Recently we reported [1] a dinuclear Cu II -phenoxyl radical complex, which catalyzes efficiently the aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones or to 1,2-glycols by oxidative C ± C coupling with concomitant formation of H 2 O 2 . This complex together with that of Stack et al. [2] are the first reported functional models for the enzyme galactose oxidase (GO). [3] We report here a new mononuclear Cu II -iminosemiquinone catalyst that selectively transforms primary alcohols (e.g. ethanol but not methanol) with O 2 to aldehydes and H 2 O 2 ; secondary alcohols are not at all substrates for the catalyst.
The trifluoroacetate salt of the cation N,N-bis(2-hydroxy-3,5-di-tert-butylphenyl)ammonium [H 4 (L 3 )](CF 3 CO 2 ) was prepared through the condensation of 3,5-di-tert-butylcatechol with NH 3 in n-heptane and subsequent acidification with trifluoroacetic acid. It is known that the diamagnetic trianion (L 3 ) 3À (Scheme 1), present as a tridentate ligand in complexes, can be easily oxidized to the radical dianion (L 2 ) 2À and then to the diamagnetic monoanion (L 1 ) 1À in two successive one-electron oxidation steps. Speier and Pierpont et al. have, for example, described the complexes [Cu II (L 1 ) 2 ]