Phosphonium phenoxide

The reaction of 34 with triethylethylidenephosphorane is more complex. According to the multinuclear NMR data, the reaction occurs at the 1 2 ratio of the reactants. The Sn-O bond is cleaved to give phosphonium phenoxide (38) and stannylene (37) in which the tin atom is also bound to the ylide carbon atom of phosphorane (Scheme 17).61 Metallation reactions of this type are well known.61,75... 

Tetrahydrocarbyl phosphonium phenoxide salts 36 Butyl tri-phenylphosphonium salt of... 

The dependency on TPP concentration in Equation 50 for the first-order constant, ki ss provides a clue as to how the magnitude of the rate constant depends on the concentration of the active catatytic species. All the mechanisms which possess an activation step require the creation of one catalytic or reactive species per TPP molecule the Sorokin model predicts a quaternary phosphonium phenoxide complex, the Shechter and Gagnebien model predicts a zwitterion. Thus, the maximum concentration of activated complexes, Cac,max hi given formulation is limited by the concentration of TPP. If this activated complex is denoted genericalfy by Cac. then Cac,max = tO and the fraction of active complex formed is, xac = Cac/ tO- Equation 50 for ki can be rewritten in terms of Cac. as... 

PhP(OPh)4 Ki = (3 5)xl0-10 and Kz< x. 10 3 mol l-1. In general, the more oxygens attached to phosphorus the less the dissociation of the phenoxyphosphorane. The rate constants for the dissociation of a number of the phenoxyphosphoranes (26) were obtained from a study of thevariable-temperature n.m.r. of equimolar mixtures of the phosphoranes and the related phosphonium triflates RwP(0Ph)4-nCF3S03-.28 Together with the equilibrium constants for these dissociations, these led to the conclusion that the reactions of the cations Rw (OPh)4- with phenoxide ion in acetonitrile proceed with the speed of collision. 

A slow non-competing liquid/liquid reaction with no catalyst present gave only 78 % O-alkylation. Thus the active site of the lipophilic phosphonium ion catalysts appears to be aprotic, just as in analogous phase transfer catalyzed alkylations with soluble quaternary ammonium salts 60), Regen 78) argued that the onium ion sites of both the 17% and the 52% RS tri-n-butylphosphonium ion catalysts 1 are hydrated, on the basis of measurements of water contents of the resins in chloride form. Mon-tanari has reported measurements that showed only 3.0-3.8 mols of water per chloride ion in similar 25 % RS catalysts 74). He argued that such small hydration levels do not constitute an aqueous environment for the displacement reactions. No measurements of the water content of catalysts containing phenoxide or 2-naphthoxide ions have been reported. 

When the reactions of alkyl bromides (n-Q-Cg) with phenoxide were carried out in the presence of cosolvent catalyst 51 (n = 1 or 2,17 % RS) under triphase conditions without stirring, rates increased with decreased chain length of the alkyl halide 82). The substrate selectivity between 1-bromobutane and 1-bromooctane approached 60-fold. Lesser selectivity was observed for polymer-supported HMPA analogue 44 (5-fold), whereas the selectivity was only 1,4-fold for polymer-supported phosphonium ion catalyst 1. This large substrate selectivity was suggested to arise from differences in the effective concentration of the substrates at the active sites. In practice, absorption data showed that polymer-supported polyethylene glycol) 51 and HMPA analogues 44 absorbed 1-bromobutane in preference to 1-bromooctane (6-7 % excess), while polymer-supported phosphonium ion catalyst 1 absorbed both bromides to nearly the same extent. 

Polymeric phosphonium salt-bound carboxylate, benzenesulphinate and phenoxide anions have been used in nucleophilic substitution reactions for the synthesis of carboxylic acid esters, sulphones and C/O alkylation of phenols from alkyl halides. The polymeric reagent seems to increase the nucleophilicity of the anions376 and the yields are higher than those for corresponding polymer phase-transfer catalysis (reaction 273). 

At room temperature, the chloride ion in the labile phosphonium chloride [88] can be replaced by phenoxide ion or by pentachlorobenzoate, with silver phenoxide or silver pentachlorobenzoate respectively (p. 324) (Espinosa, 1972). 

