Issue 12, 2002

Effect of the metal ion on the regiochemical outcome of substitution reactions promoted by crown-bearing cyclophosphazenes

Abstract

The regiochemical outcome of nucleophilic substitution reactions of PNP16C6 (1) by a series of alkaline-earth metal p-nitrophenoxides (6–8) in chlorobenzene–solid salt two-phase systems strongly depends on the identity of the metal ion M2+ (Ca2+, Sr2+, Ba2+). The regiochemistry observed on changing the salt (i.e., geminal mono- and/or disubstitution in the 'P-crown’ position), in apparent contrast with the rules of classical phosphazene chemistry, has been rationalised on the basis of a transition state in which the metal cation M2+ interacts with the oxygens of the polyether 1 ('host-guest’ complex) while the ion-paired anion simultaneously attacks the adjacent phosphorus atoms, following a concerted mechanism. According to the proposed mechanism the effect is not observed when the metal ion charge is shielded by a complexing agent, such as perhydrodibenzo-18-crown-6 (14), or when the bulky non-complexable tetrahexylammonium cation is used.

Graphical abstract: Effect of the metal ion on the regiochemical outcome of substitution reactions promoted by crown-bearing cyclophosphazenes

Article information

Article type
Paper
Submitted
21 May 2002
Accepted
11 Sep 2002
First published
05 Nov 2002

New J. Chem., 2002,26, 1817-1821

Effect of the metal ion on the regiochemical outcome of substitution reactions promoted by crown-bearing cyclophosphazenes

A. Maia, D. Landini, M. Penso and K. Brandt, New J. Chem., 2002, 26, 1817 DOI: 10.1039/B204923F

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