The ability of the telluronium cation [Ar3Te]+ to bind crown ethers and acyclic polyethers through chalcogen bonding is investigated in both the solid state and in solution. Several 1:1 molecular complexes with polyoxygenated ligands of varying size and functionality were crystallized and analyzed by X-ray diffraction, revealing 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 for the

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 unique stereoselectivity of the reaction is rationalised by the joint use of the new Steric-Exclusion Localisation Function.

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}CoIV(X{Y})]+ (X{Y} = 1 electron ligand, {Y} = assisting atom) prereactive complex (RC). The IGM interfragment Δginter 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 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 Ka1 > Ka2 > Ka3, 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.

Four cis-chelating diphosphanes derived from cyclodextrins (CDs), each featuring a distinct intracavity environment, compel NiII or PdII metal centers to reside within α- or β-CD cavities. Nickel(II) complexes of these metal-confining ligands act as active catalysts in ethylene oligomerization upon activation with modified methylaluminoxane (MMAO). The size of the cavity and the position of the P2Ni fragment relative to the cavity affect both the activity and selectivity of the reaction. In all instances, 1-butene is the major product (up to 98% C4 products and 90% 1-butene within the C4 fraction). Extensive theoretical studies with state-of-the-art methods carried out on the most selective system suggest that the CD cavity restricts isomerization pathways by limiting the mobility of the coordinated olefin in this constrained supramolecular environment, thereby enhancing α-olefin formation.

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 JH-H (99-162 Hz), nonlinear Arrhenius behavior of the exchanging hydrogens, and the absence of detectable JH-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 T1,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 JH-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 mechanism of isomerization of the known 2-phenyl,pyridine (phpy) derivatives [Ru(phpy-κC,N) (MeCN-trans-N)(terpy)]PF6, 2, to [Ru(phpy-κC,N)(MeCN-trans-C)(terpy)]PF6 (terpy = 2,2';6',2″-terpyridine), 3, at temperatures >50 °C has been investigated both by 1H NMR spectroscopy and by DFT calculations. The photoisomerization of 2 to 3 by UV light occurred also quantitatively in MeCN after 20 h at room temperature. A similar behavior to that of 2 could be established for the related compound [Ru(3-acridine-2'-C5H4N-κC,N)(MeCN-trans-N)(2,2';6',2″-terpyridine)]PF6, 6 (acridine = dibenzo[b,e]pyridine or 2,3-benzoquinoline), that was obtained from the reaction between [Ru(3-acridine-2'-C5H4N-κC,N) (MeCN)4]PF6, 4, and terpy in MeOH/MeCN at 60 °C for 24 h. Similar to 2, the isomerization of 6 to [Ru(3-acridine-2'-C5H4N-κC,N)(MeCN-trans-C) (terpy)]PF6, 7, could be induced thermally (48 h at 60 °C in pure MeOH) or photochemically under UV radiation in MeCN at room temperature. A compound closely related to 7 but in which MeCN was replaced by H2O was described earlier (Tanaka et al. Inorg. Chem. 2012, 51, 5386-539). The presence of water on this compound had a dramatic effect as far as the coordination of terpy was concerned as its isomerization to a compound related to 6 (in which H2O instead of MeCN is coordinated to Ru) occurred indeed photochemically via irradiation with visible light.

The Kumada-Corriu hetero-coupling between an halogeno-arene and an arylmagnesiumbromide can be catalyzed with yields >80 % by the new hydrotris(3,5-diisopropylpyrazolyl)boratocobalt(III)diiodide, i. e. Tp(iPr)CoI(2). The catalysis, which is significantly improved upon exposure to light as compared to darkness, is determined by the coexistence of low and high spin states in a respective ratio of similar to 3 : 2 for the crucial "Tp(iPr)CoAr(2)" intermediate. The pivotal cobalt(I) Tp(iPr)Co((I))(thf)(n) intermediate is shown to be exclusively a triplet state in the ground state with a measured mu(eff) value of 3.08 mu(B) at 293 K in C6D6. DFT investigations confirm the key role of triplet states for the bisaryl-cobalt(III) intermediates in that they provide a reaction pathway with much lower activation barriers as compared to the singlet state. The low-to-high spin state transition in THF enhances the reactivity of the "Tp(iPr)CoAr(2)" intermediate, which changes its coordination geometry from singlet spin state 18 electron OC-6 Tp(iPr)CoAr(2)(thf) to a triplet spin state 16 electron SPY-5 Tp(iPr)CoAr(2) where the Tp(iPr) ligand adopts a nearly kappa(2) bonding mode. The quantitative Independent Gradient Model analysis of the noncovalent interactions that prefigure the C-C covalent bond in the key Co(Ar)(2) intermediates informs of the peculiar importance of the singlet to triplet spin state crossover in catalysis.

