N-HETEROCYCLIC Carbene Complexes

A wide range of platinum(0)-η2 -( E )-1,2-ditosylethene complexes bearing isocyanide, phosphine and N -heterocyclic carbene ancillary ligands have been prepared with high yields and selectivity. All the novel products underwent thorough characterization using spectroscopic techniques, including NMR and FT-IR analyses. Additionally, for some compounds, the solid-state structures were elucidated through X-ray diffractometry. The synthesized complexes were successively evaluated for their potential as anticancer agents against two ovarian cancer cell lines (A2780 and A2780 cis ) and one breast cancer cell line (MDA-MB-231)...

The targeting of human thioredoxin reductase is widely recognized to be crucially involved in the anticancer properties of several metallodrugs, including Au(I) complexes. In this study, the mechanism of reaction between a set of five N-heterocyclic carbene Au(I) complexes and models of the active Sec residue in human thioredoxin reductase was investigated by means of density functional theory approaches. The study was specifically addressed to the kinetics and thermodynamics of the tiled process by aiming at elucidating and explaining the differential inhibitory potency in this set of analogous Au(I) bis-carbene complexes...

N -heterocyclic carbene (NHC) silver(I) and gold(I) complexes have found different applications in various research fields, as in medicinal chemistry for their antiproliferative, anticancer, and antibacterial activity, and in chemistry as innovative and effective catalysts. The possibility of modulating the physicochemical properties, by acting on their ligands and substituents, makes them versatile tools for the development of novel metal-based compounds, mostly as anticancer compounds. As it is known, chemotherapy is commonly adopted for the clinical treatment of different cancers, even though its efficacy is hampered by several factors...

Most 3d metal-based single-molecule magnets (SMMs) use N-ligands or ligands with even softer donors to impart a particular coordination geometry and increase the zero-field splitting parameter | D |, while complexes with hard O-donor ligands showing slow magnetization relaxation are rare. Here, we report that a diamagnetic NiII complex of a tetradentate ligand featuring two N -heterocyclic carbene and two alkoxide-O donors, [LO,O Ni], can serve as a {O,O'}-chelating metalloligand to give a trinuclear complex [(LO,O Ni)Co(LO,O Ni)](OTf)2 ( 2 ) with an elongated tetrahedral {CoII O4 } core, D = -74...

A series of terminal mono- and disubstituted beryllium azides of the form [(CAAC)Be(N3)R] (R = CAACH, Dur; CAACH / CAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-yl/idene, Dur = 2,3,5,6-tetramethylphenyl) and [L2Be(N3)2] (L = CAACNH = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-imine, IiPrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene), respectively, were synthesized and characterized by NMR spectroscopy and X-ray crystallography. Thermolysis and photolysis products of these first examples of tricoordinate azidoberyllium complexes evidence extensive ligand scrambling and the formal insertion of nitrenes into the CAAC-Be bond, generating cyclic alkyl(amino)imine (CAAI) ligands...

Cationic Au(I)─NHC (NHC = N-heterocyclic carbene) complexes have become an important class of catalysts for alkyne π-activation reactions in organic synthesis. In particular, these complexes are characterized by high stability of catalytic species engendered by strong σ-donation and metal backbonding. Herein, we report the synthesis and characterization of well-defined [Au(NHC)Cl] complexes featuring recently discovered IPr# family of ligands that hinge upon modular peralkylation of aniline...

Gold complexes, because of their unique carbophilic nature, have evolved as efficient catalysts for catalyzing various functionalization reactions of C-C multiple bonds. However, the realization of enantioselective transformations via gold catalysis remains challenging due to the geometrical constraints and coordination behaviors of gold complexes. In this context, merged gold/organocatalysis has emerged as one of the intriguing strategies to achieve enantioselective transformations which could not be possible by using a single catalytic system...

