'Click'-Derived 1,2,3-Triazolium Salts Featuring a 4-Halo-phenyl Group: Precursors for Heterobimetallic Complexes

The 'click'-derived 1,2,3-triazolium salts [L1/L2-H]I (1-(4-iodo/bromo-phenyl)-1H-1,2,3-triazolium salt) featuring two distinct coordination sites, one via oxidative addition and other via classical deprotonation cum metalation, were designed and explored towards the synthesis of various mono- and bimetallic complexes. Accordingly, a series of well-characterized 1,2,3-triazol-5-ylidene coordinated cyclometalated transition metal complexes (1-3) were obtained. However, these complexes were found to be ineffective in accessing the desired heterobimetallic complexes. Nevertheless, same ligand systems readily underwent oxidative addition with Pd⁰ metal precursors, to give the Pd^II complexes 4/5, and the considerable change and reversal in chemical shift values of the triazole C4/C5-backbone protons (C4-H being downfield shifted than that of C5-H) of these oxidatively added Pd^II complexes were detected. The Pd^II complex 5 with chelating DPPE was finally successfully applied for the synthesis of the heterobimetallic Pd^II -Ru^II complex 6 and 2D NMR analyses, as well as DFT calculations supported the formation of the rare C4/C5-unprotected 1,2,3-triazol-4-ylidene coordinated Ru^II -complex.