Substituted (pyridinyl)benzoazole palladium complexes: Synthesis and application as Heck coupling catalysts

Abstract

The synthesis of 2-(4- tert-butylpyridin-2-yl)-benzooxazole ( L3), 2-(4- tert-butyl-pyridin-2-yl)-benzothiazole ( L4) and 6- tert-Butyl-2-(4- tert-butyl-pyridin-2-yl)-benzothiazole (L5) by intramolecular cyclization under basic conditions is described. Reactions of 2-pyridin-2-yl-1 H-benzoimidazole ( L1), 2-pyridin-2-yl-benzothiazole ( L2) and L3– L5 with either [Pd(NCMe) 2Cl 2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [Pd( L1)MeCl] ( 1), [Pd( L2)MeCl] ( 2), [Pd( L3)Cl 2] ( 3), [Pd( L3)MeCl] ( 4), [Pd( L4)Cl 2] ( 5), [Pd( L4)MeCl] ( 6) and [Pd( L4)MeCl] ( 7) as confirmed by mass spectrometry and elemental analyses. The palladium complexes are efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions. Benzothiazole and benzooxazole containing complexes show faster induction periods compared to the benzoimidazole analogues.