Interaction of the buchwald seven-membered zirconacyclocumulene complex with carbonyl compounds

The interaction of the Buchwald seven-membered zirconacyclocumulene Cp2Zr[4-Me3SiC4(SiMe3)-C(C2SiMe3)=CSiMe3] (1) with a 2-fold excess of benzophenone in toluene at 100 °C for 20 h results in the formation of Me3SiCC-CCSiMe3 and a nine-membered dioxazirconacycle Cp2Zr[2-OC(Ph)2C(SiMe3)C2C(SiMe3)C(Ph)2O] (5) containing [3]cumulene group in the ring. Analogous metallacycle (6) is formed on heating of 1 with fluorenone in toluene at 100 °C. A treatment of 5 with HCl in dioxane at 20 °C affords Cp2ZrCl2 and cis-[3]cumulenic diol Ph2(HO)C(Me3Si)CC2C(SiMe3)C(OH)Ph2 (7) in 85% yield. The reaction of 1 with benzil (PhCO)2 at 80 °C in benzene proceeds differently than with benzophenone and fluorenone. In this case, a nine-membered dioxazirconacycle Cp2Zr[2-Me3SiCaC(C2SiMe3)-C(SiMe3) C(C2SiMe3)OC(Ph) C(Ph)O] (10) is produced. The nature of products formed in the interaction of 1 with acenaphthenequinone proved to be temperature dependent. Thus, on carrying out the reaction at 20 °C, an 11-membered trioxazirconacycle (11) containing three CaC bonds in the ring was isolated from the mixture, whereas at 80 °C the reaction gave a ten-membered tetraoxadizirconacycle (12) and octasubstituted cyclooctatetraene [(Me3Si)CaC(CCSiMe3)]4 (13). The structures of 5-7 and 10-13 have been determined by X-ray diffraction. The mechanism of the reactions found is discussed. © 2019 American Chemical Society.