Heterocyclic compounds are engaged into many biological processes,and are also widely used in producing medicine,dyes,insecticide and herbicide etc.Catalytic hydrogenation,especially those using hydrogen gas as resources,is one of the key reactions for the synthesis and application of heterocyclic compounds.The catalytic hydrogenation of the heterocyclic aromatic compounds have attracted great interest in recent years.Major progress have been made on the experimental field,while the mechanistic study is still inadequate.In recent yeas we have system studied the mechanism of two hydrogenation system: Ru catalyzed hydrogenation of quinoxalines[1] and Pd catalyzed hydrogenation of imines[2,3].We propose a Ru monomer compound for the active catalyst of the Ru system,and a Pd-H compound coordinated by the assymetric ligand for the active catalyst of the Pd system.For both reactions,we found that H2 was split heterolytically by transition metal and a lewis base ligand(or substrate),while the hydrogenation reaction undergo stepwise,ionic,and out-sphere mechanisms.Associate mechanisms and inner-sphere mechanisms were found to be much higher in barrier.Solvent is crucial for the reactivity,and high polar solvent is better.The experimental observed assymetric properties have been reproduced by the theoretical studies,and enantioselectivities were found to be strongly depending on the ligand and the substrate.We propose that the N-H...N hydrogen bond in the transition state are the key factor for the enantioselectivity.Both hydrogenation systems requires additional strong acid,we found that acid involves the reaction directly.For the Ru system we found that the strong acid can catalyze part of the hydrogenation reaction,while for the Pd system the strong acid involves in both H2 activation and hydrogenation.