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1.
Nat Chem ; 2020 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-32929247

RESUMO

The industrial reduction of dinitrogen (N2) to ammonia is an energy-intensive process that consumes a considerable proportion of the global energy supply. As a consequence, species that can bind N2 and cleave its strong N-N bond under mild conditions have been sought for decades. Until recently, the only species known to support N2 fixation and functionalization were based on a handful of metals of the s and d blocks of the periodic table. Here we present one-pot binding, cleavage and reduction of N2 to ammonium by a main-group species. The reaction-a complex multiple reduction-protonation sequence-proceeds at room temperature in a single synthetic step through the use of solid-phase reductant and acid reagents. A simple acid quench of the mixture then provides ammonium, the protonated form of ammonia present in fertilizer. The elementary reaction steps in the process are elucidated, including the crucial N-N bond cleavage process, and all of the intermediates of the reaction are isolated.

2.
Chemistry ; 2020 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-32957161

RESUMO

Boron tribromide and aryldihaloboranes were found to undergo 1,3-haloboration across one W-N≡N moiety of a group 6 end-on dinitrogen complex ( i.e. trans -[W(N2)2(dppe)2]). The N-borylated products consist of a reduced diazenido unit sandwiched between a W(II) center and a trivalent boron substituent (W-N=N-BXAr), and have all been fully characterized by NMR and IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Both the terminal N atom and boron center in the W-N=N-BXAr unit can be further derivatized using electrophiles and nucleophiles/Lewis bases, respectively. This mild reduction and functionalization of a weakly activated N 2 ligand with boron halides is unprecedented, and hints at the possibility of generating value-added nitrogen compounds directly from molecular dinitrogen.

3.
Artigo em Inglês | MEDLINE | ID: mdl-32662218

RESUMO

Narrow HOMO-LUMO gaps and high charge-carrier mobilities make larger acenes potentially high-efficient materials for organic electronic applications. The performance of such molecules was shown to significantly increase with increasing number of fused benzene rings. Bulk quantities, however, can only be obtained reliably for acenes up to heptacene. Theoretically, (oligo)acenes and (poly)acenes are predicted to have open-shell singlet biradical and polyradical ground states, respectively, for which experimental evidence is still scarce. We have now been able to dramatically lower the HOMO-LUMO gap of acenes without the necessity of unfavorable elongation of their conjugated π system, by incorporating two boron atoms into the anthracene skeleton. Stabilizing the boron centers with cyclic (alkyl)(amino)carbenes gives neutral 9,10-diboraanthracenes, which are shown to feature disjointed, open-shell singlet biradical ground states.

4.
Chemistry ; 2020 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-32196775

RESUMO

Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt0 2 complex. While structurally analogous to well-known µ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt-B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt-B σ-bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit.

5.
Chemistry ; 2020 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-32167200

RESUMO

Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2 F5 )4 ]- were obtained from AlCl3 and LiC2 F5 . They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2 F5 )4 ]- ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3 ) under formation of [(C2 F5 )4-n AlFn ]- (n=1-4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2 F5 )AlF3 ]- ion was structurally characterized.

6.
Angew Chem Int Ed Engl ; 59(14): 5531-5535, 2020 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-31840333

RESUMO

Herein we present the first solid-state structures of tetraiododiborane(4) (B2 I4 ), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B2 F4 , B2 Cl4 , and B2 Br4 . Single-crystal X-ray diffraction, solid-state NMR, and IR measurements indicate that B2 I4 in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid-state structures, and these are compared with the experimental spectra.

7.
Chem Commun (Camb) ; 55(63): 9351-9354, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31313764

RESUMO

A set of mono- and dinuclear AuI and AgI alkynyl complexes bearing the carba-closo-dodecaboranylethynyl ligand show intense room temperature phosphorescence. The {closo-1-CB11} cage participates in an unprecedented way as an electron donating moiety, changing the direction of the charge-transfer excited state.

