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1.
Angew Chem Int Ed Engl ; : e202202190, 2022 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-35230738

RESUMO

N-Heterocyclic carbenes (NHCs) are commonly prepared by deprotonation of azolium salts using strong anionic bases. This reaction is often unselective, yielding alkali metal NHC complexes or dimerized NHCs. Alternatively, free NHCs are obtained by the dechlorination of 2-chloroazolium salts using electron-rich phosphines. PPh3 , PCy3 , and PtBu3 are unsuitable for Cl+ abstraction, while the sterically encumbered tris(1,3-tert-butylimidazolidin-2-ylidenamino)phosphine 1 selectively removes Cl+ from 2-chloroazolium salts. Since bulky 1 does not bind to metal complexes, it was used for the preparation of NHC complexes via in situ Cl+ abstraction from 2-chloroazolium salts. The dechlorination was employed for the site-selective monometallation with IrI , IrIII , RhI , RhIII , and RuII of a bis-NHC precursor composed of a 2-chlorobenzimidazolium and a 2-chlorobenzimidazole group, followed by the preparation of the heterobimetallic IrIII /PdII complex [18](BF4 )2 by a dechlorination/oxidative addition reaction sequence.

2.
J Am Chem Soc ; 143(31): 12404-12411, 2021 08 11.
Artigo em Inglês | MEDLINE | ID: mdl-34337934

RESUMO

One fascinating and challenging synthetic target in the field of mechanically interlocked molecules is the family of linear [4]catenanes, which are topologically identical to the logo of automobile maker Audi. Herein, we report an "all-in-one" synthetic strategy for the synthesis of linear metalla[n]catenanes (n = 2-4) by the coordination-driven self-assembly of Cp*Rh-based (Cp* = η5-pentamethylcyclopentadienyl) organometallic rectangle π-donors and tetracationic organic cyclophane π-acceptors. We selected the pyrenyl group as the π-donor unit, leading to homogeneous metalla[2]catenanes and cyclic metalla[3]catenanes via π-stacking interactions. By taking advantage of the strong electrostatic interactions between π-donor units and π-acceptor units, a heterogeneous metalla[2]catenanes and linear metalla[3]catenanes, respectively, could be obtained by the simple stirring of homogeneous metalla[2]catenanes with a suitable tetracationic cyclophane. On this basis, this "all-in-one" synthetic strategy was further used to realize a quantitative one-step synthesis of a linear metalla[4]catenanes via the self-assembly of cyclic metalla[3]catenanes and tetracationic cyclophanes. All heterogeneous metalla[n]catenanes (n = 2-4) were fully characterized by single-crystal X-ray analysis, NMR spectroscopy and electrospray ionization mass spectrometry.

3.
Angew Chem Int Ed Engl ; 60(5): 2599-2602, 2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-33022849

RESUMO

CAAC precursors 2-chloro-3,3-dimethylindole 1 and 2-chloro-1-ethyl-3,3-dimethylindolium tetrafluoroborate 2BF4 have been prepared and oxidatively added to [M(PPh3 )4 ] (M=Pd, Pt). Salt 2BF4 reacts with [Pd(PPh3 )4 ] in toluene at 25 °C over 4 days to yield complex cis-[3]BF4 featuring an N-ethyl substituted CAAC, two cis-arranged phosphines and a chloro ligand. Compound trans-[3]BF4 was obtained from the same reaction at 80 °C over 1 day. Salt 2BF4 reacts with [Pt(PPh3 )4 ] to give cis-[4]BF4 . The neutral indole derivative 1 adds oxidatively to [Pt(PPh3 )4 ] to give trans-[5] featuring a CAAC ligand with an unsubstituted ring-nitrogen atom. This nitrogen atom has been protonated with py⋅HBF4 to give trans-[6]BF4 bearing a protic CAAC ligand. The PdII complex trans-[7]BF4 bearing a protic CAAC ligand was obtained in a one-pot reaction from 1 and [Pd(PPh3 )4 ] in the presence of py⋅HBF4 .

4.
Dalton Trans ; 49(41): 14388-14392, 2020 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-33057531

RESUMO

Bis-NHC precursors composed of an azolium and a 2-halogenoazole group connected by different linkers have been site-selectively metallated to give heterobimetallic complexes from a single-frame bis-NHC ligand. The azolium group reacts with a base and oxidized metal centers to give NHC complexes with no participation of the halogenoazole, while the halogenoazole reacts in an oxidative addition with low-valent transition metals to give azolato complexes with no participation of the azolium group.

