Bifunctional Carbenium Dications as Metal-Free Catalysts for the Reduction of Oxygen

Abstract

The development of catalysts for the oxygen reduction reaction is a coveted objective of relevance to energy research. This study describes a metal-free approach to catalyzing the reduction of O2 into H2O2, based on the use of redox-active carbenium species. The most active catalysts uncovered by these studies are the bifunctional dications 1,8-bis­(xanthylium)-biphenylene ([3]2+) and 4,5-bis­(xanthylium)-9,9-dimethylxanthene ([4]2+) which promote the reaction when in the presence of decamethylferrocene and methanesulfonic acid. Electrochemical studies carried out with [4]2+ suggest the intermediacy of an organic peroxide that, upon protonation, converts back into the starting dication while also releasing H2O2. Kinetic studies point to the second protonation event as being rate-determining.

Controlling Oxygen Reduction Selectivity through Steric Effects: Electrocatalytic Two‐Electron and Four‐Electron Oxygen Reduction with Cobalt Porphyrin Atropisomers

“…O 2 can be reduced by two electrons (2 e − ) to H 2 O 2 or by four electrons (4 e − ) to H 2 O [1–3] . The 4 e − ORR is required in many energy conversion techniques, [4–7] while the 2 e − ORR makes H 2 O 2 , which is a widely used industrial oxidant and also a promising fuel [8–10] . Recently, many molecular ORR catalysts have been reported [1–5, 11–28] .…”

“…[1][2][3] The 4 e À ORR is required in many energy conversion techniques, [4][5][6][7] while the 2 e À ORR makes H 2 O 2 , which is a widely used industrial oxidant and also a promising fuel. [8][9][10] Recently, many molecular ORR catalysts have been reported. [1][2][3][4][5][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Although achievements have been made in improving the 4 e À ORR by providing rapid electron and proton transfers, [17,29,30] introducing hydrogenbonding [31,32] and electrostatic interactions, [33] and using dinuclear cooperation, [34][35][36][37][38] realizing these functionalities is challenging from both design and synthesis points of view.…”

Metal-Free Bond Activation by Carboranyl Diphosphines

“…Activation of strong bonds has been the driver of organometallic chemistry since the early development of transition metal catalysis. Recently, significant attention has been focused on the conceptually similar metal-free redox bond activation inspired by discoveries from Power, Bertrand, Stephan, Braunschweig, Radosevich, and others (Scheme A–E). − For example, cycling between P­(III) and P­(V) states in geometrically constrained phosphorus compounds affords the possibility of oxidative addition and reductive elimination in a way that mimics the reactivity of transition metal complexes …”

Trendbericht Organische Chemie 2022

“…Dabei bilden die Dicarbeniumionen (85) nach Reduktion die μ-peroxo-Spezies, welche unter Regenerierung des Katalysators zu H 2 O 2 protoniert wird. 61) Die organokatalytische Reduktion sekundärer Amide (86) zu den Aminen (87) veröffentlichten Paradies und Mitarbeiter:innen (Abbildung 26). Dabei werden die Amide zunächst phosphanoxidkatalysiert zu den Imidoylchloriden umgesetzt, welche in Anwesenheit des Borans (89) zu den Aminen reduziert werden.…”