Diverse Coordination Modes of Bidentate COC and Tridentate CNC Ligands Comprising 1,2,3-Triazol-5-ylidenes

Two readily available bis­(1,2,3-triazol-5-ylidene) ligand precursors [H2(COC)]­(PF6)2 and [H2(CHNC)]­(PF6)2, bridged by an ether or amine functionality, respectively, were prepared. Their coordination versatility was evaluated predominantly by reacting Rh­(I) and Ir­(I) metal precursors with the in situ deprotonated salt precursors or in exceptional cases, via transmetallation from silver, to obtain those complexes not accessible via the preferred one-step route. A divergence in reactivity and coordination was observed for both ligand precursors depending on the base and metal employed. The carbon–ether–carbon (COC) ligand afforded mono- and bimetallic complexes of Rh­(I) and Ir­(I), chelates or bridges two metal centers. Conversely, the carbon–amine–carbon (CHNC) ligand displayed a greater predisposition for rhodium binding and poor coordination ability to iridium. As a result, two unusual bimetallic Rh­(I) complexes bearing two metal centers bridged by the central (deprotonated) amido functionality, along with a monometallic Rh­(I) containing the neutral amino-CNC pincer ligand were isolated. In contrast, only monometallic Ir­(I) complexes bearing a pendant triazolium arm could be prepared.