Ligands for functional metal complexes refer to ligands that coordinate with metal ions to form metal complexes with specific functions. Ligands for functional metal complexes usually have good coordination ability and chemical stability. In general, ligands are of little value when used alone. Ligands usually coordinate with different metal ions to form metal complexes with different functions, and these metal complexes play a role in many fields.
Ligands for functional metal complexes have a wide variety, and the metal complexes formed by ligands are also diverse. Therefore, they have great application value in many fields such as optoelectronic materials, biology, and medical catalysis.
- Optoelectronic materials: Organic light-emitting diodes (OLEDs) have been successfully used in mobile phones, televisions and other display screens due to their low energy consumption, high color purity, ultra-thin and flexible foldable features. Phosphorescent OLEDs based on platinum (Ⅱ) and osmium (Ⅱ) complexes emit light through the triplet exciton emission mechanism of phosphorescent materials. In the process of OLED development, the research on phosphorescent iridium (Ⅲ) complexes has become the mainstream in the field of OLED luminescent materials, and finally took the lead in commercial OLED red and green light materials. In addition, N-heterocyclic carbene (NHC) ligands have strong σ-electron donating ability and weak π-electron withdrawing ability, and can form strong coordination bonds during the coordination process with metal atoms. On the other hand, the molecule based on N-heterocyclic carbene (NHC) ligand has a high LUMO energy level, which expands the band gap of the entire molecule and realizes high-efficiency blue light emission. A series of N-heterocyclic carbene tetradentate deep blue platinum (Ⅱ) complexes have been developed due to their ideal coordination environment and good thermal stability. Using this complex as a doped luminescent material, after device optimization, the maximum external quantum efficiency (EQE) of the prepared OLED device can reach 15%.
Figure 1. NHC-platinum complex for preparing phosphorescent OLED
- Organic catalysis: Ligands can be used to prepare catalysts and thus widely used in the field of organic catalysis. The ligand can not only participate in the reaction alone, but also form complexes with the metal to participate in the reaction. For example, acylhydrazone has a special chemical structure, strong coordination ability, various coordination methods, nonlinear optical properties and excellent biological activity, so it is often used as a ligand for metal complexes. Acylhydrazone metal complexes can be used as catalysts to catalyze polymerization reactions, olefin oxidation reactions, and asymmetric hydrogenation reactions.
Figure 2. Acylhydrazone ligands are obtained by nucleophilic addition reaction between hydrazide and ketone
- Medicine: Ligands are also of great value in medical applications. Combining P atoms and N atoms can form a P-N mixed ligand with a richer structure and more coordination sites, and then can prepare metal complexes with specific structures and properties. For example, by coupling 2-diphenylphosphine benzaldehyde with various primary amines in a Schiff base condensation reaction, the imino group can be successfully reduced to a sp3-hybridized amine, thereby preparing a series of iminophosphine ligands and aminophosphine ligands. Using these P-N mixed ligands to react with tetrahydrothiophene gold, a batch of Au (I) complexes were obtained. This kind of Au (I) complex has stronger cytotoxicity to cancer cells, and shows lower cytotoxicity to normal healthy cells, so it can be used for tumor treatment.
Figure 3. Iminophosphine ligands and aminophosphine ligands prepared from diphenylphosphine benzaldehyde and primary amines
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