Tetra- -phosphonium

The reaction of a diphosphine with a dihalo compound, resulting in the formation of a di- or tetra-phosphonium salt2c, is a special case because if fits well with a cyclization on phosphorus, but also at the same time with a cyclization between two chains already linked to the second phosphorus (reaction 102). Another kind of ring closure on the phosphorus results from the biphilic character of halophosphines toward dienic392 or acetylenic28,393 systems (reaction 105). 

Benzyltriethylammonium chloride [56-37-1] is the most widely used catalyst under strongly basic conditions. Methyltrioctylammonium chloride [5137-55-3] (Ahquat 336, Adogen 464) is probably the least expensive catalyst. Others of high activity and moderate price are tetra- -butylammonium chloride [1112-67-0] bromide [1643-19-2] hydrogen sulfate [32503-27-8], tetra- -butylphosphonium chloride [2304-30-5], and other phosphonium salts of a similar number of C atoms. Many other onium salts can also be utilized. 

It is found that the tetra-isoamylphosphonium cation does not take a roughly spherical shape but accommodates an iodide ion 480 pm from the phosphorus atom. Neutron diffraction of phosphonium bromide crystals shows no evidence of hydrogen-bonding. The ructures of bis(trimethylphosphine)silicon tetrachloride and the iridium salt (134) are also reported. 

The first promising asymmetric aldol reactions through phase transfer mode will be the coupling of silyl enol ethers with aldehydes utilizing chiral non-racemic quaternary ammonium fluorides,1371 a chiral version of tetra-n-butylammonium fluoride (TBAF). Various ammonium and phosphonium catalysts were tried138391 in the reaction of the silyl enol ether 41 of 2-methyl-l-tetralone with benzaldehyde, and the best result was obtained by use of the ammonium fluoride 7 (R=H, X=F) derived from cinchonine,1371 as shown in Scheme 14. 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

The critical advantage of the quaternary phosphonium iodides is their excellent temperature stability. For example, the selected tetra(alkyl)phosphonium iodide salt, tri(n-octyl)(n-octadecyl) phosphonium iodide [(n-Oct)3(n-Octadecyl)P i, referred to as TOP18 ], shows no TGA weight loss up to 300°C. 

Table 1. Tetra(n-alkyl)phosphonium iodides tested.

Tetra(n-alkyl) phosphonium iodide Carbon Count M.W. M.P. (X) Solubility in Octane... 

A novel homogeneous process for the catalytic rearrangement of 3,4-epoxy-l-butene to 2,5-dihydrofuran has been successfully developed and scaled-up to production scale. A tri(n-alkyl)tin iodide and tetra-(n-alkyl)phosphonium iodide co-catalyst system was developed which met the many requirements for process operation. The production of a minor, non-volatile side product (oligomer) was the dominating factor in the design of catalysts. Liquid-liquid extraction provided the needed catalyst-oligomer separation process. 

Another and still more stabilized carbenium-phosphonium-oxonium-tetra-fluoroborate 225 can be prepared when bis-4.4- (l, l-dimethoxy-2.6-diphenyl-X -phosphorin)-methane 224 is treated with triphenylcarbenium-tetrafluoroborate. 

The salts of carbonyl metalates arc generally soluble only in polar solvents, in which absorptions are broader due to the dipole interactions of the solvent. The spectra are also often considerably dependent on the particular cation and solvent, due to the formation of ion pairs. The largest differences have been observed on going from alkali salts to salts of the large tetra-substituted ammonium and phosphonium cations the latter generally provide simpler spectra that indicate minor formation of ion pairs. A similar trend is observed in going from less polar (e.g., THF) to more polar solvents (e.g., CH3CN). 

Carlson et al. obtained (Z)-9-tricosene 382 by reaction of nonanal 380 with the ylide generated from the phosphonium salt 381 and butyllithium in DMSO 219>220> (Scheme 68). Bestmann et al. 221> synthesized the (Z)-olefin 382 by olefination of tetra-decanal 384, with the ylide generated by treatment of the corresponding phosphonium salt 383 with potassium in HMPA 341 (Scheme 68). 

