Visible-Light-Enhanced Cobalt-Catalyzed Hydrogenation: Switchable Catalysis Enabled by Divergence between Thermal and Photochemical Pathways

Lauren N. Mendelsohn, Connor S. MacNeil, Lei Tian, Yoonsu Park, Gregory D. Scholes, Paul J. Chirik

Research output: Contribution to journalArticlepeer-review

Abstract

The catalytic hydrogenation activity of the readily prepared, coordinatively saturated cobalt(I) precatalyst, (R,R)-(iPrDuPhos)Co(CO)2H ((R,R)-iPrDuPhos = (+)-1,2-bis[(2R,5R)-2,5-diisopropylphospholano]benzene), is described. While efficient turnover was observed with a range of alkenes upon heating to 100 °C, the catalytic performance of the cobalt catalyst was markedly enhanced upon irradiation with blue light at 35 °C. This improved reactivity enabled hydrogenation of terminal, di-, and trisubstituted alkenes, alkynes, and carbonyl compounds. A combination of deuterium labeling studies, hydrogenation of alkenes containing radical clocks, and experiments probing relative rates supports a hydrogen atom transfer pathway under thermal conditions that is enabled by a relatively weak cobalt-hydrogen bond of 54 kcal/mol. In contrast, data for the photocatalytic reactions support light-induced dissociation of a carbonyl ligand followed by a coordination-insertion sequence where the product is released by combination of a cobalt alkyl intermediate with the starting hydride, (R,R)-(iPrDuPhos)Co(CO)2H. These results demonstrate the versatility of catalysis with Earth-abundant metals as pathways involving open-versus closed-shell intermediates can be switched by the energy source.

Original languageEnglish (US)
Pages (from-to)1351-1360
Number of pages10
JournalACS Catalysis
Volume11
Issue number3
DOIs
StatePublished - Feb 5 2021

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

Keywords

  • alkene
  • cobalt
  • hydrogenation
  • radicals
  • switchable mechanism
  • visible light

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