Reductive coupling of halogenothiophenes and halogenothiazoles catalysed by PdII in a basic alcohol medium

Abstract

A catalytic reductive coupling method has been developed whereby 2- and 3-bromo- and 2-iodothiophenes, 2-bromothiazole and 2-bromofuran are converted into their corresponding bithiophene, bithiazole and bifuran derivatives. The use of a basic alcohol medium favours the reductive coupling pathway over the hydrodehalogenation pathway, which is generally more facile when other reducing agents are used. The catalytic mechanisms are discussed. The syntheses and characterization of the proposed intermediate complexes, trans-[PdBr(C₄H₃S-C)(PPh₃)₂] 1, trans-[PdI(C₄H₃S-C)(PPh₃)₂] 2 and trans-(N,P)-[{PdBr(µ-C₃H₂NS-C²,N)(PPh₃)}₂]·½CHCl₃ 3 support the proposed mechanism and the catalytic results. Single-crystal X-ray crystallographic structure determinations of 2 and 3 were carried out.