Introduction

Iron is the second most abundant metal and the fourth most abundant element found in Earth's crust. In 1951, Kealy and Pauson made the extraordinary discovery of ferrocene. Prior to that time, complexes containing transition metal-carbon bonds were rare, and it was thought that these bonds must be unstable. The high thermal stability of ferrocene changed many of these ideas, and organoiron chemistry became the focus of numerous investigations. From the initial reports on the synthesis and structure of ferrocene, there have been countless studies examining the chemistry of organoiron complexes.

The rich chemistry of ferrocene stems from the nucleophilicity of the cyclopentadienyl rings, which allows for their reactions with numerous electrophiles. Within a few years of its discovery, a number of functionalized ferrocene molecules had been prepared, and in 1955, the first polymer containing ferrocene in its structure was reported by Arimoto and Haven. In the years to follow, the fascinating chemistry associated with ferrocene led to research in the synthesis of ferrocene-based polymers in which the organometallic group exists in sidechains, the mainchain, or discrete locations within the polymer. Ferrocene-based polymers are the most well-examined class of organometallic polymer, and their methods of synthesis and their properties cover a wide spectrum. These types of polymers have been shown to exhibit interesting electrochemical, optical, thermal, morphological, pharmacological, and magnetic properties.

The displacement of one of the cyclopentadienyl rings of ferrocene by an arene allows for the isolation of cationic [[eta].sup.6]-arene-[[eta].sup.5]-cy

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