Organophosphine
Organophosphine
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Organophosphine

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Organophosphine

Organophosphines are organophosphorus compounds with the formula PRnH3−n, where R is an organic substituent. These compounds can be classified according to the value of n: primary phosphines (n = 1), secondary phosphines (n = 2), tertiary phosphines (n = 3). All adopt pyramidal structures. Organophosphines are generally colorless, lipophilic liquids or solids. The parent of the organophosphines is phosphine (PH3).

Organophophines are classified according to the number of organic substituents.

Primary (1°) phosphines, with the formula RPH2, in principle are derived by alkylation of phosphine. Some simple alkyl derivatives such as methylphosphine (CH3PH2) can be prepared by alkylation of phosphine in the presence of base:

A more common synthetic route involves reduction of chlorophosphines with hydride reagents. For example, reduction of dichlorophenylphosphine with lithium aluminium hydride affords phenylphosphine according to the following idealized equation:

Most primary phosphines are pyrophoric in air.

Secondary (2°) phosphines, with the formula R2PH, are prepared analogously to the primary phosphines. They are also obtained by alkali-metal reductive cleavage of triarylphosphines followed by hydrolysis of the resulting phosphide salt. The latter route is employed to prepare diphenylphosphine (Ph2PH). Diorganophosphinic acids, R2P(O)OH, can also be reduced with diisobutylaluminium hydride. Secondary phosphines are mildly protic in character.

Secondary phosphines occur in cyclic forms. Three-membered rings are phosphiranes (unsaturated: phosphirenes), five-membered rings are phospholanes (unsaturated: phosphole), and six-membered rings are phosphinanes.

Tertiary (3°) phosphines, with the formula R3P, are traditionally prepared by alkylation of phosphorus trichloride using Grignard reagents or related organolithium compounds:

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