Metal Dihydrogen Chemistry

Ab Initio Studies of Transition Metal Dihydrogen Chemistry... 

Although most metal-dihydrogen chemistry is carried out in organic solvents, aqueous systems have been found that have potential applications in biomimetic and green chemistry, for example, chemoselective hydrogenation catalysis.31 Protonation of a hydride complex by acids is often used13,24 and is widely applicable because it does not require an unsaturated precursor that may not be available. An example is shown in Scheme 5.3. 

Just as bridging hydrides play a central role in the chemistry of Group 13 hydrides, three centre-two electron (3c-2e) bonding is a recurrent fea- Figure 2.17 Polyhydride vs ture of binuclear (and polynuclear) hydrides of the transition metals dihydrogen coordination... 

One of the most interesting aspects of transition metal hydride chemistry is the relationship between this ligand and the rapidly developing chemistry of the dihydrogen ligand, H2. 

Kubas, G. J. Metal Dihydrogen and a-Bond Complexes Structure Theory and Reactivity. Modern Inorganic Chemistry Series Fackler, J. P., Jr., Ed. Kluwer/Plenum New York, 2001. 

The chemistry of transition metal dihydrogen complexes, such as formed in Eq. (1) is in the focus of very intensive studies [13, 14] and such complexes were shown to be involved in the mechanism of several hyrogenation processes [15]. Despite this fact, their role in aqueous-phase hydrogenations is largely unexplored, although examples of water-soluble (or water-stable) dihydrogen complexes are known [16, 17]. Reaction (1) does not involve the change of the oxidation state of... 

G.J. Kubas, Metal-dihydrogen and sigma-bond coordination the consummate extension of the Dewar-Chatt-Duncanson model for metal-olefin pi bonding . Journal of Organometallic Chemistry, 635, 37 (2001). 

In this chapter, we have summarized work from a number of laboratories that demonstrates that PHIP is a useful tool for the study of mechanistic organometallic chemistry. While the enhanced signals of PHIP provide nominally simple evidence for pairwise addition of H2, PHIP can be employed in many cases to determine much more complicated aspects of reaction mechanisms involving hydrogen addition. It is important to note, however, that PHIP has yet to be observed in cr-bond metathesis reactions or in metal-dihydrogen complexes. 

Two significant surveys are published in the sane edition of Coordination Chemistry Reviews. Oxygen donor-ligand derivatives of tri-osmium dodecacarbonyl are covered by Frauenhoff and the reactions of transition metal dihydrogen complexes (of which many are carbonyl-containing) are outlined by Jessop and Morris. The crucial role of matrix Isolation studies is well covered in this article. A shorter review of interest here has been published on the role of the phosphorus d-orbitals in M-P bonding. ... 

One family of porphyrin complexes that will be treated in the review, even though they do not contain metal-carbon bonds, are metalloporphyrin hydride and dihydrogen complexes. As in classical organometallic chemistry, hydride complexes play key roles in some reactions involving porphyrins, and the discovery of dihydrogen complexes and their relationship to metal hydrides has been an important advance in the last decade. 

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