An ionic phosphine-ligated rhodium(III) complex as the efficient and recyclable catalyst for biphasic hydroformylation of 1-octene

A novel ionic complex with insensitivity to moisture and air, bis-[1-butyl-2-diphenylphosphanyl-3-methylimidazolium]tetrachloridorhodium(III) hexafluorophosphate (1A), has been synthesized and fully characterized. The single-crystal X-ray diffraction analysis shows that 1A is composed of the Rh(III)-complex cation and the counter-anion of PF₆^-. The complex cation has highly symmetrical Rh^III-centered octahedron geometry with four Cl atoms in the equatorial plane and two imidazolium- substituted phosphine ligands in the axial position. The catalytic performance of 1A, which could be tailored by the ligands and the solvents, was investigated toward the biphasic hydroformylation of 1-octene. It was found that the presence of the hemilabile hybrid P,N-ligand of 3 (1-(2′-piperid-1′- yl-ethyl)-2-diphenylphosphino-3-methylimidazolium hexafluorophosphate), as a kind of ligand-functionalized ionic liquids (ILs), could dramatically spur the catalytic activity of 1A. The use of the RTIL of [PEmim]BF₄ (1-(2′-piperid-1′-yl-ethyl)-3-methylimidazolium tetrafluoroborate) as the solvent not only fulfilled the efficient biphasic hydroformylation of 1-octene, but also guaranteed the successful recovery and recycling of the ionic compositions of 1A and 3.