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.