Transition metal complexes supported by highly basic imidazolin-2-iminato and imidazolin-2-imine N-donor ligands

Imidazolin-2-imines represent a particularly basic and nucleophilic subclass of guanidines, and a large variety of these N-donor ligands have become available, inter alia, by the reaction of N-heterocyclic carbenes of the imidazolin-2-ylidene-type with organic azides such as trimethylsilyl azide followed by desilylation. These imidazolin-2-imines serve as precursors for the generation of anionic imidazolin-2-iminato ligands (imidazolin-2-imides), which act as imido-type ligands towards early transition metals and metals in a higher oxidation state and were used as ancillary ligands in a number of homogeneous catalysts, in particular for olefin polymerization and alkyne metathesis. Furthermore, these ligands also form strong metal-nitrogen bonds in lanthanide and actinide complexes. Linking the imidazolin-2-imines to each other or to other functional moieties affords multidentate ligands, and their rich coordination and bioinorganic chemistry developed mainly in the past 10 years comprises almost any transition metal. In addition to a detailed account of the chemistry of imidazolin-2-imides and -imines, the transition and main group element chemistry of their 4,5-dihydro congeners, imidazolidin-2-imides and -imines, is also addressed.