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We present herein anionic borate‐based bi‐mesoionic carbene compounds of the 1,2,3‐triazol‐4‐ylidene type that undergo C−N isomerization reactions. The isomerized compounds are excellent ligands for CoII centers. Strong agostic interactions with the “C−H”‐groups of the cyclohexyl substituents result in an unusual low‐spin square planar CoII complex, which is unreactive towards external substrates. Such agostic interactions are absent in the complex with phenyl substituents on the borate backbone. This complex displays a high‐spin tetrahedral CoII center, which is reactive towards external substrates including dioxygen. To the best of our knowledge, this is also the first investigation of agostic interactions through single‐crystal EPR spectroscopy. We conclusively show here that the structure and properties of these CoII complexes can be strongly influenced through interactions in the secondary coordination sphere. Additionally, we unravel a unique ligand rearrangement for these classes of anionic mesoionic carbene‐based ligands., C−N isomerization reactions on borate‐based anionic bi‐mesoionic carbene ligands are reported. The CoII complexes with these ligands display geometries, spin states, and reactivities that are controlled by agostic interactions in the secondary coordination sphere.

We demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by AuI and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au–C(alkyne) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom.