Gold(II) Porphyrins in Photoinduced Electron Transfer Reactions. Issue 23 (29th March 2019)

• Record Type: Journal Article
• Authors: Preiß, Sebastian; Päpcke, Ayla; Burkhardt, Lukas; Großmann, Luca; Lochbrunner, Stefan; Bauer, Matthias; Opatz, Till; Heinze, Katja
• Is Part Of: Chemistry. Volume 25:Issue 23(2019)
• Page Start: 5940
• Page End: 5949
• Publication Date: 2019-03-29
• Subjects: electron transfer -- gold -- paramagnetic NMR spectroscopy -- photoinduced electron transfer -- porphyrins; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201900050
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: In the context of solar‐to‐chemical energy conversion, inspired by natural photosynthesis, the synthesis, electrochemical properties and photoinduced electron‐transfer processes of three novel zinc(II)‐gold(III) bis(porphyrin) dyads [Zn II (P)–Au III (P)] + are presented (P: tetraaryl porphyrin). Time‐resolved spectroscopic studies indicated ultrafast dynamics ( k ET 1 >10 10 s −1 ) after visible‐light excitation, which finally yielded a charge‐shifted state [Zn II (P ⋅ + )–Au II (P)] + featuring a gold(II) center. The lifetime of this excited state is quite long due to a comparably slow charge recombination ( k BET 2 ≈3×10 8 s −1 ). The [Zn II (P ⋅ + )–Au II (P)] + charge‐shifted state is reductively quenched by amines in bimolecular reactions, yielding the neutral zinc(II)–gold(II) bis(porphyrin) Zn II (P)–Au II (P). The electronic nature of this key gold(II) intermediate, prepared by chemical or photochemical reduction, is elucidated by UV/Vis, X‐band EPR, gold L3 ‐edge X‐ray absorption near edge structure (XANES) and paramagnetic 1 H NMR spectroscopy as well as by quantum chemical calculations. Finally, the gold(II) site in Zn II (P)–Au II (P) is thermodynamically and kinetically competent to reduce an aryl azide to the corresponding aryl amine, paving the way to catalytic applications of gold(III) porphyrins in photoredox catalysis involving the gold(III/II) redox couple. Abstract : Long live the gold ! Long‐lived gold(II) intermediates were formed after light irradiation of zinc(II)‐porphyrin‐gold(III)‐porphyrin dyads. These gold(II) intermediates were unambiguously identified by various spectroscopic techniques and they are competent in sequential redox processes.