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1.
Angew Chem Int Ed Engl ; 58(32): 10995-11000, 2019 Aug 05.
Artículo en Inglés | MEDLINE | ID: mdl-31087755

RESUMEN

Two new zirconium-based metal-organic frameworks with the composition [Zr6 O4 (OH)4 (OAc)6 (BDC)3 ] (CAU-26) and [Zr5 O4 (OH)4 (OAc)4 (BDC)2 ] (CAU-27) are reported, which were synthesized from acetic acid, a rarely utilized but green and sustainable solvent (BDC2- : 1,4-benzenedicarboxylate). Structure determination aided by automated electron diffraction tomography revealed that CAU-26 is composed of layers of well-known {Zr6 O8 } clusters interconnected by terephthalate ions. In contrast CAU-27 exhibits a three-dimensional structure with a so far unknown type of one-dimensional inorganic building unit (IBU), which can be rationalized as condensed polyhedron-sharing chains of {Zr6 O8 } clusters. CAU-26 occurs as an intermediate of the CAU-27 synthesis and can be isolated easily, when reaction temperature and time are decreased. We were also able to synthesize two isoreticular derivatives of CAU-27 with extended linker molecules by implementing 4,4'-biphenyldicarboxylic acid (H2 BPDC) and 5,5'-dicarboxy-2,2'-bipyridine (H2 BIPY). All materials show high thermal and chemical stability as well as permanent microporosity. The excellent stability of CAU-27-BIPY was exploited to synthesize a performant iridium-supported heterogeneous MOF-based catalyst for the direct C-H borylation of arenes.

2.
Chem Commun (Camb) ; 57(51): 6324-6327, 2021 Jun 24.
Artículo en Inglés | MEDLINE | ID: mdl-34076653

RESUMEN

The catalytic conversion of crude glycerol to biopropene was investigated. A bifunctional Ru-ionic liquid system showed a high tolerance for common crude glycerol impurities like water, salts and methanol. After optimizing both dehydration and olefin selectivity, a 82% biopropene yield (94% selectivity) was obtained directly from industrial waste glycerol.

3.
ACS Appl Mater Interfaces ; 12(42): 47457-47466, 2020 Oct 21.
Artículo en Inglés | MEDLINE | ID: mdl-32970411

RESUMEN

Heterogeneous single-site catalysts contain spatially isolated, well-defined active sites. This allows not only their easy recovery by solid-liquid separation but also the detailed active site design similar to homogeneous catalysts. Here, heterogeneous Pd(II) single-site catalysts were assembled, based on mesoporous metal oxide-bisphosphonate materials as supports. This new family of hybrid organic-inorganic materials with tunable porosity was further functionalized with thioether ligands containing S,O-binding sites that enhance the activity of Pd(II) for C-H activation reactions. The structures of the resulting Pd(II) single-site catalysts were carefully analyzed via solid-state NMR spectroscopy, via texture analysis by N2 physisorption, infrared spectroscopy, and transmission electron microscopy. Furthermore, the immediate environment of the isolated Pd(II) active sites was studied with X-ray absorption spectroscopy. A clear relationship between the thioether ligand surface density and catalyst activity could be established. Significantly higher yields were obtained using highly porous metal oxide-bisphosphonate materials as supports compared to materials with lower porosities, such as conventional metal oxides, indicating that the high surface area facilitates the presence of isolated, well-accessible S,O-supported Pd(II) active sites. A wide scope of model substrates, including industrially relevant arenes, can be converted with high yields by the optimal heterogeneous Pd catalyst.

4.
Chem Commun (Camb) ; 50(35): 4624-7, 2014 May 07.
Artículo en Inglés | MEDLINE | ID: mdl-24668065

RESUMEN

Air-stable N-heterocyclic carbene-nickel(ii) complexes at concentrations as low as 1 mol% exhibit high catalytic activity for the α-arylation of acyclic ketones and join a highly restricted list of nickel catalysts for this key reaction. Mechanistic investigations suggest a radical pathway.