8.
Chem Sci ; 10(20): 5405-5422, 2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-31217943

RESUMO

A series of tetracationic quadrupolar chromophores containing three-coordinate boron π-acceptors linked by different π-bridges, namely 4,4'-biphenyl, 2,7-pyrene, 2,7-fluorene, 3,6-carbazole and 5,5'-di(thien-2-yl)-3,6-diketopyrrolopyrrole, were synthesized. While their neutral precursors 1-5 displayed highly solvatochromic fluorescence, the water-soluble tetracationic target molecules 1M-5M, did not, but their emission colour could be tuned from blue to pink by changing the π-bridge. Compound 5M, containing the diketopyrrolopyrrole bridge, exhibits the most red-shifted absorption and emission maxima and the largest two-photon absorption cross-section (4560 GM at 740 nm in MeCN). Confocal laser scanning fluorescence microscopy studies in live cells confirm localization of the dye at the lysosome. Moreover, the low cytotoxicity, and high photostability of 5M combined with two-photon excited fluorescence imaging studies demonstrate its excellent potential for lysosomal imaging in live cells.

9.
Angew Chem Int Ed Engl ; 58(29): 9782-9786, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-31062910

RESUMO

The transfer hydrogenation of N-heterocyclic carbene (NHC)-supported diborenes with dimethylamine borane proceeds with high selectivity for the trans-1,2-dihydrodiboranes. DFT calculations, supported by kinetic studies and deuteration experiments, suggest a stepwise proton-first-hydride-second reaction mechanism via an intermediate µ-hydrodiboronium dimethylaminoborate ion pair.

10.
Science ; 363(6433): 1329-1332, 2019 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-30898929

RESUMO

The coupling of two or more molecules of dinitrogen (N2) occurs naturally under the radiative conditions present in the ionosphere and may be achieved synthetically under ultrahigh pressure or plasma conditions. However, the comparatively low N-N single-bond enthalpy generally renders the catenation of the strongly triple-bonded N2 diatomic unfavorable and the decomposition of nitrogen chains a common reaction motif. Here, we report the surprising organoboron-mediated catenation of two N2 molecules under near-ambient conditions to form a complex in which a [N4]2- chain bridges two boron centers. The reaction entails reductive coupling of two hypovalent-boron-bound N2 units in a single step. Both this complex and a derivative protonated at both ends of the chain were characterized crystallographically.

11.
Chemistry ; 25(32): 7679-7688, 2019 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-30900778

RESUMO

The stability of tetracationic triarylboranes in dilute aqueous solution was investigated by tuning the steric demand of the linker in a (para-(N,N,N-trimethylammonio)xylyl)2 B-(linker)-B(para-(N,N,N-trimethylammonio)xylyl)2 structure. With increasing steric bulk of the linker, namely 1,4-phenylene, 2,2'''-(3,3'''-dimethyl)-5,2':5',2'':5'',5'''-quaterthiophene, 9,10-anthracenylene, and 4,4'''-(5'-(3,5-dimethylphenyl))(5''-(3''',5'''-dimethylphenyl))-2',2''-bithiophene, the stability of the compounds increased. The anthracene-based chromophore, compound 3M is water-stable for at least 48 h, is nontoxic to cells and exhibits an exceedingly high fluorescence quantum yield of 0.86 in water making it an ideal candidate for confocal live-cell imaging of lysosomes.


Assuntos
Boranos/síntese química , Rastreamento de Células/métodos , Corantes Fluorescentes/síntese química , Antracenos/química , Boranos/química , Sobrevivência Celular/efeitos dos fármacos , Corantes Fluorescentes/química , Células HeLa , Humanos , Estrutura Molecular , Imagem Óptica/métodos , Água/química
12.
Chemistry ; 25(14): 3560-3574, 2019 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-30600853

RESUMO

High-yield syntheses up to molar scales for salts of [BH(CN)3 ]- (2) and [BH2 (CN)2 ]- (3) starting from commercially available Na[BH4 ] (Na5), Na[BH3 (CN)] (Na4), BCl3 , (CH3 )3 SiCN, and KCN were developed. Direct conversion of Na5 into K2 was accomplished with (CH3 )3 SiCN and (CH3 )3 SiCl as a catalyst in an autoclave. Alternatively, Na5 is converted into Na[BH{OC(O)R}3 ] (R=alkyl) that is more reactive towards (CH3 )3 SiCN and thus provides an easy access to salts of 2. Some reaction intermediates were identified, for example, Na[BH(CN){OC(O)Et}2 ] (Na7 b) and Na[BH(CN)2 {OC(O)Et}] (Na8 b). A third entry to 2 and 3 uses ether adducts of BHCl2 or BH2 Cl such as the commercial 1,4-dioxane adducts that react with KCN and (CH3 )3 SiCN. Alkali metal salts of 2 and 3 are convenient starting materials for organic salts, especially for low viscosity ionic liquids (ILs). [EMIm]3 has the lowest viscosity and highest conductivity with 10.2 mPa s and 32.6 mS cm-1 at 20 °C known for non-protic ILs. The ILs are thermally, chemically, and electrochemically robust. These properties are crucial for applications in electrochemical devices, for example, dye-sensitized solar cells (Grätzel cells).

