Phosphonium dications

Besides carbo-ammonium dicationic systems, there have been studies related to carbo-phosphonium dication systems. Some of the reported chemistry suggests that superelectrophilic activation is involved. Olefinic phosphonium salts are protonated in superacid to generate dications like 140 and these species have been shown to react with benzene in good... 

Mesomeric phosphonium dications. 4 Reaction with nucleophiles to form ylides. 4 Mesomeric phosphonium inner salts. 5 A stable four-membered ring ylid-ketone adduct. 5... 

A series of phosphonium-carboxonium dications have also been studied in superacid catalyzed reactions.313 When the dicationic electrophiles are compared with similar monocationic species, it is clear that the phos-phonium group enhances the electrophilic character of the carboxonium center. For example, protonated acetone is incapable of reacting with benzene in condensation reactions, however, the phosphonium-substituted carboxonium ion (124) reacts in high yield (eq 40). 

Phosphonium and arsonium dications have been studied and their chemistry has also been recently reviewed.74... 

Other nucleophiles such as phosphines and trialkylphosphites undergo nucleophilic addition to bisbenzene ruthenium and osmium dications 235a and 142 to yield the cyclohexadienyl phosphonium adducts 237 and 238. 

A mixture of isomers of 7-chloro-7-methoxynorbomene gives an isomeric mixture of phosphonium salts (66) and (67) on reaction with triphenyl phosphine in liquid sulphur dioxide at — 60 °C. Both salts can be converted into the non-classical dication (68). The salt (67) isomerizes to (66) at temperatures above —14 °C. ... 

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