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1.
Acta Crystallogr E Crystallogr Commun ; 75(Pt 9): 1336-1338, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31523461

RESUMO

The title compound, C7H4F3NO2, 3-tri-fluoro-methyl-1H-pyrrolo-[1,2-c]oxazol-1-one, is the first crystal structure of the pyrrolo-[1,2-c]oxazole ring system: the fused ring system is almost planar (r.m.s. deviation = 0.006 Å). In the crystal, weak C-H⋯O and C-H⋯F hydrogen bonds link the mol-ecules into [001] chains and π-π stacking inter-actions consolidate the structure.

2.
Dalton Trans ; 47(44): 15801-15807, 2018 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-30357238

RESUMO

Herein we report on the synthesis, characterization and the ensuing chemistry of iminophosphorane palladacycles. Treatment of Ph3P[double bond, length as m-dash]N-(2-OHC6H4), 1, with sodium tetrachloropalladate gives 2 with the ligand as terdentate [C,N,O] allowing for only one µ-Cl ligand bonding the metal centers, resulting in a dinuclear complex. Treatment of 2 with PPh3 gives the mononuclear complex 3, whereas the reaction of 2 with diphosphanes Ph2P(CH2)nPPh2 in 1 : 2 ratio gives mixtures of 4 and 5 (n = 2) and 6 and 7 (n = 3). From them, the mononuclear complexes 4 and 6, and the dinuclear compounds, 5 and 7, were obtained with the parent ligand as bidentate [C,N]. The former two are of zwitterionic nature void of any counterion, with the phosphane ligand in the chelating mode. In a remarkable case of chemical serendipity, a solution of 2 left to stand produced crystals of complex 8: this is the missing link in the series of triphenylphosphane chalcogenide metallacycles. The experiment is repeatable; however, direct metallation of triphenylphosphane oxide was not possible.

3.
Dalton Trans ; 47(21): 7118-7122, 2018 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-29721560

RESUMO

A unique self-assembled mixed-valence FeII-FeIII tetranuclear star has been comprehensively characterised showing a large magnetic anisotropy at the peripheral FeII centres, ferromagnetic coupling between the iron centres and field-induced SMM behaviour.

4.
Chemistry ; 23(26): 6255-6258, 2017 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-28301065

RESUMO

The potential of 15-crown-5 ethers to link large cations, such as potassium, is limited by the quasi-parallel arrangement of two oxygen donor moieties upon appropriate orientation of the corresponding ether-ring-containing molecules. Substrates bearing the two crown ethers that are capable of achieving such coordination are hitherto unknown. The synthesis and isolation of a tailor-made dinuclear palladacycle bearing 15-crown-5 ether rings on the metallated phenyls offers such a possibility, providing the adequate environment for the formation of the sandwiched [K(metallacycle-15-crown-5)2 ] moiety. This synthetic strategy also culminates in the isolation of the first palladacycle able to entrap a potassium cation through bonding to two 15-crown-5 ether rings in a single molecule.

5.
Inorg Chem ; 55(24): 12568-12582, 2016 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-27989199

RESUMO

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)pyridine) derivatives, [MnBr(CO)3(IP)], are demonstrated as a new group of catalysts for CO2 reduction, which represent the first example of utilization of (phenylimino)pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV-vis-IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical-chemical-electrochemical) formation of a five-coordinate anion [Mn(CO)3(IP)]-, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)imino)methyl]pyridine), TBIMP (2-[((2-tert-butylphenyl)imino)methyl]pyridine), and TBIEP (2-[((2-tert-butylphenyl)imino)ethyl]pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr(CO)3(IMP)] (2-[(phenylimino)methyl]pyridine) by the stepwise formation of such a monoanion via an ECEC(E) mechanism involving also the intermediate Mn-Mn dimer [Mn(CO)3(IMP)]2. The complex [MnBr(CO)3(IPIMP)] (2-[((2-diisopropylphenyl)imino)methyl]pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO2 the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO2, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO2 binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. -2.2 V vs Fc/Fc+), recovering [Mn(CO)3(IP)]- and triggering the catalytic production of CO.

6.
Org Biomol Chem ; 14(46): 10953-10962, 2016 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-27819376

RESUMO

Simple haloaldehydes, including enolisable aldehydes, were found to be suitable for the formation of cyclic products by cascade (domino) condensation, cyclisation, dipolar cycloaddition chemistry. This multi-component reaction approach to heterocyclic compounds was explored by using hydroxylamine, a selection of aldehydes, and a selection of activated dipolarophiles. Initial condensation gives intermediate oximes that undergo cyclisation with displacement of halide to give intermediate nitrones; these nitrones undergo in situ intermolecular dipolar cycloaddition reactions to give isoxazolidines. The cycloadducts from using dimethyl fumarate were treated with zinc/acetic acid to give lactam products and this provides an easy way to prepare pyrrolizinones, indolizinones, and pyrrolo[2,1-a]isoquinolinones. The chemistry is illustrated with a very short synthesis of the pyrrolizidine alkaloid macronecine and a formal synthesis of petasinecine.


