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Herein, we report the Cu‐complex catalyzed, native functional group‐assisted, and TFA/NMF additives promoted (phenylsulfonyl)difluoromethylation of vinylic C(sp2)−H bond of acrylamides. Using our in‐home designed reagent, this reaction enables the construction of the C(sp2)−CF2SO2Ph bond from simple C−H bond activation by copper catalysis under mild reaction conditions with total Z‐selectivity. The versatility of utilized fluorinated group was illustrated by its conversion into value‐added CF2 moieties as well as the remarkable =CHF residue. The performed experimental and computational mechanistic studies enabled to identify the true nature of active catalyst and substrate, as well as establish critical roles of TFA and NMF additives. In this reaction, the TFA acts as a promoter of the much‐needed CuII/CuII→CuIII/CuI disproportionation, while the NMF facilitates the following ligand exchange and C−C coupling processes. We ruled out the generation of radical intermediates and established the C−H activation to be irreversible and the rate‐determining step of the entire process. [ABSTRACT FROM AUTHOR]

Transition metal‐catalyzed C−H bond oxidation of free carboxylic acid stands as an economic, selective, and efficient strategy to generate lactones, hydroxylated products, and acetoxylated products and attracts much of the chemists' attention. Herein, we performed a density functional theory study on the mechanism and selectivity in Pd‐catalyzed and MPAA ligand‐enabled C−H bond acetoxylation reaction. It was found that the ligand, base, and substrate are important in determining the reaction mechanism and the selectivity. The acetic anhydride additive is critical in leading the reaction to be acetoxylation, instead of the lactonization, through a facile σ‐bond metathesis mechanism that leads to the Pd‐OAc in‐termediate. Our study sheds light on the further development of transition metal‐catalyzed C−H bond oxidation reactions. [ABSTRACT FROM AUTHOR]

Direct and regioselective functionalization of pyridine is a topic of high scientific and technological importance. In spite of extensive efforts, the regioselective functionalization of pyridine still remains a significant challenge due to their low reactivity and presence of Lewis‐basic sp2 nitrogen. Here, we studied the effect of hydrogen bonding interactions on the regiochemical outcome of Pd‐mediated C−H activation of pyridine by utilizing DFT calculations. We demonstrated that hydrogen bonding can act as a second independent factor to override the inherent regioselectivity of pyridine. This novel approach complements previously reported strategies, such as: (a) coordination of pyridine to transition metal center via its N‐center, (b) installation of directing group (DG) and then coordination of pyridine to the transition metal center via this DG (i. e. chelation assistant strategy), (c) protection of its nitrogen lone pair with N‐oxide or N‐imino groups or with Lewis acids, (d) the inherent positional reactivity of C−H bonds based on the electronic or steric properties of the substituents, and (e) by the identity of the oxidant used. We have also demonstrated that the oxidation state of the Pd catalyst has impact on the regiochemical outcome of the C−H activation step in pyridine. The implications of our study for regioselective C−H functionalization catalyst design of heteroarenes are twofold: It demonstrates (1) hydrogen bonding as a viable design principle, and (2) Pd(IV) as a catalyst for C−H functionalization. [ABSTRACT FROM AUTHOR]

The storage of solar energy in chemical bonds will depend on pH‐universal catalysts that are not only impervious to acid, but actually thrive in it. Whereas other homogeneous water oxidation catalysts are less active in acid, we report a catalyst that maintained high electrocatalytic turnover frequency at pH values as low as 1.1 and 0.43 (kcat=1501±608 s−1 and 831±254 s−1, respectively). Moreover, current densities, related to catalytic reaction rates, ranged from 15 to 50 mA cm−2 mM−1 comparable to those reported for state‐of‐the‐art heterogeneous catalysts and 30 to 100 times greater than those measured for two prominent literature homogeneous catalysts at pH 1.1 and 0.43. The catalyst also exhibited excellent durability when a chemical oxidant was used (CeIV, 7400 turnovers, TOF 0.88 s−1). Preliminary computational studies suggest that the unusual active‐site sulfonate group acts a proton relay even in strong acid, as intended. [ABSTRACT FROM AUTHOR]

