Transition metals hydride bridge

Terminal M-H stretching modes of transition metal hydrides are readily identified in the ir around 1900 300 cm-1, with intensities that usually are stronger than CH stretching modes (14). With bridging hydrides, however, the bands often are not observed in the ir. As demonstrated in the laboratories of both Jones (15) and Kaesz (14), M-H modes of bridging hydrides are more readily... 

Nitriles are resistant to hydrometallation by transition metal hydride complexes. The complex Cp2ZrHCl reacts with nitriles A rhenium complex bridged by adinuc-lear hydride undergoes insertion with several isonitriles and with acetonitrile. The product in the case of the isonitrile results from a 1,1-inertion (see 11.2.8) ... 

The best-studied examples of bridge bonds are those in borancs and related compounds (Chapter 8) and in certain hydride complexes (pages 183 and 250). Bridge bonds in transition-metal complexes are discussed along with transition-metal hydride complexes in Chapter 22. 

When the same tin/iridium stiochiometry is employed, but a small amount of THF is added to the solvent, the major product is now an air-sensitive purple cluster, again with an Ir3Su2 framework. This material has no bridging carbonyl stretches, is diamagnetic, and shows a H NMR peak in solution at d-9.61 a region typical of late transition metal hydrides. The structure of this species, [Ir3(//-SnR2)2(CO)sH], is shown in Fig. 16. 

Oxidative addition of transition metal-hydride and transition metal-carhon bonds to zero-valent transition metal complexes provides convenient method for preparation of homo- and heterodinuclear organometallic complexes. Oxidative addition of iron-hydride to zero-valent platinum complex giving Fe-Pt heterodinuclear complexes was demonstrated hy the reaction of HFe[Si(OMe)3](CO)3(/c -dppe) with zero-valent platinum complex such as Pt(C2H4)3 or Pt( 1,5-cod)2 giving eventually heterodinuclear ethyl or cyclooctenyl complex (Scheme 3.86) [175]. The resulting heterodinuclear structure is stahihzed hy the bridging dppe ligand and the siloxo moiety. 

Covalent. Formed by most of the non-metals and transition metals. This class includes such diverse compounds as methane, CH4 and iron carbonyl hydride, H2Fe(CO)4. In many compounds the hydrogen atoms act as bridges. Where there are more than one hydride sites there is often hydrogen exchange between the sites. Hydrogens may be inside metal clusters. 

By far the most common CN of hydrogen is 1, as in HCl, H2S, PH3, CH4 and most other covalent hydrides and organic compounds. Bridging modes in which the H atom has a higher CN are shown schematically in the next column — in these structures M is typically a transition metal but, particularly in the Mi-tnode and to some extent in the x3-mode, one or more of the M can represent a main-group element such as B, Al C, Si N etc. Typical examples are in Table 3.3. Fuller discussion and references, when appropriate, will be found in later chapters dealing with the individual elements concerned. 

Transition metal complexes with bridging hydride ligands. L. M. Venazi, Coord. Chem. Rev., 1982, 43, 251-274 (40). 

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