Synthesis Of A Ferrocene-Based Polymer Via Ring-Opening Polymerization. This experiment has a number of parts. You will synthesize a strained ferrocene derivative via lithiation of ferrocene followed by treatment with dichlorodimethylsilane…

The first step involves the lithiation of ferrocene (to give 1) using two equivalents of nbutyllithium in the presence of tetramethylethylenediamine (TMEDA), which facilitates the reaction through break-up of the less reactive aggregated structures by coordinating to lithium and enhancement of the ionic character of the lithium carbon bonds. Reaction of 1 with dichlorodimethylsilane yields the red, crystalline [1]ferrocenophane 2.3 This species has a strained structure in which the cyclopentadienyl ligands are tilted with respect to one another by around 21?,4 and the strain energy of 2 has been measured to be 80 kJ mol-1.5 In contrast to 2, ferrocene has cyclopentadienyl ligands that are parallel to one another. The monomer (1) can be isolated as a red-orange crystalline solid or alternatively subjected to ROP directly. Transition-metal-catalyzed polymerization of unpurified 2 to yield the amber-colored poly(ferrocenylsilane) 3 can be performed at 50-80 ?C over 2 – 24 h in solution by the addition of very small amounts of a Pt catalyst. The polymer 3 can be isolated by precipitation from toluene or THF into a non-solvent such as hexanes and can be cast into free-standing films again from toluene or THF. Following drying, characterization of the poly(ferrocenylsilane) 3 can be achieved by 1H NMR spectroscopy. The iron centers of 3 can be readily oxidized by dipping a film of the material into a solution of iodine in hexanes; this leads to a blue coloration as the material is electrochromic. Reduction of the oxidized films to the neutral amber state can be achieved by dipping the film into a solution of a reducing agent such as methanolic hydrazine. Cyclic voltammetry gives insight into one of the most interesting characteristics of these polymers, the fact that two reversible oxidation waves are detected as the iron centers are redox coupled (oxidation of one center makes the neighboring iron centers more difficult to oxidize due to Fe•••Fe interactions)…

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