Dihydrogen cations

Many mechanistic implications have been discussed, but we will concentrate here only on the most important structures in the context of dihydrogen-cation complexes. Deuterium-labeled methane and methyl cations were employed to examine the scrambling and dissociation mechanisms. The protonated ethane decomposition yields the ethyl cation and dihydrogen. Under the assumption that the extra proton is associated with one carbon only, a kinetic model was devised to explain the experimental findings, such as H/D scrambling. ... 

The high kinetic acidity of complexes is illustrated by the system in eq 20 [40,41], For Ru and Os, the dihydrides exist as a mixture of cis and trans in an equilibrium ratio of 9 1 for Fe, the cis form is the only thermodynamically stable isomer. For Ru and Os, deprotonation of the hydride/dihydrogen cation led only to the thermally unstable trans dihydride, which rearranged to the cis... 

Like the dihydrogen cation, hJ, the trihydrogen cation, H, is known only in the gas phase. Both ions have, however, been found in interstellar space. The structure of is that of an equilateral triangle with the three H-H distances equal to 87.5 pm as compared to 74 pm in H2 or 106 pm in hJ. These distances are so short as to imply the existence of three H-H bonds, though the total number of electrons in the molecule is just two The dissociation energy, defined as the energy of the reaction... 

In Appendix 10 we look in detail at the simplest molecular system, the dihydrogen cation H2+. This is a molecule with only one electron, and so only electron-nuclear and nuclear-nuclear interactions need be considered. Here, we summarize the findings of Appendix 10 and identify the contributions to the total energy of the molecule in terms of the basis functions. 

Cationic hydrides have been important in studying dihydrogen complexes [94]... 

The fact that metal hydrides can be acidic may seem paradoxical in view of the nomenclature that insists that all complexes with a M-H bond be referred to as hydrides regardless of whether their reactivity is hydridic or not. Not only can some metal hydrides donate a proton, but some can be remarkably acidic. Some cationic dihydrogen complexes are sufficiently acidic to protonate Et20 [8], and some dicationic ruthenium complexes have an acidity comparable to or exceeding that of HOTf [9],... 

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