5.
ACS Omega ; 5(27): 16951-16958, 2020 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-32685865

RESUMO

The IrIII hydrido complexes [1] and [2] have been synthesized by the regioselective oxidative addition of the N7-H bond of 8-halogenotheophyllines to [IrCl(coe)2]2 in the presence of PPh3. The use of dppf in this reaction yielded the bimetallic IrIII/FeII hydrido complexes [3] and [4]. X-ray diffraction studies confirmed that complexes [1]-[4] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe)2]2 in the presence of PPh3 to form the IrIII hydrido complex [5] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [5] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility.

6.
Chemistry ; 26(50): 11565-11570, 2020 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-32237240

RESUMO

The tetrakisimidazolium salt H4 -2(Br)4 , featuring a central benzene linker and 1,2,4,5-(nBu-imidazolium-Ph-CH=CH-) substituents reacts with Ag2 O in the presence of AgBF4 to yield the tetranuclear, oktakis-NHC assembly [3](BF4 )4 . Cation [3]4+ features four pairs of olefins from the two tetrakis-NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF4 )4 with a high pressure Hg lamp connects the two tetra-NHC ligands through four cyclobutane linkers to give compound [4](BF4 )4 . Removal of the template metals yields the novel oktakisimidazolium salt H8 -5(BF4 )8 . The tetrakisimidazolium salt H4 -2(BF4 )4 and the oktakisimidazolium salt H8 -5(BF4 )8 have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared.

7.
Angew Chem Int Ed Engl ; 59(25): 10073-10080, 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-31589799

RESUMO

A series of supramolecular assemblies of types [Ag8 (L)4 ](PF6 )8 and [Ag4 (L)2 ](PF6 )4 , obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4-triazolium) salts H4 -L(PF6 )4 and AgI ions, is described. The assembly type obtained dependends on the N-wingtip substituents of H4 -L(PF6 )4 . Changes in the lengths of the N4-wingtip substituents enables controlled formation of assemblies with either [Ag4 (L)2 ](PF6 )4 or [Ag8 (L)4 ](PF6 )8 stoichiometry. The molecular structures of selected [Ag8 (L)4 ](PF6 )8 and [Ag4 (L)2 ](PF6 )4 assemblies were determined by X-ray diffraction analyses. While H4 -L(PF6 )4 does not exhibit fluorescence in solution, their tetra-NHC (NHC=N-heterocyclic carbene) assemblies do upon NHC-metal coordination. Upon irradiation, all assemblies undergo a light-induced, supramolecule-to-supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.

8.
Chem Sci ; 12(6): 2165-2171, 2020 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-34163981

RESUMO

Thanks to the impressive control that microenvironments within enzymes can have over substrates, many biological reactions occur with high regio- and stereoselectivity. However, comparable regio- and stereoselectivity is extremely difficult to achieve for many types of reactions, particularly photochemical cycloaddition reactions in homogeneous solutions. Here, we describe a supramolecular templating strategy that enables photochemical [4 + 4] cycloaddition of 2,6-difunctionalized anthracenes with unique regio- and stereoselectivity and reactivity using a concept known as the supramolecular approach. The reaction of 2,6-azolium substituted anthracenes H4-L(PF6)2 (L = 1a-1c) with Ag2O yielded complexes anti-[Ag2 L 2](PF6)4 featuring an antiparallel orientation of the anthracene groups. Irradiation of complexes anti-[Ag2 L 2](PF6)4 proceeded under [4 + 4] cycloaddition linking the two anthracene moieties to give cyclodimers anti-[Ag2(2)](PF6)2. Reaction of 2,6-azole substituted anthracenes with a dinuclear complex [Cl-Au-NHC-NHC-Au-Cl] yields tetranuclear assemblies with the anthracene moieties oriented in syn-fashion. Irradiation and demetallation gives a [4 + 4] syn-photodimer of two anthracenes. The stereoselectivity of the [4 + 4] cycloaddition between two anthracene moieties is determined by their orientation in the metallosupramolecular assemblies.

9.
Angew Chem Int Ed Engl ; 58(38): 13360-13364, 2019 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-31353768

RESUMO

Metallosupramolecular poly-NHC-metal assemblies were prepared from trigonal hexakis (H6 -1 a(PF6 )6 and H6 -1 b(PF6 )6 ) or nonakis (H9 -3(BF4 )9 ) imidazolium salts and Ag2 O. Complexes [Ag6 (1 a)2 ](PF6 )6 and [Ag6 (1 b)2 ](PF6 )6 are built from six Ag+ ions sandwiched between two trigonal hexacarbene ligands with an inner and an outer NHC donor in each of the three ligand arms. The metal atoms are arranged in two triangles. The hexakis-NHC ligands bear cinnamic ester groups at the outlying NHC donors, used in postsynthetic [2+2] cycloaddition reactions linking two hexakis-NHC ligands by three cyclobutane units to give complexes [Ag6 (2 a)](PF6 )6 and [Ag6 (2 b)](PF6 )6 bearing a dodecacarbene ligand. From the related nonakisimidazolium salt H9 -3(BF4 )9 , complex [Ag9 (4)](BF4 )9 bearing an octadecacarbene ligand was obtained. Removal of the template metals yielded very large, stable, polyimidazolium cations with 12 or 18 internal imidazolium groups.

