Platinum borohydride reduction

Borohydride reduction of 2-acetamido-2-deoxy-D-galactose affords 2-acetamido-2-deoxy-D-galactitol,219 whereas oxidation of the benzyl 2-(N-benzyloxycarbonyl)amino or-D-glycoside with oxygen in the presence of platinum oxide, followed by hydrogenolysis of the blocking groups, yields... 

TABLE 9.4 Hydrogenation of Nitrobenzene over Platinum Metal Catalysts Produced In Situ by Borohydride Reduction 2 ... 

In contrast to standard borohydride reductive nanoparticle synthesis, we have developed an alternative strategy to amino acid encapsulated nanoparticles by utilizing a metal nanoparticle (M°-(Ligand))/metal ion (M"+) precursor redox pair with matched oxidation/reduction potentials. Simply, a metal nanoparticle such as Pt°-(Cys) acts as the principal reductant to a complimentary selected metal ion of Au + resulting in a new stabilized metal nanoparticle of Au°-(Cys) and the oxidation product of the original nanoparticle Pt"+. Malow et al. have reported a metathesis/transmetallation type reaction between a platinum colloid and a Au cyanide compound. Similarly, we employed a Pt°-(Cys)/AuCl4 pair and 0.5-2.0 equivalents of Au to Pt -(Cys). XRD analysis of the nanoparticle products revealed differences in crystallinity... 

The treatment of solutions of platinum metals with aqueous borohydride results in the formation of finely divided black precipitates that are active catalysts for alkene hydrogenations. The platinum black obtained in this way was twice as active as that obtained by the hydrogenation of platinum oxide. The borohydride reduced rhodium black is even more active. While the borohydride reduction of base metals gives the corresponding metal borides, there is little, if any, boron incorporated into these platinum metal blacks. Analysis of the borohydride reduced palladium found that while the palladium boron ratio in the bulk was 10 1, less than 1% of the surface was boron.59 7, 5 small amount of boron, however, can impart a significant difference in catalytic activity to this catalyst as compared with other, more common, palladium catalysts. The most striking difference is the inability of the borohydride reduced palladium to promote the hydrogenolysis of activated C-0 and C-N bonds, a reaction that takes place readily over standard palladium catalysts. 

Sodium in ethanol has been used to reduce a 2//-pyrrole to the pyrrolidine,9,16 as has catalytic hydrogenation using platinum oxide.96 The latter method, however, took compound 80 only to the 3-pyrroline, as did sodium borohydride.71 Sodium borohydride reduction of the methiodide salt of 123 also gave a 3-pyrroline.119... 

Another pathway involved sodium borohydride reduction of the carbonyl group at C-9 in (246d), affording the lactone (251). Reduction with lithium aluminium hydride and boron trifluoride etherate or with hydrogen and platinum oxide in acetic acid led to the 11-oxapregnane (252), which was readily converted into the diketone (253). ... 

The reduction of metal salts with borohydride or trialkylborohydride is a widely used colloid synthesis method. The preparation of platinum microcrystals having a mean diameter of 28 A by the reduction of chloroplatinic add with sodium borohydride has been reported as a reprodudble standardized preparation. [52] PVP stabilized copper sols have been prepared by borohydride reduction of copper salts. [53, 54] In some cases, however, the formation of metal... 

Monodisperse particles present the advantage of uniform active site distribution and can be considered as models for heterogeneous catalytic reactions. Monodisperse metals, metal oxides or metal borides can now be easily obtained using microemulsions, vesicles, polymers or normal micelles (refs. 1-4). Microemulsions were used to obtain monodisperse particles of platinum (refs. 5-7), palladium (refs. 5,6), rhodium (refs. 5,6), iridium (ref. 5) and gold (ref. 8) by reducing the precursor metal ions with hydrogen, hydrazine, sodium borohydride or solvated electrons. Monodisperse nickel boride (refs. 1,9-12), cobalt boride (refs. 1,10,13-17), nickel-cobalt boride (refs. 1,10,15-17), and mixtures of iron boride and iron oxides (refs. 1,18) were prepared by sodium borohydride reduction of the precursor metal ions. Iron oxides (ref. 19), magnetite (ref. 20), calcium carbonate (ref. 21) and silver chloride (ref. 22) were obtained by precipitation reactions. 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

Reduction. Quinoline may be reduced rather selectively, depending on the reaction conditions. Raney nickel at 70—100°C and 6—7 MPa (60—70 atm) results in a 70% yield of 1,2,3,4-tetrahydroquinoline (32). Temperatures of 210—270°C produce only a slightly lower yield of decahydroquinoline [2051-28-7]. Catalytic reduction with platinum oxide in strongly acidic solution at ambient temperature and moderate pressure also gives a 70% yield of 5,6,7,8-tetrahydroquinoline [10500-57-9] (33). Further reduction of this material with sodium—ethanol produces 90% of /ra/ j -decahydroquinoline [767-92-0] (34). Reductions of the quinoline heterocycHc ring accompanied by alkylation have been reported (35). Yields vary widely sodium borohydride—acetic acid gives 17% of l,2,3,4-tetrahydro-l-(trifluoromethyl)quinoline [57928-03-7] and 79% of 1,2,3,4-tetrahydro-l-isopropylquinoline [21863-25-2]. This latter compound is obtained in the presence of acetone the use of cyanoborohydride reduces the pyridine ring without alkylation. 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

The reduction of iminium salts can be achieved by a variety of methods. Some of the methods have been studied primarily on quaternary salts of aromatic bases, but the results can be extrapolated to simple iminium salts in most cases. The reagents available for reduction of iminium salts are sodium amalgam (52), sodium hydrosulfite (5i), potassium borohydride (54,55), sodium borohydride (56,57), lithium aluminum hydride (5 ), formic acid (59-63), H, and platinum oxide (47). The scope and mechanism of reduction of nitrogen heterocycles with complex metal hydrides has been recently reviewed (5,64), and will be presented here only briefly. 

The [Pt(Se4)2]2 complex (133) has been prepared by the reduction of the platinum(IV) species [Pt(Se4)3]2 with excess borohydride.328 The X-ray structure of the complex shows that each of the five-membered rings adopts a half-chair conformation, with the platinum coordination sphere exhibiting slight distortion from a square-planar geometry.329... 

Colloidal metals are usually prepared by reduction of a salt with a reducing agent, such as phosphorus, acetone, tannin, or carbon monoxide. Platinum metals can also be prepared as finely divided very active blacks by reducing the metal salt in an aqueous solution of sodium or potassium borohydride. 

The reduction of diethyl Af-(4-methylpiperazin-l-yl)methylenemalonate over a platinum catalyst with hydrogen or with sodium borohydride af-... 

By reduction of aldehydes and ketones Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts (catalytic hydrogenation). The usual catalyst is a finely divided metal such as platinum, palladium or nickel. It is also prepared by treating aldehydes and ketones with sodium borohydride (NaBH4) or lithium aluminium hydride (LLAIH4). Aldehydes yield primary alcohols whereas ketones give secondary alcohols. 

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