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

• Ion-pair synergetic effect of the phosphino-imidazolium salts in Rh(III)-complex.
• Hydroformylation in water suspension.
• Phosphino-imidazolium salts.

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, [RhIIICl4(L)2]PF6, 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.

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