Reduction reactions Nickel boride

Nickel borides are usually prepared by reduction of nickel salts with sodium or potassium borohydride. Two types are used. PI nickel boride is prepared by the reaction between aqueous solutions of nickel salts and a borohy-... 

O-p-tolylsulfonyl-a-D-mannoside (39) in 37% yield. Treatment of (39) with sodium iodide in acetone gave the 6-iodo derivative (40), which underwent reduction with hydrogen in the presence of a nickel boride" catalyst" to give methyl 4-0-benzoyl-2,3-0 carbonyl-6-deoxy-o>-D-manno-side (41) in 95% yield. Reaction of (41) with hydrogen bromide in acetic acid effected replacement of the methoxyl group at C-l, affording crystalline... 

Dichloro-2,2-difluoroethylene, 105 (Diethylamino)sulfur trifluoride, 110 Reduction reactions (see also Deoxygenation, Reductive. . . ) of acetals and ketals Dibromoalane, 237 Diisobutylaluminum hydride, 237 Triethylsilane-Tin(IV) chloride, 237 of acetates and other esters to alkanes Nickel boride, 197 Triphenylsilane, 334 of acyl halides to alcohols Sodium cyanoborohydride-Tin(II) chloride, 280... 

Nickel boride prepared from Nil2 and two equivalents of LiBH4 [42] was utilized as an oxazaborolidine catalyst support (Scheme 4) [43]. Reaction of nickel boride with 0.1 equivalents of chiral amino alcohol in THF at room temperature gave the anchored catalyst 6, which produced chiral alcohols in optical yields of up to 95%, and which furthermore showed higher activity as regards the reduction of acetophenone derivatives than that of the corresponding homogene-... 

Selenides are also nucleophilic and produce isolable selenonium salts (9) when treated with alkyl halides. They are easily oxidized to selenoxides (10) and further to selenones (11) under more forcing conditions (see Section 4). Reduction of selenides to the corresponding hydrocarbons is most conveniently achieved with nickel boride,or with tri-n-butyl- or triphenyltin hydride under radical conditions. " Other reagents for reductive deselenization include Raney nickel, lithium triethylborohydride, and lithium in ethylamine (Scheme 4). Benzylic selenides undergo radical extrusion reactions under thermal or photolytic conditions to produce... 

Titanium(II) reagents have also been used to reduce aliphatic nitro compounds to amines halo, cyano and ester groups are not reduced. Sodium borohydride, in the presence of catalytic amounts of nickel(II) chloride, reduces a variety of aliphatic nitro compounds to amines. Nickel boride (Ni2B) is an active catalyst for reductions of primary, secondary and tertiary nitro aliphatic compounds to amines. The reduction of nitrocyclohexane (45) yields cyclohexylamine (47) as well as small amounts of dicyclohexylamine (49), the latter being formed via reaction of intermediates (46) and (48 equation 28). 

While various borohydride nickel ratios have been used in these nickel boride preparations maximum P-2 catalytic activity was observed with a 2 1 BH4 Ni ratio.However, when the reduction was run under a hydrogen atmosphere using a 4 1 BH4 Ni ratio, a hydrogenated nickel boride catalyst, the P-3 nickel boride, was obtained.27 This catalyst was somewhat more active than the P-2 catalyst for alkene hydrogenation but it induced signifieantly more double bond isomerization during the reaction. 

The horohydride reduction of a nickel salt solution containing small amounts of other metal salts can lead to co-reduced mixed metal borides that frequently have enhanced catalytic properties when compared to the unmodified nickel boride. The presence of about 2% chromium significantly increased the activity of a P-1 nickel boride toward aldehyde hydrogenation. Molybdenum, tungsten and vanadium modifiers were somewhat less effective than chromium while the presence of a small amount of cobalt had an inhibiting effect on the reaction.22 As the data in Fig. 12.2 show, the amount of chromium responsible for optimum P-1 nickel boride activity depends on the substrate being hydrogenated.39... 

The power of this methodology becomes fully apparent however on further synthetic manipulation of the geminally functionalized pyridyl sulfide adducts, with two general reactions being reductive removal of the sulfide by Raney nickel, nickel boride or tri-n-butyltin hydride, or controlled oxidation to the sulfoxide and subsequent thermal syn elimination (Scheme 31). 

The slowness of the reaction at room temperature is probably due to the preferential adsorption and/or reduction of crotononitrile on nickel boride, which hinders the radical formation reaction of cyclohexyl iodide at room temperature. Cyclohexyl iodide is quantitatively reduced to cyclohexane by BER-Ni2B (cat.) within 1 h at room temperature in the absence of excess crotononitrile [12a]. 

The reduction of nitroarenes to azoxy compounds ArN=N(0)Ar is promoted by bismuth tiichloiide/powdered zinc. Aromatic amines are formed in excellent yields in the reduction of nitroarenes with BH3/NiCl2 or nickel boride . Acyl, ester, amide and cyano groups are not affected. Reaction of the nitro compounds RCH2NO2 (R = Ph, Bz... 

Other Reductions. Aromatic and aliphatic nitro compounds are not reduced to amines by NaBHa in the absence of an activator. The NaBH4-NiCl2 system (see Nickel Boride) is a good reagent combination for this reaction, being effective also... 

This reaction was improved by sonication in the case of lipidic substrates. The reductive elimination of i /c-dinitro compounds to olefins, usually effected with tributyltin hydride, was achieved successfully by nickel boride (prepared from nickel chloride and sodium borohydride by sonication in methanol for 30 min) giving olefins in excellent yields (Eq. 37). The reagent is prepared by sonication of nickel chloride and sodium borohydride and gives the so-called nickel boride. 

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