Rare-earth metal amido complexes supported by bridged bis(β-diketiminato) ligand as efficient catalysts for hydrophosphonylation of aldehydes and ketones

A series of rare-earth metal amides supported by a cyclohexyl-linked bis(β-diketiminato) ligand were synthesized,and their catalytic activities for hydrophosphonylation of aldehydes and ketones were developed.Reaction of [(Me3Si)2N]3 RE(Cl)Li(THF)3 with the cyclohexyl-linked bis(-diketimine) H2L(1)(L=Cy[NC(Me)CHC(Me)NAr]2,Cy = cyclohexyl,Ar=2,6-i-Pr2C6H3) gave the rare-earth metal amides LREN(SiMe3)2(RE = Nd(2),Sm(3),Dy(4),Er(5),Y(6)).All complexes were fully characterized by elemental,spectroscopic and single-crystal X-ray analyses.Investigation of the catalytic properties of the complexes reveals that these complexes exhibited a high catalytic activity towards the hydrophosphonylation of aldehydes and ketones in the presence of a very low loading of rare-earth metal amides(0.1-1 mol%) at room temperature in a short time.     

Ruthenium carboxylate complexes as easily prepared and efficient catalysts for the synthesis of β-oxopropyl esters

The easily prepared complex cis-[Ru(κ²-O₂CMe)₂(PPh₃)₂] is an effective catalyst for the addition of carboxylic acids to propargyl alcohols to afford β-oxopropyl esters. The reaction is tolerant to a range of functional groups on the propargyl alcohol and is effective in the case of the steroid ethisterone. An investigation into the ruthenium-containing products from the reaction involving benzoic acid revealed that rapid exchange between coordinated acetate and benzoate ligands occurs. The synthesis of crystallographically characterised cis-[Ru(κ²-O₂CPh)₂(PPh₃)₂] was developed. This benzoate-substituted complex was shown to react with HCCPh and HCCC(OH)PhH to give [Ru(κ²-O₂CPh)(κ¹-O₂CPh)(CCPhH)(PPh₃)₂] and [Ru(κ²-O₂CPh)(κ¹-O₂CPh)(CCC{OH}PhH)(PPh₃)₂] respectively. Reaction of cis-[Ru(κ²-O₂CPh)₂(PPh₃)₂] with CO affords [Ru(κ²-O₂CPh)(κ¹-O₂CPh)(CO)(PPh₃)₂] or [Ru(κ²-O₂CPh)₂(CO)₂(PPh₃)₂] depending on the conditions employed. Related carbonyl compounds are thought to be the ruthenium-containing products from the catalytic reactions and [Ru(κ²-O₂CMe)(κ¹-O₂CMe)(CO)(PPh₃)₂] was also shown to be a competent catalyst.     

Zr(HSO4)4/SiO2: An effective heterogeneous alternative for one-pot synthesis of β-acetamido ketones

In a one-pot procedure, enolizable ketones reacted with aromatic aldehydes, acetyl chloride and acetonitrile at room temperature in the presence of Zr(HSO₄)₄/SiO₂ to furnish the corresponding β-acetamido ketones in improved yields.     

Fluorinated anilides of β-keto acids and their Cu(II) complexes

Pentafluoroanilides of acetoacetic and benzoylacetic acids and their α-SCF₃ substituted analogues have been synthesized from the respective β-keto esters. Cu(II) complexes of the compounds obtained as well as of anilide of α-(trifluoromethylthio)acetoacetic acid have been prepared and characterized. The structure of these compounds has been elucidated on the basis of the elemental analysis and IR, MS, ¹H and ¹⁹F NMR spectra.     

Enantioselective synthesis of β-hydroxy amines and aziridines using asymmetric transfer hydrogenation of α-amido ketones

A rapid, expedient and enantioselective method for the synthesis of β-hydroxy amines and monosubstituted aziridines in up to 99% e.e., via asymmetric transfer hydrogenation of α-amido ketones, is described.     

X-ray study of volatile Ni(II), Cu(II), and Pd(II) complexes of β-ketoimine pivalyltrifluoroacetone

Synthesis of volatile complexes based on -ketoimine pivalyltrifluoroacetone, C(CH₃)₃C(NH)CH₂COCF₃, is described. The general formula of the complexes is M(L)₂, where M = Cu, Ni, Pd. Complexes of this kind with Ni and Pd were obtained for the first time. The Cu and Pd complexes were found to be isostructural. A comprehensive crystal-chemical study showed that all structures are molecular and built of trans-complexes. The central atom has a square plane environment. The average M-O and M-N distances are nearly equal in all compounds: 1.84 , 1.92 , and 1.98 for Ni, Cu, and Pd complexes, respectively; the mean values of the O-M-N chelate angles are 93.4°, 91.9°, and 92.7°, respectively.Original Russian Text Copyright © 2004 by I. A. Baidina, G. I. Zharkova, N. V. Pervukhina, S. A. Gromilov, and I. K. IgumenovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 713–722, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

