Showing papers in "Canadian Journal of Chemistry in 2005"

Review of gold(I) N-heterocyclic carbenes

Abstract: This review presents an overview of the work on Au(I)–NHC chemistry. The efficiency of different synthetic strategies of Au(I)–NHCs is discussed. Transmetallation of Ag(I)–NHCs appears to be an easy method as compared with the others. The influence of aurophilicity "a traditional property of a Au(I) center" in making the supramolecular assemblies is also covered. The combination of the Au(I) center with NHCs has great potential in the fields of medicine, catalysis, liquid crystal, and optoelectronic.Key words: gold–carbenes, silver–carbenes, carbene transfer, aurophilicity.

Review on green chemistry — Suzuki cross coupling in aqueous media

Abstract: The Suzuki cross-coupling reaction is a very efficient, reliable, and environmentally friendly method for the introduction of novel carbon–carbon bonds into molecules. This review summarizes recent...

InCl3·4H2O-promoted green preparation of xanthenedione derivatives in ionic liquids

Abstract: A green procedure for the synthesis of xanthenedione derivatives (3) through InCl3·4H2O-promoted condensation of aldehydes (1) and 5,5-dimethyl-1,3-cyclohexanedione (2) in ionic liquids is described in this paper. This novel method has such advantages as operational simplicity and environmental benignancy together with enhanced atom utilization. Moreover, the reaction media and the catalyst can be recovered conveniently and reused effectively for at least six times.Key words: ionic liquid, xanthenedione derivatives, indium trichloride, green synthesis.

Research inspired by the chemistry of nitrogenase Novel metal complexes and their reactivity toward dinitrogen, nitriles, and alkynes

Abstract: Summarized here are our continuous studies of the last three decades concerning syntheses of new types of complexes learned from nitrogenase and their reactivites toward dinitrogen, nitriles, and a...

Activation of methane by gaseous platinum(II) ions PtX+ (X = H, Cl, Br, CHO)

Abstract: The gas-phase reactions of methane with the platinum(II) ions PtX+ with X = H, Cl, Br, and CHO are studied by mass spectrometry. The PtX+ ions are generated by electrospray ionization of methanolic...

Low-coordinate iron complexes as synthetic models of nitrogenase

Abstract: Three-coordinate iron sites are potentially important intermediates in the reduction of dinitrogen by the enzyme nitrogenase, but synthetic work to outline the behavior of three-coordinate iron com...

Synthesis of tungsten complexes that contain hexaisopropylterphenyl-substituted triamidoamine ligands, and reactions relevant to the reduction of dinitrogen to ammonia

Abstract: [HIPTN3N]WCl (WCl) can be synthesized readily by adding H3[HIPTN3N] to WCl4(DME) followed by LiN(SiMe3)2 ([HIPTN3N]3– = [(HIPTNCH2CH2)3N]3– where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = HexaIsoPropylTe...

In vitro and in vivo studies of neutral cyclometallated complexes against murine leukæmias

Abstract: Cyclometallated µ-halogeno dimers derived from nitrogen donor ligands (1-phenylpyrazoles, 2-phenylpyridine, and 1-(2′-pyridyl)indole) were treated with unidentate nitrogen and phosphorus donor liga...

Synthesis of acetylenic ketones by a Pd-catalyzed carbonylative three-component coupling reaction in [bmim]PF6

Abstract: A carbonylative three-component coupling reaction of aryl iodides with terminal alkynes catalyzed by PdCl2(PPh3)2 was carried out using an ionic liquid, [bmim]PF6, as the reaction medium, which res...

Structural analysis of acetylated hardwood lignins and their photoyellowing properties

Abstract: Lignin was isolated from aspen bleached chemithermomechanical pulp by employing a mild acid hydrolysis procedure, and the extracted material was acetylated with acetic anhydride. Nuclear magnetic resonance analyses indicated that the relative ease of acetylating lignin hydroxyl groups was phenolic >> γ-side chain > α-side chain. Non-acetylated and acetylated lignins were impregnated onto cellulosic test sheets, and the photo-behavior of the lignins was examined under irradiation with two light sources, a fluorescent lamp and a black lamp. Optical reflective studies indicated acetylation efficiently inhibited the photodiscoloration of aspen bleached chemithermomechanical pulp lignin under visible and near-UV light irradiation. The photostability of the lignin was correlated to the extent of lignin acetylation. The observed photo-stabilization of acetylated lignin during light irradiation was attributed to the acetylation of phenoxy and aliphatic hydroxyl groups in lignin.Key words: green chemistry, hardwoo...

