Chuanzhi Sun

Synthesis, characterization, and catalytic performance of copper-containing SBA-15 in the phenol hydroxylation.

A series of copper-containing SBA-15 samples were successfully synthesized via evaporation-induced self-assembly route. The resulting materials were characterized by X-ray diffraction (XRD), (29)Si MAS NMR spectroscopy, transmission electron microscopy (TEM), N(2) sorption, inductively coupling plasma-atomic emission spectrometer (ICP-AES), thermogravimetry, and differential thermal analysis (TG-DTA), Fourier-transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectra (UV-vis) and X-ray photoelectron spectroscopy (XPS). The results indicated that: (1) all the samples exhibited typical hexagonal arrangement of mesoporous structure; (2) copper ions could be incorporated into the framework of SBA-15; (3) the addition of urea in the hydrothermal stage efficiently reduced the leaching of copper and improved the thermal stability of the mesoporous materials. Catalytic performances of the obtained materials were evaluated in the hydroxylation of phenol with H(2)O(2). The catalytic tests showed that the synthesized materials exhibited high activity for this reaction and copper ions in the framework were more active than copper species in the extra-framework position. The nitric acid treatment on the samples removed the bulk CuO species, which resulted in a dramatic increase in the catalytic activity.

Efficient fabrication of ZrO2-doped TiO2 hollow nanospheres with enhanced photocatalytic activity of rhodamine B degradation

ZrO(2)-doped TiO(2) hollow nanospheres with anatase phase are efficiently fabricated via functionalized negatively charged polystyrene (PS) spheres without any surfactant or polyelectrolyte. The resulting Ti(1-)(x)Zr(x)O(2) (hereafter denoted as TZ) hollow nanospheres are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), nitrogen sorption, and UV-vis diffuse reflectance spectroscopy (UV-vis). The Zr(4+) incorporation decreases the anatase crystallite size, increases the specific surface area, and changes the pore size distribution. Furthermore, it induces enrichment of electron charge density around Ti(4+) ions and blueshift of absorption edges. The TZ hollow nanospheres doped with moderate ZrO(2) (molar ratio, Ti:Zr=10:1) exhibit better photocatalytic activity than the other samples for the degradation of rhodamine B in aqueous solution, which is correlated with the effect of Zr(4+) doping on the physicochemical properties in terms of surface structures, phase structures, and the electronic structures.

Density Functional Theory Study of Rh(III)-Catalyzed C–H Activations and Intermolecular Annulations between Benzamide Derivatives and Allenes

Density functional theory has been applied to gain insight into the Cp*Rh(OAc)2-catalyzed C-H activation and intermolecular annulation of benzamide derivatives with allenes. The study shows that the reactions proceed in three steps: (1) C-H activation induced by Rh catalyst reacting with benzamide derivatives, (2) carborhodation of allene, and (3) regeneration of Rh catalyst. The results indicate that the N-H deprotonation makes the following C-H activation much easier. The regio- and stereoselectivities of 1a (N-pivaloyloxy benzamide)/2a (cyclohexylallene) and 1b (N-pivaloyloxy-4-methyl-benzamide)/2b (1,1-dimethyl allene) depend on the allene carborhodation step. The steric hindrance effect is the dominant factor. We also discuss the reaction mechanism of 1c (N-methoxy benzamide)/2a. The chemoselectivity between 1c/2a is determined by the N-O cleavage step. Replacement of OPiv by OMe leads to loss of the stabilization effect provided by C=O in OPiv. Additionally, Cp*Rh(OAc)(OPiv) is produced in the Cp*Rh(OAc)2 regeneration step, which can work as catalyst as well.

