Synthesis, structure and reactions of chelate metal-olefin complexes

Abstract

The results of a series of investigations of the behaviour of potential olefin— phosphine and olefin—arsine chelate groups with transition metals are presented. After a brief discussion of the nature of the metal—olefin bond the various types of reaction which are shown by C=C double bonds which are in close proximity with or are coordinated to a transition metal atom are summarized. The coordination, isornerization and oxidation reactions of ortho—chelate ligands with transition metals are then discussed. Some interesting intramolecular re-arrangements which are analogous with organic Wagner—Meerwein re-arrangements are discussed. INTRODUCTION AND SCOPE The object of this lecture is to attempt to bring together some recent advances in the chemistry of transition metal complexes containing chelate groups in which there is one c donor atom (charged or uncharged) and one or more olefin groups suitably located for possible coordination with the metal atom. Their synthesis, structure and reactions will be discussed. In particular, the action of halogens on those complexes which contain double bonds coordinated to, or in close proximity with, metal atoms will be considered in some detail. Of the many fundamental questions concerning the metal—carbon bond in transition metal complexes the following are of special interest: 1. What properties of the metal atom (formal charge thereon, electron configuration, nature of other ligands attached thereto, etc.) determine whether stable metal olefin bonds can be formed? 2. What is the effect of substituents in the olefin group on the stability of the metal—olefin bond. 3. What properties of the metal atom and the carbon ligand decide the stability of metal—carboncy bonds? 4. What factors determine the ease of change-over from metal—olefin to metal—carbon (cr) type bonds when reaction occurs with other reagents? To help answer some of these questions, we started, some years ago, to prepare a series of potential chelating olefin ligands containing at least one strong cr donor located geometrically so as to enable the double bond to be capable of being oriented in the appropriate position for coordination. This 127