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 [H-2(COC)](PF6)(2) and [H-2((CNC)-N-H)](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 ((CNC)-N-H) 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.