Preparation of oligodiazo compounds by using the Suzuki coupling reaction and characterization of their photoproducts

[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-dimethylphenyl)diazomethane was found to be stable enough to survive under Suzuki coupling conditions and underwent mono-, di-, and trisubstitution with benzene mono-, di-, and triboronic acids to afford benzene derivatives having one, two, and three diazo units, respectively. The products from irradiation of those diazo compounds were characterized by ESR and SQUID measurements, which revealed that triplet, quintet, and septet ground states were formed from mono-, bis-, and tris(diazo) compounds, respectively. The stability of those high-spin species was estimated by temperature-dependent ESR and UV/vis measurements as well as laser flash photolysis, which indicated that all three species are stable up to 160 K and have a half-life of a few seconds in solution at room temperature. The finding unequivocally shows that a precursor diazo unit can basically be handled as a building block to construct ploydiazo compounds and that persistent triplet carbenes, even though they greatly lose typical reactivity as a triplet carbene, still retain electronic properties and act as a spin source when aligned properly in the pi-electron frameworks to generate a high-spin molecule with remarkable thermal stability.