Triazolylidene Metal Complexes Tagged with a Bodipy Chromophore: Synthesis and Monitoring of Ligand Exchange Reactions

The alkyne azide “click” reaction was successfully used to prepare new Bodipy-functionalized triazoles and triazolium salts. The Bodipy functionality was compatible with cyclometalation conditions as well as with transmetalation procedures involving a triazolyldene silver intermediate, as demonstrated by the successful formation of a metallacyclic palladium dimer and an iridium chelate. Both complexes were characterized by X-ray diffraction, and spectroscopic studies demonstrate unperturbed photoluminescence of the Bodipy chromophore (emission around 545 nm, quantum yields in the 0.35–0.7 range, and excited-state lifetimes between 3 and 7 ns). The palladium dimer 4 was cleaved using N,N-dimethylaminopyridine (dmap) and acridine to afford monomeric triazolylidene palladium complexes 5 and 6. While dmap is a classical spectator ligand, acridine acts as photoluminescence quencher and quenching constants were determined as KSV = 0.86 and 1.6 × 104 M–1 for complexes 4 and 5, respectively. This dual reactivity of acridine as ligand and quencher was utilized for a ligand displacement assay that allowed modification of the organometallic site of the hybrid complex to be monitored by emission spectroscopy.