The higher nucleophilicity of phenoxide and perchlorobenzoate counterions causes immediate nucleophilic substitution on the corresponding phosphonium ion phenoxy group, giving triphenylphosphine oxide and either perchlorodiphenyl ether or pentachlorophenyl pentachlorobenzoate respectively (p. 324) (92). Similarly, the reaction of triphenylphosphine dibromide with excess of silver pentachlorobenzoate yields pentachlorobenzoic anhydride in quantitative yield (Veciana, 1977). 

The role of bromide in DPC catalysis is still unclear. It was suggested that NR Br works as a base to ionize phenol to phenoxide anion [51] or as a surfactant to stabilize Pd(0) nanoparticles [65]. However, no other bases or surfactants have even come close to its activity in DPC synthesis. Quaternary ammonium and phosphonium bromides are expensive and difficult to recover in downstream processing and, therefore, have a substantial impact on the DPC cost structure. For the process economics, it was critical to replace these compounds with less expensive equivalents, which could be done by two ways either replacing QBrs with inexpensive NaBr or nonbromide nonquaternary salts. 

Nucleophilic attack of the phenoxide anion opens the phosphonium ring due to enhanced electrophilic reactivity of the mixed anhydride and acid structures. Salicylyl phenylphosphonite, however, in combination with 2-methyl-2-oxazoline behaves as a Me monomer. ... 

Proton abstraction from bisphenol A yields the phenoxide anion, forming a phosphonium salt. The phenoxide reacts with the electrophilic carbon attached to the positive phosphorus regenerating the catalyst ... 

Here, the nucleophilic attack by TPP opens the epoxide and then produces a zwitterion (Rxn. 18). Proton abstraction from phenol yields the phenoxide ion (Rxn. 19), which subsequently reacts with the electrophihc carbon attached to the positive phosphonium ion and, thereby, regenerates the catalyst (Rxn. 20). 

Various otiier qtproaches have been applied in changing flie Grubbs catalysts, such as the introduction of election-withdrawing phosphines, " bidentate Schiff bases, piridinyl-alcoholate ligands, pyridines (with formation of bis(py-ridine) complex 3), pyridinecarboxylate," different halides," " alkoxides,"" phenoxides," " and substituted acetic acid groiqis." IndenyUdene has been successfully introduced as a substitute for benzylidene. Furthermore, the benzylidene has been successfully altered by Piers et al. through introduction of a phosphonium salt which created a highly active and stable 14-electron initiator. " ... 

It is interesting to note that the very widely used Makosza catalyst , benzyl triethyl ammonium chloride, does not show high efficiency in this study. 4) Phosphonium ions are somewhat more effective and thermally stable than the corresponding ammonium catalysts and both are better than arsonium systems. 5) Substitution of the quaternary ion by alkyl rather than aryl groups yields more effective catalysts. 6) Reaction rates are generally greater in orf/io-dichlorobenzene (and presumably in other chlorocarbon media) than in benzene, and botli are better than heptane. In connection with this latter point, Ugelstad and coworkers have studied the reactions of quaternary ammonium phenoxide ions with alkyl halides in a variety of media and concluded that the... 

Montanari and Tundo found 95-98% 0-alkylation of sodium phenoxide in dichloromethane/water using phosphonium catalysts bound to polystyrene but only 74% 0-alkylation with a similar phos-... 

In the cationic polymerization of THF, the concentration of active species was measured by capping the growing chain with sodium phenoxide and the determination of phenoxy groups in polymers by UV spectroscopy. More general methods have been developed in the Lodz group. Active species of cationic polymerization of cyclic ethers (and other heterocyclic monomers) were trapped by reaction with tertiary phosphine. It was shown that oxonium ions are fast and irreversibly converted to corresponding phosphonium ions that could be quantitatively analyzed by NMR using a known excess of phosphine as an internal standard without the need for polymer isolation. The principle of the method, which allows determination not only of concentration but also of the structure of active species, is outlined in Scheme 12. 

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