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Hydrophobic Encapsulated Phosphonium Salts—Synthesis of Weakly Coordinating Cations and their Application in Wittig Reactions
Author(s) -
Moritz Ralf,
Wagner Manfred,
Schollmeyer Dieter,
Baumgarten Martin,
Müllen Klaus
Publication year - 2015
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.201406370
Subject(s) - phosphonium , wittig reaction , tetrafluoroborate , chemistry , phosphonium salt , cycloaddition , alkyne , polymer chemistry , catalysis , organic chemistry , ionic liquid
Large and rigid tetraarylphosphonium tetrafluoroborate salts have been synthesized representing weakly coordinating cations with diameters of several nanometers. Divergent dendritic growth by means of thermal Diels–Alder cycloaddition was employed for the construction of the hydrophobic polyphenylene framework up to the third generation. X‐ray crystal structure analysis of first‐generation phosphonium tetrafluoroborate supported the rigidity of the non‐collapsible shell around the phosphorus center and gave insight into solid‐state packing and cation–anion distances. Copper(I)‐catalyzed azide–alkyne ligation served as reliable method for the preparation of a first‐generation triazolylphenyl hybrid phosphonium cation under mild reaction conditions. Furthermore, from the synthesis of triarylbenzylphosphonium bromides, Wittig precursors with unprecedented bulky substituents in the α‐position were accessible. Employment of these precursors under Wittig conditions by treatment with base and subsequent reaction with aldehydes preferentially provided ( Z )‐olefins with bulky polyphenylene substituents.