Fragmentation pathways of negative ions produced by electrospray ionization of acyclic dicarboxylic acids and derivatives

Abstract: Fragmentation pathways have been studied on the monoanions formed during electrospray ionization of a wide range of aliphatic dicarboxylic acids and their monoesters. All negative ion spectra were obtained from alcoholic or aqueous methanolic solutions without buffers or adjustment of pH, using either a Finnigan LCQ ion trap or a VG-Micromass Quattro triple quadrupole mass spectrometer. Fragmentation pathways were studied using collision-induced dissociation and isotopic-labelling techniques. Two primary fragmentation pathways of the dicarboxylic acid monoanions were observed, namely decarboxylation of the non-ionized carboxyl group and loss of water from this group. The fragmentations were strongly dependent on the chain lengths of the diacids. In the case of a monoester anion, loss of a molecule of alcohol paralleled the loss of water from the diacid monoanion. Losses of water or alcohol were shown to lead to formation of reactive ynolate anions (HOOC(CH2)xC≡CO–, x = 3–9), which in the ion trap spectrom...

Early developments in lanthanide-based dinitrogen reduction chemistry

Abstract: Although the first crystallographically characterized lanthanide dinitrogen complex was reported in 1988 with samarium, it is only in recent years that this field has expanded to include fully characterized examples for the entire series of lanthanides. The development of lanthanide dinitrogen chemistry has been aided by a series of unexpected results that present some good lessons in the development of science. This review presents a chronological account of the lanthanide dinitrogen chemistry discovered in our laboratory through the summer of 2004.Key words: lanthanides, dinitrogen, reduction, alkali metal, nitrogen fixation, diazenido.

Comparison of the nucleophilicities of alcohols and alkoxides

Abstract: The kinetics of the reactions of benzhydrylium ions with some alcohols and alkoxides dissolved in the corresponding alcohols were photometrically investigated. Using the correlation equation log k (20 °C) = s(E + N), the N and s parameters of methoxide, ethoxide, n-propoxide, and isopropoxide in alcohol–acetonitrile (91:9, v/v) were determined. The cosolvent acetonitrile has only a little influence on the rate constants of the reactions of alcohols and alkoxides. The order of N values (OH– << MeO– < EtO– < n-PrO– < i-PrO–) shows that alkoxides differ only moderately in reactivity but are considerably more nucleophilic than hydroxide. As a consequence, the nucleophilic reactivity of a 0.5 mmol/L aqueous hydroxide solution increases by a factor of 13 when 10% (v/v) methanol is added. In 1–10 mmol/L alkoxide solutions in alcohols, weak electrophiles react considerably faster with alkoxides than with the corresponding alcohols. With increasing electrophilicity, the preference for alkoxides decreases, and elec...

Synthesis and characterization of cationic iron complexes supported by the neutral ligands NPi-Pr3, NArPi-Pr3, and NSt-Bu3

