Microwave-assisted synthesis of oligothiophene semiconductors in aqueous media using silica and chitosan supported Pd catalysts

We report an innovative heterogeneous procedure for the preparation of highly pure thiophene oligomers via microwave-assisted Pd catalysis by using silica-and chitosan- supported Pd complexes. This approach is very efficient and greener than the existing homogeneous methodology as it combines a very efficient reaction with improved catalyst separation. Our new, efficient and cleaner microwave approach smoothly afforded the preparation of coupled products in high yields ( up to 87% isolated yield, 30-100 min). Thienyl iodides or activated bromides were employed as starting materials and KF as base. The microwave reaction was carried out in aqueous ethanol. The heterogeneous catalyst can be easily removed from the reaction mixture by filtration and reused in consecutive reactions ( up to 4 times).