Synthesis and photochromic properties of tricarbonylchromium complexes of 2H-?6-benzochromenes

Abstract

Although in the 2H-chromene (benzopyran) series complexation with tricarbonylchromium, under thermal conditions, is totally regioselective, in the naphthopyran series the same reaction cannot be observed. We show here that with tricarbonyl(trispyridine)chromium as complexing agent, in the presence of Lewis acid, complexation of naphthopyrans can be achieved and is totally regioselective. The complexes formed are photochromic compounds, and their thermal bleaching kinetic constants are reduced as compared with the non-complexed homologous compound.