A new convenient method for the synthesis of mixed-ligand β-diketonato Tc(III) complexes

A new convenient method has been proposed to synthesize mixed-ligand -diketonato Tc(III) complexes, using the ligand exchange reaction [Tc(acac)₂(CH₃CN)₂]⁺+L^–[Tc(acac)₂L]+ +2CH₃CN where L is bza, dpm or dbm. The yield was about 30–40%. UV-visible and IR spectra of these complexes were measured. Characteristic features of the compounds were compared with those of the corresponding complexes of ruthenium.     

trans-Fe(II)(H)2(diphosphine)(diamine) complexes as alternative catalysts for the asymmetric hydrogenation of ketones? A DFT study

New insights into the structural, electronic and catalytic properties of Fe complexes are provided by a density functional theory study of model as well as real [Fe(II)(H)(2)(diphosphine)(diamine)] systems. Calculations conducted using several different functionals on the trans- and cis-isomers of [Fe(II)(H)(2)(S-xylbinap)(S,S-dpen)] complexes show that, as with the [Ru(II)(H)(2)(diphosphine)(diamine)] complexes, the trans-[Fe(II)(H)(2)(diphosphine)(diamine)] complex is the more stable isomer. Analysis of the spin states of the trans-[Fe(II)(H)(2)(diphosphine)(diamine)] complexes also shows that the singlet state is significantly more stable than the triplet and the quintet, as with the [Ru(II)(H)(2)(diphosphine)(diamine)] complexes. Calculations of the catalytic cycle for the hydrogenation of ketones using two model trans-[M(II)(H)(2)(PH(3))(2)(en)] catalysts, where M = Ru and Fe, show that the mechanism of reaction as well as the activation energies are very similar, in particular: (i) the ketone/alcohol hydrogen transfer reaction occurs through the metal-ligand bifunctional mechanism, with energy barriers of 3.4 and 3.2 kcal mol(-1) for the Ru- and Fe-catalysed reactions, respectively; (ii) the heterolytic splitting of H(2) across the M[partial double bond, bottom dashed]N bond for the regeneration of the Ru and Fe catalysts has an activation barrier of 13.8 and 12.8 kcal mol(-1), respectively, and is expected to be the rate determining step for both catalytic systems. The reduction of acetophenone by trans-[M(II)(H)(2)(S-xylbinap)(S,S-dpen)] complexes along two competitive reaction pathways, shows that the intermediates for the Fe catalytic system are similar to those responsible for the high enantioselectivity of (R)-alcohol in those proposed trans-[Ru(II)(H)(2)(S-xylbinap)(S,S-dpen)] catalysed acetophenone hydrogenation reaction. Thus the high enantiomeric excess in the hydrogenation of acetophenone could, in principle, be achieved using Fe catalysts.     

Studies of copper (Ⅱ) complexes as catalysts for the hydrolysis of DNA

Hydrolysis of DNA is an important enzymatic reaction , but it is exceedingly difficult to mimic in the laboratory because of the stability of hydrolysis of DNA. In this paper, the cleavage activity of complexes formed between Cu(Ⅱ) and four different amino acid or amino acid methyl ester on DNA is studied by gel elec-trophoresis. It is found that DNA could be cleaved by Cu(Ⅱ)-L-His and Cu(Ⅱ)-L-His methyl ester complexes and the efficiency of cleavage is largely dependent on the metal ion-to-ligand ratio. Further experiments show that the cleavage of DNA mediated by Cu(Ⅱ)-L-His complexes occurs via a hydrolytic mechanism and the active chemical species that affects DNA cleavage is proposed to be MI2H and ML2H22 .     

Aryloxy ‘biometal’ complexes as efficient catalysts for the synthesis of poly(butylene adipate terephthalate)

A comparative study of catalytic activity of aryloxy complexes of Mg, Zn and Al in the synthesis of poly(butylene adipate terephthalate) demonstrated the preference of Al-based catalyst containing two bulky substituents in ortho-position of phenol ligand in terms of higher values of PBAT MW and lower yields of cyclic diester side product.     

Polymer-anchored platinum complexes as catalysts for the Baeyer–Villiger oxidation of ketones: preparation and catalytic properties

The preparation of a variety of catalysts obtained by ion exchange of the complex [(dppb)Pt(μ−OH)]₂²⁺ with sulfonated styrene–divinylbenzene copolymers is reported. Copolymers used are commercial ion exchange resins containing either 4% or 20% DVB and they were loaded with either Li⁺ or NBu₄⁺ prior to exchange with the Pt complex. Metal loading in the heterogenized catalysts is in the range 2–8% by weight. Their catalytic properties in the Baeyer–Villiger oxidation of methylcyclohexanone with hydrogen peroxide appear to be best in terms of activity and productivity either in neat ketone or in EtOH as the solvent. The use of commercial resins with high exchange capacity prevents the use of DCE as the solvent, i.e., the optimum conditions for the homogeneous system, thereby leading to activities and productivities that are generally lower than their homogeneous counterpart. A discussion on the influence of the philicity properties of the support with respect to the performance of the catalyst is reported.     

