Room temperature iron-catalyzed transfer hydrogenation and regioselective deuteration of carbon-carbon double bonds

Maialen Espinal-Viguri, Samuel Neale, Nathan Coles, Stuart Macgregor, Ruth Webster

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An iron catalyst has been developed for the transfer hydrogenation of carbon-carbon multiple bonds. Using a well-defined β-diketiminate iron(II) precatalyst, a sacrificial amine and a borane, even simple, unactivated alkenes such as 1-hexene undergo hydrogenation within 1 h at room temperature. Tuning the reagent stoichiometry allows for semi- and complete hydrogenation of terminal alkynes. It is also possible to hydrogenate aminoalkenes and aminoalkynes without poisoning the catalyst through competitive amine ligation. Furthermore, by exploiting the separate protic and hydridic nature of the reagents, it is possible to regioselectively prepare monoisotopically labeled products. DFT calculations define a mechanism for the transfer hydrogenation of propene with nBuNH 2 and HBpin that involves the initial formation of an iron(II)-hydride active species, 1,2-insertion of propene, and rate-limiting protonolysis of the resultant alkyl by the amine N-H bond. This mechanism is fully consistent with the selective deuteration studies, although the calculations also highlight alkene hydroboration and amine-borane dehydrocoupling as competitive processes. This was resolved by reassessing the nature of the active transfer hydrogenation agent: experimentally, a gel is observed in catalysis, and calculations suggest this can be formulated as an oligomeric species comprising H-bonded amine-borane adducts. Gel formation serves to reduce the effective concentrations of free HBpin and nBuNH 2 and so disfavors both hydroboration and dehydrocoupling while allowing alkene migratory insertion (and hence transfer hydrogenation) to dominate.

Original languageEnglish
Pages (from-to)572-582
Number of pages11
JournalJournal of the American Chemical Society
Issue number1
Early online date5 Dec 2018
Publication statusPublished - 9 Jan 2019

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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