The reactions of alkali metal, ammonium, phosphonium, or arsonium halides with diorgano tellurium dihalides produce diorganotrihalotellurates or diorgano tetra-halotellurates1,2 (page 668). 

The compound K2 [Rh6(CO)15C] is a yellow powder. It is sensitive to air both in the solid state and in solution and is quite soluble in water, methanol, ethanol, acetone, THF, and acetonitrile. The salts of other cations can be obtained by metathesis, in water for the cesium salt and in methanol for the larger tetra-alkylammonium or phosphonium cations. The tetraethylammonium salt is sparingly soluble in THF, whereas the benzyltrimethylammonium and bis-(triphenylphosphine)imminium salts are soluble. All of these salts are soluble in acetone and acetonitrile. The yellow solution of the potassium salt in THF shows characteristic IR bands at 2040 (vw), 1990 (vs), 1885 (vw), 1845 (s), 1830 (sh, m) 1815 (sh, br) and 1775 (vw, br) cm-1. The IR spectral band shapes depend on solvents and cations. The oxidation of K2 [Rh6(CO)i5C] with iron-(III) ammonium sulfate in water under carbon monoxide leads to the octa-nuclear carbido carbonyl cluster Rhg(CO)i9C,6 whereas under nitrogen RhntCO sQ7 or [H30] [Rhls(CO)28C2]8 is obtained. 

So-called C-linked calixsugars were prepared by Wittig reaction of the calix[4]arene tetraaldehyde 33 with galactose-6- or ribose-5-phosphorus ylids (obtained in situ from the known phosphonium iodides, Figure 5)70 followed by reduction of the double bonds and deprotection of the hydroxyl groups. Thus, the tetra- and trigalactosides 34c,d (all as P-anomers) and tetra- and tri-L-lyxosides 34 (as a mixture of a- and P-anomers) were obtained. 

The inorganic cation [P(NH2)4]+ is known bnt substituted derivatives at either phosphorus or nitrogen sites are more common. Some interesting chemistry of tetra(anilino)phosphonium cation, [P(NHPh)4]+, which can be deprotonated stepwise to end np with the trianionic [P(NPh)4] species, has been described. ... 

As is usual, phosphonium cations have been used to stabilise unusual anions. The salt (Ph4P)2HP7, involving the hydrogenheptaphosphide anion, has been prepared as an ammonia solvate from the reaction of K3P7 with tetra-phenylphosphonium bromide in liquid ammonia, and characterised by low-temperature X-ray structural analysis. The reaction between the cyclic... 

The primary, secondary and tertiary phosphines are weak bases, stronger, however, than the phosphine itself which is scarcely basic at all. The tetra-alkyl phosphonium hydroxides are strong bases. 

A publication discussing the uses of reactive arsonium ylides for the stereospecific preparation of epoxides draws attention to the fact that arsonium salts are less readily prepared than phosphonium salts because of the poorer nucleophilicity of arsenic compared to phosphorus, and suggests methods for obtaining them. Primary salts were made from alkyl triflates, while a-branched salts were prepared from alkyldiphenylarsines, obtained from iodo compounds as, for example, in equation 23. Reaction of alkyl halides with arsines to form arsonium salts is also promoted by the presence of silver tetra-fluoroborate . 

Treatment of the triflate 9 with the sodio derivative of r-butyl dimethoxphosphorylacetate in dimethylformamide (DMF), at room temperature for 20 h in the presence of a crown ether, gives the epimeric phosphonates 10 in 81% yield [9]. Cleavage of the glycosidic bond by hydrogenolysis then affords the hemiacetals 11 which, with sodium hydride in tetra-hydrofuran (THF), give the C-6 phosphonium ylid, which reacts with C-1 in the aldehydo form to afford the alkene 12 in 73% (from the glycoside 10 Scheme 2). The cyclization... 

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