Theoretical characterization of the conformational features of unnatural oligonucleotides containing a six nucleotide genetic alphabet

The addition of the unnatural P:Z base pair to the four naturally occurring DNA bases expands the genetic alphabet and yields an artificially expanded genetic information system (AEGIS). Herein, the structural feature of oligonucleotides containing a novel unnatural P:Z base pair is characterized using both molecular dynamics and quantum chemistry. The results show that the incorporation of the novel artificial base pair (P:Z) preserves the global conformational feature of duplex DNA except for some local structures. The Z-nitro group imparts new properties to the groove width, which widens the major groove. The unnatural oligonucleotides containing mismatched base pairs exhibit low stability. This ensures efficient and high-fidelity replication. In general, the incorporation of the P:Z pair strengthens the stability of the corresponding DNA duplex. The calculated results also show that the thermostability originates from both hydrogen interaction and stacking interaction. The Z-nitro group plays an important role in enhancing the stability of the H-bonds and stacking strength of the P:Z pair. Overall, the present results provide theoretical insights in the exploration of artificially expanded genetic information systems.

Effect of precursors on the structure and activity of CuO-CoOx/γ-Al2O3 catalysts for NO reduction by CO

Catalytic reduction of NO by CO was studied over a series of CuO-CoOx/γ-Al2O3 catalysts prepared by co-impregnation with different copper and cobalt precursors (acetate and nitrate) to evaluate the structure-activity relationship. The obtained samples were characterized in detail by means of XRD, LRS, XPS, H2-TPR and in situ FT-IR technologies. Results indicate that copper oxide is agglomerated while cobalt oxide is dispersed on γ-Al2O3 for the catalyst prepared from copper acetate and cobalt acetate precursors (CuACoA); CuxCo3-xO4 spinel is formed and agglomerated on the catalyst prepared from copper nitrate and cobalt nitrate precursors (CuNCoN); while both copper oxide and cobalt oxide could be homogeneously dispersed for the catalyst prepared from copper nitrate and cobalt acetate precursors (CuNCoA), which exhibits the best activity for NO reduction by CO. Probably the synergistic effect between dispersed copper oxide and cobalt oxide is propitious to the oxygen transfer, which could be the reason for its high activities. Finally, a possible reaction mechanism was tentatively proposed to explore the different catalytic performances in NO reduction by CO model reaction.

The stabilizing effect of the transient imine directing group in the Pd(II)-catalyzed C(sp3)–H arylation of free primary amines

A transient directing group (DG) has been successfully applied to assist the activation of C–H bonds. In this paper, we have performed density functional theory (DFT) calculations to investigate the mechanism of ligand-assisted Pd(II)-catalyzed C(sp3)–H arylation. In the presence of a quinoline-8-carbaldehyde (ArQCHO) ligand, the reaction starts with the nucleophilic addition of 2-butylamine with the ligand to generate the transient imine DG, which binds to the Pd(II) center via bidentate coordination. The sequential C(sp3)–H activation, oxidative addition of [Ph2I]+ with a palladacycle, and C–C reductive elimination yield the final product of arylation. Instead of the traditional inner-sphere concerted metalation deprotonation (CMD) mechanism, a novel deprotonation mechanism for the rate-determining C(sp3)–H activation is discovered; that is, the methyl group is deprotonated by an outer-sphere pivalate. A comparison with the results of the reaction without the ligand indicates that the square planar geometry formed by the transient DG with Pd(II) significantly reduces the distortion energies, which ultimately makes the C(sp3)–H activation kinetically favorable.

Comprehensive Mechanistic Insight into Cooperative Lewis Acid/Cp*CoIII-Catalyzed C–H/N–H Activation for the Synthesis of Isoquinolin-3-ones

The mechanism of B(C6F5)3 promoted Cp*CoIII-catalyzed C-H functionalization was investigated in detail employing density functional theory (DFT). The formation free energy of every possible species in the multicomponent complex system was explored and the optimal active catalyst was screened out. The results uncover the role of B(C6F5)3 played in forming active catalyst is from the coordination with OAc-, but not from the formation of [I(C6F5)3B]-, and no acceleration effect is found in C-H activation as well as the formation of CoIII-carbene intermediate. Moreover, present theoretical results elucidate the Cp*CoIII-catalyzed C-H activation is mediated by imine N-coordination other than general proposed the sequence of N-deprotonation directed C-H activation. The metal-controlled C-H/N-H selectivity was then elucidated by insighting into [Cp*CoIIIOAc]+/[Cp*RhIIIOAc]+-catalyzed C-H and N-H activations, respectively.

