Metal-free catalytic reduction of aldehydes,ketones,aldimines,and ketimines

<正>The metal-free combination of catalytic amounts of PPh_3,B(C_6F_5)_3,and PhSiH_3 can efficiently hydrosilylate aldehydes, ketones,aldimines and ketimines to afford the corresponding reduction products in good yields.     

Further ‘tethered’ Ru(II) catalysts for asymmetric transfer hydrogenation (ATH) of ketones; the use of a benzylic linker and a cyclohexyldiamine ligand

The synthesis and characterisation of two new Ru(II) catalysts for the asymmetric transfer hydrogenation (ATH) of ketones is described. In the case of 4, the novelty lies in the use of a benzyl tethering group between the asymmetric ligand part (TsDPEN) and the η⁶-arene ring, which increases the complex rigidity. For 5, the use of a cyclohexyldiamine as a chiral ligand is described for the first time. In the ATH of ketones in formic acid/triethylamine, alcohols with ees of up to 97% were formed.     

Chemoselective reduction of aldehydes and ketones by potassium diisobutyl-t-butoxy aluminum hydride (PDBBA)

t-Butoxy derivatives of DIBALH [lithium diisobutyl-t-butoxyaluminum hydride (LDBBA), sodium diisobutyl-t-butoxyaluminum hydride (SDBBA), and potassium diisobutyl-t-butoxyaluminum hydride (PDBBA)] were examined as chemoselective reducing agents of carbonyl compounds. Among them, PDBBA was found to be the most efficient for the reduction of aldehydes and ketones to the corresponding alcohols in the presence of ester, amide, and nitrile substituents at ambient temperature. In addition, the optimal conditions gave higher chemoselectivity for aldehydes in the presence of ketones.     

Highly efficient and convenient asymmetric hydrosilylation of ketones catalyzed with zinc Schiff base complexes

Several chiral Schiff base ligands derived from α-amino acids were prepared, and zinc complexes with these chiral Schiff base ligands prepared were tested for the catalytic asymmetric hydrosilylation of ketones, and the results showed that excellent ee values were obtained, which are the prominent examples of catalytic asymmetric hydrosilylation of ketones catalyzed with zinc complexes in the presence of readily available and inexpensive α-amino acids based Schiff base ligands.     

Highly efficient reduction of ferrocenyl aldehyde and ketones in ionic liquids

For the first time ferrocenyl aldehyde and ketones were effectively reduced to alkylferrocene using sodium borohydride and aluminum chloride in an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF₄). Mild reaction conditions, enhanced rates, improved yields, and recyclable ionic liquid are the remarkable features exhibited in this process.     

Highly enantioselective cyanosilylation of ketones catalyzed by a bifunctional Ti(IV) complex

A bifunctional catalyst system composed of (S)-prolinamide (2a), titanium(IV) isopropoxide, and phenolic N-oxide (3f) exhibited high catalytic efficiency in the enantioselective cyanosilylation of ketones. In the presence of 2.5 mol % catalyst, a variety of aromatic and aliphatic ketones were converted into the corresponding tertiary cyanohydrin O-TMS ethers in excellent yields (up to 96%) and high enantioselectivities (up to 96% ee). A proposed catalytic cycle was illustrated to explain the origin of the asymmetric induction.     

Facile and efficient preparation of α-halomethyl ketones from α-diazo ketones catalyzed by iron(III) halides and silica gel

An efficient and mild method for the synthesis of α-halomethyl ketones from α-diazo ketones was developed using ferric chloride or bromide as the halogen source and silica gel as the hydrogen source, with good to excellent yields.     

Catalytic asymmetric hydrosilylation of ketones: I. Chiral phosphine-platinum(II) complex-catalyzed hydrosilylation.

Dichlorobis(dimethylphenylphosphine)di-μ-chlorodiplatinum(II) was found to be an effective catalyst for the hydrosilylation of alkyl phenyl ketones with methyldichlorosilane to give the corresponding silyl ethers of 1-phenylalkanols. In the case of dialkyl ketones, the reaction was accompanied by formation of silyl enol ethers in considerable amounts. Asymmetric hydrosilylation of a series of alkyl phenyl ketones catalyzed by chiral phosphine- platinum(II) complexes was undertaken. The products were readily converted into partially active 1-phenylalkanols.     