This work reports the cooperative reactivity of rare-earth aryloxide complexes with N-heterocyclic carbene (NHC) or N-heterocyclic olefin (NHO), showcasing their synergistic effect in the activation of H2 and diverse organic substrates.  Reactions of RE(OAr)3 (RE = La, Sm, and Y; Ar = 2,6-tBu2-C6H3) with unsaturated NHC ItBu (:C[N(R)CH]2, R = tBu) isolate abnormally bound RE metal NHC complexes RE/aNHC. In contrast, no metal-NHO adducts were formed when RE(OAr)3 were treated with NHO (R2C=C[N(R)C(R)]2, R = CH3)...

The discovery of ferrocene in 1951 was a significant landmark in the field of organometallic chemistry, and since then, numerous sandwich- or half-sandwich metallic complexes have been reported. However, silver stands as an intriguing exception in this regard, and knowledge of its bonding situation has remained undisclosed. Herein, unprecedented 12-vertex metallacarboranes of Ag(I) ( 2a and 2b ) were synthesized through the reaction of sodium hexamethyldisilazide (NaHMDS) with the mixture of nido -C2 B9 carborane anion-supported N -heterocyclic carbene precursors ( 1a and 1b ) and [Ag(PPh3 )Cl]4 ...

Building molecular complexity from simple feedstocks through precise peripheral and skeletal modifications is central to modern organic synthesis. Nevertheless, a controllable strategy through which both the core skeleton and the periphery of an aromatic heterocycle can be modified with a common substrate remains elusive, despite its potential to maximize structural diversity and applications. Here we report a carbene-initiated chemodivergent molecular editing of indoles that allows both skeletal and peripheral editing by trapping an electrophilic fluoroalkyl carbene generated in situ from fluoroalkyl N-triftosylhydrazones...

Two iron complexes featuring the bidentate, nonconjugated N-heterocyclic carbene (NHC) 1,1'-methylenebis(3-methylimidazol-2-ylidene) (mbmi) ligand, where the two NHC moieties are separated by a methylene bridge, have been synthesized to exploit the combined influence of geometric and electronic effects on the ground- and excited-state properties of homoleptic FeIII -hexa-NHC [Fe(mbmi)3 ](PF6 )3 and heteroleptic FeII -tetra-NHC [Fe(mbmi)2 (bpy)](PF6 )2 (bpy = 2,2'-bipyridine) complexes. They are compared to the reported FeIII -hexa-NHC [Fe(btz)3 ](PF6 )3 and FeII -tetra-NHC [Fe(btz)2 (bpy)](PF6 )2 complexes containing the conjugated, bidentate mesoionic NHC ligand 3,3'-dimethyl-1,1'-bis( p -tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene) (btz)...

A comprehensive study on the synthesis and characterization of NHC-ligated nickel(II) cyanoborates (CBs) is presented (NHC = N-heterocyclic carbene). Nickel(II) cyanoborates Ni[BH2 (CN)2 ]2 ·H2 O (Ib·H2 O), Ni[BH(CN)3 ]2 ·0.5H2 O (Ic·0.5H2 O), Ni[B(CN)4 ]2 ·H2 O (Id·H2 O) were reacted with selected NHCs of different steric size. The reaction of the nickel cyanoborates with small to medium-sized NHCs Me2 ImMe and iPr2 Im (R2 Im = 1,3-di-organyl-imidazolin-2-ylidene; R2 ImMe = 1,3-di-organyl-4,5-dimethyl-imidazolin-2-ylidene) afforded cyanoborate salts containing the rare homoleptic fourfold NHC-ligated nickel(II) cations [Ni(NHC)4 ]2+ (NHC = Me2 ImMe (1c-d), iPr2 Im (2c-d)) and cyanoborate counter-anions...

