Constitutional Isomers of Macrocyclic Tetraruthenium Complexes with Vastly Different Spectroscopic and Electrochemical Properties

Abstract

Two constitutionally isomeric tetraruthenium macrocycles were constructed from either symmetrically (2-S) or unsymmetrically (2-A) functionalized thiophene-based building blocks. Both compounds were fully characterized by NMR spectroscopy and high-resolution ESI MS. Despite their identical composition and close structural resemblance, the two isomers exhibit vastly different electrochemical and spectroscopic properties as a consequence of the different extensions of their π-conjugated subunits. In particular, mixed-valent 2-A+/2+/3+ absorb weakly in the near infrared as a consequence of electronic through-bond coupling between neighboring oxidized and reduced sites, whereas 2-S+/2+/3+ do not.