Water-insoluble Ag-U-organic assemblies with photocatalytic activity

Two metal-organic coordination polymers [Ag(bipy)(UO(2))(bdc)(1.5)] (bipy=2,2'-bipyridyl, bdc=1,4-benzenedicarboxylate) and [Ag(2)(phen)(2)UO(2)(btec)] (phen=1,10-phenanthroline, btec=1,2,4,5-benzenetetracarboxylate) were obtained by hydrothermal assembly of the d(10) metal silver and the 5f metal uranium with mixed ligands. Both compounds form two-dimensional networks with pi-pi overlap interactions between the aromatic fragments in the neighboring layers. In aqueous suspension the two water-insoluble materials show photocatalytic degradation performance superior to that of commercial TiO(2) (Degussa P-25) when tested on nonbiodegradable rhodamine B (RhB) as model pollutant. The relationship between the structure of the photocatalysts and the photocatalytic activity was also elucidated. On the basis of the monitored intermediate species and the final mineralized products, it is proposed that the possible reaction mechanism for the photodegradation (oxidation) of RhB in aqueous solution catalyzed by the two assembly compounds involves photoexcitation of uranyl centers and molecular oxygen.     

Spectral, structural, and electrochemical properties of ruthenium porphyrin diaryl and aryl(alkoxycarbonyl) carbene complexes: influence of carbene substituents, porphyrin substituents, and trans-axial ligands

A wide variety of ruthenium porphyrin carbene complexes, including [Ru(tpfpp)(CR(1)R(2))] (CR(1)R(2) = C(p-C(6)H(4)Cl)(2) 1 b, C(p-C(6)H(4)Me)(2) 1 c, C(p-C(6)H(4)OMe)(2) 1 d, C(CO(2)Me)(2) 1 e, C(p-C(6)H(4)NO(2))CO(2)Me 1 f, C(p-C(6)H(4)OMe)CO(2)Me 1 g, C(CH==CHPh)CO(2)CH(2)(CH==CH)(2)CH(3) 1 h), [Ru(por)(CPh(2))] (por=tdcpp 2 a, 4-Br-tpp 2 b, 4-Cl-tpp 2 c, 4-F-tpp 2 d, tpp 2 e, ttp 2 f, 4-MeO-tpp 2 g, tmp 2 h, 3,4,5-MeO-tpp 2 i), [Ru(por)[C(Ph)CO(2)Et]] (por=tdcpp 2 j, tmp 2 k), [Ru(tpfpp)(CPh(2))(L)] (L = MeOH 3 a, EtSH 3 b, Et(2)S 3 c, MeIm 3 d, OPPh(3) 3 e, py 3 f), and [Ru(tpfpp)[C(Ph)CO(2)R](MeOH)] (R = CH(2)CH==CH(2) 4 a, Me 4 b, Et 4 c), were prepared from the reactions of [Ru(por)(CO)] with diazo compounds N(2)CR(1)R(2) in dichloromethane and, for 3 and 4, by further treatment with reagents L. A similar reaction of [Os(tpfpp)(CO)] with N(2)CPh(2) in dichloromethane followed by treatment with MeIm gave [Os(tpfpp)(CPh(2))(MeIm)] (3 d-Os). All these complexes were characterized by (1)H NMR, (13)C NMR, and UV/Vis spectroscopy, mass spectrometry, and elemental analyses. X-ray crystal structure determinations of 1 d, 2 a,i, 3 a, b, d, e, 4 a-c, and 3 d-Os revealed Ru==C distances of 1.806(3)-1.876(3) A and an Os==C distance of 1.902(3) A. The structure of 1 d in the solid state features a unique "bridging" carbene ligand, which results in the formation of a one-dimensional coordination polymer. Cyclic voltammograms of 1 a-c, g, 2 a-d, g-k, 3 b-d, 4 a, b, and 3 d-Os show a reversible oxidation couple with E(1/2) values in the range of 0.06-0.65 V (vs Cp(2)Fe(+/0)) that is attributable to a metal-centered oxidation. The influence of carbene substituents, porphyrin substituents, and trans-ligands on the Ru==C bond was examined through comparison of the chemical shifts of the pyrrolic protons in the porphyrin macrocycles ((1)H NMR) and the M==C carbon atoms ((13)C NMR), the potentials of the metal-centered oxidation couples, and the Ru==C distances among the various ruthenium porphyrin carbene complexes. A direct comparison among iron, ruthenium, and osmium porphyrin carbene complexes is made.     

Imido transfer from bis(imido)ruthenium(VI) porphyrins to hydrocarbons: effect of imido substituents, C-H bond dissociation energies, and Ru(VI/V) reduction potentials

[Ru(VI)(TMP)(NSO2R)2] (SO2R = Ms, Ts, Bs, Cs, Ns; R = p-C6H4OMe, p-C6H4Me, C6H5, p-C6H4Cl, p-C6H4NO2, respectively) and [Ru(VI)(Por)(NTs)2] (Por = 2,6-Cl2TPP, F20-TPP) were prepared by the reactions of [Ru(II)(Por)(CO)] with PhI=NSO2R in CH2Cl2. These complexes exhibit reversible Ru(VI/V) couple with E(1/2) = -0.41 to -0.12 V vs Cp2Fe(+/0) and undergo imido transfer reactions with styrenes, norbornene, cis-cyclooctene, indene, ethylbenzenes, cumene, 9,10-dihydroanthracene, xanthene, cyclohexene, toluene, and tetrahydrofuran to afford aziridines or amides in up to 85% yields. The second-order rate constants (k2) of the aziridination/amidation reactions at 298 K were determined to be (2.6 +/- 0.1) x 10(-5) to 14.4 +/- 0.6 dm3 mol(-1) s(-1), which generally increase with increasing Ru(VI/V) reduction potential of the imido complexes and decreasing C-H bond dissociation energy (BDE) of the hydrocarbons. A linear correlation was observed between log k' (k' is the k2 value divided by the number of reactive hydrogens) and BDE and between log k2 and E(1/2)(Ru(VI/V)); the linearity in the former case supports a H-atom abstraction mechanism. The amidation by [Ru(VI)(TMP)(NNs)2] reverses the thermodynamic reactivity order cumene > ethylbenzene/toluene, with k'(tertiary C-H)/k'(secondary C-H) = 0.2 and k'(tertiary C-H)/k'(primary C-H) = 0.8.     

