Chiral Nickel Complexes Research Articles

Synthesis, characterization, and spontaneous resolution of chiral nickel(II) complexes with the tripod ligand tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine.

The chiral nickel(II) complexes of a tripod-type ligand with the chemical formulas [Ni(H3L)](NO3)2.MeOH (1), [Ni(H3L)](ClO4)2.MeOH (2), and [Ni(H3L)](C6H5COO)2.6H2O (3) were synthesized and characterized (H3L = tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine). The crystal structures of 1-3 were determined by their single-crystal X-ray analyses. 1, C37H40N12O7Ni: orthorhombic, P2(1)2(1)2(1); a = 14.198(2) A, b = 22.422(2) A, c = 12.019(2) A, Z = 4. 2, C37H40N10O9Cl2Ni: orthorhombic, P2(1)2(1)2(1); a = 14.206(2) A, b = 22.735(3) A, c = 12.696(3) A, Z = 4. 3, C50H58N10O10Ni: triclinic, P1; a = 14.191(5) A, b = 16.048(4) A, c = 13.692(4) A, alpha = 115.25(2) degrees, beta = 111.07(3) degrees, gamma = 64.75(2) degrees, Z = 2. Each complex has an octahedral coordination environment for the nickel(II) ion, formed by the six nitrogen donor atoms, and is either a delta (clockwise) or a lambda (anticlockwise) enantiomorph, depending on the screw arrangement of the tripod-type ligand around the nickel(II) ion. The circular dichroism (CD) spectrum of a powdered sample of a crystal of 1 showed a positive and a negative peak at 915 and 630 nm, respectively, and that of another crystal showed an enantiomeric pattern. The observation of the Cotton effect and the crystal structure provided evidence for spontaneous resolution of the chiral complex molecule.

Syntheses, characterization, redox behavior and Lewis acidity of chiral nickel(II) and copper(II) Schiff base complexes

Chiral nickel(II) and copper(II) Schiff base complexes with [N 2O 2] coordination derived from (1 R.2 R)- and (1 S.2 S)-1,2-diamino- cyclohexane were prepared and characterized by 1H, 13C NMR, IR and mass spectroscopy and polarimetric measurement in the case of the ligands. Cyclovoltammetric and spectrophotometric measurements revealed that the redox behavior and the Lewis acidity are influenced strongly by the substituents of the ligand. Substituents with high electron-withdrawing effect stabilize the lower oxidation state and promote the addition of axial ligands. The new nickel complex NiIc fits in a diagram which presents the correlation between the reduction potentials and lg β 2 values of a variety of known nickel(II) Schiff base complexes with different substituents R t, R 2 and bridges X. No significant differences 1g β 2 with ( R)-(+)-1-phenylethylamine were observed for RRNiIc and SSNiIc. Ligand SS2HIa (C 20H 30N 2O 6) crystallized in the orthorhombic system ( P2 12 12 1) with unit cell dimensions a = 11.035(2), b = 16.126(3), c = 24.676(5) A ̊ , and Z = 8; R = 0.045 and wR 2 = 0.115. The nickel complex RRNiIb (C 18H 14O 2N 2Ni · 0.5CH 2Cl 2) cyrstallized in the orthorhombic system ( P2 12 12) with unit cell dimensions a = 18.404(1), b = 18.657(1), c = 5.621(1) A ̊ , and Z = 4; r = 0.044 and wR 2 = 0.0108 . The structures were solved by direct methods and were refined by full-matrix least-squares procedures.

Nickel-catalyzed oxidations: from hydrocarbons to DNA.

Nickel(II) complexes of tetradentate ligands such as cyclam and salen are catalysts for olefin epoxidation using PhIO and NaOCl, respectively. In order to understand the lack of enantioselectivity observed with chiral cyclam and salen complexes, studies of DNA and RNA oxidation were carried out in which evidence for diffusible oxidants might be found. A variety of square-planar, tetradentate nickel(II) complexes were observed to mediate guanine-specific modification in the presence of KHSO5 or magnesium monoperphthalate. In particular, the cationic complex, [(2,12-dimethyl-3,7,11,17-tetraazabicyclo [11.3.1]heptadeca-1(17),2,11,13,15-pentaenato)nickel]2+, [NiCR]2+, has been studied as a probe of nucleic acid folding. The extent of guanine reaction depends upon the exposure of N7, a good transition metal binding site, thus implicating nickel-guanine binding during DNA oxidation. If this is the case, related systems should be able to confer enantioselectivity during the use of chiral nickel complexes and achiral substrates for oxidation. Mechanistic studies, including radical quenching and DNA enantioselectivity, are described and their mechanistic implications discussed.

