Niobium cyanides

Niobium, tris(diethyldilhiocarbamato)oxy-stereochemistry, 1,82 structure, 1, 83 Niobium, tris(oxa ato)oxy-stereochcmistry, 1, 82 Niobium, tris(phcnylcncdirhio)-structure, 1, 63 Niobium alanate, 3, 685 Niobium complexes alkyl alkoxy reactions, 2, 358 amides, 2,164 properties, 2, 168 synthesis, 2, 165 applications, 6,1014 carbamicacid, 2, 450 clusters, 3, 672,673,675 hexamethylbenzene ligands, 3, 669 cyanides synthesis, 2, 9 p-dinitrogen, 3, 418 fluoro... 

Nickel carbonyl Niobium Nitrates Air, bromine, oxidizing materials Bromine trifluoride, chlorine, fluorine Aluminum, BP, cyanides, esters, phosphorus, tin(II) chloride, sodium hypophos-... 

The A-trimethylsilylimines 68 (R = t-Bu, Ph, 2-MeCgH4 or 2-BrC6H4), which are prepared by the reaction of non-enolizable aldehydes with lithium bis(trimethylsilyl)amide, followed by trimethylsilyl chloride, undergo pinacolic coupling induced by NbCLt 2THF to yield the vicinal diamines 69 as mixtures of dl- and meso-isomers, in which the former predominate. Another method for the preparation of 1,2-diamines is by the combined action of the niobium tetrachloride/tetrahydrofuran complex and tributyltin hydride on cyanides RCN (R = /-Hu. Ph, cyclopentyl or pcnt-4-en-l-yl) (equation 32)82. 

Ferrocyanides.—As might be anticipated from its very weakly acid nature, niobium pentoxide does not give rise to any cyanides. By the action of hydrochloric acid and potassium ferrocyanide on solutions of niobic acid, three brown powders have been obtained. The following are some of the formulae that have been allotted to them I Nb[Fe(CN)6]2 K2Nb12[Fe(CN)e] K9(NbO)5.[Fe(CN)e]6.10H2O but the evidence for these is weak.6... 

CO2 and N2. Excess chlorine gas (i.e., chlorine which did not form hypochlorite) converted the cyanide to cyanate, which was subsequently oxidized by hypochlorite. Cadmium was precipitated from the water due to an increase in the solution pH. A platinum-plated niobium screen was the anode and a stainless steel screen was used as the cathode. At an applied potential of 6.0 V, resulting in a current of 6.0 A, the cadmium concentration decreased from 17.4mg/dm to 0.01 mg/dm, while the cyanide concentration declined from 54 mg/dm to zero in 80 min of cell operation. 

Even fewer complexes with nitrogen donor ligands have been reported and all are methyl cyanide adducts (Tables X and XI). Protactinium pentabromide forms a soluble 1 3 complex in contrast to the 1 1 complexes formed by niobium and tantalum pentahalides (46). Other actinide pentahalide-methyl cyanide complexes are still unknown. Protactinium tetrachloride, tetrabromide, and tetraiodide react with anhydrous, oxygen-free methyl cyanide to form slightly soluble 1 4 complexes (44, 48) which are isostructural with their actinide tetrahalide analogs. 

The full report of the preparation and properties of two octacyanoniobates has appeared (Vol. 4, p. 75). Impure K5[Nb(CN)8] can be obtained from the reaction of an excess of aqueous potassium cyanide with an electrolytically reduced solution of niobium pentachloride in methanol. Oxidation of the product by air or H2O2 gives orange K4[Nb(CN)8],2H20 (see p. 73). Solutions of this salt are stable in the dark but disproportionate photolytically to the Nb complex, Nb20s, and HCN. M5[Nb-... 

Enantioselective vanadium and niobium catalysts provide chemists with new and powerful tools for the efficient preparation of optically active molecules. Over the past few decades, the use of vanadium and niobium catalysts has been extended to a variety of different and complementaiy asymmetric reactions. These reactions include cyanide additions, oxidative coupling of 2-naphthols, Friedel-Crafts-type reactions, pinacol couplings, Diels-Alder reactions, Mannich-type reactions, desymmetrisation of epoxides and aziridines, hydroaminations, hydroaminoalkylations, sulfoxida-tions, epoxidations, and oxidation of a-hydroxy carbo) lates Thus, their major applications are in Lewis acid-based chemistiy and redox chemistry. In particular, vanadium is attractive as a metal catalyst in organic synthesis because of its natural abundance as well as its relatively low toxicity and moisture sensitivity compared with other metals. The fact that vanadium is present in nature in equal abundance to zinc (albeit in a more widely distributed form and more difficult to access) is not widely appreciated. Inspired by the activation of substrates in nature [e.g. bromoperoxidase. 

Hydrogen cyanide ferromagnetic fluid, separation Ferric lignosulfonate ferroniobium, alloy steels Niobium fertility test mfg. 

Wohler described a simple method for the preparation of boron nitride, which had been discovered by Balmain by melting boric acid with potassium cyanide. Wohler in 1828 just failed to discover vanadium in a Mexican lead mineral (see p. 153), and failed to anticipate H. Rose in discovering niobiiun in Bavarian tantalite and pyrochlor. He prepared a specimen of niobium pentoxide and sent it to Berzelius, who could not say if it was a new substance or not. ... 

---