Quantitative and Mechanistic Mechanochemistry in Ferrocene Dissociation

Abstract

Ferrocene is classically regarded as being highly inert owing to the large dissociation energy of metal-cyclopentadienyl (Cp) bonds. We show that the Fe-Cp bond in ferrocene is the preferential site of mechanochemical scission in the pulsed ultrasonication of main-chain ferrocene-containing polybutadiene-derived polymers. Quantitative studies reveal that the Fe-Cp bond is similar in strength to the carbon-nitrogen bond of an azobisdialkylnitrile (bond dissociation energy < −0 kcal/mol), despite the significantly higher Fe-Cp bond dissociation energy (approximately 90 kcal/mol). Mechanistic studies are consistent with a predominately heterolytic mechanism of chain scission. DFT calculations provide insights into the origins of ferrocene’s mechanical lability.

Metallocene as Mechanophore in Polymers Leads to Metal Ion Release & Oxidation

“…[3] In a recent study, [4] we investigated mechanoresponsive polymers containing ferrocene as a mechanophore. We, and in the meantime others, [5] demonstrated the mechanical breaking of the sandwich complex, and a related release of metal ions in solution (Fig. 1).…”

“…Our finding that ferrocence, and possibly other metallocenes, can be used as a mechanophore in polymers that allow the mechanically induced release of metal ions has recently been confirmed by Sha et al, who conducted a similar study with several other polymers and corroborated that the Fe-Cp bond is the favorite cleavage site in ultrasound-induced degradation. [5] The mechanistic studies are consistent with a heterolytic dissociation of ferrocene into Cpand [CpFe] + .…”

Investigating Chain Dynamics in Highly Crosslinked Polymers using Solid‐State 1H NMR Spectroscopy

“…Ferrocene‐containing polymers have been developed for multiple electrochemistry, catalysis, molecular electronics, biomedical, and nanostructured composite applications. Ferrocene polymers have also recently been described that utilize the mechanochemical scission on the Fe─Cp bond under mechanical stress . The local cooperative chain dynamics in ferrocene‐containing polymers and their connection to stress relaxation have not been thoroughly studied.…”

“…Ferrocene polymers have also recently been described that utilize the mechanochemical scission on the Fe─Cp bond under mechanical stress. 27,28 The local cooperative chain dynamics in ferrocene-containing polymers and their connection to stress relaxation have not been thoroughly studied.…”

Ferrocenyl amphiphilic Janus dendrimers as redox‐responsive micellar carriers

“…[35,36] For example, Liu et al described a redox-controlled drug delivery system based on ferrocene (Fc)-containing amphiphilic block copolymers (PEG-b-PMAEFc) that were fabricated via atom transfer radical polymerization (ATRP) using a PEGbased macro-ATRP agent. [37][38][39][40][41][42] And notably, this redox process is attributed to the gain and loss of one electron, and the molecular structure of Fc group is not destroyed, which is a great benefit for the reversible self-assembly and disassembly of Fc-containing amphiphilic macromolecules. [37][38][39][40][41][42] And notably, this redox process is attributed to the gain and loss of one electron, and the molecular structure of Fc group is not destroyed, which is a great benefit for the reversible self-assembly and disassembly of Fc-containing amphiphilic macromolecules.…”