Diphenylphosphide

Submitted by GEORGE W. LUTHER, III, and GORDON BEYERLE Checked by DANIEL COXt and KIM COHNt 

A previous description of the synthesis of (CH3)3SiP(C6H5)2 in Inorganic Syntheses1 involves the initial preparation of sodium diphenylphosphide from diphenylphosphinous chloride. This method of preparation of the diphenylphosphide anion requires rigorous conditions and long reaction times. At least two other easier methods of preparation of the diphenylphosphide anion (lithium counterion) are known. One synthesis uses diphenyl-phosphine and n-butyllithium2 as reactants, whereas the second uses triphenylphosphine and elemental lithium.3,4 The second method is described here. 

The phosphorus-carbon bond of triphenylphosphine is easily cleaved by lithium in THF (tetrahydrofuran) at room temperature. The phenyllithium which is also formed in this reaction is destroyed in situ by allowing it to react with 2-chloro-2-methylpropane. Isobutylene gas is given off and the diphenylphosphide ion is then allowed to react with chlorotrimethylsilane. The product, diphenyl(trimethylsilyl)phosphine, is formed in 80% yield. The diphenylphosphide ion is usually formed in 85-95% yield, based on the lithium consumed. 

A clean, dry, 100-mL, two-necked, round-bottomed flask is set up with a reflux condenser (air-cooled) in a nitrogen-filled glove bag. To the second neck, a septum is attached. Twenty-five milliliters of freshly-dried THF and 10.5 g (0.04 mol) of triphenylphosphine are added to the flask, which contains a Teflon-coated magnetic stirring bar. Lithium metal (0.55 g, 0.08 mol) from which oil has been cleaned, is scraped, cut, and pressed into flat rods and is added to the THF-phosphine solution. After the solution is stirred, a red color forms which indicates formation of the diphenylphosphide ion. The air-cooled condenser is used because the heat liberated by this reaction causes the solvent to reflux. Within 2 hr the reaction is 85-95% complete, based on unreacted lithium, and the solution is dark-red. It has been observed that the smaller the amount of THF used, the faster the reaction proceeds and the greater is the rate of refluxing. 

The properties of (CH3)3SiP(C6H5)2 have been described previously in Inorganic Synthesesf 

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Lithium diphenylphosphide [4S41 -02-2] and related oiganophosphides are chemiluminescent in reaction with oxygen (127). Chemiluminescence is... 

The present procedure illustrates the facile demethylation of methyl aryl ethers by lithium diphenylphosphide.3 This reaction is specific for methyl ethers and may be carried out in the presence of ethyl ethers in high yield.4 Use of excess reagent allows cleavage in the presence of enolizable ketones.5 In the present case, the cleavage may be performed without protection of the aldehyde, but two equivalents of reagent are required, and the yield is reduced to ca. 60%. 

The exact time and temperature required for complete reaction must be determined for each individual compound. It has been observed that nucleophilic demethylation of methyl o-alkoxyaryl ethers is accelerated relative to anisole [Benzene, methoxy-],6 and this reaction is no exception. Lithium diphenylphosphide cleavage of anisole is complete in about 4 hours in refluxing tetrahydrofuran, whereas the present reaction is complete within 2 hours at 25°. 

Amos prepared his polymer-supported reagent in two steps from commercially available polystyrene beads (bromination, then condensation with lithium diphenylphosphide). He found that a useful range of sulphoxides could be reduced effectively, in good yields and in a few hours, to give clean samples of sulphides. 

A solution of the sodium salt of yV-methylaniline in HMPA can be used to cleave the methyl group from aryl methyl ethers ArOMe + PhNMe —> ArO + PhNMca- This reagent also cleaves benzylic groups. In a similar reaction, methyl groups of aryl methyl ethers can be cleaved with lithium diphenylphosphide (PH2PLi). " This reaction is specific for methyl ethers and can be carried out in the presence of ethyl ethers with high selectivity. 

B. From Metallated Phosphines.—Lithium diphenylphosphide and ethylene oxide produce (7), which when added to chlorodibutyl- or chlorodiphenyl-phosphine yields 2-diphenylphosphinoethyl phosphinites (8). 

Quinolylphosphines have been prepared from the reaction of 8-chloroquinoline and potassium diphenylphosphide, or the quinolyl-lithium derivative and a chlorophosphine. ... 

The ditertiary phosphines (11), prepared from the corresponding alkyl chloride and lithium diphenylphosphide (10), - react with sodium in liquid ammonia to give the phosphines (12). 

