Search results for "N-heterocyclic carbene"

tBuLi-Mediated One-Pot Direct Highly Selective Cross-Coupling of Two Distinct Aryl Bromides.

2015

A Pd-catalyzed direct cross-coupling of two distinct aryl bromides mediated by tBuLi is described. The use of [Pd-PEPPSI-IPr] or [Pd-PEPPSI-IPent] as catalyst allows for the efficient one-pot synthesis of unsymmetrical biaryls at room temperature. The key for this selective cross-coupling is the use of an ortho-substituted bromide that undergoes lithium-halogen exchange preferentially.

N‐Heterocyclic Carbene Catalyzed Asymmetric Synthesis of Pentacyclic Spirooxindoles via [3+3] Annulations of Isatin‐Derived Enals and Cyclic N‐Sulfon…

2019

New Gold(I) Organometallic Compounds with Biological Activity in Cancer Cells

2014

N-Heterocyclic carbene gold(I) complexes bearing a fluorescent coumarin ligand were synthesized and characterized by various techniques. The compounds were examined for their antiproliferative effects in normal and tumor cells in vitro; they demonstrated moderate activity and a certain degree of selectivity. The compounds were also shown to efficiently inhibit the selenoenzyme thioredoxin reductase (TrxR), whereas they were poorly effective towards the glutathione reductase (GR) and glutathione peroxidase enzymes. Notably, {3-[(7-methoxy-2-oxo-2H-chromen-4-yl) methyl]-1-methylimidazol-2-ylidene}(tetra-O-acetyl-1-thio-beta-D-glucopyranosido) gold(I) (3) showed a pronounced inhibition of TrxR…

N-heterocylic and mesoionic carbene complexes of the group 4 metals

2020

International audience; N-heterocyclic carbene (NHC) complexes of group 4 metals have been far less studied than their late metal counterparts. However, the field has been explored for over 25 years, and there is now a much clearer understanding of the metal-NHC interaction. Some exceptionally robust and active catalysts have been reported for a number of group 4 metal-catalyzed reactions, and recent developments suggest that NHCs are well-suited to enable the isolation of otherwise difficult to tame species, such as low-valent complexes.

Unprecedented use of silver(I) N-heterocyclic carbene complexes for the catalytic preparation of 1,2-bis(boronate) esters.

2005

Catalytic diboration of internal and terminal alkenes with Ag(I) N-heterocyclic carbene complexes leads to 1,2-bis(boronate) esters as single intermediates, that can be oxidised towards the corresponding diols. Sanau Torrecilla, Mercedes, Mercedes.Sanau@uv.es

Isolation of Free Phenylide-like Carbanions with N-Heterocyclic Carbene Frameworks

2009

A series of 1,3-bis(2,6-diisopropylphenyl)-5-methyl-1,3-diaza-4,6-diborabenzenes with methyl, phenyl, and dimethylamino substituents on the ring boron atoms were prepared using the cyclocondensation reaction between N,N′-bis(2,6-diisopropylphenyl)trimethylsilylformamidine and the appropriately substituted 1,1-bis(organochloroboryl)ethane, followed by deprotonation of the cationic ring intermediate. The planar, heterocyclic benzene analogues could be further deprotonated at the other ring carbon using an additional equivalent of potassium hexamethyldisilazide to yield organometallic derivatives akin to the potassium phenylide. The potassium cations could be efficiently sequestered in both so…

Asymmetric Synthesis of Spirobenzazepinones with Atroposelectivity and Spiro-1,2-Diazepinones by NHC-Catalyzed [3+4] Annulation Reactions

2016

A strategy for the NHC-catalyzed asymmetric synthesis of spirobenzazepinones, spiro-1,2-diazepinones, and spiro-1,2-oxazepinones has been developed via [3+4]-cycloaddition reactions of isatin-derived enals (3C component) with in-situ-generated aza-o-quinone methides, azoalkenes, and nitrosoalkenes (4atom components). The [3+4] annulation strategy leads to the seven-membered target spiro heterocycles bearing an oxindole moiety in high yields and excellent enantioselectivities with a wide variety of substrates. Notably, the benzazepinone synthesis is atroposelective and an all-carbon spiro stereocenter is generated.

Cathodic behaviour of dicationic imidazolium bromides: the role of the spacer

2019

The cathodic reduction of dicationic imidazolium bromides, whose spacer is either an aliphatic chain or a xylyl group, leads to the formation of the corresponding N-heterocyclic carbenes (NHCs), which were isolated as the corresponding thiones, after reaction with elemental sulfur. The behaviour of the dications was compared with the corresponding monocations. The behaviour of dicarbenes depends on the nature of the spacer. This study evidenced that dicarbenes deriving from xylyl dications are less stable than the corresponding aliphatic ones (giving lower yields in thiones), due to a debenzylation reaction. On the other hand, the yields in thiones starting from aliphatic dications are high…

Nickel as a Lewis Base in a T‐Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand

2018

Flexible, chelating bis(NHC) ligand 2, able to accommodate both cis- and trans-coordination modes, was used to synthesize (2)Ni(η 2 -cod), 3. In reaction with GeCl2, this produced (2)NiGeCl2, 4, featuring a T-shaped Ni(0) and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2, in a reaction that formally involved Ni-Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ-donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2Ni(cod) complexes 9 and 10, as well as (NHC)2GeCl2 derivative 11, incor…

Mono‐ and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis‐1,4‐([3]Cumulene)‐p-carboquinoid System

2017

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. peerReviewed