ROMP of t-butyl-substituted ferrocenophanes affords soluble conjugated polymers that contain ferrocene moieties in the backbone

A substituted ferrocenophane, 1,1′-((1-tert-butyl)-1,3-butadienylene)ferrocene, was synthesized and polymerized via ring-opening metathesis polymerization (ROMP) to give soluble high molecular weight polymers with ferrocenylene units in the backbone. The monomer readily underwent polymerization upon exposure to a tungsten-based metathesis initiator, W(CHC₆H₄-o-OMe)(NPh)OCMe(CF₃)₂]₂ (THF), to give high molecular weight polymers (M_w=ca. 300,000). The molecular weights could be varied systematically by adjusting the monomer-to-catalyst ratio. UV/vis spectra revealed a bathochromic shift for the polymer, consistent with enhanced conjugation compared to the monomer. The polymer exhibited thermal properties similar to oligomeric poly(ferrocenylene). Cyclic voltammetry of the polymer suggested that the iron centers are coupled electronically. Upon doping with I₂ vapor, the polymers displayed semiconducting properties (σ=10⁻⁵ S cm⁻¹). Theoretical calculations were used to evaluate the nature of the bonding in these and related polymers.