Diphenyl diselenide

Diphenyl diselenide is the chemical compound with the formula ₂Se₂, abbreviated Ph₂Se₂. This yellow-coloured solid is the oxidized derivative of benzeneselenol. It is used as a source of the PhSe unit in organic synthesis.

Structure

Ph₂Se₂ has idealized C₂-symmetry, like hydrogen peroxide and related molecules. The Se-Se bond length of 2.29 Å the C-Se-Se-C dihedral angle is 82° and the C-Se-Se angles are near 110°.

Preparation

The molecule is prepared by the oxidation of benzeneselenoate, the conjugate base of benzeneselenol which is generated via the Grignard reagent:
Alternatively, phenyl iodide undergoes photoinduced radical-nucleophilic aromatic substitution with sodium selenide to make benzeneselenoate ions:

Medical applications

Diphenyl diselenide alleviates methylmercury poisoning in grass carp.

Reactions

A reaction characteristic of Ph₂Se₂ is its reduction:
PhSeNa is a useful nucleophile used to introduce the phenylselenyl group by nucleophilic substitution of alkyl halides, alkyl sulfonates and epoxides. The example below was taken from a synthesis of morphine.
Another characteristic reaction is chlorination:
PhSeCl is a powerful electrophile, used to introduce PhSe groups by reaction with a variety of nucleophiles, including enolates, enol silyl ethers, Grignard reagents, organolithium reagents, alkenes and amines. In the sequence below, a PhSe group is introduced by reaction of a lactam enolate with PhSeCl. This sequence is a powerful method for the conversion of carbonyl compounds to their α,β-unsaturated analogs.
Diphenyl diselenide itself is also a source of a weakly electrophilic PhSe group in reactions with relatively powerful nucleophiles like Grignard reagents, lithium reagents and ester enolates. PhSeCl is both more reactive, and more efficient, since with Ph₂Se₂ half of the selenium is wasted.
N-Phenylselenophthalimide can be used if PhSeCl is too strong and diphenyl diselenide is too weak or wasteful.