A density functional theory study of gold clusters supported on layered double hydroxides

The geometrical structure and electronic properties of a series of Au _N (N = 1–8) clusters supported on a Mg²⁺, Al³⁺-containing layered double hydroxides (MgAl–LDH) are investigated using density functional theory. The Au clusters are supported on two typical crystal faces of the LDH platelet, the basal {0001} and the lateral $ \{ 10\,\bar{1}\,0\} $ crystal face, respectively, corresponding to the top and edge site of monolayer MgAl–LDH lamella for the sake of simplicity. It is revealed that an increase in the charge transfer from the LDH lamella to the Au _N clusters at the edge site rather than clusters on the top surface, demonstrating a preferential adsorption for Au _N clusters at the edge of LDH lamella. Moreover, the calculated adsorption energy of the Au _N clusters on the LDH lamella increases with the cluster size, irrespective of the adsorption site. The investigation on the interaction between O₂ and Au _N clusters on the LDH lamella is further carried out for understanding the catalytic oxidation properties of the LDH-supported Au catalyst. The formation of reactive O₂ ^? species, a necessary prerequisite in catalytic oxidation of CO, by O₂ bridging two Au atoms of Au _N clusters indicates that the LDH-supported Au catalyst has the required characteristics of a chemically active gold catalyst in CO oxidation.     

Enantioselective amination of silylketene acetals with (N-arylsulfonylimino)phenyliodinanes catalyzed by chiral dirhodium(II) carboxylates: asymmetric synthesis of phenylglycine derivatives

The first catalytic enantioselective amination of silylketene acetals with (N-arylsulfonylimino)phenyliodinanes is described. The reaction of silylketene acetals derived from methyl phenylacetates with [N-(2-nitrophenylsulfonyl)imino]phenyliodinane (NsN = IPh) under the catalysis of dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], Rh₂(S-TCPTTL)₄, proceeds in benzene at room temperature to give N-(2-nitrophenylsulfonyl)phenylglycine derivatives in high yields and with enantioselectivities of up to 99% ee.     

A New Route for the Synthesis of Dialkyl Tellurides and Dialkyl Ditellurides

Sodium cleaves elemental tellurium, Te_X, quantitatively to Te^2– ₂ and Te^2- in anhydrous tetrahydrofuran in the presence of catalytic amounts of naphthalene. Subsequent addition of alkylating agent affords dialkyl tellurides and dialkyl ditellurides in excellent yields.     

A dipole moment study of the structures of some ketene acetals

The dipole moments of several acyclic and cyclic ketene acetals have been determined in benzene solution at 293 K using the Halverstadt-Kumler method. For ketene dialkyl acetals (alkyl = Me, Et) the results point to a predominance of the s-cis,s-trans retamer, which disagrees with the conclusions drawn previously from ¹³C NMR chemical shift data, i.e. the s-cis,s-cis form is the more stable species. In the case of 2-methoxyfuran, the dipole moment measurements confirm the previous findings based on the ¹³C NMR spectra, viz the s-cis form is the predominating rotamer. The dipole moments and structures of some other ketene acetals are also discussed.     

Dodecacarbonyltriruthenium catalyzed one-to-one addition of N-substituted formamide to olefins

Dodecacarbonyltriruthenium (Ru₃(CO)₁₂) showed high catalytic activity for the first one-to-one addition of N-substituted formamides to both terminal and internal olefins at 180-200°C under a carbon monoxide pressure of 20 kg cm⁻². The addition of N-metylformamide to cyclopentene afforded N-methylcyclopentanecarboxamide in 90% yield.     

Efficient synthesis of functionalized spiro-2,5-dihydro-1,2-λ-oxaphospholes

The reaction of ethyl propiolate with triphenylphosphine (Ph₃P) in the presence of N-alkylisatins led to ethyl 2,2,2-triphenyl-2,5-dihydro-1,2-λ⁵-oxaphosphole-4-carboxylate-spiro-1-alkyl-1,3-dihydro-2H-indol-2-ones in good yield. The reaction of dialkyl acetylenedicarboxylates with Ph₃P in the presence of N-alkylisatins led to dialkyl 2,2,2-triphenyl-2,5-dihydro-1,2-λ⁵-oxaphosphole-3,4-dicarboxylate-spiro-1-alkyl-1,3-dihydro-2H-indol-2-ones and alkyl 4-(alkoxy)-5-oxo-2,5-dihydro-3-furancarboxylate-spiro-1-alkyl-1,3-dihydro-2H-indol-2-ones.     