Here, we describe a cooperative Pd(0)/chiral phosphoric acid catalytic system that allows us to realize the first chemo-, regio-, and enantioselective sequential cross-[4 + 2]-cycloaddition/decarboxylation reaction between 2-pyrones and unactivated acyclic 1,3-dienes. The key to the success of this transformation is the utilization of an achiral N- heterocyclic carbene (NHC) as the ligand and a newly developed chiral phosphoric acid as the cocatalyst. Experimental investigations and computational studies support the idea that the Pd(0)/NHC complex acts as a π-Lewis base to increase the nucleophilicity of 1,3-dienes via η2 coordination, while the chiral phosphoric acid simultaneously increases the electrophilicity of 2-pyrones by hydrogen bonding...

Molecular-level understanding of the acid/base properties of heterogeneous catalysts requires the development of selective spectroscopic probes to establish structure-activity relationships. In this work we show that substituting the surface protons in oxide supports by isolobal N-heterocyclic carbene (NHC) Ag cations and measuring their 109 Ag nuclear magnetic resonance (NMR) signatures enables to probe the speciation and to evaluate the corresponding Brønsted acidity of the substituted OH surface sites...

To explore green gold leaching reagents, a series of imidazolium cyanate ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium cyanate ([C2 MIM][OCN]), 1-propyl-3-methyl-imidazolium cyanate ([C3 MIM][OCN]) and 1-butyl-3-methyl-imidazolcyanate ([C4 MIM][OCN]) were synthesized and characterized by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric (TG) analysis. In this research, the imidazolium cyanates were utilized as a solute, which not only decreased the usage of ILs but also increased their gold dissolution capability...

N-heterocyclic carbene (NHC) iridium(III) complexes are considered as promising candidates for blue emitters in organic light-emitting diodes. They can play the roles of the emitter as well as of electron and hole transporters in the same emission layer. We investigate optical transitions in such complexes with account of geometry and electronic structure changes upon excitation or charging and exciton transfer between the complexes from first principles. It is shown that excitation of NHC iridium complexes is accompanied by a large reorganization energy ∼0...

Meta [ n ]cycloparaphenylenes ( m [ n ]CPPs) as well as N -heterocyclic carbene (NHC) gold(I)-complexes are intriguing building blocks for material and life sciences due to their extraordinary structures resulting in unique photophysical properties. Herein, we report the combination of a m [6]CPP with a N -heterocyclic carbene serving as a ligand in a linear gold(I)-complex possessing the form [AuBr(NHC)]. Solid-state structures of both the precursor and the complex are presented and discussed. Moreover, we investigated the luminescence properties of both the imidazolium intermediate and the corresponding gold(I)-complex...

Phosphorus-bridged rigid, bent bis(N-heterocyclic) carbenes have not been reported, so far, despite having structural features that could make them interesting ligands in coordination and main group element chemistry. In previous reports, we had demonstrated that tuning of σ3 - and σ4 -phosphorus environments in planarised bis(NHCs) affects electronic properties and can provide additional coordination sites. Herein, we report on first examples of synthesis and conversion of 1,4-diphosphabarrelene-related compounds into rigid bent, doubly P-bridged bis(NHCs)...

Liquid assisted ball milling of [NHC]HBr (NHC = N-heterocyclic carbene) salts with copper(I) chloride, and a range of alkali metal complexes was shown to efficiently produce (NHC)CuX (NHC = normal or RE-NHC, X = halide, alkoxide, amide, alkyl, aryl; RE-NHC = ring-expanded NHC).

The synthesis and isolation of stable heavier analogues of nitrile ylide as N-heterocyclic carbene (NHC) adducts of phosphasilenyl-tetrylene [(NHC)(Ter Ar)Si(H)PE14 (Ter Ar)] (E14 = Ge 1, Sn 2; Ter Ar = 2,6-Mes2 C6 H3 , NHC = IMe4 ) are reported. The delocalized Si-P-E14 π-conjugation was examined experimentally and computationally. Interestingly, the germanium derivative 1 exhibits a 1,3-dipolar nature, leading to an unprecedented [3 + 2] cycloaddition with benzaldehyde, resulting in unique heterocycles containing four heteroatoms from group 14, 15, and 16...