Phanephos

Phanephos[Chlorodiphenylphosphine|] is an organophosphorus compound with the chemical formula ₂₂. It is a white solid that is soluble in organic solvents. It is an example of a chiral C₂-symmetric diphosphine ligand used in asymmetric hydrogenation. Many substituents have been introduced in place of the phenyl groups, e.g., i-Pr, C₆H₁₁, etc. and a variety of chiral diphosphine ligands have been reported in asymmetric catalysis since the 1960s.

Preparation

Phanephos can be prepared in two steps from Paracyclophane|paracyclophane. In the first step, paracyclophane is dibrominated to give a pseudo-para dibromide. Thermal isomerisation then gives pseudo-ortho atropisomer of the dibromide. This isomer is subjected to lithium-halogen exchange by nBuLi and the resulting dilithium compound is treated with
PPh₂Cl to give a racemic mixture of phanephos.

Uses

Phanephos has been used in rhodium- and ruthenium- mediated stereoselective hydrogenation of dehydro amino acid methyl esters and asymmetric reduction of various β-ketoesters with about 90% ee.