Synthesis of fluorine-containing quinoline-2,3-dicarboxylates from products of vicarious nucleophilic substitution of hydrogen in 3-fluoronitroarenes

The reactions of 3-fluoro-4-R-6-phenylsulfonylmethylnitrobenzenes with dimethyl fumarate or diethyl maleate in acetonitrile in the presence of an excess of K₂CO³ and a catalytic amount of 18-crown-6 afforded mixtures of dialkyl 6-R-7-fluoro- and dialkyl 6-R-7-phenylsulfonylquinoline-2,3-carboxylate N-oxides, as well as dialkyl 6-R-7-fiuoro- quinoline-2,3-carboxylates (alkyl is methyl or ethyl), which were resolved by column chromatography and identified by ¹H NMR spectroscopy and X-ray diffraction.     

Synthesis of the C9-C21 fragment of debromoaplysiatoxin and oscillatoxins A and D

A highly stereoselective synthesis of the C9-C21 fragment of debromoaplysiatoxin and oscillatoxins A and D has been devised. This new approach relies on the cross coupling of titanium enolates from N-acyl-1,3-thiazolidine-2-thiones and dialkyl acetals and the selective hydrogenolysis of O-benzyl protecting groups.     

Dialkyl Ether Formation by Nickel‐Catalyzed Cross‐Coupling of Acetals and Aryl Iodides

A new substrate class for nickel‐catalyzed C(sp³) cross‐coupling reactions is reported. α‐Oxy radicals generated from benzylic acetals, TMSCl, and a mild reductant can participate in chemoselective cross‐coupling with aryl iodides using a 2,6‐bis(N‐pyrazolyl)pyridine (bpp)/Ni catalyst. The mild, base‐free conditions are tolerant of a variety of functional groups on both partners, thus representing an attractive C? C bond‐forming approach to dialkyl ether synthesis. Characterization of a [(bpp)NiCl] complex relevant to the proposed catalytic cycle is also described.     

A new method for the synthesis of mixed orthoesters from O-allyl acetals

Two new methods for the synthesis of orthoesters and compounds containing an orthoester moiety (dihydroisoxazoles) are presented. Mixed orthoesters of general formulas RC(OR¹)(OR²)₂ and RC(OR¹)(OR²)(OR³) were prepared via addition of ROH (R = Bu or m-methylphenyl) to O-allyl acetals (acrolein acetals: diethyl or cyclic, i.e., 2-vinyl-1,3-dioxanes or dioxolanes). The catalytic systems for these reactions were generated from [RuCl₂(PPh₃)₃] and Na₂CO₃; {[RuCl₂(COD)]_x} or {[OsCl₂(1,5-COD)]_x}, PPh₃, and Na₂CO₃. Compounds containing an orthoester moiety (dihydroisoxazoles) were prepared via tandem isomerization of O-allyl acetals (to O-vinyl acetals) catalyzed by ruthenium complexes followed by cycloaddition to in situ-generated 2,6-dichlorophenylnitrile oxide.     

Heterodyne measurements of hot bands and isotopic transitions of N2O near 7.8 µm

Heterodyne frequency measurements are reported for absorption transitions of N₂O in the frequency range from 1257 to 1335 cm^?1. The measurements use a CO laser as a transfer oscillator whose frequency is measured directly against combinations of frequencies of two stabilized CO₂ lasers whose frequencies are well known. A tunable diode laser is locked to the N₂O absorption feature and the frequency difference is measured between the diode laser and the CO laser. Thev ₃ fundamental bands of the¹⁵N¹⁴N¹⁶O and¹⁴N¹⁵N¹⁶O isotopes are reported. Measurements are also given for the 00⁰2–00⁰1, 02⁰1–02⁰0, and 02²1–02²0 vibrational transitions of N₂O. A table of frequencies is given for the 00⁰2–00⁰0 band near 2560 cm^?1 based on these and earlier measurements.     

