Coordinated dihydrogen

The high concentration of dihydrogen gas in our experiments has allowed us to stabilize complexes which previously had only a fleeting existence at ambient temperatures. For example, the species W(CO)5(H2) has a lifetime in conventional solvents of somewhat less than one second at room temperature. Under our supercritical conditions, however, the lifetime may be extended to more than three minutes. Furthermore, the stability conferred upon this molecule by our supercritical system, and the unique spectroscopic transparency of scXe have allowed us to detect the very weak v(H-H) band of coordinated dihydrogen using only a conventional FTIR spectrometer and a powerful UV lamp (4) as shown in Figure 3. 

In this biomimetic system, cis-V02+ coordinates dihydrogen peroxide, forming the monoperoxo or diperoxo species, in ratios dependent on the dihydrogen peroxide and acid concentrations [74],... 

Fig. 6.15 How the six degrees of freedom of free dihydrogen become six internal modes of vibration of an ti -coordinated dihydrogen molecule, (a) Vhh — Vhh. (b) x axis rotation becomes the M-H2 antisymmetric stretch (vHMuasym), (c)y axis rotation becomes the M-H2 torsion, (d) z axis translation becomes the MH2 rock, (e) y axis translation becomes the M-H2 symmetric stretch (vHMusym) and (f) x axis translation becomes the MH2 wag.

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... 

In the reaction of coordinated dinitrogen with acidic ruthenium dihydrogen complexes shown in the previous section, only one of the two hydrogen atoms of the coordinated dihydrogen is used for the N-H bond formation, while the other is not used for the product formation and remains at the Ru center. However, several examples are now known where both of the hydrogen atoms of coordinated dihydrogen are catalytically transferred to products via the heterolytic splitting. 

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