Synthetic Diversity in the Formation of Triazoles from Nitriles and Diazo Compounds Using Metallocenes of Electropositive Metals

Reactions of [(C5Me5)2Ln][(μ-Ph)2BPh2] complexes with Li[Me3SiCN2] form dimeric isocyanotrimethylsilyl amide complexes {(C5Me5)2Ln[μ-N(SiMe3)NC]}2, not only for Ln = Sm (1-Sm) and La (1-La) but also for the intermediate and small size metal ions Ln = Nd, Y, Yb, and Lu. Complexes 1-Y and 1-Yb were characterized by X-ray crystallography and are structurally similar to 1-Sm and 1-La. A more convenient synthesis of 1-Sm and 1-La from the corresponding (C5Me5)2LnCl2K(THF)2 “ate” salts with Li[Me3SiCN2] is also reported. Analogues of reactions of 1-Sm and 1-La with Me3CCN that form the 1,2,3-triazolato complexes (C5Me5)2Ln(NCCMe3)[NNC(SiMe3)C(CMe3)N] (2-Sm, 2-La) were examined with C6H5CH2CN and Me3SiCN to investigate the diversity of the triazoles accessible by this route. Complex 1-La reacts with C6H5CH2CN to make a 1,2,3-triazole complex, but in contrast to 2-La, the product is a base-free dimer in which each triazole is ligated by two metallocenes, {(C5Me5)2La[μ-η1:η2-NNC(SiMe3)C(CH2C6H5)N]}2, 3. The reaction of 1-La with Me3SiCN involves Si−C bond cleavage, and a nitrile-solvated cyanide trimer, [(C5Me5)2La(μ-CN)(NCSiMe3)]3, 4, was isolated. The reaction of 1-La with the isocyanide reagent Me3SiCH2NC also generated a cyanide trimer, this time via N−C bond cleavage as an isocyanide solvate, [(C5Me5)2La(μ-CN)(Me3SiCH2NC)]3, 5. Unsubstituted 1,2,3-triazoles {(C5Me5)2Ln[μ-η1:η2-NNC(SiMe3)C(H)N]}2 (6-Sm, 6-La) can be isolated directly from 1-Sm and 1-La in reactions that involve N−N bond cleavage.