Borohydride tetrakis

Palladium(II) trifluoroacetate, 236 Sodium borohydride-Tetrakis(tri-phenylphosphine)palladium(O), 168 Tetrakis(triphenylphosphine)palla-dium(0), 34, 103, 126, 142, 169, 202, 211, 220, 271, 289 Tetrakis(triphenylphosphine)palla-dium(0)-l, 2-Bis(diphenylphos-phine)ethane, 290 Tetrakis(triphenylphosphine)palla-dium(0)-Zinc, 346 Tributyltin hydride-Dichlorobis-(triphenylphosphine)palladium(II), 319... 

Fig. 5.6. Crystal structure of tetrakis-P, P, P P -(4-methylphenyl)-l,l -binaphthyldi-phosphine-1,2-diphenyl-1,2-ethanediamine ruthenium borohydride catalyst. Reproduced from J. Am. Chem. Soc., 124, 6508 (2002), by permission of the American Chemical Society.

Tetrakis(triphenylphosphine)palla-dium(0)-Zinc, 346 Titanium(IV) chloride-Zinc, 310 Titanium(III) chloride-Zinc / copper couple, 303 Zinc, 298, 346, 348 Zinc amalgam, 347 Zinc borohydride, 167 Zinc bromide, 349... 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

Bis[tetraethylammonium] Tetrakis(benzenetellurolate] ferrate(II)3 Under an atmosphere of nitrogen, 1.83 g (4.0 mmol) bis[tetraethylammonium] tetrachloroferratc(II) dissolved in 25 ml acetone are mixed with a solution of 16 mmol sodium benzenetellurolate prepared from 3.27 g (8.0 mmol) diphenyl ditellurium and 0.61 g (16 mmol) sodium borohydride, in 10 m/ ethanol. The immediately formed red precipitate is filtered and dried under a vacuum yield 100%. 

Tris[tetraethylammonium] Tetrakis [benzenetellurolate(tellurido) ferrate]3 Under an atmosphere of nitrogen, 4.54 g (4 mmol) of bis[tetraethylammonium] tetrakis[benzenetellurolato]ferrate(II) dissolved in 40 m/ acetonitrile are dropped into a solution of sodium hydrogen telluride in 30 ml acetonitrile. (The sodium hydrogen telluride was prepared from 0.51 g (4.0 mmol) tellurium powder and a three-fold excess of sodium borohydride in ethanol, evaporation of the ethanol, and dissolution of the residue in 30 ml acetonitrile.) The... 

Reduction of acid chlorides to aldehydes One of the most useful synthetic transformations in organic synthesis is the conversion of an acid chloride to the corresponding aldehyde without over-reduction to the alcohol. Until recently, this type of selective reduction was difficult to accomplish and was most frequently effected by catalytic hydrogenation (the Rosenmund reduction section 6.4.1). However, in the past few years, several novel reducing agents have been developed to accomplish the desired transformation. Among the reagents that are available for the partial reduction of acyl chlorides to aldehydes are bis(triphenylphosphine)cuprous borohydride , sodium or lithium tri-terf-butoxyaluminium hydride, complex copper cyanotrihydridoborate salts °, anionic iron carbonyl complexes and tri-n-butyltin hydride in the presence of tetrakis(triphenylphosphine)palladium(0). ... 

This reaction can be stopped, through careful temperature control, to yield bis-, tris-, and in the case of 5-unsubstituted pyrazoles, tetrakis(pyrazolyl)borates. Syntheses of the parent ligands Bp, Tp, and pzTp have been described in detail.24 A large variety of 1-H pyrazoles may be employed to synthesize poly(pyrazolyl)borate by this route, with the exception of those containing functionalities incompatible with the borohydride ion. 

A ketone added to the aged solution is reduced effectively, but a carboxylic acid or ester is not reduced. This weak hydride donor is thus useful for the selective reduction of a keto acid to the corresponding hydroxy acid. Both intermolecular 2md intramolecular competition experiments with tetrakis-(N-dihydropyridyl)-aluminate showed that diaryl ketones are more reactive to this reagent than either dialkyl or aralkyl ketones. This relationship is the opposite of that found by H. C. Brown for reduction with sodium borohydride in isopropyl alcohol, where the order of reactivity is acetone > acetophenone > benzophenone. 

The preparation of colloidal gold is generally accomplished by reduction of chloroauric acid (HAUCI4) solution with sodium citrate [19-23], which is known to be influenced by several factors such as temperature and reactant concentrations [22]. Alternatively, other reducing agents can be used such as tetrakis(hydroxymethyl)phosphonium chloride (THPC) [24], borohydride [20,25] and toluene [26]. 

Four of the seven known metal tetrakis-borohydrides—Zr, Hf, Th, and U borohydrides (1,2)—were first synthesized about 30 years ago during the Manhattan project. They were found to be very volatile and reactive compounds. In recent years, much structural, spectroscopic, and chemical studies were done on these molecules. New tetrakis-borohydrides of the actinides Pa, Np, and Pu have recently been prepared by analogous reactions used in the syntheses of U and Th borohydrides (3). The Pa compound, Pa(BHi+K, is iso-morphous to and behaves like U(BHi+)i+ and Th(BHi+)i+ while x-ray studies on Np(BHi+)i+ and the isostructural Pu(BHi+)i+ have shown that they resemble the highly volatile Zr and Hf compounds both in structure and properties. All seven compounds contain triple hydrogen bridge bonds connecting the boron atom to the metal. 

Some of the physical properties of metal tetrakis-boro-hydrides, which are primarily determined by their solid-state structure, are listed in Table 1. The polymeric Th, Pa, and U borohydrides are of much lower volatility than the monomeric Zr, Hf, Np, and Pu compounds. The intermolecular bonds connecting molecules together decrease their volatility substantially since these bonds break when the solid vaporizes (12). A plot of log p(mmHg) vs 1/T yields the equation log p(mmHg) = -A/T + B, where T is in K. Values of A and B allow the calculation of the heats (AH) and entropies (AS) for phase-change processes as shown in Table 1. The actinide ions in the polymeric compounds are 14 coordinate however, in the gaseous state they are 12 coordinate (12). 

Alternatively, the C5 hydroxy group can be protected as 5-0-allyloxycarbonyl derivative instead (not shown in Scheme 29.6.1). This is done by reaction of abamectin with allylchloroformate and tetraethylendiamine in t-butyl methyl ether. In this case, the C5 hydroxy group can be deprotected in the last step by treatment with sodium borohydride in ethanol in the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium. 

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