Tantalum amidate

Closely related mixed amido/imido/guanidinato tantalum complexes of the type Ta(NR R )[(R R2N)C(NR )2]( = NR ) (R R = Me, Et R = Cy, Pr R = Pr", BuO were synthesized by the insertion of carbodiimides into to tantalum-amide bonds in imidotantalum triamide precursors, and the effects of ligand substitution on thermal properties were studied by TGA/DTA measurements. In addition, selected compounds were pyrolyzed at 600 °C and the decomposition products were studied by GC-MS and NMR spectroscopy. ... 

Nieves JS, Royo P (2001) Insertion of carbon dioxide and isocyanide into tantalum-amide and tantalum-methyl bonds. J Organomet Chem 621 299-303... 

The experimental conditions for conducting the above reaction in the presence of dimethylformamide as a solvent are as follows. In a 250 ml. three-necked flask, equipped with a reflux condenser and a tantalum wire Hershberg-type stirrer, place 20 g. of o-chloronitrobenzene and 100 ml. of diinethylform-amide (dried over anhydrous calcium sulphate). Heat the solution to reflux and add 20 g. of activated copper bronze in one portion. Heat under reflux for 4 hours, add another 20 g. portion of copper powder, and continue refluxing for a second 4-hour period. Allow to cool, pour the reaction mixture into 2 litres of water, and filter with suction. Extract the solids with three 200 ml. portions of boiling ethanol alternatively, use 300 ml. of ethanol in a Soxhlet apparatus. Isolate the 2 2- dinitrodiphenyl from the alcoholic extracts as described above the 3ueld of product, m.p. 124-125°, is 11 - 5 g. 

Tantalum Nitrides. Tantalum nitride [12033-62-4] TaN, is produced by direct synthesis of the elements at 1100°C. Very pure TaN has been produced by spontaneous reaction of lithium amide, L1NH2, and TaCl ( )- The compound is often added to cermets in 3—18 wt %. Ta N [12033-94-2] is used as a red pigment in plastics and paints (78). 

Mercury(II) /V-pcrchlory lbcnzylamidc. 3651 Monopotassium perchlorylamide, 3994 Nitrogen triiodide-silver amide, 4634 Nitrosylruthenium trichloride, 4144 Pentaamminedinitrogenruthenium(II) salts, 4596 Pentakis(dimethylamino)tantalum, 3384 Pentasilver diamidophosphate, 0046 Pentasilver orthodiamidophosphate, 0044 Plutonium nitride, 4726 Poly (dimercury immonium hydroxide), 4422... 

During the course of our investigations we found that various tantalum sil-sesquioxanes are readily accessible via a versatile amide route. Commercially available tantalum diethylamide, Ta(NMe2)5, was chosen as the key starting material for the development of a salt-free route leading to tantalum silsesquioxane derivatives. Clean protonation and liberation of three equivalents of dimethylamine took place upon reaction of Ta(NMe2)5 with 3 in a 1 1 molar ratio. Pale yellow... 

In NaxW03-yFy Doumerc (1978) observed a transition that has all the characteristics of an Anderson transition similar phenomena are observed in NaxTayW3 y03. The results are shown in Fig. 7.14. It is unlikely that this transition is generated by the overlap of two Hubbard bands with tails (Chapter 1, Section 4) this could only occur if it took place in an uncompensated alkali-metal impurity band, which seems inconsistent with the comparatively small electron mass. We think rather that in the tungsten (or tungsten-tantalum) 5d-band an Anderson transition caused by the random positions of Na (and F or Ta) atoms occurs. The apparent occurrence of amiD must, as explained elsewhere, indicate that a at the temperature of the experiments. Work below 100 K, to look for quantum interference effects, does not seem to have been carried out. 

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. 

Tantalum complexes alkyl alkoxy reactions, 358 amides synthesis, 165 imido... 

