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Visible light enables catalytic formation of weak chemical bonds with molecular hydrogen


The synthesis of weak chemical bonds at or near thermodynamic potential is a fundamental challenge in chemistry, with applications ranging from catalysis to biology to energy science. Proton-coupled electron transfer using molecular hydrogen is an attractive strategy for synthesizing weak element–hydrogen bonds, but the intrinsic thermodynamics presents a challenge for reactivity. Here we describe the direct photocatalytic synthesis of extremely weak element–hydrogen bonds of metal amido and metal imido complexes, as well as organic compounds with bond dissociation free energies as low as 31 kcal mol−1. Key to this approach is the bifunctional behaviour of the chromophoric iridium hydride photocatalyst. Activation of molecular hydrogen occurs in the ground state and the resulting iridium hydride harvests visible light to enable spontaneous formation of weak chemical bonds near thermodynamic potential with no by-products. Photophysical and mechanistic studies corroborate radical-based reaction pathways and highlight the uniqueness of this photodriven approach in promoting new catalytic chemistry.

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Fig. 1: Strategies to synthesize weak chemical bonds.
Fig. 2: Proof-of-concept for photoinduced catalytic PCET using H2.
Fig. 3: N–H and O–H bond formation by catalytic PCET using H2 as the reductant.
Fig. 4: Mechanistic investigations.
Fig. 5: Photophysical studies on the excited states of Ir2.
Fig. 6: General applicability of photoinduced catalytic PCET of H2.

Data availability

The data that support the findings of this study are included with the Article and Supplementary Information. Crystallographic data for the structure of Ir5 reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition number CCDC 2021155. Copies of the data can be obtained free of charge via data are provided with this paper.


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This research was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Catalysis Science Program, under Award DE-SC0006498 and the Andlinger Center for Energy and the Environment (Princeton University). S.K. acknowledges a Samsung Scholarship for partial financial support. L.T. and G.D.S. acknowledge support from the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the US DOE through Grant No. DE-SC0019370. G.D.S. is a CIFAR Fellow in the Bio-Inspired Energy Program. We are grateful to K. Conover (Princeton University) for assistance with photo-NMR experiments and L. Mendelsohn and D. Wang (Princeton University) for helpful discussions.

Author information




Y.P., S.K. and P.J.C. conceived the project and designed the initial experiments. Y.P. and P.J.C. wrote the manuscript. Y.P. performed experiments regarding the synthesis and characterization of the metal complexes and the organic compounds and computational calculations. Y.P. and L.T. performed photophysical measurements under the supervision of G.D.S. Single-crystal X-ray diffraction analysis was performed by H.Z. All authors analysed the data, discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Paul J. Chirik.

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Extended data

Extended Data Fig. 1

Gibbs free energy surface of the catalytic process was estimated based on thermochemical data from photophysical measurements and computational analysis.

Supplementary information

Supplementary Information

Supplementary Figs. 1–71, Note 1, Tables 1–10.

Supplementary Data

Source data

Source Data Fig. 2

Plot of data points for Fig. 2c,d.

Source Data Fig. 4

Plot of data points for Fig. 4d and its inset.

Source Data Fig. 5

Plot of data points for Fig. 5a,c and its inset.

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Park, Y., Kim, S., Tian, L. et al. Visible light enables catalytic formation of weak chemical bonds with molecular hydrogen. Nat. Chem. 13, 969–976 (2021).

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