ABSTRACT
This chapter presents the nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopic detections and characterizations of various metal–oxygen intermediates. The attention to metal-catalyzed oxidations is caused by the growing demand in novel, more efficient, and "green" catalyst systems for chemo-, regio-, and stereo selective oxidation of organic substrates, which is mostly dictated by toughening economic and environmental constraints. The only fairly well-understood preparative catalytic reaction incorporating superoxo complex as an active intermediate was the oxidation of 2,6-disubstituted phenols to the corresponding quinones, promoted by cobalt(II) complexes. In the past decade, superoxo complexes of copper have attracted the most significant interest among related complexes of other metals because cupric superoxo species are assumed to be responsible for initiating the oxidation of various organic substrates by copper enzymes. Molybdenum(VI) complexes have been among the best catalysts for the epoxidation of olefinic substrates with alkylhydroperoxides as terminal oxidants.
