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An open-shell Ir(II)/Ir(IV) redox couple outperforms an Ir(I)/Ir(III) pair in olefin isomerization

Nature Chemistry volume 17, pages 606–613 (2025)Cite this article

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Abstract

Open-shell systems based on first-row transition metals and their involvement in various catalytic processes are well explored. By comparison, mononuclear open-shell complexes of precious transition metals remain underdeveloped. This is particularly true for IrII complexes, as there is very limited information available regarding their application in catalysis. Here we show that a family of IrII metalloradicals, featuring a C6H3-2,6-(OP(tBu)2)2 (POCOP) pincer ligand, effectively catalyses olefin isomerization—a key step in alkane metathesis—exhibiting up to 20 times higher activity than their IrI counterparts. Computational studies reveal that the IrII/IrIV redox cycling enables faster kinetics than the traditional IrI/IrIII pathway owing to reduced barriers for the oxidative addition and reductive elimination steps. Thus, this study presents a redox catalyst involving an IrII/IrIV pair, highlighting the capabilites of precious-metal systems that extend beyond traditional redox cycles. These findings emphasize the need for expanding catalytic design principles, especially for platinum-group metals.

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Fig. 1: Closed-shell versus open-shell catalytic cycle for a mononuclear iridium catalyst.
Fig. 2: Synthesis and characterization of IrII complexes.
Fig. 3: Mechanism for olefin isomerization comparing IrI versus IrII.
Fig. 4: Activation strain and EDAs of the C–H oxidative addition step.

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Data availability

All data supporting the findings of this study are available within the Article and its Supplementary Information. Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers CCDC 2352734 (2·BF4), 2352735 (2·NTf2), 2352737 ([2·C2H4][BArF]) and 2352737 (2·Cl). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. Atomic coordinates of the optimized computational models are provided in Supplementary Data 1–5. Source data are provided with this paper.

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Acknowledgements

The project that gave rise to these results received the support of a fellowship from ‘laCaixa’ Foundation (ID 100010434; fellowship code B005930; A.P.-M.). This work was also supported by the Spanish MCIN/AEI/10.13039/501100011033 (grants PID2022-139782NB-I00, J.C.; PID2022-139318NB-I00, I.F.; TED2021-132225B-I00, J.C. and RED2022-134287-T, J.C. and I.F.). We acknowledge support from the European Commission under Marie Skłodowska-Curie fellowships, project numbers 101067947 (TRUFA, J.J.M.) and 101109769 (READHY, N.H.). We acknowledge the use of CESGA computational facilities. T. J. Gerard and P. L. Holland are acknowledged for their help with EPR spectroscopy. E. Carmona is acknowledged for helpful discussions.

Author information

Authors and Affiliations

  1. Instituto de Investigaciones Químicas, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Sevilla, Spain

    Alejandra Pita-Milleiro, Nereida Hidalgo, Juan J. Moreno & Jesús Campos

  2. Departamento de Química Orgánica and Centro de Innovación en Química Avanzada, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Madrid, Spain

    Israel Fernández

Authors
  1. Alejandra Pita-Milleiro
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  2. Nereida Hidalgo
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Contributions

A.P.-M. and N.H. carried out the experimental work: synthesis and characterization of new complexes, reactivity studies, catalytic and kinetic investigations and substrate scope. A.P.-M., J.J.M. and I.F. carried out the computational studies. J.C. supervised the overall work and wrote the manuscript with participation of all authors.

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Correspondence to Jesús Campos.

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Extended data

Extended Data Fig. 1 Monitoring olefin isomerization with IrI and IrII.

Conversion of 1-octene at 125 °C (dashed line) or 1-hexene at 70 °C (solid line) over time mediated by 1 (blue) and after adding 1 equivalent of Ag[BArF] (pink).

Extended Data Fig. 2 Computational mechanistic profile for N2/olefin ligand substitution in IrI vs IrII.

Free energy profile for the dissociation of N2 and coordination of 1-hexene. For clarity, only the structures for the IrII are drawn. Level of theory: PBE0-D3/LANL2TZ(Ir) augmented by a diffuse d-type function (exponent=0.07645)/6-311 G(d,p) all other atoms.

Extended Data Fig. 3 Kinetic profiles.

a) Initial rates plot: Ln of the initial rate, v0, of the isomerization of 1-hexene (M) vs Ln of the initial concentration of 1-hexene, v0 in M·s-1, [1-hexene]0 in M. b) Eyring plot: Ln of k/T vs 1/T·103, k in s-1·M-1, T in K, t in s.

Supplementary information

Supplementary Information

Data relating to the characterization of iridium compounds, NMR, UV–vis and EPR spectra, kinetic and mechanistic studies, crystal structure determination and computational studies.

Supplementary Data 1

Crystallographic data for structure 2·BF4 (CCDC 2352734).

Supplementary Data 2

Crystallographic data for structure 2·NTf2 (CCDC 2352735).

Supplementary Data 3

Crystallographic data for structure 2·C2H4][BArF] ((CCDC 2352736).

Supplementary Data 4

Crystallographic data for structure 2·Cl (CCDC 2352737).

Supplementary Data 5

Atomic coordinates of the optimized computational model.

Source data

Source Data Fig. 2

Source data for Fig. 2.

Source Data Fig. 4

Source data for Fig. 4.

Source Data Extended Data Fig./Table 1

Source data for Extended Data Fig. 1.

Source Data Extended Data Fig./Table 3

Source data for Extended Data Fig. 3.

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Pita-Milleiro, A., Hidalgo, N., Moreno, J.J. et al. An open-shell Ir(II)/Ir(IV) redox couple outperforms an Ir(I)/Ir(III) pair in olefin isomerization. Nat. Chem. 17, 606–613 (2025). https://doi.org/10.1038/s41557-024-01722-7

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