Metal hydrides are key intermediates in catalytic proton reduction and dihydrogen oxidation. There is currently much interest in appending proton relays near the metal centre to accelerate catalysis by proton-coupled electron transfer (PCET). However, the elementary PCET steps and the role of the proton relays are still poorly understood, and direct kinetic studies of these processes are scarce. Here, we report a series of tungsten hydride complexes as proxy catalysts, with covalently attached pyridyl groups as proton acceptors. The rate of their PCET reaction with external oxidants is increased by several orders of magnitude compared to that of the analogous systems with external pyridine on account of facilitated proton transfer. Moreover, the mechanism of the PCET reaction is altered by the appended bases. A unique feature is that the reaction can be tuned to follow three distinct PCET mechanisms—electron-first, proton-first or a concerted reaction—with very different sensitivities to oxidant and base strength. Such knowledge is crucial for rational improvements of solar fuel catalysts.
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T.L. acknowledges S.D. Glover, R. Fernandez-Teran and S. Wang for fruitful discussions. This work was supported by The Swedish Research Council (grant no. 2016-04271) and The Knut and Alice Wallenberg Foundation (grant no. 2011.0067). Correspondence and requests for materials should be addressed to L.H.
The authors declare no competing interests.
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Supplementary Methods, Supplementary Figures 1–46, Supplementary Tables 1–7, Supplementary Experimental Data, Supplementary Theoretical Data
CIF for compound 3a; CCDC reference: 1552847
CIF for compound 3d; CCDC reference: 1552848
CIF for compound 3e; CCDC reference: 1552849
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Liu, T., Guo, M., Orthaber, A. et al. Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions. Nature Chem 10, 881–887 (2018). https://doi.org/10.1038/s41557-018-0076-x
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