Reversible hydrides applications

The Meerwein-Ponndorf-Verley (MPV) reduction is generally mediated by aluminum triiso-propoxide, Al(01Pr)3. In MPV reduction, reversible hydride transfer occurs via a six-membered transition state (Scheme 67). By removing acetone from the reaction system, the reversible reaction proceeds smoothly. The advantages of the reduction are the mildness of the reaction conditions, chemoselectivity, safety, operational simplicity, and its applicability to large-scale synthesis. It is reported that the addition of trifluoroacetic acid, significantly accelerates the reduction (Scheme 68) 304,305 in which case a catalytic amount of Al(0 Pr)3 is enough to complete the reaction. 

Volume I treats basic properties and volume II is devoted to application-oriented properties. Hydrogen in Intermetallic Compounds I, published in 1988, and Hydrogen in Intermetallic Compounds II, published in 1992, contain perhaps the most comprehensive information on the reversible hydrides of intermetallic compounds and on their applications.[6] Another good review is by Buschow et al.[7] Sandrock has written several fine reviews,[8-10] the comprehensive and highly application-oriented one, published as a Report to the US Office of Naval Research, is especially recommended. [9] A guide to the metal hydride literature is also available.[ll]... 

This survey presents an overview of the chemistry of metal-hydrogen systems which form hydride phases by the reversible reaction with hydrogen. The discussion then focuses on the AB5 class and, to a lesser extent, the AB2 class of metal hydrides, both of which are of interest for battery applications. 

Although the fundamental properties of metal hydride systems are still under intensive study, increased emphasis is being placed on developing the known applications for reversible metal hydrides, while the search for new applications continues. In this paper, we will summarize the current development status of a few selected applications. 

There are a number of engineering properties relating to practical applications of hydrides hysteresis, reversible capacity, decrepitation, activation, reaction kinetics, impurity tolerances, chemical stability, heat transfer, safety, cost and... 

Two factors currently limit reversible metal hydride storage applications cost and weight. The relatively high cost of the elemental constituents for the hydriding alloys (Ni, 3. 5/lb ... 

Other Applications. Metal hydrides are unique in that they are one of the few compounds that selectively and reversibly absorb large quantities of hydrogen at practical temperatures and pressures. This property enables one to treat dilute hydrogen streams that cannot be otherwise economically treated. 

In the scheme above, the role of the hydride may very well be played by an alkyl group, particularly for the reverse reaction Figure 13.10 shows the basis for the most important industrial application of organometallic chemistry, the homogeneous polymerization of alkenes, modeled on the heterogeneous system first discovered by Ziegler et al. [288]. The... 

Considerations of enthalpy, as illustrated by the rule of reversed stability, and of configurational entropy provided insight into the factors governing the stabilities of the AB5 hydrides. Theoretical understanding to predict dissociation pressures should be developed on heat pump application, for example. Although... 

A tandem 1,4-addition-Meerwein-Ponndorf-Verley (MPV) reduction allows the reduction of a, /i-unsaturated ketones with excellent ee and in good yield using a camphor-based thiol as reductant.274 The 1,4-addition is reversible and the high ee stems from the subsequent 1,7-hydride shift the overall process is thus one of dynamic kinetic resolution. A crossover experiment demonstrated that the shift is intramolecular. Subsequent reductive desulfurization yielded fiilly saturated compounds in an impressive overall asymmetric reductive technique with apparently wide general applicability. 

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