Alkyne metathesis with simple catalyst systems: Efficient synthesis of conjugated polymers containing vinyl groups in main or side chain

The synthesis of novel conjugated polymers by acyclic diyne metathesis (ADIMET) is reported. These polymers are hybrids between poly(p-phenylenevinylene) and poly(p-phenyleneneethynylene) (PPE). They contain phenylene, ethynylene, and vinylene groups (-=-Ph-=-Ph-, PPVE). Simple in situ catalysts formed from Mo(CO)(6) and 4-chlorophenol were used to metathesize the dipropynyl(tetraalkyl)stilbene monomers. The monomers are made by a combination of Horner reactions and Heck-type couplings. The PPVEs form in high yields and are structurally defined. They show degrees of polymerization (P-n) of 30-220 repeating units (i.e. 60-450 benzene rings), demonstrating that the presence of the double bonds does not interfere with alkyne metathesis. The PPVEs were structurally characterized by XRD and electron microscopy. They show fibrillar and network-type morphologies, which should make them interesting for applications in molecular electronics. Solid samples of PPVEs display powder XRD patterns almost identical to those of the PPEs. PPVEs thus assume similar doubly lamellar structures as the PPEs. The aggregation behavior of PPVEs was studied. In addition, ADIMET to a poly(2,7-fluorenyleneethynylene) carrying unsaturated side chains is reported. In this case the presence of unsaturation does neither interfer with efficient alkyne metathesis.