Lone-Pair-π Bond Strength Unveiled by a Combined Experimental and Computational Study.

A series of naphthalene-diimide (NDI) and perylene-diimide (PDI) connected bis-N-heterocyclic carbene complexes of iridium(III) have been prepared and fully characterized. The analysis of their NMR spectroscopic features, together with their molecular structures show that these species display lone-pair-π interactions between the chloride ligands of the Ir(III) complex and the heterocycles of the NDI/PDI moieties. The detection of this type of interaction in solution is due to the formation of two atropisomers, which are formed as a result of the restricted rotation about the Ir-C bond imposed by the (Cl)lp⋅⋅⋅π interaction.

Tuning the Catalytic Activity of a Pincer Complex of Rhodium(I) by Supramolecular and Redox Stimuli.

We report the rhodium(I) complex [Rh(CNC-NDI)(CO)] , in which CNC-NDI refers to a pincer-CNC ligand decorated with a naphthalenediimide moiety. Due to the presence of the planar CNC ligand and the naphthalenediimide moiety, the electronic nature of the complex can be modulated by means of supramolecular and redox stimuli, respectively. The metal complex shows a strong π-π-stacking interaction with coronene.

Supramolecular Control of the Oxidative Addition as a Way To Improve the Catalytic Efficiency of Pincer-Rhodium (I) Complexes.

H NMR studies using a cationic complex with a pyridine-di-imidazolylidene pincer ligand of formula [Rh(CNC)(CO)] revealed that this compound showed high binding affinity with coronene in CH Cl . The interaction between coronene and the planar Rh complex is established by means of π-stacking interactions. This interaction has a strong impact on the electron-donating strength of the pincer CNC ligand, which is increased significantly, as demonstrated by the shifting of the ν(CO) stretching bands to lower frequencies.

A redox-switchable catalyst with an 'unplugged' redox tag.

Two bis-(propyl-imidazolium)-napthalenediimide (NDI) salts were prepared and used as N-heterocyclic carbene (NHC) precursors for the preparation of dimetallic complexes of rhodium and iridium. Infrared spectroelectrochemical studies indicate that the metals are sensitive to changes in the electronic state of the NDI moiety. The catalytic behavior of the rhodium and iridium complexes was tested in the cycloisomerization of alkynoic acids, where the complexes showed effective redox-switching properties.

Redox-Switchable Complexes Based on Nanographene-NHCs.

A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies.

Insights into the past and future of Janus-di-N-heterocyclic carbenes.

Janus di-N-heterocyclic carbene (NHC) ligands are a subclass of poly-NHCs that feature coordination to two transition metals in a facially opposed manner. The combination of the structural features of Janus type ligands, with the properties conferred by the NHC ligands, has conferred Janus-di-NHCs with privileged attributes for their use in diverse areas of research, such as homogeneous catalysis, materials chemistry and supramolecular chemistry. In molecular chemistry, Janus di-NHCs constitute one of the most useful chemical platforms for constructing dimetallic structures, and this includes both homo- and hetero-dimetallic compounds.

Redox-Switchable Cycloisomerization of Alkynoic Acids with Napthalenediimide-Derived N-Heterocyclic Carbene Complexes.

Two naphthalene-diimide (NDI) bis-imidazolium salts have been used as N-heterocyclic carbene (NHC) precursors for the preparation of NDI-functionalized complexes of rhodium and iridium of general formula [MCl(NDI-NHC)(COD)] (M=Rh, Ir; NDI-NHC=NDI-functionalized NHC ligand). Comparison of the IR spectra of the complexes [IrCl(NDI-NHC)(CO) ] and their related one- and two-electron reduced forms, reveal that each one-electron reduction produces a decrease of the average ν(CO) of 9-10 cm , indicating a significant enhancement of the electron-richness of the metal. The [MCl(NDI-NHC)(COD)] complexes were tested in the catalytic cycloisomerization of alkynoic acids.

N-Heterocyclic Carbenes: A Door Open to Supramolecular Organometallic Chemistry.

The field of metallosupramolecular chemistry is clearly dominated by the use of O-, N-, and P-donor Werner-type polydentate ligands. These molecular architectures are of high interest because of their wide range of applications, which include molecular encapsulation, stabilization of reactive species, supramolecular catalysis, and drug delivery, among others. Only recently, organometallic ligands have allowed the preparation of a variety of supramolecular coordination complexes, and the term supramolecular organometallic complexes (SOCs) is gaining space within the field of metallosupramolecular chemistry.

