Palladium on Carbon-Catalyzed Silane-Reduction of Tertiary Carboxamides: Soluble Palladium Colloids are an Active Catalyst Species

摘要

The combination of commercially available palladium on carbon (Pd/C) with 1,1,3,3-tetramethyldisiloxane (TMDS) was found to be an effective catalyst system for the production of tertiary amines by deoxygenative silane-reduction of carboxamides. Facile removal of both the metallic species and silane residues can be achieved by simple extraction, and the recovered Pd/C was reusable. Other palladium complexes and salts, Pd2(dba)3(CHCl3) [dba = dibenzylideneacetone], Pd(OAc)2, and PdCl2, were also effective for the reduction of tertiary carboxamides with TMDS. Detailed mechanistic studies of the present Pd/C–TMDS system revealed that the catalytically active species is the soluble palladium colloids leached from the palladium particles on the carbon support by treating with TMDS, and carboxamides, amine products, and TMDS act as a stabilizer for the generated palladium species in solution.