Photo‐Chromium: Sensitizer for Visible‐Light‐Induced Oxidative C−H Bond Functionalization—Electron or Energy Transfer?. Issue 8 (1st June 2017)

• Record Type: Journal Article
• Authors: Otto, Sven; Nauth, Alexander M.; Ermilov, Eugenyi; Scholz, Norman; Friedrich, Aleksej; Resch‐Genger, Ute; Lochbrunner, Stefan; Opatz, Till; Heinze, Katja
• Is Part Of: ChemPhotoChem. Volume 1:Issue 8(2017)
• Page Start: 344
• Page End: 349
• Publication Date: 2017-06-01
• Subjects: aminonitriles -- chromium -- photocatalysis -- photophysics -- singlet oxygen; Photochemistry -- Periodicals; Periodicals; Electronic journals; 541.35
• DOI: 10.1002/cptc.201700077
• Languages: English
• ISSNs: 2367-0932

Abstract

Abstract: The chromium(III) sensitizer[Cr(ddpd)2 ] 3+ (ddpd= N, N ′‐dimethyl‐ N, N ′‐dipyridine‐2‐ylpyridine‐2, 6‐diamine), based on an earth‐abundant metal centre, possesses a unique excited‐state potential‐energy landscape. The very large energy gap between the redox‐active and substitutionally labile 4 T2 state and the long‐lived low‐energy 2 E spin‐flip state enables a selective, efficient sensitization of triplet dioxygen to give singlet dioxygen. Ultrafast intersystem crossing after the Franck Condon point from the 4 T2 to the 2 E excited state within 3.5 ps precludes intermolecular electron‐transfer pathways from the ultrashort‐lived excited 4 T2 state. This specific excited‐state reactivity enables a selective visible‐light‐induced C−H bond activation of tertiary amines with 1 O2 and subsequent trapping with cyanide to yield α‐aminonitriles in good to excellent yields. Abstract : In two minds : The unique excited‐state potential‐energy landscape of the Cr III sensitizer [Cr(ddpd)2 ] 3+ enables a selective sensitization of 3 O2 to give 1 O2 . Ultrafast intersystem crossing precludes electron‐transfer pathways from the ultrashort‐lived redox‐active excited state and enables a selective visible‐light‐induced C−H bond activation of tertiary amines with 1 O2 and subsequent trapping with cyanide to yield α‐amino‐nitriles.