Photocatalytic C-F alkylation of trifluoromethyls using o-phosphinophenolate: mechanistic insights and substrate prediction.

Density functional theory computations reveal the radical mechanism of photocatalytic defluoroalkylation and hydrodefluorination of N-phenyl-2,2,2-trifluoromethylacetamide with o-phosphinophenolate (PO) cooperative catalysis. The energy gaps between the singlet substrate LUMOs and triplet photocatalyst SOMOs can be used as an effective "chemical descriptor" for predicting catalyst activity. Cesium formate assisted C-F bond activation is the most favorable path. A series of available organic structures are computationally predicted as potential substrates.

Racemic Benzenesulfonohydrazide Enantioconvergent Tertiary C(sp3 )-H Amination Catalyzed by Copper and Chiral Phosphoric Acid: Mechanistic Insights and Computational Prediction.

Density functional theory computations reveal mechanistic insights into Cu and chiral phosphoric acid (CPA) catalyzed enantioconvergent amination of racemic benzenesulfonohydrazide. The O-O bond homolysis of tert-butyl 4-phenylbutaneperoxoate was found to be the turnover-limiting step with a total free energy barrier of 19.1 kcal/mol. The enantioconvergent amination is realized to obtain the same intermediate through prochiral carbon atom. The order and mode of hydrogen atom transferred by CPA and tert-butyloxy have a significant influence on the enantioselectivity and energy barriers. The olefinic side product generated by ß-hydride elimination is 9.9 kcal/mol thermodynamically less favourable. A series of phosphoric acids are predicted as promising co-catalysts with lower barriers for O-O bond homolysis.

Pyridine coordination enabled stepwise PT/ET N-H transfer and metal-independent C-C cleavage mechanism for Cu-mediated dehydroacylation of unstrained ketones.

A density functional theory study of copper-mediated dehydroacylation of 4-phenyl-2-butanone to the corresponding olefin reveals a flexible N-H transfer process and a metal-independent C-C cleavage mechanism. When N'-methylpicolinohydrazonamide (MPHA) acts as the activating reagent, N-H cleavage can easily take place via stepwise proton transfer/electron transfer (PT/ET) and the rate-determining step is C-C homolysis with a total free energy barrier of 22.6 kcal mol-1, which is consistent with experimental observation of no kinetic isotope effects (KIE) at ß-H. Besides, copper is found to have little influence on C-C cleavage, but is responsible for triggering single electron oxidation of the pre-aromatic intermediate (PAI). When replacing MPHA with picolinohydrazonamide (PHA), the second N-H transfer is 2.7 kcal mol-1 more favorable than C-C cleavage and dominates the pathway to aromatization, which explains there being no C-C cleavage product well. When N'-methylbenzohydrazonamide (MBHA) is adopted, the lack of pyridine coordination significantly reduces the stability of CuII and N-H transfer proceeds via a much more difficult proton coupled electron transfer (PCET) pathway, thus making N-H cleavage a rate-determining step with a total free energy barrier of up to 28.1 kcal mol-1.

Fluorinated 2,6-bis(arylimino)pyridyl iron complexes targeting bimodal dispersive polyethylenes: probing chain termination pathways via a combined experimental and DFT study.

In this work, fluorinated 2,6-bis(arylimino)pyridyl iron(II) complexes, [2-[CMeN{2,4-{(4-FC6H4)2CH}2-6-F}]-6-(CMeNAr)C5H3N]FeCl2 (Ar = 2,6-Me2C6H3Fe1, 2,6-Et2C6H3Fe2, 2,6-iPr2C6H3Fe3, 2,4,6-Me3C6H2Fe4, and 2,6-Et2-4-MeC6H2Fe5) and [2-[CMeN{2-{(4-FC6H4)2CH}-4-{(C6H5)CHAr'}-6-F}]-6-(CMeN(2,6-iPr2C6H3))C5H3N]FeCl2 (Ar' = 3-{(4-FC6H4)2CH}2-4-NH2-5-FC6H2Fe6), verified with different steric substituents, were synthesized and characterized. The molecular structures of Fe2 and Fe3 were determined by X-ray diffraction, revealing a pseudo-square-pyramidal geometry. High activities were achieved toward ethylene polymerization in each iron complex case. The sterically least demanding ligand enhanced the activity of its complex Fe1 with the highest activity up to 16.8 × 106 g of PE (mol of Fe)-1 h-1at 70 °C, while the bulkiest ligand led to the formation of the highest molecular weight of the resulting polyethylene using Fe6. Generally, the resulting polyethylenes are highly linear and most of them have a tendency to display bimodal distributions by virtue of the presence of multiple sites or competing chain transfer reactions. End-group analysis of polyethylenes confirms that the end groups include both unsaturated vinyl-end groups and saturated n-propyl or i-butyl, revealing the co-existence of two chain termination pathways including primary chain transfer to aluminium and secondary ß-H transfer. The chain termination processes were interpreted with the 1D sequence inverse-gated decoupled 13C NMR measurement of the resulting polyethylenes and DFT calculations along with the relevant polymerization mechanism.