This study addresses the chemoselectivity of the catalyzed reduction of a series of variously substituted γ-lactams by Et3SiH mediated by a pentamethylcyclopentadienyl iridacyclic acetonitrilo salt derived from benzo[h]quinoline. Introduction of an unsaturation within the 5-membered ring of the γ-lactam annihilates the precedence of the amide function over the capture of the silylium cation, which results in a lower chemoselectivity. Monitoring over time the catalyzed reduction of a γ-lactam bearing a carboxylic ester appendage by 1H NMR spectroscopy revealed pseudo-zero-order kinetics for the prior hydrosilylation of the lactam’s amide. This primary hydrosilylation reaction is followed by the full conversion of the formed intermediate into a pyrrolidine following a pseudo-first-order rate law. Under anhydrous conditions, the hydrosilylation of the pendant ester function occurs only in a late stage once the γ-lactam’s amide function has underwent full reduction of the carbonyl function. DFT investigations show that chemoselectivity is governed (1) by the affinity of the organic substrate for the triethylsilylium cation produced by the electrophilic activation of Et3SiH by the Ir(III) catalyst and (2) by the ability of the in situ-formed hydrido-iridium(III) intermediate to transfer hydride to the activated substrate.

Telluronium salts [Ar2MeTe]X were synthesized and their Lewis acidic properties towards a number of Lewis bases were addressed in solution by physical and theoretical means. The structural X-ray diffraction analysis of 21 different salts revealed the electrophilicity of the Te centers in their interactions with anions. Telluroniums' propensity to form Lewis pairs was investigated with OPPh3. Diffusion-ordered NMR spectroscopy suggests that telluroniums may bind up to three OPPh3 molecules. Isotherm titration calorimetry showed that the related heats of association in 1,2-dichloroethane depend on the electronic properties of the substituents of the aryl moiety and on the nature of the counterion. The enthalpies of first association of OPPh3 span -0.5 to -5 kcal/mol. The study of the affinity of telluroniums for OPPh3 by state-of-the-art DFT and ab initio methods reveals the dominant Coulombic and dispersion interactions as well as an entropic effect favoring association in solution. Intermolecular orbital interactions between [Ar2MeTe]+ cations and OPPh3 are deemed insufficient to ensure alone the cohesion of [Ar2MeTe•Bn]+ complexes in solution (B= Lewis base). Comparison of Grimme's and Tkatchenko's DFT-D4 / MBD-vdW thermodynamics of formation of higher [Ar2MeTe•Bn]+ complexes reveals significant molecular size-dependent divergence of the two methodologies, with MBD yielding better agreement with experiment.

In this joint theoretical and experimental study, an analysis of weak interligand noncovalent interactions within Co(IV) [Cp*Co(phpy)X](+) cobaltacycles (phpy = 2-phenylenepyridine, kappa(C,N)) was carried out by using the independent gradient model/intrinsic bond strength index (IGM/IBSI) method to evaluate the dependency of the catalytically desired reductive elimination pathway (RE) on the nature of the X ligand. It is shown that the barrier for activation of the RE pathway correlates directly with the IBSI of the X-to-carbanionic chelate's carbon. This correlation suggests that in silico prediction of which X ligand is more prone to operate an efficient Cp*Co-catalyzed directed X-functionalization of an aromatic C-H bond is attainable. A set of experiments involving various sources of X ligands supported the theoretical conclusions.

The performance of six newly synthesized benzo[h]quinoline-derived acetonitrilo pentamethylcyclopentadienyl iridium(III) tetrakis(3,5-bis-trifluoromethylphenyl)borate salts bearing different substituents -X (-OMe, -H, -Cl, -Br, -NO2 and -(NO2 )2 ) on the heterochelating ligand were evaluated in the dehydro-O-silylation of benzyl alcohol and the monohydrosilylation of 4-methoxybenzonitrile by Et3 SiH, two reactions involving the electrophilic activation of the Si-H bond. The benchmark shows a direct dependence of the catalytic efficiency with the electronic effect of -X, which is confirmed by theoretical assessment of the intrinsic silylicities Π of hydridoiridium(III)-silylium adducts and by the theoretical evaluation of the propensity of hydridospecies to transfer the hydrido ligand to the activated substrate. The revisited analysis of the Ir-Si-H interactions shows that the most cohesive bond in hydridoiridium(III)-silylium adducts is the Ir-H one, while the Ir-Si is a weak donor-acceptor dative bond. The Si…H interaction in all the cases is noncovalent in nature and dominated by electrostatics confirming the heterolytic cleavage of the hydrosilane's Si-H bond in this key catalytically relevant species.

