Homoleptic Lanthanide Amides as Homogeneous Catalysts for Alkyne Hydroamination and the Tishchenko Reaction
✍ Scribed by Markus R. Bürgstein; Helga Berberich; Peter W. Roesky
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 135 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
The homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides of the general type [Ln{N(SiMe 3 ) 2 } 3 ] (1) (Ln Y, lanthanide) represent a new class of Tishchenko precatalysts and, to a limited extent, precatalysts for the hydroamination/cyclization of aminoalkynes. It is shown that 1 is the most active catalyst for the Tishchenko reaction. This contribution presents investigations on the scope of the reaction, substrate selectivity, lanthanide-ion size-effect, and kinetic/ mechanistic aspects of the Tishchenko reaction catalyzed by 1. The turnover frequency is increased by the use of large-center metals and electron-withdrawing substrates. The reaction rate is second order with respect to the substrate. While donor atoms, such as nitro-gen, oxygen, or sulfur, on the substrate decrease the turnover frequency, 1 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 accessible (one-step synthesis or commercially available), than the metallocenes and might therefore be an attractive alternative catalyst.
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