Mechanistic insights into the α-branched amine formation with pivalic acid assisted C-H bond activation catalysed by Cp*Rh complexes.

Density functional theory computations revealed a pivalic acid assisted C-H bond activation mechanism for rhodium catalyzed formation of α-branched amines with C-C and C-N bond couplings. The reaction energies of the [Cp*RhCl2]2 dimer and silver cations indicate that the Cp*RhCl+ cation is the active catalyst. The essential role of pivalic acid is a co-catalyst for the activation of the ortho-C(sp2)-H bond in phenyl(pyrrolidin-1-yl)methanone, while the reaction of NaHCO3 and HCl reduces the overall barrier of the catalytic cycle. In the presence of both pivalic acid and NaHCO3 in the reaction, the C(sp2)-H bond is activated through a concerted metallation deprotonation process, and the C-C bond coupling is the rate-determining step with a total free energy barrier of 23.9 kcal mol-1. Without pivalic acid and NaHCO3, the C(sp2)-H bond can only be activated through a σ-bond metathesis process and the free energy barrier increases to 32.2 kcal mol-1. We also investigated the mechanisms of a side reaction for ß-branched amine formation and the reaction without styrene and found that their free energy barriers are 33.4 and 30.5 kcal mol-1, respectively.

Unexpected binuclear O-O cleavage and radical C-H activation mechanism for Cu-catalyzed desaturation of lactone.

A density functional theory study of Cu-catalyzed desaturation of δ-valerolactone into α,ß-unsaturated counterparts reveals an unexpected binuclear di-tert-butyl peroxide (DTBP) homolysis with spin-crossover and a radical α-C-H bond activation mechanism. The rate-determining step in the reaction catalyzed by CuIOAc-CyPPh2 is the homolysis of the O-O bond in DTBP with a total free energy barrier of 26.9 kcal mol-1, which is consistent with the observed first-order dependences on LCuI-PR3 and DTBP, as well as the pseudo-zeroth-order with lactone. The α- and ß-H transfer steps have 0.3 and 14.8 kcal mol-1 lower barriers than the O-O cleavage process, respectively. Such different barriers well explain the observed weak kinetic isotopic effect (KIE) at α-H and no KIE at ß-H. In addition, we found that the replacement of CyPPh2 for pyridine in the Cu complexes leads to much higher barriers for O-O bond cleavage and C-H bond activations with the formation of more stable binuclear Cu complexes.

Computational Prediction of Chiral Iron Complexes for Asymmetric Transfer Hydrogenation of Pyruvic Acid to Lactic Acid.

Density functional theory calculations reveal a formic acid-assisted proton transfer mechanism for asymmetric transfer hydrogenation of pyruvic acid catalyzed by a chiral Fe complex, FeH[(R,R)-BESNCH(Ph)CH(Ph)NH2](η6-p-cymene), with formic acid as the hydrogen provider. The rate-determining step is the hydride transfer from formate anion to Fe for the formation and dissociation of CO2 with a total free energy barrier of 28.0 kcal mol-1. A series of new bifunctional iron complexes with η6-p-cymene replaced by different arene and sulfonyl groups were built and computationally screened as potential catalysts. Among the proposed complexes, we found 1g with η6-p-cymene replaced by 4-isopropyl biphenyl had the lowest free energy barrier of 26.2 kcal mol-1 and excellent chiral selectivity of 98.5% ee.

