A Twisted Tetragold Cyclophane from a Fused Bis-Imidazolindiylidene

Self-Assembly and Dynamic Equilibrium of Trinuclear and Tetranuclear Cu(I) Supramolecules Featuring nido-Carborane-Supported N-Heterocyclic Carbene Ligands

The self-assembly of metallo-supramolecules has attracted considerable attention in recent decades. These discrete architectures are primarily driven by coordination interactions, typically involving M-N/O (Werner-type) or M-C (organometallic) bonding. However, the use of M-π interactions for constructing these multinuclear complexes remains largely unexplored. In this work, we report the self-assembly of trinuclear and tetranuclear copper(I) complexes driven by a combination of M-π and M-C coordination interactions. These multinuclear Cu(I)-NHC complexes were synthesized from the nido-carborane-supported N-heterocyclic carbene (NHC) precursors and Cu(I) ions. In solution, a dynamic equilibrium between the trinuclear and tetranuclear species was observed, as confirmed by the variable-temperature NMR spectrum. Van't Hoff analysis revealed that the equilibrium is endothermic (ΔHeq = 53.6 kJ mol-1) and entropically driven (ΔSeq = 158 J mol-1 K-1). The solid-state structures of both forms were elucidated through single-crystal XRD analysis. Density functional theory calculations showed that the Cu-CNHC bonds in these complexes are relatively weak (∼100 kJ mol-1, approximately one-third of the strength of typical Cu-CNHC bonds). This is attributed to the strong Coulombic attraction between positively charged Cu(I) and negatively charged nido-carborane ligands (M-π interactions), which significantly reduces the bond strength between Cu(I) and neutral NHC moieties (M-C bonding).

Evolution of Polynuclear Gold(I) Sulfido Complexes from Clusters and Cages to Macrocycles

Two unprecedented tetratriacontanuclear and tetraicosanuclear gold(I) sulfido clusters (denoted as Au34-LMe and Au24-LCbz) with different temperature-induced stimulus-responsive behavior and emission property have been constructed by taking advantage of the judiciously designed bidentate phosphine ligand. Au34-LMe represents the highest nuclearity of the gold(I) sulfido cluster with more than a thousand atoms in the molecule. Octagonal macrocycles based on metal-cluster nodes have been assembled for the first time. The self-assembly and temperature-induced stimulus-responsive processes were monitored by 1H and 31P{1H} NMR spectroscopy, and the identities of the discrete gold(I) complexes were established by single-crystal structural analysis and high-resolution electrospray ionization mass spectrometry data. The steric effects exerted by the substituents on the V-shaped 1,3-bis(diphenylphosphino)benzene ligand have been shown to govern the self-assembly from the 1D cluster and 3D cage to 2D macrocycles. This work not only offers a new strategy to construct and regulate the structure of 2D macrocyclic gold(I) sulfido complexes but also lays the foundation for the future precise design and controlled construction of higher polygonal and cluster-node macrocycles.

Nickelacarborane-Supported Bis-N-heterocyclic Carbenes

Metallacarboranes have attracted significant attention due to their unique properties. Considerable efforts have been made on the reactions around the metal centers or the metal ion itself, while transformations of functional groups of the metallacarboranes have been much less explored. We presented here the formation of imidazolium-functionalized nickelacarboranes (2), their subsequent conversion to nickelacarborane-supported N-heterocyclic carbenoids (NHCs, 3), and the reactivities of 3 toward Au(PPh₃)Cl and Se powder, which resulted in the formation of bis-gold carbene complexes (4) and NHC selenium adducts (5). Cyclic voltammetry of 4 shows two reversible peaks, corresponding to the interconversion transformations Ni^II ↔ Ni^III and Ni^III ↔ Ni^IV. Theoretical calculations demonstrated relatively high-lying lone-pair orbitals, weak B-H···H-C interactions between the BH units and the methyl group, and weak B-H···π interactions between the BH groups and the vacant p-orbital of the carbene.

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

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. This review aims to cover the most relevant advances in the use of Janus-di-NHCs during the last 15 years, by classifying them according to their specific structural features.

Main Avenues in Gold Coordination Chemistry

In this contribution, we provide an overview of the main avenues that have emerged in gold coordination chemistry during the last years. The unique properties of gold have motivated research in gold chemistry, and especially regarding the properties and applications of gold compounds in catalysis, medicine, and materials chemistry. The advances in the synthesis and knowledge of gold coordination compounds have been possible with the design of novel ligands becoming relevant motifs that have allowed the preparation of elusive complexes in this area of research. Strong donor ligands with easily modulable electronic and steric properties, such as stable singlet carbenes or cyclometalated ligands, have been decisive in the stabilization of gold(0) species, gold fluoride complexes, gold hydrides, unprecedented π complexes, or cluster derivatives. These new ligands have been important not only from the fundamental structure and bonding studies but also for the synthesis of sophisticated catalysts to improve activity and selectivity of organic transformations. Moreover, they have enabled the facile oxidative addition from gold(I) to gold(III) and the design of a plethora of complexes with specific properties.

