Phosphonium compounds, supported

Since the buckminsterfullerenes and C70 were discovered in 1990, there has been extreme interest in these compounds and their derivatives. The first fulleride radical anion, Cgo, was prepared by bulk electrolysis using tetraphenyl-phosphonium chloride supporting electrolyte in dichlorobenzene [76]. Since there are no protons, the spectrum exhibits only one line. Furthermore, because the spin density is so uniformly distributed in the molecule, HFS from naturally... 

Polymer-supported catalysts, especially those based on polystyrene resins, have been used on many occasions but they also suffer from low thermal stability as well as high cost and a tendency to swell in solvent.147,148 Simple physisorbed supported PTCs can be prepared by the incipient wetting method. In this way, alumina-supported phosphonium compounds have been prepared and used to catalyse various halogen exchange reactions in the gas phase along with various other nucleophilic substitutions (Figure 4.24). 

NMR spectroscopic studies f111,13C, and 31P) are consistent with the dipolar ylide structure and suggest only a minor contribution from the ylene structure.234 Theoretical calculations support this view.235 The phosphonium ylides react with carbonyl compounds to give olefins and the phosphine oxide. 

A number of A5 n3 compounds (18) have chemical shifts in the range 127 to 178.37 A theoretical study supports the suggestion made in the last volume that these compounds are represented as phosphonium ylides with the negative charge distributed between the two sp carbon atoms bound to the phosphorus atom.3 ... 

This reaction is only of limited synthetic utility, and has mainly been used to verify that metallations had indeed taken place [1-3], or for the regioselective introduction of deuterium or tritium into a molecule. The solvolysis of silanes, organogermanium compounds, and phosphonium salts to yield alkanes with simultaneous cleavage from the support is discussed in Section 3.16. 

The name phosphorin is used to describe compounds which follow below, because it is still in general use, but it must be noted that in the revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles, phosphorin becomes phosphinine (Pure appl. Chem., 1983, 55, 409). An investigation of the nature of the bonding in A -phosphorins (W. Schafer et al., J. Amer. chem. Soc., 1976, 98, 4410) and studies supporting the phosphonium ylide structure (1) for -phosphorins (A.J. Ashe and T.W. Smith, ibid. p.7861 ... 

Polymer-supported Wittig reagents were first prepared more than 20 years ago [32]. It has been shown that the success of the reaction depends strongly upon (i) the preparation of the reagent by bromination and phosphination of cross-linked polystyrene rather than by co-polymerization using styryldi-phenyl phosphine, and (ii) the generation of the phosphorane with a base/ solvent system that swells the phosphonium sites in the polymer network (Scheme 6) [33]. Thus, bromination of polystyrene 1 yielded phenyl bromide 32, and this was followed by phosphination with n-butyUithium and chlor-odiphenylphosphine or with Hthium diphenylphosphide to give 33, a compound which is commercially available (Scheme 6). 

The use of PEG-supported ammonium or phosphonium salts for PTC was introduced relatively late in this field. Preparation of compounds 95 and 96 and the corresponding monofunctional derivatives (i.e. 97) were reported in 1991 (Scheme 10.18) [269]. These catalysts were shown to be more active than PEG or tetrabutylammonium bromide for several elimination reactions. More recently,... 

Electrochemical syntheses of Zintl ions were proposed and preliminarily investigated by E. Zintl himself as early as 1933, but was not revitalized until the 1980s.f This synthetic route, as currently applied by Haushalter et involves the application of a cathodic current to an electrode made from the alloy under study in a supporting electrolyte of large cations (typically, solutions of quarternary ammonium or phosphonium salts). The cathodic production of polyanions is rapid and normally allows for the isolation of crystalline compounds in a few days. 

The direct attack on the halogen of a-halocarbonyl compounds by a tertiary phosphine is implicated by substrate reactivity indices (22). The change of venue from the Perkov and Arbuzov pathways concurs with the HSAB rationale as the phosphine P is softer than the phosphite P. Studies on enol phosphonium salt formation (23) support this contention. 

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