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The interaction of the Buchwald seven-membered zirconacyclocumulene Cp 2 Zr[η 4 -Me 3 SiC 4 (SiMe 3 )− C(C 2 SiMe 3 )=CSiMe 3 ] (1) with a 2-fold excess of benzophenone in toluene at 100 °C for 20 h results in the formation of Me 3 SiCC−CCSiMe 3 and a nine-membered dioxazirconacycle Cp 2 Zr[η 2 -OC(Ph) 2 C(SiMe 3 )C 2 C(SiMe 3 )C(Ph) 2 O] (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 Cp 2 ZrCl 2 and cis-[3]cumulenic diol Ph 2 (HO)C(Me 3 Si)-CC 2 C(SiMe 3 )C(OH)Ph 2 (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 Cp 2 Zr[η 2 -Me 3 SiCC(C 2 SiMe 3 )− C(SiMe 3 )C(C 2 SiMe 3 )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 CC bonds in the ring was isolated from the mixture, whereas at 80 °C the reaction gave a ten-membered tetraoxadizirconacycle (12) and octasubstituted cyclooctatetraene [(Me 3 Si)CC(CCSiMe 3 )] 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.

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