Syntheses of the heterodinuclear hydride complexes and their applications to catalytic hydrometallation reactions are described. Series of heterodinuclear palladium and platinum hydride complexes, L'2HPdMLn and L'2HPtMLn [L' = 1/2 dppe, PMe3, PEt3 P(CH2Ph)(3), PMe2Ph, PMePh2, PPh3, PCy3; MLn = MoCP(CO)(3), WCp(CO)(3), Mn(CO)(5)] are prepared by (i) the metathetical reaction of a mononuclear (halogeno)(hydrido)metal complex with an ate complex, (ii) the beta-hydride elimination from the heterodinuclear ethyl complex, and (iii) the oxidative addition of a mononuclear hydride complex to a zerovalent metal complex. The reactions of L'2HPtMLn with electron-deficient alkenes lead to the reductive elimination to give the corresponding alkene complex of Pt (0) and MHLn. However, the similar treatment of L'2HPdMLn with electron-deficient alkenes gives the corresponding mononuclear alkyl complex MRLn. Mono(phosphine)palladium (0) complexes, Pd(diallyl ether)L' (L' = PPh3, PCy3, PMe3, PEt3) are found to be efficient active catalysts for the hydrometallation of electron-deficient alkenes of unreactive Mo, W, and Mn hydrides, MoHCp(CO)(3), WHCp(CO)(3), and MnH(CO)(5). Scope and reaction mechanisms of the hydrometallation are described. This reaction involves a heterodinuclear hydridopalladium complex, L'HPdMLn as an active intermediate. An application of this catalysis to hydrosilylation of electron-deficient alkenes is also described.