Nickel reduction chlorides

A plausible mechanism accounting for the catalytic role of nickel(n) chloride has been advanced (see Scheme 4).10 The process may be initiated by reduction of nickel(n) chloride to nickel(o) by two equivalents of chromium(n) chloride, followed by oxidative addition of the vinyl iodide (or related substrate) to give a vinyl nickel(n) reagent. The latter species may then undergo transmetala-tion with a chromium(m) salt leading to a vinyl chromium(m) reagent which then reacts with the aldehyde. The nickel(n) produced in the oxidative addition step reenters the catalytic cycle. 

The reduction of different aliphatic or aromatic aldehydes or ketones 15 was easily achieved using the combination of dihydrated nickel(II) chloride, lithium and a catalytic amount of naphthalene (16%) or DTBB (8%) in THF, yielding the corresponding alcohols without (534) or with (535) deuterium labelling in 57-86% yield. For imines 536, the same process afforded the corresponding amines 537 or deuterio amines 538 in 54- >95% yield . 

Hydroborate Reduction. Lithium or sodium tetrahydroborate and diborane can be used for reduction of metal ions, especially light transition metal ions, to produce colloidal metals. For example, colloidal copper protected by polymer was prepared by reduction of copper(II) sulfate by a large excess of sodium tetrahydroborate in the presence of PVP or other polymers (12). A similar procedure for nickel(III) chloride produced nickel boride, not zero-valence nickel metal particles. 

From epoxides by reduction Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281... 

The two substituents on the four-membered ring may be short carbon chains selective reduction of the aldehydes 255 with sodium borohydride produced the cyclic hemiketamine 256 <1995TL7771>. One chain may be longer. For instance, the aldehyde 257 was cyclized by a mixture of chromium(ll) chloride and nickel(n) chloride in THF to the racemic alcohol 258 <1998EJO 543>. 

Thiazolecarboxylic acids, esters or acid chlorides react readily with ammonia or various amines, affording the corresponding carboxamides. Dehydration of the amides with phosphorus pentoxide or phosphoryl chloride occurs readily and gives the corresponding nitriles (Scheme 99). Thiazolecarboxylic acid hydrazides are obtained in a similar way, using hydrazine or substituted hydrazines instead of ammonia or amines. The Raney nickel reduction of cyanothiazoles leads to the corresponding amino compounds, the 4-cyano derivative being the isomer most readily reduced. 

Quinoxaline derivatives give, after reduction with sodium borohydride-transition-metal salt system, e.g. nickel(II) chloride, 1,2,3,4-tetrahydroquinoxaline derivatives. ... 

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). 

The advantages of using chloride electrolytes compared with sulfate electrolytes are higher electrical conductivity, lower electrolyte viscosity, lower overpotential for nickel reduction, and higher solubility and activity of nickel. An important factor is the lower anode potential of chlorine evolution compared with oxygen evolution in sulfate electrolytes using the common lead anodes. Chloride electrolytes require insoluble or dimensionally stable anodes, usually titanium coated with an electroactive noble metal or oxide, and a diaphragm system to collect the CI2 gas from the anode. The chlorine liberated at the anode is recycled for use in the leach circuits. In practice, some decomposition of water... 

Truce has reported that a reagent prepared from nickel (II) chloride hexahydrate in ethanol by reduction with sodium borohydride and evidently similar to Brown and Brown s nickel boride can be used to effect desulfurization. Thus the diphenyl-... 

The second Tsuji synthesis, which appeared (see Scheme 1.6) in the latter part of 1978, employed a strategy similar to his earlier work for construction of the basic carbon framework. Ketal diene 19 was transformed to halo alcohol 22 by the use of chemistry established in his previous synthesis. Acylation with phenylthioacetyl chloride readily afforded ester 23. Intramolecular alkylation resulting in ring closure was brought about by deprotonation with sodium hexa-methyldisilazane to give lactone 24 in 71% yield. Synthetic 1 was then obtained in 90% yield following Raney nickel reduction. 

This zerovalent nickel reagent can be generated in situ by reduction of bis(triphenylphospine)nickel(II) chloride with zinc in the presence of triphenyl-phosphine in DMF. 

The reduction equilibrium of nickel(Il) chloride was studied by a flow method. The results were probably flawed by vaporisation of NiCb, thus they were not subjected to a third law analysis. The experimental data depicted in Figure V-16 are listed in... 

Primary Amines. - Reductive methods in the preparation of amines continue to be popular. In particular, anilines can be prepared under mild conditions and in good yields by reduction of nitrobenzenes with the new system of diborane-nickel (II) chloride." Selective reduction in the presence of a number of functional groups is the chief advantage of the method. Nitrobenzenes are also... 

