Bis-Triazolylidenes of Manganese and Rhenium and Their Catalytic Application in N-Alkylation of Amines with Alcohols

A new family of air-stable Mn and Re complexes bearing bidentate bis(1,2,3-triazol-5-ylidene) ligands with the general formula [M(bis-triazolylidene)(CO)3X] (M = Mn or Re; X = Cl or Br), containing a methylene linker or a direct link between the two triazolylidene ligands, is presented. All complexes have been applied as catalysts for the N-alkylation of anilines with benzylic alcohols. The Mn complex bearing a bis-triazolylidene with a methylene bridge between the two triazolylidene fragments was shown to be a highly efficient catalyst, affording the corresponding amine in 92% yield in the presence of a low base loading (t-BuOK, 0.1 equiv). Comparison between Mn complexes bearing imidazolium-and triazolium-derived N-heterocyclic carbene ligands showed that Mn triazolylidenes displayed higher catalytic activity when a low base loading was used.