Jean-Pierre Djukic

The ability of telluronium [Ar3Te]+ to bind crown ethers and acyclic polyethers through chalcogen bonding is investigated in the solid state and in solution. X-ray diffraction of several 1:1 complexes revealed short Te···O interactions (dTe–O below the sum of van der Waals radii) and high linearity (Ar–Te–O angles in the range 163–178°). NMR and DOSY (diffusion-ordered NMR spectroscopy) experiments confirm that these interactions persist in solution. Isothermal titration calorimetry provides the thermodynamic parameters for the telluronium–crown ether and telluronium–polyether equilibria, with association constants reaching Ka ∼ 106 M–1 for the 5- to 7-membered crown ethers. Based on these results, selective coordination of certain crown ethers was efficiently achieved. Furthermore, the templating effect of the telluronium on acyclic polyethers is further demonstrated by its ability to promote the ring closure of a long polyether bearing both bromo and hydroxy termini. Theoretical analysis of the ligand-Te interaction points to a dominant Coulombic contribution, supported by dispersion forces, in stabilizing polyether binding to the Te center. Although the minor covalent contribution operates a crucial anchoring role, it is not sufficient to restrict the O atoms to exclusive σ-hole interactions, suggesting a fluxional dynamic behavior in solution in which all O atoms dynamically interact with the Te center.

Spin crossover (SCO) is a well-established phenomenon by which transition-metal complexes can reversibly switch between low- and high-spin states, a phenomenon widely studied in materials chemistry. Recently, transition metal complexes that exhibit SCO have attracted increasing attention as catalysts in chemical reactions. Combining SCO with catalysis presents a promising strategy for creating switchable catalytic systems sensitive to light, pressure, and thermal stimuli. This review briefly covers the basics of SCO studies and the primary external stimuli that influence them. The following sections examine recent research on the role of SCO in homogeneous catalytic reactions with various transition-metal complexes and highlight its impact on reaction pathways, recommending the systematic evaluation of SCO’s effect on catalysis when investigating new 3 d transition-metal-based catalysts.

The Independent Gradient Model (IGM) reveals interaction signatures by analyzing the electron density (ED) gradient. In this report it is used to analyze the variations of the electronic structure of a molecular system undergoing, along a series of highly sampled Intrinsic Reaction Coordinates (IRC), a concerted reductive elimination reaction staging a doublet ground state metallacyclic [Cp*{C,N}Co^IV(X{Y})]⁺ (X{Y} = 1 electron ligand, {Y} = assisting atom) prereactive complex (RC). The IGM interfragment Δg^inter score and the degree of interaction (DOI(Co)) of the cobalt center reveal meaningful electronic changes occurring during the reaction, which inform of the active interactions of the ligands with the metal: the Cp* ligand intervenes in the reductive-elimination reaction as an ED reservoir supplementing the Co center. The sourcing of atomic contributions of peripheral atoms to the changes of DOI(Co) at valleys and peaks of DOI reveals, in a nonintuitive way, the role of cobalt's ligands when the system passes through remarkable transient structures. The peaks of DOI either precede or follow the transition state (TS) and are similar to σ-complex structures, suggesting, counterintuitively, that significant electronic changes do not occur at the TS.

The title compound, C ₁₈ H ₁₄ N ₂ O ₃ , crystallizes with two zwitterionic molecules ( A and B ) in the asymmetric unit, each featuring an intramolecular N—H...O hydrogen bond. In the extended structure, A + A and B + B carboxylic-acid inversion dimers linked by pairwise O—H...O hydrogen bonds arise, which generate R ² ₂ (8) loops in each case. The dimers are linked by weak C—H...π and π–π stacking interactions.

The independent gradient model, applied to the dynamics of carbene ligand insertion into a C–Mn bond, reveals details of electron density redistribution events, challenging earlier assumptions.

The Independent Gradient Model (IGM) reveals interaction signatures through the analysis of the electron density gradient. In this report it is used to analyze the variations of the electronic structure of a molecular system undergoing, along a series of highly sampled Intrinsic Reaction Coordinates (IRC), a concerted reductive elimination reaction staging a doublet ground state metallacyclic [Cp*{C,N}Co(IV)-X{Y}]+ ( –X{Y}= 1 electron ligand, {Y}= assisting atom) reactant complex (RC).

