Transition metal complexes homonuclear

The activation of simple organic molecules by more than one transition metal constitutes an area of research which has grown in interest since the mid 1970s. Transition metal clusters, homonuclear and later heteronu-clear compounds, have been widely studied because of the potential for application in catalysis. The chemistry of such complexes has been the topic of many review articles, some of which appeared in this series (1-5). The concept of utilizing binuclear complexes with metal-metal bonds for ligand activation has been recognized (6-8), and, as stated by Casey and Audett, there is some hope that a smooth transition from the chemistry of mononuclear compounds to dinuclear compounds to metal clusters to metal surfaces may be found (9). 

Parallel to the development of the chemistry of dinuclear transition metal complexes with metal-metal bonds, studies related to bimetallic complexes, hetero- and homonuclear, without metal-metal bonds are appearing in the literature at ever increasing frequency (10-13). In these complexes, two or more metals are separated by a common ligand which acts as a bridge between them. Two metal centers acting in a joint fashion could enhance the activation of an organic substrate considerably and in... 

Rate constant data for several homonuclear electron transfer reactions involving transition metal complex ions in water are summarized in table 7.1. The striking feature of the results is that the rate constants vary over a very wide range from a low 2x 10 s to a high of 4 x lO M s. Since these... 

Table 7.1 Kinetic Data for Homonuclear Electron Transfer Reactions Involving Transition Metal Complex Ions in Water at 25°C [5] ...

The above example illustrates the estimation of for a homonuclear reaction involving octahedral transition metal complexes. Most systems are more complicated. Flowever, if the details of the changes in bond lengths and bond angles which accompany electron transfer are known, estimates of can be made. Quantum-mechanical calculations are often required to obtain the necessary information. 

Fig. 5.16 Substitution, addition and elimination reactions of transition metal complexes. L = Lewis base, two electron ligand. X = one electron ligand, e.g. Cl, H, R, COR, SiR3. XY includes homonuclear species, e.g. H, Cl. ...

Table 20 Homonuclear transition metal hydride complexes and formal electron configurations...

---