Niobium methyls

Tantalum (and niobium) methyl/chloride combinations containing a maximum of three methyl groups, e.g., TaMe3Cl2, [12] were the only alkyl complexes of tantalum that existed in 1973. Such species were prepared from ZnMe2... 

The coordinated ethylene is readily expelled at 25 °C by the attack of a conjugated diene and the hydride is transferred to the sterically less crowded diene terminus. Thus the niobium hydrido-olefin complexes serve as convenient reagents for the preparation of 1,2- or 1,3-dialkyl-substituted allylniobium compounds starting from butadiene, (E,E) and (/i,Z)-2,4-hcxadicnc, (E)- and (Z)-l,3-pentadiene (equation 1), 3-methyl-l,3-pentadiene and isoprene (equation 2). All the allyl niobium compounds synthesized were isolated as air-sensitive pale-yellow crystals by crystallization from hexane. 

Separation of tantalum from niobium in hydrofluoric acid is carried out by solvent extraction due to solubility difference, using a suitable organic solvent such as methyl isobutyl ketone. At low acidity tantalum partitions from water into immiscible organic solvent leaving behind niobium in the aqueous HF extract. Tantalum is thus separated from this aqueous HF solution. The acidity of the aqueous HF solution is now increased and the solution again extracted with fresh methyl isobuty ketone to recover niobium, which partitions into the organic solvent, leaving any impurity that may remain dissolved in the HF solution. 

Complex formation between Nb(OH)s and methylamine has been established582 by an n.m.r. study. Two signals are observed in the n.m.r. spectrum of an aqueous solution of methylamine containing Nb(OH)5. One of these is due to the methyl protons of the amine and the other to the rapidly exchanging protons of the OH, NH2, and H20 groups. The i.r. spectra of solutions and precipitates formed by Nb(OH)5 and methylamine or monoethanolamine have been interpreted583 in terms of Nb—N co-ordination. Niobium oxohalide complex formation with tri-n-octylamine has been studied by reverse ebullioscopy.584... 

Organometallic Niobium ) and Tantalum ) Compounds. Reports this year have concerned two main areas of interest the preparation of alkyl-niobium and tantalum halides and their reactions with donor ligands, and insertion reactions into methyl-metal bonds. The first examples of monomethyl niobium and tantalum compounds have been prepared by the low-temperature methylation of the appropriate halides... 

Niobium and tantalum methyls, Me3MCl2, were among the first known stable transition metal methyls. Other partially substituted alkyls, as well as the penta-methyl, are also known. The structure of TaMe5 is square-pyramidal73 but Me3TaF2 is trigonal-bipyramidal.74 These compounds are made by the reactions ... 

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. 

As Cl6Nb2C2H54, Niobium(III), hexachlo-robis[[2-[(dimethylarsino)methyl]-2 methyl-1,3-propanediyl]bis(dimethyl-arsine)]-, 21 18... 

Niobium and tantalum can also be separated by solvent extraction (p. 572) Nb is extracted almost quantitatively from HCl solution by methyldioctyl-amine in xylene while Ta remains in the acid. (Leddicotte and Moore, 1952). Chromatographic methods (p. 570) are also possible. Thus Mercer and Williams (1952) separated Nb and Hf from ores containing Ti and other metals. The fluorides were adsorbed on paper pulp elution with methyl ethyl ketone saturated with water extracted the tantalum equilibration of the column with a 1% solution of HF in the ketone arrested the movement of Ti, Zr... 

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