Electrophilic Iron Catalyst Paired with a Lithium Cation Enables Selective Functionalization of Non-Activated Aliphatic C?H Bonds via Metallocarbene Intermediates

Article abstract of DOI:10.1002/anie.201905986

Combining an electrophilic iron complex [Fe(^Fpda)(THF)]₂ (3) [^Fpda=N,N′-bis(pentafluorophenyl)-o-phenylenediamide] with the pre-activation of α-alkyl-substituted α-diazoesters reagents by LiAl(OR^F)₄ [OR^F=(OC(CF₃)₃] provides unprecedented access to selective iron-catalyzed intramolecular functionalization of strong alkyl C(sp³)?H bonds. Reactions occur at 25 °C via α-alkyl-metallocarbene intermediates, and with activity/selectivity levels similar to those of rhodium carboxylate catalysts. Mechanistic investigations reveal a crucial role of the lithium cation in the rate-determining formation of the electrophilic iron-carbene intermediate, which then proceeds by concerted insertion into the C?H bond.