Promoting effect of water on 1-hexene hydroformylation catalyzed by aminophosphine–rhodium complexes

A series of ( o -alkylaminophenyl)diphenylphosphine ligands (P–N ligands) containing different alkyl carbon numbers or amino groups have been synthesized and characterized by IR and NMR ( 1 H, 13 C, 31 P). The rhodium complexes ligated with P–N ligands in the hydroformylation of 1-hexene showed a considerable enhancement with the addition of water. NMR characterization studies suggested that the addition of water would engage in hydrogen bonding to the nitrogen atom of the coordinated P–N ligand, inhibiting the internal Rh–N interaction and generating more of the active unsaturated Rh-species that could react with 1-hexene to start the hydroformylation.