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1.
Chemistry ; 26(34): 7711-7719, 2020 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-32298506

RESUMO

Catenation is common for the light main-group elements whereas it is rare for the heavy elements. Herein, we report the first example of a neutral molecule containing a Bi4 chain. It is prepared in a one-step reaction between bismuth trichloride and bis(diisopropylphosphino)amine in methanol suspension. The same reaction carried out in dichloromethane gives quite different products. All products have been characterized spectroscopically and using single-crystal X-ray analysis.

2.
Chem Commun (Camb) ; 56(58): 8027-8030, 2020 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-32159538

RESUMO

Air-stable secondary phosphine oxides (SPOs) are readily formed from diazaphospholene bromides. In the presence of pinacolborane, these SPOs are transformed into catalytically active diazaphospholene hydrides. A silyl triflate transforms the SPOs into phosphenium triflates. The use of diazaphospholene SPOs as reduction reaction precatalysts was validated by imine reduction, conjugate reduction, pyridine hydroboration, and asymmetric reduction.

3.
Org Biomol Chem ; 18(11): 2139-2147, 2020 03 18.
Artigo em Inglês | MEDLINE | ID: mdl-32134102

RESUMO

The synthesis and characterisation of the BCl2-chelated complexes of both archetypal aza-dipyrrin sub-types are presented. A stepwise halogen exchange, leading to a mixed-halide Cl-B-F intermediate, is implicated in the conversion of F-aza-BODIPYs to Cl-aza-BODIPYs upon treatment with BCl3. The utility of the Cl-aza-BODIPY scaffold to facilitate substitutions at boron is demonstrated under mild conditions through treatment with aryl Grignard reagents. Additionally, the lability of the B-Cl bond enables facile removal of the BCl2 group, i.e. deprotection of F-aza-BODIPYs, under aqueous conditions. Three aza-dipyrrin HX salts were also synthesised and characterised. The pKa of the protonated aza-dipyrrin was determined to be 4, thereby providing insight regarding the storage and stability of such species.

5.
J Am Chem Soc ; 141(36): 14083-14088, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31441650

RESUMO

The first use of phosphenium cations in asymmetric catalysis is reported. A diazaphosphenium triflate, prepared in two or three steps on a multigram scale from commercially available materials, catalyzes the hydroboration or hydrosilylation of cyclic imines with enantiomeric ratios of up to 97:3. Catalyst loadings are as low as 0.2 mol %. Twenty-two aryl/heteroaryl pyrrolidines and piperidines were prepared using this method. Imines containing functional groups such as thiophenes or pyridyl rings that can challenge transition-metal catalysts were reduced employing these systems.

6.
Org Biomol Chem ; 17(25): 6158-6164, 2019 06 26.
Artigo em Inglês | MEDLINE | ID: mdl-31183491

RESUMO

Certain borenium cations supported by carbenes can function as hydrogenation catalysts for imines. While many carbenes have been explored, variation of the other groups on boron has been less common. We have investigated several carbene-borane adducts in an attempt to understand the ability of a bis-amino cyclopropenylidene (BAC) carbene dicyclohexylborane adduct to hydrogenate relatively sterically unhindered benzyl imines. As an additional variant, a BAC carbene adduct of diphenylborane was prepared. A convenient preparation of diphenylboron fluoride via a potassium fluoroborinate salt was employed in this chemistry. Reaction of diphenylboron fluoride with a BAC carbene afforded a modest yield of a carbene-fluoroborane adduct. Reaction between the fluoroborinate salt and a lithium tetrafluoroborate adduct of the carbene provided the adduct in much improved yield and cleanliness, and the product was structurally characterized. The fluoroborate could be converted to a boron hydride through fluoride-hydride exchange with dimethylchlorosilane. The boron hydride adduct was also structurally characterized. Unlike the BAC carbene dicyclohexylborane adduct, the BAC carbene diphenylborane adduct showed essentially no activity in hydrogenation of imines or enamines.

