Unusual Nitrile-Nitrile and Nitrile-Alkyne Coupling of Fc-C equivalent to N and Fc-C equivalent to C-C equivalent to N

The reactions of the Group4 metallocene alkyne complexes, [Cp*M-2((2)-Me3SiC2SiMe3)] (1a: M=Ti, 1b: M=Zr, Cp*=(5)-pentamethylcyclopentadienyl), with the ferrocenyl nitriles, FcCN and FcCCCN (Fc=Fe((5)-C5H5)((5)-C5H4)), is described. In case of FcCN an unusual nitrile-nitrile CC homocoupling was observed and 1-metalla-2,5-diaza-cyclopenta-2,4-dienes (3a, b) were obtained. As the first step of the reaction with 1b, the nitrile was coordinated to give [Cp*Zr-2((2)-Me3SiC2SiMe3)(NC-Fc)] (2b). The reactions with the 3-ferrocenyl-2-propyne-nitrile FcCCCN lead to an alkyne-nitrile CC coupling of two substrates and the formation of 1-metalla-2-aza-cyclopenta-2,4-dienes (4a, b). For M=Zr, the compound is stabilized by dimerization as evidenced by single-crystal X-ray structure analysis. The electrochemical behavior of 3a, b and 4a, b was investigated, showing decomposition after oxidation, leading to different redox-active products.