Phosphanes, halide

The reaction of 3,3-disubstituted cyclopropenes with mono- and 1,2-disubstituted alkenes proceeds only with difficulty and leads to low yields of cyclopropanes. In the case of but-l-ene, an 8% yield, with hex-1-ene and hept-l-ene between 5 and 10% yield, and with cyclooctene about 10% of the cyclopropane product is formed. In these cases, the major product is the formal dimer of the intermediate ethenylcarbene complex, i.e. the corresponding (fj-hexatriene. When copper(I) chloride is used as catalyst rather than the copper halide/phosphane or phosphite system, about half the yield of the [2-f-1] cycloadduct is obtained along with an increased amount of the hexatriene. Mechanistically, these acyclic trienes could also be formed from an (alk-l-enyl)bicyclo[1.1.0]butane intermediate without any carbene being involved. Bicyclo[1.1.0]butanes are low yield (< 20%) byproducts of the thermal dimerization reaction of methyl 3,3-dimethylcyclopropenecarboxylate (1). On the other hand, bicyclo[l. 1. Ojbutanes, such as 3, are known to undergo isomerization to form 1,3-dienes. ... 

The transmetalation of trimethylsilylphosphanes with germanium and tin halides is a useful way to prepare compounds with P—Ge and P—Sn bonds by simple chlorosilane elimination. The reverse reaction, i. e. formation of P—Si bonds by chlorosilane cleavage of germyl- and stannylphosphanes has not yet been reported. Recently, we observed that hexachlorodisilane "transsilylates di-r-butyl(trimethyl-silyl)phosphane 1 much faster than tetrachlorosilane to give trichlorosilylphosphane 2 ... 

Hierso et al reported a copper-free, Sonogashira reaction for a number of activated and deactivated aryl halides with alkyl-/aryl acetylenes and using a variety of metallic precursors, bases and tertiary phosphanes in [bmim][BF4]. They found that a combination of [Pd(/7 -C3H5)Cl]2/PPh3 with 1 % pyrrolidine in the absence of copper showed the highest activity. 

When phosphaalkynes are exposed to bis- and tris(diazo) compounds, bis- or tris(l,2,4-diazaphosphol-5-yl) compounds are formed that may be further converted into a variety of novel heterocyclic systems. For example, bis- and tris[diazo(tri-methylsilyl)methyl]phosphanes 237 and 240 afforded bis- and tris(diazaphospho-lyl)phosphanes 238 and 241 after cycloaddition with terf-butylphosphaacetylene followed by a subsequent 1,5-silyl shift (Scheme 8.56) (300). Reaction with electrophilic halides at the Wsilyl functions allows the introduction of a heteroatom bridge between the diazaphosphole ring leading to polycyclic ring systems such as 239 and 242. 

Scheme 6. Carboxylation of halides via electro-generated Ni(O) phosphane complexes 3.3.2.3 Ni(I)-Complexes as Redox Catalysts...

Finally, there are two examples of intramolecular C,P chelates, viz. LPd k2-C,P-2-CH2C6H4P(o-To1)2 (L = Tp 468, Bp 469), both prepared by cleavage of the halide bridged dimer with KL (Scheme 46). 43 These complexes were targeted to explore their potential in the guise of catalysts for organic synthesis, a role to which the cyclopalladated tris(o-tolyl) phosphane precursor had been previously applied. However, this preliminary study revealed these materials to be unreactive toward electrophiles (see also Section III.C.3.b), and no further investigations have been reported. 

This variation of the Wittig reaction uses ylides prepared from phosphonates.12 The Horner-Wadsworth-Emmons method has several advantages over the use of phosphoranes. These ylides are more reactive than the corresponding phosphoranes, especially when substituted with an electron withdrawing group. In addition the phosphorus product is a phosphate ester and soluble in water - unlike the Ph3PO product of the Wittig reaction - which makes it easy to separate from the olefin product. Phosphonates are also cheaper than phosphonium salts and can easily be prepared by the Arbuzov reaction from phosphanes and halides. 

