Homoleptic lanthanide amides as homogeneous catalysts for alkyne hydroamination and the Tishchenko reaction

The homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides of the general type [Ln{N(SiMe3)(2)}(3)] (1) (Ln=Y, lanthanide) represent a new class of Tishchenko precatalysts and, to a limited extent, precatalyst s for the hydroamination/cyclization of aminoalkynes. It is shown that I is the most active catalyst for the Tishchenko reaction. This contribution pr esents investigations on the scope of the reaction, substrate selectivity, lanthanide-ion size-effect, and kinetic/mechanistic aspects of the Tishchen ko reaction catalyzed by 1. The turnover frequency is increased by the use of large-center metals and electron-withdrawing substrates. The reaction ra te is second order with respect to the substrate. While donor atoms, such a s nitrogen, oxygen, or sulfur, on the substrate decrease the turnover frequ ency, I shows a tolerance for a large number of functional groups. For the hydroamination/cyclization of aminoalkynes, 1 is less active than the well- known metallocene catalysts. On the other hand, 1 is much more readily acce ssible (one-step synthesis or commercially available), than the metallocene s and might therefore be an attractive alternative catalyst.