10.
Chemistry ; 25(41): 9764-9770, 2019 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-31087691

RESUMO

The development of highly emissive dinuclear AgI or AuI complexes [M2 L](PF6 )2 (L=2 a, 2 b; M=Ag, Au) derived from tetraphenylethylene (TPE)-based tetrabenzimidazolin-2-ylidene ligands is reported. The new complexes exhibit a remarkable fluorescence enhancement compared to their parent benzimidazolium salts. The quantum yield (ΦF ) value for salt H4 -2 a(PF6 )4 in dilute solution (c=10-5 m) was found to be less than 1 %, whereas its metal complexes show ΦF values up to 55 % at similar solution concentration. This observation can be attributed to the rigidification of the TPE skeleton upon metalation resulting in a restriction of the intramolecular rotation of the phenyl groups. Functionalization of the complexes [M2 2 b](PF6 )2 (M=Ag, Au) with terminal coumarin groups and subsequent photoirradiation yielded the complexes [M2 3 b](PF6 )2 (M=Ag, Au) bearing a new type of ligand with an unaffected TPE moiety.

11.
Angew Chem Int Ed Engl ; 58(18): 5882-5886, 2019 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-30888717

RESUMO

A series of molecular metalla[2]catenanes featuring Cp*Ir vertices have been prepared by the template-free, coordination-driven self-assembly of dinuclear iridium acceptors and 1,5-bis[2-(4-pyridyl)ethynyl]anthracene donors. The metalla[2]catenanes were formed by using a strategically selected linker type that is capable of participating in sandwich-type π-π stacking interactions. In the solid state, the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear metal complex bridge. Altering the solvent or the concentration, as well as the addition of guest molecules, enabled controlled transformations between metalla[2]catenanes and tetranuclear metallarectangles.

12.
Angew Chem Int Ed Engl ; 58(12): 3986-3991, 2019 03 18.
Artigo em Inglês | MEDLINE | ID: mdl-30650221

RESUMO

A new class of supramolecular metallacycles capable of undergoing photochemical reactions and in situ release of cyclobutanes in solution is described. The molecular metallacycles were generated through coordination-driven self-assembly of dinuclear metal-carbene complexes as organometallic clips with olefin-functionalized bridging ligands. Photolysis of these molecular metallacycles in situ led to structural interconversion and release of the formed cyclobutane products with quantitative conversion. Further modifications of the obtained cyclobutanes provided a series of new species containing the cyclobutane skeleton.

13.
Chem Commun (Camb) ; 54(91): 12887-12890, 2018 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-30379174

RESUMO

An imidazolium/2-chlorobenzimidazole bis-NHC precursor has been reacted with Ag2O followed by transmetallation with [AuCl(THT)] to give the Au-NHC complex via metallation of the imidazolium site, while the reaction of the same bis-NHC precursor with [Pd(PPh3)4] yields exclusively the azolato complex by oxidative addition of the C2-Cl bond to Pd0. Both complexes have been converted into the heterobimetallic Au/Pd-complex by reaction with [Pd(PPh)3]4 (for the NHC complex) or Ag2O/[AuCl(THT)] (for the azolato complex), respectively.

14.
Angew Chem Int Ed Engl ; 57(48): 15767-15771, 2018 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-30306679

RESUMO

Homoleptic and heteroleptic cylinder-shaped poly-NHC metallosupramolecular assemblies [Ag3 (L)2 ](BF4 )3 have been prepared by control of the shape, size, and electronic properties of disk-shaped trisimidazolium salts of type H3 -L(BF4 )3 . Both imidazolium salts with an electron-deficient triazine backbone H3 -A(BF4 )3 or an electron-rich benzene backbone H3 -D(BF4 )3 have been employed. Reaction of H3 -A(BF4 )3 or H3 -D(BF4 )3 with Ag2 O yield trinuclear homoligand complexes [Ag3 (L)2 ](BF4 )3 (L=A, D). However, equimolar mixtures of H3 -A(BF4 )3 and H3 -D(BF4 )3 react with Ag2 O under social self-sorting to give the heteroligand assembly [Ag3 (A)(D)](BF4 )3 . The same heteroligand assembly was obtained by transmetallation from mixtures of complexes [Ag3 (A)2 ](BF4 )3 and [Ag3 (D)2 ](BF4 )3 . The transmetallation from [Ag3 (A)(D)](BF4 )3 to [Au3 (A)(D)](BF4 )3 is also demonstrated. The study expands to concepts of narcissistic and social self-sorting from classical Werner-type ligands to organometallic NHC chemistry thereby opening new routes for the construction of poly-NHC metal assemblies with increasing complexity.

