A phosphine ligand is a type of ligand containing a P atom in an atom, a molecule or an ion, which is bonded to a central atom (metal or metalloid). The simplest phosphine ligand is triphenylphosphine. The synthesis of phosphine ligands began as early as the 1860s, and the initial phosphine ligands were mainly used for chiral catalysis in the field of organic synthesis. Phosphine ligands are among the most widely studied ligands, not only in a wide variety, but also in a wide range of applications.
Figure 1. Triphenyphosphine
As a basic raw material for complex catalysts of metals and phosphines, phosphine ligand has broad applications in petrochemical industry. Phosphine ligands are also used in the fields of pharmaceutical industry, organic synthesis, analysis and so on. The phosphine ligands can also be used as brighteners in dye processes, as polymerizers for polymers, as antioxidants for color film development, as stabilizers for polyepoxidation, and as analytical reagents.
- Metal catalyst: In the field of organic synthesis, phosphine ligands can be used as ligands for many metal catalysts (such as ruthenium catalysts, palladium catalysts), and thus are widely used in the synthesis of metal catalysts, as well as many catalytic reactions such as hydrogenation reaction, N-methylation reaction, formylation reaction, and coupling reaction.
- Raw material: Certain phosphine ligands, such as triphenylphosphine, can be used as polymerization initiators and raw materials for the antibiotic drug clindamycin.
- Analytical reagent: When determining the phosphorus content by organic microanalysis, the phosphine ligand can be used as a standard sample.
- Brightener: In the dyeing process, the phosphine ligand can be used as a brightening agent for the improvement of fabric gloss.
- Reducing agent: Phosphine ligand is a fairly common reducing agent. In most cases, the thermodynamically favorable reactions can be driven by the formation of a phosphine ligand oxide.
- Other uses: As accelerators or flame retardants, phosphine ligands are widely used in petrochemical, coating, rubber and other industries.
Phosphine ligands have different classification methods, such as whether they are chiral, whether they are directly connected to phosphorus atoms and the number of phosphorus atoms involved in coordination. Phosphine ligands can also be classified into chiral phosphine ligands and achiral phosphine ligands depending on whether they contain a chiral center.
O-P ligand: A phosphine ligand whose atom is directly bonded to a phosphorus atom is called an O-P ligand.
C-P ligand: A phosphine ligand with a C directly attached to a phosphorus atom is called a C-P ligand.
N-P ligand: A phosphine ligand whose atom is bonded to a phosphorus atom is called an N-P ligand.
According to the number of phosphorus atoms involved in coordination in the ligand, phosphine ligands can be divided into monodentate phosphine ligands, bidentate phosphine ligands and polydentate phosphine ligands.
- Monodentate phosphine ligand: Monodentate phosphine ligand has only one P-coordinating atom in one ligand.
- Bidentate phosphine ligand: Bidentate phosphine ligand has two P-coordinating atoms in one ligand.
- Polydentate phosphine ligand: Polydentate phosphine ligand has a plurality of P coordinating atoms in one ligand.
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- Pei Cheng-chao. (2002). “Synthesis of new chiral diphosphine ligand (BisbenzodioxanPhos) and its application in asymmetric catalytichydrogenation.” Tetrahedron Lett 43(15), 2789-2792.
- Fan Qing-hua．(2001). “Preparation and use of MeO-PEG-supported chiral diphosphine ligands: soluble polymer-supported catalystsfor asymmetric Hydrogenation.” Tetrahedron: Asymmetry 12(8), 1241-1247.