Using sterically demanding Cp′ (Cp′ = η 5 -1,2,4-t Bu 3 C 5 H 2 ) as auxiliary ligands, coordinatively unsaturated thiolate-bridged Cr II Cr II complexes were obtained by a facile salt metathesis strategy. This dichromium system with vacant coordination sites can easily cleave the two carbon−halogen bonds of dihalomethane by a cooperative activation effect. Meanwhile, it can accommodate the resulting methylene moiety and two halide groups. Notably, an unprecedented thiolate-bridged Cr III Cr III methylene complex was successfully isolated and unambiguously characterized by X-ray crystallography. Unlike the common chemical inertness of the {Cr−CH 2 −Cr} subunit, this bridging methylene fragment not only can interact with CH 2 Br 2 to give ethylene but can also transfer to styrene to generate the corresponding cyclopropanated product. In addition, the Cr III Cr III complex containing two halides can be easily reduced by mild Zn powder to regenerate the initial Cr II Cr II complex. Furthermore, this [Cr 2 S 2 ] reaction scaffold can catalyze the cyclopropanation of styrenes using CH 2 Br 2 as the methylene source.
Several thiolate‐bridged dichromium complexes with Cp* (Cp*=η5‐C5Me5) as auxiliary ligands were designed and synthesized through the salt metathesis, which all contain two six‐coordinate chromium centers in the formal valence of +3. These complexes are all paramagnetic species, which are in good agreement with the experimental results that broad and paramagnetically shifted proton resonances appear in the 1H NMR spectra. Furthermore, variable‐temperature solid‐state magnetic susceptibility studies reveal the two chromium centers of these complexes are both in an S=3/2 high‐spin state with a strong antiferromagnetic coupling. Simulated values of antiferromagnetic coupling constant for these complexes are directly related to the distances of the two CrIII centers confirmed by X‐ray crystallography. In addition, in the presence of dehalogenation agent AgPF6, complexes [Cp*CrCl(μ‐SR)2CrClCp*] (3, R=Et; 4, R=iPr) and [Cp*Cr(μ‐Cl)(μ‐SEt)2CrCp*][BPh4] (5) containing easily removable chloride can achieve the catalytic oxidation of organic substrates, such as PPh3, 1,4‐cyclohexadiene and 1,2‐diphenylhydrazine under an oxygen atmosphere.
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