Abstract: This paper compares the local geometries, spin states, and redox properties of a series of iron complexes supported by neutral, tetradentate NP_3 (tris(phosphine)amine) and NS_3 (tris(thioether)amine) ligands. Our consideration of an Fe-mediated N_2 fixation scheme similar to that proposed by Chatt for molybdenum motivates our interest in systems of these types. This report specifically describes the synthesis and characterization of cationic Fe(II) chloride complexes supported by the neutral ligands NP^(i-Pr)_3 (NP^(i-Pr)_3 = [N(CH_2CH_2P-i-Pr_2_)3]), NArP^(i-Pr)_3 (NArP^(i-Pr)_3 = [N(2-diisopropylphosphine-4-methylphenyl)_3]), and NS^(t-Bu)_3 (NS^(t-Bu)_3 = [N(CH_2CH_2S-t-Bu)_3]). The solid-state structures, electrochemistry,and magnetic properties of these complexes are reported. Whereas the NPV(i-Pr)_3 and NArP^(i-Pr)_3 ligands provide pseudotetrahedral S = 2 ferrous cations [Fe(NP^(i-Pr)_3)Cl]PF_6 (1[PF_6]) and [Fe(NArP^(i-Pr)_3)Cl]BPh_4 (2[BPh_4]) featuring a long Fe—N bond distance, the NS^(t-Bu)_3 ligand gives rise to a trigonal bipyramidal structure with a S = 1 ground state and a much shorter Fe–N interaction. The complexes 1[BPh_4] and 2[BPh_4] can be reduced under CO to give rise to the five-coordinate Fe(I) monocarbonyls [Fe(NP^(i-Pr)_3)CO]BPh_4 (4[BPh_4]) and [Fe(NAr^(Pi-Pr)_3)CO]BPh_4 (5[BPh_4]). The solidstate structures and electrochemistry of 4[BPh_4] and 5[BPh_4] are described, as is the EPR spectrum of 4[BPh_4]. The synthesis and characterization of the hydride–dinitrogen complex [Fe(NP^(i-Pr)_3)(N_2)(H)]PF_6 (6[PF_6]) has also been accomplished and its properties are also reported.

Palladium-catalysed synthesis of nonsymmetrically disubstituted-1,1'-biphenyls from o-substituted aryl iodides through aryl coupling and delayed hydrogenolysis

Abstract: In the presence of Pd(OAc)2 and norbornene as catalysts, two molecules of an ortho-substituted aryl iodide undergo aryl–aryl coupling to a palladium-bonded biphenylyl intermediate, which is hydroge...

Oxidative addition chemistry of dimethyl(dipyridyl ketone)platinum(II)

Abstract: The dimethylplatinum(II) complex [PtMe2(DPK)] (DPK = di-2-pyridyl ketone) undergoes easy oxidative addition to give platinum(IV) complexes. For example, reaction of [PtMe2(DPK)] with MeI gave [PtIM...

Thermodynamics of organic mixtures containing amines. IV. Systems with aniline

Abstract: Binary mixtures of aniline with benzene, toluene, alkane, alkanol, or N,N-dialkylamide have been investigated in the framework of the DISQUAC model. The reported interaction parameters change regul...

Functionalization and cleavage of coordinated dinitrogen via hydroboration using primary and secondary boranes

Abstract: The reaction of the side-on, end-on ditantalum dinitrogen complex ([NPN]Ta)2(µ-η1:η2-N2)(µ-H)2 (where NPN = PhP(CH2SiMe2NPh)2) with a variety of secondary and primary boranes is reported. With 9-BB...

Fluorinated 9-borafluorenes vs. conventional perfluoroaryl boranes Comparative Lewis acidity

Abstract: Perfluorinated 9-phenyl-9-borafluorene, 1, is an antiaromatic analog of the well-known tris(pentafluorophenyl)borane. Spectroscopic, structural, and electrochemical studies have been performed on 1 and its Lewis base adducts with MeCN, THF, and PMe3 with a view to assessing its comparative Lewis acid strength relative to B(C6F5)3. For the sterically undemanding Lewis base MeCN, 1 and B(C6F5)3 have comparable LA strengths, while for more sterically prominent THF, 1 is clearly the stronger Lewis acid (LA) based on competition experiments. We conclude that steric factors, rather than antiaromaticity, are the most important determinants in the LA strength differences between 1 and B(C6F5)3.Key words: boranes, Lewis acids, fluorinated compounds, heterocycles.

Ligand-assisted reduction of Co(II) to Co(I) and subsequent coordination of dinitrogen

Abstract: Reaction of the bis-aminopyridine dianion {[2,6-[2,6-(i-Pr)2PhN-C=(CH2)]2(C5H3N)]Li(THF)}{Li(THF)4} with CoCl2(THF)1.5 under Ar afforded the dinuclear complex {[2,6-(i-Pr)2PhN-C=(CH2)](C5H3N)[2,6-(i-Pr)2PhN=C(CH2)]}2[Co(µ-Cl)Li(THF)3]2·4(THF) (1) in which the ligand is coupled to a second identical unit at a terminal methylene carbon. In turn, the C—C bond formation caused reduction of the Co(II) center to the monovalent state. The same reaction performed under a nitrogen atmosphere afforded the double dinitrogen complex {[2,6-(i-Pr)2PhN-C=(CH2)](C5H3N)[2,6-(i-Pr)2PhN=C(CH2)]}2[Co(N2)]2·2(toluene) (2). Key words: low-valent Co, diiminopyridinato, dinitrogen fixation.

