Hydride complexes of copper, silver, and gold encompass a broad array of structures, and their distinctive reactivity has enabled dramatic recent advances in synthesis and catalysis. This Review summarizes the synthesis, characterization, and key stoichiometric reactions of isolable or observable coinage metal hydrides. It discusses catalytic processes in which coinage metal hydrides are known or probable intermediates, and presents mechanistic studies of selected catalytic reactions. The purpose of this Review is to convey how developments in coinage metal hydride chemistry have led to new organic transformations, and how developments in catalysis have in turn inspired the synthesis of reactive new complexes.

Coinage Metal Hydrides: Synthesis, Characterization, and Reactivity.

New important applications of copper metal, e.g., in the areas of hydrogen production, fuel cell operation, and spent nuclear fuel disposal, require accurate knowledge of the physical and chemical properties of stable and metastable copper compounds. Among the copper(I) compounds with oxygen and hydrogen, cuprous oxide Cu(2)O is the only one stable and the best studied. Other such compounds are less known (CuH) or totally unknown (CuOH) due to their instability relative to the oxide. Here we combine quantum-mechanical calculations with experimental studies to search for possible compounds of monovalent copper. Cuprous hydride (CuH) and cuprous hydroxide (CuOH) are proved to exist in solid form. We establish the chemical and physical properties of these compounds, thereby filling the existing gaps in our understanding of hydrogen- and oxygen-related phenomena in Cu metal.

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Exploring monovalent copper compounds with oxygen and hydrogen

The mechanisms of chemical vapor generation (CVG) of transition and noble metals by reaction with tetrahydroborate(III) have been investigated in an effort to reconcile fundamental properties of compounds containing metal–hydride bonds with the experimental evidence collected in the present work and in the recent analytical literature on CVG. Silver, gold and rhodium were investigated in detail. Various materials constituting the wetted surfaces of the reaction apparatus (Ryton, glass, silanized glass) were examined for their effect on the overall process, as was the presence of surface-active agents (Triton X-100TM, antifoam B). Two types of reactions contribute to the formation of volatile species. The first (primary reaction) occurs through homogeneous liquid phase reactions between aqueous analyte complexes (MLn) and hydroboron species (BH4− and its hydrolysis products). The second (secondary reaction) is a surface mediated reaction between reaction intermediates, mostly formed in the primary reaction and chemisorbed by active sites on surfaces, and hydroboron species. The participation of active surface sites generally improves the efficiency of CVG compared with use of an inert surface, but this feature cannot always be usefully employed in analytical applications due to slow reaction kinetics producing memory effects. Reaction intermediates which can be classified as hydrido metal complexes, LnMHx, possess complex chemistry, making interpretation of experimental results difficult. Hydrido metal complexes, in addition to free atoms and nanoparticles, may constitute the volatile species leaving the solution and/or reaching the atomizer.

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M. Tkacz

Papers

Studies of the thermal decomposition of copper hydride

Heat capacity of copper hydride