Computational studies revealed that dirhodium tetrakis(1,2,2‐triarylcyclopropanecarboxylate) (Rh2(TPCP)4) catalysts adopt distinctive high symmetry orientations, which are dependent on the nature of the aryl substitution pattern. The parent catalyst, Rh2(TPCP)4, and those with a p‐substituent at the C1 aryl, such as Rh2(p‐BrTPCP)4 and Rh2(p‐PhTPCP)4, adopt a C2‐symmetric structure. Rh2(3,5‐di(p‐tBuC6H4)TPCP)4, 3,5‐disubstituted at the C1 aryl, adopts a D2‐symmetric structure, whereas catalysts with an o‐substituent at the C1 aryl, such as Rh2(o‐Cl‐5‐BrTPCP)4, adopt a C4‐symmetric structure. [ABSTRACT FROM AUTHOR]

We describe a bulk adjusted linear combination of atomic orbitals (BA‐LCAO) approach for nanoparticles. In this method, we apply a many‐body scaling function (in similar manner as in the environment‐modified total energy based tight‐binding method) to the DFT‐derived diatomic AO interaction potentials (like in the conventional orbital‐based density‐functional tight binding approach) strictly according to atomic valences acquired naturally in a bulk structure. This modification, (a) facilitates all atom orbital‐based electronic structure calculations of charge carrier dynamics in nanoscale structures with a molecular acceptor, and (b) allows to closely match high‐level density functional calculation data (previously adjusted to the available experimental findings) for bulk structures. To advance practical application of the BA‐LCAO approach we parameterize the Hamiltonian of wurtzite CdSe by fitting its band structure to a high‐level DFT reference, corrected for experimentally measured band edges. Here, unlike in conventional DFTB approach, we: (1) use hydrogen‐like AOs for the basis as exact atomic eigenfunctions, while orbital energies of which are taken from experimentally measured ionization potentials, and (2) parameterize the many‐body scaling functions rather than the atomic wavefunctions. Development of this approach and parameters is guided by our goals to devise a method capable of simultaneously treating the problems of (i) interfacial electron/hole transfer between finite, variable size nanoparticles and electron scavenging molecules, and (ii) high‐energy electronic transitions (Auger transitions) that mediate multi‐exciton decay in quantum dots. Electronic structure results are described for CdSe quantum dots of various sizes. © 2018 Wiley Periodicals, Inc. The authors describe a (bulk adjusted) BA‐LCAO method that provides greater flexibility for improving the band structure of nanoparticles. The authors have shown that such key properties as the valence and conduction band edges, crucial in electron/hole transfer processes and consequently the band gap, which also controls Auger assisted electron/hole transfer, can be reproduced exactly for given empirical reference data. [ABSTRACT FROM AUTHOR]

A RhII-catalyzed method for intermolecular alkylation of the β-C(sp2)−H bond of enol ethers, enamides, and enecarbamates with α-diazo-1,3-dicarbonyl compounds is reported. The products are formed in up to 99 % yield and can be readily derivatized under a variety of conditions. By utilizing a combination of experimental and computational studies, the presumptive addition-elimination reaction mechanism was investigated and found to proceed under thermodynamic control at higher temperature. The acquired fundamental knowledge was translated into a strategic reaction design and yielded the first example of the β-C−H functionalizations of acyclic enol ethers using α-diazo-1,3-dicarbonyl compounds. [ABSTRACT FROM AUTHOR]