2003 alcan award lecture : Roles of the adjacent metals in the coupling of methylene groups promoted by heterobinuclear complexes of group 8 and 9 metals

Abstract: The reactivities of the heterobinuclear complexes, [MM′(CO)4(dppm)2][X] (MM′ = RhOs, RhRu, IrRu; dppm = µ-Ph2PCH2PPh2; X– = BF4–, CF3SO3–) with diazomethane are reported. The RhOs species reacts to give three products of methylene-group incorporation, depending on the temperature; at –80 °C the methylene bridged product, [RhOs(CO)4(µ-CH2)(dppm)2][X], is formed exclusively, at ambient temperature only [RhOs(η1-C3H5)(CH3)(CO)3(dppm)2][X], having the allyl group bound to Rh and the methyl group bound to Os, is obtained, while at intermediate temperatures [RhOs(η1:η1-C4H8)(CO)3(dppm)2][X], having the butanediyl fragment chelating on Os, is generated. Based on labeling studies a mechanism is proposed rationalizing formation of the different products. Under the same range of conditions the Rh/Ru and Ir/Ru species yield only the methylene bridged products, [MM′(CO)4(µ-CH2)(dppm)2][X] (MM′ = RhRu, IrRu). A rationalization for the different reactivities observed and a description of the roles of the different meta...

Aromatization of 1,4-dihydropyridines with selenium dioxide

Abstract: 1,4-Dihydropyridines were aromatized to corresponding pyridines using stoichiometric selenium dioxide at ambient temperature in a yield of 87%~98%.Key words: 1,4-dihydropyridines, aromatization, oxidation, pyridine derivatives, selenium dioxide.

Synthesis of some heterocyclic systems of anticipated biological activities via 6-aryl-4- pyrazol-1-yl-pyridazin-3-one

Abstract: 6-Aryl-4-pyrazol-1-yl-pyridazin-3-one (1) reacted with a PCl5–POCl3 mixture to give the 3-chloropyridazine derivative 3. Reaction of 3 with 2-hydroxybenzoylhydrazide and semicarbazide hydrochloride afforded 4 and 5. Reaction of 1 with ethyl chloroacetate gave 8. Reaction of 8 with hydrazine hydrate yielded the hydrazide 9. The hydrazide 9 condensed with the acetylenic ketones and esters 10a–10d and acetylacetone to give the adducts 11a, 11b, 12, 13, and 14. Reacting 1 with formaldehyde and piperidine, morpholine, or piperazine, 3-bromopropanoic acid, acetic anhydride, p-toluenesulphonyl chloride, succinyl chloride, oxalyl chloride, ethanolamine, or ethyl chloroacetate gave the adducts 15–22. The structures of all newly synthesized compounds were evidenced from their spectral and microanalytical data. Key words: 6-aryl-4-pyrazol-1-yl-pyridazinone derivative, 6-aryl-3-chloropyridazine derivative, 3,6-diaryl-1,2,4-triazino[4,3-b]pyridazine derivative, 6-aryl-3-ethoxycarbonylmethoxypyridazine derivative, 6-ar...

Pd(0)PhCOOH catalyzed addition of oxygen pronucleophiles to allenes and internal alkynes

Abstract: We have developed a catalytic system that enables the addition of alcohols to allenes using a combination of 5 mol% Pd(PPh3)4 and 10 mol% benzoic acid. Likewise, the addition reaction of carboxylic...

Oxazoline chemistry. Part VIII. Synthesis and characterization of a new class of pincer ligands derived from the 2-(o-anilinyl)-2-oxazoline skeleton Applications to the synthesis of group X transition metal catalysts

Abstract: The synthesis and characterization of a new and readily synthesized class of potentially anionic pincer ligands with C1 point group symmetries is described. These materials can be made via amide co...

