Coordinated pyrazoles exhibit a nucleophilic addition to the cyanate ligand inside the transition metal coordination sphere and new chelate complexes are formed; the new anionic ligand of the carbamoylpyrazolate type can be released. The conditions for such an addition were studied and established by selecting various central atoms and different N-donor heterocyclic ligands.Some non-linear pseudohalides, namely N(CN) 2 - , C(CN) 3 - and ONC(CN) 2 - , are also capable of such reactions but the addition proceeds under different conditions due to different electronic and steric requirements.A new type of isomerism-coligand isomerism-has been discovered: one isomer is the usual complex of the [MX 2 (pzt) 2 ] type (pzt, pyrazole-type ligand) whereas in the second isomer [M(pzt.X) 2 ] a new anionic chelating ligand formed by nucleophilic addition is present.Another type of nucleophilic addition, reaction of methanol with the N(CN) 2 - specifically in the coordination sphere of Cu I I leads to the formation of a six-membered metallacycle. Nucleophilic addition of methanol to the ONC(CN) 2 - anion in the transition metal coordination sphere results in formation of a five-membered metallacycle.All nucleophilic additions studied have a common feature in a coordinative activation of the carbon β-site of the pseudohalides changing its hybridization and providing an unsaturated valency for a nucleophilic attack.