7.
Dalton Trans ; 48(22): 7546-7550, 2019 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-31070213

RESUMO

A parameter is reported by which to use 13C NMR chemical shifts to measure and predict the donor capabilities of N^N dipyrrinato and aza-dipyrrinato ligands chelating in L^X fashion. The results enable the rationalisation of the properties of these ligands and their complexes, as well as enable rational design incorporating both steric and electronic considerations when tuning to effect desired applications. Complexes containing these ligands are prevalent due to their desirable photophysical properties such as high chemical stability, resistance to photodegradation, strong absorbance, and ease of chemical modifiability.

8.
Dalton Trans ; 48(18): 6248-6260, 2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-30985844

RESUMO

Cobalt(ii) and (iii) complexes bearing tetradentate amino-bis(phenolate) ligands containing either pendent dimethylaminoethylene or pyridyl groups and phenolates bearing electron-donating alkyl or electron-withdrawing chloro substituents were synthesized. The compounds were characterized by mass spectrometry, elemental analysis and NMR for diamagnetic compounds. The influence of the electron donating ability and steric demand of the ligands on CO2/epoxide ring-opening copolymerization (ROCOP) and coupling reactions was investigated. Of the Co(ii) systems studied, complex 3, which has an amino-bis(phenolate) ligand possessing chlorine-functionalized phenolates and a pyridyl pendent group, [L3] = 2-methylene-pyridyl-N,N-bis(2-methylene-2,4-dichlorophenolate), was active for poly(cyclohexene carbonate) formation. The complex showed up to 98% epoxide conversion, up to 98% polymer selectivity and up to 97% carbonate linkages. By comparison, Co(ii) compounds 1 and 2 bearing alkyl groups on the phenolate donors were inactive for ROCOP. Structural characterization of 3 by X-ray diffraction (and supported by mass spectrometry and elemental analysis) showed the potassium acetate (KOAc), which formed as a synthetic by-product, remains coordinated to the Co[L3] unit through binding of the K+ ions to the chlorine substituents on the phenolate groups and acetate anions, resulting in a hexacobalt cluster in the solid state. Cobalt(iii) compounds were prepared from the Co(ii) complexes by aerobic oxidation in the presence of 2,4-dinitrophenol. The resulting 2,4-dinitrophenolate (2,4-DNP) complexes were diamagnetic species of which 7, possessing a dimethylamino-N,N-bis(2-methylene-2-tert-butyl-4-methyl-phenolate) ligand [L4], was characterized by single crystal X-ray diffraction. The Co(iii) complexes 5-7 were inactive for ROCOP of cyclohexene oxide or propylene oxide but were active for cyclic carbonate formation for a variety of epoxides studied. A maximum turnover frequency of 20 h-1 was attained for conversion of epichlorohydrin to (chloromethyl)ethylene carbonate.

9.
Chem Commun (Camb) ; 54(93): 13139-13142, 2018 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-30402640

RESUMO

We report the lithium, sodium and potassium salts of aza-dipyrrins and detail their use as anionic aza-dipyrrinato ligand sources in complexation. Of the three types of alkali salts studied, those of lithium are found to be most useful as synthetic precursors. For example, they selectively afford heteroleptic aza-dipyrrinato zinc complexes which can be further modified via ligand exchange.

10.
Dalton Trans ; 47(30): 10195-10205, 2018 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-30014057

RESUMO

In this paper we describe the synthesis, characterization, and X-ray crystal structures of two ligands, diethyl-N,N'-bis(p-tolyl)malonimidate and 1,3-bis(dimethylamino)-N,N'-bis(p-tolyl)propanediimidate. Their corresponding rhodium(i) dicarbonyl, dimethylaluminium, and bis-ligated zinc complexes have also been prepared and characterized. The donor properties of the ligands have been studied and have been compared to those of the traditional anionic N,N'-chelating ligand nacnac.

