Tunable Electron Density at a Rhenium Carbonyl Complex Coordinated to the Conducting Polymer Poly[5,5′-(2-thienyl)-2,2′-bithiazole]

The synthesis of a conducting polymer by electropolymerization of 5,5′-(2-thienyl)-2,2′-bithiazole is reported. Films of this polymer exhibit electrochemical behavior typical of conducting polymers and have a conductivity of ~0.2 Ω⁻¹ cm⁻¹ at 25 °C in 0.1 M [n-Bu₄N]PF₆/CH₂Cl₂ at the potential of maximum conductivity (~+1.5 V vs Ag). The activation energy for conductivity for partially oxidized (~+1.3 V vs Ag) films is 0.25 eV. Reaction of these polymer films with refluxing solutions of Re(CO)₅Cl in CHCl₃ yields polymers in which the [Re(CO)₃Cl] moiety is bound to the bithiazolyl sites in the polymer. Subsequent reaction with AgPF₆ converts the Re centers to cationic [Re(CO)₃(CH₃CN)]⁺ groups. These polymers were characterized by XPS and surface reflectance FTIR. The polymer containing the cationic Re groups is conducting (∼2 × 10⁻³ Ω⁻¹ cm⁻¹ at +1.5 V vs Ag). The potential region in which the polymer is conducting does not overlap with any Re-centered oxidations, but oxidation of films of the polymer to the conducting state causes electron density to be removed from the Re center, resulting in a shift of the carbonyl stretching frequencies to higher energy. At the potential of maximum conductivity this shift is 4–6 cm⁻¹.