To assess the oxidizing capacity of [Co( -diketonate) 2 (L)OOR] complexes, four such species, namely, [Co-(acac) 2 (L)(OO t Bu)] (acacH ) acetylacetone; L ) pyridine (py) (1), 4-methylpyridine (4-Mepy) (2), 1-methylimidazole (1-MeIm) (3)) and [Co(dbm) 2 (py)(OO t Bu)] (4, dbmH ) dibenzoylmethane), have been synthesized and the structures of 1, 3, and 4 have been determined by X-ray crystallography. Complex 1 crystallizes in the triclinic space group P1 h with a ) 9.149(2) Å, b ) 9.741(2) Å, c ) 13.067 (2) Å, R ) 84.22 (2)°, ) 77.89(2)°, γ ) 67.83(2)°, V ) 1054.1(4) Å 3 , and Z ) 2. Complex 3 crystallizes in the monoclinic space group P2 1 /n with a ) 11.341(2) Å, b ) 10.485(2) Å, c ) 18.863(2) Å, R ) 90°, ) 106.230(15)°, γ ) 90°, V ) 2153.6(8) Å 3 , and Z ) 4. Complex 4‚1.5C 6 H 6 crystallizes in the monoclinic space group P2 1 /c with a ) 14.907(5) Å, b ) 18.701-(5) Å, c ) 15.207(4) Å, R ) 90°, ) 103.52 (2)°, γ ) 90°, V ) 4122(2) Å 3 , and Z ) 4. The geometry around the Co(III) center in all four complexes is distorted octahedral, and the two -diketonate ligands are cis to each other. The Co-O and O-O bond distances in the Co-OO t Bu moiety fall in the narrow ranges of 1.860(3)-1.879 (2) and 1.451(3)-1.466(3) Å, respectively. Although stable in the solid state, these complexes decompose in benzene or halocarbon solutions to afford t BuOO • and t BuO • radicals. When alkanes like cyclohexane are present in the reaction mixture, these radicals initiate oxidation of the C-H bond. The oxidizing capacity follows the order 1 > 2 > 3 > 4. Decomposition of the complexes in the presence of cyclohexene and an aldehyde results in selective epoxidation in high yield.