Thermal ring-opening polymerization of hydrocarbon-bridged [2]ferrocenophanes: Synthesis and properties of poly(ferrocenylethylene)s and their charge-transfer polymer salts with tetracyanoethylene

The poly(ferrocenylethylene)s [Fe(eta-C5H3RCH2)(2)](n) 5a and 5b (a: R = H, b: R = Me) have been prepared by thermal ring-opening polymerization of the corresponding strained hydrocarbon-bridged [2]ferrocenophanes [Fe(eta-C-5-H3RCH2)(2)] (4a and 4b). An X-ray diffraction study of 4a indicated significant strain. Polymer 5a was crystalline and insoluble in common organic solvents and was characterized by solid-state C-13 NMR. Polymer 5b, which was soluble in organic solvents, was characterized by H-1 and C-13 NMR, UV/visible spectroscopy and elemental analysis. Its molecular weight distribution was bimodal (gel permeation chromatography: M-w = 9.6 x 10(4), M-n = 8.6 x 10(4) for the high molecular weight fraction, M-w = 4.8 x 10(3), M-n = 3.5 x 10(3) for the oligomeric fraction), suggesting two polymerization mechanisms. The UV/visible spectrum implied a localized structure for the polymer backbone. Cyclic voltammetry revealed that 5b undergoes two reversible oxidations in CH2Cl2 solution at -0.25 and -0.16 V. The redox coupling is indicative of only a small degree of interaction between the iron centres. Thermogravimetric analysis indicated that 5a and 5b are thermally stable to ca. 300-350 degrees C under N-2. At higher temperatures they yield ferromagnetic iron carbide ceramics 6a and 6b (ca. 50% and 32%, respectively, at 600 degrees C) together with molecular depolymerization products. The reaction of 5b with tetracyanoethylene (TCNE) yielded insoluble and soluble oxidized products 11 and 12, which differed in the degree of oligomerization of the TCNxy- counterions. These products were characterized by IR, elemental analysis, ESR spectroscopy, and magnetic susceptibility measurements. The last revealed the presence of significant antiferromagnetic interactions in 12.