Rhodium(I)-catalyzed Addition of Tolane to Azobenzene: A New Route to Indole Derivatives

Article abstract of DOI:10.1007/BF00811752

RhCl(PPh3)3 catalyzes the formation of N-anilino-2,3-diphenylindole (1) and small amounts of 2,3-diphenylindole (2) from azobenzene and diphenylacetylene.Weak acids or silica gel accelerate the reaction and induce an almost quantitative conversion to 1.Other rhodium(I) complexes are less active while rhodium(III) compounds inhibit the reaction.A preliminary reaction mechanism of the homogeneous catalysis is proposed and the structure of two key intermediates is substantiated by ab initio MO calculations. - Keywords: Azobenzene; Diphenylacetylene; Indoles; Rhodium(I)-catalysis; Silica gel supported catalysis.