Complexation of Phenol and Thiophenol by Amine N‐Oxides: Isothermal Titration Calorimetry and ab Initio Calculations

To develop a new solvent‐impregnated resin (SIR) system for removal of phenols from water, the complex formation of dimethyldodecylamine N‐oxide (DMDAO), trioctylamine N‐oxide (TOAO), and tris(2‐ethylhexyl)amine N‐oxide (TEHAO) with phenol (PhOH) and thiophenol (PhSH) is studied. To this end we use isothermal titration calorimetry (ITC) and quantum chemical modeling (on B3LYP/6‐311G(d,p)‐optimized geometries: B3LYP/6‐311+G(d,p), B3LYP/6‐311++G(2d,2p), MP2/6‐311+G(d,p), and spin component scaled (SCS) MP2/6‐311+G(d,p); M06‐2X/6‐311+G(d,p)//M06‐2X/6‐311G(d,p), MP2 with an extrapolation to the complete basis set limit (MP2/CBS), as well as CBS‐Q). The complexes are analyzed in terms of structural (e.g., bond lengths) and electronic elements (e.g., charges). Furthermore, complexation and solvent effects (in benzene, toluene, and mesitylene) are investigated by ITC measurements, yielding binding constants K, enthalpies ΔH⁰, Gibbs fre energies ΔG⁰, and entropies ΔS⁰ of complex formation, and stoichiometry N. The ITC measurements revealed strong 1:1 complex formation between both DMDAO–PhOH and TOAO–PhOH. The binding constant (K=1.7–5.7×10⁴ M ^?1) drops markedly when water‐saturated toluene was used (K=5.8×10³ M ^?1), and π–π interaction with the solvent is shown to be relevant. Quantum mechanical modeling confirms formation of stable 1:1 complexes with linear hydrogen bonds that weaken on attachment of electron‐withdrawing groups to the amine N‐oxide moiety. Modeling also showed that complexes with PhSH are much weaker than those with PhOH, and in fact too weak for ITC determination. CBS‐Q incorrectly predicts equal or even higher binding enthalpies for PhSH than for PhOH, which invalidates it as a benchmark for other calculations. Data from the straightforward SCS‐MP2 method without counterpoise correction show very good agreement with the MP2/CBS values.     

Facile Synthesis and Versatile Reactivity of an Unusual Cyclometalated Rhodium(I) Pincer Complex

The synthesis of the reactive PN(C^H) ligand 2‐di(tert‐butylphosphanomethyl)‐6‐phenylpyridine ( 1^H ) and its versatile coordination to a Rh^I center is described. Facile C?H activation occurs in the presence of a (internal) base, thus resulting in the new cyclometalated complex [Rh^I(CO)(κ³‐P,N,C‐ 1 )] ( 3 ), which has been structurally characterized. The resulting tridentate ligand framework was experimentally and computationally shown to display dual‐site proton‐responsive reactivity, including reversible cyclometalation. This feature was probed by selective H/D exchange with [D₁]formic acid. The addition of HBF₄ to 3 leads to rapid net protonolysis of the Rh?C bond to produce [Rh^I(CO)(κ³‐P,N,(C?H)‐ 1 )] ( 4 ). This species features a rare aryl C?H agostic interaction in the solid state, as shown by X‐ray diffraction studies. The nature of this interaction was also studied computationally. Reaction of 3 with methyl iodide results in rapid and selective ortho‐methylation of the phenyl ring, thus generating [Rh^I(CO)(κ²‐P,N‐ 1^Me )] ( 5 ). Variable‐temperature NMR spectroscopy indicates the involvement of a Rh^III intermediate through formal oxidative addition to give trans‐[Rh^III(CH₃)(CO)(I)(κ³‐P,N,C‐ 1 )] prior to C?C reductive elimination. The Rh^III–trans‐diiodide complex [Rh^I(CO)(I)₂(κ³‐P,N,C‐ 1 )] ( 6 ) has been structurally characterized as a model compound for this elusive intermediate.     

Engineering Crystals Using sp3-C Centred Tetrel Bonding Interactions

1,1,2,2-Tetracyanocyclopropane derivatives 1 and 2 were designed and synthesized to probe the utility of sp³-C centred tetrel bonding interactions in crystal engineering. The crystal packing of 1 and 2 and their 1,4-dioxane cocrystals is dominated by sp³-C(CN)₂⋅⋅⋅O interactions, has significant C⋅⋅⋅O van der Waals overlap (≤0.266 Å) and DFT calculations indicate interaction energies of up to −11.0 kcal mol⁻¹. A cocrystal of 2 with 1,4-thioxane reveals that the cyclopropane synthon prefers interacting with O over S. Computational analyses revealed that the electropositive C₂(CN)₄ pocket in 1 and 2 can be seen as a strongly directional ‘tetrel-bond donor’, similar to halogen bond or hydrogen bond donors. This disclosure is expected to have implications for the utility of such ‘tetrel bond donors’ in molecular disciplines such as crystal engineering, supramolecular chemistry, molecular recognition and medicinal chemistry.     