Ligand & band gap engineering: tailoring the protocol synthesis for achieving high-quality CsPbI quantum dots.

Hot-injection has become the most widespread method used for the synthesis of perovskite quantum dots (QDs) with enormous interest for application in optoelectronic devices. However, there are some aspects of the chemistry involved in this synthesis that have not been completely investigated. In this work, we synthesized ultra-high stable CsPbI QDs for more than 15 months by controlling two main parameters: synthesis temperature and the concentration of capping ligands.

Template-Controlled Synthesis of Polyimidazolium Salts by Multiple [2+2] Cycloaddition Reactions.

The tetrakisimidazolium salt H -2(Br) , featuring a central benzene linker and 1,2,4,5-(nBu-imidazolium-Ph-CH=CH-) substituents reacts with Ag O in the presence of AgBF to yield the tetranuclear, oktakis-NHC assembly [3](BF ) . Cation [3] features four pairs of olefins from the two tetrakis-NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF ) with a high pressure Hg lamp connects the two tetra-NHC ligands through four cyclobutane linkers to give compound [4](BF ) .

The Complex Coordination Landscape of a Digold(I) U-Shaped Metalloligand.

A U-shaped di-gold metallotweezer with two pyrene-imidazolylidene edges and a xanthenyl-bis-alkynyl connector was prepared. This metallotweezer acts as metalloligand in the presence of Cu , Tl , or Ag , showing three clearly distinct coordination patterns depending on the cation used. The coordination to Cu leads to a complex in which the metalloligand is coordinated in a pincer form.

Gold(I) Metallo-Tweezers for the Recognition of Functionalized Polycyclic Aromatic Hydrocarbons by Combined π-π Stacking and H-Bonding.

Two gold(I)-based metallo-tweezers with bis(Au-NHC) pincers and a carbazole connector have been obtained and used for the recognition of polycyclic aromatic hydrocarbons (PAHs). In the case of the tweezer with pyrene-NHC ligands, the presence of the pyrene fragment and the N-H bond in the carbazole linker enable the receptor to show significant enhanced binding abilities toward PAHs functionalized with H-bonding groups, through combined π-π stacking and H-bonding.

Cation-Driven Self-Assembly of a Gold(I)-Based Metallo-Tweezer.

A combination of self-complementary π-π-stacking interactions and metallophilic interactions triggered the self-assembly of a new digold(I) metallo-tweezer in the presence of several types of M ions. Titrations by fluorescence spectroscopy enabled the determination of the association constants of the resulting inclusion duplex complexes.

Platinum-Based Organometallic Folders for the Recognition of Electron-Deficient Aromatic Substrates.

A series of platinum complexes with cis-oriented polyaromatic N-heterocyclic carbene ligands were prepared and characterized. The relative disposition of the polyaromatic ligands about the metal cause these compounds to behave as metallofolders, featuring a cavity defined by the void space between the polyaromatic functionalities. The complexes were used as receptors of organic molecules, whereby selective affinity was displayed for electron-deficient aromatic substrates, such as 1,2,4,5-tetracyanobenzene (TCNB), 2,4,7-trinitro-9-fluorenone (TNFLU), and 1,4,5,8-naphtalenetetracarboxylic dianhydride (NTCDA).

Fluorescent Pyrene-Based Bis-azole Compounds: Synthesis and Photophysical Analysis.

A rational synthetic procedure for the preparation of a series of pyrene-based neutral and dicationic bis-azole compounds is reported. The method allows the tailored design of pyrene-based azoles with different substituents at the nitrogen atoms of the heterocycles, for which the relative conformation of the resulting bis-azoles can be easily controlled. The bis-azoliums were used for the preparation of the related diplatinum complexes by reaction with [{Pt(ppy)(μ-Cl)2 }2 ] (ppy=2-phenylpyridinate).

Postmodification of the electronic properties by addition of π-stacking additives in N-heterocyclic carbene complexes with extended polyaromatic systems.

