Showing papers in "Canadian Journal of Chemistry in 2006"

Metallocenes as references for the determination of redox potentials by cyclic voltammetry Permethylated iron and cobalt sandwich complexes, inhibition by polyamine dendrimers, and the role of hydroxy-containing ferrocenes

Abstract: Measurement of the redox potentials (E1/2) of ferrocene (1), decamethylferrocene (2), decamethylcobaltocene (3), and [FeICp*(η6-C6Me6)] (4) (Cp* = η5-C5Me5) in DMF, CH3CN, THF, DME, CH2Cl2, and DMSO were recorded vs. the saturated calomel electrode (SCE), showing that the E1/2 value of 1 was more solvent dependent than those of 2–4, and that the difference in E1/2 values among 2–4 was solvent independent, unlike those found between 1 and 2–4. This shows that 2–4 are much more reliable internal references for determining redox potentials than 1, but using data from this article, one can convert the literature values reported vs. 1 into values vs. 2, 3, or 4. The electrochemistry of 1 and 2 is all the more inhibited by polyamine dendrimers as the dendrimer generation is higher. On the other hand, ferrocenes or other iron sandwich compounds containing hydroxy groups can reestablish reversible cyclic voltammograms. It is shown, using a tetra(ferrocenylmethylamine), that this phenomenon is due to hydrogen bond...

Chemicals and energy from biomass

Abstract: Approximately 89 million metric tonnes of organic chemicals and lubricants are produced annually in the United States (TM Carole, J Pellegrino, and MD Paster Appl Biochem Biotechnol 115, 871 (2004)) The majority of these materials are fossil fuel based and may load the environment during use and at the end of their life cycle Is- sues, such as disposal, pollution, and degradation, must be considered and weighed As a result, the need to decrease pollution caused by petrochemical usage is currently impelling the development of green technologies It is virtually inarguable that the dwindling hydrocarbon economy will eventually become unsustainable The cost of crude oil contin- ues to increase, while agricultural products see dramatic decreases in world market prices These trends provide suffi- cient basis for renewed interest in the use of biomass as a feedstock and for the development of a carbohydrate-based economy as the logical alternative to fossil fuel resources

Room-temperature NIR phosphorescence of new iridium (III) complexes with ligands derived from benzoquinoxaline

Abstract: A new series of new iridium (III) complexes (1–5) bearing ligands derived from benzoquinoxaline were designed and synthesized. X-ray structural analyses of 1 reveal a distorted octahedral geometry ...

Quantum mechanics studies of cellobiose conformations

Abstract: Three regions of the conformation space that describes the relative orientations of the two glucose residues of cellobiose were analyzed with quantum mechanics. A central region, in which most crys...

Novel synthesis of 2-naphthol Mannich bases and their NMR behaviour

Abstract: A novel two-step procedure involving the formation of 1-arylidene-2-tetralones from 2-tetralone and subsequent Michael addition of a cyclic secondary amine on the alkenone followed by in situ aeria...

DNA and RNA enzymes with peroxidase activity An investigation into the mechanism of action

Abstract: A DNA–hemin complex (PS2.M–hemin), and its RNA counterpart (rPS2.M–hemin), have previously been reported, in the presence of nitrogenous buffers such as HEPES, to show enhanced peroxidative activit...

Reconciling solvent effects on rotamer populations in carbohydrates - A joint MD and NMR analysis.

Abstract: The rotational preferences of the hydroxymethyl group in pyranosides is known to depend on the local environment, whether in solid, solution, or gas phase. By combining molecular dynamics (MD) simulations with NMR spectroscopy the rotational preferences for the ω angle in methyl 2,3-di-O-methyl-α-D-glucopyranoside (3) and methyl 2,3-di-O-methyl-α-D-galactopyranoside (6) in a variety of solvents, with polarities ranging from 80 to 2.3 D have been determined. The effects of solvent polarity on intramolecular hydrogen bonding have been identified and quantified. In water, the internal hydrogen bonding networks are disrupted by competition with hydrogen bonds to the solvent. When the internal hydrogen bonds are differentially disrupted, the rotamer populations associated with the ω angle may be altered. In the case of 3 in water, the preferential disruption of the interaction between HO6 and O4 destabilizes the tg rotamer, leading to the observed preference for gauche rotamers. Without the hydrogen bond enhan...

