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Metal-free dihydrogen oxidation by a borenium cation: a combined electrochemical/frustrated Lewis pair approach.

Lawrence EJ, Herrington TJ, Ashley AE, Wildgoose GG - Angew. Chem. Int. Ed. Engl. (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK) http://wildgooseresearch.com.

No MeSH data available.


Electrooxidation of the H2-activated tBu3P/1[B(C6F5)4] frustrated Lewis pair (FLP) results in the electrochemical generation of two protons and two electrons.
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f3: Electrooxidation of the H2-activated tBu3P/1[B(C6F5)4] frustrated Lewis pair (FLP) results in the electrochemical generation of two protons and two electrons.

Mentions: Herein, we extend our “combined electrochemical/FLP approach” beyond simple arylborane Lewis acid catalysts, to the NHC-stabilized borenium cation [(IiPr2)(BC8H14)]+, (1+ in Scheme 1; IiPr2=C3H2(NiPr)2, NHC=N-heterocyclic carbene). The ability of 1+ to activate H2, when combined with Lewis base tBu3P, has been reported previously, and the lack of electron-withdrawing groups in 1+ imparts considerable hydridic character to the neutral NHC–borane adducts, even in comparison with anionic borohydrides such as [HB(C6F5)3]−.6, 7 Indeed, B(C6F5)3 is capable of abstracting H− from 1-H to give the salt 1[HB(C6F5)3].6 In addition, the bond-dissociation energy of the B—H bond is weakened by the coordination of a carbene ligand.8, 9 As we demonstrate herein, the combination of these properties improves the chemical stability of borenium Lewis acid catalysts toward unwanted side reactions (e.g. reaction with the solvent) and further decrease the voltage required to oxidize H2 at a carbon electrode by 910 mV (equivalent to 175.6 kJ mol−1).


Metal-free dihydrogen oxidation by a borenium cation: a combined electrochemical/frustrated Lewis pair approach.

Lawrence EJ, Herrington TJ, Ashley AE, Wildgoose GG - Angew. Chem. Int. Ed. Engl. (2014)

Electrooxidation of the H2-activated tBu3P/1[B(C6F5)4] frustrated Lewis pair (FLP) results in the electrochemical generation of two protons and two electrons.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4257500&req=5

f3: Electrooxidation of the H2-activated tBu3P/1[B(C6F5)4] frustrated Lewis pair (FLP) results in the electrochemical generation of two protons and two electrons.
Mentions: Herein, we extend our “combined electrochemical/FLP approach” beyond simple arylborane Lewis acid catalysts, to the NHC-stabilized borenium cation [(IiPr2)(BC8H14)]+, (1+ in Scheme 1; IiPr2=C3H2(NiPr)2, NHC=N-heterocyclic carbene). The ability of 1+ to activate H2, when combined with Lewis base tBu3P, has been reported previously, and the lack of electron-withdrawing groups in 1+ imparts considerable hydridic character to the neutral NHC–borane adducts, even in comparison with anionic borohydrides such as [HB(C6F5)3]−.6, 7 Indeed, B(C6F5)3 is capable of abstracting H− from 1-H to give the salt 1[HB(C6F5)3].6 In addition, the bond-dissociation energy of the B—H bond is weakened by the coordination of a carbene ligand.8, 9 As we demonstrate herein, the combination of these properties improves the chemical stability of borenium Lewis acid catalysts toward unwanted side reactions (e.g. reaction with the solvent) and further decrease the voltage required to oxidize H2 at a carbon electrode by 910 mV (equivalent to 175.6 kJ mol−1).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK) http://wildgooseresearch.com.

No MeSH data available.