Beyond Takai's Olefination Reagent: Persistent Dehalogenation Emerges in a Chromium(III)-μ3-Methylidyne Complex

Reaction of CHI3 with six equivalents of CrCl2 in THF at low temperatures affords [Cr3Cl3(mu(2)-Cl)(3)(mu(3)-CH)(thf)(6)] as the first isolable high-yield Cr-III mu(3)-methylidyne complex. Substitution of the terminal chlorido ligands via salt metathesis with alkali-metal cyclopentadienides generates isostructural half-sandwich chromium(III)-mu(3)-methylidynes [Cp(R)(3)Cr-3(mu(2)-Cl)(3)(mu(3)-CH)] (Cp(R)=C5H5, C5Me5, C5H4SiMe3). Side and decomposition products of the Cl/Cp(R) exchange reactions were identified and structurally characterized for [Cr-4(mu(2)-Cl)(4)(mu(2)-I)(2)(mu(4)-O)(thf)(4)] and [(eta(5)-C5H4SiMe3)CrCl(mu(2)-Cl)(2)Li(thf)(2)]. The Cl/Cp(R) exchange drastically changed the ambient-temperature effective magnetic moment mu(eff) from 9.30/9.11 mu(B) (solution/solid) to 3.63/4.32 mu(B) (Cp(R)=C5Me5). Reactions of [Cr3Cl3(mu(2)-Cl)(3)(mu(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 H-1 NMR spectroscopy.

Automated summary

The reaction of CHI3 with six equivalents of CrCl2 at low temperatures resulted in the first isolable high-yield Cr-III mu(3)-methylidyne complex. Substitution of terminal chlorido ligands with alkali-metal cyclopentadienides produced isostructural half-sandwich chromium(III)-mu(3)-methylidynes. Side and decomposition products of the Cl/Cp(R) exchange reactions were identified and characterized.