Halbleiterphotokatalyse – mechanistische und präparative Aspekte

Abstract

Basierend auf frühen Arbeiten zur Photoelektrochemie an Halbleitereinkristallelektroden hat das Gebiet der Photokatalyse an Halbleiterpulvern in den letzten drei Dekaden ein erstaunliches Wachstum erlebt. Dies ist in der einzigartigen Fähigkeit anorganischer Halbleiteroberflächen begründet, konzertierte Reduktionen und Oxidationen einer großen Vielzahl von Elektronendonor‐ und Elektronenakzeptorsubstraten zu photokatalysieren. Während die Spaltung von Wasser und der erschöpfende aerobe Abbau von Schadstoffen große Beachtung fanden, befasste sich nur ein kleiner Teil der Forschung mit präparativen Aspekten. Nach Einführung der mechanistischen Grundlagen folgen Standardexperimente zur Herstellung und Charakterisierung von Photokatalysatoren, die mit sichtbarem Licht aktiv sind. Anschließend illustrieren neuartige atomökonomische C‐C‐ und C‐N‐Kupplungsreaktionen die Relevanz der Halbleiterphotokatalyse für die organische Synthese. Beispielhaft zeigen sie, dass in diesem multidisziplinären Gebiet klassische Photochemie mit Elektrochemie, Festkörperchemie und heterogener Katalyse vereint sind.

Solvent‐Free One‐Step Photochemical Hydroxylation of Benzene Derivatives by the Singlet Excited State of 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone Acting as a Super Oxidant

“…[18] The catalytic turnover number was determined to be 4.8 based on the initial concentration of DDQ in oxygen-saturated benzene containing DDQ (0.30 mm), H 2 O (50 mm) and TBN (3.0 mm) under visible-light irradiation by a xenon lamp for 48 h. The overall stoichiometry is shown in Equation (2). [19] Photocatalytic hydroxylation of PhCN also occurred under the similar conditions to yield cyanophenols with turnover number (TON) of 1.2.…”

“…Photoredox catalysts have been widely investigated and utilized to photoinduced organic syntheses by using inorganic [1][2][3][4][5][6][7][8][9][10][11][12] and organic photosensitizers.…”

“…The photoinduced electron-transfer reaction has enabled highly reactive radical cations and anions to be produced, leading to the finely tuned new organic synthetic transformations. [1][2][3][4][5][6][7][8][9][10][11][12][13] We have reported the catalytic hydroxylation of benzene to phenol under ambient conditions through photoinduced one-electron oxidation of benzene with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as a triplet photooxidant. [14] The one-electron reduction potential of the triplet excited state of DDQ ( 3 DDQ*: in which "*" denotes the excited state) is 3.18 V versus SCE, which is high enough to oxidize benzene by electron transfer to produce the benzene radical cation as a key intermediate.…”

Photocatalytic Carboxylation of Organic Substrates with Carbon Dioxide at Zinc Sulfide with Deposited Ruthenium Nanoparticles

“…Therefore, the probability of a one-electron process is much higher than that of a multiple-electron process. [22][23][24] The photocatalytic carboxylation of organic compounds under mild conditions extends this list. [17] Various organic reactions, realised in homo-and heterogeneous photocatalytic systems, are known.…”

“…[17] Various organic reactions, realised in homo-and heterogeneous photocatalytic systems, are known. [24,26] The coupling of photogenerated radicals is an exceptional process because a huge majority of photocatalytic CO 2 reduction processes, leading to simple C 1 products, are type A reactions. [22][23][24] The photocatalytic carboxylation of organic compounds under mild conditions extends this list.…”