Protolysis of Seven-Membered Zirconacyclocumulene Complexes of Zirconocene

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The interaction of the seven-membered zirconacyclocumulene complex Cp 2 Zr[η 4 -Me 3 SiC 4 (SiMe 3 )–C(C 2 SiMe 3 )=CSiMe 3 ] ( 1 ) with an equimolar amount of HCl in dioxane at 20 °C results in the formation of the complex Cp 2 Zr(Cl)–C(C≡CSiMe 3 )═C(SiMe 3 )–C(C≡CSiMe 3 )=CH(SiMe 3 ) ( 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 Cp 2 ZrCl 2 and a mixture cis, cis- and cis, trans -unsaturated compounds H(Me 3 Si)C═C(C 2 SiMe 3 )–C(SiMe 3 )═CH(C 2 SiMe 3 ) ( 5 ) and H(Me 3 Si)C═C(C 2 SiMe 3 )–C(SiMe 3 )═C(H)C 2 SiMe 3 ( 6 ). The isomeric seven-membered zirconacyclocumulene Cp 2 Zr[η 4 -Me 3 SiC 4 (SiMe 3 )–C(SiMe 3 )═C(C 2 SiMe 3 )] ( 2 ) reacts with 2 equiv of HCl in dioxane to give Cp 2 ZrCl 2, H(Me 3 SiC 2 )C═C(SiMe 3 )–C(SiMe 3 )═C(C 2 SiMe 3 )H ( 7 ), and H(Me 3 SiC 2 )C═C(SiMe 3 )–C(SiMe 3 )═C═C═C(SiMe 3 )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* 2 ZrCl 2 and Mg in THF, complex 11, analogous to 9, was isolated. The protolysis of the seven-membered zirconacyclocumulene Cp 2 Zr[η 4 -PhC 4 (Ph)–( o -C 6 H 4 )] ( 3 ) with 2 equiv of HCl yields Cp 2 ZrCl 2 and Ph 2 C═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.