Dehydrative condensation of the hydroxopalladium complex (Tp(iP12))(py)Pd-OH (1) with hydroperoxides (XOOH: X = H, t-Bu) produces the corresponding (hydroperoxo)-, (Tp(iPr2))(py)Pd-OOH (2a), and (tert-butylperoxo)palladium complexes, (Tp(iPr2))(py)Pd-OOBut (3). Treatment of 2a with PPh3 results in concomitant ligand displacement giving (Tp(iPr2))((PhP)-P-3)Pd-OOH (2b) and oxygenation of PPh3 giving O PPh3. Further condensation between 1 and 2a gives the mu-kappa(1):kappa(1)-peroxo complex (Tp(iPr2))(py)Pd-OO-Pd(Tp(iPr2))(py) (4), while condensation between the bis(mu-hydroxo)dipalladium complex (PdTp(iPr2))(2)(mu-OH)(2) (7) with 2a affords the unsymmetrical mu-kappa(1):kappa(2)-peroxo complex(Tp(iPr2))-(py)Pd-OO-PdTp(iPr2) (5). These peroxopalladium complexes 2-5 have been fully characterized by a combination of spectroscopic and crystallographic analyses, which lead to description of the O-O moieties in these complexes as peroxide (O-2(2-)) with sp(3)-hybridized oxygen atoms. The OOH moiety in 2b is found to interact with the noncoordinated nitrogen atom of the pendant pyrazolyl group through hydrogen bond. The O-2 moieties in 2-5 turn out to be so nucleophilic (basic) as to add across carbon-heteroatom multiple bonds in acetonitrile and acetaldehyde to give the peroxometallacycle Tp(iPr2)Pd[OOC(Me)=N)]Pd(Tp(iPr2))(py) (8) (from 2, 4, and 5) and the acetato complex (Tp(iPr2))(py)Pd-OC(=O)CH3 (9) (from 2-4), respectively. Methyl vinyl ether and styrene, CH2=CHY (Y = OMe, Ph), are converted to the corresponding methyl ketones-, CH3C(=O)Y, upon treatment with 2-4.