amidinatetype

Amidinates are a class of ligands used in organometallic and coordination chemistry. Amidinate-type ligands are derived from amidines by deprotonation at the central carbon, producing a monoanionic, bidentate ligand that binds a metal through two nitrogen atoms. The negative charge is delocalized over the NCN core, providing strong, chelating support.

The typical amidinate-type motif features a five-membered chelate ring that includes the metal, two nitrogens, and the central carbon. Substitution on the nitrogens (R groups) and on the central carbon allows precise tuning of the ligand’s steric and electronic properties. Ligands can be symmetrical or unsymmetrical, enabling fine control of metal coordination environments and reactivity.

Synthesis generally involves deprotonation of an amidine with a strong base such as n-butyllithium, sodium hydride, or potassium tert-butoxide in coordinating solvents. The resulting amidinate salts (for example, Li or Na salts) can react with metal precursors to form a wide range of metal complexes. Transmetalation from the alkali or alkaline-earth salts to transition metals is common, yielding discrete or polymeric species depending on the metal and substituents.

Amidinate-type ligands are valued for their strong sigma-donor character, tunable sterics, and robustness, enabling stabilization of metals in various oxidation states and coordination geometries. They find broad use in homogeneous catalysis, including polymerization, cross-coupling, hydrofunctionalization, and small-molecule activation, as well as in the synthesis of metal clusters and advanced materials. See also amidines and related N-donor ligands for related chemistry.