Metal-phosphine complex

This property is illustrated by the synthesis of many platinum-metal complexes of triphenylphosphine:[6] Phosphines are L-type ligands.

[8] In early work, phosphine ligands were thought to utilize 3d orbitals to form M-P pi-bonding, but it is now accepted that d-orbitals on phosphorus are not involved in bonding.

[9] The energy of the σ* orbitals is lower for phosphines with electronegative substituents, and for this reason phosphorus trifluoride is a particularly good π-acceptor.

The difference between the coordinating power of PR3 and NR3 reflects the greater steric crowding around the nitrogen atom, which is smaller.

[11] The steric properties of phosphine ligands can be ranked by their Tolman cone angle[7] or percent buried volume.

One of the first applications of phosphine ligands in catalysis was the use of triphenylphosphine in "Reppe" chemistry (1948), which included reactions of alkynes, carbon monoxide, and alcohols.

[16] In his studies, Reppe discovered that this reaction more efficiently produced acrylic esters using NiBr2(PPh3)2 as a catalyst instead of NiBr2.

Most work focuses on complexes of triorganophosphines, but primary and secondary phosphines, respectively RPH2 and R2PH, also function as ligands.