Rare Earth Metal Complexes Supported by Ancillary Imidazolin-2-iminato Ligands

The coordination chemistry of imidazolin-2-iminato ligands towards rare earth metal atoms is reviewed. The structural characterization of a large number of mono-, bis- and tris(imidazolin-2-iminato) complexes in most cases scandium, yttrium, gadolinium, and lutetium complexes reveals almost exclusively the formation of mononuclear complexes with very short metal nitrogen bonds, which confirms the ability of imidazolin-2-iminato ligands to efficiently act as imido-type 2 sigma,4 pi-electron donors. In particular, mono(imidazolin-2-iminato) metal dichlorides proved to be excellent starting materials for the introduction of alkyl, amido, cyclopentadienyl, cyclooctatetraenyl, and carboranyl ligands and also for the preparation of efficient pre-catalysts for ring-opening, hydroamination and hydrosilylation reactions, which allow to establish imidazolin-2-iminato ligands as novel valuable members of the growing family of ancillary ligands in organo rare earth metal and organolanthanide chemistry. In addition, the coordination chemistry of several imidazolin-2-imine-hybrid ligands such as cyclopentadienyl-imine and pincer-type diimine ligands is described, and the structural characterization of the resulting complexes indicates that also neutral imidazolin-2-imines act as strong amido-type donor ligands towards rare earth metal ions.