The synthesis and catalytic activity of poly(bis(imino)pyridyl) iron(II) metallodendrimer

The first and second generation carbosilane dendrimers with silicon hydride terminated were synthesized, and then reacted with bis(imino)pyridyl containing allyl [4-CH₂CHCH₂-2,6-ⁱPr₂C₆H₃NCMe(C₅H₃N)MeCN(2,6-ⁱPr₂C₆H₃)], in the presence of H₂PtCl₆ as a hydrosilylation catalyst, to afford the first and second generation carbosilane supported ligands. Complexation reactions with FeCl₂ · 4H₂O give rise to iron-containing carbosilane dendrimers with FeCl₂ moieties bound on the periphery. The metallodendrimers were used as catalyst precursors, activated with modified methylaluminoxane, for the polymerization of ethylene. In the case of low Al/Fe molar ratio, the metallodendrimers display much higher catalytic activity towards ethylene polymerization and produce much higher molecule weight polyethylenes than the corresponding single-nuclear complex under the same conditions.     

1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride in combination with triethylamine: an improved catalytic system for hydroacylation/reduction of activated ketones

A rapid, economic, and high yielding methodology has been developed for hydroacylation/reduction of activated ketones by using 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride as a catalyst in combination with triethylamine. The reaction proceeded at an ambient temperature via generating N-heterocyclic carbene in situ that interacted with the (hetero)aryl aldehyde employed. While the reduction of ketones takes place in MeOH, the hydroacylation process was found to be effective in THF for both electron rich and deficient aldehydes.     

Highly efficient alkylation to ketones and aldimines with Grignard reagents catalyzed by zinc(II) chloride

A highly efficient alkylation to ketones and aldimines with Grignard reagents in the presence of catalytic trialkylzinc(II) ate complexes derived from ZnCl2 (10 mol %) in situ was developed. This simple Zn(II)-catalyzed alkylation could minimize the well-known but serious problems with the use of only Grignard reagents, which leads to reduction and aldol side products, and the yield of desired alkylation products could be improved.     

Determination of cobalt(II), copper(II) and iron(II) by ion chromatography with chemiluminescence detection

An optimized flow-injection manifold for the chemiluminescence determination of cobalt(II), copper(II), iron(II) and chromium(III) by their catalytic effect on the luminol reaction is described. Detection limits are 0.0006, 0.08, 0.3 and 0.1 ng ml^?1, respectively. The suppression effect of several carboxylic acids on the emission intensity is discussed. A procedure for the separation of cobalt(II), copper(II) and iron(II) on a low-capacity, silica-based cation-exchange column, using 5 mM oxalic acid at pH 4.2 as the mobile phase and post-column detection via the luminol reaction, is also described. Detection limits for cobalt(II) and copper(II) are 0.01 and 5 ng ml^?1, respectively.     

钌(II)-吡啶基NNN配合物催化酮的室温(不对称)氢转移反应

合成了一种基于吡啶骨架含有苯并咪唑和手性咪唑啉基团的三齿NNN配体及其二价钌(II)配合物,通过核磁共振波谱学和X射线单晶晶体结构测定确认了钌(II)配合物的分子结构.这些配合物在室温下催化酮的氢转移反应,表现出了优异的催化活性,收率和ee值最高分别可达99%和97%.     

Highly efficient copper catalytic system for the O-arylation of phenol with iodoarene

An efficient Cu-catalyzed O-arylation was carried out by involving phenols with iodoarenes to afford various substituted diarylether derivatives with tiny loading of Cu₂O and 1H-imidazole-4-carboxylic acid as catalytic system under mild conditions, which provided good to excellent yields with good tolerance of functional groups.     

Highly efficient catalytic system for electrophilic amination of arylzinc reagents

The effect of catalyst on the yield of amine in the amination of three classes of arylzinc reagents with acetone oxime O‐tosylate was investigated. Since they allowed the preparation of arylamines in excellent yields in the presence of a minimum amount of copper (I) or copper (II) compounds, the catalytic systems using copper (I) or copper (II) combined with a P‐, N‐ or S‐donor ligand were revealed to be the best catalysts for the electrophilic amination of arylzinc reagents with acetone oxime O‐tosylate in the presence of DMPU. Copyright © 2009 John Wiley & Sons, Ltd.     