Exploration of new organometallic systems based on polyhedral boron clusters has the potential to solve challenging chemical problems such as the stabilization of reactive intermediates and transition-state-like species postulated for E-H (E = H, B, C, Si) bond activation reactions. We report on facile and clean B-H activation of a hydroborane by a new iridium boron cluster complex. The product of this reaction is an unprecedented and fully characterized transition metal-stabilized boron cation or borenium. Moreover, this intermediate bears an unusual intramolecular B···H interaction between the hydrogen originating from the activated hydroborane and the cyclometallated metal-bonded boron atom of the boron cluster. This B···H interaction is proposed to be an arrested insertion of hydrogen into the Bcage-metal bond and the initiation step for iridium "cage-walking" around the upper surface of the boron cluster. The "cage-walking" process is supported by the hydrogen-deuterium exchange observed at the boron cluster, and a mechanism is proposed on the basis of theoretical methods with a special focus on the role of noncovalent interactions. All new compounds were isolated and fully characterized by NMR spectroscopy and elemental analysis. Key compounds were studied by single crystal X-ray diffraction and X-ray photoelectron spectroscopy.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The theory developed in an accompanying paper [Déjardin, Phys. Rev. E 105, 024109 (2022)10.1103/PhysRevE.105.024109] is used to compute the Kirkwood correlation factor of simple polar fluids of different nature. From this calculation, the theoretical static permittivity is readily obtained, which is compared with experimental values. This is accomplished by fitting only one parameter accounting for induction or dispersion forces and torques, which is necessarily connected with the individual molecular polarizability but not explicitly related to the physical properties due to the nonadditivity of such energies. Excellent agreement between theoretical and experimental static permittivities is obtained over a very broad temperature range for a number of associated and nonassociated liquids. Finally, limitations of the present theory are given.

This work reports a combined experimental and theoretical study on the new dibenzo-1,5-ditellurocine 2-Te in order to get an overview on the parameters controlling conformational change and to explain the differences with sulfur and selenium analogues. The preference of the boat conformer over the chair one is revealed by DFT calculations. For 2-Te, a ΔG value of about 3 kJ/mol was calculated, close to the value measured by NMR (5 kJ/mol). However, DFT calculations with implicit solvation effects could not clearly establish the presence of an intramolecular Te…HC noncovalent interaction (NCI), as observed in the solid state. The Independent Gradient Model (IGM) methodology discloses an existent but probably not sufficiently discriminating Te…HC NCI. It also confirms that van der Waals interactions between phenyl rings is a source of stabilization of the boat conformer. Furthermore, electrostatic potential analysis suggests that chalcogen bonds between Te σ-holes and solvent might play an important role.

Recent reports have identified Cp*Co-based complexes to be powerful catalysts for aromatic C-H bond activation under oxidative conditions. However, little is known about the speciation of Cp*Co species during catalysis. We now show that key intermediates, Cp*Co-III metallacycles derived from 2-phenylpyridine (phpy-H), react swiftly in solution with one-electron oxidants to irreversibly collapse by a cyclocondensation of the organic ligands to afford cationic alkaloids in yields of >70%. A low-temperature EPR analysis of a mixture of the cobaltacycle with the tritylium cation reveals the signatures of trityl and Co(IV)-centered radicals. Electrochemical analyses show that the oxidation of these cobaltacycles is irreversible and gives rise to several products in various amounts, among which the most salient ones are a cationic alkaloid resulting from the cyclocondensation of the phpy and Cp* ligands and the dimeric cation {[Cp*Co](2) (mu-I)(3)}(+). DFT investigations of relevant noncovalent interactions using QTAIM-based NCI plots and intrinsic bond strength indexes suggest a ligand-dependent predisposition by "NCI-coding" for the Co(IV)-templated cyclocondensation, the computed reaction network energy profile for which supports the key roles of a short-lived Co(IV) metallacycle and of a range of triplet state organocobalt intermediates.

In an effort to determine the thermochemistry of established organometallic transformation, the well documented reaction of alkynes with a palladacycle was investigated by isothermal titration calorimetry (ITC). Although the mechanism of the insertion of unsaturated substrates into the Pd-C bond of cyclopalladated compounds is known, no information is available so far about their thermochemistry. The enthalpies of the reactions of Ph-C equivalent to C-Ph and MeOC(O)-C equivalent to C(O)COMe with the bisacetonitrilo salt of the N,N-benzylamine palladacycle were determined by ITC in chlorobenzene after having optimized the conditions to ensure that only the double and a single insertion of alkynes were occurring respectively. The reaction energy profile established by DFT for the double insertion process involving Ph-C equivalent to C-Ph confirmed earlier conclusions on the rate determining character of the first insertion. Further computations of reaction enthalpies reveal significant discrepancies between ITC and DFT-D/continuum solvation enthalpies, that are suspected to arise from an unexpected explicit noncovalent interaction of PhCl with the components of the reaction.