Orientation-Controlled 2D Anisotropic and Isotropic Photon Transport in Co-crystal Polymorph Microplates.

2D anisotropic transport of photons/electrons is crucial for constructing ultracompact on-chip circuits. To date, the photons in organic 2D crystals usually exhibit the isotropic propagation, and the anisotropic behaviors have not yet been fully demonstrated. Now, an orientation-controlled photon-dipole interaction strategy was proposed to rationally realize the anisotropic and isotropic 2D photon transport in two co-crystal polymorph microplates. The monoclinic microplate adopts a nearly horizontal transition dipole moment (TDM) orientation in 2D plane, exhibiting anisotropic photon-dipole interactions and thus distinct re-absorption waveguide losses for different 2D directions. By contrast, the triclinic plate with a vertical TDM orientation, shows 2D isotropic photon-dipole interactions and thus the same re-absorption losses along different directions. Based on this anisotropy, a directional signal outcoupler was designed for the directional transmission of the real signals.

Computational Study of the Substituent Effects for the Spectroscopic Properties of Thiazolo[5,4-d]thiazole Derivatives.

Inspired by the structure and optical properties of N,N'-dialkylated/dibenzylated 2,5-bis(4-pyridinium)thiazolo[5,4-d]thiazole, we proposed a series of disubstituted thiazolo[5,4-d]thiazole derivatives as promising materials for multifunctional optoelectronic, electron transfer sensing, and other photochemical applications. Density functional theory study of the electronic structures and transition properties of those newly proposed molecules indicates that the electron-donating and electron-withdrawing groups introduced to the peripheral pyridyl ligands extend the distributions of molecular frontier orbitals, increase the electron density in thiazolo[5,4-d]thiazolea, and therefore lead to remarkable red-shifts of their absorption and emission peaks.

Computational Prediction of Ammonia-Borane Dehydrocoupling and Transfer Hydrogenation of Ketones and Imines Catalyzed by SCS Nickel Pincer Complexes.

Inspired by the catalytic mechanism and active site structure of lactate racemase, three scorpion-like SCS nickel pincer complexes were proposed as potential catalysts for transfer hydrogenation of ketones and imines with ammonia-borane (AB) as the hydrogen source. Density functional theory calculations reveal a stepwise hydride and proton transfer mechanism for the dehydrocoupling of AB and hydrogenation of N-methylacetonimine, and a concerted proton-coupled hydride transfer process for hydrogenation of acetone, acetophenone, and 3-methyl-2-butanone. Among all proposed Ni complexes, the one with symmetric NH2 group on both arms of the SCS pincer ligand has the lowest free energy barrier of 15.0 kcal/mol for dehydrogenation of AB, as well as total free energy barriers of 17.8, 18.2, 18.0, and 18.6 kcal/mol for hydrogenation of acetone, N-methylacetonimine, acetophenone, and 3-methyl-2-butanone, respectively.

Mechanistic insights into asymmetric transfer hydrogenation of pyruvic acid catalysed by chiral osmium complexes with formic acid assisted proton transfer.

A density functional theory study of the asymmetric transfer hydrogenation of pyruvic acid to l- and d-lactic acids catalysed by a chiral osmium complex OsH[(R,R)TsNCH(Ph)CH(Ph)NH2](η6-p-cymene) reveals a formic acid assisted enantio-determining proton-coupled hydride transfer mechanism. Activation strain model analysis indicates that the C-H/π interaction between η6-arene and carboxyl ligands has a significant influence on the enantioselectivity. The replacement of p-cymene by 4-isopropyl biphenyl or phenyl is highly likely to improve the catalytic performance of the complex.

Computational prediction of pentadentate iron and cobalt complexes as a mimic of mono-iron hydrogenase for the hydrogenation of carbon dioxide to methanol.

A series of amidate-ligated pentadentate iron and cobalt complexes with N-heterocyclic pyridinol groups were proposed and computationally screened as potential catalysts for CO2 reduction. Density functional theory calculations reveal a ligand assisted heterolytic H2 cleavage mechanism with a total free energy barrier of 23.3 kcal mol-1 for the hydrogenation of CO2 to methanol catalysed by a pentadentate Co complex with a 2-[bis(pyridine-2-ylmethyl)]amino-N-3,9-purin-2-one ligand.