Di(carbene)gold(I) salts, oxidation, 2, 293—294 Dicarbido clusters, with decarutheniums, 6, 1036 Dicarbollide amides, with tantalum, 5, 184 Dicarbollide thorium complexes, synthesis and characterization, 4, 224—225 Dicarbollyl ligands, in nickel complexes, 8, 185 Dicarbonyl complexes arylation with lead triacetates diastereoselectivity, 9, 389 enantioselectivity, 9, 391 mechanisms, 9, 387 reaction examples, 9, 382 indium-mediated allylation, 9, 675 with iridium, 7, 287 reductive cyclization, 10, 529 in Ru and Os half-sandwiches, 6, 508 with Zr—Hf(II), 4, 700... 

Recently, we reported for the first time that tantalum can be electrodeposited as thin layers in the water and air stable ionic liquid 1-butyl-l-methyl pyrrolidinium bis (trifluoromethylsulfonyl) amide at 200 °C using TaFs as a source of tantalum [88]. The quality of the deposit was found to be improved on addition of LiF to the... 

Fig. 4.17 SEM picture of a tantalum deposit made from TaFs in 1 -butyl-1 -methylpyrrolidinium bis(trifluoromethylsulfonyl)amide. The deposit is obviously amorphous, with EDX a Ta/F ratio of 4/1 is obtained.

Mass transport may influence material growth in ionic liquids. 1-Butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, for example, is, at room temperature, about 60 times more viscous than water. At temperatures above 150°C its viscosity is similar to most molecular solvents at ambient conditions. Indeed, temperatures between 150 and 200 °C were best to deposit tantalum from TaFs in the presence of LiF. One has to keep in mind that the deposition of tantalum from TaFs or an anionic complex delivers one Ta atom and 5-7 fluorides. If the deposition is too fast F may not diffuse rapidly enough from the surface to the bulk of the solution and may be trapped in the deposit. This might explain why we only got crystalline tantalum layers at low current densities. 

These observations, along with kinetic isotope effect studies and Hammett correlation studies, support a concerted elimination by a-bond metathesis involving a four-membered transition state (Eq. 2) [23]. A large kinetic isotope effect is observed for the loss of methane from methyl amide complexes lb and lh (Eqs. 3 and 4), comparable to those observed by Buchwald and coworkers for formation of zirconium rj2-thioaldehyde complexes [25] and by Bercaw and coworkers for formation of tantalum rf- imine complexes [5a] through similar transition states. 

The reaction between pentahalides or aUcoxides and carboxylic acids gives oxochloro- or oxoaUcoxocarboxylates. Chiral tantalum cyclopentadienyl carboxylates mediate acylation reactions of amides, giving dipeptides in good yield with high stereochemical purity. ... 

Under the attack of one equivalent OH in H2O, MeO in MeOH, or pure NH3 a silicon vertex was removed from the c/oso-cluster l.[21 A plausible mechanistic sequence for the degradation involves as the first step formation of an adduct consisting of the nucleophile and the c/oso-cluster. Afterwards this adduct should react with a protic solvent to give the isolated reaction product. In order to get indications for the expected adduct we studied the attack of nucleophiles in an aprotic solvent. Three types of nucleophiles were studied in this reaction. In the case of the dialkylamide nucleophile best results were achieved from the reaction of the close-cluster with transition metal amides of zirconium and tantalum,17,81 The anionic adduct cluster features a dialkylamide bridging both silicon centres of the silaborane cluster. 

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. 

Group 5 pyridonate complexes are also readily prepared by salt metathesis and protonolysis routes to access both mono- and bis(pyridonate) tantalum complexes (Figure 12). [41] Such complexes can be difficult to rigorously characterize in the solid state as they are much more soluble than their group 4 pyridonate, or their group 5 amidate, counterparts. 

Scheme 19 intramolecular hydroaminoalkylation of unactivated olefins with secondary amines catalyzed by mono- and bis(amidate) tantalum ami do complexes... 

Amides from nitriles.1 Nitriles are converted into amides in high yield when heated at 250° (2 hours) with an equimolar amount of 100% formic acid in a pressure vessel which is preferentially cased with tantalum or silver. 

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