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 II 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 i-site of the pseudohalides changing its hybridization and providing an unsaturated valency for a nucleophilic attack.