Metal-ligand cleavage, homolytic heterolytic

DR. JAMES ESPENSON (Iowa State University) I should like to raise a slightly different aspect of substitution reactions, an aspect which relates to a different kind of mechanism. This involves a change from the conventional heterolytic process of metal ligand bond cleavage to one dealing with homolytic bond cleavage. 

First-Order Kinetics, K[A] Unimolecular processes, such as ligand dissociation from a metal center or a simple homolytic or heterolytic cleavage of a single bond, provide a straightforward example of a first-order reaction. The kinetics of this simple scheme, Equation 8.5, is described by a first-order rate law, Equation 8.6, where A stands for reactants, P for products, [A]0 for initial concentration of A, and t for time. The integrated form is shown in Equation 8.7 and a linearized version in Equation 8.8. 

Although alkoxide hgands are often stable and fairly unreactive ancillary ligands, particularly when bonded to early transition metals, the C-0 bond in an alkoxide ligand can undergo special types of reactions when a related oxo complex is accessible [114]. Two mechanisms of both homolytic and heterolytic fashions for C-O bond cleavage in alkoxide hgands have been discussed. 

Moreover, the electrode processes of the protonated OMnplexes are shown to involve the following types of electroinduced reactions, which are also discussed anodic N-H, C-H or metal-H heterolytic bond cleavage cathodic N-H, C-H or metal-H homolytic bond rupture anodic nucleophilic attack at the metal anodic ligand isomerization. 

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