A wide range of chemical warfare agents and their simulants are catalytically decontaminated by a new one-dimensional polymeric polyniobate (P-PONb), K12[Ti2O2][GeNb12O40]⋅19 H2O ( KGeNb) under mild conditions and in the dark. Uniquely, KGeNb facilitates hydrolysis of nerve agents Sarin (GB) and Soman (GD) (and their less reactive simulants, dimethyl methylphosphonate (DMMP)) as well as mustard (HD) in both liquid and gas phases at ambient temperature and in the absence of neutralizing bases or illumination. Three lines of evidence establish that KGeNb removes DMMP, and thus likely GB/GD, by general base catalysis: a) the k(H2O)/k(D2O) solvent isotope effect is 1.4; b) the rate law (hydrolysis at the same pH depends on the amount of P-PONb present); and c) hydroxide is far less active against the above simulants at the same pH than the P-PONbs themselves, a critical control experiment. [ABSTRACT FROM AUTHOR]

In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition-metal-substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt-containing Keggin POMs, [CoIIW12O40]6− ( 1 a), [CoIIIW12O40]5− ( 2 a), [SiCoII(H2O)W11O39]6− ( 3 a), and [SiCoIII(H2O)W11O39]5− ( 4 a), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited-state dynamics of these compounds at an unprecedented level. All species exhibit a bi-exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1 a and 3 a are considered to result from metal-to-polyoxometalate charge transfer (MPCT) from CoII to W, while the longer-lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion ( 1 a) is far longer-lived ( τ=420 ps in H2O; τ=1700 ps in MeCN) than that of 3 a ( τ=1.3 ps), in which the single CoII atom is located in a pseudo-octahedral addendum site. Short-lived states are observed for the two CoIII-containing heteropolyanions 2 a ( τ=4.4 ps) and 4 a ( τ=6.3 ps) and assigned solely to O→CoIII charge transfer. The dramatically extended lifetime for 1 a versus 3 a is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single W atom, a phenomenon not noted previously in POMs. [ABSTRACT FROM AUTHOR]

Water oxidation catalysts (WOCs) are of core importance in several green energy production technologies, including water splitting and water reduction of CO driven by electrochemical potential and/or photons (radiant energy). General challenges in solar fuel generating structures, WOC design concepts, and some success-limiting considerations in WOC development are described. The first class of WOCs are presented that combine the stability benefits of heterogeneous WOCs with the reactivity and other benefits of homogeneous WOCs. [ABSTRACT FROM AUTHOR]

Reductase activity of ebtellur was studied at the density functional level. For this purpose, the mechanism and controlling factors of the reactions EbTe&dbond;O + 2GSH → EbTe + GS-SG + H2O (2) and EbTe&dbond;O + H2O + 2GSH → EbTe(OH)2 + 2GSH → EbTe + GS-SG + 2H2O (3) were analyzed. It was shown that the addition of the first thiol molecule to 2_TeO (model of EbTe&dbond;O), which occurs with a few kcal/mol activation barrier and exothermic by 20–25 (9–13) kcal/mol, leads to 2_TeO, 2_Te(OH)(SMe), II, intermediate. Addition of the next thiol molecule to II may proceed via the both “concerted” and “stepwise” pathways with a rate-determining S&bond;S bond formation step. It was found that the “concerted” pathway is slightly favorable at the enthalpy level than the “stepwise” pathway. Overall reaction (2) is found to be exothermic by 41.6 (41.4) kcal/mol. Calculations show that the MeS&bond;H bond activation by oxo species, 2_TeO, is much easier process than that by dihydroxy species, 2_Te(OH)2. Comparison of the calculated barriers for rate-determining steps of the reaction 2_Te&dbond;O + 2 MeSH with that, 19.4 (30.3) kcal/mol, for the reaction 2_Te&dbond;O + H2O + 2 MeSH → 2_Te(OH)2 + MeSH indicates that in the presence of water molecule ebtellur should show less (slow) thiol reductase activity. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Binding of two ligands trans to each other by some transition metal complexes may be cooperative [Khoroshun et al., Mol Phys 2002, 100, 523]. Several interesting consequent effects include (i) inverse relationship between bond strength and binding affinity; (ii) smaller coordination barriers to formation of weaker bonds; (iii) enhancement of Lewis acidity with increased number of ligands. We describe a simple model, σ trans promotion effect (TPE), which considers electronic reorganization between two Lewis structures, and predicts the above-mentioned effects. The applied result of present study is the unified perspective on several facts of heme chemistry. Particularly, we reiterate an important but often overlooked notion, developed previously within the spin pairing model [Drago and Corden, Acc Chem Res 1980, 13, 353], that, in hemoproteins, the proximal histidine and the distal ligand such as O2 or CO cooperate in promoting electronic reorganization. As a result, depopulation of dz2 orbital upon ligand binding contributes to the phenomenon of hemoglobin cooperativity. The presented density functional (B3LYP) calculations on realistic models, the processes of carbon monoxide binding by Fe(II) porphyrins and dinitrogen binding by triamido/triamidoamine Mo(III) complexes, particularly the evaluation of the coordination barriers due to spin-state change by location of the minima on seams of crossing, support the TPE model predictions. From a broader theoretical perspective, the present study would hopefully stimulate the development of much needed frameworks and tools for facile comparisons of wave functions and their properties between different geometries, species, and electronic states. Advancement of practical wave function comparisons may yield fresh qualitative perspectives on chemical reactivity, and promote better understanding of related concepts such as electronic reorganization. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 423–441, 2007 [ABSTRACT FROM AUTHOR]

