Studies on the preference of multiple coupling in the introduction of thiophene ring into poly-halogenated aromatic compounds with nickel NHC catalyst

Several thiophene derivatives can be deprotonated by the combination of ethyl magnesium chloride (EtMgCl) and a catalytic amount of 2,2,6,6-tetramethylpiperidine (TMP-H). The metalated 3-hexylthiophene reacts with 2,3- and 2,5-dibromothiophenes in the presence of a nickel catalyst bearing NHC ligand (IPr) to afford the di-coupled product exclusively along with recovery of dibromothiophene albeit the equimolar reaction. The 1:1 reaction of 3-hexylthiophene with dibrominated benzene derivatives also gives di-coupled product as a sole product.