Biomimetic aromatization of Hantzsch 1,4-dihydropyridines with sodium periodate catalyzed by a new polystyrene-bound manganese porphyrin

Abstract: Efficient oxidation of Hantzsch 1,4-dihydropyridines with sodium periodate catalyzed by a polystyrene-bound manganese(III) porphyrin is reported. This catalyst shows high activity in the oxidation ...

Synthesis of β-hydroxy dithiocarbamate derivatives via regioselective addition of dithiocarbamate anion to epoxide in water

Abstract: The reactions of different dithiocarbamate anions with epoxides were investigated in water. With this method, β-hydroxy dithiocarbamate derivatives were synthesized in high yields. The reaction was also carried out in DMF in the presence of lithium perchlorate with a simple work-up procedure, and the results are compared.Key words: hydroxy dithiocarbamate, dithiocarbamate anion, epoxide, water.

Efficient RuIII-catalyzed condensation of indoles and aldehydes or ketones

Abstract: Synthesis of bis(indolyl)methanes through condensation of indoles and various aldehydes or ketones, using RuIII as catalyst, is reported. It was found that the catalytic system involving RuIII affo...

Cyclotrimerization approach to unnatural structural modifications of pancratistatin and other amaryllidaceae constituents — Synthesis and biological evaluation

Abstract: The phenanthridone core of pancratistatin lacking all aromatic oxygenation was prepared by cyclotrimerization of acetylene-containing scaffolds 30 and 41, reflecting the natural and the C-1 epi con...

(–)-Sparteine-mediated stereoselective directed ortho metalation of ferrocene diamides

Abstract: The utility of (–)-sparteine-mediated directed ortho metalation (DoM) has been investigated in stereoselective preparation of planar chiral ferrocenes derived from 1,1′-N,N,N′,N′-tetraisopropylferrocenedicarboxamide (5). In the synthesis of C2-symmetric analogs of 5, the protocol (base, solvent, and two-step DoM) was found to be crucial for obtaining high enantio- and diastereo-selectivities of the products. A variety of highly enantioenriched mono and doubly functionalized derivatives of 5 have been synthesized. The synthetic applications of these compounds as chiral ligands in asymmetric alkylation of aldehydes and asymmetric palladium-catalyzed allylic substitutions have been demonstrated.Key words: directed ortho metalation, stereoselective deprotonation, ferrocene ligands, asymmetric catalysis.

Carbonate radical anion — Thermochemistry

Abstract: High level ab initio calculations along with isodesmic reactions have been used to derive a set of self-consistent free energies of formation for carbonate and nitrate species in the gas phase and in aqueous solution. The results show that HCO3· is a strong acid, pKa = –4.1, and that E°(CO3·–/CO32) = 1.23 ± 0.15 V.Key words: carbonate radical anion, theoretical, thermochemistry, acidity, reduction potentials.

A simple and facile solventless procedure for the cyclization of 2′-amino- and 2′-hydroxy-chalcones using silica-supported sodium hydrogen sulphate as heterogenous catalyst

Abstract: A simple environmentally friendly method for the cyclization of 2′-amino- and 2′-hydroxy-chalcones under solventless conditions using silica-supported sodium hydrogen sulphate has been reported.Key...

Medium effects on the α-effect in DMSO-H2O mixtures - : Comparative studies of p-nitrophenyl benzoate and acetate -Dissection of ground-state and transition-state effects

Abstract: In a study of the origin of the α-effect and its dependence on the nature of the reaction medium as well as structural effects, we report herein a kinetic study of the reactions of p-nitrophenyl be...

Complexation of diazinon, an organophosphorus pesticide, with α-, β-, and γ-cyclodextrin NMR and computational studies

Abstract: Complexation of the organophosphorus pesticide, diazinon, with α-, β- and γ- cyclodextrin has been investigated through NMR and computational methodologies. Binding constants (Kb) determined by 1H ...

Cucurbit[7]uril host-guest complexes with cationic bis(4,5-dihydro-1H-imidazol-2-yl) guests in aqueous solution

Abstract: The host–guest interactions between cucurbit[7]uril and a series of novel cationic bis(4,5-dihydro-1H-imidazol-2-yl)arene and 1-(4,5-dihydro-1H-imidazol-2-yl)- and 1,3-bis(4,5-dihydro-1H-imidazol-2...

Indium(I) iodide promoted cleavage of dialkyl disulfides Application of the Michael addition of thiolate anions to conjugated carbonyl compounds and regioselective ring opening of epoxides

Abstract: Indium(I) iodide promotes cleavage of dialkyl disulfides generating thiolate anions that then undergo facile addition to α,β-unsaturated ketones, aldehydes, carboxylic esters, and nitriles under ne...

