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

Abstract

Combining an electrophilic iron complex [Fe(^F pda)(THF)]₂ (3) [^F pda=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.

Keywords: C−H activation; carbenes; iron; lithium; reaction mechanisms.