Oxides complex hydrides

Ketenes can react in several ways with organometaUic compounds and complexes. They can add as ligands to coordinated metals forming stable ketene, ketenyl, and ketenyfldene complexes. Ketenes can be inserted into metal—hydride, metal—alkyl, metal—OR, and metal—NR2 bonds, react with metal—oxide complexes, and with coordinated Hgands. This chemistry has been reviewed (9,51). 

Superimposed on this simple equiUbrium are complex reactions involving the oxides and hydrides of the respective metals. At about 400°C, the metal phase resulting from the reaction of sodium and potassium hydroxide contains an unidentified reaction product that precipitates at about 300°C (15). 

There have been only a few examples of reduction of the C=N+ function of catalytic hydrogenation since the reductions with complex hydrides are so easy to do in the laboratory. A possible reduction of an iminium salt 45 to 46 with platinum oxide was reported by McKay et al. (91). A report that platinum oxide reduces 2l tio).jgj yjj.Qqyjp Qjj2idijjjujn perchlorate (25) in quantitative yield to 47 indicates that such reduction should be facile (47). 

In reactions carried out for 24 h at room temperature, a 95% yield of cyclo-hexanol from cyclohexanone was obtained. Other ketones and aldehydes were also hydrogenated under identical conditions, but with slower rates (38% conversion for hydrogenation of 2-hexanone, 25% conversion of acetophenone, 45% for 3-methyl-2-butanone). Insertion of the C=0 bond of the ketone or aldehyde into the Cr-H bond was proposed as the first step, producing a chromium alk-oxide complex that reacts with acid to generate the alcohol product. The anionic chromium hydride [(COJsCrH]- is regenerated from the formate complex by... 

ACID ANHYDRIDES, ACYL HALIDES, ALKALI METALS ALKYLALUMINIUM DERIVATIVES, ALKYLNON-METAL HALIDES COMPLEX HYDRIDES, METAL HALIDES, METAL HYDRIDES METAL OXIDES, NON-METAL HALIDES (AND THEIR OXIDES)... 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Reagents of choice for reduction of epoxides to alcohols are hydrides and complex hydrides. A general rule of regioselectivity is that the nucleophilic complex hydrides such as lithium aluminum hydride approach the oxide from the less hindered side [511, 653], thus giving more substituted alcohols. In contrast, hydrides of electrophilic nature such as alanes (prepared in situ from lithium aluminum hydride and aluminum halides) [653, 654, 655] or boranes, especially in the presence of boron trifluoride, open the ring in the opposite direction and give predominantly less substituted alcohols [656, 657,658]. As far as stereoselectivity is concerned, lithium aluminum hydride yields trans products [511] whereas electrophilic hydrides predominantly cis products... 

It has been shown in Chapter VI that the stability of most complexes formed by two halides, oxides or hydrides follows the rules for complex formation of two ionic compounds. The formation of the complex ions BFt and NH " was described as an addition of the ions F and H+ to the molecules BF3 and NH3, caused by the attraction of the highly-charged ions B3+ and N3-. However, this complex formation can be given quite a different interpretation, and it can be argued that F ions combine with BF3 because, in this process, the octet of the B atom is completed... 

METAL OXIDES, NON-METAL SULFIDES N-HALOGEN COMPOUNDS, NON-METAL HYDRIDES METAL NON-METALLIDES, COMPLEX HYDRIDES or the more complex... 

ALKYLALUMINIUM DERIVATIVES ALKYLNON-METAL HALIDES COMPLEX HYDRIDES METAL HALIDES METAL HYDRIDES METAL OXIDES... 

Acetyl ligands, in niobium complexes, C-H BDEs, 1, 298 Achiral phosphines, on polymer-supported peptides, 12, 698 Acid halides, indium compound reactions, 9, 683 Acidity, one-electron oxidized metal hydrides, 1, 294 Acid leaching, in organometallic stability studies, 12, 612 Acid-platinum rf-monoalkynes, interactions, 8, 641 Acrylate, polymerization with aluminum catalysts, 3, 280 Acrylic monomers, lanthanide-catalyzed polymerization,... 

Borane-methyl sulphide complex 4-Toluenesulfonyl chloride cis-3,5-Cyclohexadiene-l,2-diol l -Dynamax 83,123-6 column Silver oxide Sodium hydride Palladium on charcoal Tetrabenzylpyrophosphate... 

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