Antimony(III) chloride impregnated on alumina — An efficient and economical Lewis acid catalyst for one-pot synthesis of dihydropyrimidinones under solvent-free conditions

Abstract: The antimony(III) chloride impregnated on alumina efficiently catalyses a one-pot, three-component condensation reaction among an aldehyde, a β-ketoester, and urea or thiourea to afford the corresponding dihydropyrimidinones in good to excellent yields. The reactions are probed in microwave (MW), ultrasonic, and thermal conditions and the best results are found using MW under solvent-free conditions.Key words: Biginelli dihydropyrimidinones synthesis, SbCl3–Al2O3, MW, sonication, solid supported.

Syntheses, characterization, and crystal structures of the tetramethylammonium salts of the novel weakly coordinating anions [MeCO2{B(C6F5)3}] and [MeCO2{B(C6F5)3}2]

Abstract: The novel compounds [Me4N][MeCO2{B(C6F5)3}] and [Me4N][MeCO2{B(C6F5)3}2] are prepared and characterized spectroscopically and crystallographically. The compounds are salts of the unisolable acids M...

Synthesis of 8-homocastanospermine

Abstract: The 1,3-dipolar cycloaddition of a five-membered cyclic nitrone derived from malic acid (4) and unsaturated D-threo-hexaldonolactone (1) leads to a single adduct 6, which can be transformed into th...

Rhodium(I) acetylacetonato complexes containing phosphinoalkynes as catalysts for the hydroboration of vinylarenes

Abstract: Three novel rhodium(I) acetylacetonato (acac) complexes bearing phosphinoalkynes (Ph2PC≡C-t-Bu, Ph2PC≡CPPh2, and Ph2PC≡CC≡CPPh2) have been prepared and characterized fully. Addition of B2cat3 (cat = 1,2-O2C6H4) to Rh(acac)(Ph2PC≡C-t-Bu)2 (1a) led to zwitterionic Rh(η6-catBcat)(Ph2PC≡C-t-Bu)2 (2a), the first example of this type of compound to contain monodentate phosphine ligands. All new rhodium complexes have been investigated for their ability to catalyse the hydroboration of vinylarenes.Key words: catalysis, hydroboration, phosphinoalkynes, regioselectivity, rhodium.

One-pot, solvent-free synthesis of α-aminonitriles under catalysis by magnesium bromide ethyl etherate

Abstract: A three-component, efficient, and facile procedure has been developed for the synthesis of α-aminonitriles from aldehydes, amines, and trimethylsilyl cyanide using a catalytic amount of magnesium b...

A novel and green version of the Passerini reaction in an ionic liquid ([bmim][BF4])

Abstract: The Passerini three-component condensation among a carboxylic acid (1), an aldehyde or ketone (2), and an isocyanide (3) was carried out for the first time in an ionic liquid, [bmim][BF4], and a se...

An examination of VANOL, VAPOL, and VAPOL derivatives as ligands for asymmetric catalytic Diels–Alder reactions

Abstract: Several derivatives of the vaulted biaryl ligand VAPOL were prepared and evaluated as chiral ligands for aluminum Lewis acids in the catalytic asymmetric Diels–Alder reactions of methyl acrylate an...

One-electron oxidation of methionine peptides — Stability of the three-electron S—N(amide) bond

Abstract: The possibility of sulfur–nitrogen (S—N) three-electron bond formation in a one-electron oxidized methionine peptide model was investigated computationally following the detection of such species in pulse radiolysis experiments (C. Schoneich, D. Pogocki, G.L. Hug, and K. Bobrowski. J. Am. Chem. Soc. 125, 13700 (2003)). Geometry optimiza tions were carried out at the B3LYP/6-31G(d) level of theory. Relative free energies in aqueous solution at pH 7 were predicted for all intermediates with enthalpy evaluations at the CCSD(T)/6-31+G(d′) level and free energies of solvation predicted using a continuum model (CPCM). Both the initial oxidation product and the intermediate formed at higher pH were identified as cyclic S—N bonded species in which the intramolecular three-electron interaction is between the S atom and the π orbital of the amide group. TD-B3LYP calculations of the UV spectra support the assignments. A mechanism for the conversion to the most stable α-C-centered radical is proposed. The mechanism i...

