Xenon(IV)–Carbon Bond of [C6F5XeF2]+; Structural Characterization and Bonding of [C6F5XeF2][BF4], [C6F5XeF2][BF4]·2HF, and [C6F5XeF2][BF4]·nNCCH 3 (n = 1, 2); and the Fluorinating Properties of [C6F5XeF2][BF4]

Fluorination/Dearomatization of C6F5 Groups: An FLP Route to an Electrophilic Borane and Non-Coordinating Anions

B(C6F5)3 and the corresponding anion [B(C6F5)4]- are ubiquitous in main group and transition metal chemistry. Known derivatives are generally limited to the incorporation of electron donating substituents. Herein we describe electrophilic fluorination and dearomatization of such species using XeF2 in the presence of BF3 or Lewis acidic cations. In this fashion the anions [HB(C6F5)3]-, [B(C6F5)4]- and [(C6F5)3BC≡NB(C6F5)3]-, are converted to [FB(C6F7)3]-, [B(C6F7)4]-, and [(C6F7)3BC≡NB(C6F7)3]-, respectively. Similarly, the borane adducts (L)B(C6F7)3 (L=MeCN, OPEt3) are produced. These rare examples of electrophilic attack of electron deficient rings proceed as [XeF][BF4] acts as a frustrated Lewis pair effecting fluorination and dearomatization of C6F5 rings.

Chiral copper-hydride nanoclusters: synthesis, structure, and assembly

An effective strategy is developed to synthesize a novel and stable layered Cu nanocluster using a one-pot reduction method. The cluster, with a molecular formula of [Cu₁₄(^tBuS)₃(PPh₃)₇H₁₀]BF₄ which has been unambiguously characterized by single crystal X-ray diffraction analysis, exhibits different structures from previously reported analogues with core-shell geometries. In the absence of chiral ligands, the cluster displays intrinsic chirality owing to the non-covalent ligand-ligand interactions (e.g., C-H⋯Cu interactions and C-H⋯π interactions) to lock the central copper core. The interlacing of chiral-cluster enantiomers forms a large cavity, which lays the foundation for a series of potential applications such as drug filling and gas adsorption. Moreover, the C-H⋯H-C interactions of phenyl groups between different cluster moieties promote the formation of a dextral helix and realization of the self-assembly of nanostructures.

Xenon Derivatives as Aerogen Bond-Donating Catalysts for Organic Transformations: A Theoretical Study on the Metaphorical "Spherical Cow in a Vacuum" Provides Insights into Noncovalent Organocatalysis

Computations indicate that cationic and noncharged xenon derivatives should exhibit higher catalytic activity than their iodine-based noncovalent organocatalytic congeners. Perfluorophenyl xenonium(II) is expected to demonstrate the best balance between catalytic activity and chemical stability for use in organocatalysis. Comparing its catalytic activity with that of isoelectronic perfluoroiodobenzene indicates that the high catalytic activity of cationic noncovalent organocatalysts is predominantly attributed to the electrostatic interactions with the reaction substrates, which cause the polarization of ligated species during the reaction progress. In contrast, the electron transfer and covalent contributions to the bonding between the catalyst and substrate have negligible effects. The dominant effect of electrostatic interactions results in a strong negative correlation between the calculated Gibbs free energies of activation for the modeled reactions and the highest potentials of the σ-holes on the central atoms of the catalysts. No such correlation is observed for noncharged catalysts.

Covalent and Non-covalent Noble Gas Bonding Interactions in XeF n Derivatives (n = 2-6): A Combined Theoretical and ICSD Analysis

