Recent Advances of Imidazolin-2-iminato in Transition Metal Chemistry
Abstract
The reactivity of N-heterocyclic carbenes (NHCs) towards organic azides produced a new class of monoanionic nitrogen donor ligands imidazolin-2-iminato (ImRN‒), which are isolobally related to imido ligands (RN2‒). The imidazolin-2-iminato ligands essentially can be derived by substituting alkyl or aryl group from imido moieties. The proton abstraction from imidazolin-2-imine resulted in the monoanionic imidazolin-2-iminato ligands that possessed the exocyclic nitrogen, which strongly favors the binding with electrophiles. The nucleophilicity of anionic nitrogen is markedly increased by the charge (positive) delocalization into the five-membered heterocyclic ring. Altering the N-substitutions could meet the necessities for kinetic stabilization of high valent reactive species. Slowly these ligands cemented its status as a potential alternative for ubiquitous cyclopentadienyl ligand and continued receiving attention. These ligands progressively accustomed as the ancillary ligands for early transition metals, rare earth elements, or early actinides affording pincer complexes or "pogo stick" type compounds. In this article, we summarized the present chemistry of transition metal elements bearing imidazolin-2-iminato/imine ligands from the year 2015 to date.
