tert-Butyl-Substituted Poly(ferrocenylene persulfides)

The trithiaferrocenophanes (RC5H3)2FeS3 (where R = t-Bu, H) were prepared by dilithiation of the t-Bu-substituted ferrocenes followed by treatment with elemental sulfur. t-BufcS3 was obtained as the 1,3,1'-isomer. This chiral compound exists in solution as a 1:l mixture of conformers by virtue of the relative orientation of the trisulfide strap. The species (t-Bu)2fcS3 was obtained as the 1,3,1',4'-isomer, as established by lH NMR measurements and X-ray crystallography. The trisulfides were converted to the polymers [(RC5H3)2FeS2In upon desulfurization with B u ~ P , which was shown by 31P NMR spectroscopy to be converted to Bu3PS. The rate of this desulfurization increases with the polarity of the reaction solvent. GPC measurements indicated that the t-Bu-and (t-Bu)2-substituted polymers are polydis-perse with Mn = 3700 (M, = 26000) and Mn = 2400 (M, = 19000), respectively. The soluble ferrocenylene persulfide polymers undergo reversible electrochemical oxidation in two steps, separated by 290 mV. The first oxidation potential is similar to that for the trisulfide monomer and is thought to correspond to oxidation of alternating Fe centers. The second oxidation converts the remaining Fe" sites. Reduction of [(t-Bu)zfcSz]n with LiBHEt3 gave (t-Bu)afcSzLi2, which can be reoxidized (12) to the polymer, sulfurized (Sa) to give the trisulfide, and selenized (Sed to give (t-Bu)2fcS&e.