Tantalum chloride structure

Tantalum. tris(diethyldithiocarbamato)thio-stereochemistry, 1, 82 Tantalum, tris(phenylenedithio)-structure, 1, 63 Tantalum chloride Ta4Cl2o structure, 1,28 Ta6Qi5... 

Probably the first isolated tungsten alkylidene complex active in metathesis and completely characterised is the one shown in Figure 16.10 reported by Wengrovius and Schrock the analysis included an X-ray structure determination by Churchill and co-workers [18], The alkylidene was transferred from a tantalum complex to yield the hexacoordinate tungsten complex containing two PEt3 ligands. One of these can be removed by the addition of half an equivalent of palladium chloride. The total turnover number of these catalysts with Lewis acids added was 50 in 24 hours. 

The form of molybdenum(IV) chloride obtained by the above method has been labeled the low-temperature a-isomer because of its structural similarity with the other tetrachlorides of tungsten, niobium, and tantalum and to distinguish it from the higher-temperature /8-isomer prepared from molybdenum(III) chloride and molybdenum(V) chloride. The /3-isomer may be obtained by heating the low-temperature form at 250°C. in a sealed tube with molybdenum(V) chloride for 24 hours. The excess molybdenum (V) chloride is sublimed away at 125°C. Because of its structural difference, the /S-isomer possesses a considerably higher paramagnetism and thermal stability than the a-isomer. 

Literature presents numerous data on the syntheses by ML method of oxide layers of titanium, aluminum, chromium, phosphorus, tantalum and series of other elements on silica and alumina surfaces, when appropriate chloride and vapour of water are used as initial reagents [13,35,18,42]. The synthesis thus proceeds without the change of oxidation state of elements. But the stability of Si-O-M bonds in the process of gaseous treatment of element-chloride surface structures is of significant importance. Our researches have shown [44,68], that the strength of Si-O-M bonds is influenced by the thermal stability of element-oxide chloride groups, quantity of their bonds with surfaces (factor m) and series other ones. The reason for the destruction is the hydrogen chloride which educes in the process of vapour hydrolysis [68]. 

The most important starting materials for organometallic complexes of niobium and tantalum are their pentachlorides, NbCls and TaCls. The commercially available pentachlorides can be sublimed if further purification is necessary. They are commonly used for access to both high-valency and low-valency compounds. The crystal structure of NbCl5 consists of dimeric Nb2Cl owith two chlorides bridging as shown in Scheme 7.8, and the Ta analogue is presumed to have a similar structure. In non-... 

The combined action of zinc and tantalum(V) chloride on alkynes generates low-valent tantalum-alkyne complexes, which react with carbonyl compounds to yield ( )-allylic alcohols stereoselectively. The tantalum-6-dodecyne complex, for instance, and j -phenyl-propionaldehyde afford the alcohol 370 in 96% yield. Mixtures of structurally isomeric a,/ -unsaturated ( )-amides 371 and 372 (R, = alkyl or Mc3Si) are obtained from the... 

Several years ago Fischer and ROhrscheid (165) prepared hexamethylbenzene complexes of niobium and tantalum of the type [M3 [Cg (CH3) g] 3C10] by reaction of a mixture of the metal halide, hexamethylbenzene, alum-invim, and aluminum chloride at 130 C these cations could be isolated either as the chlorides or as hexa-fluorophosphates. The same workers (165) presented conductivity data in support of the above-mentioned trimetallic formulations, but x-ray data seem necessary before their structures can be considered certain. The reported preparations of the [M3[Cg (CH3)g] 3Clg] ... 

Mild oxidant agents often permit oxidations with retention of the cluster structures. One example of this kind of simple chemical electron-transfer reactions are the oxidations of niobium and tantalum clusters [M6Xi2] to the species with charges 3+ and 4+. The reaction with iron(III) chloride and cerium (IV) salts leads directly to the cations [M6Xi2] . ... 

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