Rhodium-catalyzed hydroformylation of strained dialkenes: Ligand effect on product selectivity and complex coordination mode

We reported the synthesis of new and easily tunable diphosphine ligands L1-L5 based on bis(1H-indol-3-yl)methane. Strained 2,5-norbornadiene and dicyclopentadiene were used as the substrates to elucidate the relationship between ligand structure and product selectivity in Rh-catalyzed hydroformylation. Details in NMR, HRMS and single-crystal X-ray diffraction revealed that the coordination number and oxidation state could change rapidly upon exposure of RhI-L complexes to air. More importantly, the special structure of ligand which led to intramolecular methylene C–H oxidative addition to metal center could facilitate the hydroformylation reaction in an unexpected way.