P(RNCH2CH2)N: efficient catalysts for the cyanosilylation of aldehydes and ketones

The 1,2-addition of trialkylsilylcyanides to aldehydes and ketones produces the corresponding protected cyanohydrins in good to excellent yields when carried out at 0 °C to room temperature in the presence of catalytic amounts of the nonionic strong base P(RNCH₂CH₂)N (R = Me, i-Pr) in THF. These catalysts are easily removed from the product by hydrolysis or column filtration through silica gel.     

C-H activation of diphenylphosphinoaryl-derivatives with dimethyltetrakis(trimethylphosphine)iron(II)

Fe(CH₃)₂(PMe₃)₄ reacts with 1-(diphenylphosphino)naphthalene or benzyldiphenylphosphine within 4 h at 20 °C to give the novel metallated methyl iron complexes Fe(CH₃){P(C₆H₅)₂(C₁₀H₆)}(PMe₃)₃ (1) and Fe(CH₃){(C₆H₄)CH₂P(C₆H₅)₂}(PMe₃)₃ (3), respectively, via selective activation of the C-H bond of the pre-chelating ligands. The complexes are thermally unstable releasing metal through a reductive elimination of the aromatic backbone and leading to a C,C-coupling product that is regiospecifically methylated, namely 8-methyl(diphenylphosphino)naphthalene (2). Carbonylation (1 bar, 20 °C, 1 h) of complex 1 effects monosubstitution of a trimethylphosphine ligand trans to the metallated 8-C atom to afford Fe(CH₃){P(C₆H₅)₂(C₁₀H₆)}(CO)(PMe₃)₂ (4). The remaining methyl group in the parent complex 1 reacts with trimethylsilylethyne and tert-butylethyne affording the new complexes 5 and 6 bearing an alkynyl substituent trans to the diphenylphosphino anchoring group. The complexes 1 and 3-6 are diamagnetic and possess octahedral coordination geometry. All novel complexes were fully characterized by spectroscopic methods and by X-ray diffraction.     

Highly efficient B(C(6)F(5))(3)-catalyzed hydrosilylation of olefins

A convenient and highly efficient method for the Lewis acid-catalyzed trans-selective hydrosilylation of alkenes has been developed. The mechanism of this novel protocol operates via direct addition of silylium type species across C=C bond followed by trapping of the resultant carbenium ion with boron-bound hydride. A number of diversely substituted silanes possessing both aryl and alkyl groups at silicon atom were efficiently prepared using this hydrosilylation methodology. The possibility to employ aryl-containing hydrosilanes in this reaction opens broad capabilities for the synthesis of alcohols via a trans-selective hydrosilylation/Tamao-Fleming oxidation sequence, complementary to the existing cis-selective hydroboration/oxidation protocol.     

Cobalt(II)-catalyzed asymmetric hydrosilylation of simple ketones using dipyridylphosphine ligands in air

In the presence of PhSiH(3) as the hydride donor, catalytic amounts of non-racemic dipyridylphosphine and an easy-to-handle cobalt salt Co(OAc)(2)·4H(2)O formed in situ an effective catalyst system for the asymmetric reduction of a diverse range of aryl alkyl ketones with moderate-to-excellent enantioselectivities (up to 96% ee). This approach tolerated the handling of both catalyst and reactants under air without special precautions.     

Synthesis, characterization and catalytic behavior toward ethylene of cobalt(II) and iron(II) complexes bearing 2-(1-aryliminoethylidene)quinolines

A series of 2-(1-aryliminoethylidene)quinolines (L) were synthesized and used as bidentate N^N ligands in coordinating with metal (cobalt and iron) chlorides to form complexes of the type LMCl₂, cobalt(II) (Co1-Co5) and iron(II) (Fe1-Fe5). All organic compounds and metal complexes were fully characterized, and the molecular structures of the representative complexes Co3·DMF and Fe4·DMF were confirmed as distorted bipyramidal geometry at the metal by single-crystal X-ray diffraction. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) under 10 atm ethylene, all complexes showed high activities in ethylene dimerization with activities of up to 1.82 × 10⁶ g mol⁻¹ (Co) h⁻¹ and 5.89 × 10⁵ g mol⁻¹ (Fe) h⁻¹, respectively.