Dihydrogen exchange

Dyotropic rearrangements are uncatalyzed concerted dihydrogen exchange reactions, another class of orbital symmetry controlled processes, which involve the simultaneous migration of two cr-bonds. These conversions can be both thermal and photochemical. They can be subdivided into two types (1) reactions in which two migrating cr-bonds interchange their positions (equation 78), and (2) reactions without such positional interchange (equation 79)91,92. 

Figure 6.1 One-dimensional double oscillator models for hydrogen transfer and dihydrogen exchange under different conditions.

In summary the calculations presented in Ref. [62] represent the missing theoretical link between the phenomena of incoherent and coherent dihydrogen exchange in transition metal hydrides and the PHIP effect. Moreover, PHIP is identified as a powerful and sensitive tool to study reaction pathway effects via analysis of the polarization patterns of the final hydrogenation products. 

Symmetry Effects on NMR Lineshapes of Intramolecular Dihydrogen Exchange Reactions... 

Symmetry Effects on NMR Uneshapes of Intramolecular DIhydrogen Exchange Reactions 671... 

The above described experiments allow determination of the coherent and incoherent dihydrogen exchange rates of the two complexes. 

Figure 9. Calculated low-lying isomers (6-8) and transition state (9) for hydride dihydrogen exchange process for [Ru(PH3)4H3] species [39].

The kinetics of dihydrogen exchange has been described previously [5,6]. In the present experiments, the component under observation is the molecular hydrogen, which contains two equal hydrogen atoms per molecule. Three isotopic molecules can be formed by D labelling HH, HD and DD, the corresponding concentrations being [HH], [HD] and [DD]. 

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