Mechanistic Exploration of Cp*CoIII/RhIII-Catalyzed Carboamination/Olefination of N-Phenoxyacetamides with Alkenes

A computational study of Cp*CoIII/RhIII-catalyzed carboamination/olefination of N-phenoxyacetamides with alkenes was carried out to elucidate the catalyst-controlled chemoselectivity. The reaction of the two catalysts shares a similar process that involves N-H and C-H activation as well as alkene insertion. Then the reaction bifurcates at the generated seven-membered metallacycle. For Cp*CoIII catalyst, the resulting metallacycle undergoes oxidation addition, reductive elimination, and protonation to yield the carboamination product exclusively. However, the Cp*RhIII catalyst could promote the subsequent olefination pathway via sequential β-H elimination, reductive elimination, oxidation addition, and protonation, which enables the experimentally observed mixtures of both carboamination and olefination products. Our results uncover that the higher propensity for the β-H-elimination of the Cp*RhIII than the Cp*CoIII catalyst in the olefination pathway could be responsible for the different selectivity and reactivity of the two catalysts.

Solvent Mediating a Switch in the Mechanism for Rhodium(III)-Catalyzed Carboamination/Cyclopropanation Reactions between N-Enoxyphthalimides and Alkenes

Recently, a new synthetic methodology of rhodium-catalyzed carboamination/cyclopropanation from the same starting materials at different reaction conditions has been reported. It provides an efficient strategy for the stereospecific formation of both carbon- and nitrogen-based functionalities across an alkene. Herein we carried out a detailed theoretical mechanistic exploration for the reactions to elucidate the switch between carboamination and cyclopropanation as well as the origin of the chemoselectivity. Instead of the experimentally proposed RhIII-RhI-RhIII catalytic mechanism, our results reveal that the RhIII-RhV-RhIII mechanism is much more favorable in the two reactions. The chemoselectivity is attributed to a combination of electronic and steric effects in the reductive elimination step. The interactions between alkene and the rhodacycle during the alkene migration insertion control the stereoselectivity in the carboamination reactions. The present results disclose a dual role of the methanol solvent in controlling the chemoselectivity.

Mechanistic insight into Ni-mediated decarbonylation of unstrained ketones: the origin of decarbonylation catalytic activity

Mechanistic details of the decarbonylation of unstrained ketones by (IMesMe)Ni and (IMesMe)NiCO complexes with a N-heterocyclic carbene ligand (IMesMe) have been explored by density functional theory calculations. The calculated mechanism sheds light on the origin of realization for the decarbonylation catalytic cycle. (IMesMe)Ni mediates the first decarbonylation cycle and generates a biaryl product and (IMesMe)NiCO, which is inactive for the substrate 4-methyl-4′-trifluoromethyl benzophenone 1. However, (IMesMe)NiCO can mediate the decarbonylation of 3-quinolinyl ketone 2 and realize the catalytic cycle. The decarbonylation step is the rate-determining step controlling whether the transformation can be mediated catalytically. The stabilization energy E(2) of BDC(O)–C(methyl phenyl) → LVNi for the decarbonylation transition state plays a dominant role in the catalytic cycle. In addition, an electron-withdrawing group on the arene can stabilize the orbital energies facilitating the initial C–C(O) oxidative addition step. A moderate linear correlation is observed between the oxidative addition barriers and the charges transferred from (IMesMe)Ni to the benzoyl moiety.