A noble gas bond (also known in the literature as aerogen bond) can be defined as the attractive interaction between any element of group-18 acting as a Lewis acid and any electron rich atom of group of atoms, thus following the IUPAC recommendation available for similar π,σ-hole interactions involving elements of groups 17 (halogens) and 16 (chalcogens). A significant difference between noble gas bonding (NgB) and halogen (HaB) or chalcogen (ChB) bonding is that whilst the former is scarcely found in the literature, HaB and ChB are very common and their applications in important fields like catalysis, biochemistry or crystal engineering have exponentially grown in the last decade. This article combines theory and experiment to highlight the importance of non-covalent NgBs in the solid state of several xenon fluorides [XeF_n]^m+ were the central oxidation state of Xe varies from +2 to +6 and the number of fluorine atoms varies from n = 2 to 6. The compounds with an odd number of fluorine atoms (n = 3 and 5) are cationic (m = 1). The Inorganic Crystal Structural Database (ICSD) strongly evidences the relevance of NgBs in the solid state structures of xenon derivatives. The ability of Xe compounds to participate in π,σ-hole interactions has been studied using different types of electron donors (Lewis bases and anions) using DFT calculations (PBE1PBE-D3/def2-TZVP) and the molecular electrostatic potential (MEP) surfaces.

Aerogen bonds formed between AeOF2 (Ae = Kr, Xe) and diazines: comparisons between σ-hole and π-hole complexes

The interaction between KrOF₂ or XeOF₂ and the 1,2, 1,3, and 1,4 diazines is characterized chiefly by a Kr/XeN aerogen bond, as deduced from ab initio calculations. The most stable dimers take advantage of the σ-hole on the aerogen atom, wherein the two molecules lie in the same plane. The interaction is quite strong, as much as 18 kcal mol^-1. A second class of dimer geometry utilizes the π-hole above the aerogen atom in an approximate perpendicular arrangement of the two monomers; these structures are not as strongly bound: 6-8 kcal mol^-1. Both sorts of dimers contain auxiliary CHF H-bonds which contribute to their stability, but even with their removal, the aerogen bond energy remains as high as 14 kcal mol^-1. The nature and strength of each specific interaction is confirmed and quantified by AIM, NCI, NBO, and electron density shift patterns. There is not a great deal of sensitivity to the identity of either the aerogen atom or the position of the two N atoms in the diazine.

On the nature of interactions in the F2 OXe(…) NCCH3 complex: Is there the Xe(IV)N bond?

Nature of the bonding in isolated XeOF2 molecule and F2 OXe(…) NCCH3 complexes have been studied in the gas phase (0 K) using Quantum Chemical Topology methods. The wave functions have been approximated at the MP2 and DFT levels of calculations, using the APFD, B3LYP, M062X, and B2PLYP functionals with the GD3 dispersion correction. The nature of the formal XeO bond in the XeOF2 monomer depends on the basis set used (all-electron vs. the ecp-28 approximation for Xe). Within the all-electron basis set approach the bond is represented by two bonding attractors, Vi = 1,2 (Xe,O), with total population of about 1.06e and highly delocalized electron density in both bonding basins. No bonding basins are observed using the ecp-28 approximation. These results shows that the nature of xenon-oxygen is complicated and may be described with mesomeric equilibrium of the Lewis representations: Xe((+)) O((-)) and Xe((-)) O((+)) . For both the xenon-oxygen and xenon-fluorine interactions the charge-shift model can be applied. The F2 OXe(…) NCCH3 complex exists in two structures: "parallel," stabilized by non-covalent C(…) O and Xe(…) N interactions and "linear" stabilized by the Xe(…) N interaction. Topological analysis of ELF shows that the F2 OXe(…) NCCH3 molecule appears as a weakly bound intermolecular complex. Intermolecular interaction energy components have also been studied using Symmetry Adapted Perturbation Theory. © 2016 Wiley Periodicals, Inc.

Aerogen Bonding Interaction: A New Supramolecular Force?

We report evidence of the favorable noncovalent interaction between a covalently bonded atom of Group 18 (known as noble gases or aerogens) and a negative site, for example, a lone pair of a Lewis base or an anion. It involves a region of positive electrostatic potential (σ-hole), therefore it is a totally new and unexplored σ-hole-based interaction, namely aerogen bonding. We demonstrate for the first time the existence of σ-hole regions in aerogen derivatives by means of high-level ab initio calculations. In addition, several crystal structures retrieved from the Cambridge Structural Database (CSD) give reliability to the calculations. Energetically, aerogen bonds are comparable to hydrogen bonds and other σ-hole-based interactions but less directional. They are expected to be important in xenon chemistry.