Amidate-bridged Pt-III dinuclear complexes [Pt-2(NH3)(4)(Am)(2)(H2O)(2)](4+) (Am = amidate ligand) catalyze oxidation of olefins-in acidic aqueous solution. Linear olefins are oxidized to ketones, whereas cyclic olefins are oxidized to epoxides : GC-MS analysis of the oxidation products obtained from the reaction in (H2O)-O-18 showed that the oxygen atoms in the products are exclusively from water, suggesting that the reaction mechanism is basically similar to that of the Wacker reaction. In accordance with this mechanism, pivalamidate-bridged Pt-III complex [Pt-2(III)(NH3)(4)((CH3)(3)CCONH)(2)(H2O)(2)](4+) has been found to react with olefins to give alkyl complexes. Reactions with 4-penten-1-ol and ethylene glycol vinyl ether in acidic aqueous solution gave [Pt-2(III)(NH3)(4)((CH3)(3)CCONH)(2)(CH2CH(CH2)(3)O)](NO3)(3) . H2O (7) and [Pt-2(III)(NH3)(4)((CH3)(3)CCONH)(2)(CH2CHO)](NO3)(3) . H2O (9), respectively. The two compounds have been structurally confirmed by X-ray diffraction analysis and H-1, C-13, and Pt-195 NMR spectroscopy. The H-1 NMR of 9 shows that both pi- and sigma-complexes exist in equilibrium in D2O, although the X-ray structure is close to the sigma-complex. High electrophilicity of the ct-carbon atoms of the compounds has been shown in the reactions with OH-. The above reactions with olefins can be a general route to prepare dimeric Pt-III-alkyl complexes.