Synthesis of 2,4,6‐Triaryl‐1,3,5‐triazines via the Cyclotrimerization of Benzonitriles with Catalytic Systems Composed of Titanium Chlorido Complexes and Magnesium

Abstract

AbstractThe catalytic activity of low‐valent transition metals for the cyclotrimerization of nitriles has rarely been investigated to date. Here, we report on the cyclotrimerization of benzonitrile (PhCN) and its derivatives using catalytic systems composed of magnesium and bis(indolyl)TiCl2 (bis(indolyl)=di(3‐methylindol‐2‐yl)phenylmethane), Cp2TiCl2 (Cp=η5‐C5H5), (CGC)TiCl2 (CGC=Me2Si(Me4C5)(tBuN)), TiCl4(thf)2 (thf=tetrahydrofuran), Cp*TiCl3 (Cp*=η5‐Me5C5), or CpTiCl3, which can be expected to generate coordinatively unsaturated Ti(II) complexes as the catalytically active species. All the investigated catalytic systems were active for the cyclotrimerization of PhCN. Notably, even the simple catalytic precursor (TiCl4(thf)2) mediated the cyclotrimerization of PhCN as well as p‐ and m‐tolunitriles. Moreover, these reactions can be carried out on the gram scale and the cyclotrimerized products can be isolated via recrystallization of the reaction mixture from hot toluene. The findings of this study suggest that low‐valent titanium species have the potential to serve as catalysts for the cyclotrimerization of PhCN and its derivatives. During this study, we also found that 2,4,6‐tri(p‐tolyl)‐1,3,5‐triazine, which is obtained from the cyclotrimerization of p‐tolunitrile, exhibits fluorescent properties in both the solid state and in solution.