Reactions of superoxo and oxo metal complexes with aldehydes. Radical-specific pathways for cross-disproportionation of superoxometal ions and acylperoxyl radicals

The aquachromyl(IV) ion, CraqO2+, reacts with acetaldehyde and pivaldehyde by hydrogen atom abstraction and, in the presence Of O-2, produces acylperoxyl radicals, RC(O)OO.. In the next step, the radicals react with CraqOO2+, a species accompanying CraqO2+ in our preparations. The rate constant for the CraqOO2+/CH3C(0)OO. cross reaction, k(Cr) = 1.5 x 108 M-1 s(-1), was determined by laser flash photolysis. The evidence points to radical coupling at the remote oxygen of CraqOO2+, followed by elimination Of O-2 and formation of CH3COOH and (CraqO3+)-O-V. The latter disproportionates and ultimately yields Cr-aq(3+) and HCrO4-. No CO2 was detected. The CraqOO2+/C(CH3)(3)C(O)OO. reaction yielded isobutene, CO2, and Cr-aq(3+), in addition to chromate. In the suggested mechanism, the transient CraqOOOO(O)CC(CH3)(3)(2+) branches into two sets of products. The path leading to chromate resembles the CH3C(0)OO. reaction. The other products arise from an unprecedented intramolecular hydrogen transfer from the tert-butyl group to the CrO entity and elimination Of CO2 and O-2. A portion of C(CH3)(3)C(O)OO. was captured by (CH3)(3)COO., which was in turn generated by decarbonylation of acyl radicals and oxygenation of tert-butyl radicals so formed.