Organometallic polymers based on S-S and Se-Se linked n-butylferrocenes

Polyferrocenylene persulfides, [(BUC5H3)(C5H4)FeS2](n), have been prepared by desulfurization of butyltrithiaferrocenophane (BUC5H3)(C5H4)FeS3. The molecular precursor was prepared by dilithiation of butylferrocene followed by treatment with elemental sulfur and isolated as a 7:1 mixture of the 1,3,1' and 1,2,1' isomers. The trisulfide was converted to polymer by treatment with the desulfurization agent PBu(3). The rate of this desulfurization and the nature of the polymer depends critically on the reaction solvent. Desulfurization in DMF and THF afforded insoluble but swellable rubbers. Desulfurization of BufcS(3) in mixed CH2Cl2-THF solutions gave soluble polymers with M(n) ranging from 12000 to 359000, with lower molecular weight products being favored at high [CH2Cl2]. The effect of high [CH2Cl2] was modeled by the reaction of [fcS(2)](n) with a CH2Cl2 solution of PBu(3) to give fcS(2)CH(2). Molecular weights for [BufcS(2)](n) were confirmed by light scattering measurements. Soluble [BufcS(2)](n) undergoes reversible electrochemical oxidation in two steps, centered at 780 V (vs Ag/AgCl) and separated by similar to 300 mV. The first oxidation potential is similar to that for the trisulfide monomer and is thought to correspond to oxidation of alternating Fe centers, followed by conversion of the remaining Fe-II sites. The polymers photodegrade upon exposure to UV light in air. Deselenization of BufcSe(3) gave red soluble [BufcSe(2)](n) with only moderate molecular weights and with high polydispersities. The microstructure of this polymer was established by Se-77 NMR studies which support the presence of head-to-head, head-to-tail, and tail-to-tail dyads.