Oligomeric ferrocene rings

Abstract

Cyclic oligomers comprising strongly interacting redox-active monomer units represent an unknown, yet highly desirable class of nanoscale materials. Here we describe the synthesis and properties of the first family of molecules belonging to this compound category-differently sized rings comprising only 1,1'-disubstituted ferrocene units (cyclo[n], n = 5-7, 9). Due to the close proximity and connectivity of centres (covalent Cp-Cp linkages; Cp = cyclopentadienyl) solution voltammograms exhibit well-resolved, separated 1e(-) waves. Theoretical interrogations into correlations based on ring size and charge state are facilitated using values of the equilibrium potentials of these transitions, as well as their relative spacing. As the interaction free energies between the redox centres scale linearly with overall ring charge and in conjunction with fast intramolecular electron transfer (∼10(7) s(-1)), these molecules can be considered as uniformly charged nanorings (diameter ∼1-2 nm).

Ferrocene‐ and Biferrocene‐Containing Macrocycles towards Single‐Molecule Electronics

“…Such bands were recently observed for the MV states of cyclic sexiferrocene 2. With the aim to probe for such IVCT bands, we compared the electronic spectra of 2 , 2 + , 2 2+ , and 2 3+ in the UV/Vis/NIR range.…”

“…Cyclic structures have enthralling beauty that has attracted chemists for generations 1, 2. Such structures display a wide range of unusual electronic properties, not seen in linear analogues 3, 4.…”

“…Multiple redox‐active groups within molecular wires show interesting results in conductance modulation 12, 13, 14. Currently, little research has been pointed towards redox‐active groups in parallel or in rings within electronic systems 2, 15, 16, 17. Ferrocene is often incorporated into molecular wires due to its stability, high conductance levels, and ability to act as a redox switch 18, 19, 20, 21.…”

“…Biferrocene has been incorporated into molecular electronic wires but not yet into cyclic systems 22. Several ferrocene containing cyclic structures have been synthesized 2, 23, 24. Organization of ferrocene into such structures can be problematic due to its flexibility, creating diversity of structures.…”

“…We devised a route to the triferrocene cyclic system through a stepwise assembly to a covalently bonded system (Scheme 1). 1,1′‐Diiodoferrocene was synthesized by a recently developed, improved procedure and coupled with 1,3‐diethynylbenzene using a Sonogashira cross‐coupling with Pd(P t Bu 3 ) 2 as the catalyst 2. Within our group, this catalyst has been found to show superior results for coupling alkynes with ferrocene due to the large cone angle of the P t Bu 3 ligand 28.…”