Niobium complexes amides

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... 

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. 

Dithioalkoxo- and dithiophenoxo-niobium(V) trichlorides [MCl3(SR)2] were obtained from NbCl5 and thiols and benzenethiol respectively.240 The synthesis of tris(benzenedithiolato) complexes was accomplished by reaction of the appropriate metal amide with a mixture of the dithiol and its sodium salt in THF. The structures of (AsPh4)[M(S2C6H4)3]241""243 showed the... 

Besides the phosphoranes, the homoleptic amides of niobium(V) and tantalum(V) are the only pentamides known.1 These compounds, exemplified by M(NMe2)5 (M = Nb, Ta) are volatile, hydrocarbon-soluble solids.37 All physical and spectroscopic data are consistent with a strictly mononuclear existence for these complexes. 

Cyclopentadienyl aryl complexes, with niobium, 5, 66 Cyclopentadienyl bis(phosphine)amide zirconium compounds, dicarbonyl complexes, 4, 702. -Cyclopentadienyl-carbanionic complexes, with Zr(IV),... 

Bemo, P. and Gambarotta, S., Formation of a metalaaziridine ring and dinitrogen fixation promoted by a niobium amide complex. Organometallics, 14 (1995) 2159-2161. 

Schrock discovered that the r-butylalkylidene complex of tantalum (and in lower yield, niobium) was a structural analog to the phosphorus ylide. The complex proved to be a reagent for r-butylalkene formation. Of the Wittig-type reactions tried, most notable was the ability of the complex to react with esters and amides to form the corresponding r-butylalkenes in good yields. 

Niobium can be separated from Ta and other metals in HF or HCl media by extracting into CHCI3, CCI4, cyclohexane, 1,2-dichloroethane, or xylene the ion-associates, which are formed by Nb (and Ta) complexes with tetraphenylarsonium cation, TO A [8,9], DAM [10], or Aliquat 336 [11-13]. The thiocyanate complexes of Nb with triphenylphosphonium cation [14] or with amides [15] have also been extracted. 

Atmospheric pressure CVD of NbCi-yN, using NbCl, NH3, and CH4 has been employed in three separate approaches toward the optimization of reaction characteristics [69]. These were (i) simultaneous deposition of niobium, carbon, and nitrogen by hydrogen reduction of NbCls with decomposition of methane and ammonia at a temperature of 900-1000°C (ii) deposition of a niobium amide complex derived from NbCl.s/NHi in nitrogen as a carrier gas at 250-350 °C, and subsequent conversion in ammonia/methane at 1 000-1 100 °C (iii) separate deposition of elemental niobium or NbCl.3 by hydrogen reduction at 500-1000°C and subsequent conversion to NbCi yNy in an ammonia/methane atmosphere at 1000-1 100°C. The results of these three approaches are given below. 

The development of niobium and tantalum dithiocarbamate chemistry is relatively recent, the first well authenticated examples coming from the insertion of carbon disulfide into metal amide complexes to give [M(S2CNR2)4] (193, 666). Dithiocarbamates are now known to stabilize niobium and tantalum in the +3 to +5 oxidation states. 

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