Redox active macrocycles, such as porphyrins, are of unbroken interest due to their facile generation of aromatic and antiaromatic states by redox processes. A major proportion of research, thus, focused on their inherent aromaticity, conductance, and charge-transfer properties through the building block.[1] This led to the development of three-dimensional objects, such as gigantic porphyrin P12 nano rings where computational and experimental results verified aromatic and anti-aromatic ring currents in addition to the porphyrin’s local aromatic π-system on a global scale.[2]
In addition to such well-studied systems based on pyrrole precursors, other building blocks are similarly suited to generate large, conjugated cycles. One of the most prominent examples are di-oxo-cyclobutenes as they are key elements during the synthesis of the carbon allotrope C18, an cyclic all-carbon polyyne.[3] However, the so far used di-oxo derivative does not allow for functionalization, including the steric and electronic modification. Furthermore, little is known about the electronic communication through the cyclobutene entity itself. Thus, a variety of novel sterically and electronically-modified cyclobutene derivatives were synthesized and investigated towards their electrochemical properties. Selected examples were functionalized with ferrocenyl-entities allowing for the quantification of charge-transfer properties in the mixed-valent state to ultimately describe macromolecular systems. Ultimately, macrocyclic structures of various size were obtained, and their crystal structures will be discussed in detail, including packing effects, halogen-chalcogen interactions as well as chiral aspects.