Organophosphine
They are also obtained by alkali-metal reductive cleavage of triarylphosphines followed by hydrolysis of the resulting phosphide salt.
Tertiary (3°) phosphines, with the formula R3P, are traditionally prepared by alkylation of phosphorus trichloride using Grignard reagents or related organolithium compounds: In the case of trimethylphosphine, triphenyl phosphite is used in place of the highly electrophilic PCl3:[6] Slightly more elaborate methods are employed for the preparation of unsymmetrical tertiary phosphines, with the formula R2R'P.
For example, in the presence of basic catalysts PH3 adds of Michael acceptors such as acrylonitrile:[7] Tertiary phosphines of the type PRR′R″ are "P-chiral" and optically stable.
From the commercial perspective, the most important phosphine is triphenylphosphine, several million kilograms being produced annually.
As a result, the lone pair of trimethylphosphine has predominantly s-character as is the case for phosphine, PH3.
When the organic substituents all differ, the phosphine is chiral and configurationally stable (in contrast to NRR'R").
Like amines, phosphines have a trigonal pyramidal molecular geometry although often with smaller C-E-C angles (E = N, P), at least in the absence of steric effects.
When used as ligands, the steric bulk of tertiary phosphines is evaluated by their cone angle.
The reactivity of phosphines matches that of amines with regard to nucleophilicity in the formation of phosphonium salts with the general structure PR4+X−.
For example, silver chloride reacts with triphenylphosphine to 1;1 and 1:2 complexes: The adducts formed from phosphines and borane are useful reagents.
The reducing properties of organophosphiines is also illustrated in the Staudinger reduction for the conversion of organic azides to amines and in the Mitsunobu reaction for converting alcohols into esters.
[13] In the proposed reaction mechanism, the first proton is on loan from the methyl group in trimethylphosphine (triphenylphosphine does not react).
Primary (RPH2) and secondary phosphines (RRPH and R2PH) add to alkenes in presence of a strong base (e.g., KOH in DMSO).
Primary and secondary phosphines do not normally add to ketones and aldehydes unless the addition closes a ring:[15]