Highly Ordered Mesoporous Cobalt-Copper Composite Oxides for Preferential CO Oxidation

Highly ordered mesoporous cobalt-copper composite oxides were prepared by the nanocasting method with various Co and Cu ratios. The catalysts obtained were characterized by X-ray diffraction, N₂ adsorption–desorption, H₂-temperature programmed reduction, CO-temperature programmed desorption and X-ray photoelectron spectroscopy. All of the catalysts had uniform mesopores and high surface areas. The distinct catalytic properties of these well-characterized mesoporous materials were demonstrated for preferential CO oxidation. It is found that the mesoporous cobalt-copper composite oxides, exhibited the higher catalytic activity for CO conversion and selectivity compared with the mesoporous Co₃O₄ and mesoporous CuO. Among these catalysts the mesoporous cobalt-copper catalyst with Co:Cu molar ratio of 70:30, shows the best catalytic activity and the broadest operating temperature “window” for the high CO conversion in the range of 125–200^oC. The higher catalytic activity was attributed to the higher CO adsorption and oxygen vacancies.     

Electrocatalytic reduction of carbon dioxide by a polymeric film of rhenium tricarbonyl dipyridylamine

A dipyridylamine ligand with a pendant pyrrole (N-(3-N,N′-bis(2-pyridyl)propylamino)pyrrole, PPP) and its corresponding rhenium(I) complex, Re(CO)₃(κ²-N,N-PPP)Cl, were synthesized. The structure of Re(CO)₃(κ²-N,N-PPP)Cl was determined by X-ray crystallography. Electrochemical polymerization of the pyrrole moiety resulted in the immobilization of poly[Re(CO)₃(κ²-N,N-PPP)Cl] film onto a glassy carbon electrode, which exhibited electrocatalytic activity for the reduction of CO₂ to CO.     

A selective convenient ruthenium-mediated synthesis of mixed acetals

Addition of alcohols and phenols to allyl ethers catalyzed mainly by ruthenium complexes was studied. Complexes of ruthenium generated in situ from precursors such as {[RuCl₂(1,5-COD)]_x} or [Ru₃(CO)₁₂] and from external ligands such as phosphines (e.g. PPh₃, PBu₃, BINAP) or phosphites (e.g. P(OPh)₃, P(OMe)₃) were found to be particularly efficient catalysts of the studied reactions. Transacetalization reaction could be practically completely eliminated by the addition of a base (particularly Na₂CO₃) to the catalytic systems. It was observed that the selectivity of mixed acetals formation increases with increasing value of Θ parameter of phosphines. Especially interesting results (0–5% of transacetalization) have been obtained for catalytic systems generated from {[RuCl₂(1,5-COD)]_x} or [Ru₃(CO)₁₂], phosphines (PPh₃, BINAP, dppe, tris(2,4,6-tri-metylphenyl)phosphine, or dppf) and Na₂CO₃. The mechanism of mixed acetals formation has been investigated using deuterated reagents. It is postulated that the examined reaction is a nucleophilic addition of ROH to a hydrido-π-allyl complex formed during oxidative addition of allyl substrate to metal complex. As a result, a new, selective, and convenient method of the synthesis of symmetrical and, in particular, unsymmetrical (mixed) acetals has been developed. Mixed acetals CH₃CH₂CH(OR¹)(OR²) may be obtained in the reaction of R¹-O-allyl with R²OH or R¹OH with R²-O-allyl, depending on the structure of R¹ and R².     

Regulation of electron donating ability to metal center: isolation and characterization of ruthenium carbonyl complexes with N,N- and/or N,O-donor polypyridyl ligands

Polypyridyl ruthenium(II) dicarbonyl complexes with an N,O- and/or N,N-donor ligand, [Ru(pic)(CO)₂Cl₂]⁻ (1), [Ru(bpy)(pic)(CO)₂]⁺ (2), [Ru(pic)₂(CO)₂] (3), and [Ru(bpy)₂(CO)₂]²⁺ (4) (pic=2-pyridylcarboxylato, bpy=2,2′-bipyridine) were prepared for comparison of the electron donor ability of these ligands to the ruthenium center. A carbonyl group of [Ru(L1)(L2)(CO)₂]ⁿ (L1, L2=bpy, pic) successively reacted with one and two equivalents of OH⁻ to form [Ru(L1)(L2)(CO)(C(O)OH)]ⁿ⁻¹ and [Ru(L1)(L2)(CO)(CO₂)]ⁿ⁻². These three complexes exist as equilbrium mixtures in aqueous solutions and the equilibrium constants were determined potentiometrically. Electrochemical reduction of 2 in CO₂-saturated CH₃CN–H₂O at −1.5 V selectively produced CO.     

