Alkylidene complexes of heavy group 6 metals (Mo and W) are well known for their reactivity in olefin metathesis. However, chromium(VI) alkylidenes are very rare. No crystal structure has been reported for this kind of complex to date. Here, we describe the synthesis and structural characterization of two chromium(VI) alkylidenes, namely (ArN)2Cr(=CHCMe3)(PPh3) and (ArN)2Cr(=CHSiMe3)(PPh3) (aryl = 2,6-diisopropylphenyl). Both were synthesized from the corresponding dialkyls, (ArN)2Cr(CH2CMe3)2 and (ArN)2Cr(CH2SiMe3)2, in the presence of triphenylphosphine. It is worth noting that the former can activate SiMe4 to form (ArN)2Cr(CH2CMe3)(CH2SiMe3) and (ArN)2Cr(CH2SiMe3)2. The likely mechanism involves α-H elimination to form a 3-coordinate (ArN)2Cr(=CHCMe3) intermediate, which undergoes C-H activation of ambient solvent.

Synthesis, characterization and reactivity of chromium(VI) alkylidene complexes

255th National Meeting (2018)

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