Novel α-pinene-derived mono- and bisphosphinite ligands: Synthesis and application in catalytic hydrogenation

Novel mono- and bisphosphinite (−)-pinane-based ligands have been synthesized from (−)-α-pinene. Mixed with [(COD)2Rh]+[BF4]−, these ligands displayed moderate up to high catalytic activity in hydrogenation of dimethyl itaconate with dihydrogen. It has been observed that the structure of the ligand, the reaction temperature and solvent are important to define productivity of the phosphinite-based Rh-catalysts. Bisphosphinite ligands in hydrogenation reactions suffered from an Arbuzov rearrangement, leading to fast deactivation of the hydrogenation catalyst. In contrast, monophosphinite-derived Rh-catalysts showed increased productivity as well as thermal stability. An almost quantitative conversion of dimethyl itaconate has been achieved at elevated temperatures in toluene. Alternatively, hydrogenation of dimethyl itaconate with monophosphinite ligands has been carried out in MeOH at room temperature or 40 °C and has led to a nearly quantitative conversion.