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1.
Molecules ; 25(11)2020 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-32485968

RESUMO

New soluble and intensely near-IR-absorbing transition metal (Ti, Zr, V, Ni) complexes were synthesized using a redox non-innocent N,N'-bis(3,5-di-tertbutyl-2-hydroxy-phenyl) -1,2-phenylenediamine (H4L) as a ligand precursor. In all the complexes, ([Ti(Lox)2, [Zr(Lox)2], [V(Lsq1)(HLox)] and [Ni(HLox)2], two organic molecules coordinate to the metal center as tri- or tetradentate ligands. The solid-state structures of the complexes were determined using single crystal XRD, and the compounds were further characterized with Electrospray Ionisation Mass Spectrometry (ESI-MS). Thermoanalytical measurements indicated the thermal stabilities of the complexes. All compounds absorb strongly in the near-IR region and show very interesting magnetic and electrochemical properties. Moreover, it was shown that the V and Ni complexes can also convert absorbed near-IR photons to (un)paired electrons, which indicates great promise in photovoltaic applications.

2.
Chemistry ; 25(6): 1481-1487, 2019 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-30536482

RESUMO

The allosteric control of the receptor properties of two flexible covalent cages is reported. These receptors consist of two zinc(II) porphyrins connected by four linkers of two different sizes, each incorporating two 1,2,3-triazolyl ligands. Silver(I) ions act as effectors, responsible for an on/off encapsulation mechanism of neutral guest molecules. Binding silver(I) ions to the triazoles opens the cages and triggers the coordination of pyrazine or the encapsulation of N,N'-dibutyl-1,4,5,8-naphthalene diimide. The X-ray structure of the silver(I)-complexed receptor with short connectors is reported, revealing the hollow structure with a cavity well-defined by two eclipsed porphyrins. Rather unexpectedly, the crystallographic structure of this receptor with pyrazine as a guest molecule showed that the cavity is occupied by two pyrazines, each binding to the zinc(II) porphyrin in a monotopic fashion.

3.
Cryst Growth Des ; 18(5): 3151-3160, 2018 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-30258305

RESUMO

The major diastereomer formed in the Barbier-type metal-mediated allylation of d-mannose has previously been shown to adopt a perfectly linear conformation, both in solid state and in solution, resulting in the formation of hydrogen-bonded networks and subsequent aggregation from aqueous solution upon stirring. Here, a comprehensive study of the solid state structure of both the allylated d-mannose and its racemic form has been conducted. The binary melting point diagram of the system was determined by differential scanning calorimetry analysis, and the obtained results, along with structure determination by single crystal X-ray diffraction, confirmed that allylated mannose forms a true racemate. Further examination by powder X-ray diffraction and CP MAS 13C NMR spectroscopy revealed polymorphism both in the pure enantiomer and in the racemate. In addition, the propargylated and hydrogenated analogues of allylated d-mannose were prepared and subjected to thermal and spectroscopic analyses. The crystal structure of the propargylated compound was successfully determined, showing a linear molecular conformation similar to that found for allylated d-mannose. Both new compounds likewise display aggregation behavior in water, further verifying that the low-energy linear conformation plays a significant role in this unusual behavior of these rodlike mannose derivatives.

4.
Chemistry ; 24(39): 9735-9738, 2018 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-29847691

RESUMO

A highly efficient strategy for the kinetic resolution of Michael adducts was realized using a chiral N-heterocyclic carbene catalyst. The kinetic resolution provides a new convenient route to single diastereomers of cyclohexenes and Michael adducts in good yields with high enantiomeric excesses (up to 99 % ee with a selectivity factor of up to 458). This "two flies with one swat" concept allows the synthesis of these two synthetically valuable compound classes at the same time by a single transformation.

5.
J Am Chem Soc ; 140(5): 1937-1944, 2018 02 07.
Artigo em Inglês | MEDLINE | ID: mdl-29314833

RESUMO

The Plakortin polyketides represent a structurally and biologically fascinating class of marine natural products. Herein, we report a unified strategy that enables the divergent syntheses of various Plakortin polyketides with high step-economy and overall efficiency. As proof-of-concept cases, the enantioselective total syntheses of (+)-hippolachnin A, (+)-gracilioether A, (-)-gracilioether E, and (-)-gracilioether F have been accomplished based on a series of bio-inspired, rationally designed, or serendipitously discovered transformations, which include (1) an organocatalytic asymmetric 1,4-conjugate addition to assemble the common chiral γ-butenolide intermediate enroute to all of the aforementioned targets, (2) a challenging biomimetic [2+2] photocycloaddition to forge the oxacyclobutapentalene core of (+)-hippolachnin A, (3) a [2+2] photocycloaddition followed by one-pot oxidative cleavage of methyl ether/Baeyer-Villiger rearrangement to access (-)-gracilioether F, and (4) an unprecedented hydrogen-atom-transfer-triggered oxygenation of vinylcyclobutane to afford (+)-gracilioether A and (-)-gracilioether E in one pot.

