'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 Pd metal precursors, to give the Pd 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 complexes were detected. The Pd complex 5 with chelating DPPE was finally successfully applied for the synthesis of the heterobimetallic Pd -Ru 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 -complex.