Beyond Takai's Olefination Reagent: Persistent Dehalogenation Emerges in a Chromium(III)‐μ(3)‐Methylidyne Complex

Reaction of CHI(3) with six equivalents of CrCl(2) in THF at low temperatures affords [Cr(3)Cl(3)(μ(2)‐Cl)(3)(μ(3)‐CH)(thf)(6)] as the first isolable high‐yield Cr(III) μ(3)‐methylidyne complex. Substitution of the terminal chlorido ligands via salt metathesis with alkali‐metal cyclopentadienides generates isostructural half‐sandwich chromium(III)‐μ(3)‐methylidynes [Cp(R) (3)Cr(3)(μ(2)‐Cl)(3)(μ(3)‐CH)] (Cp(R)=C(5)H(5), C(5)Me(5), C(5)H(4)SiMe(3)). Side and decomposition products of the Cl/Cp(R) exchange reactions were identified and structurally characterized for [Cr(4)(μ(2)‐Cl)(4)(μ(2)‐I)(2)(μ(4)‐O)(thf)(4)] and [(η(5)‐C(5)H(4)SiMe(3))CrCl(μ(2)‐Cl)(2)Li(thf)(2)]. The Cl/Cp(R) exchange drastically changed the ambient‐temperature effective magnetic moment μ (eff) from 9.30/9.11 μ (B) (solution/solid) to 3.63/4.32 μ (B) (Cp(R)=C(5)Me(5)). Reactions of [Cr(3)Cl(3)(μ(2)‐Cl)(3)(μ(3)‐CH)(thf)(6)] with aldehydes and ketones produce intricate mixtures of species through oxy/methylidyne exchange, which were partially identified as radical recombination products through GC/MS analysis and (1)H NMR spectroscopy.