A series of chiral tetradentate diimino- and diamino-diphosphine ligands (PNNP-type) have been synthesized and characterized. These ligands contain two “soft” phosphorus atoms and two “hard” nitrogen atoms, which display the rich coordination chemistry and easily modify the steric and electronic properties of the resulting metal complexes. Based on these polydentate mixed-P, N ligands, chiral PNNP-Ru(II), Rh(I) and Ir(I) complexes were prepared and used as catalysts in asymmetric transfer hydrogenation (ATH) of aromatic ketones using 2-propanol as hydrogen source. So far we have developed several very efficient chiral PNNP ligands / metal complex catalytic systems, which include chiral PNNP-RuCl₂ complex, chiral PNNP/[IrHCl₂(COD)]₂, PNNP/Ru₃(CO)₁₂, chiral iridium-hydride complex catalyst under base-free condition and a catalyst system using HCOONa as hydrogen source in water. These catalytic systems have been proved to be excellent catalyst precursors for the enantioselective reduction of a series of aromatic ketone, leading to corresponding optically alcohols with up to 99% ee and even the molar ratio of ketone to catalyst up to 10000:1. The PNNP ligands extensively used in asymmetric epoxidation, cyclopropanation and kinetic resolution by other researchers and us are also reviewed. The catalytic reaction mechanism of ATH will be discussed. The chiral diiminodiphophine and diaminodiphosphine ligands, which have similar geometrical parameters, however possess a very difference in reactivity and enantioselectivity. The latter is an excellent ligand for transfer hydrogenation of ketones, suggesting that an “NH” function in the ligand may promote the formation of a six-membered cyclic transition state through hydrogen bonding to a ketone substrate.