Well‐Defined Regioselective Iminopyridine Rhodium Catalysts for Anti‐Markovnikov Addition of Aromatic Primary Amines to 1‐Octyne

Abstract

Abstractmagnified imageA series of cationic rhodium(I) complexes of the type [Rh(N‐N)(COD)][BPh4], containing the following iminopyridine‐based bidentate nitrogen donor ligands (N‐N): 2,6‐diisopropyl‐N‐[1‐(pyridin‐2‐yl)ethylidene]aniline (dipea, 1), 2,6‐dimethyl‐N‐[1‐(pyridin‐2‐yl)ethylidene]aniline (dmpea, 2), 2,4,6‐trimethyl‐N‐[1‐(pyridin‐2‐yl)ethylidene]aniline (tmpea, 3) and 2,6‐diisopropyl‐N‐[1‐(4‐methylpyridin‐2‐yl)ethylidene]aniline] (dipmpea, 4), were synthesized and fully characterized. The intermolecular hydroamination of a terminal alkyne, such as 1‐octyne, with primary aromatic amines in the presence of these cationic rhodium(I) catalysts occurred in an anti‐Markovnikov fashion. The rhodium complexes catalyzed the regioselective formation of the E‐isomer of the corresponding imine, without the formation of the Z‐isomer or the Markovnikov product. These compounds are also presented as efficient regioselective catalysts for the hydroamination of anilines in the presence of air and/or water.