Abstract
Reaction of CHI3 with six equivalents of CrCl2 in THF at low temperatures affords [Cr3Cl3(μ2‐Cl)3(μ3‐CH)(thf)6] as the first isolable high‐yield CrIII μ3‐methylidyne complex. Substitution of the terminal chlorido ligands via salt metathesis with alkali‐metal cyclopentadienides generates isostructural half‐sandwich chromium(III)‐μ3‐methylidynes [CpR 3Cr3(μ2‐Cl)3(μ3‐CH)] (CpR=C5H5, C5Me5, C5H4SiMe3). Side and decomposition products of the Cl/CpR exchange reactions were identified and structurally characterized for [Cr4(μ2‐Cl)4(μ2‐I)2(μ4‐O)(thf)4] and [(η5‐C5H4SiMe3)CrCl(μ2‐Cl)2Li(thf)2]. The Cl/CpR 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 (CpR=C5Me5). Reactions of [Cr3Cl3(μ2‐Cl)3(μ3‐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 1H NMR spectroscopy.
Highlights
Carbyne or alkylidyne moieties display archetypal ligands in organo(transition)metal chemistry.[1]
The decent yields of the methylidyne complex enabled a series of reactivity studies
The terminal chlorido ligands can be selectively displaced via salt metathesis with alkali-metal cyclopentadienides to afford rare examples of half-sandwich chromium(III) methylidynes, [(h5CpR)3Cr3(m2-Cl)3(m3-CH)]
Summary
Angewandte Chemie International Edition published by Wiley-VCH GmbH Well-defined alkylidene species are just as rare as alkylidyne complexes.[15,16] The most prominent chromium alkylidene complex is Takais olefination/cyclopropanation reagent [Cr2Cl2(m2-Cl)2(m2-CHI)(thf)4] (B, shown in Scheme 1).[16] The active reagent is routinely generated in situ applying the dehalogenation protocol, with CrCl2 and CHX3 (X = Cl, Br, I) as the main components in varying ratios.[17] Recently, we succeeded in determining the solid-state structure of the Takai haloalkylidene complex B,[18] only confirming the connectivity originally proposed by Takai. By taking a closer look at the formation of the Takai olefination reagent, we have uncovered the chromium(III) methylidyne species [Cr3Cl3(m2-. Preliminary conversions of aldehydes or ketones revealed reaction pathways involving radical intermediates
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