Chloroprop-l-yne reacts with sodium diphenylphosphide in liquid ammonia to give diphenyl prop-1-ynyl phosphine (19). However, when the addition is carried out in THF a mixture of the prop-2-ynylphosphine... 

Selective demethylation of (63) to the phenolic ether (64) has been achieved by the use of lithium diphenylphosphide. ... 

Various type (967) dinuclear complexes with phosphido bridges have been prepared, usually by reduction of [(R3P)2NiX2] with, for example, sodium.2372-237 The terminal phosphines can be exchanged by other phosphines or by CO, yielding (968) and (969) in the latter case.2373,2374 Diphenylphosphide Ni1 complexes have also been prepared electrochemically.2376... 

In the early 1970 s, Bayer et al. reported the first use of soluble polymers as supports for the homogeneous catalysts. [52] They used non-crosslinked linear polystyrene (Mw ca. 100 000), which was chloromethylated and converted by treatment with potassium diphenylphosphide into soluble polydiphenyl(styrylmethyl)phosphines. Soluble macromolecular metal complexes were prepared by addition of various metal precursors e.g. [Rh(PPh3)Cl] and [RhH(CO)(PPh3)3]. The first complex was used in the hydrogenation reaction of 1-pentene at 22°C and 1 atm. H2. After 24 h (50% conversion in 3 h) the reaction solution was filtered through a polyamide membrane [53] and the catalysts could be retained quantitatively in the membrane filtration cell. [54] The catalyst was recycled 5 times. Using the second complex, a hydroformylation reaction of 1-pentene was carried out. After 72 h the reaction mixture was filtered through a polyamide membrane and recycled twice. 

The only ditelluro-phosphorus acid reported to date is lithium dip-henylditellurophosphinate, [Ph2PTe2] Li+, prepared from the reaction of lithium diphenylphosphide with elemental tellurium (analogous to Equation 30).36,45... 

From MetallatedPhosphines. The synthesis of polymeric tertiary phosphines based on the reaction of lithium diphenylphosphide with chloromethylated polystyrenes continues to attract interest.9 10 Considerable breakdown of the carbon-carbon back-bone of PVC occurs on reaction with lithium diphenylphosphide in THF, and only oligomers of low molecular weight result.11 The potassium salt (9) reacts with chloromethylated polystyrene to form the polymeric diphosphine (10).12... 

The w-chloroalkyldiphenylphosphines (11) have been prepared by the reaction of equimolar quantities of sodium diphenylphosphide with aco-dichloroalkanes. Whereas the phosphine (11 n = 3) can be converted into the Grignard reagent (12), which reacts with dimethylchlorophosphine to form the unsymmetrical diphosphine (13), the Grignard reagent (14) undergoes a -elimination reaction to regenerate diphenylphosphide ion.13... 

Similarly, the chloroalkylarsine (15) (obtained from lithium diphenylarsenide and 1,2-dichloroethane) reacts with lithium diphenylphosphide to form the mixed phosphine-arsine (16).14... 

The product of the reaction between lithium diphenylphosphide (or trimethyl-silyldiphenylphosphine) and dimethyl 2,3-dichloromaleate has been shown to be the fumarate (17)17 and not (as previously supposed)18 the expected maleate (18). 

Nucleophilic displacement of halide ion from a saturated carbon atom by alkali-metal diphenylphosphide reagents occurs with inversion of configuration at carbon, as is found in normal Sn2 displacements.19 Thus menthyl chloride or bromide gives ... 

An improved procedure has been reported for the synthesis of the C-functionalized tertiary phosphine (20), based on the reaction of potassium diphenylphosphide with ethyl chloroacetate.20... 

Chlorides RMe2CCH2Cl [(a) R = Me, R = Ph and (b) R = CH2Ph] reacted with diphenylphosphide ions in liquid ammonia, via a proposed 5rn 1 mechanism and their reactivities were measured. The higher reactivity of (a) has been attributed to efficient intramolecular electron transfer from the phenyl ring to the C—Cl a bond (intra-ET catalysis). The lower reactivity of (b) is ascribed to a decrease in the rate of the intra-ET by elongation of the bridge by one methylene unit. The relative reactivity of (a) versus (b) is proposed to indicate the ratio of the intra-ET rates of the radical anions of both compounds. ... 

Similarly, ethylzinc diphenylphosphide (244) was prepared from diphenylphosphine and Et2Zn (Fignre 111). An X-ray crystal strncture determination revealed a central six-membered metaUacycle. To two of the zinc atoms additional diphenylphosphine... 

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