Fluxional Behavior and Isomerization Reactions

5 Pt Chemical Shift Data for Hetero-Platinum Clusters 

Three major classes of fluxional behavior are commonly observed in clusters  

Metal localized ligand scrambling, most commonly seen in the M(CO)3 or M(CO)2L groups. For Pt clusters some examples of PtL2 localized scrambling have also been observed. 

These three classes are not mutually exclusive, and all have been observed in hetero-Pt clusters. Whereas most examples of fluxional behavior seen in hetero-Pt clusters are common to other systems, there are several interesting examples that appear to be intimately connected with formal 16 - 18-electron conversions at Pt centers. 

Modern NMR techniques such as quantitative analysis of multisite exchange using either ID magnetization transfer experiments (JOS) or the 2D exchange spectroscopy (EXSY) method (104,105) promise to be of great help in unraveling the complex stereochemical exchange networks involved in cluster fluxionality. The usefulness of EXSY in the context of this article is illustrated by the phase-sensitive 13C 1H EXSY spectrum (255 K, tm = 0.5 sec) 

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