Hydrogen-Phosphorus Bonds

Phosphorus—Hydrogen Bond. A hydrogen bound to phosphoms has Httie acidic or hydric character. Most of the reactions the bond undergoes are those of a reducing agent. P—H bonds are formed by hydrolysis of active metal phosphides or phosphoms haUdes, by the rearrangement of P—O—H or P—S—H linkages, or by the hydrolysis of P—P bonds (6,17). 

B. Electrophilic Reactions.—Transesterification followed by rearrangement is a common route from simple phosphites to more complex phos-phonates. This has now been applied to the preparation of cyclic phos-phonates (85). Both phosphites (86) and phosphoranes (87) containing phosphorus-hydrogen bonds are obtained from the cyclic biphosphite (88) and butanol. ... 

Presence of a polar phosphorus-hydrogen bond makes hydridophosphazenes as versatile reagents to generate a large variety of phosphazene... 

Two general methods are available for preparing polyphosphines containing PCH2CH2P structural units and phosphorus-hydrogen bonds ... 

Consider the following reaction sequence involved in the successive base-catalyzed addition of the two phosphorus-hydrogen bonds in a primary phosphine to a vinylphosphorus derivative ... 

Other neutral fragments eliminated in the fragmentation processes of tris-(dimethylamino) phosphine metal carbonyl complexes appear to contain phosphorus-hydrogen bonds, e. g. 

Transformations of phosphines to difluorophosphoranes proceed with xenon difluoride under mild conditions and in high yields, and the phosphorus-hydrogen bond is stable chlorine atoms are replaced by fluorine in chlorine-phosphorus molecules, while triphenyl and trimethyldifluorophosphorane are isolated in 90-100% yield130-132. Reactions of compounds containing P—N, P—O and P—S bonds with xenon difluoride proceed by fragmentation or dimerization133 (Scheme 55). 

Linear tetratertiary phosphine, P4, was obtained by King and Kapoor (27), by the addition of phosphorus-hydrogen bonds in 1,2-bisphenylphosphinoethane to the carbon-carbon double bonds in two equivalents of diphenylvinylphosphine, according to the following equation ... 

Phosphorus-hydrogen bonds form in intermolecular exchange. Trimethylstannane or MejSiH with PFj reacts ... 

These results indicate that acetyl phosphinate is the most potent active site-directed inactivator of PFL now known. Although it is not yet clear what the overall mechanism of inactivation might be, consistent with the mechanism for the normal PFL reaction proposed by Kozarich and co-workers (Scheme 41) (187), there is the intriguing possibility that phosphorus-carbon or phosphorus-hydrogen bond cleavage might occur. These possibilities are currently being... 

Phosphorus Compounds.—Treatment of the dioxaphospholen (635) with sulphur yields a mixture of the oxathiole (636) and fran -dibenzoylstilbene, PhCOCPh=CPhCOPh." 2-Phenyl-l,3,2-dioxaphospholan (637 R = Ph) dimerizes in solution to a ten-membered-ring compound, which was isolated as (638) by sulphurization." The cyclic thiophosphorous acid (639) exists in equilibrium with the betaine (640) in aqueous ethanol/ The spiro-compound (641), which contains a phosphorus-hydrogen bond, is formed by the action of (637 R = Cl) on diethyl tartrate. The phosphazene (642) spontaneously cyclizes to the spiro-compound (643). " Stable derivatives (645) and (646 R = Br) of five-co-ordinate phosphorus have been obtained by the action of bromine on the o-phenylene phosphite (644)/ The chlorine analogue (646 R Cl) reacts with 3,5-dimethylpyrazole to give the corresponding pyrazole derivative (646 R = 3,5-dimethylpyrazol-l-yl), which reversibly dimerizes to the zwitterion (647). ... 

King et developed a route to poly(tertiary phosphines) by use of a base-catalyzed addition of a phosphorus-hydrogen bond to the carbon-carbon double bond of various vinylphosphine derivatives the first extensive series of methylated polyphosphines were prepared this way. The synthesis of unsymmetrical diphosphines of the type i 2PCH2CH2P(CH3)2 involves addition of a P-H bond to CH2=CHP(S)(CH3)2 via potassium tert-bwioxxdQ catalysis, followed by desulfurization with LiAlH4 in boiling dioxane (i.e.. Equations 10,11). 

A semiempirical bond energy/bond order method was used to calculate the kinetic parameters for the photoreductions of carbonyl triplets by PH3. Phosphorus-hydrogen bonds were found to be highly reactive for the hydrogen abstraction via PH3 + R R2CO - PH2 + R R C OH [148]. 

Reactions with alkynes may lead to the formation of cyclized products. The reaction of iodobenzenes with two equivalents of an alkyne has been shown to give naphthalene derivatives in the presence of cobalt catalyst with a manganese reduc-tant. The process, shown in Scheme 15, is thought to involve oxidative addition of the aryliodide to cobalt followed by double alkyne insertion. The cobalt-catalysed annulation step probably involves an pathway. The cyclopentadienyl-rhodium-catalysed annulation of benzoic acids with alkynes has been used to form isocoumarin derivatives, such as (126). The process is thought to involve cyclorhodation at the ortho-position of a rhodium benzoate intermediate, followed by alkyne insertion to form a seven-membered rhodacycle and reductive elimination The silver-catalysed annulations of diphenylphosphine oxides with alkynes proceed in the absence of rhodium. Benzophosphole oxides such as (127), formed with diphenylethyne, are produced. Here, the proposed mechanism involves homolytic cleavage of the phosphorus-hydrogen bond to give a radical which can add to the alkyne and subsequently cyclize. ... 

---