{
  "abstract": "Molybdenum complexes supported by phosphine–ligand–phosphine (PLP) pincers, combined with samarium diiodide and water, convert dinitrogen to ammonia under mild conditions with nitrogenase-like activities. Using explicitly correlated coupled-cluster calculations, spin–orbit corrections, and realistic concentration and speciation models, we elucidate the cleavage mechanism from N 2 -bound Mo(I) complexes to ammonia release. Dimerisation proceeds through pentacoordinate Mo(I)–N 2 complexes, and N 2 activation is controlled by terminal N 2 dissociation, which converts a [Mo]–N≡N–[Mo] unit into cleavage-ready [Mo]=N=N=[Mo] before spin crossover and bond scission. The resulting nitrido intermediates are reduced by outer-sphere, Sm-mediated concerted proton-coupled electron transfer (cPCET). This pathway avoids the high-energy charge-separated intermediates of stepwise PT/ET and the loss of strong azaphilic Sm(III)–N interactions upon Sm–OH formation in inner-sphere alternatives. Aggregation into ammonia-binding Sm(III) hydroxide oligomers and precipitation stabilise the product states and render reduction effectively irreversible. These features explain the exceptional activity of Mo/SmI 2 /H 2 O systems. The first cPCET is rate-determining under typical conditions, whereas N 2 activation becomes limiting at low catalyst concentrations or with electron-withdrawing ligands. Pincer geometry and π-acidity facilitate cPCET, but efficient catalysis requires ligands that avoid over-stabilising low Mo oxidation states during N 2 activation while accommodating changing coordination numbers across the cycle.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Chemistry, University of Bergen, Allégaten 41, Bergen, Norway, 5072"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 3,
  "authors": [
    {
      "name": "Jonas Himmelstrup",
      "orcid": "0000-0001-6168-5128"
    },
    {
      "name": "Leif E. Hertwig",
      "orcid": "0009-0001-3690-2124"
    },
    {
      "affs": [
        0
      ],
      "name": "Vidar Remi Jensen",
      "orcid": "0000-0003-2444-3220"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3d4zq67nzhgr3.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15008872/v1",
  "fulltext_url": null,
  "id": "3d4zq67nzhgr3",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008872/v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "1503|Ammonia Synthesis and Nitrogen Reduction"
    ]
  ],
  "openalex": "W7213328440",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15008872/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-15",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/3d4zq67nzhgr3.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:19Z",
      "native_id": "10.26434/chemrxiv.15008872",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008872/v1"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:1503|Ammonia Synthesis and Nitrogen Reduction",
      "subfield": "catalysis"
    }
  ],
  "title": "Origin of the Exceptional Activity in Molybdenum-Catalysed Dinitrogen Reduction with Samarium Diiodide and Water",
  "title_text": "Origin of the Exceptional Activity in Molybdenum-Catalysed Dinitrogen Reduction with Samarium Diiodide and Water",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:19Z",
  "url": "https://research.draconitic.com/paper/3d4zq67nzhgr3",
  "venue": "ChemRxiv",
  "versions": []
}