Hydride lanthanide

The lanthanides can form hydrides (qv) of any composition up to LnH. Lanthanide hydrides can desorb hydrogen reversibly with temperature. Therefore, the lanthanides and some of thek alloys ate good candidates for hydrogen (qv) storage, of which LaNi is probably the most promising (see... 

The addition of the lanthanide hydride to the cyclohexene double bond is the rate-limiting step (Equation (19)),... 

Lanthanide hydrides of type CpfSmH are capable of both reducing and coupling carbon monoxide (Scheme 38) [282]. The initially formed cis enediolate isomerizes to trans-[Cp Sm(Ph3pO)]2(jt-OCH=CHO) at ambient temperature in hours to days depending on sample concentration. The Sm-O bond of the bridging enediolate moiety is in the range of terminal Sm-0(alkoxide, enolate) bonds (Table 18). 

Lanthanide hydride derivatives are commonly synthesized by hydrogenol-ysis of lanthanide alkyl complexes [212], In order to further exploit the thermodynamic stability of the Al-N bond dizsobutylaluminum hydride (DIBAH), a common cocatalyst in diene polymerization mixtures and well-established reducing agent in organic synthesis, was used in the hydrogenol-... 

The presence of H- in metallic lanthanide hydrides was proposed by Dialer (9), and the idea later extended to other metallic hydrides (11, 23). As at present interpreted the model suggests that H is associated with a helium-like configuration of electrons, in a rather low-density electron sea. The metal is considered to be the inert-gas core (or a stable non-inert-gas core) with a localized net positive charge derived from the stoichiometry of the hydride. The remaining electrons of the metal are considered to be in the usual directed hybrid orbitals, whose directions help determine the crystal structure and whose bonding to nearest metal neighbors stabilizes the structure. Electrons in these directed orbitals are sufficiently delocalized to provide a conduction band and metallic or semimetallic properties. [Compare the model of TiO and VO proposed by Morin (29).]... 

Magnetic Characteristics of Gadolinium, Terbium, and Ytterbium Hydrides in Relation to the Electronic Nature of the Lanthanide Hydrides... 

The foregoing remarks do not hold, of course, for the dihydrides of the triva-lent lanthanides. They exhibit metallic conduction (10), as would be expected, since their conduction band is only somewhat depleted. One would expect them to display a tendency to order at low temperatures, but it seems not unreasonable to expect that this tendency would be weaker than the corresponding element, in view of the decreased electron concentration, and the ordering would hence occur at lower temperatures. This was in fact observed for HoH2, which exhibits (6) a Neel point at 8° K., as coippared to 135° K. for Ho. It is also observed in the present work for the terbium dihydrides, whose Neel points are 40° to 50° K., whereas that for the element is 241° K. These properties are compatible with the notion that hydrogen in all the lanthanide hydrides is anionic. On this basis the dihydrides appear as an intermediate form between the truly metallic elements on the one hand and the truly ionic or saline trihydrides on the other. 

Most, but not all, of the observed magnetic behavior of the lanthanide hydrides fits in with the notion that the hydrogen-saturated metal lacks conduction electrons. The hydride of europium is an exception EuH186, the highest hydride that has been formed in this laboratory, has been shown (15) to be ferromagnetic below 25° K. This would ordinarily imply the existence of electrons in the con-... 

To avoid the complication of hydrolysed product or partial decomposition during dehydration, anhydrous diketonate complexes can be prepared by the reaction of diketone with lanthanide 2-propanolate [47] in benzene, with a lanthanide hydride or with metallic europium [48]. 

Pnictides LnQ (Q = Group 15 element) having the NaCl structure are made by direct synthesis, with other routes for the nitrides including the reaction of the lanthanide hydride with either nitrogen or aimnonia hke the carbides, they are readily hydrolyzed to the hydride QH3. 

Another approach to bis(cyclopentadienyl)lanthanide alkoxides is the cleavage of ethers by bis(cyclopentadienyl) lanthanide hydrides. DiaUcyl ethers, ROR, are cleaved by (Cp 2LnH)2 (Ln = Y, La, Ce) to form Cp 2LnOR, Cp 2LnOR, R H, and RH. The extent to which either of the C-0 bonds of asymmetrically substituted dialkyl ethers ROR ... 

Recent advances in (C5Hs)2LnR chemistry have involved primarily structural characterization and reactivity studies. The synthesis of new Ln—C complexes starting from lanthanide hydrides is described in Section V,C. The chemistry of (CsMe5)2LnR complexes is described in Section VII. 

CHj, R = C2H5]. Indeed, [(C5H4R)2Y( t-H)( ]2 and (CsH4R)2Y-[C(R )=CHR ](thf) can be interconverted in this way and both initiate catalytic hydrogenation of alkynes to cis alkenes ( 5). Hence, one plausible rationale exists for the lanthanide-based catalytic hydrogenation reaction which originally stimulated the study of molecular lanthanide hydrides (50, 60). 

Lanthanide alkyl and aryl complexes can readily react with a range of substrates with acidic protons, such as alcohols, phenols, phenylacetylene, and amine, to be converted into the corresponding lanthanide derivatives. Lanthanide alkyl complexes react with H2 to form the corresponding hydride complex, which is the popular route to lanthanide hydride. Various unsaturated small molecules can insert into an Ln-alkyl bond to form the derivates containing Ln-heteroatom bonds. The reaction modes found are summarized in Figure 8.14 [59-62]. 

A metathesis reaction is a convenient route to lanthanide tetrahydroaluminate and lanthanide tetrahydroborate complexes. Using tetrahydroaluminate complexes as the hydride source, a number of structurally characterized lanthanide tetrahydroaluminate complexes are prepared via metathesis reactions in the presence of an excess of a Lewis base (Equation 8.24) [79]. Metathesis reaction of organolanthanide chlorides with alkali metal tetrahydroborate generates the corresponding lanthanide tetrahydroborate. The same reaction with sodium hydride in THE is reported to afford a lanthanide hydride however, no molecular structure for the hydride has been presented up till now. 

Figure 8.25 Synthesis of lanthanide hydride via fSdiydrogen ehmination.

Cleavage of Ln-C a-bonds of lanthanide alkyls and aryls by a hydrogen molecule at ambient pressure and room temperature is a popular method for the synthesis of neutral lanthanide hydride complexes (Equation 8.25). The first structurally characterized neutral lanthanide hydrides were prepared by hydrogenolysis of bi(cyclopentadienyl) lanthanide alkyl... 

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