Phosphonium salts geometry

Pure tetrahedral coordination probably occurs only ia species where there are four identical groups and no steric distortions. Both PCU and PBr" 4, present ia soHd phosphoms haUdes, appear to have poiat symmetry. Other species, eg, H PO and POCl, have only slightly distorted tetrahedra. Similar geometries occur ia salts, esters, and other derivatives of phosphoric, phosphonic, and phosphinic acids as well as phosphine oxides and phosphonium salts. 

Phosphonium salts 1 (m = n = 4) were shown to have tetrahedral geometry with small endocyclic C-P-C bond angles 97-98° <2002JA6126>. 

This extremely air-sensitive compound, which is valence isoelectronic to an olefin, has been structurally characterized by X-ray diffraction. It has a short carbon-phosphorus double bond (1.62 A) the phosphorus and carbon atoms adopt a trigonal planar geometry with a dihedral angle of 60° (Fig. 3). This value is significantly larger than that reported for the most crowded olefin.61 Formally, this compound can be viewed as the product of a car-bene-carbenoid coupling between bis(trimethylsilyl)carbene and bis(diiso-propylamino)phosphenium triflate. Note that another route to methylene-phosphonium salt has been reported by Griitzmacher et al.62... 

The thus-formed peroxide then adds to the end of the eneone. Ozonization of the terminal olefin then leads to the aldehyde (63-5). The newly formed carbonyl group is then reacted with the ylide from phosphonium salt (63-6) under salt-free conditions. This results in the addition of the f7W-trifluoromethylbenzyl moiety with cis geometry about the double bond. There is thus obtained arteflene (63-7) [72]. 

Structure and bonding in phosphonium salts has not been a controversial subject4,5,7-11199- Approximately regular tetrahedral geometry is expected from four nearly... 

Most of the problems related to the phosphonium salts stereochemistry are discussed under synthesis (Section II), reactivity (Section III) and spectrometric characteristics (Section I.C.). Because of the tetrahedral geometry of phosphorus, chirality arises from the presence of four different substituents. Enantiomeric forms may be separated by... 

The Wittig Reaction allows the preparation of an alkene by the reaction of an aldehyde or ketone with the ylide generated from a phosphonium salt. The geometry of the resulting alkene depends on the reactivity of the ylide. If R is Ph, then ihe ylide is stabilized and is not as reactive as when R=alkyl. Stabilized ylides give ( )-alkenes whereas non-stabilized ylides lead to (Z)-alkenes. 

The same year, Gerlach described a synthesis of optically active 1 from (/ )- ,3-butanediol (7) (Scheme 1.2). The diastereomeric esters produced from (-) camphorsulfonyl chloride and racemic 1,3-butanediol were fractionally recrystallized and then hydrolized to afford enantiomerically pure 7. Tosylation of the primary alcohol, displacement with sodium iodide, and conversion to the phosphonium salt 8 proceeded in 58% yield. Methyl-8-oxo-octanoate (10), the ozonolysis product of the enol ether of cyclooctanone (9), was subjected to Wittig condensation with the dilithio anion of 8 to give 11 as a mixture of olefin isomers in 32% yield. The ratio, initially 68 32 (E-.Z), was easily enriched further to 83 17 (E Z) by photolysis in the presence of diphenyl disulfide. The synthesis was then completed by hydrolysis of the ester to the seco acid, conversion to the 2-thiopyridyl ester, and silver-mediated ring closure to afford 1 (70%). Gerlach s synthesis, while producing the optically active natural product, still did not address the problem posed by the olefin geometry. 

Evidence for the formation of intermediate quasiphosphonium salts comes from the isolation of the ion 436 (A = B = EtO R = H, R = R = Me E = SPh) as the hexa-chloroantimonate and further evidence stems from reactions with cyclic esters of the (alka-l,2-dienyl)phosphonic acids. The reactions of the l,3,2-dioxaphosph(V)olanes 444, of known geometry, with CI2, Br2 and RSCl or RSeCl " are highly stereoselective and would be expected to proceed through the quasiphosphonium salts 445 such salts have been isolated from other reactions. The 1,2-oxaphosph(V)ol-3-enes 446 have been isolated (66-75%) when EY is RSCl or RSeCl, but in the former case, were accompanied by 449 (65-73%) Phosphonium salts 436 (A = B = alkyl) have been obtained from reactions of propadienyldialkylphosphineoxides. ... 

From the reaction of divalent, first-row hexaaqua transition metal ions and MS4 (M = Mo, W), [Co(MS4)2] and [Ni(MS4)2] can be isolated, typically as quaternary phosphonium salts. The [MS4] ions act as bidentate ligands to the divalent metal ion, but the coordination geometries are different - tetrahedral for Co and square planar for Ni. These compounds model, in a structurally well-defined way, sulfide-bridged Co-Mo and Ni-Mo interactions and may serve as references for such interactions in CoMoS and NiMoS phases. 

Wittig reactions of the (R)- or (S)-isomers of the aldehyde (263), readily available from serine, provide the alkenes (264) and hence the vinyl glycines (265) with defined configuration and double bond geometry (Scheme 21). 55 The reaction of cephalosporin 3 -triphenylphosphorane (266) with a-halogenoketones has been used to synthesize new tricyclic cephalosporins (267). 56 One-pot coupling of the phosphonium salt (268)... 

A mixture of cinnamyl alcohol, phenyl isocyanate, heptanal, tri-n-butylphosphine, and a little Pd(PPh3)4 in acetonitrile refluxed for 5 h - product. Y 82% (E,E E,Z 4 1). The phosphine attacks the less hindered carbon of the intermediate n-allyl complex, and the (E)-geometry of the allyl alcohol is retained for tert. allylic alcohols, reaction requires prior formation of the allyl carbamate ketones react sluggishly. Although stereoselectivity is poor, the method is interesting since intermediate phosphonium salts are formed under neutral conditions. F.e. and polyenes s. N. Okukado et al., Chem. Letters 1988, 1449-52. 

Partial substitution of halides on bismuth predictably gives alkoxy-bismuth halides, and salts of bismuth anions are obtained by reaction of the alkoxide with an ammonium or phosphonium halide (28). Two isostructural derivatives [Bi2Cl4(thf)2(ju,-OAr)2] (Ar = C6H3Me2-2,6 and C6H2Me3-2,4,6) are composed of dimeric units residing on a C2 axis 8. The bismuth is in a five-coordinate distorted square pyramidal geometry in each case. The apical sites are occupied by terminal... 

According to the density functional theory (DPT) calculations of the salt-free Wittig reaction performed by Aggarwal and Harvey et al. [33, 34], the puckering ability of the transition states in the Vedejs model does not depend on ylide stabilization. In the case of nonstabiUzed and semistabilized phosphonium ylides, the geometry of the transition states is decided by an interplay of 1,2-, 1,3-, and C-H O interactions. In contrast, a dipole-dipole interaction governs the transition state structures for stabilized phosphonium ylides. 

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