Metal-hydride complex

Reduction of tosylhydrazone derivatives to the corresponding methylene analogs with metal hydride complexes provides an excellent solution to this problem. Soon after the discovery of this reaction it was recognized... 

Reaction of metal hydride complexes with N-nitrosoamides, e.g. Af-methyl-7V-nitrosourea ... 

Photochemistry of transition metal hydride complexes. G. L. Geoffroy, Prog. Inorg. Chem., 1980, 27, 123-151 (58). 

The analogous reactions of Zn and Cd derivatives arc less well studied. Zinc alkyls ZnRi (R = Et, n-Bu) react with transition-metal hydride complexes, H2M(Cp-(M = Mo, W) ... 

Teller R, Bau RG (1981) Crystallographic Studies of Transition Metal Hydride Complexes. 44 1-82... 

In 1931, Hieber and Leutert reported Fe(CO)4(H)2 not only as the first iron hydride complex but also as the first transition-metal hydride complex (FeH2 was reported in 1929 from FeCl2 and PhMgBr under a hydrogen atmosphere. However, it exists only in a gas phase) [2, 3]. The complex synthesized from Fe(CO)5 and OH (Scheme 1) is isolable only at low temperature and decomposes at room temperature into Fe(CO)5, Fe(CO)3, and H2. 

A Fe-H bond is generally polarized as Fe -H because H is more electronegative than Fe. However, iron hydride complexes impart much less negative charge to the hydride than early transition-metal hydride complexes. 

Metal Hydride Complexes Electrogeneration and Electrocatalytic Dihydrogen Evolution 473... 

The reduction of protons is one of the most fundamental chemical redox reactions. Transition metal-catalyzed proton reduction was reviewed in 1992.6 The search for molecular electrocatalysts for this reaction is important for dihydrogen production, and also for the electrosynthesis of metal hydride complexes that are active intermediates in a number of electrocatalytic systems. 

However, since the goal of this work was the synthesis of alcohols from olefins via hydrohydroxymethylation (75, 76), little attention was given to developing a shift-catalyst per se. Pettit has recently reexamined some of this work and shown that, by careful control of the pH of the reaction mixture, systems based on either Fe(CO)5 or Cr(CO)6 can be developed for the production of either formic acid or methanol from carbon monoxide and water (77, 78). Each of these latter systems involves the formation of metal hydride complexes consequently, molecular hydrogen is also produced according to the shift reaction [Eq. (16)]. 

Many more examples have been collected for the reaction of transition metal hydride complexes with 1,3-dienes, which appear to proceed via radical pair mechanisms, even without photochemical activation72-77. The following general mechanism has been assumed to be operative for the reaction of HMn(CO)572,73, HFe(CO)4SiCl374,75, HFe(CO)2Cp76 and HCo(CO)4 (H-[M]) (equation 18)77. 

Geoffroy, George, L., Photochemistry of Transition Metal Hydride Complexes 27 123... 

As expected, many unsaturated transition metal hydride complexes catalyse isomerisation. Examples include monohydrides of Rh(I), Pd(II), Ni(II), Pt(II), Ti(IV), and Zr(IV). The general scheme for alkene isomerisation is very simple for instance it may read as follows (Figure 5.1) ... 

Metal Hydrides, Complex, Reduction of Cyclic and Bicydic Ketones by (Boone and Ashby) 11 53... 

Polymer-bound reducing agents have received significantly less attention, presumably because main group metal hydride complexes predominate as reducing... 

Since the nature of the hydride chemical shifts, particularly in transition metal hydride complexes, is not simple [32], there is no reliable correlation between Sh and the enthalpy of dihydrogen bonding. Nevertheless, the chemical shifts of hydride resonances and their changes with temperature and the concentration of proton-donor components, for example, can be used to obtain the energy parameters for dihydrogen bonding in solution. As earlier, the enthalpy (A/f°) and entropy (AS°) values can be obtained on the basis of equilibrium constants determined at different temperatures. Let us demonstrate some examples of such determinations. 

INTRAMOLECULAR DIHYDROGEN BONDS IN METAL HYDRIDE COMPLEXES... 

Figure 5.14 Neutron diffraction structure of the transition metal hydride complex (Me3P)4lr(OH)H. (Reproduced with permission from ref. 19.)...

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