Dihydrogen complexes reactivity

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],... 

Morris et al. carried out extensive studies [20] of the acidity of metal hydrides in tetrahydrofuran (THF), including metal hydrides of very low acidity as well as dihydrogen complexes that are reactive with CH3CN. The dielectric constant of THF is low compared to that of CH3CN, so ion-pairing issues must be taken into account [21], though these measurements in THF provide useful comparisons to data in CH3CN and other solvents. 

The gaseous reaction of 4 did not occur below 65 °C. Above that temperature, reactivity was indicated by colour changes of the crystalline material from red-purple to white. The reaction could also be monitored by IR spectroscopy, probing the v(N-N) absorption at 2125 cm-1, which was replaced by two v(Co-H) absorptions at 1967 and 1833 cm-1. Treatment of the dihydrogen complexes with N2 afforded the starting material 4. 

Preparation and reactivity with azo-species of hydride and dihydrogen complexes of osmium stabilised by tris(pyrazolyl)borate and phosphite ligands... 

Recent Developments in the Synthesis, Bonding Modes and Reactivity of Hydrido and Dihydrogen Complexes... 

The synthesis and characterization of hydride and dihydrogen complexes with the widest range possible of acid-base reactivity... 

THE SYNTHESIS AND CHARACTERIZATION OF HYDRIDE AND DIHYDROGEN COMPLEXES WITH THE WIDEST RANGE POSSIBLE OF ACID-BASE REACTIVITY... 

To this point, we have characterized the basicity of TMH complexes, and in the previous chapter dihydrogen bonding was described as a special interaction, which is directly related to this property. This directional bonding may also have implications for the reactivity of hydride complexes in the sense that it may be a pre-stage to protonation of TMHs, leading to dihydrogen complexes [34]. This type of reactivity is characterized by bond formation with the hydride ligand, which in this way however remains in the coordination sphere of the metal. 

Since the first discovery of dihydrogen complexes by Kubas and co-workers in 1984 [1], extensive studies on this unique class of complexes have been carried out to reveal structural and chemical properties of coordinated dihydrogen [2]. The results show that dihydrogen complexes are more than intermediates for oxidative addition of molecular dihydrogen (H ). Thus, they have their own reactivities, and participate in interesting stoichiometric and catalytic reactions, although this aspect has been less explored until recently [3]. In this article, we summarize our... 

Me). Photolysis of metal carbonyls in liquefied noble gases has been a successful approach in the charaterization of a range of highly reactive dihydrogen complexes including V(GO)s(H2), M(Gp)(GO)3(H2) (M = V or Nb), ... 

The largest amount of information on the structures, dynamics, and reactivity of a-complexes is derived from dihydrogen complexes. These complexes have been studied intensively because they are considered to be intermediates in the oxidative addition of dihydrogen and could serve as a type of interaction in a material that could reversibly store molecular hydrogen. Furthermore, many complexes of dihydrogen have succumbed to isolation, and these complexes posses a variety of properties that depend on the steric and electronic properties of the metal center. 

The properties and reactivity of alkane and silane - - complexes are closely related to those of dihydrogen complexes. However, the thermodynamic stabilities of the complexes are much different. The silane complexes have been studied in less detail than dihydrogen complexes, but, broadly speaking, they are similar in stability to the dihydrogen complexes or only slightly less stable. Alkane complexes have been studied intensively as reactive intermediates, " but detailed structural and reactivity studies have not been conducted because alkane complexes are unstable in solution. The most detailed data have been gained by NMR spectroscopic studies of CpRe(CO)2(RH) complexes. These data imply that the metal binds in an Tj -mode to a single C-H bond of the alkane. 

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