Triazolate-based pillarplexes: shape-adaptive metallocavitands via rim modification of macrocyclic ligands

Rim-modified pillarplexes are prepared by a macrocycle-templated synthesis strategy. They exhibit a shape-adaptive behaviour and complementary H-bonding, showing that rim modification can modulate the flexibility and functionality of the cavitand.

A Macrocyclic Gold(I)-Biphenylene Complex: Triangular Molecular Structure with Twisted Au2 (diphosphine) Corners and Reductive Elimination of [6]Cycloparaphenylene

The digold(I) complex [Au₂ Cl₂ (Cy₂ PCH₂ PCy₂ )] reacts with 4,4'-diphenylene diboronic acid to form a triangular macrocyclic complex with twisted Au-P-C-P-Au groups at the three corners. The synthesis of the complex and its chemical oxidation produced [6]cycloparaphenylene ([6]CPP) in 59 % overall yield.

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. While the early examples of SOCs referred to supramolecular architectures mostly containing bisalkenyl, diphenyl, or bisalkynyl linkers, the development of SOCs during the past decade has been boosted by the parallel development of multidentate N-heterocyclic carbene (NHC) ligands. The first examples of NHC-based SOCs referred to supramolecular assemblies based on polydentate NHC ligands bound to group 11 metals. However, during the last 10 years, several planar poly-NHC ligands containing extended π-conjugated systems have facilitated the formation of a large variety of architectures in which the supramolecular assemblies can contain metals other than Cu, Ag, and Au. Such ligands are Janus di-NHCs and trigonal-planar tris-NHCs-most of them prepared by our research group-which have allowed the preparation of a vast range of NHC-based metallosupramolecular compounds with interesting host-guest chemistry properties. Although the number of SOCs has increased in the past few years, their use for host-guest chemistry purposes is still in its earliest infancy. In this Account, we describe the achievements that we have made during the last 4 years toward broadening the applications of planar extended π-conjugated NHC ligands for the preparation of organometallic-based supramolecular structures, including their use as hosts for some selected organic and inorganic guests, together with the catalytic properties displayed by some selected host-guest inclusion complexes. Our contribution describes the design of several Ni-, Pd-, and Au-based metallorectangles and metalloprisms, which we used for the encapsulation of several organic substrates, such as polycyclic aromatic hydrocarbons (PAHs) and fullerenes. The large binding affinities found are ascribed to the incorporation of two cofacial panels with large π-conjugated systems, which provide the optimum conditions for guest recognition by π-π-stacking interactions. We also describe a series of digold(I) metallotweezers for the recognition of organic and inorganic substrates. These metallotweezers were used for the recognition of "naked" metal cations and polycyclic aromatic hydrocarbons. The recognition properties of these metallotweezers are highly dependent on the nature of the rigid connector and of the ancillary ligands that constitute the arms of the tweezer. A peculiar balance between the self-aggregation properties of the tweezer and its ability to encapsulate organic guests is observed.

Molecular complexes and main-chain organometallic polymers based on Janus bis(carbenes) fused to metalloporphyrins

Janus bis(N-heterocyclic carbenes) composed of a porphyrin core with two N-heterocyclic carbene (NHC) heads fused to opposite pyrroles were used as bridging ligands for the preparation of metal complexes. We first focused our attention on the synthesis of gold(i) chloride complexes [(NHC)AuCl] and investigated the substitution of the chloride ligand by acetylides to obtain the corresponding [(NHC)AuC[triple bond, length as m-dash]CR] complexes. Polyacetylides were then used to obtain molecular multiporphyrinic systems with porphyrins fused to only one NHC ligand, while main-chain organometallic polymers (MCOPs) were obtained when using Janus porphyrin bis(NHCs). Interestingly, MCOPs incorporating zinc(ii) porphyrins proved to be efficient as heterogeneous photocatalysts for the generation of singlet oxygen upon visible light irradiation.

Dinuclear gold(i) complexes: from bonding to applications

The last two decades have seen a veritable explosion in the use of gold(i) complexes bearing N-heterocyclic carbene (NHC) and phosphine (PR₃) ligands.