This study shows that the nanoparticles produced by the reductive decomposition of a cobalt (+III) metallacycle derived from 2-phenylpyridine upon treatment with the highly nucleophilic Na[Et3BH] are capable of promoting the Kumada-Corriu cross coupling of aryl halides with aryl-bromomagnesium compounds (Grignard reagents) in various conditions and in the presence of various stabilizing ligands to afford the non-symmetric organic bisaryl product in reasonable yields. This study provides further evidence that incidental Co nanoparticles possess a reasonable capability in homogeneous catalysis, thereby complementing a prior report on their ability to promote the hydrosilylation of unsaturated organic substrates, such as nitriles. Co nanoparticles were characterized by HRTEM, EDX, EELS, and SAED techniques. TEM analyses revealed that the nanoparticles were uniformly spherical in shape, with a narrow size distribution; no nanoparticles larger than 3 nm were observed. EDX analysis displaying a characteristic Co signature at about 7 keV. The magnetic behavior of the nanoparticles studied by SQUID analysis in toluene using a temperature varied from 2 to 300 K, and a low magnetic field (10-3T) in ZFC-FC conditions.

Quantum mechanical tunneling (QMT) is the mechanism by which a particle can pass through a high potential energy barrier. Although rooted in quantum physics, QMT influences key chemical reactions in a number of ways. Here, we show that a new iridium dihydride complex IrH2 bearing a N,B-bidentate pyridine carboranyl ligand [(C₅H₄N)CB₁₁H₁₀] undergoes H···H exchange coupling via QMT, as supported by variable temperature NMR studies showing large temperature-dependent exchange coupling constants J_H-H (99-162 Hz), nonlinear Arrhenius behavior of the exchanging hydrogens, and the absence of detectable J_H-D coupling in the deuterium-enriched complex IrHD. These observations agree with the predicted existence of quantum exchange coupling in metal dihydrides reported by Zilm and Heinekey [J. Am. Chem. Soc. 1990, 112, 3, 920-929]. The observed high relaxation rates T_1,min (0.250-0.262 s) support the assignment for IrH2 as being a metal dihydride rather than a nonclassical dihydrogen complex, thus ruling out any major involvement from a classical scalar coupling to the observed large J_H-H coupling constants. The reactivity of complex IrH2 against various bases, nucleophiles, and electrophiles was investigated, and X-ray photoelectron spectroscopy as well as computational studies were conducted, all of which support an Ir in the formal + III oxidation state for IrH2.

The reaction of tris[3,5-bis(trifluoromethyl)phenyl]telluronium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF^-) salt with phosphine oxides OPR₃ in 1,2-dichloroethane is exothermic and leads to the population of the three Te σ-holes. Quite unprecedented, careful adjustment of the stoichiometry of reagents allowed the selective crystallization of the Lewis adducts containing one, two, or three Te-bonded OPR₃, according to X-ray diffraction. ¹H and ¹⁹F Diffusion-ordered NMR spectroscopy-monitored titrations of the telluronium salt by OPPh₃ reveal the growth of the hydrodynamic volume of the various cationic adducts, alongside a unique behavior of the BArF^- counterion that suggests its aggregation at high cationic molecular sizes. Isotherm titration calorimetry experiments show that the association equilibrium constants of OPR₃ binding to Te σ-holes follow the order K_a1 > K_a2 > K_a3, with respective values decreasing by 1 up to 2 orders of magnitude as the σ-holes are populated. Analysis of Te-O bonding by DFT methods confirms their dominant Coulombic character. The minor covalent character is nonetheless required to ensure telluronium-ligand cohesion. DFT calculations of the association thermochemistry raise the tangible contribution of ion "pairs" to the association enthalpy as a major issue for modeling: the allegedly "non-coordinating" BArF^- taking part in elusive multipolar ion-pairs is far from being an irrelevant thermochemical contributor.