CC and CN Coupling of Nitriles Mediated by B(C6F5)3 and Cp2ZrPh2

Syntheses and structural characterizations of various zirconocenes have been explored from the reaction of the Cp2ZrPh2 precursor and nitriles (RCN) in the absence or in the presence of B(C6F5)3. In the absence of B(C6F5)3, the thermolysis of Cp2ZrPh2 with RCN affords azametallacyclic dimer complexes [Cp2Zr{C6H4(RCN)}]2 (1, R = CH3; 2, p-F3C-C6H4). Reaction of complex 2 with 1 equiv of B(C6F5)3 in toluene gives the monomeric borane adduct [Cp2Zr{η2-C,N-C6H4C(F3CC6H4)N·B(C6F5)3}] (3). When Cp2ZrPh2 is treated in toluene at 80 °C with CH3CN in the presence of B(C6F5)3, a complex formulated as [Cp2Zr{η2-C,N-C6H4C(CH3)NH}{NCCHC(CH3)NH·B(C6F5)3}] (4) is formed, which results from an unprecedented C,C coupling between two acetonitrile molecules and insertion of a CN group of one acetonitrile molecule into the benzyne. By contrast, the reaction of Cp2ZrPh2 with p-F3C-C6H4CN in the presence of B(C6F5)3 produces [Cp2Zr{η3-C,N,N‘-C6H4C(F3CC6H4)N-C(F3CC6H4)N·B(C6F5)3}] (5), due to the insertion of a CN bond of the nitrile into the benzyne moiety and a C,N coupling between the benzylic carbon atom of a second Lewis acid adduct p-F3C-C6H4CN·B(C6F5)3 and the nitrogen atom of the first inserted nitrile.