Ion-pair effect of phosphino-imidazolium salts on Rh(III)-complex catalyzed hydroformylation of 1-octene in water suspension

A series of phosphino-imidazolium salts (1-4), which are composed of the phosphine-incorporated imidazolium cations and the corresponding counter-anions of PF₆^-, TfO^-, and BF₄^-, are used in Rh-catalyzed hydroformylation. It was found that when the ionic Rh(III)-complex (1A, [Rh^IIICl₄(L)₂]PF ₆, L = 1-butyl-2-diphenylphosphino-3-methylimidazolium) was used as the pre-catalyst for hydroformylation of 1-octene, its inert catalytic activity could be efficiently tailored by the ion-pair synergetic effect of ligand 1-4 in water suspension. The single crystal structures of 1, 2, and 4 indicate that the hydrogen bonding network is developed between the cation and anion of ion-pairs 1 and 4, but is completely non-inexistent in 2.