Protolysis of five-membered metallacyclocumulene complexes of zirconocene and hafnocene

The reactions of the five-membered metallacyclocumulene complexes Cp₂M[η⁴Bu^tC₄Bu^t] (M = Zr, Hf) with an equimolar amount of HCl in dioxane at 20 °C result in linear complexes Cp₂M(Cl)–C(Bu^t)=CH–C≡CBu^t, whereas the reaction with an excess of HCl affords Cp₂MCl₂ and trans-Bu^tCH=CH–C≡CBu^t. The reaction of the latter hydrocarbon with an equivalent amount of the bis(trimethylsilyl)acetylene complex of zirconocene Cp₂Zr(Me₃SiC₂SiMe₃)(Py) leads to bis(trimethylsilyl)acetylene and a five-membered zircona-cycloallene complex. This complex can also be obtained in ‘one-pot’ via the reactions of five-membered zircona-cyclocumulene with two equivalents of HCl and subsequent treatment with magnesium in THF.