Biphasic hydroformylation in new molten salts—analogies and differences to organic solvents

Abstract

New ionic compounds 1,2,3-trimethylimidazolium triflate (1) and 1-ethyl-2,3-dimethylimidazolium triflate (2) and (3-butylimidazole)triphenylboron (4) have been formed by alkylation and condensation reactions. An ion exchange reaction yielded the ionic compound 1-butyl-3-methylimidazolium tetraphenylborate (3). Molecular structures of all four compounds were determined by single crystal X-ray diffractometry. Utilizing two known rhodium complexes as catalyst precursors, compounds 1, 2 and 4 were used as solvents for biphasic hydroformylation reactions of two long chain 1-olefins. The results were compared to reactivities in the conventional solvent toluene in which similar turnover numbers but a higher tendency towards isomerization and hydrogenation occurred.