6.
Dalton Trans ; 46(46): 16004-16008, 2017 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-29116268

RESUMO

The condensation reaction of 2-aminobenzenethiols and 3-aminopyrazinethiols with 2-amino-6-fluoro-N-methylpyridinium triflate afforded thioether derivatives that were found to undergo Smiles rearrangement and cyclocondensation with sulphur monochloride to yield new hybrid 1,4-thiazine-1,2,3-dithiazolylium cations. The synthesized cations were readily reduced to the corresponding stable neutral radicals with spin densities delocalized over both 1,4-thiazinyl and 1,2,3-dithiazolyl moieties.

7.
Angew Chem Int Ed Engl ; 56(29): 8516-8521, 2017 07 10.
Artigo em Inglês | MEDLINE | ID: mdl-28568965

RESUMO

A novel NHC-catalyzed annulation protocol for the asymmetric synthesis of biologically important ß-lactam fused spirocyclopentane oxindoles with four contiguous stereocenters, including two quaternary carbon centers, was developed. Alternatively, spirocyclopentane oxindoles containing an enaminone moiety can be achieved using the same starting materials, isatin-derived enals, and N-sulfonyl ketimines, in the presence of a slightly different NHC catalytic system. This switchable annulation strategy enables the selective assembly of both heterocyclic scaffolds with good yields and excellent enantioselectivities for a broad range of substrates.

8.
Chemistry ; 23(48): 11714-11718, 2017 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-28631856

RESUMO

Tripodal N-donor ligands are used to form halogen-bonded assemblies via structurally analogous Ag+ -complexes. Selective formation of discrete tetrameric I6 L4 and dimeric I3 L2 halonium cages, wherein multiple [N⋅⋅⋅I+ ⋅⋅⋅N] halogen bonds are used in concert, can be achieved by using sterically rigidified cationic tris(1-methyl-1-azonia-4-azabicyclo[2.2.2]octane)-mesitylene ligand, L1(PF6 )3 , and flexible ligand 1,3,5-tris(imidazole-1-ylmethyl)-2,4,6-trimethylbenzene, L2, respectively. The iodonium cages, I6 L14 (PF6 )18 and I3 L22 (PF6 )3 , were obtained through the [N⋅⋅⋅Ag+ ⋅⋅⋅N]→ [N⋅⋅⋅I+ ⋅⋅⋅N] cation exchange reaction between the corresponding Ag6 L14 (PF6 )18 and Ag3 L22 (PF6 )3 coordination cages, prepared as intermediates, and I2 . The synthesized metallo- and halonium cages were studied in solution by NMR, in gas phase by ESI-MS and in the solid-state by single crystal X-ray diffraction.

9.
J Org Chem ; 82(13): 7050-7058, 2017 07 07.
Artigo em Inglês | MEDLINE | ID: mdl-28541704

RESUMO

A new series of N-Boc ketimines derived from pyrazolin-5-ones have been used as electrophiles in asymmetric Mannich reactions with pyrazolones. The amino-bis-pyrazolone products are obtained in excellent yields and stereoselectivities by employing a very low loading of 1 mol % of a bifunctional squaramide organocatalyst. Depending on the substitution at position 4 of the pyrazolones, the new protocol allows for the generation of one or two tetrasubstituted stereocenters, including a one-pot version combing the Mannich reaction with a base-mediated halogenation.

10.
Angew Chem Int Ed Engl ; 56(22): 6241-6245, 2017 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-28429516

RESUMO

A strategy for the N-heterocyclic carbene (NHC) catalyzed asymmetric synthesis of 3,5-diaryl substituted cyclohexenones has been developed via oxidative [4+2] annulation of enals and alkenylisoxazoles. It is the first example of using NHC organocatalysis in a double vinylogous Michael type reaction, a challenging but highly desirable topic. This unprecedented protocol affords good yields as well as high to excellent diastereo- and enantioselectivities.

11.
Dalton Trans ; 46(5): 1377-1381, 2017 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-28091656

RESUMO

The first examples of p-block coordination complexes of biquinoline, namely [(biq)BCl2]Cl and [(biq)BCl2]˙, were synthesized and structurally characterized. The acquired data allowed the estimation of the ligand charge state based on its metrical parameters. The subsequent use of this protocol, augmented with theoretical calculations, revealed ambiguities in the published data for transition metal complexes of biquinoline.

12.
Chem Commun (Camb) ; 50(41): 5469-72, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24718313

RESUMO

Tripodal cationic N-donor ligands exhibit sterically controlled self-assembly of tetrahedral M6L4 coordination cages that promote selective anion encapsulation (PF6(-) > OTf(-)) in the solid state. The described method is a potential template for stepwise assembly of hetero-ligand coordination cages and polymers.

