Variations on the Theme of JohnPhos Gold(I) Catalysts: Arsine and Carbene Complexes with Similar Architectures

Pnictogen Bonding at the Core of a Carbene-Stiborane-Gold Complex: Impact on Structure and Reactivity

Our interest in the design of ambiphilic ligands and their coordination to gold has led us to synthesize an indazol-3-ylidene gold chloride complex functionalized at the 4-position of the indazole backbone by a stibine functionality. The antimony center of this new complex cleanly reacts with o-chloranil to afford the corresponding stiborane derivative. Structural analysis indicates that the stiborane coordination environment is best described as a distorted square pyramid whose open face is oriented toward the gold center, allowing for the formation of a long donor-acceptor, or pnictogen, Au → Sb bonding interaction. The presence of this interaction, which has been probed computationally, is also manifested in the enhanced catalytic activity of this complex in the cyclization of N-propargyl-4-fluorobenzamide.

Exploring the Effects of Se Basicity on a Te···Se Interaction Supported by a Rigid Indazolium Backbone

With an interest in chalcogen bonding, we use a rigid indazolium backbone to install a formally zero-valent Se center next to a divalent Te center, allowing us to investigate the effects of oxidation of the Se center on the observed Te···Se interaction. Through spectroscopic and computational comparison of the Se(0) species with its Se(II) counterpart and their monochalcogen analogues, we experimentally and computationally investigate the effect of modulating Se basicity on the resulting Te···Se interaction. Comparison with well-studied naphthalene and acenaphthene variants indicates that the increased basicity of the Se(0) center allows for a comparably strong Te···Se interaction despite longer peri distances and a larger splay angle. Finally, our study illuminates the potential non-innocence of cationic organic substituents in chalcogen-bonding catalysis of the transfer hydrogenation of quinolines.

Indazolin-3-ylidenes (Indy*): easily accessible, sterically-hindered indazole-derived N-heterocyclic carbenes and their application in gold catalysis

Sterically-hindered N-heterocyclic carbenes (NHCs) with functionalized N-wingtips are a pivotal class of ligands in organic synthesis. Herein, we report the first class of sterically-hindered N-heterocyclic carbenes based on the indazole framework. These ligands combine the strong σ-donation of the carbene center due to the carbene placement at the C3-indazole position with the sterically-hindered and flexible N-substitution with the versatile 2,6-bis(diphenylmethyl)aryl moiety that extends beyond the metal centre for the first time in non-classical N-heterocyclic carbenes. The ligands are readily accessible by the rare Cadogan indazole synthesis of sterically-hindered N-aryl-1-(2-nitrophenyl)methanimines. Steric and electronic characterization as well as catalytic studies in the synthesis of oxazolines are described. Considering the unique properties of indazole-derived carbenes, we anticipate that this class of compounds will find broad application in organic synthesis and catalysis.

The Elusive Au(I)···H-O Hydrogen Bond: Experimental Verification

Our long-standing interest in atypical bonding situations has recently led us to target complexes in which a metallobasic gold(I) center is hydrogen-bonded to a nearby OH functionality. Here, we report on the synthesis and characterization of two neutral gold(I) indazol-3-ylidene complexes bearing a carbinol or silanol group at the 4-position. As indicated by X-ray diffraction, ¹H NMR spectroscopy, IR spectroscopy, and extensive computational modeling, the OH group of these derivatives is engaged in a bona fide Au···H-O interaction. In addition to shedding light on an elusive bonding situation, these results also indicate that increasing the acidity of the OH functionality is not necessarily beneficial to the stability of the Au(I)···H-O interaction.

Diarsine- vs diphosphine-protected Au13 clusters: Effect of subtle geometric differences on optical property and electronic structure

In the design of ligand-protected metal clusters, the choice of protecting ligands is a critical factor because they can profoundly affect the nuclearity, geometry, and electronic structures to afford a diverse range of cluster compounds. Here, we report the synthesis of two novel diarsine-protected Au₁₃ clusters ([Au₁₃L₅Cl₂]³⁺, L = diarsine) and compare these clusters with diphosphine analogs in terms of the core geometry and optical properties. In the crystal structure, the cluster bearing C3-bridged diarsines {[Au₁₃(dpap)₅Cl₂]³⁺, 3} had an apparently identical icosahedral Au₁₃ core to [Au₁₃(dppe)₅Cl₂]³⁺ (1) with C2-bridged diphosphines, but slight structural differences associated with the bridging unit of the ligands were found. Despite similar icosahedral Au₁₃ cores 1 and 3, their absorption and photoluminescence profiles were evidently different. Theoretical calculations revealed that the subtle deformation of the Au₁₃ icosahedron, rather than the coordinating atoms (As or P), notably influences the electronic structure to cause the difference in the absorption profiles.