Efficient Hydrogenation of Biomass Oxoacids to Lactones by Using NHC-Iridium Coordination Polymers as Solid Molecular Catalysts.

A series of NHC-iridium coordination polymers have proven to be robust, efficient and recyclable solid molecular catalysts toward the hydrogenation of biomass levulinic acid (LA) to γ-valerolactone. Along with quantitative yields attained at 0.01 mol % catalyst loading under 50 atm of H2 , the solid molecular catalyst was readily recovered and reused for 12 runs without obvious loss of the selectivity and activity. Remarkably, up to 1.2×105  TON, an unprecedented value could be achieved in this important transformation. In addition, a number of LA homologues, analogues and derivatives were well tolerated to deliver various intriguing and functional lactones in good to excellent yields, which further confirmed the feasibility of the solid molecular catalysts.