13.
Angew Chem Int Ed Engl ; 57(48): 15896-15901, 2018 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-30276985

RESUMO

Sterically unencumbered diborenes based on a benzylphosphine chelate undergo diboration reactions with bis(catecholato)diboron in the absence of a catalyst to yield tetraboranes. The symmetrical diborenes studied undergo 1,2-diborations, whereas an unsymmetrical derivative was found to yield a triborylborane-phosphine adduct as the result of a formal 1,1-diboration. A related borylborylene compound also underwent a 1,2-diboration to produce a borylene-borane adduct.

14.
J Am Chem Soc ; 140(40): 13056-13063, 2018 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-30222320

RESUMO

The reaction of the tetrahalodiboranes(4) B2F4, B2Cl4, and B2Br4 with a Lewis basic platinum(0) complex led to the isolation of the cis-bis(difluoroboryl) complex cis-[(Cy3P)2Pt(BF2)2] (1) and the novel borylborato complexes trans-[(Cy3P)2Pt{B(X)-BX3}] (2, X = Cl; 3, X = Br), respectively. The trans influence of the borylborato group was found to be one of the strongest ever observed experimentally. Furthermore, the reactivity of little-explored diaryldifluorodiboranes(4) F2B-BMes2 and the new derivative F2B-BAn2 (An = 9-anthryl) toward a range of platinum(0) complexes was investigated. Reactions with relatively nonbulky platinum(0) complexes led to the formation of unsymmetrical cis-bis(boryl) complexes cis-[(R3P)2Pt(BF2)(BMes2)] (6, R = Me; 7, R = Et) as well as the first example of a fourfold-unsymmetrical bis(boryl) complex, [(Me3P)(Cy3P)Pt(BF2)(BMes2)] (12). The use of a more bulky Pt complex provided access to the unprecedented dinuclear bis(boryl) complexes [{( iPr3P)Pt}2(µ-BF2)(µ-BAr2)] (8, Ar = Mes; 9, Ar = An), which feature two different µ2-bridging boryl ligands.

15.
Angew Chem Int Ed Engl ; 57(41): 13671-13675, 2018 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-30048568

RESUMO

The investigation of the mechanisms of mechanochromic luminescence is of fundamental importance for the development of materials for photonic sensors, data storage, and luminescence switches. The structural origin of this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structure-property relationships remains challenging. Changes in the M-M interactions have been proposed as the main mechanism with d10 coinage metal compounds. Herein, we describe a new mechanism-a mechanically induced reversible formation of a cation-anion exciplex based on Cu-F interactions-that leads to highly efficient mechanochromic phosphorescence and unusual large emission shifts from UV-blue to yellow for CuI complexes. The low-energy luminescence is thermo- and vaporesponsive, thus allowing the generation of white light as well as for recovering the original UV-blue emission.

