| Chiral alcohols are important organic intermediates and components of various chiral drugs.Asymmetric transfer hydrogenation of prochiral ketones is one of efficient way to obtain chiral alcohols.Nowadays the design and synthesis of a new,efficient and environmentally friendly cheap metal catalysts are the trends of green catalytic chemistry.In this dissertation,we studied the asymmetric transfer hydrogenation of aromatic ketones catalyzed by chiral macrocyclic aminophosphine ligands and cheap cobalt complexes.Moreover,we studied the active effect of NH4I on the Rh-catalyzed the asymmetric transfer hydrogenation of ketones.The main content of the paper includes the following three parts:1.Catalysts generated in situ from chiral aminophosphine ligands and cheap cobalt complexes were applied to asymmetric transfer hydrogenation of aromatic ketones.It showed that the catalytic system formed in situ from chiral macrocyclic iminophosphine ligand and CoBr2·xH2O exhibited high catalytic activity and enantioselectivity.Using iPrOH as solvents and hydrogen sources,asymmetric transfer hydrogenation of various ketones proceeded smoothly,giving up to 99%conversion and 99%ee.2.Addition of NH4I greatly improve the catalytic activity and enantioselectivity of the Rh-catalyzed asymmetric transfer hydrogenation of ketones.On the basis of the spectroscopic evidence and catalytic performance,we postulate that NH4I helps with the coordination between chiral macrocyclic ligands and rhodium center.On one hand,NH4+ interacted with chiral macrocycle through hydrogen bonds.On the other hand,I-is coordinated to the rhodium center.3.Using RhH(CO)(PPh3)3 and chiral macrocycle ligand as starting material,the air-stable Rh-based macrocycle complex could be conveniently obtained by simple one-pot method.It was further characterized by NMR,IR and HRMS.Notably,the Rh-based macrocycles could be successfully used to catalyze the ATH of ketones in air,with high catalytic activity(99%)and enantioselectivity(96%ee).It further highlights its advantage over those air-sensitive transition catalysts and offers an easy,convenient and efficient method to achieve chiral alcohols with high ee values. |
