Presented in part as lectures at Imperial College (London), Geneva (Cynamid European Research Institute), and St. Andrews (Scotland).
The Concept of Hard and Soft Acids and Bases as Applied to Multi-Center Chemical Reactions†
Article first published online: 17 DEC 2003
Copyright © 1967 by Verlag Chemie, GmbH, Germany
Angewandte Chemie International Edition in English
Volume 6, Issue 11, pages 928–939, November 1967
How to Cite
Saville, B. (1967), The Concept of Hard and Soft Acids and Bases as Applied to Multi-Center Chemical Reactions. Angew. Chem. Int. Ed. Engl., 6: 928–939. doi: 10.1002/anie.196709281
- Issue published online: 17 DEC 2003
- Article first published online: 17 DEC 2003
- Manuscript Received: 7 MAR 1966
- HSAB concept (hard and soft acids and bases);
- Multicenter reactions
Many chemical bonds of differing types and strengths have recently been regarded by Pearson as representing partnerships between (Lewis) acids and (Lewis) bases. Most acceptor molecules or ions (acids) can be placed in one or other of two categories, graphically termed “Hard” and “Soft”. There are also two broad categories of donor molecules or ions (bases) which can also be termed Hard and Soft. On the whole, strong chemical bonds are partnerships between either a Hard base and a Hard acid or a Soft base and Soft acid, whereas weaker bond types most usually result in cases of either Hard base-Soft acid or Soft base-Hard acid interactions. The present paper shows how this concept of acidity and basicity can be applied in the interpretation of multi-center chemical reactions involving interconnected acid-base relationships. In particular, fourcenter substitutions and additions involving cooperative attack by nucleophiles and electrophiles at various chemical bonds have been examined, and a conclusion is reached that especially reactive patterns of reactants can be developed if the substrates contain bonds between either a hard acid and a soft base, or a soft acid and a hard base. Indeed, the arguments can be elaborated to provide two distinct Rules which should be of interest in the interpretation of metal-ion assisted reactions and in the design of novel syntheses.