Octahedral complexes Bailar twist

In the absence of a dissociative process, the remaining mechanistic options are only intramolecular nondissociative of the pseudorotation family. The nondissociative site-exchange reactions commonly discussed for octahedral complexes are the Ray-Dutt [10] and Bailar twist mechanisms [11], by which three ligands are rotated relative to the other three via a trigonal prism transition state. None of these processes effects a topomerization in one step. At least two consecutive such twists are necessary in order to bring about the observed topomerizations. However, with these mechanisms it would be difficult to rationalize the observation of two distinct barriers in 1-4. 

Fig. 5.14 Bailar twist mechanism for the racemisation of an octahedral tiis-chelate complex via a trigonal prismatic transition state or intermediate.

Figure 11 Ray-Dutt twist (top) and Bailar twist (bottom) in the isomerization of an octahedral complex.

The two popular mechanisms for the intramolecular rearrangement in octahedral complexes, known as Bailar twist and Ray-Dutt twist occurring through prismatic intermediates, are shown in Figure 11. 

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