Synthesis of phosphorus amidite ligand and investigation of its flexibility impact on rhodium-catalyzed hydroformylation of 1-octene

Abstract

A new flexible 2,2′-bis((dipyrrolylphosphinooxy)methyl)-1,1′-(±)-biphenyl ligand (L1) was synthesized, characterized and employed in the hydroformylation of 1-octene. In order to investigate the influence of ligand flexibility on the catalytic performance, its analogue 2,2′-bis (dipyrrolylphosphinooxy)-1,1′-(±)-biphenyl (L3) was also applied in the hydroformylation of 1-octene. With the presence of L1, the aldehyde selectivity was approximately 10% higher than that with the relevant less flexible ligand L3. Theoretical calculation indicated that the olefin-insertion into the Rh–H bond of intermediate III and the CO-insertion into Rh–alkyl bond of intermediate V were favorable in terms of thermodynamics, which were vital to the generation of aldehyde. Meanwhile, the ligand flexibility was indeed improved by adding a methylene between benzene and oxygen atom that connected with P, as the calculation showed the variation of the bite angle ∠P–Rh–P of the intermediates I–VI was 8.7° in L1-system, as for L3-system, the variation was 14.0°. This structural feature might make the olefin-insertion and the CO-insertion occur more easily in the L1-system and resulted in higher aldehyde selectivity.