or ortho-(1H,1H-perfluoroalkoxy)-substituted fluorous phosphane P(C ₆H₄-ORf)₃ (Rf = CH₂C ₇F₁₅, CH₂CH₂CH₂C ₈F₁₇) and CO (1 atm) gives the corresponding trans-[Ir(μ-Cl)(CO){P(C₆H₄ORf)₃} ₂]. The IR ν_CO values of these complexes give some information on the donor/ acceptor properties of the phosphanes. These fluorous derivatives of triphenylphosphane, as well as a phosphane bearing two (1H,1H-perfluoroalkyloxy) chains at the 3,5-positions, were used in association with [Rh(μ-Cl)(COD)]₂ or [Rh(COD)₂]PF₆ in the reduction of methyl cinnamate, 2-cyclohexen-1-one, cinnamaldehyde, and methyl α-acetamidocinnamate in a two-phase system D-100/ethanol under 1 bar hydrogen at room temperature. Some differences in catalytic activity were observed in the reduction of methyl cinnamate, the most active catalyst being the rhodium complex containing the phosphane with the p-fluorous ponytail. Recycling of the fluorous catalyst was possible, particularly using the p-substituted phosphane, where no significant loss of catalyst or activity was observed, and generally with very low leaching of rhodium or phosphane in the organic phase.