Metal-Involving Halogen Bonding Including Gold(I) as a Nucleophilic Partner. The Case of Isomorphic Dichloroaurate(I)·Halomethane Cocrystals

Conformation-Associated C···dz2-PtII Tetrel Bonding: The Case of Cyclometallated Platinum(II) Complex with 4-Cyanopyridyl Urea Ligand

The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea (1) to cis-[Pt(CNXyl)2Cl2] (2) gave a new cyclometallated compound 3. It was characterized by NMR spectroscopy (1H, 13C, 195Pt) and high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms (3 and 3·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of 3, two conformers (3A and 3B) were identified, while the structure 3·2MeCN had only one conformer 3A. The conformers differed by orientation of the N,N-dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals 3 and 3·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either {3A}2 or {3B}2, via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C···dz2(Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer [3A]2 and reveals the dz2(Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction).

Halogen Bond Catalysis: A Physical Chemistry Perspective

As important noncovalent interactions, halogen bonds have been widely used in material science, supramolecular chemistry, medicinal chemistry, organocatalysis, and other fields. In the past 15 years, halogen bond catalysis has become a developed field in organocatalysis for the catalysts' advantages of being environmentally friendly, inexpensive, and recyclable. Halogen bonds can induce various organic reactions, and halogen bond catalysis has become a powerful alternative to the fully explored hydrogen bond catalysis. From a physical chemistry view, this perspective provides an overview of the latest progress and key examples of halogen bond catalysis via activation of the lone pair systems of organic functional group, π systems, and metal complexes. The research progresses in halogen bond catalysis by our group were also introduced.

Solvent-Mediated Modulation of the Au-S Bond in Dithiol Molecular Junctions

Gold-dithiol molecular junctions have been studied both experimentally and theoretically. However, the nature of the gold-thiolate bond as it relates to the solvent has seldom been investigated. It is known that solvents can impact the electronic structure of single-molecule junctions, but the correlation between the solvent and dithiol-linked single-molecule junction conductance is not well understood. We study molecular junctions formed with thiol-terminated phenylenes from both 1-chloronaphthalene and 1-bromonaphthalene solutions. We find that the most probable conductance and the distribution of conductances are both affected by the solvent. First-principles calculations show that junction conductance depends on the binding configurations (adatom, atop, and bridge) of the thiolate on the Au surface, as has been shown previously. More importantly, we find that brominated solvents can restrict the binding of thiols to specific Au sites. This mechanism offers new insight into the effects of the solvent environment on covalent bonding in molecular junctions.

Exploring Au(i) involving halogen bonding with N-heterocyclic carbene Au(i) aryl complexes in crystalline media

Among the known types of non-covalent interactions with a Au(i) metal center, Au(i) involving halogen bonding (XB) remains a rare phenomenon that has not been studied systematically. Herein, using five N-heterocyclic carbene (NHC) Au(i) aryl complexes and two iodoperfluoroarenes as XB donors, we demonstrated that the XB involving the Au(i) metal center can be predictably obtained for neutral Au(i) complexes using the example of nine co-crystals. The presence of XB involving the Au(i) center was experimentally investigated by single-crystal X-ray diffraction and solid-state ¹³C CP-MAS NMR methods, and their nature was elucidated through DFT calculations, followed by electron density, electrostatic potential, and orbital analyses. The obtained results revealed a connection between the structure and HOMO localization of Au(i) complexes as XB acceptors, and the geometrical, electronic, and spectroscopic features of XB interactions, as well as the supramolecular structure of the co-crystals.

Noncovalent Chelation by Halogen Bonding in the Design of Metal-Containing Arrays: Assembly of Double σ-Hole Donating Halolium with CuI-Containing O,O-Donors

Five new copper(I) complexes─composed of the paired dibenzohalolium and [CuL₂]^- (L = 1,2,4-oxadiazolate) counterions in which O,O-atoms of the anion are simultaneously linked to the halogen atom─were generated and isolated as the solid via the three-component reaction between [Cu(MeCN)₄](BF₄), sodium 1,2,4-oxadiazolates, and dibenzohalolium triflates (or trifluoroacetates). This reaction is different from the previously reported Cu^I-catalyzed arylation of 1,2,4-oxadiazolones by diaryliodonium salts. Inspection of the solid-state X-ray structures of the complexes revealed the strong three-center X···O,O (X = Br, I) halogen bonding occurred between the oxadiazolate moieties and dibenzohalolium cation. According to performed theoretical calculations, this noncovalent interaction (or noncovalent chelation) was recognized as the main force in the stabilization of the copper(I) complexes. An explanation for the different behavior of complexes, which provide either chelate or nonchelate binding, is based on the occurrence of additional -CH₃···π interactions, which were also quantified.

Halogen Bonding Involving Gold Nucleophiles in Different Oxidation States

A single-crystal X-ray diffraction (XRD) study of diaryliodonium tetrachloroaurates (or, in the recent terminology, tetrachloridoaurates), [(p-XC₆H₄)₂I][AuCl₄] (X = Cl, 1; Br, 2), was performed for 1 (the structure is denoted as 1a to show similarity with the isomorphic structure 2a) and two polymorphs─2a (obtained from MeOH) and 2b (from 1,2-C₂H₄Cl₂). Examination of the XRD data for these three structures revealed 2-center C-X···Au^III (X = Cl and Br) and 3-center bifurcated C-Br···(Cl-Au) halogen bonding (abbreviated as XB) between the p-Cl or p-Br atoms of the diaryliodonium cations and the gold(III) atom of [AuCl₄]^-. The noncovalent nature of Au^III-involving interactions, the nucleophilicity of the gold(III) atoms, and the electrophilic role of p-X atoms of the diaryliodonium cations in the XBs were studied by a set of complementary computational methods. Combined experimental and theoretical studies allowed the recognition of the d-nucleophilicity of the [d⁸Au^III] atom which, regardless of its rather substantial formal 3+ charge, can function as a d-nucleophilic partner of XB. This conclusion was also supported by theoretical calculations performed for the structures' refcodes BINXOM and ICSD 62511; the obtained data verified the nucleophilicity of Au^III toward a K⁺ ions or a σ-(Cl)-hole, respectively. All our results, together with consideration of relevant literature, indicate that gold atoms in the three oxidation states (0, I, and even III) exhibit nucleophilicity in XBs.