Mechanism of the iron(II)-catalyzed hydrosilylation of ketones

• Verfasst von: Bleith, Tim Manuel [VerfasserIn]
• Verfasst von: Gade, Lutz H. [VerfasserIn]
• Titel: Mechanism of the iron(II)-catalyzed hydrosilylation of ketones
• Titelzusatz: activation of iron carboxylate precatalysts and reaction pathways of the active catalyst
• Verf.angabe: Tim Bleith and Lutz H. Gade
• E-Jahr: 2016
• Jahr: March 24, 2016
• Umfang: 12 S.
• Fussnoten: Gesehen am 13.05.2020
• Titel Quelle: Enthalten in: American Chemical SocietyJournal of the American Chemical Society
• Ort Quelle: Washington, DC : ACS Publications, 1879
• Jahr Quelle: 2016
• Band/Heft Quelle: 138(2016), 14, Seite 4972-4983
• ISSN Quelle: 1520-5126
• DOI: doi:10.1021/jacs.6b02173
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 169811236X

Abstract

A detailed mechanistic study of the catalytic hydrosilylation of ketones with the highly active and enantioselective iron(II) boxmi complexes as catalysts (up to >99% ee) was carried out to elucidate the pathways for precatalyst activation and the mechanism for the iron-catalyzed hydrosilylation. Carboxylate precatalysts were found to be activated by reduction of the carboxylate ligand to the corresponding alkoxide followed by entering the catalytic cycle for the iron-catalyzed hydrosilylation. An Eyring-type analysis of the temperature dependence of the enantiomeric ratio established a linear relationship of ln(S/R) and T-1, indicating a single selectivity-determining step over the whole temperature range from −40 to +65 °C (ΔΔG‡sel, 233 K = 9 ± 1 kJ/mol). The rate law as well as activation parameters for the rate-determining step were derived and complemented by a Hammett analysis, radical clock experiments, kinetic isotope effect (KIE) measurements (kH/kD = 3.0 ± 0.2), the isolation of the catalytically active alkoxide intermediate, and DFT-modeling of the whole reaction sequence. The proposed reaction mechanism is characterized by a rate-determining σ-bond metathesis of an alkoxide complex with the silane, subsequent coordination of the ketone to the iron hydride complex, and insertion of the ketone into the Fe-H bond to regenerate the alkoxide complex.