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The use of electron-poor phosphine-substituted cobaltocenium salts as ligands for the biphasic hydroformylation in ionic liquids has been investigated. Using improved oxidation methods, 1,1‘-bis(diphenylphosphino)cobaltocenium nitrate, 1,1‘-bis(diphenylphosphino)cobaltocenium hexafluorophosphate, and 1,1‘-bis1-methyl(1-diphenylphosphino)ethylcobaltocenium hexafluorophosphate have been synthesized. 1,1‘-Bis(diphenylphosphinocobaltocenium hexafluorophosphate in particular proved to be a very suitable ligand for the biphasic hydroformylation of 1-octene in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF 6 ), enabling high catalyst activity, high selectivity to the n -product, and no detectable catalyst leaching. In contrast to aqueous biphasic systems, the ionic liquid BMIM PF 6 provides for the rhodium catalyst a low-coordinating medium with limited but sufficient solubility for 1-octene to allow high reaction rates.
Brasse et al. (Tue,) studied this question.