Metal-ligand a bonds

The valence bond picture for six-coordinate octahedral complexes involves hybridization of the metal (Fig. I l.lc. d). The specific d orbitals that meet the symmetry requirements for the metal-ligand a- bonds are the dj and (page 396). As with the four-coordinate d complexes discussed above, the presence of unpaired electrons in some octahedral compounds renders the valence level (n - l)d orbitals unavailable for bonding. This is true, for instance, for paramagnetic [CoFf p (Fig. 

Fig. 6.8 The metal-ligand a bonding in an octahedral complex involving orbitals ofA g symmetry. The metal s orbital is shown at the centre.

Metal-Ligand a-Bonding and Pauling 3-Electron Bonds ... 

The essential aspect of the u-bond metathesis mechanism is the concerted exchange of a metal-ligand a-bond with one of an incoming substrate where the reaction proceeds via a [2o-+2o-] cycloaddition, as illustrated in the transitions state in Figure 14.6. The key concept is that CT-bond metathesis is a one-step reaction with two u-bonds breaking (M-C and C -H) and two u-bonds forming (M-C and C-H). Therefore, there is no change involved in the oxidation state of the metal center. This reaction mechanism has been proposed for the d° and d°P metal compounds, and has been recently reviewed for transition metals. [58,59]... 

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