Assuntos
Óxidos de Nitrogênio/química , Oximas/química , Oximas/síntese química , Alcenos/química , Ciclização , Reação de Cicloadição
7.
Dalton Trans ; 45(44): 17598-17601, 2016 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-27774544

RESUMO

Herein we report a Suzuki-Miyaura type cross-coupling between an aryl halide and a functionalized boronic acid palladacycle in the absence of an external catalyst. This reaction is an unprecedented case of catalysis in palladium metallacycle chemistry.

8.
J Org Chem ; 81(18): 8386-93, 2016 09 16.
Artigo em Inglês | MEDLINE | ID: mdl-27529354

RESUMO

A range of 7-oxo, 8-oxo, and 9-oxo amino acids, analogues of 8-oxo-2-aminodecanoic acid, one of the key components of the cyclic tetrapeptide apicidin, have been prepared by a three-step process involving copper-catalyzed allylation of serine-, aspartic acid-, and glutamic acid-derived organozinc reagents, followed by cross-metathesis of the resulting terminal alkenes with unsaturated ketones and hydrogenation. The intermediate 7-oxo-5-enones underwent a highly diastereoselective (dr ≥96:4) acid-catalyzed aza-Michael reaction to give trans-2,5-disubstituted pyrrolidines, 5-substituted proline derivatives. The aza-Michael reaction was first observed when the starting enones were allowed to stand in solution in deuterochloroform but can be efficiently promoted by catalytic amounts of dry HCl.

9.
Chemistry ; 22(35): 12430-8, 2016 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-27465819

RESUMO

Ten borylated bipyridines (BOBIPYs) have been synthesized and selected structural modifications have been made that allow useful structure-optical property relationships to be gathered. These systems have been further investigated using DFT calculations and spectroscopic measurements, showing blue to green fluorescence with quantum yields up to 41 %. They allow full mapping of the structure to determine where selected functionalities can be implemented, to tune the optical properties or to incorporate linking groups. The best derivative was thus functionalised with an alkyne linker, which would enable further applications through click chemistry and in this optic, the stability of the fluorophores has been evaluated.


Assuntos
Alquinos/química , Boratos/química , Corantes Fluorescentes/química , Química Click , Fluorescência
10.
IUCrJ ; 2(Pt 2): 188-97, 2015 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-25866656

RESUMO

A family of one-dimensional coordination polymers, [Ag4(O2C(CF2)2CF3)4(phenazine)2(arene) n ]·m(arene), 1 (arene = toluene or xylene), have been synthesized and crystallographically characterized. Arene guest loss invokes structural transformations to yield a pair of polymorphic coordination polymers [Ag4(O2C(CF2)2CF3)4(phenazine)2], 2a and/or 2b , with one- and two-dimensional architectures, respectively. The role of pre-organization of the polymer chains of 1 in the selectivity for formation of either polymorph is explored, and the templating effect of toluene and p-xylene over o-xylene or m-xylene in the formation of arene-containing architecture 1 is also demonstrated. The formation of arene-free phase 2b , not accessible in a phase-pure form through other means, is shown to be the sole product of loss of toluene from 1-tol·tol [Ag4(O2C(CF2)2CF3)4(phenazine)2(toluene)]·2(toluene), a phase containing toluene coordinated to Ag(I) in an unusual µ:η(1),η(1) manner. Solvent-vapour-assisted conversion between the polymorphic coordination polymers and solvent-vapour influence on the conversion of coordination polymers 1 to 2a and 2b is also explored. The transformations have been examined and confirmed by X-ray diffraction, NMR spectroscopy and thermal analyses, including in situ diffraction studies of some transformations.

11.
Dalton Trans ; 44(26): 11705-16, 2015 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-25683063

RESUMO

The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(II) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(II) complex. Pt(II) catecholates containing 2,2'-bipyridine-4,4'-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2'-bipyridine-4,4'-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(II) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-di(t)Bu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)((t)Bu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02­0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COO(I)Pr)2bpy)(3,5-di-(t)Bu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(II) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(II) complexes in general.

