Stimulus Responsive Poly(ferrocenylsilanes): Redox Chemistry of Iron in the Main Chain

Redox chemistry of organometallic poly(ferrocenylsilane) polymers (soluble in organic or aqueous environment) is discussed. Poly(ferrocenyldimethylsilane) (PFDMS) was oxidized in CH2Cl2 solution with different oxidants. Oxidation was accomplished with stepwise increasing amounts of ferric chloride (FeCl3), iodine (I2) and tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA· +.SbCl6). The process was followed by UV–visible spectroscopy. Mixed-valence salts with different Fe(III)/Fe(II) ratios were obtained. The oxidation products were characterized by Mössbauer spectroscopy, which proved to be a very valuable tool to analyze mixed valence ferrocenyl compounds. Mössbauer analysis demonstrated that 100% oxidation could be achieved with TBPA· +. Decamethylferrocene (DMFC) was found to be a suitable reducing agent for the oxidized polymer. The reduction process was monitored by UV–visible spectroscopy. The polymer was characterized by gel permeation chromatography (GPC) following the oxidation/reduction cycle and evidence of some fragmentation of the chains was observed. A water-soluble PFS polycation was successfully oxidized with FeCl3 for pH values between 4 and 5. Ascorbic acid (vitamin C) was found to completely reduce the oxidized water-soluble polymer.