Metal-Free Dihydrogen Oxidation by a Borenium Cation: A Combined Electrochemical/Frustrated Lewis Pair Approach

• Published in: Angewandte Chemie 2014-09, Vol.126 (37), p.10080-10083
• Main Authors: Lawrence, Elliot J., Herrington, Thomas J., Ashley, Andrew E., Wildgoose, Gregory G.
• Format: Article
• Language: eng ; ger
• Subjects: Boreniumkationen; Carbon; Catalysts; Cations; Chemistry; Electric potential; Electrodes; Elektrokatalyse; Energy conservation; Frustrierte Lewispaare; Lewis acid; Oxidation; Voltage; Wasserstoff
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201405721

In order to use H2 as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H2 into 2 H+ and 2 e−. Herein, we report a metal‐free approach to catalyze the oxidation of H2 by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H2 with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC‐stabilized borenium cation [(IiPr2)(BC8H14)]+ (IiPr2=C3H2(NiPr)2, NHC=N‐heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H2 oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol−1. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C6F5)3, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach. Das Potential, das für die nichtwässrige H2‐Oxidation an einer Kohlenstoffelektrode benötigt wird, kann durch die Verwendung eines Boreniumkations und die Kombination von Elektrochemie mit frustrierten Lewis‐Paaren maßgeblich abgesenkt werden. Das System ist durch schnelle Elektrodenkinetik, hohe Stabilität der elektro‐erzeugten Protonen und gutes Katalysatorrecycling gekennzeichnet.