Deltoid versus Rhomboid: Controlling the Shape of Bis-ferrocene Macrocycles by the Bulkiness of the Substituents

Precise structural control of heteroannularly disubstituted ferrocene (Fc) structures is very challenging as the high rotational mobility of the Fc unit allows a large conformational diversity. Herein we present the syntheses, characterization, and electrochemical investigation of two complementary bis-ferrocene macrocycles, built up via Sonogashira cross coupling and intramolecular ring-closing reaction. While the X-ray structure of 1,2-ethynylbenzene bridged bis-ferrocene complex 1 shows a deltoidal conformation, a stretched oriented rhomboidal bis-ferrocene metallacycle 2 is formed when the peripheral benzene rings are decorated with bulky tert-butylsulfanyl groups. VT-NMR spectroscopy is used to assign the rotation of the embedded Fc units in rhomboid 2. Moreover, cyclic voltammetry (CV) of deltoid 1 and rhomboid 2 indicate that electronic communication between both ferrocenyl groups can be neglected, while the electrostatic through space coupling is significant.