Hydrogenation of CO2 to Methanol Catalyzed by Cp*Co Complexes: Mechanistic Insights and Ligand Design.

A direct hydride transfer mechanism with three cascade cycles for the conversion of carbon dioxide and dihydrogen to methanol (CO2 + 3H2 → CH3OH + H2O) catalyzed by a half-sandwich cobalt complex [Cp*Co(bpy-Me)OH2]2+ (1) is proposed based on density functional theory calculations. The formation of methanediol via hydride transfer from Co to formic acid (4 → TS8,11) is the rate-determining step with a total barrier of 26.0 kcal/mol in free energy. Furthermore, 15 analogues of 1 are constructed by replacing the hydrogen atoms at the two meta and para positions of the bipyridine ligand with different functional groups (1b-1l), the carbon atoms in the bipyridine ligand with nitrogen atoms (1m-1o), and one pyridine ligand with N-heterocyclic carbene (1p). Among all newly proposed complexes, [Cp*Co(2,2'-bipyrazine)OH2]2+ (1n) is the most active one with a total barrier of 19.6 kcal/mol in free energy. Such a low barrier indicates 1n is a promising catalyst for efficient conversion of CO2 and H2 to methanol at room temperature.

Eosin†Y-Functionalized Conjugated Organic Polymers for Visible-Light-Driven CO2 Reduction with H2 O to CO with High Efficiency.

Visible-light-driven photoreduction of CO2 to energy-rich chemicals in the presence of H2 O without any sacrifice reagent is of significance, but challenging. Herein, Eosin Y-functionalized porous polymers (PEosinY-N, N=1-3), with high surface areas up to 610 m2 g-1 , are reported. They exhibit high activity for the photocatalytic reduction of CO2 to CO in the presence of gaseous H2 O, without any photosensitizer or sacrifice reagent, and under visible-light irradiation. Especially, PEosinY-1 derived from coupling of Eosin Y with 1,4-diethynylbenzene shows the best performance for the CO2 photoreduction, affording CO as the sole carbonaceous product with a production rate of 33 µmol g-1 h-1 and a selectivity of 92 %. This work provides new insight for designing and fabricating photocatalytically active polymers with high efficiency for solar-energy conversion.

Tailoring the Energy Levels and Cavity Structures toward Organic Cocrystal Microlasers.

Organic cocrystals with unique energy-level structures are potentially a new class of materials for the development of versatile solid-state lasers. However, till now, the stimulated emission in cocrystal materials remains a big challenge possibly because of the nonradiative charge-transfer (CT) transitions. Here, for the first time, we report organic cocrystal microlasers constructed by simultaneously tailoring the energy levels and cavity structures based on the intermolecular halogen-bonding interactions. The intermolecular interactions triggered different self-assembly processes, resulting in distinct types of high-quality resonant microcavities. More importantly, the halogen-bonding interactions alleviated intermolecular CT and thus brought about a favorable four-level energy structure for the population inversion and tunable lasing in the cocrystals.

One-Pot Catalytic Cleavage of C═S Double Bonds by Pd Catalysts at Room Temperature.

The C═S double bonds in CS2 and thioketones were catalytically cleaved by Pd dimeric complexes [(N∧N)2Pd2(NO3)2](NO3)2 (N∧N, 2,2'-bipyridine, 4,4'-dimethylbipyridine or 4,4'-bis(trifluoromethyl)) at room temperature in one pot to afford CO2 and ketones, respectively, for the first time. The mechanisms were fully investigated by kinetic NMR, isotope-labeled experiments, in situ ESI-MS, and DFT calculations. The reaction is involved a hydrolytic desulfurization process to generate C═O double bonds and a trinuclear cluster, which plays a pivotal role in the catalytic cycle to regenerate the dimeric catalysts with HNO3. Furthermore, the electronic properties of catalyst ligands possess significant influence on reaction rates and kinetic parameters. At the same temperature, the reaction rate is consistent with the order of electronegativity of N∧N ligands (4,4'-bis(trifluoromethyl) > 2,2'-bipyridine > 4,4'-dimethylbipyridine). This homogeneous catalytic reaction features mild conditions, a broad substrate scope, and operational simplicity, affording insight into the mechanism of catalytic activation of carbon sulfur bonds.