13.
Inorg Chem ; 53(1): 33-5, 2014 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-24328150

RESUMO

A neutral air- and moisture-stable N,N'-chelating radical ligand, 1-phenyl-3-(pyrid-2-yl)benzo[e][1,2,4]triazinyl (1) was synthesized and characterized by electron paramagnetic resonance spectroscopy, X-ray crystallography, and magnetic measurements. Subsequent reaction of 1 with Cu(hfac)2·2H2O (hfac = hexafluoroacetylacetonate) under ambient conditions afforded the coordination complex Cu(1)(hfac)2 in which the radical binds to the metal in a bidentate fashion. Magnetic susceptibility data collected from 1.8 to 300 K indicate a strong ferromagnetic metal-radical interaction in the complex and weak antiferromagnetic radical···radical interactions between the Cu(1)(hfac)2 units. Detailed computational investigations support this assignment. Radical 1 is a new addition to the growing library of 1,2,4-triazinyl radicals and the first member of this family of paramagnetic species synthesized specifically for coordination purposes.

14.
Acta Crystallogr Sect E Struct Rep Online ; 68(Pt 7): o1986, 2012 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-22807819

RESUMO

The title compound, C(18)H(28)N(5)O(2) (+)·I(-), was observed as a main product in an intended 1:1 reaction between 4-iodo-nitro-benzene and 1,4-diaza-bicyclo-[2.2.2]octane (DABCO). In the reaction, DABCO undergoes a ring opening to yield a quaternary salt of DABCO and 1-ethyl-4-(4-nitro-phen-yl)piperazine with an iodide anion. The crystal structure determination was carried out as no crystal structure had been previously reported in the investigations describing the corresponding reaction with 4-chloro-nitro-benze. Indeed, the crystal structure of the title compound confirms the mol-ecular composition proposed earlier for the analogous chloride salt. The cation conformation is similar to the previously reported dinitro analogue 1-{2-[4-(2,4-dinitro-phen-yl)piperazin-1-yl]eth-yl}-4-aza-1-azoniabicyclo-[2.2.2]octane chloride [Clegg et al. (2004 ▶). Acta Cryst. E60, o291-o293]. The crystal packing is dominated by cation⋯I(-) inter-actions in addition to weak inter-molecular C-H⋯O(2)N and C-H⋯N inter-actions between the cations.

15.
Inorg Chem ; 51(4): 2577-87, 2012 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-22313370

RESUMO

A high-level theoretical investigation of 1,2-cyclopentadiene (4) was performed using density functional theory and wave function methods. The results reveal that, in contrast to earlier assumptions, the ground state of this ephemeral "allene" is carbene-like with a small diradical component. Furthermore, the electronic structure and chemistry of 4 are found to parallel that of 1,2,4,6-cycloheptatetraene: both molecules possess a low-lying excited singlet state with a closed-shell carbenic structure, enabling rich coordination chemistry. Energy decomposition analyses conducted for currently unknown metal complexes of 4 as well as those involving stable carbenes based on the pyrazolium framework (aka "bent allenes" or remote N-heterocyclic carbenes) indicate that all investigated ligands form particularly strong metal-carbon bonds. Most notably, without exocyclic π-type substituents, 4 and pyrazolin-4-ylidenes are the strongest donor ligands examined, in large part because of the energy and shape of their highest occupied molecular orbital. As a whole, the current work opens a new chapter in the chemistry of 1,2-cyclopentadiene, which is hoped to spark renewed interest among experimentalists. In addition, results from the conducted bonding analyses underline that more emphasis should be placed on purely carbocyclic carbenes as unprecedented σ-donor strengths can be realized through this route.

16.
Acta Crystallogr Sect E Struct Rep Online ; 68(Pt 12): m1453-4, 2012 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-23468682

RESUMO

The asymmetric unit of the title three-dimensional coordination polymer, [Mn2Br6(C11H28N2O2)] n , consists of one Mn(II) cation, half of a dicationic N,N'-bis-(2-hy-droxy-eth-yl)-N,N,N',N'-tetra-methyl-propane-1,3-diaminium ligand (L) (the other half being generated by a twofold rotation axis), and three bromide ions. The Mn(II) cation is coordinated by a single L ligand via the hy-droxy O atom and by five bromide ions, resulting in a distorted octa-hedral MnBr5O coordination geometry. Four of the bromide ions are bridging to two adjacent Mn(II) atoms, thereby forming polymeric chains along the a and b axes. The L units act as links between neighbouring Mn-(µ-Br)2-Mn chains, also forming a polymeric continuum along the c axis, which completes the formation of a three-dimensional network. Classical O-H⋯Br hydrogen bonds are present. The distance between adjacent Mn(II) atoms is 4.022 (1) Å.

17.
Chemistry ; 15(30): 7287-91, 2009 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-19551788
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