Unusual weakly coordinating anion reactivity in metallocene chemistry. Formation of tantalocene cation-dinuclear anion pairs

Unlike the clean reaction of group 4 metallocene alkyls with B(C6F5)(3), the reaction of Cp2TaMe3 with M(C6F5)(3) (M = B, Al) in benzene or toluene produces an oily product mixture containing the expected Cp2TaMe2+CH3M(C6F5)(3)(-) as well as the unexpected Cp2TaMe2+ [(C6F5)(3)MCH3M(C6F5)(3)](-) in equilibrium, along with unreacted Cp2TaMe3. The surprising reactivity of weakly coordinating anions CH3M(C6F5)(3)(-) in the abstractive metallocene chemistry renders formation of novel mu -Me-bridged dinuclear anions. Subsequently, the reaction of Cp2TaMe3 with 2 equiv of Al(C6F5)(3) cleanly generates the tantalocene cation-dinulcear anion ion pair Cp2TaMe2+ [(C6F5)(3)AlCH3Al(C6F5)(3)](-) as colorless crystals in, a quantitative yield. A crystallographic. study confirms the structure, which reveals unassociated cation-anion pairs' with nearly symmetrical mu -CH3 bridging in the anion portion.