12.
Chem Sci ; 6(2): 1334-1340, 2015 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-29560220

RESUMO

Metal directed self-assembly has become a much-studied route towards complex molecular architectures. Although studies on mixed valence, MV, systems accessible through this approach are almost non-existent, the potential applications of such systems are very exciting as MV states provide the basis of a number of molecular-scale devices, including single electron wires and switches. Furthermore, while many novel hosts for guest ions and molecules have been developed through metal directed self-assembly, as these products tend to be kinetically labile, very few electrochemical studies have been reported. Herein, we report that the interplay between the binding properties and redox activity of a self-assembled trinuclear RuII macrocycle leads to an hitherto unreported phenomenon, in which access to specific MV states can be gated by host-guest chemistry. Thus, this system is the first in which MV states and the extent of electron delocalisation are switched by an ion without any change in electrochemical potential.

13.
Chem Sci ; 6(7): 4373-4374, 2015 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-30123453

RESUMO

[This corrects the article DOI: 10.1039/C4SC02799J.].

14.
Molecules ; 19(12): 21324-34, 2014 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-25529019

RESUMO

The synthesis and structural characterisation of phosphine-substituted alkynylboronates is reported. A P(III)-centred alkynylboronate (2) was prepared that showed little evidence for the conjugation of the P-lone pair to the boron via the alkyne π-system, as judged by X-ray crystallography studies of 2 and a related P(V) compound, 3. In addition, corresponding alkynyltrifluoroborate salts were prepared that showed improved stability by comparison to their boronic ester counterparts. These salts undergo Pd-catalysed cross-coupling reactions with aryl halides.


Assuntos
Ácidos Borônicos/síntese química , Fosfinas/síntese química , Cristalografia por Raios X , Sais
15.
Dalton Trans ; 43(46): 17509-18, 2014 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-25347546

RESUMO

The reaction of Fe(NCS)3 prepared in situ in MeOH with Hqsal-X (Hqsal-X = 5-X-N-quinolylsalicylaldimine) in CH2Cl2 yields the FeIII complexes, [Fe(qsal-X)2]NCS·solvent (X = F 1; X = Cl, 2, Br, 3 solvent = MeOH; X = I, solvent = 0.25CH2Cl2·0.5MeOH 4) in moderate to good yields. IR spectroscopy confirms that NCS− acts as a counteranion only and that the qsal-X ligand is bound to the FeIII centre. SQUID magnetometric studies reveal stepped hysteretic spin crossover in 1 and 2, which is abrupt in both steps in latter compound. Mössbauer spectroscopic studies of 1 and 2 support these conclusions. The bromo derivative, 3, undergoes half spin crossover up to 340 K while 4 is low spin at all temperatures measured. The spin transition temperature, T1/2 is found to increase on moving from F to Br. UV-Vis and NMR spectroscopic studies indicate that 1­4 have spin states intermediate between HS and LS in solution. Structural studies show that 1, 2 and 3 crystallize in triclinic P while 4 is in monoclinic P21/c. Crystallographic studies of 1 at 100, 200 and 270 K show that spin crossover proceeds from a [LS­LS] state through a [LS­HS] intermediate to a [HS­HS] state (LS = low spin, S = 1/2, HS = high spin, S = 5/2). Similar results are found for 3 although this time a [LS­IS] state exists at 123 K while a [LS­HS] state is found at 295 K (IS = intermediate spin state where partial spin crossover has occurred). Both 2 and 4 are found to have LS FeIII centres although the latter contains two crystallographically independent FeIII centres in the asymmetric unit. The crystal packing in 1­4 consists of extensive π­π interactions through the planar qsal-X ligands and CH∙∙∙X (X = O, halogen) and/or X∙∙∙π (X = halogen) interactions which result in pseudo 3D supramolecular networks. This results in high cooperativity in 1 and 2 and is probably responsible for the hysteretic stepped spin crossover in these compounds.

16.
J Org Chem ; 79(21): 10196-202, 2014 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-25310719

RESUMO

Multicomponent synthesis of 3-aminoimidazo[1,2-a]pyrimidines usually affords a product mixture containing varying amounts of the corresponding 2-amino regioisomer. Modified methods, particularly microwave heating, have been employed to suppress formation of this side-product, but none of the revised protocols are readily amenable to scale. A continuous flow adaptation was found to offer improved regioselectivity toward the targeted 3-amino regioisomer with significantly shorter reaction times and also widened the scope of the reaction to permit the use of aliphatic aldehyde building blocks.