Mechanistic insights into the iridium catalysed hydrogenation of ethyl acetate to ethanol: a DFT study.

Density functional theory study of the hydrogenation of ethyl acetate catalysed by iridium complexes [Cp*Ir(bpy)OH2]2+ reveals a direct C-O bond cleavage mechanism with two cascade catalytic cycles for the hydrogenation of ethyl acetate to aldehyde and the hydrogenation of aldehyde to ethanol. Calculation results indicate that the rate-determining state in the whole catalytic reaction is the direct C-O bond cleavage for the formation of aldehyde and ethanol with a total free energy barrier of 25.5 kcal mol-1, which is 0.6 kcal mol-1 more favorable than the mechanism proposed by Goldberg and co-workers in their experimental study.

A bio-inspired design and computational prediction of scorpion-like SCS nickel pincer complexes for lactate racemization.

Inspired by the structures of the active site of lactate racemase and recent reported SCS nickel pincer complexes, we built a series of scorpion-like SCS nickel pincer complexes with an imidazole tail and computationally predicted their catalytic activities for the racemization of lactic acid. Density functional theory calculations reveal a proton coupled hydride transfer mechanism for the dehydrogenation of l-lactate and the formation of d-lactate with a free energy barrier as low as 25.9 kcal mol-1.

Controlling the Compositional Chemistry in Single Nanoparticles for Functional Hollow Carbon Nanospheres.

Hollow carbon nanostructures have inspired numerous interests in areas such as energy conversion/storage, biomedicine, catalysis, and adsorption. Unfortunately, their synthesis mainly relies on template-based routes, which include tedious operating procedures and showed inadequate capability to build complex architectures. Here, by looking into the inner structure of single polymeric nanospheres, we identified the complicated compositional chemistry underneath their uniform shape, and confirmed that nanoparticles themselves stand for an effective and versatile synthetic platform for functional hollow carbon architectures. Using the formation of 3-aminophenol/formaldehyde resin as an example, we were able to tune its growth kinetics by controlling the molecular/environmental variables, forming resin nanospheres with designated styles of inner constitutional inhomogeneity. We confirmed that this intraparticle difference could be well exploited to create a large variety of hollow carbon architectures with desirable structural characters for their applications; for example, high-capacity anode for potassium-ion battery has been demonstrated with the multishelled hollow carbon nanospheres.

Low expression levels of insulin-like growth factor binding protein-3 are correlated with poor prognosis for patients with hepatocellular carcinoma.

Insulin-like growth factor binding protein-3 (IGFBP-3) has previously been identified as a putative tumor suppressor gene. The present study investigated the clinical and prognostic significance of IGFBP-3 expression levels in patients with hepatocellular carcinoma (HCC). Immunohistochemistry (IHC) probing for IGFBP-3 was performed on paraffin-embedded tissue samples obtained from 120 patients with HCC, including tissue samples from 120 primary cancer sites and 50 matched adjacent non-malignant sites. Receiver-operator curve (ROC) analysis was used to determine the cut-off scores for the presence of IGFBP-3-positive tumor cells and to estimate the survival time of the patients. The threshold for marking the positive expression of IGFBP-3 was 65%, based on the area under the ROC. Positive expression of IGFBP-3 was observed in 65/120 (54.2%) of the HCC tissues, and in 36/50 (72%) of the adjacent non-malignant liver tissues. Low levels of IGFBP-3 expression were correlated with tumor size (P=0.003), tumor multiplicity (P=0.044), node (P=0.008), metastasis (P=0.001) and clinical stage (P=0.001), as well as reduced survival time (P=0.015). Using univariate survival analysis, a significant direct correlation between high and low IGFBP-3 expression levels, and patient survival time (mean survival time high IGFBP-3, 39.4 vs. low IGFBP-3, 18.7 months) was identified. Kaplan-Meier analysis demonstrated that IGFBP-3 expression levels and patients survival time were significantly correlated (P<0.001). Multivariate analysis revealed IGFBP-3 expression to be an independent parameter (P=0.003). Therefore, low levels of IGFBP-3 expression are associated with advance clinicopathological classification and may be a predictor of poor survival in patients with HCC. Furthermore, these findings suggest that IGFBP-3 may serve as an independent molecular marker for the evaluation of prognosis in patients with HCC.