The method has been further improved." Trimethyl(perfluoroalkyl)silanes RpTMS (Rp = c, -C, perfluoroaliphatic groups) are prepared by reaction of perfluoroalkyl halides RpX (X = Br, I) with chlorotrimethylsilane in the presence of tris(dialkylamino)phosphanes in acetonitrile. For example, chlorotrimethylsilane was treated with bromotrifluoromethane and tris(diethylamino)phosphane in acetonitrile at — 40"C for 1 hour to give trimethyl(trifluo-romethyl)silane in 90% yield. Bis(dimethylamino)(trifluoromethyl)silane is available from the reaction of chlorobis(dimethylamino)silane with the system bromotrifluoromethane/tris-(diethylamino)phosphane, while trichloro(trifluoromethyl)silane is prepared by nucleophilic trifluoromethylation of tetrachlorosilane with bromotrifluorornethane/tris(diethylamino)phos-phane. " ... 

Perfluorinations of many ethers [155], cryptands [156], polyethers [119, 157], including the largest perfluoro-macrocycle [158], perfluoro [60]-crown-20 [123, 159], and the first perfluorinated sugar [160], orthocarbonates [161, 162], ketones [163, 164], esters [124, 165], phosphanes [166] and alkyl halides [167, 168] have been successfully accomplished by the LaMar or aerosol processes (Table 2.4). 

B. Reaction of perfluoroalkyl halides with the system chlorotrimethylsilane/trisfdiethyl-amino)phosphane. 

A similar exchange reaction produced the 1 1 complexes of phenyl tellurium thiocyanate with ethylenethiourea when the phenyl tellurium chloride complex was treated with potassium thiocyanate in aqueous methanol. However, the phenyl tellurium chloride -selenourea adduct and potassium selenocyanate yielded bis[phenyltelluro] selenium. Phosphane selenides also coordinate to phenyl tellurium halides. ... 

The principal synthetic application of cyclopropylidenetriphenylphosphoranes 4 is the conversion with carbonyl compounds (aldehydes and ketones) into alkylidenecyclopropanes 5. As cyclopropyl halides do not react with phosphanes to form cyclopropylphosphonium halides vide supra), the generation of these precursors 3 is generally performed by condensation of 1,3-dibromopropanes 1 with triphenylphosphane and subsequent 1,3-dehydrobromination of the resulting salt 2 with one equivalent of base. A second equivalent of base generates the... 

The sign of /C( Sn, P) is negative in all tin-phosphorus compounds (dominant influence of the lone pair of electron at the phosphorus atom), except of phosphane adducts of tin(IV) halides. Even in transition metal complexes of stannylphosphanes or in borane complexes of stannylphosphanes the coupling sign does not change, although the phosphorus lone pair of electrons is engaged. 

In the presence of anhydrous KF, difluorophosphorane decomposes to give only phosphane PH3. Under basic conditions, in the presence of NH3 or NMe3, the dehydrofluorination product (5) is observed as a transient species and reacts further by elimination of HF to yield a polymeric form of (PH)n. In the presence of electrophilic halides, such as BF3 or TiCU, H3PF2 afforded the monochlorophosphane H2PCI.12... 

Palladium(II) acetate and palladium(II) chloride (often applied as the soluble dibenzonitrile complex) are especially suited for cyclopropanation of strained double bonds as well as styrene and its ring-substituted derivatives.152,154,155 The good coordinating abilities of these palladium ) compounds, however, somewhat complicate the catalytic action and may even limit it. Thus, the presence of phosphane ligands in palladium(II) halides causes a significant induction period for decomposition of the diazocarbonyl compound,156 and the formation of stable palladium diene complexes may even prevent the cyclopropanation reaction.155,157 Furthermore, alkenes such as 4-dimethylaminostyrene and 4-vinylpyridine cannot be cyclo-propanated since their basic center deactivates the catalyst.155... 

Phosphanes are widely used as reagents in organic synthesis, triphenylphos-phane being the most commonly applied due to its stability towards oxidation. The polymer-supported analog has so far found use in the transformation of alcohols into alkyl halides and acids into acid halides, using either carbon tetrachloride or carbon tetrabromide as the halogen source (Scheme 6.4) [7, 11-14], This system can also successfully transform primary amides and oximes into nitriles, whereas secondary amides are transformed into imidoyl chlorides (Scheme 6.5) [15],... 

---