16.
Chemistry ; 24(3): 608-623, 2018 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-28884848

RESUMO

The potassium perfluoroalkyltricyanoborates K[Cn F2 n+1 B(CN)3 ] [n=1 (1 d), 2 (2 d)] and the potassium mono(perfluoroalkyl)cyanofluoroborates K[Cn F2 n+1 BF(CN)2 ] [n=1 (1 c), 2 (2 c)] and [Cn F2 n+1 BF2 (CN)]- [n=1 (1 b), 2 (2 b), 3 (3 b), 4 (4 b)] are accessible with perfect selectivities on multi-gram scales starting from K[Cn F2 n+1 BF3 ] and Me3 SiCN. The K+ salts are starting materials for the preparation of salts with organic cations, for example, [EMIm]+ (EMIm=1-ethyl-3-methylimidazolium). These [EMIm]+ salts are hydrophobic room-temperature ionic liquids (RTILs) that are thermally, chemically and electrochemically very robust, offering electrochemical windows up to 5.8 V. The RTILs described herein, exhibit very low viscosities with a minimum of 14.0 mPa s at 20 °C for [EMIm]1 c, low melting points down to -57 °C for [EMIm]2 b and extraordinary high conductivities up to 17.6 mS cm-1 at 20 °C for [EMIm]1 c. The combination of these properties makes these ILs promising materials for electrochemical devices as exemplified by the application of selected RTILs as component of electrolytes in dye-sensitised solar cells (DSSCs, Grätzel cells). The efficiency of the DSSCs was found to increase with a decreasing viscosity of the neat ionic liquid. In addition to the spectroscopic characterisation, single crystals of the potassium salts of the anions 1 b-d, 2 d, 3 b and 4 c as well as of [nBu4 N]2 c have been studied by X-ray diffraction.

17.
Org Lett ; 19(24): 6590-6593, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29190108

RESUMO

This communication describes an efficient palladium pincer complex-catalyzed allylic C-H borylation of alkenes. The transformation exhibits high regio- and stereoselectivity with a variety of linear alkenes. A synthetically useful feature of this allylic C-H borylation method is that all allyl-Bpin products can be isolated in usually high yields. Preliminary mechanistic studies indicate that this C-H borylation reaction proceeds via Pd(IV) pincer complex intermediates.

18.
Org Lett ; 19(24): 6586-6589, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29181971

RESUMO

An efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via Cu-catalyzed borylation under mild conditions is reported. In the presence of commercially available Cu(OAc)2 or Cu(acac)2 and Xantphos, the reaction affords the desired products in up to 92% yield with a broad substrate scope (43 examples). Isolation of an allenyl boronate as the reaction intermediate suggests that an insertion-elimination-type reaction, followed by borylcupration, is involved in the borylation of propargylic alcohols.

19.
Chemistry ; 23(50): 12387-12398, 2017 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-28603878

RESUMO

The synthesis of mono-NHC alane adducts of the type (NHC)⋅AlH3 (NHC=Me2 Im (1), Me2 ImMe (2), iPr2 Im (3 and [D3 ]-3), iPr2 ImMe (4), Dipp2 Im (10); Im=imidazolin-2-ylidene, Dipp=2,6-diisopropylphenyl) and (NHC)⋅AliBu2 H (NHC=iPr2 Im (11), Dipp2 Im (12)) as well as their reactivity towards different types of carbenes is presented. Although the mono-NHC adducts remained stable at elevated temperatures, ring expansion occurred when (iPr2 Im)⋅AlH3 (3) was treated with a second equivalent of the carbene iPr2 Im to give (iPr2 Im)⋅AlH(RER-iPr2 ImH2 ) (6). In 6, {(iPr2 Im}AlH} is inserted into the NHC ring. In contrast, ring opening was observed with the sterically more demanding Dipp2 Im with the formation of (iPr2 Im)⋅AlH2 (ROR-Dipp2 ImH2 )H2 Al⋅(iPr2 Im) (9). In 9, two {(iPr2 Im)⋅AlH2 } moieties stabilize the ring-opened Dipp2 Im. If two hydridic sites are blocked, the adducts are stable with respect to further ring expansion or ring opening, as exemplified by the adducts (iPr2 Im)⋅AliBu2 H (11) and (Dipp2 Im)⋅AliBu2 H (12). The adducts (NHC)⋅AlH3 and (iPr2 Im)⋅AliBu2 H reacted with cAACMe by insertion of the carbene carbon atom into the Al-H bond to give (NHC)⋅AlH2 /iBu2 (cAACMe H) (13-18) instead of ligand substitution, ring-expansion, or ring-opened products.

20.
Angew Chem Int Ed Engl ; 56(37): 11263-11267, 2017 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-28640395

RESUMO

Deprotonation of [(cAAC)BH2 (CN)] provided clean access to the stable boryl anion, [(cAAC)BH(CN)]- . Whereas the addition of soft electrophiles occurred at the nucleophilic boron center, harder silyl electrophiles added to the harder terminal cyano nitrogen. The resulting [(cAAC)BH(CNSiPh3 )] species behaved like a silylium boryl nucleophile as well as a neutral silylisonitrile borylene.

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