Synthesis, structure, and ring-opening polymerization (ROP) of a phosphonium-bridged [1]ferrocenophane

The stable phosphonium-bridged [1]ferrocenophane [(eta-C5H4)(2)FePPhMe][OTf] (10b) was synthesized by the reaction of the phosphorus-bridged [1]ferrocenophane (eta-C5H4)(2)FePPh (3a) with methyl triflate (MeOTf). A single-crystal X-ray diffraction study of 10b revealed an angle of 24.4(5)degrees between the planes of the cyclopentadienyl rings, less than the respective angle (26.7 degrees) for 3a. Compound 10b and a number of other tetracoordinate, phosphorus-bridged [1]ferrocenophanes, (eta-C5H4)(2)FeP(S)Ph (5a), (eta-C5H4)(2)FeP[Fe(CO)(4)]Ph (6), and [(eta-C5H4)(2)FePFpPh][PF6] (7) (where Fp = (eta-C5H5)Fe(CO)(2)), were investigated with respect to their ring-opening polymerization (ROP) behavior. Only compound 10b was found to undergo ROP, which occurred both thermally and in the presence of a transition-metal catalyst (PtCl2). The resultant ionomeric polymer {[(eta-C5H4)(2)FePPhMe][OTf]}(n) (11) was found to be soluble in dimethylformamide (DMF), dimethyl sulfoxide (DMSO), methanol, and acetone but displayed only limited stability in these solvents. The thermally ring-opened polymer was found to possess a glass transition temperature of 176 degrees C and was thermally stable to weight loss up to ca. 400 degrees C. Analysis by wide-angle X-ray scattering (WAXS) revealed that the polymer was amorphous. A study on the partial to full methylation of the polymer [(eta-C5H4)(2)FePPh](n) (14) gave results that were consistent with those from the ROP of 10b. Dynamic light scattering studies on polymer 11 produced via thermal ROP and transition-metal-catalyzed ROP gave hydrodynamic radii in the range of 30-45 nm, which suggested that the compounds were polymeric rather than oligomeric in nature. On the basis of the glass transition temperatures for a series of samples of polymers 11 of known molecular weight with varying numbers of repeat units (from 20 to 100), the molecular weight (M-n) of the transition-metal-catalyzed ROP product was greater than 46 000 (ca. 100 repeat units) and the molecular weight of the thermally produced polymer was even higher.