Dynamic intramolecular rearrangements

Dynamic intramolecular rearrangements are observed for a variety of diene-metal complexes at, or near, ambient temperature. This stereochemical non-rigidity may be detected by variable temperature NMR experiments40 in which the signals observed for a static structure coalesce into time averaged signals for the fluxional process. For purposes of this section, processes with activation energies > ca 25 kcal mol 1 or which are irreversible will be considered to be isomerization phenomena and will be discussed in Section IV. 

Fig. 16.61 Dynamic intramolecular rearrangement of Wj(0-/-Pr) 2. [From Chisholm, M. H. Clark, D. L. Hampden-Smilh, M. J. J. Am. Chan. Soc. 15)89, III, 574-586. Reproduced wilh permission. ...

Three dynamic intramolecular rearrangements have been identified in the cyclic-triene complexes (36a) and (36b) by variable-temperature C n.m.r. methods. The spectrum of (36b) at -120 °C exhibits six signals of equal intensity for... 

Ammal, S. C. Yamataka, H. Aida, M. Dupuis, M. Dynamics-driven reaction pathway in an intramolecular rearrangement, Science 2003, 299, 1555-1557. 

As stated in the previous section, dynamic behaviour involving intramolecular rearrangements of the metal skeletons of Group 11 metal heteronuclear clusters is relatively common, in marked contrast to the situation observed for almost all other transition metal clusters, which have metal frameworks that are stereochemically rigid in solution. The mechanisms of these metal core rearrangements are, therefore, of considerable interest. 

Ruthenium and Osmium.—Square-pyramidal compounds [M(X)(Y)(PPh3)3] exhibit a dynamic process in solution which according to P n.m.r. spectroscopy equilibrates apical and basal phosphine sites. The measured values of A5 (Table 5) are consistent with this being an intramolecular rearrangement (probably Berry pseudorotation) and since addition of PPh3 does not effect the process a bimolecular exchange is also excluded. 

Dynamics of intramolecular metal-centred rearrangement reactions of tris-chelate complexes. L. H. Pignolet, Top. Curr. Chem., 1975,56,93-137 (85). 

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