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Enzyme-like water preorganization in a synthetic molecular cleft for homogeneous water oxidation catalysis

Abstract

Inspired by the proficiency of natural enzymes, mimicking of nanoenvironments for precise substrate preorganization is a promising strategy in catalyst design. However, artificial examples of enzyme-like activation of H2O molecules for the challenging oxidative water splitting reaction are hardly explored. Here, we introduce a mononuclear Ru(bda) complex (M1, bda = 2,2′-bipyridine-6,6′-dicarboxylate) equipped with a bipyridine-functionalized ligand to preorganize H2O molecules in front of the metal centre as in enzymatic clefts. The confined pocket of M1 accelerates chemically driven water oxidation at pH 1 by facilitating a water nucleophilic attack pathway with a remarkable turnover frequency of 140 s−1 that is comparable to the oxygen-evolving complex of photosystem II. Single crystal X-ray analysis of M1 under catalytic conditions allowed the observation of a seventh H2O ligand directly coordinated to a RuIII centre. Another H2O substrate is preorganized via a well-defined hydrogen-bonding network for the crucial O–O bond formation by nucleophilic attack.

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Fig. 1: Enzyme-mimetic approach and synthesis of mononuclear Ru(bda) complexes.
Fig. 2: Chemical and photochemical water oxidation catalysis with M1 and M2.
Fig. 3: pD-Dependent 1H NMR experiments of M1 and M2.
Fig. 4: Single-crystal X-ray structures of M1, M2 and [(M1 + H)(H2O)]2+(PF6)2.
Fig. 5: Three different states for the hydrogen-bonding network inside [(M1 + H)(H2O)]2+(PF6)2.
Fig. 6: Mechanisms for water oxidation catalysis and proposed key intermediates for M1 and M2.

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Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2157734 (M1), 2157733 (M2) and 2157735 ([(M1 + H)(H2O)]2+(PF6)2). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/structures/. All other source data are available from the authors upon reasonable request.

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Acknowledgements

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program (grant agreement No. 787937). The authors thank M. Roth for synthetic support and K. Shoyama for valuable discussions on X-ray crystallography.

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Contributions

F.W. initiated the project and supervised it together with F.B. All experiments including the synthesis, NMR studies, the characterization of the catalytic properties and the growth of the single crystals for crystallographic analysis were performed by N.N. The crystallographic measurements and analysis were conducted by A.-M.K. All authors contributed to writing the manuscript.

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Correspondence to Frank Würthner.

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Supplementary information

Supplementary Information

Details of synthesis, characterization, catalytic, electrochemical, spectroscopic and crystallographic results of M1 and M2. Supplementary Methods, Notes 1–4, Tables 1–6, Figs. 1–55 and references.

Supplementary Data 1

Crystal structure of M1 @ pH 1.

Supplementary Data 2

Crystal structure of M1 @ pH 7.

Supplementary Data 3

Crystal structure of M2 @ pH 7.

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Noll, N., Krause, AM., Beuerle, F. et al. Enzyme-like water preorganization in a synthetic molecular cleft for homogeneous water oxidation catalysis. Nat Catal 5, 867–877 (2022). https://doi.org/10.1038/s41929-022-00843-x

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