Dihydrogen homolytic splitting

In the past this was referred to as a homolytic reaction [23], It is clear that it would be highly unlikely that dihydrogen would be split into a metal hydride and a highly energetic hydrogen radical in this sense the term homolytic splitting is misleading. 

Obviously, there is a great deal of analogy between the mechanisms of hydrogen activation and hydrogenation in aqueous and nonaqueous systems. The most common made of activation of dihydrogen is its homolytic splitting by oxidative addition [Eq. (1)]. 

In reactions involving heterolytic splitting, an essential role is played by the presence of the base which reacts with the resulting proton. This base may even be the ligand bonded to the central atom which activates hydrogen. Square-planar, complexes, particularly those of Rh(I) and Ir(I), as well as [Co(CN)5], [CoH(N2)(PPh3)3], etc., homolytically split dihydrogen ... 

Scheme 20.4 shows a set of dynamics involving the binding and splitting of H2 that essentially represent the reaction coordinate for homolytic H-H bond cleavage or in the reverse process, the formation of H2 from a dihydride species. Remarkably these can be equilibrium processes in certain cases. Solutions of the complex W(CO)3(PTr3)2(H2) were observed by NMR spectroscopy to contain about a 4 1 ratio of dihydrogen to dihydride complex, proving that side-on bonded H2 complexes were the first step in formation of hydride complexes (Eq. (20.1) P = PiPrj) [lb, 2]. 

Crabtree. R.H. Siegbahn. P.E.M. Eisenstein, O. Rheingold. A.L. A new intermolecular interaction Unconventional hydrogen bonds with element-hydride bonds as proton acceptor. Acc. Chem. Res. 1996. 29. 348. Morris, R.H. 1995 Alcan award lecture—New intermediates in the homolytic and heterolytic splitting of dihydrogen. Can. J Chem. 1996. 74, 1907. 

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