Carbene-Induced Reversible and Complete Decoordination of Tridentate Trispyrazolylborate Ligands in Copper Complexes

M.Casciotti, M. Álvarez, G. Sciortino, A. Lledós, T. R. Belderrain, P. J. Pérez. ChemistryEurope, 2026

https://doi.org/10.1002/ceur.70296

The chelate effect is one of the main factors contributing to the stability of transition-metal complexes. When one ligand binds to the metal center via two or more sites to form one or more metallo-rings, the resulting structures are generally highly stable and maintain a fixed structural skeleton. Here, we present a rare example of copper complexes bearing trispyrazolylborate (Tp^x) ligands acting in a tricoordinate fashion and expelling the Tp^x ligand from the first coordination sphere to the outer sphere, acting as a counterion, by adding a nucleophilic carbene ligand. Thus, κ³-Tp^xCu(NCCH₃) complexes are converted into [Cu(carbene)₂][Tp^x] in smooth processes that take place at room temperature. DFT calculations clarify the experimental behavior and propose the mechanism governing this transformation.