(Guanidine)copper complexes: structural variety and application in bioinorganic chemistry and catalysis

In this paper, guanidine copper compounds are reviewed with an emphasis on structural characteristics and their application in bioinorganic chemistry and catalysis. The literature survey includes the copper coordination chemistry of biological guanidine derivatives, peralkylated guanidines including bicyclic ones and of further nitrogen-rich guanidine-type systems such as azoimidazoles, triazolopyrimidines and triaminoguanidines. From a sporadic interest dating back to the 1960s, research on this ligand class and its use in copper coordination chemistry has gained new impetus since 2000. With the synthesis of examples with sophisticated substitution at the characteristic CN3 framework, complex problems can be addressed in several fields of chemistry. This paper analyses the different types of guanidines for their special donor properties and highlights the specific advantages of guanidines as neutral donor ligands in copper coordination chemistry where a great variety of coordination modes was found. These compounds offer the ability to distribute the formal positive charge of the metal throughout the guanidine unit and represent more than simple sigma-donating ligands.