Reversible CO<sub>2</sub> Hydrogenation, Neutron Crystallography, and Hydride Reactivity of a Triiridium Heptahydride Complex
The authors report the structure, reactivity, and catalytic utility of a triiridium complex, [Ir<sub>3</sub>H<sub>6</sub>(μ<sub>3</sub>-H)(PN)<sub>3</sub>]<sup>2+</sup> (2-H, PN = (2-pyridyl)CH<sub>2</sub>PBu<sup>t</sup> <sub>2</sub>). Despite its unusual stability to unsaturated organics, electrophiles, and even CF<sub>3</sub>SO<sub>3</sub>D, they find that complex 2-H catalyzes hydrogenation of CO<sub>2</sub> to formate (TON<sub>Ir</sub> = 9600) and reverse formic acid dehydrogenation (TON<sub>Ir</sub> = 54 400). The hydrogenation operates via a reactive intermediate [Ir<sub>3</sub>H<sub>4</sub>(μ-H)<sub>4</sub>(PN)<sub>3</sub>]<sup>+</sup> (5). Neutron crystallography and DFT-supported neutron vibrational spectroscopy of 2-H reveal Ir─H bond lengths and elucidate the vibration modes within the Ir<sub>3</sub>H<sub>7</sub> core. Stoichiometric oxidation of 2-H produces four classes of iridium complexes of varied nuclearity and hydride structure: tetra- and pentanuclear clusters [Ir<sub>3</sub>H<sub>6</sub>(μ<sub>3</sub>-AuPPh<sub>3</sub>)(PN)<sub>3</sub>]<sup>2+</sup> (2-Au) and [Ag{Ir<sub>2</sub>H<sub>4</sub>(μ-OAc)(PN)<sub>2</sub>}<sub>2</sub>]<sup>3+</sup> (6) are generated using AuPPh<sub>3</sub> <sup>+</sup> and AgOAc, respectively. Further oxidation to class [Ir<sub>2</sub>H<sub>3</sub>(μ-X)<sub>2</sub>(PN)<sub>2</sub>]<sup>+</sup> is possible with AgOAc, Hg(OAc)<sub>2</sub>, or I<sub>2</sub>. Finally, a TEMPO/HCl system completely oxidizes the hydrides and gives [Ir<sub>2</sub>Cl<sub>4</sub>(μ-Cl)<sub>2</sub>(PN)<sub>2</sub>] (11).
Authors
- Yongqiang Q. Cheng (ORCID: https://orcid.org/0000-0002-3263-4812)
- Travis J. Williams (ORCID: https://orcid.org/0000-0001-6299-3747)
- Văn Mãi Đỗ (ORCID: https://orcid.org/0000-0001-8974-0221)
- Anthony J. Chavez (ORCID: https://orcid.org/0000-0003-2357-1060)
- Eric Novak (ORCID: https://orcid.org/0000-0001-7813-1180)
- Valeriy Cherepakhin (ORCID: https://orcid.org/0000-0003-1966-9794)
- Craig M. Brown (ORCID: https://orcid.org/0000-0002-9637-9355)
- Ryan A. Klein (ORCID: https://orcid.org/0000-0002-6807-6701)
- J. A. Kelber
- Xiaoping P. Wang (ORCID: https://orcid.org/0000-0001-7143-8112)
Institutions
- University of Southern California (US)
- Oak Ridge National Laboratory (US)
- National Laboratory of the Rockies (US)
- NIST Center for Neutron Research (US)
- University of Delaware (US)
Publication Details
- Journal
- Angewandte Chemie International Edition
- Published
- 2025-03-11
- DOI
- https://doi.org/10.1002/anie.202501943
- Primary Topic
- Asymmetric Hydrogenation and Catalysis
- Type
- article
- Field-Weighted Citation Impact
- 0.00