Catalytic Dibenzocyclooctene Synthesis via Cobalt(III)–Carbene Radical and ortho‐Quinodimethane Intermediates

The metalloradical activation of ortho‐benzallylaryl N‐tosyl hydrazones with [Co(TPP)] (TPP=tetraphenylporphyrin) as the catalyst enabled the controlled exploitation of the single‐electron reactivity of the redox non‐innocent carbene intermediate. This method offers a novel route to prepare eight‐membered rings, using base metal catalysis to construct a series of unique dibenzocyclooctenes through selective C_carbene?C_aryl cyclization. The desired eight‐membered‐ring products were obtained in good to excellent yields. A large variety of aromatic substituents are tolerated. The proposed reaction mechanism involves intramolecular hydrogen atom transfer (HAT) to Co^III–carbene radical intermediates followed by dissociation of an ortho‐quinodimethane that undergoes 8π cyclization. The mechanism is supported by DFT calculations, and the presence of radical‐type intermediates was confirmed by trapping experiments.     

Uniformly Oriented Zeolite ZSM‐5 Membranes with Tunable Wettability on a Porous Ceramic

Facile fabrication of well‐intergrown, oriented zeolite membranes with tunable chemical properties on commercially proven substrates is crucial to broadening their applications for separation and catalysis. Rationally determined electrostatic adsorption can enable the direct attachment of a b‐oriented silicalite‐1 monolayer on a commercial porous ceramic substrate. Homoepitaxially oriented, well‐intergrown zeolite ZSM‐5 membranes with a tunable composition of Si/Al=25–∞ were obtained by secondary growth of the monolayer. Intercrystallite defects can be eliminated by using Na⁺ as the mineralizer to promote lateral crystal growth and suppress surface nucleation in the direction of the straight channels, as evidenced by atomic force microscopy measurements. Water permeation testing shows tunable wettability from hydrophobic to highly hydrophilic, giving the potential for a wide range of applications.     

Dynamic Interplay between Defective UiO-66 and Protic Solvents in Activated Processes

UiO-66, composed by Zr-oxide inorganic bricks [Zr₆(μ₃-O)₄(μ₃-OH)₄] and organic terephthalate linkers, is one of the most studied metal–organic frameworks (MOFs) due to its exceptional thermal, chemical, and mechanical stability. Thanks to its high connectivity, the material can withstand structural deformations during activation processes such as linker exchange, dehydration, and defect formation. These processes do alter the zirconium coordination number in a dynamic way, creating open metal sites for catalysis and thus are able to tune the catalytic properties. In this work, it is shown, by means of first-principle molecular-dynamics simulations at operating conditions, how protic solvents may facilitate such changes in the metal coordination. Solvent can induce structural rearrangements in the material that can lead to undercoordinated but also overcoordinated metal sites. This is demonstrated by simulating activation processes along well-chosen collective variables. Such enhanced MD simulations are able to track the intrinsic dynamics of the framework at realistic conditions.     

Charge transfers influence on the spin ground state of manganese and iron superoxide dismutases: a DFT study on a model of the reduced active site interacting with O2-

From DFT and time-dependent DFT calculations on Mn(II)SOD and Fe(II)SOD active site models interacting with O2- we have determined that metal-to-ligand charge transfers stabilise the S = 2 and S = 5/2 spin states as ground spin states for the [Mn(II)SOD-02-] and [Fe(II)SOD-O2-] model complexes, respectively. These charge transfers are ruled by the electronic configuration of the metal ion, and they can be determinant in the catalysis reaction.     

Bromo-Derivatives of 2′-NHR-3,4-methylenedioxychalcone and Its 4-Quinolone Isomer

Bromination reaction of 2′-NHR-3,4′-methylenedioxychalcone (1) and 2,3-dihydro-2-(3′,4′-methylenedioxyphenyl)-4(1H)-quinolone (7) with bromine and N-bromosuccinimide are discussed. Depending on the character of the R group and on the reagent used nuclear or side-chain brominated or side-chain bromo-methoxylated products were obtained.     

Local Polynomial Regression: Optimal Kernels and Asymptotic Minimax Efficiency

We consider local polynomial fitting for estimating a regression function and its derivatives nonparametrically. This method possesses many nice features, among which automatic adaptation to the boundary and adaptation to various designs. A first contribution of this paper is the derivation of an optimal kernel for local polynomial regression, revealing that there is a universal optimal weighting scheme. Fan (1993, Ann. Statist., 21, 196-216) showed that the univariate local linear regression estimator is the best linear smoother, meaning that it attains the asymptotic linear minimax risk. Moreover, this smoother has high minimax risk. We show that this property also holds for the multivariate local linear regression estimator. In the univariate case we investigate minimax efficiency of local polynomial regression estimators, and find that the asymptotic minimax efficiency for commonly-used orders of fit is 100% among the class of all linear smoothers. Further, we quantify the loss in efficiency when going beyond this class.     

Successive approximations for average reward Markov games

This paper considers two-person zero-sum Markov games with finitely many states and actions with the criterion of average reward per unit time. Two special situations are treated and it is shown that in both cases the method of successive approximations yields anε-band for the value of the game as well as stationaryε-optimal strategies. In the first case all underlying Markov chains of pure stationary optimal strategies are assumed to be unichained. In the second case it is assumed that the functional equation Uv=v+ge has a solution.