The initial tests of the sodium dispersion-metal halide system were made with ferric chloride, fortunately, and with a nonaqueous solvent in which ferric chloride was soluble. Thus, ferric chloride was present as a solution and, consequently, presented maximum surface for contact with the sodium particles. This feature, coupled with the lower activation energy requirements, permitted the reaction to proceed at temperatures well below room temperature and established the operability of the method. The success of the initial (ferric chloride) tests lent encouragement to tests on other metal systems and prompted continued investigations when the initial runs at lower temperatures failed. The discovery of the threshold, or trigger, temperature for nickel (II) chloride reduction paved the way for successful reduction of other metal halides such as manganese (II) chloride, cobalt (II) chloride, and cadmium bromide. 

Selective reduction of either the pyridine or the benzene rings in quinolines and isoquinoline can be achieved the heterocyclic ring is reduced to the tetrahydro level by sodium cyanoborohydride in acid solution,by sodium borohydride in the presence of nickel(II) chloride, by zinc borohydride," or, traditionally, by room temperature and room pressure catalytic hydrogenation in methanol. However, in strong acid solution it is the benzene ring which is selectively saturated " longer reaction times can then lead to decahydro-derivatives. 

Recent studies on the allylation of alkynes with bis (7r-allyl) nickel have revealed that the Ni(0) generated in this process causes the trimeri-zation and, more importantly, the reductive dimerization of a portion of the alkyne (8). A deuterolytic work-up led to the terminally di-deuter-ated diene (5), supporting the presence of a nickelole precursor (4) (Scheme 1). The further interaction of 4 with 1, either in a Diels-Alder fashion (6) or by alkyne insertion in a C-Ni bond (7), could lead to the cyclic trimer 8 after extrusion of Ni(0), thereby accounting for the trimerizing action of Ni(0) on alkynes. This detection of dimer 5 then provided impetus for the synthesis of the unknown nickelole system to learn if its properties would accord with this proposed reaction scheme. Therefore, E,E-l,4-dilithio-l,2,3,4-tetraphenyl-l,3-butadiene (9) was treated with bis (triphenylphosphine) nickel (II) chloride or l,2-bis(di-phenylphosphino ethane)nickel(II) chloride to form the nickelole 10 (9) (Scheme 2). The nickelole reacted with dimethyl acetylenedicarboxylate to yield 11 and with CO to produce 12. Finally, in keeping with the hypothesis offered in Scheme 1, 10a did act as a trimerizing catalyst toward diphenylacetylene (13) to yield 14. 

In further studies of the synthesis of porphobilinogen and isoporphobilinogen, a-free pyrroles (prepared by Knorr type syntheses) were aminomethylated by the Tschemiak-Einhom reaction, for example, treatment with A -hydroxy-methylchloroacetamide in hot ethanolic hydrogen chloride. The resulting chloro-acetylamino derivatives (14) could be reduced catalytically to the acetylamino-methyl pyrroles (15). In related studies an acetylaminomethyl pyrrole (16b) was also prepared by treatment of 2,4-dimethylpyirole with acetyl thiocyanate followed by Raney nickel reduction of the intermediate acetyl thiocarbamide (16a). 

The synthesis was completed by reduction of 206 with the nickel boride catalyst derived from nickel(ll) chloride and sodium borohydride directly producing ( )-stemoamide in 73% yield. In addition, a 15% yield of the cfr-lactone 207, derived from a-face reduction of 206 followed by epimerization at C-10, was also obtained. 

Tetrathiabenzo[l,3-cfirst time by dimerization of thieno[2,3- >]thiophene (142) (92PS73). More recently, it was found that catalytic reduction of 3,4-dibromothieno[2,3-i]thiophene (227) with an excess of activated zinc in the presence of bis(triphenyl-phosphine)nickel(II) chloride and tetraethylammonium iodide afforded only 4,4 -dibromo-3,3-bis(thieno[2,3- )]thiophene) (228) (in a maximum yield of 28%) (89AG1254). However, the reaction in the presence of a larger amount of the nickel catalyst afforded also dipenatlene 225. Optimization of the reaction conditions made it possible to increase the yield of the latter to only 14%. An alternative procedure was employed to transform thienothiophene 227 into trimethylstannyl derivative 229. The reaction of thienothiophene 227 with organotin intermediate 229 in the presence of the palladium triphenylphosphine complex afforded dipentalene 225 (13% yield). Derivatives 226 were prepared by lithiation of... 

The photoinduced two-electron reduction of a polypyridyl nickel(ii) chloride complex provides a route to generate H2 from HCl. The excited state of the polypyridine leads to a photoreduced radical, that mediates HX activation by producing a Ni centre by halogen-atom abstraction. The photogenerated Ni intermediate then disproportionates, giving Ni and Ni species. Ni reacts with HX producing H2 and the polypyridyl Ni dichloride, thus closing the photocycle. 

---