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Scope and Mechanistic Insights into the Use of Tetradecyl(trihexyl)phosphonium Bistriflimide: A Remarkably Selective Ionic Liquid Solvent for Substitution Reactions
Author(s) -
McNulty James,
Nair Jerald J.,
Cheekoori Sreedhar,
Larichev Vladimir,
Capretta Alfredo,
Robertson Al J.
Publication year - 2006
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.200600653
Subject(s) - phosphonium , ionic liquid , chemistry , substitution reaction , chemoselectivity , phosphinate , electrophile , elimination reaction , carbocation , organic chemistry , combinatorial chemistry , catalysis , fire retardant
A survey of substitution reactions conducted in a phosphonium bistriflimide ionic liquid is presented. The results demonstrate high selectivity favoring substitution over typically competitive elimination and solvolytic processes even when challenging secondary and tertiary electrophiles are employed. The first reports of Kornblum substitution reactions in an ionic liquid are described that proceed with very high chemoselectivity in favor of nitro over nitroso products and elimination side products. The structure–reactivity study indicates that these reactions proceed through a narrow spectrum of pathways ranging from straight S N 2 to a preassociation pathway along a saddle point that approaches the S N 1 limit. The barrier to the formation of dissociated carbocations is attributed to the structural features of this ionic liquid that favor intervention of the associated nucleophile over dissociation, also preventing cross over to E1 processes. The lack of any basic entity in the phosphonium bistriflimide ionic liquid appears to prevent any potential base‐mediated elimination reactions, which makes this a highly selective medium for use in general substitution reactions.