Trialkylphosphonium

It was noted that, on going from tetrabutylammonium to tetrabutylphosphoni-um, salts with a common anion displayed identical solvation properties. FLence, with these simple cations, the solvent properties are dominated by the choice of anion. It is possible that, had cations with acidic protons, such as triallcylammoni-um and trialkylphosphonium, been included in the study, these may then have also had an influence. 

While these systems are dominated by the ylidic form, the phosphorus atom does aid in stabilizing the carbanion. It is well known that the trialkylphosphonium ylides are more reactive than the triarylphosphonium ylides. The aryl substituents remove some of the positive charge from phosphorus (as seen in the ESC A studies listed in Table 9), overall stabilizing the molecule. 

ESR data obtained on y-irradiation of tetraalkylphosphonium salts in solution (96% sulphuric acid) at 77 K differ markedly from those for the trialkylphosphonium ions44. The latter irradiation produces the expected phosphabetaine radical cation and, for example, tetrabutylphosphonium iodide has features assigned previously to I2 45. On the other hand, PH was not detected44,46. Trialkylphosphonium salts, such as trimethyl and triethyl compounds, produce radicals whose ESR spectra are characteristic of the radical cations of R3P +. The central region of the ESR spectra is dominated by features from... 

Netherton MR, Fu GC (2001) Air-stable trialkylphosphonium salts simple, practical, and versatile replacements for air-sensitive trialkylphosphines. Applications in stoichiometric and catalytic processes. Org Lett 3 4295 1298... 

For initial studies using trialkylphosphonium tetrafluoroborate salts as air-stable... 

In a case where betaine formation is reversible, the thermodynamically more stable isomer will be formed before elimination occurs. This is normally (3.112b), which leads to trans alkene. Generally trialkylphosphonium yUds, or those containing stabilising groups, give mainly trans alkenes. 

As previously discussed, the unfavorable equilibria associated with ligand dissociation during the initiation step of an olefin metathesis reaction have traditionally hindered the direct observation of metathesis-active ruthenacyclobutane intermediates [24]. Thus far, we have seen that the use of phosphonium alkylidene complexes, such as 22, can enable facile access to metallacycle formation by providing an alternative route for catalyst initiation. However, despite the utility of these trialkylphosphonium alkylidene catalysts, their preparation requires a multi-step synthetic route that requires the use of costly reagents [28]. In addition, the vinyl trialkylphosphonium salt generated following the reaction of 22 presents a less relevant model in comparison to the styrene (34) formed from the commercially available benzylidene catalysts. 

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