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

Abstract

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