CONSPECTUS: Noncovalent interactions (NCIs) have long interested a vast community of chemists who investigated their "canonical categories" derived from descriptive crystallography, e.g., H-bonds, pi-pi interactions, halogen/chalcogen/tetrel bonds, cation-pi and C-H-pi interactions, metallophilic interactions in the broad sense, etc. Recent developments in theoretical chemistry have enabled the treatment of noncovalent interactions under new auspices: dispersion-force-inclusive density functionals have emerged, which are reliable for modeling small to large molecular systems. It is possible to perform the full analysis of the contributions of London, Debye, and Keesom forces, i.e., the main components of van der Waals forces, by the DFT-D and ab initio methods at a reasonable computational cost. Our research has been focusing for now 15 years on the role of NCIs in the cohesion of organometallic complexes. NCIs are not only effective in Werner's secondary coordination sphere but also in the metal's primary one. The stabilization of electron-unsaturated transition metal complexes by hemichelation, metal-metal donor-acceptor complexes, and self-aggregation of cationic Rh(I) chromophores have indeed outlined the significance of the London dispersion force as an attractive force operating throughout the whole molecule or molecular assembly. The recent outburst of interest in C-H bond functionalization led us to address the broader question of reaction and catalyst engineering: although one can now satisfactorily analyze bonding and molecular cohesion in transition-metalbased organometallic systems, can modern theoretical methods guide reactivity exploration and the engineering of novel catalytic systems? We addressed this question by investigating the ambiphilic metal-ligand activation/concerted metalation-deprotonation mechanism involved in transition-metal-catalyzed directed C-H bond functionalization. This endeavor was initiated having in scope the construction of a rationale for the transposition of 4-5d metal chemistry to earth-abundant 3d metals. In this base-assisted mechanism of C-H bond metalation, agostic interactions are necessary but not sufficient because C-H bond breaking actually relies on the attractive NCI coding of a proton-transfer step and the minimization of metal-H repulsion. This Account introduces the recent shift of our research toward the construction of an NCI-inclusive paradigm of chemical reactivity engineering based on experimental efforts propped up by state-of-the-art theoretical tools.

ConspectusNoncovalent interactions (NCIs) have long interested a vast community of chemists who investigated their "canonical categories" derived from descriptive crystallography, e.g., H-bonds, π-π interactions, halogen/chalcogen/tetrel bonds, cation-π and C-H-π interactions, metallophilic interactions in the broad sense, etc. Recent developments in theoretical chemistry have enabled the treatment of noncovalent interactions under new auspices: dispersion-force-inclusive density functionals have emerged, which are reliable for modeling small to large molecular systems. It is possible to perform the full analysis of the contributions of London, Debye, and Keesom forces, i.e., the main components of van der Waals forces, by the DFT-D and ab initio methods at a reasonable computational cost. Our research has been focusing for now 15 years on the role of NCIs in the cohesion of organometallic complexes. NCIs are not only effective in Werner's secondary coordination sphere but also in the metal's primary one. The stabilization of electron-unsaturated transition metal complexes by hemichelation, metal-metal donor-acceptor complexes, and self-aggregation of cationic Rh(I) chromophores have indeed outlined the significance of the London dispersion force as an attractive force operating throughout the whole molecule or molecular assembly. The recent outburst of interest in C-H bond functionalization led us to address the broader question of reaction and catalyst engineering: although one can now satisfactorily analyze bonding and molecular cohesion in transition-metal-based organometallic systems, can modern theoretical methods guide reactivity exploration and the engineering of novel catalytic systems? We addressed this question by investigating the ambiphilic metal-ligand activation/concerted metalation-deprotonation mechanism involved in transition-metal-catalyzed directed C-H bond functionalization. This endeavor was initiated having in scope the construction of a rationale for the transposition of 4-5d metal chemistry to earth-abundant 3d metals. In this base-assisted mechanism of C-H bond metalation, agostic interactions are necessary but not sufficient because C-H bond breaking actually relies on the attractive NCI coding of a proton-transfer step and the minimization of metal-H repulsion. This Account introduces the recent shift of our research toward the construction of an NCI-inclusive paradigm of chemical reactivity engineering based on experimental efforts propped up by state-of-the-art theoretical tools.