Transition-metal-hydride

Although these compounds were originally described as interstitial hydrides, implying that they were formed by entry of H atoms into interstices (usually tetrahedral) in the metal structure, it is now known that the arrangement of metal atoms in the hydride is usually different from that in the parent metal. The hydride has a definite structure and in this respect is not different from other compounds of the metal  

The hydrides of V, Nb, and Ta probably come closest to the idea of an interstitial compound and are discussed later. In other cases where the arrangement of metal atoms in the hydride is the same as in (one form of) the metal there may be a discontinuous increase in lattice parameter when the hydride is formed (Pd) or there may be an intermediate hydride with a different metal arrangement. For example, the h.c.p. 4f metals Gd-Tm form hexagonal trihydrides, but the intermediate dihydrides have the fluorite structure with c.c.p metal atoms. 

Moreover, the volume of the MH3 phase is some 15-25 per cent greater than that of the metal. The hydride YbH2.ss has, like Yb, a f.c.c arrangement of metal atoms but this phase is only made under pressure and has a smaller cell dimension 

Composition limits (H Cubic dihydride M) at room temperature Hexagonal trihydride 

The hexagonal MH3 phase has the (revised) LaFa structure (p. 356) which may be regarded as derived from an expanded h.c.p. metal structure. A n.d. study of H0D3 (with which the other phases are isostructural) shows that H (D) occupies all the tetrahedral and octahedral holes, but because of the close proximity of the pairs of tetrahedral holes there is some displacement of the H atoms from the ideal positions and this in turn necessitates some displacement of the H atoms from the octahedral holes. In the resulting structure H atoms have 3 nearest metal atom neighbours and the metal atom has 9 (+2) H neighbours  

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Transition metal hydrides. These are formed by hydrogen uptake by the metal. The phases are often non-stoicheiometric. 

Vidal V, Theolier A, Thivolle-Cazat and Basset J M 1997 Metathesis of alkanes catalyzed by silica-supported transition metal hydrides Soienoe 276 99-102... 

R. Bau, "Transition Metal Hydrides," ddvances in Chemistry Series, Vol. 167, American Chemical Society, Washington, D.C., 1978. 

A. Dedieu, (Ed.), Transition Metal Hydrides, J. Wiley Sons, New York, 1992. ISBN 0471187682... 

These compounds are generally believed to have square pyramidal structures (X-ray, PPr3) [157d] and have typical spectroscopic properties of transition-metal hydrides (IrHCl2(PBu2Me)2 i/(Ir—H) 1998 cm-1). 

Figure 2.86 The 1H NMR spectrum in the hydride region of the isomers of [IrH3(PEt2Ph)j] top, /ac-isomer bottom, mer-isomer. (Reproduced with permission from E.L. Muetterties (ed.), Transition Metal Hydrides, published by Marcel Dekker, 1971, p. 80.)...

Neutron diffraction studies have shown that in both systems Pd-H (17) and Ni-H (18) the hydrogen atoms during the process of hydride phase formation occupy octahedral positions inside the metal lattice. It is a process of ordering of the dissolved hydrogen in the a-solid solution leading to a hydride precipitation. In common with all other transition metal hydrides these also are of nonstoichiometric composition. As the respective atomic ratios of the components amount to approximately H/Me = 0.6, the hydrogen atoms thus occupy only some of the crystallographic positions available to them. 

Manganese oxide in catalytic converter, 62 Metal hydrides, see also Transition metal hydrides... 

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

The Bronsted acidity of transition metal hydrides. R. G. Pearson and P. C. Ford. Comments Inorg. Chem., 1982, 1, 279-291 (33). 

When a transition-metal hydride reacts with EtZnCl the organic moiety, rather than the halogen, is replaced ... 

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... 

Two closely related reactions, (a) and (b), illustrated by Eq. (12) (Rj = HPhj, Etj, Phj, CI3, CljPh) and (13), of silicon hydrides with transition metal complexes generate compounds with Si—M bonds with elimination of hydrogen (a) cleavage of metal-metal bonds and (b) reaction with transition metal hydrides. Reactions discussed in this section are relevant to... 

An obvious limitation to the hydrogen-elimination method, especially for early transition metal elements, is the availability of transition metal hydrides (this applies also to the HCl elimination) or binuclear complexes. 

After graduating from Mikunigaoka High School, Osaka, he studied chemistry at the University of Tokyo from 1968 to 1972 and continued research on hydrido complexes and transition metal hydrides to earn the Dr. sc. degree under the supervision of Professor Yukiyoshi Sasaki in 1977. As a postdoctoral fellow, he worked with Professor John D. Corbett at the Ames Laboratory from 1977 to 1979, and with Professor Arndt Simon at Max-Planck-Institut fur Festkorperforschung, Stuttgart, Germany from 1979 to 1981. In... 

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. 

Usui, Y, Hrrano, M., Fukuoka, A. and Komiya, S. (1997) Hydrogen abstraction from transition metal hydrides by gold alkoxides giving gold-containing heterodinuclear complexes. Chemistry Letters, 26, 981. 

Barone, V., Adamo, C., 1997a, First Row Transition-Metal Hydrides A Challenging Playground for New Theoretical Approaches , J. Comput. Chem., 61, 443. 

The interstitial hydrides of transition metals differ from the salt-like hydrides of the alkali and alkaline-earth metals MH and MH2, as can be seen from their densities. While the latter have higher densities than the metals, the transition metal hydrides have expanded metal lattices. Furthermore, the transition metal hydrides exhibit metallic luster and are semiconducting. Alkali metal hydrides have NaCl structure MgH2 has rutile structure. 

W. Bronger, Complex transition metal hydrides, Angew. Chem. Int. Ed. 30 (1991) 759. 

Norton JR (1992) In Dedieu A (ed) Transition metal hydrides, chap 9. Wiley-VCH, New York... 

Conjugate reduction by the transition metal-hydride (TM - H) accompanied by transition metal enolate formation... 

After the initial two reports of Rh- and Co-catalyzed reductive aldol couplings, further studies did not appear in the literature until the late 1990s. Beyond 1998, several stereoselective and enantioselective reductive aldol reactions were developed, which are catalyzed by a remarkably diverse range of metal complexes, including those based upon Pd, Cu, Ir, and In. In this chapter, transition metal-catalyzed aldol, Michael, and Mannich reactions that proceed via transition metal hydride-promoted conjugate reduction are reviewed. 

Ojima, I. Eguchi, M. Tzamarioudaki, M. Transition Metal Hydrides Hydrocarboxylation, Hydroformylation, and Asymmetric Hydrogenation. In Wilkinson, G. Stone, F. B. A. Abel, E. W., Eds., Comprehensive Organometallic Chemistry 2, Vol. 12, Pergamon, Oxford, 1995, Chapter 2. 

Bronger, W. and G. Auffermann, New ternary alkali-metal-transition-metal hydrides synthesized at high pressures Characterization and properties, Chem. Mater., 10, 2723,1998. 

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