In the present DFT study, the catalytic mechanism of H2O2 formation in the oxidative half-reaction of NiSOD, E-Ni(II) + O2- + 2H+ → E-Ni(III) + H2O2, has been investigated. The main objective of this study is to investigate the source of two protons required in this half-reaction. The proposed mechanism consists of two steps: superoxide coordination and H2O2 formation. The effect of protonation of Cys6 and the proton donating roles of side chains (S) and backbones (B) of His1, Asp3, Cys6, and Tyr9 residues in these two steps have been studied in detail. For protonated Cys6, superoxide binding generates a Ni(III)–O2H species in a process that is exothermic by 17.4 kcal/mol (in protein environment using the continuum model). From the Ni(III)–O2H species, H2O2 formation occurs through a proton donation by His1 via Tyr9, which relative to the resting position of the enzyme is exothermic by 4.9 kcal/mol. In this pathway, a proton donating role of His1 residue is proposed. However, for unprotonated Cys6, a Ni(II)–O2- species is generated in a process that is exothermic by 11.3 kcal/mol. From the Ni(II)–O2- species, the only feasible pathway for H2O2 formation is through donation of protons by the Tyr9(S)–Asp3(S) pair. The results discussed in this study elucidate the role of the active site residues in the catalytic cycle and provide intricate details of the complex functioning of this enzyme. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1438–1445, 2006 [ABSTRACT FROM AUTHOR]

The protein effects on the initial step of O2 binding to the diiron active site in the Methane Monooxygenase (MMO) were studied at the ONIOM(QM:MM) level with and without electronic embedding. The significant part of the hydroxylase component of MMO, every aminoacid residue at least one atom of which is within 11 Å radius from either of the iron-centers of the active site, was included into the calculations. The computed ‘real’ system contained almost 1200 atoms and we treated it at, ONIOM low level, Amber molecular mechanics force field. Position of every atom of each amino acid residue within 7-Å radius from either of the iron atoms as well as all hydrogen atoms was optimized. The ‘model’ system, treated at the B3LYP/lan12dz level (ONIOM high level) encompassed 44 atoms including: (i) two iron atoms, (ii) functional groups forming first coordination sphere, such as two water molecules, two imodazoles, two bridging (between the Fe atoms) and two terminal carboxylates, as well as (iii) the dioxygen molecule. The comparison of the obtained results in vacuo and in protein, both with and without electronic embedding, clearly indicates that the protein profoundly affects initial binding of dioxygen molecule to the diiron center of the MMOHred. It was shown that at the early stages methane monooxygenase protein environment plays a crucial role as it effectively facilitates the activation of the dioxygen molecule. Furthermore, the obtained results demonstrated the usefulness of the ONIOM approach in studying such large systems including a dozen of hundreds atoms. [ABSTRACT FROM AUTHOR]

Review: 253 refs. [ABSTRACT FROM AUTHOR]