Assuntos
Imidazóis/síntese química , Pirimidinas/síntese química , Aldeídos/química , Catálise , Imidazóis/química , Estrutura Molecular , Pirimidinas/química , Estereoisomerismo
17.
Chemistry ; 20(43): 14004-11, 2014 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-25208528

RESUMO

The synthesis of two new luminescent dinuclear Ir(III)-Ru(II) complexes containing tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (tpphz) as the bridging ligand is reported. Unlike many other complexes incorporating cyclometalated Ir(III) moieties, these complexes display good water solubility, allowing the first cell-based study on Ir(III)-Ru(II) bioprobes to be carried out. Photophysical studies indicate that emission from each complex is from a Ru(II) excited state and both complexes display significant in vitro DNA-binding affinities. Cellular studies show that each complex is rapidly internalised by HeLa cells, in which they function as luminescent nuclear DNA-imaging agents for confocal microscopy. Furthermore, the uptake and nuclear targeting properties of the complex incorporating cyclometalating 2-(4-fluorophenyl)pyridine ligands around its Ir(III) centre is enhanced in comparison to the non-fluorinated analogue, indicating that fluorination may provide a route to promote cell uptake of transition-metal bioprobes.


Assuntos
Sondas de DNA/metabolismo , Irídio/metabolismo , Substâncias Luminescentes/metabolismo , Fenazinas/metabolismo , Rutênio/metabolismo , Permeabilidade da Membrana Celular , Complexos de Coordenação/química , Complexos de Coordenação/metabolismo , DNA/metabolismo , Sondas de DNA/química , Células HeLa , Humanos , Irídio/química , Luminescência , Substâncias Luminescentes/química , Modelos Moleculares , Fenazinas/química , Rutênio/química
18.
Chemistry ; 20(40): 12889-93, 2014 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-25145488

RESUMO

The aza-Diels-Alder cycloaddition of 1,2,4-triazines with alkynes offers a rapid and convenient method for the synthesis of highly substituted pyridines, but often requires harsh conditions and long reaction times. The present study offers a solution to these limitations by use of a temporary tether established by a Lewis acid-base complexation of in situ generated alkynylboranes and triazines bearing a Lewis basic donor. The cycloaddition reactions take place within 20 min at 40 °C and provide direct access to a broad range of pyridines with complete and predictable regiocontrol. The carbonboron bond can be further functionalised by cross-coupling allowing further functionality to be introduced after cycloaddition.

19.
Chemistry ; 20(31): 9693-701, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-24981819

RESUMO

A series of bis-chelate pseudo-octahedral mononuclear coordination complexes of manganese with the chromophore [MnN4 O2 ](n+) (n=0, 1) have been generated in all three principal oxidation states of this transition-metal center under ambient conditions by utilizing a readily tunable, versatile phenolic pyridylhydrazone ligand system (i.e., H2 (3,5-R(1) ,R(2) )-L; L=ligand). Strategic combinations of the nature and position of a variety of substituent groups afforded selective, spontaneous stabilization of multiple spin states of the manganese center, which, upon close crystallographic scrutiny, appears to be in part due to the occurrence or absence of hydrogen-bonding interactions that involve the phenolate/phenolic oxygen atom. The divalent complexes are isolable in two forms, namely, molecular [Mn(II) {H(3,5-R(1) ,R(2) )-L}2 ] and ionic [Mn(II) {H2 (3,5-R(1) ,R(2) )-L}{H(3,5-R(1) ,R(2) )-L}]ClO4 , with the latter complex converting easily into the former complex on deprotonation. Accessibility of the higher-valent states is achievable only when the phenolate oxygen atom is sterically hindered from participation in hydrogen bonding. The [Mn(III) {H(3,5-tBu2 )-L}2 ]ClO4 complex is the first example of a hydrazone-based Mn(III) complex to exhibit spin crossover. Formation of the tetravalent complexes [Mn(IV) {(3,5-R(1) ,R(2) )-L}2 ] (R(1) =tBu, R(2) =H; R(1) =R(2) =tBu) necessitates base-assisted abstraction of the hydrazinic proton.

20.
Angew Chem Int Ed Engl ; 53(31): 8246-50, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-24919567

RESUMO

Creating efficient artificial catalysts that can compete with biocatalysis has been an enduring challenge which has yet to be met. Reported herein is the synthesis and characterization of a series of zinc complexes designed to catalyze the hydrolysis of phosphate diesters. By introducing a hydrated aldehyde into the ligand we achieve turnover for DNA-like substrates which, combined with ligand methylation, increases reactivity by two orders of magnitude. In contrast to current orthodoxy and mechanistic explanations, we propose a mechanism where the nucleophile is not coordinated to the metal ion, but involves a tautomer with a more effective Lewis acid and more reactive nucleophile. This data suggests a new strategy for creating more efficient metal ion based catalysts, and highlights a possible mode of action for metalloenzymes.


Assuntos
Fosfatos/química , Zinco/química , Catálise , Cristalografia por Raios X , Ésteres/química , Hidrólise , Metilação
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