Lithium metalations, phosphine, tris

Secondary aromatic phosphines can be prepared from tertiary phosphines by cleavage with sodium in liquid ammonia, and the detailed preparation of diphenylphosphine by this method has been reported. Diphenylphosphine has also been prepared by the reaction of chlorodiphenylphosphine with alkali metals or with lithium tetrahydroaluminate. This phosphine has been also obtained from diphenyltrichlorophosphorane or tetraphenyldiphosphine-disulfide with lithium aluminum hydride. A faster and easier method of preparation, which gives equally high yields, consists in the cleavage of tri-phenylphosphine with lithium metal in tetrahydrofuran, followed by hydrolysis of lithium diphenylphosphide with water to generate the phosphine. ... 

Metalation and Subsequent Reactions. Metalation of tris(TMS)phosphine by methyllithium gives lithium bis(TMS)-phosphide as a bis(THF) complex (eq 14). The extent of reaction could be monitored by the NMR resonance signal of LiP(TMS)2 that appeared at —302.4 ppm. ... 

Tri-(l-naphthyl)phosphine is cleaved by alkali metals in THF solution. " Reaction with sodium gives the naphthalene radical-ion, with lithium the perylene radical-ion, and with potassium the radical-ion (22). Hydrocarbon radical-ion formation was thought to occur via naphthalene derived from the metal naphthalenide. E.s.r. spectra of further examples of phosphorus-substituted picrylhydrazyl radicals have been reported. ... 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

Excluding the a-P-, a-Si-substituted carbanions which are listed in Table 2, there exist relatively few simple a-P-substituted carbanions whose structures are known. References to the crystal structures of some tri (alkyl or aryl) substituted phosphines are listed in Table 4. Few if any of these compounds have been utilized as synthetic reagents. Only two synthetically useful phosphorus-stabilized carbanions of Group la or Ila metal cations have been examined by X-ray diffraction analysis. Hie lithium carbanion of 2-benzyl-2-oxo-l,3,2-diazaphosphorinane (198) crystallizes as a monomeric bis-THF solvate (199) with a tricoordinate lithium atom. The magnesium salt of diethoxyphosphinyl acetone (200) is cluirac-terized as an intramolecularly chelated trimer similar in structure to [Mg(acac)]3. The Cu salt of this 3-keto phosphorus-stabilized anion exists only as a monomer. 

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