Small bite-angle diphosphines — Synthesis and structure of low-valent complexes of bis(di-ortho-tolylphosphino)methane (dotpm) and related ligands

Abstract: The coordination chemistry of bis(di-ortho-tolylphosphino)methane (dotpm) has been studied. It is an excellent chelating ligand and a range of low-valent mononuclear complexes have been prepared; cis-[M(CO)(4)(eta(2)-dotpm)] (M = Cr, Mo, W; 1-3), [CpRuCl(eta(2)-dotpm)] (4), and cis-[MX2(eta(2)-dotpm)] (M = Pt, X = Cl, Br, I; 5a-5c, M = Pd, X = Cl; 6). The backbone protons are relatively acidic and can be deprotonated using n-BuLi or LiN(SiMe3)(2). Subsequent alkylation by RX (X = halogen; R = Me, Et, CH2Ph) affords cis-[M(CO)(4)(eta(2)-Rdotpm)] (M = Cr, Mo, W, R = Me; 7-9, M = Mo, W, R = Et, CH2Ph; 12-15), [CpRuCl(eta(2)-Medotpm)] (10), and cis-[PtI2(eta(2)-Medotpm)] (11). Thermolysis of cis-[Mo(CO)(4)(eta(2)-Medotpm)] (8) yields what is believed to be the coordinately and electronically unsaturated complex [Mo(CO)(3)(eta(2)-Medotpm)] (16), suggesting that derivatives of dotpm (cone angle 194 degrees) are bulky enough to stabilize a 16-electron complex. Crystal structures of 2, 3, 7-9, 13, and 14 have been determined (diphosphine bite angles ranging from 66.58(3)degrees to 70.96(5)degrees.

Organogold(I) macrocycles and [2]catenanes containing pyridyl and bipyridyl substituents Organometallic catenanes as ligands

Abstract: The synthesis of achiral gold(I) macrocycles [RCH(4-C6H4OCH2C≡CAu)2(µ-Ph2PZPPh2)] and the corresponding chiral gold(I) [2]catenanes, bearing substituents R = 2-pyridyl, 4-pyridyl, and 4-(2,2′-bipyridyl), is reported. The gold(I) compounds form by self-assembly on reaction of oligomeric digold(I) diacetylides [{RCH(4-C6H4OCH2C≡CAu)2}n] or the isocyanide complexes [RCH(4-C6H4OCH2C≡CAuC≡N-t-Bu)2] with diphosphine ligands Ph2PZPPh2, Z = CC or (CH2)n with n = 2–5, or on reaction of [Au2(O2CCF3)2(µ-Ph2PZPPh2)] with diacetylenes RCH(4-C6H4OCH2C≡CH)2 in the presence of a base. The equilibrium between macrocycles and chiral [2]catenanes in solution was established by NMR spectroscopy, while the structures of several [2]catenanes in the solid state were established crystallographically. The coordination of the gold(I) compounds with R = 4-(2,2′-bipyridyl) to platinum(IV), by formation of the corresponding [PtIMe3(bipy)] units, is established, showing that organometallic [2]catenanes can act as ligands.Key words: go...

Component analysis of the X-C-Y anomeric effect (X = O, S; Y = F, OMe, NHMe) by DFT molecular orbital calculations and natural bond orbital analysis

Abstract: Six 2-Y-substituted oxacyclohexane and thiacyclohexane heterocycles (Y = F, OMe, NHMe) were examined using DFT molecular orbital calculations. Natural bond orbital (NBO) analysis of the total energy behaviour yielded the orbital-interaction factors contributing to the conformational equilibria. The dipole moments of the optimized systems were used to estimate the electrostatic contributions to the anomeric effect. The primary determinant of the X-C-Y anomeric effect was found to be the orbital interaction components associated with the combined endo- and exo-anomeric effects acting in concert in the axial conformers. Electrostatic interactions made a contribution to the observed conformer stabilization in all cases, but did not account for the relative magnitudes of the energy differences among conformers of homologous molecules. In the case of the methylamino substituent, accentuated steric interactions in the axial conformer precluded stabilization by the exo-anomeric interaction and consequently, the n...

Hydrosilylation of ketones catalyzed by C2-symmetric proline-derived complexes

Abstract: Extracoordinate chiral hydrosilanes were generated in situ from triethoxysilane and a C2-symmetric ligand derived from bisproline 7. In the presence of a catalytic amount of ligand 7, prochiral ket...