11.
Dalton Trans ; 47(18): 6299-6303, 2018 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-29670979

RESUMO

Lawesson's reagent (LR) has been shown to react with the N-heterocyclic carbenes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)] to give adducts of the general form NHC·P(S)2-C6H4OCH3. Full characterizations, including X-ray crystal structures, are provided. The reaction of Woollins' reagent (WR) with IMes gave the known selanone, (IMes)Se.

12.
Angew Chem Int Ed Engl ; 57(3): 749-754, 2018 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-29152832

RESUMO

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.

13.
Photochem Photobiol Sci ; 17(1): 89-98, 2018 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-29218351

RESUMO

A series of synthetic analogs of the tripyrrolic natural product prodigiosin were complexed with boron trifluoride to generate the corresponding F-BODIPYs. The maximum wavelengths of absorption and emission of the pyrrolyldipyrrin F-BODIPYs were tuned through variation of the substituents about the pyrrolyldipyrrinato core. The limited variation of substituents on the C-ring did not significantly affect absorption and emission. However, variation of substituents on the B-ring and A-ring resulted in a corresponding red-shift in absorption and emission reaching maximum wavelengths of 600 nm. The presence of electron donating substituents on the B-ring caused a decrease in the Stokes shift, while the presence of electron-withdrawing substituents caused an increase, ranging from 3-25 nm. Stokes shifts were solvent-dependant for some compounds. The inclusion of a dimethylamino group resulted in photo-induced electron transfer and thus quenched fluorescence which was restored upon protonation.

14.
Acta Crystallogr E Crystallogr Commun ; 73(Pt 11): 1735-1738, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-29152362

RESUMO

The title compound, C20H22O3, was formed in the reaction between 2,4,6-tri-methyl-benzoic acid and N,N-diiso-propyl-ethyl-amine in the presence of 1,3-di-chloro-1,3-bis-(di-methyl-amino)-propenium hydrogen dichloride, and was recrystallized from diethyl ether solution. It is the first exclusively alkyl-substituted benzoic anhydride to have been structurally characterized. The asymmetric unit consists of a half mol-ecule, the other half of which is generated by twofold rotation symmetry; the dihedral angle between the symmetry-related aromatic rings is 54.97 (3)°. The geometric parameters of the aromatic ring are typical of those for 2,4,6-tri-methyl-phenyl substituted groups. The C=O and C-O bond lengths are 1.1934 (12) and 1.3958 (11) Å, respectively, and the angle between these three atoms (O=C-O) is 121.24 (9)°. In the crystal, mol-ecules are linked by weak C-H⋯O hydrogen bonds and C-H⋯π inter-actions. The packing features wavy chains that extend parallel to [001].

15.
J Org Chem ; 82(13): 7059-7064, 2017 07 07.
Artigo em Inglês | MEDLINE | ID: mdl-28648076

RESUMO

An asymmetric meso-H dipyrrin featuring a conjugated terminal alkyne substituent was converted to its corresponding difluoro boron complex, and the extent of π-conjugation was extended using Sonogashira cross-coupling. Treatment of the alkyne-substituted dipyrrin with BF3·OEt2 and NEt3 revealed the reactivity of the conjugated terminal alkyne toward Lewis-activated electrophilic substitution and led to the isolation of F-BODIPYs bearing terminal bromovinyl and enol substituents.

16.
Acta Crystallogr E Crystallogr Commun ; 72(Pt 9): 1301-1304, 2016 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-27920922

RESUMO

The title compound, [Co(C10H15)(C2H4)2], was prepared by Na/Hg reduction of [Co2(C10H15)2(µ-Cl)2] in THF under an ethyl-ene atmosphere and crystallized from pentane at 193 K. The Co-C(olefin) bonds have an average length of 2.022 (2) Å, while the Co-C(penta-dien-yl) bonds average 2.103 (19) Å. The olefin C=C bonds are 1.410 (1) Å. The dihedral angle between the planes defined by the cyclo-penta-dienyl ligand and the two olefin ligands is 0.25 (12)°. In the crystal, mol-ecules are linked into chains by C-H⋯π inter-actions.

