Ligand Substitution Processes

Download or read book Ligand Substitution Processes written by Cooper Harold Langford and published by . This book was released on 1966 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: The subject of the mechanistic study of ligand substitution reactions is currently undergoing an exciting growth. New fast-reaction techniques have removed the upper limit on rates that can be measured, and extension to less familiar central metal atoms has begun in earnest. This might seem the wrong moment for review of the field. As yet, definitive treatment is possible only for those complexes involving monodentate ligands with cobalt(III) and platinurn(II). But, because information is so extensive for these systems, it is clear that they are functioning as models from which concepts and experiments are generated for application over the fast-growing range of the subject. We believe that this is an important moment to reopen debate on fundamentals so that concepts will be most felicitously formulated to aid growth of understanding. This monograph is centrally concerned with three aspects of those fundamentals. We have attempted to develop an approach to classification of ligand substitution reactions that is adapted to what seem to have emerged as the characteristic features of these reactions and is susceptible to operational tests. (We do recognize that any such scheme of ideas is necessarily obsolescent once it is formulated since new experiments will certainly follow immediately.) We have tried to evaluate the basis for making generalizations about ligand substitution processes and to formulate tests to show whether new reactions fall within familiar patterns. Finally, we have sought to base the models of ligand substitution processes in the language of molecular-orbital theory. We believe that MO theory is most useful, because it may be used to correlate rate data on complexes with the extensive information available from spectral and magnetic studies, yet differs from crystal-field theory in providing a natural place for consideration of the bonding electrons, which must be a principal determinant of reaction processes. To keep this essay within bounds, we assume familiarity with the elements of experimental kinetics, transition-state theory, and the simple molecular-orbital theory of complexes. Introductory physical chemistry, some familiarity with the study of reaction mechanisms, and mastery of one of the qualitative treatments of MO theory as applied to transition-metal complexes should provide sufficient background. Thus, we hope that this book will be useful to students, relatively early in their careers, who wish to explore this field.