Stereocontrolled synthesis of (E)- and (Z)-poly(p-phenylenevinylene)s via ruthenium-catalyzed hydrosilylation of p-diethynylbenzene

Stereocontrolled synthesis of poly(phenylenevinylene)s (PPVs) with (E)- and (Z)-vinylene units has been examined. Ruthenium complex-catalyzed hydrosilylation of p-diethynylbenzene with HSiMe2Ar (Ar=2-thienyl (Th), 3,5-(CF3)2C6H3) proceeds readily in CH2Cl2 at room temperature to give (E,E)- or (Z,Z)-bis(2-silylethenyl)benzenes (3a, 3b) in 89–40% yields. The geometries of 3a and 3b are clearly dependent on ruthenium catalysts employed. Thus, RuHCl(CO)(PPh3)3 forms (E,E)-isomers in over 99% selectivities, whereas RuCl2(CO)(PPri3)2 affords (Z,Z)-3a and 3b with 92 and 91% geometrical purities, respectively. The (E,E)- and (Z,Z)-isomers of 3a and 3b undergo polycondensation with 2,5-dioctyloxy-1,4-diiodobenzene in THF in the presence of a palladium catalyst ([PdCl(η3-allyl)]2, Pd(dba)2) and tetrabutylammonium fluoride hydrate, giving (E)-rich and (Z)-rich PPVs in high yields.