Synthesis and characterization of sterically encumbered β-ketoiminate complexes of iron(II) and zinc(II)

The synthesis, structure, and spectroscopic signatures of a series of four-coordinate iron(II) complexes of β-ketoiminates and their zinc(II) analogues are presented. An unusual five-coordinate iron(II) triflate with three oxygen bound protonated β-ketoimines is also synthesized and structurally characterized. Single-crystal X-ray crystallographic analysis reveals that the deprotonated bis(chelate)metal complexes are four-coordinate with various degrees of distortion depending on the degree of steric bulk and the electronics of the metal center. Each of the high-spin iron(II) centers exhibits multiple electronic transitions including ligand π to π*, metal-to-ligand charge transfer, and spin-forbidden d-d bands. The (1)H NMR spectra of the paramagnetic high-spin iron(II) centers are assigned on the basis of chemical shifts, longitudinal relaxation times (T(1)), relative integrations, and substitution of the ligands. The electrochemical studies support variations in the ligand strength. Parallel mode EPR measurements for the isopropyl substituted ligand complex of iron(II) show low-field resonances (g > 9.5) indicative of complex aggregation or crystallite formation. No suitable solvent system or glassing mixture was found to remedy this phenomenon. However, the bulkier diisopropylphenyl substituted ligand exhibits an integer spin signal consistent with an isolated iron(ii) center [S = 2; D = -7.1 ± 0.8 cm(-1); E/D = 0.1]. A tentative molecular orbital diagram is assembled.     

Nano TiO_2 as a heterogeneous catalyst in an efficient one-pot three-component Mannich synthesis of β-aminocarbonyls

TiO₂ nanoparticles（TiO₂ NPs） worked as an efficient heterogeneous catalyst in a one-pot,three-component,and solvent free Mannich reaction;producing variousβ-aminocarbonyls in good yields,and with good stereoselectivities.The catalyst was easily separated from the reaction mixture and was recycled four times with no significant loss of its catalytic activity.     

Design and synthesis of palladium (II) OCO pincer type complexes and their catalytic role towards the α-arylation of ketones

Twelve OCO bisacetamide ligands 4aa-4dc were synthesized after condensation of isophenylenediamines 1a-1d and anhydride/acyl chlorides. The corresponding Pd(II)–OCO–H(5aa-5ac), Pd(II)–OCO–Me(5ba-5bc), Pd(II)–OCO–OMe(5ca-5?cc), Pd(II)–OCO–NO₂(5da-5dc) pincer complexes were prepared via C-H activation of precursors and Pd(OAc)₂, and characterized by IR, ¹H NMR, ¹³C NMR and elemental analysis. The α-arylation of ketones and aryl bromides catalyzed by 5 under low catalyst loadings (0.1?mol%) show that 5da exhibits the highest catalytic activity, resulting in a 98% isolated yield.     

Thermochemical study of new volatile palladium(II) and copper(II) β-ketohydrazonates for CVD application

Journal of Thermal Analysis and Calorimetry - The volatile palladium(II) and copper(II) {O,N}-coordinated bis-chelate complexes of a new type, Pd(dmht)2 and Cu(dmht)2, where...     

Cu(I)-catalyzed annulation for the synthesis of substituted naphthalenes using o-bromobenzaldehydes and β-ketoesters as substrates

Cu(I)-catalyzed reaction of o-bromobenzaldehydes with β-ketoesters using Cs(2)CO(3) as a base and 2-picolinic acid as an additive proceeds under mild conditions and gives access to substituted naphthalenes in a single step with yields ranging from 71 to 86%. The new annulation process relies on a domino Knoevenagel condensation/C-arylation/1,2-addition/carboxylic acid cleavage. The annulation can also be achieved with o-iodobenzaldehyde.     

Synthesis and structures of nickel(ii) complexes with thioether-containing β-aminovinyl ketones

New ligands, viz., thioether-containing -aminovinyl ketones, and Ni^II complexes with these ligands were synthesized. The compounds were characterized by X-ray diffraction analysis, EXAFS, NMR, and IR spectroscopy, and magnetochemistry.     

DMF-dimethyl sulfate as a new reagent for the synthesis of β-lactams

A number of 2-azetidinones were synthesized in good to excellent yields by a novel reaction between Schiff bases, substituted acetic acids and alkoxymethylene-N,N-dimethyliminium salts, the adduct formed from DMF and O-alkylating agents. The advantages of this new method are mild reaction conditions, low cost, avoiding the use of chlorinating agents and easy purification of the products. The best results were obtained when DMF and dimethyl sulfate were used at room temperature.