Unusually Mild and Selective Hydrocarbon C-H Bond Activation with Positively Charged Iridium(III) Complexes

Abstract

Certain transition metal complexes can react to break normally inert carbon-hydrogen (C-H) bonds, but these metal-based processes typically require photochemistry or elevated temperatures. In addition, most are unselective toward complicated functionalized substrates, which has limited their synthetic usefulness. The cationic iridium complex Cp*(P(CH₃)₃)Ir(CH₃)(ClCH₂Cl)⁺BAr_f⁻ [Cp* = η⁵-C₅(CH₃)₅, BAr_f = B(3,5-C₆H₃(CF₃)₂)₄] can thermally activate methane and terminal alkanes at unprecedentedly mild temperatures (10°C). This complex will also induce C-H activation reactions in various functionalized substrates at ambient temperatures. High steric and electronic selectivity is observed, leading invariably to only one reaction product; the initial C-H activation reaction is typically followed by rapid metal-based rearrangements (that is, functionalization).