Phosphites, phosphonites, and phosphinites Phosphites, sometimes called
phosphite esters, have the general structure P(OR)3 with oxidation state +3. Such species arise from the alcoholysis of phosphorus trichloride: :PCl3 + 3 ROH → P(OR)3 + 3 HCl The reaction is general, thus a vast number of such species are known. Phosphites are employed in the
Perkow reaction and the
Michaelis–Arbuzov reaction. They also serve as ligands in organometallic chemistry. Intermediate between phosphites and phosphines are
phosphonites (P(OR)2R') and
phosphinite (P(OR)R'2). Such species arise via alcoholysis reactions of the corresponding phosphonous and phosphinous chlorides ((PCl2R') and (PClR'2), respectively). The latter are produced by reaction of a
phosphorus trichloride with a
poor metal-alkyl complex, e.g.
organomercury,
organolead, or a mixed
lithium-
organoaluminum compound.
Phosphines The parent compound of the phosphines is PH3, called
phosphine in the US and British Commonwealth, but phosphane elsewhere. Replacement of one or more hydrogen centers by an organic substituents (alkyl, aryl), gives PH3−xRx, an organophosphine, generally referred to as phosphines. From the commercial perspective, the most important phosphine is
triphenylphosphine, several million kilograms being produced annually. It is prepared from the reaction of
chlorobenzene,
PCl3, and sodium. Phosphorus halides undergo
nucleophilic displacement by organometallic reagents such as
Grignard reagents. Organophosphines are nucleophiles and
ligands. Two major applications are as reagents in the
Wittig reaction and as supporting
phosphine ligands in
homogeneous catalysis. Their nucleophilicity is evidenced by their reactions with
alkyl halides to give
phosphonium salts. Phosphines are
nucleophilic catalysts in
organic synthesis, e.g. the
Rauhut–Currier reaction and
Baylis-Hillman reaction. Where the nucleophilicity or basicity of organophosphines causes trouble, they can be protected as
phosphine-boranes. Phosphines are also
reducing agents, as illustrated in the
Staudinger reduction for the conversion of organic azides to amines and in the
Mitsunobu reaction for converting alcohols into esters. In these processes, the phosphine is oxidized to phosphorus(V). Phosphines have also been found to reduce activated carbonyl groups, for instance the reduction of an α-keto ester to an α-hydroxy ester. A few halophosphines are known, although phosphorus' strong
nucleophilicity predisposes them to decomposition, and
dimethylphosphinyl fluoride spontaneously disproportionates to
dimethylphosphine trifluoride and
tetramethylbiphosphine. One common synthesis adds halogens to
tetramethylbiphosphine disulfide. Alternatively alkylation of
phosphorus trichloride gives a halophosphonium cation, which metals reduce to halophosphines.
Phosphaalkenes and phosphaalkynes Compounds with carbon phosphorus(III) multiple bonds are called
phosphaalkenes (R2C=PR) and
phosphaalkynes (RC≡P). They are similar in structure, but not in reactivity, to
imines (R2C=NR) and
nitriles (RC≡N), respectively. In the compound
phosphorine, one carbon atom in benzene is replaced by phosphorus. Species of this type are relatively rare but for that reason are of interest to researchers. A general method for the synthesis of phosphaalkenes is by
1,2-elimination of suitable precursors, initiated thermally or by base such as
DBU,
DABCO, or
triethylamine: :
Thermolysis of Me2PH generates CH2=PMe, an unstable species in the condensed phase. ==Organophosphorus(0), (I), and (II) compounds==