Ligand-metal cooperative effects

Cooperative effects in which, for example, a reagent is activated by coordination to one metal center and then induced to react with a ligand on an adjacent metal center or in a bridging position can occur. A search for such model reactions has been initiated. 

Fig. 6.41 Possible cooperative effect between the salen units of the dendritic catalyst 17 as well as monomeric (15) and dimeric model substances (16) M symbolises the metal site, and the (red) ellipses the salen ligands...

Nature of Cooperative Effects in Mixed-Ligand Thiocyanate Complexes Various explanations have been put forward to account for the effects of neutral ligands on the nature of the metal-thiocyanate bond TT-bonding, symbiosis, and antisymbiosis of hard and soft acids and bases as well as steric effects have all been discussed. In addition, directional... 

Another feature of the metal surface that may be important for certain reactions is its electrophilic character. The interesting catalytic behavior of the [Af(diene)L2]A systems, mentioned in this review, may in part depend on the ligand-deficiency and electrophilicity of these systems. In these two properties, they may parallel the properties of a metal surface. It remains to be seen whether those cooperative effects that may occur are incidental or essential to catalytic action in heterogeneous, as well as homogeneous, systems. 

In a fifth contribution, Pierre Le Gendre et al. review the catalytic performances of early-late bimetallic complexes. After an introduction dealing with bifunctional and cooperative dual catalysis in which the cooperative effects arise from two catalytic functions present in the same or two different molecules, this paper focuses on an inventory of early-late heterobimetallic complexes in catalysis. It includes those where the two metal centers belong to the same complex, with bridging ligands as in the following example in which the chiral information is provided by the titanium metal center ... 

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