Asunto(s)
Acetona/química , Complejos de Coordinación/química , Hidrocarburos Aromáticos/química , Cetonas/química , Metano/análogos & derivados , Níquel/química , Catálisis , Compuestos Heterocíclicos/química , Metano/química , Modelos Moleculares
5.
Dalton Trans ; 43(9): 3722-9, 2014 Mar 07.
Artículo en Inglés | MEDLINE | ID: mdl-24434813

RESUMEN

The one-step synthesis of a mesoporous silica of SBA type, functionalized with a 1-(2,6-diisopropylphenyl)-3-propyl-imidazolium (iPr2Ar-NHC-propyl) cation located in the pore channels, is described. This material was obtained by the direct hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and 1-(2,6-diisopropylphenyl)-3-[3-(triethoxysilyl)propyl]-imidazolium iodide in the presence of Pluronic P123 as a non-ionic structure-directing agent and aqueous HCl (37%) as an acid catalyst. Small-angle X-ray diffraction measurements, scanning and transmission electron microscopies, as well as dinitrogen sorption analyses revealed that the synthesized material is highly mesoporous with a 2D hexagonal arrangement of the porous network. (13)C and (29)Si CP-MAS NMR spectroscopy confirmed that the material contains intact iPr2Ar-NHC-propyl cations, which are covalently anchored via silicon atoms fused into the silica matrix. Moreover, comparison of the latter data with those of an analogous post-synthetic grafted SBA-NHC material allowed us to establish that, as expected, (i) it is most probably more homogeneous and (ii) it shows a more robust anchoring of the organic units. Finally, elemental mapping by energy dispersive X-ray spectroscopy in the scanning electron microscope demonstrated a very homogeneous distribution of the imidazolium units within the one-pot material, moreover with a high content. This study thus demonstrates that a relatively bulky and hydrophilic imidazolium unit can be directly co-condensed with TEOS in the presence of a structure-directing agent to provide in a single step a highly ordered and homogeneous mesoporous hybrid SBA-NHC material, possessing a significant number of cationic NHC sites.

6.
Chem Commun (Camb) ; 49(57): 6424-6, 2013 Jul 21.
Artículo en Inglés | MEDLINE | ID: mdl-23752919

RESUMEN

The η(5)-cyclopentadienyl (Cp) ligands of 18-electron half-sandwich alkyl,NHC-nickel complexes are readily displaced under acidic conditions to afford a novel class of cis-C,C-nickel square planar complexes. Remarkably, the nickel-alkyl and nickel-carbene bonds are not ruptured in these unprecedented Cp acidolysis reactions.

7.
Dalton Trans ; 40(38): 9889-98, 2011 Oct 14.
Artículo en Inglés | MEDLINE | ID: mdl-21879086

RESUMEN

The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised. Reaction of 2 in dioxane with PdCl(2) in the presence of CsCO(3) and KBr (80 °C, 24 h) gives the carbene complex trans-[PdBr(2)(calix-monocarbene)(2)] (14), containing two N-heterocyclic carbene ligands derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed pyridine-carbene complex trans-[PdBr(2)(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the bis-imidazolium salt 3a with [Pd(OAc)(2)] affords a chelate complex, trans-[PdI(2){calix-bis(carbene)}] (16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex 16, as well as its analogue 17, obtained from 3b, display apparent C(s)-symmetry in solution. This is not the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone structure for the calixarene skeleton, which reduces the symmetry to C(1). The chelate complex 17 shows poor activity in Suzuki-Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene ligands of 14 and 15 operate typically as bulky NHC-ligands.


Asunto(s)
Calixarenos/química , Complejos de Coordinación/síntesis química , Compuestos Heterocíclicos/química , Imidazoles/química , Metano/análogos & derivados , Fenoles/química , Complejos de Coordinación/química , Cristalografía por Rayos X , Compuestos Heterocíclicos/síntesis química , Metano/química , Modelos Moleculares , Conformación Molecular , Paladio/química , Estereoisomerismo
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