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Revealing Phenylium, Phenonium, Vinylenephenonium, and Benzenium Ions in Solution
Author(s) -
Manet Ilse,
Monti Sandra,
Grabner Gottfried,
Protti Stefano,
Dondi Daniele,
Dichiarante Valentina,
Fagi Maurizio,
Albini Angelo
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701043
Subject(s) - chemistry , flash photolysis , diradical , photochemistry , anisole , photodissociation , radical ion , density functional theory , ion , thiophene , cationic polymerization , nucleophile , electrophile , computational chemistry , organic chemistry , singlet state , excited state , reaction rate constant , kinetics , physics , quantum mechanics , nuclear physics , catalysis
The 4‐methoxyphenylium ion has been generated in the triplet state ( 3 An + ) by photolysis of 4‐chloroanisole in polar media and detected by flash photolysis ( λ ma x =400 nm). This is the first detection of a phenylium ion in solution by flash photolysis and the assignment is supported by time‐dependent density functional theory (TD‐DFT) calculations. In neat solvents, the cation was reduced to anisole, a process initiated by electron transfer from the starting compound ( 3 An + +AnCl→An . +AnCl .+ , with the radical cation detected at 470 nm, then An . →AnH). Addition of π nucleophiles to the 3 An + cation offers a novel access to a number of other cationic intermediates under mild, nonacidic conditions. Two intermediates are successively formed with alkenes, a diradical cation and the phenonium ion, which are detected at 440 and 320 nm, respectively, by flash photolysis and are in accordance with calculations. Allylanisoles or β‐alkoxyalkylanisoles are the end products, with a small amount of α‐alkoxyalkylanisoles that arises from a Wagner–Meerwein rearrangement to form benzyl cations. Further intermediates that have been predicted and detected are the phenylvinylium ion, possibly in equilibrium with the vinylenephenonium ion, with 1‐hexyne ( λ max =340 nm) and the benzenium ion with benzene ( λ max =380 nm). The final products were anisylhexyne and methoxybiphenyl (an analogous product and intermediate were detected with thiophene).