Dihydrogen bonding

In another example of hydrogen-bond interaction-driven coordination, Teixidor and Lledos have exploited C—H S—H H—B hydrogen/dihydrogen-bond... 

Figure 88 The supramolecular architectures (171) assembled by the C—H S—H H—B hydrogen/dihydrogen-bond interactions between mercaptane and metallacarborane complexes. (Adapted from ref. 167.)...

A novel form of Y HX hydrogen bonding49 results when the Lewis base Y is itself a hydride ion (H-). Because the electron affinity of a hydrogen atom is extremely weak (21 kcal mol-1), the H- ion is among the most weakly bound and diffuse anionic species known, and hence a powerful Lewis base. In this case, the H - -HX complex can be referred to as a dihydrogen bond 50 to denote the unusual H-bonding between hydrogen atoms. A water complex of this type was... 

Ionic or semi-ionic Y—H bonds of sufficient hydridic character (Y+—H-) can also be expected to make dihydrogen bonds of the form... 

As a second example of dihydrogen bonding, let us consider the borohydride anion (BH4-) in complexation with water (as analyzed by Jackson53),... 

Charge-transfer complexes involving one-center n acceptor orbitals (n-n, a-n, and 7t-n Lewis-base-Lewis-acid adducts) have been discussed in Sections 3.2.10 and 3.6. Many CT complexes involving a acceptors have been illustrated for H-bonds (n-a ) and dihydrogen bonds (a-o ), as well as for the Cg H6 -B (7t-a ) example above. In the remainder of this section we shall therefore focus on CT... 

Other, the dihydrogen bond is already broken and the unsaturated bond is weakened. Next, the unsaturated bond inserts into one of the Rh-H bonds and thus the first hydrogen is transferred to the product molecule. Transfer of the second hydrogen leads to reductive elimination of the product molecule and the catalyst is ready for the next cycle. 

Dihydrogen Bonds Principles, Experiments, and Applications, By Vladimir I. Bakhmutov Copyright 2008 John Wiley Sons, Inc. 

The aim of the book is to show (1) a diversity of dihydrogen bonds (2) the nature, geometry, energetics, and dynamics of these bonds and (3) the factors that control the energy of dihydrogen bonds from very weak to very strong. 

The world of hydrogen bonds, always very diverse, became more so after the discovery of dihydrogen bonds and dihydrogen interactions. It should be pointed... 

The above-mentioned topological criteria are very useful since the geometrical criteria are often not sufficient to establish whether or not hydrogen bonding exists. As we will see below, these theoretical criteria are universal and quite suitable for nonconventional hydrogen bonds as well as for dihydrogen bonding. 

It is also remarkable that M- H-X systems show proton transfer which is mechanistically close to that of classical hydrogen bonds. Protonation of the metal atom occurs via M- H bonds and ion pairs (Scheme 2.4) lying as intermediates on the reaction coordinate. As we will see below, a very similar mechanism operates in the case of dihydrogen-bonded complexes. 

Figure 3.1 Area occupied by dihydrogen bonds among other hydrogen-bonded complexes according to Alkorta et al. [2].

GENERAL VIEW FROM AN H2 MOLECULE TO A DIHYDROGEN BOND VIA A DIHYDROGEN LIGAND... 

In the framework of AIM theory, which well be used extensively to describe dihydrogen bonds, the situation above corresponds to the electron density distribution in the H2 molecule, where the pc parameter takes the very large value 1.857 au and the Laplacian, V pc, is strongly negative ( —34.15 au). These data have been obtained by ab initio calculations at the MP2/6-31G level [4],... 

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