Reaction classification coordinated ligand reactions

Template processes and reactions of coordinated ligands, in situ, direct complex-ation, demetallation, transmetallation and catalytic transformations all exhibit similar features. This sometimes leads to unjustifiable classification of such reactions as template processes and vice versa. To define the relationships between template reactions and other coordination chemistry processes. Scheme 1-5 is proposed, constructed on the principle of Venn logic diagrams [78]. 

Langford and Gray proposed in 1965 (13) a mechanistic classification for ligand substitution reactions, which is now generally accepted and summarized here for convenience. In their classification they divided ligand substitution reactions into three categories of stoichiometric mechanisms associative (A) where an intermediate of increased coordination number can be detected, dissociative (D) where an intermediate of reduced coordination number can be detected, and interchange (I) where there is no kinetically detectable intermediate [Eqs. (2)-(4)]. In Eqs. (2)-(4), MX -i and... 

Intensive efforts by various workers to study coordination compounds from the standpoint of ligand reactivity seem to have matured only during the last three decades. Different authors have divided ligand reactions into various classifications as to type (8, 39j 4 ). For the purposes of the present discussion, ligand reactions are divided into the following types ... 

The catalytic efficiency is also often determined by the nature of the coordinating ligands. The electronic and steric nature of the ligand has a remarkable influence on the activity of the catalytic systems and many attempts have been made to obtain a comprehensive system of ligand classification that allows correlation of catalytic activity and ligand structure. In this section it will be shown how homogeneous catalysts for CO2 transforming reactions can be developed and optimized on the basis of these concepts by combination of experimental and theoretical work. 

The removal of ligands (including H2O) from coordination compounds may be accompanied by recrystallization and either a change in coordination number, structure or ligands present through formation of new bonds with the anions, anation, etc. Constituent water in crystalline hydrates may be as coordinated ligands and/or structural water. A scheme for the classification of dehydration reactions is described in Table 7.3. 

A further factor which must also be taken into consideration from the point of view of the analytical applications of complexes and of complex-formation reactions is the rate of reaction to be analytically useful it is usually required that the reaction be rapid. An important classification of complexes is based upon the rate at which they undergo substitution reactions, and leads to the two groups of labile and inert complexes. The term labile complex is applied to those cases where nucleophilic substitution is complete within the time required for mixing the reagents. Thus, for example, when excess of aqueous ammonia is added to an aqueous solution of copper(II) sulphate, the change in colour from pale to deep blue is instantaneous the rapid replacement of water molecules by ammonia indicates that the Cu(II) ion forms kinetically labile complexes. The term inert is applied to those complexes which undergo slow substitution reactions, i.e. reactions with half-times of the order of hours or even days at room temperature. Thus the Cr(III) ion forms kinetically inert complexes, so that the replacement of water molecules coordinated to Cr(III) by other ligands is a very slow process at room temperature. 

Classification exclusively in terms of a few basic mechanisms is the ideal approach, but in a comprehensive review of this kind, one is presented with all reactions, and not merely the well-documented (and well-behaved) ones which are readily denoted as inner- or outer-sphere electron transfer, hydrogen atom transfer from coordinated solvent, ligand transfer, concerted electron transfer, etc. Such an approach has been made on a more limited scale. Turney has considered reactions in terms of the charges and complexing of oxidant and reductant but this approach leaves a large number to be coped with under further categories. 

The first step is carbon-metal bond formation via coordination. This process may be followed by one or more steps, leading to transformation of ligands and/or reaction between ligands. In a final step, the metal is removed from the organic moiety. Reactions are catalytic or stoichiometric, depending on whether or not the metal is eliminated in its original oxidation state. The following is a broad classification of these processes. 

Metal compounds are often used to stabilize reactive organic fragments via complexation and intriguing alkyne ligand in this classification is benzyne. A series of iridium benzyne complexes has been made with compound (44) as an example and the reaction chemistry of coordinated benzyne has been explored. ... 

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