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

Abstract

Stereocontrolled synthesis of poly(phenylenevinylene)s (PPVs) with ( E)- and ( Z)-vinylene units has been examined. Ruthenium complex-catalyzed hydrosilylation of p-diethynylbenzene with HSiMe 2Ar (Ar=2-thienyl (Th), 3,5-(CF 3) 2C 6H 3) proceeds readily in CH 2Cl 2 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)(PPh 3) 3 forms ( E, E)-isomers in over 99% selectivities, whereas RuCl 2(CO)(PPr i 3) 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(η 3-allyl)] 2, Pd(dba) 2) and tetrabutylammonium fluoride hydrate, giving ( E)-rich and ( Z)-rich PPVs in high yields.