Semiconducting polymers via microwave-assisted Suzuki and Stille cross-coupling reactions

A fully conjugated para-phenylene ladder polymer (PI) and the alternating copolymers {2,7-[9,9-bis(2-ethylhexyl)fluorene]-5,5'-(2,2'-bithiophene)} (P3) and {2,7-[9,9-dioctylfluorene]-5,5'-(2,2'-bithiophene)} (P4) have, been prepared via metal-mediated cross-coupling reactions, using microwaves as a heat source. The procedure, which yields polymeric material in ca. ten minutes, has no adverse effects on the quality of the polymers and displays a high degree of reproducibility. Transfer of the optimized conditions to the synthesis of a new naphthalene-based polyarylene-ketone (P2) and a (1,5-dioctoxynaphthylene-2,6-diyl-alt-2,2'-bithiophene-5,5'-diyl) copolymer (P5) confirmed the versatility of the procedure and the dramatic reduction in reaction times compared with conventional heating. In the case of the Stille-type coupling reaction of the electron-rich, less reactive dibromo monomer 1,5-dioctoxy-2,6-dibromo-naphtalene, the microwave-assisted protocol results in a marked increase in both yield and molecular weight.