Phosphonium dimers

Synthesis of phosphonium dimers protected phosphine aldehydes... 

Scheme 11 Syntheses of phosphonium dimers and a-phosphinoacetaldehyde diethyl acetals (DIBAL = diisobutylaluminum hydride)...

When the phosphonium dimers were reacted with base in the presence of Fe ", there was evidence for the formation of new intermediate iron complexes, which were characterized as bis-tridentate iron complexes when using smaller PR groups (R = Et, Ph) on phosphorus (Scheme 12). These complexes were isolated as the BPh salts after salt exchange of BF and FeBr - by the addition of NaBPh. When these kinetic products were left in refluxing acetonitrile for several days, the desired tetradentate complexes were formed. " ... 

New enantiopure P-NH-NH ligands required for the synthesis of complexes leading to 81 can by prepared in an iron-template procedure (Scheme 15) that makes use of the phosphonium dimers described above (Scheme 11 ).[ After the formation of bis(tridentate) complexes, they can be released from their template and isolated to afford enantiopure P-NH-NH synthons. 

The P-NH-NHj ligands are then condensed with another 0.5 equiv. of phosphonium dimer in the presence of base and [Fe(H20)g][BF ]2 to give partially unsaturated P-NH-N-P frameworks on iron (II) (Scheme 16). The resulting iron complexes are then reacted with NaCl under a CO atmosphere to give the iron complexes (S,5 )-104 and... 

A new dimension of ligand variation can now be incorporated by using a different combination of phosphonium dimer and P-NH-NH ligand, as illustrated by the synthesis of (5,5)-106. This new pathway allows the synthesis of a wide range of iron complexes with unsymmetrical P-NH-N-P ligands. ... 

The mercuration of phosphonium derivatives has also been observed. The methylene group of the dimeric palladium complex 63 substituted by a carbonyl and a phosphonium functionality is readily mercurated upon reaction with Hg(OAc)2 to afford complex 64 (Equation (22)).7 Further studies demonstrated that the presence of a triphenylphosphonium group alone is sufficient to promote proton-mercury exchange. For example, the reaction of... 

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... 

A related dihydrido iridium complex of formula [(T -C6H5CH2CH2P Pr3-K-P)lrH2]BF4 [24] can be prepared by treatment of the dimer [Ir( x-OMe)(COD)]2 [15] with the phosphonium salt, [HPTr2CH2CH2QH5]BF4, in acetone followed by the reaction of hydrogen (Scheme 2.26). 

Nickel (continued) polysulfide complex, 31 98 half chair conformation, 31 115 porphyrin complexes, 32 13 in proteins, 47 284-285 quadruply bridged dimers, 40 211-214 steric structures, 40 190-194 quaternary phosphonium salts of, 6 31-32 redox chemistry probes of structure, 32 243-245 steric and electronic requirements, 32 242-243... 

The metal-free eyclobutane-1,2-dioxime can be generated by oxidative displacement. It is interesting to note that, unlike ketene dimerization, head-to-head dimerization takes place here. The chromium ketenimine complex 20 is prepared by reaction of the Fischer-type chromium carbene complex with alkyl isocyanides.60 A cyclobutane-1,2,3,4-tetraimine 24 has been reported from the reaction of the ketenimine phosphonium ylide 22.61 Bisimine 23 has been proposed as the intermediate in this transformation. 

In some cases, the anion exchange can also take place in solid-liquid biphasic conditions either for monomeric or dimeric phosphonium salts, in suspension or by using an anion-exchange resin, or for polymeric phosphonium salts, by washing with solutions of salt MX. Finally, it must be pointed out that the new anion Y can be generated in situ by a classical preparation of such anions (e.g. addition of cyanide anion to CS2 for NCCS2-527 or aromatic substitution with fluoride anion on substituted nitrobenzene derivatives for N02-528). Several recent examples of the various anions exchanges are shown in Table 10. 

In media of low proton availability (MeCN, dmf, hmpa)762, ylide formation was found and products derived from the radical cleavage of the phosphonium ion have been observed. The initial cation would interfere in the reaction process as an acid. A competition can exist between the one-electron pathway (dimerization, disproportionation of R ) and the two-electron pathway (ylide formation, Hofmann degradation, phosphine oxide formation) (Table 24). 

Side Reactions. There are three secondary reactions which can be observed during cyanation substitutive hydrogenation (Reaction 5) (8, 17, 18, 19) aryl dimerization (Reaction 6) (8, 17, 18, 19), and catalytic formation of phosphonium salts (Reaction 7) (14). 

A further simplification is obtained by the oxidative dimerization of the C20 phosphonium salt (45). The oxidation with molecular oxygen and with phosphite-ozone adducts was described by H. J. Bestmann and co-workers43 . The use of... 

Canthaxanthine (53) is to be regarded as an oxidative metabolite of P-carotene (1). In its industrial production, 4,4 -diacetoxy-p-carotene (52) is used as a starting compound, being hydrolyzed and oxidized 51). This compound, in turn, is obtained by the dimerization of 4-acetoxy-retinal or its phosphorus ylide (51), according to one of the methods described above48. The reaction of 4-oxo-Cls-phosphonium salt (54) with C10 dialdehyde (22) likewise leads to canthaxanthine (53)48b). In a further production process, P-carotene (1) is directly oxidized with chlorate, under catalysis with iodine 49). 

According to a patent [Y. Tokitoh, T. Higashi, K. Hino, M. Murosawa and N. Yoshimura, US Patent 5 057 631 (1991), to Kuraray Industries] the reaction is conducted with butadiene in sulfolane / water in the presence of Pd(OAc)2 as catalyst precursor and a soluble triarylphosphine (or its phosphonium bicarbonate, which is formed from octadienol itself and carbon dioxide) as ligand. The selectivity to 2,7-octadien-l-ol is 92-94% (TOF > 1000), while the isomeric l,7-octadien-3-ol accounts for another 3 5%. The product is extracted with hexane, while the aqueous sulfolane solution, containing the catalyst ca. 1 mmol/1) and triethylamine, is recycled. In the absence of carbon dioxide, the main product is 1,3,7-octatriene, an open-chain butadiene dimer. 

The formation of desaurins from ketones, carbon disulfide, and base 1275,1281,1282,1285-1290 believed to involve nucleophilic attack on a thioketene by the dianion of a 1,1-dimercaptoalkene, as shown for the synthesis of 572. Related syntheses involve the use of thiophosgene instead of carbon disulfide and the use of diazoalkanes or phosphonium and sulfonium ylides instead of a ketone and base. Treatment of perfluoroiso-butylene with fluoride ion and elemental sulfur in a dipolar, aprotic solvent ° °° or with sources of anionic sulfur (potassium sulfide, sodium hydrosulfide,potassium thiocyanate,sodium thiosulfate, dithiocarbamate salts, dithiophosphate salts ) give the dimer (573) of bis(trifIuoromethyl)-thioketene. Similarly, other 2,4-bis(methylene)-l,4-dithietanes are obtained by treating 2,2-dichlorovinyl ketones with anionic sulfur re-... 

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