Chemistry

Olefin hydrogenations

Olefin hydrogenations


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Dihydrogen Complexes - Examples

The following two equations demonstrate the two synthetic routes for dihydrogen complexes.

In particular d6-Metals are used to form η2-H2-Complexes empowered. On the other hand, the oxidative addition of H2 preferred if a classic dihydrido complex with a d6-Electronic configuration is formed. Both apparently depend on the particularly high ligand field stabilization energy d6-Complexes together. So [Cr (η2-H2) (CO)5] (Cr0,d6) a nonclassical dihydrogen complex and [Fe (H)2(CO)4] (FeII,d6) a classic dihydrido complex.

The coordination of dihydrogen can result in a large increase in the acidity of H.2 accompanied.

That's how it is Osmium complex with a pKa = -2 a very strong acid. Such reactions correspond to heterolytic bond cleavage of H.2. This is also at H.2-binding hydrogenases detected and possibly play η2-H2-Complexes also play a role in these.

It's not always easy to get between non-classic η2-H2-Complexes and classic Differentiate between dihydrido complexes. In general, it is difficult to precisely localize hydrogen atoms in the immediate vicinity of heavy metals in X-ray single crystal structure studies. Neutron diffraction experiments, on the other hand, require very large single crystals. Deliver by NMR spectroscopy T1- Relaxation measurements and the size of H-D coupling constants in η2-HD complexes statements about the bond relationships.

Besides the ones discussed here η2-H2-Complexes (H-H 0.8-0.9 Å) there are also those with an extended length H-H-Bond (1.1-1.6 Å).H-HDistances> 1.7 Å indicate classical dihydrido complexes. In the complex [ReH7(dtpe)2] (dtpe: 1,2-bis (ditolylphosphano) ethane) two of the seven H ligands are only 1.357 Å apart, so that an H2-Complex with extended H-H-Binding exists. So it should [ReH5(H2) (dtpe)2] to be written.


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