Linear 6,6′-biazulenyl framework featuring isocyanide termini: Synthesis, structure, redox behavior, complexation, and self-assembly on Au(111)

The key step in accessing the title species (5), the first nonbenzenoid diisocyanobiaryl, involved an unexpected homocoupling of a 6-bromoazulene derivative. The reversible 2e^- reduction of 5 was addressed electrochemically and computationally. The shifts in energies of the S ₀→S₁ and S₀→S₂ transitions for a series of related 6,6′-biazulenyl derivatives correlate with the e^--donating/-withdrawing strength of their 2,2′-substituents but follow opposite trends. Species 5 adsorbs end-on (η¹) to the Au(111) surface via one of its -NC groups to form a 2-nm-thick film. In addition, bimetallic coordination of 5's -NC termini can be readily achieved.