Platinum hydrides

Among the three commonly used metal catalysts mentioned above which activate hydrogen, nickel and palladium form hydride phases of essentially the same type. The existence of a platinum hydride has not so far been proved. 

Hydrogen cyanide reactions catalysts, 6,296 Hydrogen ligands, 2, 689-711 Hydrogenolysis platinum hydride complexes synthesis, 5, 359 Hydrogen peroxide catalytic oxidation, 6, 332, 334 hydrocarbon oxidation iron catalysts, 6, 379 reduction... 

Fig. 11.24. Positive-ion ESI spectrum of a cationic dinuclear platinum hydride complex from dichloromethane solution. The insets compare experimental and theoretical isotopic patterns. By courtesy of P. Hofmann, University of Heidelberg.

Stern showed rather conclusively that the palladium does not depart to leave a carbonium ion but that both hydride migration and collapse to an aldehyde proceed simultaneously. The removal of the /3 hydrogen in a complexes by the heavier Group VIII metals has been documented. Thus Chatt and Shaw (63) showed that a platinum hydride complex could undergo the reversible addition of ethylene ... 

Practically all the heavy transition metals can be made to eatalyze olefin isomerization, presumably through transient formation of metal hydrides. A stable platinum hydride has been shown to react with ethylene to form a cT-CjHjPt complex which can eliminate ethylene to regenerate the hydride. The commercially successful processes for the conversion of ethylene to acetaldehyde and ethylene to vinyl acetate via PdClj catalysis have stimulated enormous interest in the mechanism of these reactions, their application to other conversions, and their extension to other catalytic systems. The various stages in the conversion of ethylene are quite well-understood and an important step in the reaction involves hydride migration. The exact role of Pd in the migration has not yet been elucidated. It seems almost certain that the phenomenal interest in the whole area of transition metal isomerization in the last several years will be more than matched by the wealth of work that is certain to pour out of research laboratories in the next few years. 

Except for 1-ethynylcyclohexanol, it appears that the addition of protonic acid to triphenylphosphine platinum hydrides is unfavorable. Nevertheless, the existence of such complexes with triethylphosphine ligands is proved sufficiently since, in addition to the isolation of complexes with hydrochloric acid (10, 14), good evidence is presented for the intermediacy of triethylphosphine Pt(IV) hydrides with silanes and phosphines (15,16). 

Graefe and Robeson (12) presented evidence for the preparation of impure Li3IrH6, lithium palladium hydride, and lithium platinum hydride. Li3IrH6 was formed by reacting LiH and iridium at 500 Torr of H2 for 8 hr at 539°C. Li3IrH6, a light yellow solid, reacted readily with the atmosphere. 

In 1898, Cowper-Coles 2 claimed to have successfully effected the electrolytic reduction of an acid solution of vanadium pentoxide to metallic vanadium, but the product was subsequently shown by Fischer 3 to have been a deposit of platinum hydride. Fischer, in a series of over three hundred experiments, varied the temperature, current density, cathode material, concentration, electrolyte, addition agent, and construction of cell, but in not one instance was the formation of any metallic vanadium observed. In most cases reduction ceased at the tetravalent state (blue). At temperatures above 90° C. reduction appeared to proceed to the divalent state (lavender). The use of carbon electrodes led to the trivalent state (green), but only lead electrodes produced the trivalent state at temperatures below 90° C. Platinum electrodes reduced the electrolyte to the blue vanadyl salt below 90° C. using a divided cell and temperatures above 90° C. the lavender salt was obtained. 

The earlier literature on patterns of reactivity in the formation of platinum hydrides by protonation reactions of platinum in zerovalent and divalent oxidation states has been briefly... 

Platinum hydrides have been primarily characterized by the Pt—H stretch in the IR spectrum and the high field shift of the hydride NMR resonance. The NMR technique is particularly... 

When the cyclopropyl platinum(II) complex dA-P(.(CHCH2CH2)2(PMe2Ph)2 is treated with HC1 then AgN03, the jr-allyl complex is formed (equation 285).866 -Allyl complexes can also be formed by insertion of alkenes into platinum-hydride bonds, and this reaction is discussed in Section 52.2.3.3. 

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