Ligands containing alternating 2,6-linked pyridine and 2,5-linked thiophene units1

Abstract

A variety of linear assemblies of alternating pyridine (2,6-linked) [P] and thiophene (2,5-linked) [T] units have been generated with up to seven units and their macrocyclisation investigated. The optimal methods involved the palladium(>0>) catalysed reaction of thienyl Grignard reagents with bromopyridines. In this way were made TPT, TPTPT, TPTPTPT, BrPTPBr and various XCH₂PTPTPCH₂X derivatives (X = H, Br, OH, OR and SBu-t). Alternative routes whereby pyridine units were 2,6-linked by CH₂SCH₂ units, with the intention of converting the bridge groups into thiophenes by a Hinsberg reaction, were also studied. The latter products {(HOCH₂[P]CH₂)₂S and (HOCH₂[P]CH₂SCH₂)₂[P]} proved to be highly effective ligands for transition metals, especially divalent ones such as Co²⁺, Ni²⁺ and Zn²⁺. No macrocyclisations were effective.