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Protolysis of Seven-Membered Zirconacyclocumulene Complexes of Zirconocene

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journal contribution
posted on 15.06.2020 by Vladimir V. Burlakov, Maxim V. Andreev, Vyacheslav S. Bogdanov, Perdita Arndt, Wolfgang Baumann, Anke Spannenberg, Uwe Rosenthal, Vladimir B. Shur
The interaction of the seven-membered zirconacyclocumulene complex Cp2Zr­[η4-Me3SiC4(SiMe3)–C­(C2SiMe3)=CSiMe3] (1) with an equimolar amount of HCl in dioxane at 20 °C results in the formation of the complex Cp2Zr­(Cl)–C­(CCSiMe3)C­(SiMe3)–C­(CCSiMe3)=CH­(SiMe3) (4), wherein one of the CC groups is coordinated with the Zr atom. Under similar conditions, the reaction of 1 with an excess of HCl affords Cp2ZrCl2 and a mixture cis,cis- and cis,trans-unsaturated compounds H­(Me3Si)­CC­(C2SiMe3)–C­(SiMe3)CH­(C2SiMe3) (5) and H­(Me3Si)­CC­(C2SiMe3)–C­(SiMe3)C­(H)­C2SiMe3 (6). The isomeric seven-membered zirconacyclocumulene Cp2Zr­[η4-Me3SiC4(SiMe3)–C­(SiMe3)C­(C2SiMe3)] (2) reacts with 2 equiv of HCl in dioxane to give Cp2ZrCl2, H­(Me3SiC2)­CC­(SiMe3)–C­(SiMe3)C­(C2SiMe3)H (7), and H­(Me3SiC2)­CC­(SiMe3)–C­(SiMe3)CCC­(SiMe3)H (8). The subsequent reaction of this mixture with Mg in THF yields zirconabicycles 9 and 10, respectively, containing fused zirconacyclopentadiene and cyclohexadiene rings, and, correspondingly, zirconacyclopentene and cyclopentadiene cycles. From the interaction of 7 with Cp*2ZrCl2 and Mg in THF, complex 11, analogous to 9, was isolated. The protolysis of the seven-membered zirconacyclocumulene Cp2Zr­[η4-PhC4(Ph)–(o-C6H4)] (3) with 2 equiv of HCl yields Cp2ZrCl2 and Ph2CC­(H)–CCPh (16). The structures of 4, 7, 10, and 11 have been established by X-ray crystallography. The mechanisms of the reactions found are discussed.