True phosphinous acids

IR spectra of (F3Q2POH and (F3C 2POD and their assignments. Redrawn with permission from [60]. Copyright 1962 American Chemical Society. 

In order to use variable-temperature gas-phase IR spectroscopy to investigate gas-phase equilibria, it is necessary to determine first the relative extinction coefficients for the two conformers once this has been done the quantitative analysis is straightforward. A van t Hoff plot [In(Ap) versus 7 ] can be drawn and this can then be used to extract the required thermodynamic data, i.e. the enthalpy difference between the two structures and the corresponding entropy terms. On this basis, the experimental data returned a value for of —6.92 0.05 kJ mol , in good agreement with the theoretical value of 7.3 kJ mol , and AS —8.37 0.15 kJ moP.  

Parts of the crystal structures of (a) (F3Q2POH and (b) (F3CF2C)2POH illustrating their aggregation into (a) chain polymers and (b) cyclic tetramers. 

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For the purposes of this chapter, the term polyhydroxy phosphonic (or phosphinic) acid is used in the widest possible context, and some discussion is therefore directed towards those carbohydrate analogues, both isosteric and non-isosteric, of true natural carbohydrate molecules, and which include at least one direct phosphorus-carbon bond ... 

The anhydrosulphides of polythio-phosphonic and -phosphinic acids occupy a special place in the chemistry of those acids which warrants a separate and more detailed consideration, since this is one area in which true advances have been made during the two past decades both in the discovery of new structures and in the application of organophospho-rus chemistry to conventional organic synthesis. 

After publishing what we considered the startling fact that a (AlkO)2-PO(OH), where Aik is 2-ethyl hexyl, is an extremely stable dimer in benzene, we discovered that KosolapofT and Powell had, nearly seven years earlier, shown (Alk)2PO(OH), where Aik is n-butyl or n-hexyl, to be dimeric in naphthalene. It is true that the existence of di-alkyl phosphinic acids as dimers doesn t prove that di-alkyl phosphoric acids are dimers, but it would certainly have provided a valuable hint. 

This is almost completely miscible with H2O. Its alkali salts are soluble most of the others are not (distinction from phosphinates). True phosphorous acid would be the isomeric H3PO3, i.e., P(OH)3, of which we do have organic derivatives. 

The mechanism of the reaction may involve a cationic nickel hydride associated with a weakly coordinated counterion (4, Scheme 1) as the true catalyst. This species is formed by the Lewis acid-assisted dissociation of the Ni-X bond from the 16-electron phosphine complex 3, coordination of ethylene (or styrene), coupling of the allyl and vinyl moieties, and subsequent 3-hydride elimination [11a]. Insertion of the vinylarene into the Ni-H bond gives a benzylic complex 5, which can be stabilized as an rj -intermediate 5. The coordinately unsaturated 5 can react with ethylene (and possibly not another vinylarene, if the phosphine is sufficiently bulky) to give 6, which can undergo an insertion followed by P-hydride... 

Warren has used a variation of his phosphine oxide-based olefination method to synthesise single isomers (E or Z) of unsaturated carboxylic acids.23 a-Diphenylphosphinoyl ketones (32) are reduced by sodium borohydride to give diastereomeric mixtures of the corresponding alcohols (33) and (34). These alcohols can be converted to the lactones (35) and (36) which can be separated and individually converted stereospecifically into (Z)-(37) and (E)-(38) alkenes by base treatment (Scheme 6). In many cases it is possible to reduce p-ketophosphine oxides (39) and enones (41) stereoselectively to the ery/Aro-alcohols (40) and (42), respectively, using sodium borohydride in the presence of cerium chloride (Scheme 7).24 An earlier report that reduction in the presence of cerium salts did not cause reversal of stereochemistry compared to reduction with borohydride alone appears to be true only of the compounds studied in that report. The carbanions of 3-hydroxypropylphosphine oxides (43) have been reported to undergo O- to C-acyl transfer to give the p-ketoalkylphosphine oxides... 

In an earlier report, polarised resonances were observed that could be attributed to a true mononuclear intermediate in the catalytic process [31]. These resonances were assigned to a dihydride species that contained an alkene ligand and cis phosphines. Hydrogenation of itaconic acid by the rhodium catalysts... 

Only development of ruthenium-based catalysts has allowed tolerance to a singular functional group to operate without requiring experiments to be conducted under an inert atmosphere [5]. They can be used with substrates that carry an alcohol, a carboxylic acid, or an aldehyde, but can be rendered inactive in the presence of structurally exposed amines and phosphines. The reverse is true for molybdenum-based catalysts, but they are generally more active than ruthenium catalysts, and demand preparation and handling under an inert atmosphere [1]. Table 5.1 is a summary of the functional-group tolerance of some general catalysts for olefin metathesis [8]. 

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