Protolysis of five-membered metallacyclocumulene complexes of zirconocene and hafnocene

The reactions of the five-membered metallacyclocumulene complexes Cp2M[h4-ButC4But] (M = Zr, Hf) with an equimolar amount of HCl in dioxane at 20 degrees C result in linear complexes Cp2M(Cl)-C(But)=CH-C=CBut, whereas the reaction with an excess of HCl affords Cp2MCl2 and trans- ButCH=CH-C=CBut. 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.