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.