Phosphines with 2-imidazolium and para-phenyl-2-imidazolium moieties — synthesis and application in two-phase catalysis

Deprotonation of 1-n-butyl-3-methyl-imidazolium chloride or hexafluorophosphate with n-butyl lithium and subsequent reaction of the intermediate 2,3-dihydro-imidazol-2-ylidene with diphenylchlorophosphine affords the 2-imidazolium phosphines 3a or 3b. The phosphine 4 with a para-phenylene spacer between the imidazolyl moiety and the phosphorus atom has been obtained by Kosugi–Stille coupling between 2-tri-n-butyl-stannyl-1-methylimidazole and 4-fluoroiodobenzene followed by nucleophilic substitution of fluorine with PPh2K. The X-ray structure of 4 (space group ) has been determined. Selective N-protonation or N-quaternization of 4 affords the corresponding imidazolium phosphines 5a–5c. The ligands 3b and 5c have been tested in the biphasic Rh-catalyzed hydroformylation of 1-octene employing the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate as catalyst solvent.