Schiff base nickel catalyst

On the other hand, Matsunaga and Shibasaki have observed an opposite syn diastereoselectivity in the enantioselective conjugate addition of a-keto anilides to nitroalkenes under dinuclear nickel catalysis. Indeed, the use of 10 mol% of dinuclear chiral Schiff base nickel catalyst 9 in the presence of HFIP and 5 A MS as additives in 1,4-dioxane as solvent allowed the corresponding Michael adducts to be achieved in moderate to good yields, with good syn diastereoselectivities of up to >90% de and combined with good to excellent enantioselectivities of up to 98% ee (Scheme 2.15). The substrate... 

In another context, excellent enantioselective nickel-catalysed a-ami-nations of N-Boc-oxindoles with azodicarboxylates have been achieved by using chiral Schiff base nickel catalysts. BINAP ligands have also encountered success in asymmetric nickel-catalysed electrophilic a-aminations and also in combination with other metals such as palladium. On the other hand, the use of other sources of electrophilic nitrogen, such as nitroso compounds and iodinanes, in reactions catalysed by nickel has so far not been described. 

On the other hand, a dinuclear chiral nickel catalyst, (R)-3, was developed by Mitsunuma and Matsunaga to promote the conjugate addition of a-sub-stituted p-keto esters to nitroethylene. " As shown in Scheme 2.6 the use of 1-10 mol% of this Schiff base dinuclear catalyst in a mixture of EtOAc and toluene as solvent allowed a range of cyclic as well as acyclic p-keto esters to be added to nitroethylene, providing the corresponding chiral Michael products in moderate to almost quantitative yields (73-92%), combined with good to high enantioselectivities of up to 98% ee in the case of cyclic substrates, and... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

The third class of metal catalysts includes nickel and cobalt complexes of Schiff bases and nitrogen macrocyclic ligands, which can form on electroreduction cobalt(I) and nickel(I) reactive intermediates for the activation of organic halides. 

Eichhom and his co-workers have thoroughly studied the kinetics of the formation and hydrolysis of polydentate Schiff bases in the presence of various cations (9, 10, 25). The reactions are complicated by a factor not found in the absence of metal ions, i.e, the formation of metal chelate complexes stabilizes the Schiff bases thermodynamically but this factor is determined by, and varies with, the central metal ion involved. In the case of bis(2-thiophenyl)-ethylenediamine, both copper (II) and nickel(II) catalyze the hydrolytic decomposition via complex formation. The nickel (I I) is the more effective catalyst from the viewpoint of the actual rate constants. However, it requires an activation energy cf 12.5 kcal., while the corresponding reaction in the copper(II) case requires only 11.3 kcal. The values for the entropies of activation were found to be —30.0 e.u. for the nickel(II) system and — 34.7 e.u. for the copper(II) system. Studies of the rate of formation of the Schiff bases and their metal complexes (25) showed that prior coordination of one of the reactants slowed down the rate of formation of the Schiff base when the other reactant was added. Although copper (more than nickel) favored the production of the Schiff bases from the viewpoint of the thermodynamics of the overall reaction, the formation reactions were slower with copper than with nickel. The rate of hydrolysis of Schiff bases with or/Zw-aminophenols is so fast that the corresponding metal complexes cannot be isolated from solutions containing water (4). 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Unsymmetrical secondary amines are readily prepared in good yields by the catalytic reduction of Schiff bases at moderate temperatures in high-or low-pressure equipment. Many examples have been cited. The intermediate imines are prepared from primary amines and aldehydes—very seldom from ketones—and may be used without isolation (cf. method 431). For the preparation of aliphatic amines, e.g., ethyl-w-propylamine and n-butylisoamylamine, a prereduced platinum oxide catalyst is preferred with alcohol as the solvent. Schiff bases from the condensation of aromatic aldehydes with either aromatic or aliphatic amines are more readily prepared and are reduced over a nickel catalyst. In this manner, a large number of N-alkylbenzylamines having halo, hydroxyl, or methoxyl groups on the nucleus have been made. Reductions by means of sodium and alcohol and lithium aluminum hydride have also been described,... 

