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Cyclopentadienyl (Cp), a classic ancillary ligand platform, can be chemically noninnocent in electrocatalytic H−H bond formation reactions via protonation of coordinated η5-Cp ligands to form η4-CpH moieties. However, the kinetics of η5-Cp ring protonation, ligand-to-metal (or metal-to-ligand) proton transfer, and the influence of solvent during H2 production electrocatalysis remain poorly understood. We report in-depth kinetic details for electrocatalytic H2 production with Fe complexes containing amine-functionalized CpN3 ligands that are protonated via exogenous acid to generate via η4-CpN3H intermediates (CpN3 = 6-amino-1,4-dimethyl-5,7-diphenyl-2,3,4,6-tetrahydrocyclopenta[b]pyrazin-6-yl). Under reducing conditions, state-of-the-art DFT calculations reveal that a coordinated solvent plays a crucial role in mediating stereo- and regioselective proton transfer to generate (endo-CpN3H)Fe(CO)2(NCMe), with other protonation pathways being kinetically insurmountable. To demonstrate regioselective endo-CpN3H formation, the isoelectronic model complex (endo-CpN3H)Fe(CO)3 is independently prepared, and kinetic studies with the on-cycle hydride intermediate CpN3FeH(CO)2 under CO cleanly furnish the ring-activated complex (endo-CpN3H)Fe(CO)3 via metal-to-ligand proton migration. The on-cycle complex CpN3FeH(CO)2 reacts with acid to release H2 and regenerate [CpN3Fe(CO)2(NCMe)]+, which was found to be the TOF-determining step via DFT. Collectively, these experimental and computational results underscore the emerging importance of Cp ring activation, inner-sphere solvation, and metal−ligand cooperativity to perform proton-coupled electron transfer catalysis for chemical fuel synthesis.
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This content will become publicly available on July 30, 2026
Primary and Secondary Coordination Sphere Lewis Acid Interactions in β-Phosphinoethylborane-ligated Rhodium and Iridium Complexes
Flexible ambiphilic ligand scaffolds have garnered attention in catalysis due to their ability to adopt multiple binding orientations. Recently, several platinum group metal complexes featuring the flexible, ambiphilic b-phosphinoethylborane ligand were reported in the literature; however, the impact of primary coordination sphere ligands and solvent on the properties of the Lewis acidic borane moiety remain underexplored. Rhodium and iridium complexes ligated by 9-borabicyclo[3.3.1]nonanyl-based b- diphenylphosphinoethylborane were studied using a combination of crystallography and 11B NMR spectroscopy. The studies revealed that both the primary coordination sphere and solvent had an impact on the formation of Lewis acid–base adducts. Specifically, inner-sphere Lewis pair formation was dependent on the nature of the X-type ligand bound to the metal center. Similar dependencies were identified with solvents in which Lewis acid interaction was found to correlate with solvent donor number.
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- PAR ID:
- 10621137
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- New Journal of Chemistry
- ISSN:
- 1144-0546
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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