{"doi":"10.1073/pnas.2502484122","title":"On the mechanism of photodriven hydrogenations of N <sub>2</sub> and other substrates by Hantzsch ester: Buffer is key to reactive H-atom donors","abstract":"The Hantzsch ester (HEH 2 ) has found considerable utility as a photoreductant in synthesis, with photodriven transfer hydrogenation reactions typically limited to activated substrates. We recently established that the addition of an organic buffer of collidinium triflate [(ColH)OTf] and collidine (Col) allows photodriven transfer hydrogenation from HEH 2 to N 2 forming NH 3 (nitrogen reduction; N 2 R) in the presence of a Mo catalyst. Given the requirements for Mo-catalyzed thermally driven N 2 R, this result suggested the generation of a significant driving force for proton-coupled electron transfer (PCET) when irradiating HEH 2 in the presence of Col-buffer. In this study, we probe how Col-buffer enables efficient photodriven proton-coupled reductions with HEH 2 . Wavelength-dependent NH 3 yields are consistent with HEH 2 photoexcitation, and the combination of HEH 2 with Col-buffer is privileged. Data are presented, suggesting that HEH 2 is statically quenched via ET to [ColH]OTf through an H-bonded association complex to release ColH • and [HEH 2 ] •+ . Transient absorbance data and EPR studies establish that the resulting [HEH 2 ] •+ intermediate is rapidly deprotonated by Col to yield HEH • , in net furnishing HEH • and ColH • as potent H-atom donors. Broader utility of this reagent combination is demonstrated in the photoreduction of a range of C=O and N=O π-bonds by HEH 2 , with a significant boost in rates and yield, and altered reactivity, observed on addition of Col-buffer. ColH • is posited as the most potent PCET donor generated (BDFE N−H of 28 kcal mol −1 ).","journal":"Proceedings of the National Academy of Sciences","year":2025,"id":526078,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":3,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9519,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1401148,"name":"Elisabetta Benazzi","orcid":"0000-0001-6756-3842","position":1,"is_corresponding":false},{"id":25233,"name":"Jonas C. Peters","orcid":"0000-0002-6610-4414","position":2,"is_corresponding":false},{"id":995731,"name":"Christian M. Johansen","orcid":"0000-0003-0066-4424","position":0,"is_corresponding":true}],"reference_count":74,"raw_metadata":null,"created_at":"2026-07-19T02:50:25.860105Z","pmid":"40560619","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}