Phosphines dihalo

Other sources of Ru(0) can also be used for this synthesis. For example, it was recently demonstrated that [Ru(arene)(diene)] complexes such as 39 undergo double oxidative addition of heterosubstituted dihalo compounds 40 in the presence of phosphine ligands (Eq. 5) [21]. 

With two molar amounts of the hydrogen chloride or bromide, the dihalo-borane adducts of phosphine were formed. 

The most direct synthesis is performed by reaction of a dihalo compound with a tricoordinated phosphorus compound including a reactive P—Y bond (reaction 101). This synthesis, first used with secondary phosphines, the corresponding phosphides or diphosphines (Y = H, Na, K, PPh2)2b,38°, has subsequently been developed also with silylphosphines (Y = SiMe3),132,381-383 which are easier to handle (reaction 102). The same kind of cyclization by intramolecular alkylation can be achieved using a functional phosphine prepared in a multi-step synthesis380,384,385 (reaction 103). 

The dithienophospholes 74 are obtained in good yields by lithiation of dibromo-bithiophenes 73, followed by addition of dihalo (aryl) phosphines (Scheme 4.22) [57]. The Lewis basicity of the P center of 74 enables a broad range of facile chemical modifications to be undertaken, as exemplified with the synthesis of derivatives 75-77 (Scheme 4.22) [57]. 

Elemental phosphorus reacts with alkyl and aryl halides to give products that vary according to the experimental conditions. When heated with white phosphorus in a bomb tube at 250-300°, benzyl chloride, bromobenzene, m-bromotoluene, and octyl bromide give mixtures of halo and dihalo phosphines, sometimes in appreciable yield ... 

Preparation. - Fluorophosphines have been obtained from the reactions of the related chlorophosphines with trimethyl tin fluoride. Phenyl(isopropyl)-fluorophosphine has been resolved via a chiral amine-palladium(II) complex, providing the first example of the resolution of a free fluorophosphine chiral at phosphorus. This compound racemises at 20 °C in benzene solution over six hours. The neat compound rapidly decomposes by redox disproportionation. The same approach has been used for the resolution of the related chloro-phosphine, but the optically active compound could not be liberated unchanged from the crystallised diastereoisomeric palladium complex. The dihalo-genophosphines... 

An alternative method to prepare aromatic halo- or dihalo-phosphines is the reaction of a phosphorus trihalide with an arylmetal compound. Like the alkyl compounds, the metal must be a less electropositive one to avoid the formation of a tertiary phosphine, unless the arylmetal compound is sterically hindered. Older examples of syntheses by this method are the preparation of dichloro(l-naphthyl)phosphine (equation 25) and some dichloro(4-substituted-phenyl)phosphines (equation 26)". More recently, hindered aryllithium compounds have been treated with PCI3 to give dichloro(mesityl)phosphine or chlorodime-sitylphosphine" (equation 27), dichloro (2,4,6-tri-r rr-butylphenyl)phosphine (15) and dichloro[2,6-bis(trifluormethyl)phenyl]phosphine (16)." Aryldifluorophosphines have... 

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 ". ... 

Despite statements made in Chapter 2 about the unpopularity of this procedure for the preparation of phosphonic and phosphinic esters from those of phosphonous and phos-phinous acids by the addition of oxygen, partly because of the lack of availability of the phosphorus(III) esters, but also because of the high reactivity exhibited by those esters towards oxidizing agents, the reduced reactivity shown towards the higher chalcogens by phosphonous and phosphinous halides (dihalo- and monohalo-phosphines), and even by some of the more reactive phosphorus(III) species, e.g. amides, makes such addition reactions feasible propositions. 

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