Reductive coupling of halogenothiophenes and halogenothiazoles catalysed by Pd~(II) in a basic alcohol medium

摘要

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 bithiopherne, 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 sued. The catalytic mechanisms are discussed. The syntheses and characterization of the proposed intermediate complexes, trans-[PdBr(C_4H_3S-C)(PPh_3)_2] 1, trans-[PdI(C_4H_3S-C)(PPh_3)_2] 2 and trans-(N, P)-[{PdBr(#mu#-C_3H_2S-C~2, N)(PPh_3)}_2] centre dot 1/2CHCl_3 3 support the proposed mechanism and the catalytic results. Single-crystal X-ray crystallographic structure determinations of 2 and 3 were carried out.