17.
Angew Chem Int Ed Engl ; 54(26): 7484-7, 2015 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-26036318

RESUMO

Out of focus: A recent Communication published in this journal describes the synthesis of [nBu4 N]HCO3 . The authors performed a single-crystal X-ray study that revealed a putative species described as an incipient hydroxide ion engaging in a long, and presumably weak, interaction with CO2 . Our recent exploration of the coordination chemistry of CO2 with small ions leads us to believe that such an exceptional bonding situation is unlikely. Instead, we argue that the crystal structure is that of [nBu4 N]O2 CCH3 and therefore not representative of the bulk powder from the synthesis.


Assuntos
Dióxido de Carbono/química , Cristalografia por Raios X/métodos , Biomimética , Estrutura Molecular
18.
Chem Commun (Camb) ; 51(19): 3942-56, 2015 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-25601453

RESUMO

The ability to bind CO2 through the formation of low-energy, easily-broken, bonds could prove invaluable in a variety of chemical contexts. For example, weak bonds to CO2 would greatly decrease the cost of the energy-intensive sorbent-regeneration step common to most carbon capture technologies. Furthermore, exploration of this field could lead to the discovery of novel CO2 chemistry. Reduction of complexed carbon dioxide might generate chemical feedstocks for the preparation of value-added products, particularly transportation fuels or fuel precursors. Implementation on a large scale could help to drastically reduce CO2 concentrations in the atmosphere. However, literature examples of weakly bonded complexes of CO2 are relatively few and true coordination complexes to a 'naked' CO2 fragment are nearly unheard of. In this review article, a variety of complexes of CO2 featuring diverse binding modes and reactivity will be examined. Topics covered include: (A) inclusion complexes of CO2 in porous materials. (B) Zwitterionic carbamates produced from the reaction of CO2 with polyamines. (C) Carbamate salts produced from reaction of CO2 with two equivalents of an amine. (D) Insertion products of CO2 into acid-base adducts (e.g., metal complexes). (E) Lewis acid-base activated CO2, such as frustrated Lewis pair complexes. (F) Simple base-CO2 adducts, wherein the base-CO2 bond is the only interaction formed. Complexes in the last category are of particular interest, and include imidazol-2-carboxylates (N-heterocyclic carbene adducts of CO2) as well as a few other examples that lie outside NHC chemistry.

19.
Science ; 344(6179): 75-8, 2014 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-24700853

RESUMO

Why does cyanide not react destructively with the proximal iron center at the active site of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, an enzyme central to the biosynthesis of ethylene in plants? It has long been postulated that the cyanoformate anion, [NCCO2](-), forms and then decomposes to carbon dioxide and cyanide during this process. We have now isolated and crystallographically characterized this elusive anion as its tetraphenylphosphonium salt. Theoretical calculations show that cyanoformate has a very weak C-C bond and that it is thermodynamically stable only in low dielectric media. Solution stability studies have substantiated the latter result. We propose that cyanoformate shuttles the potentially toxic cyanide away from the low dielectric active site of ACC oxidase before breaking down in the higher dielectric medium of the cell.


Assuntos
Aminoácido Oxirredutases/metabolismo , Formiatos/isolamento & purificação , Nitrilos/isolamento & purificação , Aminoácido Oxirredutases/química , Dióxido de Carbono/química , Domínio Catalítico , Cristalização , Cianetos/química , Etilenos/metabolismo , Formiatos/química , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Nitrilos/química , Termodinâmica , Difração de Raios X
20.
Chem Commun (Camb) ; 48(9): 1227-9, 2012 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-22158693

RESUMO

Amines dissolved in ionic liquids react rapidly with SO(2) to produce new materials. Compounds related to the stepwise conversion of SO(2) to sulfite and sulfate salts have been isolated. Trapping SO(2) in the form of the sulfite anion does not change the oxidation state of sulfur and should maintain the reversibility of the capture system.

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