Dichlorophosphines chlorophosphines

If trivalent phosphoms compounds are to be treated as electron-deficient species, then reactions of oxadiazoles with some Lewis acids should be reported here. 2-Phenyl-l,3,4-oxadiazole reacting with phosphoms trichloride in pyridine solution in the presence of triethylamine at low temperature furnished the respective dichlorophosphine and chlorophosphine, which were trapped by dimethylamine to give the corresponding amides. 2-Phenyl-l,3,4-oxadiazole also interacts over 24 h with the less reactive chlorodiphenylphosphine and dichlorophenylphosphine at room temperature to give phosphines (Scheme 14) <1999CHE1117>. These reactions of oxadiazoles resemble the behavior of 1-alkylimidazoles toward trivalent phosphorus derivatives. 

In addition to the conventional McBride synthesis using simple alkenes, a few other unsaturated substrates serve as starting materials for the construction of phosphetane rings. For example, the reaction of norbornadiene with chlorophosphines (ClP(OEt)2), instead of dichlorophosphines, afforded tetracyclic phosphetane oxides (Equation 23) <1996JHC979>. 

Several reports have appeared of the application of unusual organometallic reagents in phosphine synthesis. Treatment of 2-lithiopyridine with anhydrous zinc chloride results in the formation of a 2-pyridylzinc reagent which can be used to introduce the 2-pyridyl group at phosphorus in a controlled manner. Thus, e.g., in its reaction with phenyldichlorophosphine, the 2-pyridyl-(phenyl)chlorophosphine (15) is formed. This has then been converted via the phosphide route into a new class of binucleating ligands (16). The sterically crowded dichlorophosphine (17) (accessible from the reaction of phosphorus trichloride with lithium diphenyl(2-pyridyl)methanide) is converted into the thermally stable phosphirane (18) on treatment with calcium, strontium or barium cyclooctatetraenide.The reaction of phenyldichlorophosphine with the readily accessible titanacycle (19) affords a convenient route to the phosphetene (20). ... 

Several papers this year have been devoted to the effect of acids, notably acetic acid, on reactions between carbonyl compounds and chlorophosphines. Thus dichlorophosphines react with cyclic ketones to give the phosphinic chlorides (40), but in the presence of acetic acid the products are a-hydroxyalkyl derivatives, such as (41). When phosphorus trichloride and acetic acid are added to 1,5-diketones, bicyclic phosphonates (42) are formed the authors suggest that the reaction is... 

Other methods to prepare aromatic halo- or dihalo-phosphines are occasionally used. Arylbis(dialkylamino)phosphines have been converted into aryldihalophosphines with dry HCl or HBr, e.g. dichloro(2-methoxy- or 2-dimethylaminophenyl)phosphine (equation 29) the o- and m-phenylenebis(dichlorophosphine)s 20 and 21" and the p-phenylenebis(dichlorophosphine) 22. The c -phenylenebis(dibromophosphine) 23 has been prepared similarly Aryldiazonium tetrafluoroborates with PCI3 give chlorophos-phonium salts, which can be reduced to aryldichlorophosphines (equation 30). Primary and secondary phosphines may be chlorinated with phosgene to give chlorophosphines, e.g. hexamethylenebis[chloro(phenyl)phosphine] (equation 31) and 20 ". ... 

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