Nucleophilic additions to pseudohalides in the coordination sphere of transition metal ions and coligand isomerism

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 r eleased. The conditions for such an addition were studied and established b y selecting various central atoms and different N-donor heterocyclic ligand s. 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 d ifferent 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 [MX2(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 formati on 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 beta-site of the pseudohalides changing its hybrid ization and providing an unsaturated valency for a nucleophilic attack. (C) 1998 Elsevier Science S.A. All rights reserved.