Metal hydride carbon oxides

Although a nonflammable gas, it reacts explosively with many substances, including organics, metals, metal sulfides, sulfur, phosphorus, nitric oxide, ammonia, carbon disulfide, metal hydrides, and charcoal. It is a severe irritant to the eyes, nose, skin, and respiratory tract. Inhalation of the gas at 100 ppm can be fatal to humans. 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

Organometals and metal hydrides as electron donors in addition reactions 245 Oxidative cleavage of carbon-carbon and carbon-hydrogen bonds 253 Electron-transfer activation in cycloaddition reactions 264 Osmylation of arene donors 270... 

Iron has a rich surface coordination chemistry that forms the basis of its important catalytic properties. There are many catalytic applications in which metallic iron or its oxides play a vital part, and the best known are associated with the synthesis of ammonia from hydrogen and nitrogen at high pressure (Haber-Bosch Process), and in hydrocarbon synthesis from CO/C02/hydrogen mixtures (Fischer-Tropsch synthesis). The surface species present in the former includes hydrides and nitrides as well as NH, NH2, and coordinated NH3 itself. Many intermediates have been proposed for hydrogenation of carbon oxides during Fischer-Tropsch synthesis that include growing hydrocarbon chains. 

Next to the cyclopropane formation, elimination represents the simplest type of a carbon-carbon bond formation in the homoenolates. Transition metal homoenolates readily eliminate a metal hydride unit to give a,p-unsaturated carbonyl compounds. Treatment of a mercurio ketone with palladium (II) chloride results in the formation of the enone presumably via a 3-palladio ketone (Eq. (24), Table 3) [8], The reaction can be carried out with catalytic amounts of palladium (II) by using CuCl2 as an oxidant. Isomerization of the initial exomethylene derivative to the more stable endo-olefin can efficiently be retarded by addition of triethylamine to the reaction mixture. 

The second group starts with compounds of the same carbon-nitrogen framework as in the desired amine but with nitrogen in a higher oxidation state. The amine then is obtained from these compounds by catalytic hydrogenation or metal-hydride reduction, as will be described in the next section ... 

Addition of hydride to the carbonyl carbon to form an alcohol, or the reverse, changes the oxidation state and so is usually classified separately from other carbonyl reactions. Some of these processes are nevertheless fundamentally similar to the ones we have been considering. Reductions by complex metal hydrides, such as lithium aluminum hydride or sodium borohydride, are additions ofH - (Equation 8.27) the metal hydride ion is simply a convenient source of this extremely basic species. The carbonyl oxygen takes the place of the hydride in coordination with the boron (or aluminum in the case of an alumino-... 

Asymmetric hydrometallation of ketones and imines with H-M (M = Si, B, Al) catalyzed by chiral transition-metal complexes followed by hydrolysis provides an effective route to optically active alcohols and amines, respectively. Asymmetric addition of metal hydrides to olefins provides an alternative and attractive route to optically active alcohols or halides via subsequent oxidation of the resulting metal-carbon bonds (Scheme 2.1). 

A convenient method for the specific introduction of 2H or 3h (or both) into a molecule is by ketone reduction with labeled metal hydride. Beale and MacMillan (10) have utilized this method for the preparation of GAs labeled at the 1, 2 or 3 positions from GA3 or GA7 (Figure 12). One point of interest is the lithium borohydride reduction of the enone formed by manganese dioxide oxidation of GA3 or GA7. When the reaction is carried out in anhydrous tetrahydrofuran it proceeds in two steps. Initially the lithium enolate is formed which incorporates a proton at carbon-2 from the acid used in the work-up, forming the 3 ketone. This ketone is reduced to the 3 -alcohol by the borohydride which is decomposed more slowly than is the lithium enolate. Thus it is possible to introduce two different labels in a single reaction. 

The concept has been extended to the C-H activation of nitriles, which coordinate strongly with metals. As shown in Scheme 3, coordination of a nitrile to low-valent metal complex (M) would increase both the basicity of the metal complex and the acidity of the C-H bond adjacent to the nitrile, and hence oxidative addition of the metal into the a-C-H bond of the nitrile would occur readily to afford an a-cya-noalkyl metal hydride complex (7), which undergoes isomerization to a N -bonded nitrile complex (8). The reaction of 8 with an C-electrophile forms a carbon-carbon... 

These are generally limited to what are termed kinetically stabilized alkyls, i.e. those devoid of protons p to the metal (Figure 4.5). These also include norbornyl and adamantyl examples since decomposition via p-metal hydride elimination (see below) would require the installation of an alkenic bond between the a and p carbons of the precursor alkyl. This is precluded for these two alkyls because of the prohibitive strain associated with forming a double bond to a bridgehead atom within a small cage structure (Brendt s rules). The tetrakis(norbornyl) complexes are also remarkable because some uncharacteristic oxidations states can be attained, e.g. Cr(IV), Co(IV) (low-spin e4t2°). The second factor which may confer stability is steric bulk bimolecular decomposition routes are thereby discouraged. 

Carbon dioxide readily undergoes insertion reactions probably via initial C02 complexing, with metal alkoxides, hydroxides, oxides, dialkylamides, and metal hydrides and alkyls 103... 

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