Studies of Coordinated Dihydrogen

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... 

Commonly, any experimental study of dihydrogen bonds is undertaken to clarify the following aspects (1) establishment of intra- or intermolecular coordination, (2) determination of its stoichiometry, (3) reliable establishment of a proton-donor site and a proton-acceptor center, (4) description of the geometry of dihydrogen-bonded complexes, and (5) correct measurement of bonding energies. In this chapter we demonstrate how to approach these factors using various experimental methods that work in the solid state, the gas phase, and in solution. 

The study of species in which ethylene is coordinated to transition metal centres holds great interest in areas of catalytic and polymerization chemistry (7). The bonding of the ethylene ligand to the metal centre in such species has been compared to that of the dihydrogen complexes described above (14,15,22). Photolysis of chromium hexacarbonyl, Cr(CO)6, in conventional solvents in the presence of dissolved ethylene gas is known to lead initially to a highly labile species in which one CO ligand is replaced by ethylene. Further photolysis leads to a more stable compound which contains two ethylene ligands trans to each other across the metal centre (25), equation 3. The conventional synthesis is experimentally difficult the two photochemical... 

---