Synthesis of poly(biphenylene ruthenacyclopentatrienylene), a new organometallic conducting polymer with ferromagnetic interaction in its reduced state.

A ruthenacyclopentatriene polymer 2 was synthesized by metallacycling polymerization (MCP). Polymer 2 with Mn = 3400 and Mw = 5800 consisted of identical ruthenacyclopentatriene units. The UV-vis spectra of 2 showed a shift of the pi-pi* band to a longer wavelength due to the enlargement of the pi-conjugation. Polymer 2 underwent reversible reduction due to the ruthenacycle moiety at -1.01 V versus ferrocenium/ferrocene. The EPR spectrum of the reduced form of 2 in frozen THF indicated ferromagnetic interaction of spins at ruthenacyclopentatriene units.