Efficient Rhodium-Catalyzed Multicomponent Reaction for the Synthesis of Novel Propargylamines

[{Rh(mu-Cl)(H)(2)(IPr)}(2)] (IPr = 1,3-bis-(2,6-diisopropylphenyl) imidazole-2-ylidene) was found to be an efficient catalyst for the synthesis of novel propargylamines by a onepot three-component reaction between primary arylamines, aliphatic aldehydes, and triisopropylsilylacetylene. This methodology offers an efficient synthetic pathway for the preparation of secondary propargylamines derived from aliphatic aldehydes. The reactivity of [{Rh(mu-Cl)(H)(2)(IPr)}(2)] with amines and aldehydes was studied, leading to the identification of complexes [RhCl(CO) IPr(MesNH(2))] (MesNH(2) = 2,4,6-trimethylaniline) and [RhCl(CO)(2)IPr]. The latter shows a very low catalytic activity while the former brought about reaction rates similar to those obtained with [{Rh(mu-Cl)(H)(2)(IPr)}(2)]. Besides, complex [RhCl(CO)IPr(MesNH(2))] reacts with an excess of amine and aldehyde to give [RhCl(CO) IPr{MesN= CHCH2CH(CH3)(2)}], which was postulated as the active species. A mechanism that clarifies the scarcely studied catalytic cycle of A(3)-coupling reactions is proposed based on reactivity studies and DFT calculations.