Linear-selective cross-coupling polymerization of branched oligothiophene by deprotonative metalation and cross-coupling

Abstract

Brominated oligothiophene with a branched structure was subjected to deprotonative metalation with a bulky magnesium amide chloromagnesium 2,2,6,6-tetramethylpiperidine-2-yl lithium chloride salt (TMPMgCl·LiCl), which is known as the Knochel–Hauser base. The thus metalated oligothiophene was polymerized in the presence of a nickel(II) NHC (N-heterocyclic carbene) complex to afford polymers of M_n of 4400 to 44 000, which corresponds well with the monomer feed/catalyst loading ratio. Analysis by MALDI-TOF MS suggests the formation of a linear polymer with oligothiophene as the monomer. Polymerization of 7-mer (7T-Br₄) also affords polythiophene of a similar structure.