Copper complexes as functional models for dopamine beta-hydroxylase mechanistic study of oxygen atom transfer from Cu/O species to benzylic C-H bonds

The mechanism of the oxygen atom transfer reaction mediated by copper-oxyge n species has been studied through a substrate-binding ligand approach. Oxi dations of copper 5-X-IndPY2 type complexes in which an electron donating ( X = OMe) or withdrawing group (X = CN) substitutes the aromatic nucleus in position 5, lead to compounds 2b,c and 3b,c resulting from benzylic hydroxy lations. With these complexes, where one of the beazylic positions is influ enced by a para substituent (leading to 2b,c) while the other suffers influ ence from the meta group (leading to 3b,c), we observe that the ratio 2:3 > 1 is in favor of a certain electrophilicity of the copper/oxygen species r esponsible for the hydroxylations. While a concerted mechanism cannot be ex cluded, the results are in favor of a two-step mechanism involving radical species.