A corresponding equilibrium between the pyrrolidine form, the Schiff base, and the dimer exists in aqueous solutions of 4-amino-4,5-dideoxy-L-xylose. Its synthesis proceeds from D-arabinose to 5-O-p-tolylsulfonyl-D-arabinose diediyl dithioacetal, which is reduced to 5-deoxy-D-arabinose diethyl dithioacetal. This compound, in the form of its 2,3-0-isopropylidene acetal, is transformed into 5-deoxy-2,3-O-isopropylidene-D-arabinose diethyl acetal. p-Toluenesulfonyl-ation followed by treatment with sodium azide gives 4-azido-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl acetal, which is reduced in the presence of Raney nickel catalyst to 4-amino-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl acetal (104). 

Phenylacetone reacts with methylamine to produce a Schiff s base and a molecule of water. This Schiff s base then reacts with hydrogen and Raney nickel catalyst and gets reduced to methamphetamine. To encourage the formation of this Schiff s base, the amount of water in the reaction mixture is held to less than 10% 5% is even better. If the underground chemist is able to get methylamine gas in a cylinder, it is easy to control... 

The nickel complex 11, with a fluorous Schiff base as ligand, was prepared from salicylaldehyde and 4-perfluorodecylaniline (Scheme 15). This fluorous Ni complex was used as a catalyst for the conjugate addition of -diketones to diethyl azodicarboxylate (DEAD). The mixture was stirred at 60 C in a mixture of... 

In the presence of bis(0,0-dibenzyl)dithiophosphate)nickel(II) the hydrolysis at pH g of p-nitrophenyl picolinate (PNPP) (67) was enhanced more than a 1000-fold. The proposed mechanism of this biomimetic model involved the intramolecular attack of a metal hydroxide species on the bound ester. An unsymmetrical bis-Schiff base Mn(III) complex with a morpholino pendant (68 M=MnCl) also catalysed the alkaline hydrolysis of PNPP (67) very effectively, but was not so effective as a catalyst as Co and Mn complexes with a benzo-lO-aza-crown ether pendant (69 M = MnCl, M = Co). One of the latter (69 M = MnCl) showed an enhancement factor at pH 7.6 of 1.67 X 10 ... 

Chiral Catalysts Containing Group 10 Metals (Ni, Pd, and Pt). The catalyst formed in situ from Ni(acac)2 and bomane aminoalcohols (DAB or DAIB) catalyze the enantioselective addition of diethylzinc to chalcones (254) (Fig. 21). Nickel(II)-chiral Schiff-base (the ligand derived from 1,2-diaminocyclohexane or 1,2-diaminopropane with pyrone derivative) complexes were efficient in epoxida-tion of nonfunctionalized olefins (255). Bis-ferrocenyl-triphosphane (PIGIPHOS) formed catalytically active complex with Ni(II) (256). Nickel-catalyzed asymmetric hydrocyanation of vinylarenes using glucose-derived phosphinite ligands was observed (257). 

In this paper, the electrochemical reduction of cobalt and nickel complexes of the ligand N,N -l,2-phenylenebis(salicylideneiminato] (salophen = L) and its relation to the electrochemical activation of CO2 is discussed. These complexes have been investigated as potential electrocatalysts of CO2 reduction. Indeed, cobalt and nickel complexes containing tetraazamacrocycles or tetradentate Schiff base ligands have been recognized as powerful catalysts in the electrochemical reduction of CO2 [4,5]. Bifunctional fixation of CO2 by nucleophilic CofQ-Schiff base complexes assisted by alkali cations coordinated to the same ligand has oeen reported [6. ... 

Scheme 6.13 a-Aminations of iV-Boc-oxindoles with Schiff base mononuclear and dinuclear nickel catalysts. 

Scheme 8.1 Aldol reaction of formaldehyde with P-keto esters in the presence of a preformed dinuclear nickel catalyst derived from a Schiff base ligand.

On the other hand, Mannich-type reactions of homoenolates or their synthetic equivalents for the production of y-amino acids have been less studied than those involving enolates. In this context, the same authors applied a closely related preformed dinuclear nickel catalyst derived from Schiff base ligand 8 to induce the asymmetric direct Mannich-type reaction of a-keto anilides with o-Ns-protected imines (Scheme 8.11). The corresponding... 

Henrici-Olive, G., and Olive, S., Catalyst selectivity in the dimerization reaction of propylene. I. Square-planar nickel (II) complex with a chelating Schiff base. Transition Met. Chem., 1, 109, 1976. 

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