A Chromium(III)‐Superoxo Complex as a Three‐Electron Oxidant with a Large Tunneling Effect in Multi‐Electron Oxidation of NADH Analogues. Issue 13 (7th March 2017)

• Record Type: Journal Article
• Authors: Devi, Tarali; Lee, Yong‐Min; Jung, Jieun; Sankaralingam, Muniyandi; Nam, Wonwoo; Fukuzumi, Shunichi
• Is Part Of: Angewandte Chemie international edition. Volume 56:Issue 13(2017)
• Page Start: 3510
• Page End: 3515
• Publication Date: 2017-03-07
• Subjects: chromium(III)-superoxo complexes -- hydride transfer -- hydrogen atom transfer -- NADH analogues -- three-electron oxidant; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201611709
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Metal‐superoxo species are involved in a variety of enzymatic oxidation reactions, and multi‐electron oxidation of substrates is frequently observed in those enzymatic reactions. A Cr III ‐superoxo complex, [Cr III (O2 )(TMC)(Cl)] + (1 ; TMC=1, 4, 8, 11‐tetramethyl‐1, 4, 8, 11‐tetraazacyclotetradecane), is described that acts as a novel three‐electron oxidant in the oxidation of dihydronicotinamide adenine dinucleotide (NADH) analogues. In the reactions of 1 with NADH analogues, a Cr IV ‐oxo complex, [Cr IV (O)(TMC)(Cl)] + (2 ), is formed by a heterolytic O−O bond cleavage of a putative Cr II ‐hydroperoxo complex, [Cr II (OOH)(TMC)(Cl)], which is generated by hydride transfer from NADH analogues to 1 . The comparison of the reactivity of NADH analogues with 1 and p ‐chloranil (Cl4 Q) indicates that oxidation of NADH analogues by 1 proceeds by proton‐coupled electron transfer with a very large tunneling effect (for example, with a kinetic isotope effect of 470 at 233 K), followed by rapid electron transfer. Abstract : A Cr III ‐superoxo complex involved in the oxidation of dihydronicotinamide adenine dinucleotide analogues functions as a novel three‐electron oxidant with a very large tunneling effect. The hydride‐transfer reaction occurs by a concerted proton‐coupled electron transfer mechanism.