Ｎ，Ｎ‐ジアルキルノルエフェドリンおよびピロリジニルメタノール誘導体を不斉触媒・配位子に用いる不斉合成

A series of N, N-dialkylnorephedrines and pyrrolidinylmethanol derivatives are synthesized as chiral catalysts and as chiral ligands for the highly enantioselective 1, 2- and conjugate additions of organozinc reagents to aldehydes, ketones, phosphinylimines and α, β-unsaturated ketones. N, N-Dibutylnorephedrine (DBNE) and diphenyl (1-methylpyrrolidin-2-yl) methanol (DPMPM) are used as chiral catalysts in the enantioselective addition of dialkylzincs to aldehydes (up to 100% ee). Chiral thiophosphoramidate and N-benzyl-N-methylephedrinium halides are also enantioselective catalysts. Polystyrene and silica gel (and alumina) supported N-alkylnorephedrines with or without a spacer are used as heterogeneous chiral catalysts. Chiral compounds prepared include sec- alcohols, furylalcohols, alkynylalcohols, allylalcohols, β-hydroxynitrile, fluorine- containing alcohols, deuterated alcohols, γ-hydroxyketones, pyridylalkylalcohols, diols, hydroxyaldehyde, γ- and δ-hydroxyesters, butyro-and δ- valerolactones. Enantioselective Reformatsky reaction with aldehydes and ketones using DPMPM and N, N-diallylnorephedrine affords chiral β-sec-, and β-t-hydroxyesters, respectively. Enantioselective alkylation of aldehydes using DBNE is applied to the synthesis of chiral alkylphthalides, (+) -Iepicidin A, and a precursor of tacalcitol. Diastereodivergent alkylations of α or β-chiral aldehydes are achieved by using the appropriate enantiomer of DBNE or DPMPM. Self-replication and auto-multiplication of chiral zinc alkoxides of pyridylalkylalcohols and diols as asymmetric autocatalysts is described. Enantioselective and/or diastereoselective alkylation of diphenylphosphinylimine affords chiral amine. Chiral nickel complex with DBNE catalyzes the enantioselective conjugate addition of dialkylzincs to α, β-unsaturated ketones.

Stereoselective radical addition of carbon-centred radicals to the dehydroalanine moiety of the chiral nickel(II) complex of the Schiff′s base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone and dehydroalanine

A new approach to the asymmetric synthesis of β-substituted α-aminopropanoic acids by 2,2′-azoisobutyronitrile (AIBN) and Bu3SnH-initiated radical addition of Etl, PriBr, ButBr, and PhCH2Br to the dehydroalanine moiety of the NiII complex 1 of a Schiff′s base derived from (S)-o-[N-(N′-benzylprolyl)amino]benzophenone (BPB) and dehydroalanine is described. The radical addition produced a mixture of diastereoisomeric complexes 4a–d with a 40–90% excess of (S,S)diastereoisomers over the (S,R)-ones, giving the reaction products in almost quantitative yields. The diastereoselectivity of the reaction depended on the size of the entering radicals, the most effective asymmetric induction being achieved for the But radical addition. Enantiomerically pure ‘(S)-2-amino3-(tert-butyl)propanoic acid’[(S)-γ-methylleucine] and the chiral auxiliary BPB were recovered from compound 4d after its decomposition with HCl. The reactivities of the carbon–centred radicals towards the carbon-carbon double bond in the amino acid moiety of the complex 1 was quantitatively established by using ESR spectroscopy in the spin-trap technique.

Synthesis of a chiral nickel(II) complex of an electrophilic glycinate, and its use for asymmetric preparation of α-amino acids

A chiral NiII complex of a Schiff's base derived from (S)-o-[(benzylpropyl)amino]benzophenone and α-bromoglycine has been obtained and its stereoselective reaction with nucleophiles studied; the synthesis of aspartic acid with 80% optical purity is described.

ChemInform Abstract: Asymmetric Nickel‐Catalyzed Cross‐Coupling Reaction of Allylic Substrates with Grignard Reagents.

AbstractScope and limitations of the title reaction arc studied, using a number of chiral nickel complexes [e.g.

ChemInform Abstract: PREPARATION OF OPTICALLY PURE α‐METHYL‐α‐AMINO ACIDS VIA ALKYLATION OF THE NICKEL(II) SCHIFF BASE OF (R,S)‐ALANINE WITH (S)‐2‐N‐(N′‐BENZYLPROLYL)AMINOBENZALDEHYDE

Chiral nickel(II) complexes of Ala with (S)-2-N-(N′-benzylprolyl)aminobenzaldehyde [(S)-bba] were alkylated with alkyl halides and the diastereoisomeric complexes formed were separated on SiO2; their decomposition led to the isolation of enantiomerically pure (R)- and (S)-α-alkyl-α-amino acids with recovery of the initial (S)-bba.

Preparation of optically pure α-methyl-α-amino acids via alkylation of the nickel(II) Schiff base of (R,S)-alanine with (S)-2-N-(N′-benzylprolyl)aminobenzaldehyde

Chiral nickel(II) complexes of Ala with (S)-2-N-(N′-benzylprolyl)aminobenzaldehyde [(S)-bba] were alkylated with alkyl halides and the diastereoisomeric complexes formed were separated on SiO2; their decomposition led to the isolation of enantiomerically pure (R)- and (S)-α-alkyl-α-amino acids with recovery of the initial (S)-bba.

Cyclodimerization of butadiene in presence of secondary amines and catalyzed by chiral nickel complexes

In the presence of secondary amines, nickel complexes with chiral phosphorus-containing ligands catalyze the asymmetric cyclodimerization of butadiene to 4-ethyl-1-cyclohexene and 4-vinyl-1-cyclohexene.

Synthesis and tautomerism of persubstituted 1,3-dianils, and substituent rotation in their chiral nickel complexes

Synthesis and tautomerism of persubstituted 1,3-dianils, and substituent rotation in their chiral nickel complexes