Nickel borohydride complex

Treatment of aldehydes or ketones with ammonia, primary or secondary amines in reducing media is called reductive alkylation (of ammonia or amines) or reductive amination (of aldehydes or ketones). Reducing agents are most frequently hydrogen in the presence of catalysts such as platinum, nickel or Raney nickel [955], complex borohydrides [705, 954, 955], formaldehyde or formic acid [522]. 

There are apparently no discrete TpxNi hydrides in the literature, nor any dihydrogen complexes. A single borohydride complex, Tp Ni(BH4) (92), has been obtained recently via ligand metathesis from Tp NiX (X = NO3, Cl).41 This complex was comprehensively characterized, and shown (crystallographically) to possess an octahedral nickel center, with facially tridentate Tp and BH4 ligands. In contrast to most nickel(II)... 

The borohydride reduction of nickel(II) compounds in protic solvents may result either in the formation of nickel(O) complexes or in the formation of hydrido complexes of nickel(II). Two easily interconvertible isomers, Ni(triphos)2, have been obtain in the reduction of Ni(N03)2 in the presence of the ligand tiiphos, but their structures are not known with certainty. ... 

Alkyl chlorides are with a few exceptions not reduced by mild catalytic hydrogenation over platinum [502], rhodium [40] and nickel [63], even in the presence of alkali. Metal hydrides and complex hydrides are used more successfully various lithium aluminum hydrides [506, 507], lithium copper hydrides [501], sodium borohydride [504, 505], and especially different tin hydrides (stannanes) [503,508,509,510] are the reagents of choice for selective replacement of halogen in the presence of other functional groups. In some cases the reduction is stereoselective. Both cis- and rrunj-9-chlorodecaIin, on reductions with triphenylstannane or dibutylstannane, gave predominantly trani-decalin [509]. 

Alkyl bromides and especially alkyl iodides are reduced faster than chlorides. Catalytic hydrogenation was accomplished in good yields using Raney nickel in the presence of potassium hydroxide [63] Procedure 5, p. 205). More frequently, bromides and iodides are reduced by hydrides [505] and complex hydrides in good to excellent yields [501, 504]. Most powerful are lithium triethylborohydride and lithium aluminum hydride [506]. Sodium borohydride reacts much more slowly. Since the complex hydrides are believed to react by an S 2 mechanism [505, 511], it is not surprising that secondary bromides and iodides react more slowly than the primary ones [506]. The reagent prepared from trimethoxylithium aluminum deuteride and cuprous iodide... 

Consequently, by choosing proper conditions, especially the ratios of the carbonyl compound to the amino compound, very good yields of the desired amines can be obtained [322, 953]. In catalytic hydrogenations alkylation of amines was also achieved by alcohols under the conditions when they may be dehydrogenated to the carbonyl compounds [803]. The reaction of aldehydes and ketones with ammonia and amines in the presence of hydrogen is carried out on catalysts platinum oxide [957], nickel [803, 958] or Raney nickel [956, 959,960]. Yields range from low (23-35%) to very high (93%). An alternative route is the use of complex borohydrides sodium borohydride [954], lithium cyanoborohydride [955] and sodium cyanoborohydride [103] in aqueous-alcoholic solutions of pH 5-8. 

Considerable inter-element interference effects have been reported on the actual hydride-forming step. Elements easily reduced by sodium borohydride (e.g. silver, gold, copper, nickel) give rise to the greatest suppressions. These interfering ions may be removed by the addition of masking agents that complex with them. 

Reduction reactions of nickel(If) compounds. The reduction of nickel(II) compounds to yield nickel(0) phosphine complexes has been carried out using a variety of reducing agents such as sodium amalgam, sodium sand, sodium borohydride, sodium naphthalenide and aluminum trialkyls. In some cases the phosphine ligand itself was found to act as the reducing agent. 

The hydrido complexes are diamagnetic, and are square planar or five-coordinate. Their stability, in general, increases with the number of coordinated phosphines. In the complex [Ni(BH4)(H)(PCy3)2] (153) the nickel atom is coordinated in the equatorial positions by two hydrogens of the borohydride and by one hydride anion. 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

The standard synthesis for cyclam was developed by Barefield and Wagner in 1976.29 They used similar starting materials to the van Alphen procedure but the cyclisation yield is improved through the use of a nickel (II) template. Glyoxal completes the macrocycle by a Schiff base condensation reaction. The resulting imine functionalities are reduced with sodium borohydride to leave the complexed macrocycle. The metal ion is then removed by reaction with cyanide and the free ligand extracted with chloroform (Scheme 3.19). Yields are typically in the region of 60%. 

With the tripod ligand np3 an entire series of compounds with tbp structures Ni(np3)X (X = Cl, Br, I, CN, CO, and H) can be prepared by reaction of nickel halides with the np3 ligand in the presence of borohydride, followed, if necessary, by metathesis with other X groups. The comproportionation of the Ni complex Ni2(CO)2(/i.-CO)(/i.-dppm)2 with NiG2(dppm)2 (dppm = Ph2PCH2PPh2) gives the iluxional A-frame compound (17-G-XIX).18... 

The requirement for sodium borohydride in the nickel-catalyzed reactions with amines is presumably owing to its ability to prevent complex formation between Ni(acac)2 and the amine. Even in cases where the borohydride is not essential, its addition results in some enhancement of the rate. The role of the phosphine is to reduce Ni(ll) to Ni(0). 

When a functional group is selectively attacked in the presence of a different functional group, the reaction is said to be chemoselective A number of reagents have been found to reduce aldehydes much faster than ketones. Among these are sodium triacetoxyborohydride (NaBR)—HCOOH), zinc borohydride in THF, bis-(iso-propoxytitanium borohydride), a complex of Lialll, and A-methyl-2-pyrrolidinone (of particular interest since it is stable in air and to heating), and Raney nickel. On... 

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