Phosphorus halides anions

There are several different preparations of metal phosphides. Secondary phosphines can be metallated by strong bases such as butyl-lithium or alkali metals (Scheme 5). Primary phosphines can be doubly lithiated using LDA or BuLi.11 Both the anion and dianion metal phosphides can be generated in situ before adding the electrophile into the same pot.12,13 Phosphorus halides can be metallated using lithium metal. 

A theoretical study of nucleophilic substitution of halophosphines by halide anions indicates the involvement of an anionic tetra-coordinated intermediate species (X-PH2-Y) , rather than a transition state structure. The authors predict that this intermediate should be detectable, and that the Sn2 reaction at trivalent phosphorus is exothermic when the reactant halide anion is more electronegative... 

Product isolation is very simple as only the solvent has to be removed after separation from the polymer. The polymer can be returned to the active chlorinating agent by reaction with carbonyl chloride. A variation of this procedure does not require polymer-bound phosphorus halide but uses Lewis acid-Lewis base complexes between anion-exchange resins, such as Amberlite IRA 93, and phosphorus pentachloride (equation 4). Again, isolation of the resultant acid chloride is simple and the exhausted polymer can be regenerated for further use by simply washing it with aqueous acidic and basic solutions. Yields range from 51 % for crotonic acid chloride to 86% for decanoic acid chloride. 

Because of the radical mechanism for SET reactions, introduction of both a perfluoroalkyl group and a heteroatom moiety to the carbon-carbon double [17-20] and even triple [21] bonds is possible. The initially generated perfluoroalkyl radicals add first to olefins to form a new radical intermediate (23), which then couples with anions (22) to form new anion radicals (24). The formation of the product (25) and the chain propagation via electron transfer from anion radicals (24) to perfluoroalkyl halides constitutes a chain reaction as shown in Scheme 2.38. Sulfur [19], selenium [20], tellurium [21], and phosphorus [22] anions (22) have been employed for these reactions [23]. 

The carbonyl tautomers deprotonate at N-H, generating ambident anions that can react at either oxygen or nitrogen, depending on the exact conditions for example 0-alkylation can be achieved with silver carbonate. They are converted, as with the pyridones, into halo-quinolines and halo-isoquinolines by reaction with phosphorus halides. 

Diazinones, like pyridones, react with phosphorus halides with overall conversion into halides. Anions produced by A-deprotonation of diazinones are ambident, with phenolate-like resonance contributors, but they generally react with electrophilic alkylating agents at nitrogen, rather than oxygen, giving A-alkyl diazinones. 

The trans effect of the halide anion favors dissociation of one phosphorus... 

Trivalent and pentavalent phosphorus halides will form addition complexes with metals or metal salts. While the trivalent complexes contain metal-phosphorus bonds (Chapter 8), the pentavalent complexes involve rearrangements to produce ionised assemblies of tetrahedral PX4 cations and various complex anions. 

Known compounds with a 6-coordinated phosphorus atom (6.542) are still relatively few in number. Apart from the long-established PFg and PClg and some mixed halide anions (Chapter 4.6), only within the last few decades have compounds been prepared with several kinds of atom directly linked to P in six-coordination. 

Both neutral and anionic phosphorus compounds are good nucleophiles toward alkyl halides. We encountered examples of these reactions in Chapter 2 in connection with the preparation of the valuable phosphorane and phosphonate intermediates used for Wittig reactions. 

Lithium salts of resonance-stabilized organic anions have also found a role in carbon-phosphorus bond formation by displacement at phosphorus. The generation of the lithium salt derived from acetonitrile (or other aliphatic nitriles by reaction with butyl lithium or lithium diisopropylamide) provides for carbon-phosphorus bond formation by displacement of halide from phosphorus (Equation 4.24).68... 

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