N-Heterocyclic Carbene Complexes of Mercury, Silver, Iridium, Platinum, Ruthenium, and Palladium Based on the Calix[4]arene Skeleton

Inherently dinuclear iridium(III) meso architectures accessed by cyclometalation of calix[4]arene-based bis(aryltriazoles)

Conventional cyclometalation of calix[4]arene bis(aryltriazoles) with iridium(III) chloride hydrate leads to unique meso architectures in which the Ir₂Cl₂ core is cross-bound by two (C^N)₂ ligands, which allows further replacement of the chloride bridges with ancillary ligands while maintaining the dinuclear structures of the complexes having independent or coupled iridium pairs.

New Amphiphilic Imidazolium/Benzimidazolium Calix[4]arene Derivatives: Synthesis, Aggregation Behavior and Decoration of DPPC Vesicles for Suzuki Coupling in Aqueous Media

In this study, new types of amphiphilic calix[4]arene derivatives bearing N-alkyl/aryl imidazolium/benzimidazolium fragments were designed and synthesized by two step transformation: Regioselective Blanc chloromethylation of distal-di-O-butyl calix[4]arene and subsequent interaction with N-Substituted imidazole/benzimidazole. Critical aggregation concentration (CAC) values were estimated using pyrene fluorescent probe. Obtained macrocycles were found to form submicron particles with electrokinetic potential +44–+57 mV in aqueous solution. For the first time it was found that amphiphilic calixarene causes the fast transformation of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multilamellar vesicles into unilamellar ones and leads to the ordering of the lipid in membranes at the molar calixarene/DPPC ratio more than 0.07. In situ complexes of calixarene aggregates with Pd(OAc)₂ were found to be active in Suzuki–Miyaura coupling of 1-bromo-4-nitrobenzene with phenylboronic acid in water. It was shown that bulky N-substituents of heterocycle decrease the catalytic activity of the aggregates. These result can be assigned to the inhibition effect of Pd(II) complex in situ formation by bulky substituents located on the aggregate surface. Embedding of the most active palladium N-heterocyclic carbene (NHC) complex with methylimidazolium headgroups into DPPC vesicles enhances its catalytic activity in Suzuki–Miyaura coupling.

Upper-Rim Monofunctionalisation in the Synthesis of Triazole- and Disulfide-Linked Multicalix[4]- and -[6]arenes

Covalently linked multiple calixarenes are valued in supramolecular chemistry. This work reports an easy and versatile synthetic route to covalently linked double and triple calix[4]arene and calix[6]arenes by a novel DMF-controlled selective alkylation of a convenient and readily available upper-rim dimethylaminomethyl-substituted tetrahydroxy and hexahydroxy calix[4]arene and -[6]arenes. Synthetic routes to upper-rim functionalised redox active disulfide-linked double-, tetra- and peptidohybrid-calixarenes employing either redox chemistry (CH₂ SH) or thiolates (CH₂ S^- ) are also opened up from the same key starting material.

Coordination chemistry of a calix[4]arene-based NHC ligand: dinuclear complexes and comparison to I(i)Pr2Me2

The preparation and coordination chemistry of 5,17-bis(3-methyl-1-imidazol-2-ylidene)-25,26,27,28-tetrapropoxycalix[4]arene (1) is described. Starting from the bis(imidazolium) pro-ligand 1·2HI, the free carbene 1 was readily generated in solution through deprotonation using K[O(t)Bu] and its reactivity with rhodium(i) dimers [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) and [Rh(CO)2Cl]2 investigated. Dinuclear complexes were isolated in both cases, where the calix[4]arene-based NHC ligand adopts a bridging μ(2)-coordination mode, and in one case characterised in the solid-state by X-ray diffraction. Using instead an isolated and well-defined (mononuclear) silver transfer agent, generated by reaction of 1·2HI with Ag2O in the presence of a halide extractor, reactions with [Rh(COD)Cl]2 and [Rh(CO)2Cl]2 produced cationic dinuclear complexes bearing μ(2)-1 and μ(2)-Cl bridging ligands. The structural formulation of the novel dinuclear adducts of 1 was aided through spectroscopic congruence with model complexes, containing monodentate 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (I(i)Pr2Me2).

Unraveling the synthesis of homoleptic [Ag(N,N-diaryl-NHC)2]Y (Y = BF4, PF6) complexes by ball-milling

A user-friendly and general mechanochemical method was developed to access rarely described NHC (N-heterocyclic carbene) silver(i) complexes featuring N,N-diarylimidazol(idin)ene ligands and non-coordinating tetrafluoroborate or hexafluorophosphate counter anions.

AuICl-bound N-heterocyclic carbene ligands form MII4(LAuCl)6 integrally gilded cages

The incorporation of an N-heterocyclic carbene (NHC) moiety into a self-assembled MII4L6 cage framework required the NHC first to be metallated with gold(i). Bimetallic cages could then be constructed using zinc(ii) and cadmium(ii) templates, showing weak luminescence. The cages were destroyed by the addition of further gold(i) in the form of AuI(2,4,6-trimethoxybenzonitrile)2SbF6, which caused the reversibly-formed cages to disassemble and controllably release the AuI-NHC subcomponent into solution. This release in turn induced the growth of gold nanoparticles. The rate of dianiline release could be tuned by capsule design or through the addition of chemical stimuli, with different release profiles giving rise to different nanoparticle morphologies.

Structures of NHC Hg(ii) and Ag(i) complexes and selective recognition of nitrate anion

Eight N-heterocyclic carbene Hg(ii) and Ag(i) complexes were prepared, and the selective recognition of nitrate anion was studied.

1,3-Bis(2-cyano-benz-yl)imidazolium bromide

In the title salt, C₁₉H₁₅N₄⁺·Br⁻, the central imidazole ring makes dihedral angles of 83.1 (2) and 87.6 (2)° with the terminal benzene rings. The dihedral angle between the terminal benzene rings is 6.77 (19)°; the cyanide substituents have an anti orientation. In the crystal, the cations and anions are linked via C—H⋯N and C—H⋯Br hydrogen bonds, forming sheets lying parallel to the ac plane.