Metal‐Free,Room‐Temperature Oxygen‐Atom Transfer in the N2O/CO Redox Couple as Catalyzed by [Si2Ox].+ (x=2–5)

The thermal reduction of N₂O by CO mediated by the metal‐free cluster cations [Si₂O_x]^.+ (x =2–5) has been examined in the gas phase using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with quantum chemical calculations. Three successive oxidation/reduction steps occur starting from [Si₂O₂]^.+ and N₂O to form eventually [Si₂O₅]^.+; the latter as well as the intermediate oxide cluster ions react sequentially with CO molecules to regenerate [Si₂O₂]^.+. Thus, full catalytic cycles occur at ambient conditions in the gas phase. Mechanistic aspects of these sequential redox processes have been addressed to reveal the electronic origins of these unparalleled reactions.     

Reductive carbonylation of nitrobenzene to phenylurethane catalyzed by Ru(III)-schiff base complexes

Ruthenium complexes containing Schiff bases with N₂O₂, N₄ and N₅ donor groups with the general formula [Ru^III(X)Cl_{1 or 2}], where X = Schiff base such as bis(salicylaldehyde)-o-phenylenediimine (saloph), bis(salicylaldehyde)ethylenediimine (salen), bis(picolaldehyde)ethylenediimine (picen), bis(picolaldehyde)-o-phenylenediimine (pic-opd), bis(picolaldehyde)diethylenetriimine (pic-dien), were tested for their catalytic activity towards the reductive carbonylation of nitrobenzene in ethanol to give phenylurethane. The five Ru(III) complexes tested towards reductive carbonylation showed different catalytic activities in the range 160 – 200 °C and CO partial pressure of 15 atm.Among the complexes tested, [Ru(saloph)Cl₂] showed the highest catalytic activity with a turnover rate greater than 80 mol product per mol catalyst per hour at 160 °C and 15 atm CO. [Ru(pic-en)Cl₂]Cl and [Ru(picopd)Cl₂]Cl complexes with N₄ donor systems were found to be less active towards carbonylation of nitrobenzene, as indicated by their turnover rates of 20 and 15 mol product per mol catalyst per hour, respectively, at 200 °C and 15 atm CO. The complex [Ru(pic-dien)Cl]Cl₂N₅ donor system was completely inactive even at 200 °C and 15 atm CO, and no conversion of nitrobenzene was seen even after 12 h contact time.     

Regio- and diastereoselective SN2′ or SN2″ reactions on chiral acetals of cyclic aldehydes promoted by PhCu,BF3

The regio- and diastereoselectivity of the addition of PhCu, BF₃ reagent on chiral acetals derived from several mono or dienic aldehydes was studied. It was found that monoethylenic acetals react regio- and diastereoselectively via an overall anti S_N2′ reaction. The regioselectivity observed with the dienic acetals seems to be strongly dependent on the nature of the acetal. In all cases the S_N2″reaction was the result of an anti process.     

Metal‐to‐Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole‐Containing Amidopyridinate Ligands: Synthesis,Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y^III dialkyl complexes supported by tridentate N^?,N,N monoanionic methylthiazole– or benzothiazole–amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole‐containing system through an unprecedented metal‐to‐ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N^?,N,N^?,S^? ligand as the result of metal‐to‐ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y?H group to the imino fragment of a second equivalent of the ring‐opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph₃C⁺[B(C₆F₅)₄]^?, were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.     

Carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes: an unexpectedly complex network of catalytic reactions, centred around a Pd-imido intermediate

The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P₂) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N′‐diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co‐produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H₂O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P₂Pd⁰ compound formed in situ, oxidation to a palladium imido compound P₂Pd^II?NPh, can be achieved by de‐oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P₂Pd^II?NPh to P₂Pd⁰ makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd–imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.