Nonstoichiometric Stille Coupling Polycondensation via an Intramolecular Pd(0) Catalyst Transfer Using Excess Phthalimide Monomer

Nonstoichiometric polycondensations via Stille coupling reactions are successfully used to obtain high-molecular-weight -conjugated polymers using 2,5-bis(trimethylstannyl)thiophene and a dibromo phthalimide monomer, N-hexyldecyl-3,6-dibromophthalimide (2), in excess from 1:1 to 1:10. The intramolecular Pd(0) catalyst transfer on 2 substituted at the polymer terminal occurs as suggested by the model reaction between 2-(tributylstannyl)thiophene and an equimolar amount of N-octyl-3,6-dibromophthalimide (4), and the reaction generates only the disubstituted compound and excess 4 in an almost 1:1 ratio. The effect of the structures of the ligands and monomers on the polymerization under nonstoichiometric conditions is investigated to elucidate the criteria for the successful intramolecular catalyst transfer. The combination of the imide structure and an electron-rich ligand is important for promoting the catalyst transfer.