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

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, κ 3 ‐Tp x Cu(NCCH 3 ) 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.