A series of iridium complexes containing phenanthro[4,5-abc]phenazino[11,12-d]imidazol-2-ylidene and acetonaphtho[1,2-b]quinoxaline[11,12-d]imidazol-2-ylidene ligands have been obtained and fully characterized. These complexes display highly extended polyaromatic systems attached to the backbone of the N-heterocyclic carbene. The presence of this extended polyaromatic system makes the electron-donating character of these ligands sensitive to the presence of π-stacking additives, such as pyrene and hexafluorobenzene.

Experimental and theoretical approaches to the influence of the addition of pyrene to a series of Pd and Ni NHC-based complexes: catalytic consequences.

A series of Ni and Pd complexes with three different N-heterocyclic carbene (NHC)-based ligands (imidazolylidene, benzimidazolylidene and pyrene-imidazolylidene) has been prepared and fully characterized. The influence of the addition of pyrene to solutions containing these complexes is studied by means of NMR and UV/Vis spectroscopies and by cyclic voltammetry. The addition of pyrene to the pyrene-NHC-containing Pd and Ni complexes gives rise to the formation of adducts by π-π stacking interactions between pyrene and the pyrene group of the NHC ligand.

Pyrene-based bisazolium salts: from luminescence properties to janus-type bis-N-heterocyclic carbenes.

A series of pyrene-based bisazolium salts have been obtained starting from 4,5,9,10-tetrabromo-2,7-di-tert-butylpyrene. The synthetic procedure to the pyrene-bisazoliums (PBIs) reveals an unexpected behavior, as a consequence of the presence of the alkyl groups (alkyl=Me, Et, n-Pr, and n-Bu) coming from the trisalkoxyformate in the final products, instead of the expected tBu of tAmyl groups from the starting tetra-aminated pyrenes. All bisazoliums show fluorescence properties, with emissions in the range of 370-420 nm, and quantum yields ranging from 0.

Main-chain organometallic microporous polymers bearing triphenylene-tris(N-heterocyclic carbene)-gold species: catalytic properties.

Two triphenylene-based tris(N-heterocyclic carbene)-gold-acetylide main-chain organometallic microporous polymers (MOMPs) were obtained and fully characterized. Both materials show spherical shapes, and their size is highly dependent on the type of acetylene used in the synthetic protocol. The new solids were tested in the catalytic reduction of nitroarenes with NaBH4 and in the three-component Strecker reaction for the synthesis of α-aminonitriles, and showed high activity in both processes.

Unveiling the stereoelectronic properties of a triphenylene-based tris N-heterocyclic carbene.

Two rhodium complexes with a triphenylene-based tris-NHC have been fully characterized. DFT and electrochemical studies suggest that the electronic communication between the metals is very weak, and that the electron donating properties of the ligand are very similar to those shown by its benzimidazolylidene analogue.

Rhodium-NHC complexes mediate diboration versus dehydrogenative borylation of cyclic olefins: a theoretical explanation.

In rhodium catalysed borylation of cyclic olefins, the synergy between bidentate NHC ligands, that modify cationic Rh(I) species, and the use of non-polar solvents, such as cyclohexane, is the key factor to favour a less energetically demanding route towards the formation of diborated products versus allyl boronate esters.

Biomedical properties of a series of ruthenium-N-heterocyclic carbene complexes based on oxidant activity in vitro and assessment in vivo of biosafety in zebrafish embryos.

N-Heterocyclic carbene (NHC) ligands have attracted great interest over the last decade for their use in the design of homogenous catalysts. NHC-based metal complexes have interesting potential biomedical applications, such as in antimicrobial and cancer therapy, which are beginning to be explored more fully. We have studied here the oxidant activities of a series of Ru(II) complexes in vitro and zebrafish (Danio rerio) have been used as a model in vivo to investigate and characterize the toxicity of some of these compounds.

A simple catalyst for the efficient benzylation of arenes by using alcohols, ethers, styrenes, aldehydes, or ketones.

One catalyst fits all! One catalyst is active for a wide set of benzylating reactions (see scheme). A tandem process allows the use of aldehydes and ketones as benzylating agents.The compound [IrCp*(OTf)(2)(I(nBu))] (I(nBu)=1,3-di-n-butyl-imidazolylidene) is an effective catalyst in the benzylation of arenes with different benzylating agents, such as alcohols, ethers and styrenes, representing an unprecedented highly versatile catalyst for this type of process.