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Hydrides stability

Although understanding the effect of the a-substituent on relative alkyl hydride stabilities is straightforward, understanding the effect on the catalyst-enamide diastereomers is not. To clarify this matter we performed a series of calculations on a variety of substituted enamides [78], To eliminate the effect of the amide oxygen, we examined frontier orbitals of the [Rh(PH3)2(formamide)]+ fragment (15) and those of model enamides (16). [Pg.128]

Three years ago, while we were considering possible reasons for the general inability of transition metals to insert into and activate C-H bonds, our attention turned to the question of the instability of transition metal alkyl hydride complexes. We have listed the few alkyl hydride complexes of which we are aware (i) (one additional case (2) recently came to our attention) as well as some of the only slightly more numerous cases of substituted alkyl hydrides stabilized by chelation (3). In contrast, there are enormous numbers of polyalkyls (4, 5) and poly hydrides (6). While rarity does not logically imply instability, it does suggest it, so we considered possible mechanistic explanations for the assumed rapid decomposition of ci -MLn(R)(H) relative to cis-MLnR2 and cis-MLnH2. We have focused on octahedral complexes since they are both more important and more numerous. [Pg.177]

A scheme for predicting ternary hydride stability was proposed by workers at the Phillips Research Laboratories (9,15,16,17). According to this scheme, the heat of formation of a ternary hydride ABnH2m is given by ... [Pg.340]

Disproportionation, and metal hydride stability, 1, 301 Dissociative substitution, in 18-electron complexes, 1, 96... [Pg.99]

The cobalt complexes described here, together with the triethyl phosphite analog,6-8 are the only examples of simple cobalt phosphite hydride complexes reported to date and were the first examples of metal hydrides stabilized by phosphite ligands. [Pg.106]

The hydrogen atom is found to make a strong chemical bond with the Ni atoms rather than the La or the Mg atoms in pure LaNi and in pure Mg Ni hydride. For LaNij system, the La(M)-Ni and Ni(M)-Ni bond strengths in the small octahedron containing a hydrogen atom play the most dominant role to determine the hydride stability, where M is the alloying element substituted for the Ni or the La atoms in the compound. In fact, the ratio of the La(M)-Ni bond order to the Ni(M)-Ni bond order correlates well with the experimental data of the equilibrium plateau pressures... [Pg.105]

KEYWORDS electronic structure, hydrogen storage alloys hydride stability, alloy design... [Pg.193]

Through direct combination of the elements, the Group 5A(15) members form all possible trihalides (EX3) and pentafluorides (EF3), but few other pentahalides. As with the hydrides, stability of the halides decreases as the E—X bond becomes longer with larger halogens. [Pg.440]

The formed hydrides in these binary Laves phases are too stable for easy hydrogen desorption, which is a prerequisite for hydrogen storage (Ivey and Northwood, 1986 b). The hydride stability can be reduced and adjusted to practical hydrogen storage conditions by deviations from stoichiometry, substitution of the B element primarily by Fe, Co, Ni, Cu, Mn, or Cr, or substitution of the A element primarily by Ti, or any combination of these alloying possibilities. [Pg.104]

A scheme for correlating hydride stabilities, the so called rule of reversed stability see e.g., 18,19), states that for a series of analogous alloys, the more stable the alloy, the less stable (i.e., higher dissociation pressure) the corresponding hydride. Using Miedema s formula (20), the calculated heat of formation for LaNis is — II.2 kj/mol and for LaAls is — 42.1 kj/mol. Since LaAls is more stable (more negative AH) than LaNis, the rule of reversed stability predicts the LaNis- rAh hydrides to be less stable than LaNisHe contrary to observation. Similarly, Shinar et... [Pg.292]


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See also in sourсe #XX -- [ Pg.318 ]




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Hydride Ion Affinities as a Measure of Stability

Hydride stability considerations

Long-term stability of metal hydrides

Organolead hydrides stability

Radical stability metal hydrides

Rare earth hydrides, stabilities

Silicon hydride cations, stabilities

Transition metal hydrides stability

Transition metal-hydride complexes stability

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