Kinetic isotope effect evidence for the concerted transfer of hydride and proton from hydroxycyclopentadienyl ruthenium hydride in solvents of different polarities and hydrogen bonding ability

Abstract: The tolyl analogue of Shvo's hydroxycyclopentadienyl ruthenium hydride (4) efficiently transfers a hydride and proton to benzaldehyde or acetophenone to produce an alcohol. This reduction can be performed in toluene, methylene chloride, and THF. Reduction of benzaldehyde in toluene and methylene chloride occurs approximately 300 times faster than in THF at 0 °C. Reduction of acetophenone occurs between 75 and 150 times slower than benzaldehyde at 0 °C in each respective solvent. Despite the differences in rate, mechanistic studies have provided evidence for a similar concerted transfer of acidic and hydridic hydrogens in each solvent. Addition of water to THF led to further rate decrease coupled with an increase in the OH/D kinetic isotope effect and a decrease in the RuH/D kinetic isotope effect. Addition of excess alcohol to toluene or methylene chloride results in the significant retardation of the rate of reduction. The slower rate in THF and in the presence of alcohol is attributed to the stabilizati...

The importance of cyclopentadienyl substituent effects in group 4 metallocene dinitrogen chemistry

Abstract: This article highlights some of our recent efforts and presents new data on the importance of cyclopentadienyl substituent effects on group 4 metallocene dinitrogen chemistry. Reactions such as the coordination of N2 to an isolated titanium sandwich complex, alkali-metal reductions of zirconocene dihalide complexes, alkane reductive elimination reactions, and the hydrogenation of zirconium dinitrogen complexes are all extremely sensitive to the groups present on the cyclopentadienyl rings. These results are promising for the future of N2 fixation, as the reactivity of a specific metallocene can be dramatically altered by subtle manipulations in ligand substituents.Key words: cyclopentadienyl, zirconium, dinitrogen, ammonia, sandwich.

Efficient one-pot transformation of aminoarenes to haloarenes using halodimethylisulfonium halides generated in situ

Abstract: Halodimethylsulfonium halide 1, which is readily formed in situ from hydrohaloic acid and DMSO, is a good nucleophilic halide. This activated nucleophilic halide rapidly converts aryldiazonium salt...

A practical guide to arylbiguanides Synthesis and structural characterization

Abstract: Monohydrochloride salts of diverse 1-arylbiguanides and 1,5-diarylbiguanides were synthesized by the reaction of anilinium chlorides with dicyandiamide or sodium dicyanamide, and the biguanidinium ...

Bonding, activation, and protonation of dinitrogen on a molybdenum pentaphosphine complex Comparison to trans-bis(dinitrogen) and -nitrile dinitrogen complexes with tetraphosphine coordination

Abstract: The molybdenum-N2 pentaphosphine complex (Mo(N2)(dpepp)(dppm)) (1) containing a bi- and a tridentate phosphine ligand (dpepp = PhP(CH2CH2PPh2)2 ,d ppm =P h 2PCH2PPh2) has been prepared and characterized. By pro- tonation of 1 with triflic acid the NNH2 complex (Mo(NNH2)(dpepp)(dppm))(CF3SO3)2 (2) is formed without loss of the pentaphosphine coordination. The electronic properties of 1 and 2 and their 15 N and (or) 2 H counterparts are inves- tigated by NMR, IR, and Raman spectroscopy coupled to DFT frequency and NMR shift calculations. Force constants are evaluated from experimental frequencies and isotope shifts by the quantum chemistry based normal coordinate anal- ysis procedure (QCB-NCA). The results for the N2 complex 1 are compared with those obtained earlier for bis(dinitrogen) and trans-nitrile dinitrogen systems. Importantly, the N2 in the pentaphosphine complex is more strongly activated com- pared to corresponding bis(dinitrogen) compounds and more weakly activated compared to trans-nitrile N2 systems. The activation of the NNH2 ligand in complex 2 is similar to trans-nitrile systems and weaker compared to correspond- ing NNH2 complexes with coordinated anions like (MoF(NNH2)(dppe)2)(BF4). These results are discussed based on the relative donor-acceptor properties of the respective trans ligands, demonstrating the influence of σ donation and π ac- ceptance on the activation of N2 in transition metal complexes.