Tantalum chloride/Zinc

Acetylenes 191 (R1 = C5H11, Me3Si or MeS R2 = C5H11 or C10H21) react with tantalum ) chloride and zinc to form tantalum complexes. Addition of the imine... 

Tantalum(V) chloride-zinc. 16. 312 I Reductive coupling of alkynes with... 

Perchloric acid Phosphomolybdic acid Phosphorus oxychloride Phosphorus pentachloride Phosphorus trichloride y-Picoline Polyphosphoric acid Potassium silicate Rhodium Selenium Selenium dioxide Silica gel Silver oxide (ous) Sodium borohydride Sodium silicate Strontium carbonate Sulfur dioxide Tantalum Tellurium Tetraisopropyl di (dioctylphosphito) titanate Titanocene dichloride Trichloromethylphosphonic acid Tristriphenylphosphine rhodium carbonyl hydride Tungsten carbide Vermiculite Ytterbium oxide Zinc chloride Zinc dust Zinc 2-ethylhexanoate Zirconium potassium hexafluoride... 

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... 

Complexes formed from tantalum(V) chloride or niobium(V) chloride, alkynes and zinc undergo analogous reactions. Mixtures of phenols are obtained from cyclobutenones and alkynes in the presence of nickel(cyclooctadiene)2 at 0°C. Thus 4-methyl-3-phenylcyclobut-2-enone and 4-methylpent-2-yne yield 593 and 594 ". ... 

The flameless atomization technique also gives slightly different results depending on the anion associated with the metal ion. Some of these results are shown in Figure 10-35. If zinc chloride is used as a source of zinc, the calibration curve rises more steeply than if either zinc nitrate or zinc sulfate is the source of zinc. Other elements that behave similarly are copper, manganese, and iron. As the temperature of the tantalum boat increases, the calibration curves move closer together thus this effect is, in part, temperature dependent. 

FIGURE 10-35. Calibration curves for zinc in the presence of chloride, nitrate, or sulfate ions using the tantalum boat analyzer. 

Other solid electrodes include tantalum and silver (for copper) and nickel (for zinc). Silver anodes prevent evolution of oxygen (which could be reduced at the cathode), and silver cathodes prevent evolution of hydrogen, with associated local pH changes. Addition of chloride allows the anode reaction (eqn. [1]) Ag -I- Cr -> AgCl -I- e [1]... 

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