15.
Chem Rev ; 118(19): 9455-9456, 2018 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-30301355
16.
Chem Rev ; 118(19): 9587-9641, 2018 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-29975040

RESUMO

Although the coordination chemistry of N-heterocyclic carbenes (NHCs) with transition metals has been explored for half a century, only in the past ten years has the chemistry of metallosupramolecular assemblies based on poly-NHC ligands been studied more extensively. Remarkable discrete assemblies featuring poly-NHC ligands including two-dimensional metallacycles and three-dimensional metallaprisms/cages have since emerged. These assemblies are mostly obtained starting from various imidazolium or benzimidazolium salts. Driven by the increasing interest in new supramolecular architectures from carbon donor ligands, design, and construction of poly-NHC metal assemblies has become a rapidly growing area of research. The metal-carbene bond length is fixed to approximately 2.0 Å in linear NHC-M-NHC complexes. This allows the use of such complexes bearing olefin-substituted NHC ligands as templates for subsequent photochemical [2 + 2] cycloaddition reactions. The postassembly modification of such assemblies has been actively explored in recent years. In this review, we focus on the synthetic methods, characterization, structural features, and postassembly modifications of metallosupramolecular assemblies obtained from poly-NHC ligands.

17.
Chem Rev ; 118(19): 9642-9677, 2018 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-29939023

RESUMO

Complexes bearing protic N-heterocyclic carbenes (protic NHCs, pNHCs), defined as cyclic carbenes stabilized by two heteroatoms including at least one NH group, have been less explored in comparison to the conventional N,N'-disubstituted NHCs. The small and reactive NH group of the pNHCs differentiates this class of compounds from the classical NR,NR-NHCs with regard to their properties and reactivity. While the free pNHCs have so far eluded isolation due to isomerization to the azole tautomer, a significant number of transition-metal pNHC complexes have by now been prepared by a variety of methods. This article reviews the coordination chemistry of the pNHCs. Synthetic approaches toward complexes of pNHCs are first described, followed by a discussion of the properties and reactivity of pNHC complexes with emphasis on the Brønsted-acidic nature of the NH wingtip. Involvement of the pNHC ligands in catalytically active intermediates and in cooperative catalysis is also discussed.

18.
Dalton Trans ; 47(28): 9442-9452, 2018 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-29955744

RESUMO

A series of bimetallic and trimetallic complexes has been prepared by N-alkylation of mononuclear half-sandwich rhodium and iridium di-NHC complexes featuring bidentate chelate ligands composed of a classical NHC and a C-azolato donor. The shape and the separation between metal centers in the obtained complexes are highly dependent on the alkylating agent used. While the polynuclear complexes were formed as diastereomeric mixtures according to NMR spectroscopy, X-ray diffraction analysis revealed their remarkable preference to crystallize as meso compounds. The reactivity of the bimetallic, olefin-bridged complexes in electrophilic addition reactions has been investigated.

19.
Angew Chem Int Ed Engl ; 57(18): 5161-5165, 2018 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-29394472

RESUMO

A procedure for the synthesis of three-dimensional hexakisimidazolium cage compounds has been developed. The reaction of the trigonal trisimidazolium salts H3 L(PF6 )3 , decorated with three N-olefinic pendants, and silver oxide yielded trinuclear trisilver(I) hexacarbene molecular cylinders of the type [Ag3 L2 ]3+ with the olefinic pendants from the two different tricarbene ligands arranged in three pairs. Subsequent UV irradiation gave three cyclobutane links between the two tris-NHC ligands in three [2+2] cycloaddition reactions, thereby generating a three-dimensional hexakis-NHC ligand. Removal of the metal ions resulted in the formation of three-dimensional hexakisimidazolium cages with a large internal cavity.

20.
Dalton Trans ; 47(7): 2240-2246, 2018 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-29363692

RESUMO

A three-dimensional heterometallic coordination macrocycle is found to be capable of encapsulating planar pyrene (G1), coronene (G4) and non-planar corannulene (G2) guest molecules in high yields, giving rise to 1 : 1 host-guest complexes. The bowl-shaped guest corannulene is found to be significantly flattened upon inclusion within the cavity. However, macrocyclic compounds with larger cavity sizes, which form 1 : 1 stoichiometry assemblies with a naphthalene bisimide planar molecule (G3), are more inclined to form infinite sandwich structures. Furthermore, these heterometallic coordination macrocycles can be destroyed in the presence of a soft base to form hexanuclear triangular prism complexes. These structures are unambiguously revealed by single-crystal X-ray analysis.

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