Reactions and Acidity of Dihydrogen Complexes

7) or an even more complicated mechanism can occur, e.g., opening up of a chelate ring in[FeH(H2)(dppe)2]+.4 

Reductive elimination of H2 from stable cis dihydride complexes can be photochemically promoted and undoubtedly M-H2 intermediates are involved.5 Theoretical studies6 of gas-phase reactions of Fe(CO)s with OH- indicate that H2 

Computations show that an H2 complex lies along the reaction coordinate, and W(H2)(CO)5 may also be an intermediate in W(CO)6-catalyzed reactions.7 Examples of the significance of a complexes in industrial and biological processes will be discussed below as well as in Chapter 10. Theoretical studies of a variety of hydrogenations and hydroborations have been reviewed by Frenking, and ff-com-plex intermediates are often identified along the reaction coordinate. 

The solid state reactivity of H2 complexes has not been extensively studied, but significantdifferencesoccurfor RuH2(H2)2(PCy3)2, which is stable to 70°C, whereas 

H2 dissociates readily in solution.8 Reaction with CO gives a mixture of species but not RuH2(CO)2(PCy3)2, which forms in solution reaction. Ethylene does not react, apparently because of steric hindrance, but does react in solution (see below). 

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