A comparative study of the reactions of alkane oxidation with peroxides in acetonitrile showed different behavior of the complexes cyclopentadienylbenzeneiridium(HI) tetrafluoroborate [pi C-5-H-5)Ir(pi-C6H6](BF4)(2) (complex 1) and tetrakis(methyldiphenylphosphine)palladium(0) [(CH3)(C6H5)(2)P](4)Pd (complex 2) as catalysts. Complex 1 was completely inactive in oxidation with hydrogen peroxide and tert-butyl hydroperoxide but exhibited a moderate activity in oxidation with m-chloroperoxylyenzoic acid (MCPBA) at room temperature. On the basis of the regio- and stereoselectivity parameters found for the latter reaction, it was assumed that the role of iridium(III) ion consists in the formation of Lewis adducts with MCPBA, which enhances the activity of the acid. Unlike the iridium derivative, palladium complex 2 showed a moderate activity in oxidation with hydrogen peroxide. The relatively high values of the regioselectivity parameters suggest the formation of oxo or peroxo complexes of palladium. Steps involving these complexes include hydrogen-atom abstraction from an alkane yielding the alkyl radical. Adding to an oxygen molecule, this radical forms the alkylperoxy radical and, ultimately, alkyl hydroperoxide. Complex 2 showed activity in the oxidation of alkanes with MCPBA, wherein the reaction with cis-2,2-dimethylcyclohexane was not stereoselective. It was supposed that iridium and palladium catalyze the reactions of alkanes with MCPBA via different mechanisms.