A poly(ethylene glycol)-supported quaternary ammonium salt for highly efficient and environmentally friendly chemical fixation of CO2 with epoxides under supercritical conditions

A PEG-supported quaternary ammonium salt is proved to be an efficient and recyclable homogeneous catalyst for solvent-free synthesis of cyclic carbonates from carbon dioxide and epoxides under supercritical conditions. Supporting Bu₄NBr on soluble polymer PEG6000 enhances the catalytic activity. The workup procedure is straightforward, and the catalyst can be reused over five times with no appreciable loss of catalytic activity and selectivity.     

Primary and secondary phosphane complexes of metalloporphyrins: isolation, spectroscopy, and X-ray crystal structures of ruthenium and osmium porphyrins binding phenyl- or diphenylphosphane

[Ru(II)(por)(PH(n)Ph(3-n))2], [Os(II)(por)(CO)(PH(n)Ph(3-n))] (n=1, 2), and [Os(II)(F20-tpp){P(OH)Ph2}(PHPh2)] (F20-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato dianion) were prepared from the reaction of [M(II)(por)(CO)] (M=Ru, Os) or [Os(VI)(por)O2] with the respective primary/secondary phosphane and characterized by 1H NMR, 31P NMR, UV/Vis, and IR spectroscopy, mass spectrometry, and elemental analysis. The reaction of [Os(VI)(por)O2] with PHPh2 also gave minor amounts of [Os(II)(por){P(OH)Ph2}2]. [Ru(II)(F20-tpp)(PH2Ph)2] exhibits a remarkable stability toward air and shows a reversible metal-centered oxidation couple at E(1/2)=0.39 V versus [Cp2Fe](+/0) in the cyclic voltammogram. The structures of [Ru(II)(F20-tpp)(PH2Ph)2] x 2CH2Cl2, [Ru(II)(4-Cl-tpp)(PHPh2)2] x 2CH2Cl2 (4-Cl-tpp=5,10,15,20-tetrakis(p-chlorophenyl)porphyrinato dianion), [Ru(II)(F20-tpp)(PHPh2)2], and [Os(II)(F20-tpp){P(OH)Ph2}2] were determined by X-ray crystallography and feature Ru-P distances of 2.3397(11)-2.3609(9) A and an Os-P distance of 2.369(2) A.     

A Convergent,Modular Approach to Trifluoromethyl-Bearing 5-Membered Rings via Catalytic C(sp3)−H Activation

Trifluoromethyl-bearing 5-membered rings are prevalent in bioactive molecules, but modular approaches to these compounds by functionalization of robust C(sp³)−H bonds in a direct and selective manner are extremely challenging. Herein we report the rhodium-catalyzed α-CF₃-α-alkyl carbene insertion into C(sp³)−H bonds of a broad range of substrates to access 7 types of CF₃-bearing saturated 5-membered carbo- and heterocycles. The reaction is particularly effective for benzylic C−H insertion exerting good site-, diastereo- and enantiocontrol, and applicable to the synthesis of chiral CF₃ analogues of bioactive molecules. Ruthenium α-CF₃-α-alkyl carbene complexes underwent stoichiometric reactions to give C−H insertion products, lending evidence for the involvement of metal α-CF₃-α-alkyl carbene species in the catalytic cycle. DFT calculations revealed that the π⋅⋅⋅π attraction and intra-carbene C−H⋅⋅⋅F hydrogen bond elucidate the origin of selectivity of the benzylic C−H insertion reactions.     

GaPO4-LTA单晶中稠环芳烃类物质(PAHs)的制备与表征

以γ-甲基吡啶(mPy)为模板剂合成了具有A型分子筛骨架结构的磷酸镓(GaPO4-LTA)单晶,并研究了mPy在GaPO4-LTA超笼内的高温热解反应.mPy在GaPO4-LTA笼中热解后形成稠环芳烃类物质PAHs(Polycyclicaromatichydrocarbons).这些PAHs物质的种类与升温速度和终止温度密切相关.在GaPO4-LTA笼中生成的PAHs可望成为合成富勒烯的前驱体.     

Highly selective intramolecular carbene insertion into primary C-H bond of α-diazoacetamides mediated by a (p-cymene)ruthenium(II) carboxylate complex

Complex [(p-cymene)Ru(η(1)-O(2)CCF(3))(2)(OH(2))] mediated transformation of α-diazoacetamides ArCH(2)N(C(CH(3))(3))C(O)CHN(2) to result in carbene insertion into the primary C-H bond exclusively, with the γ-lactam products being isolated in up to 98% yield. This unexpected reaction is striking in view of the presence of usually more reactive sites such as secondary C-H bonds in the substrates. DFT calculations based on proposed Ru-carbene species provide insight into this unique selectivity.     

光驱动多孔无定形TiO2的形成机制与光催化性能的研究

以钛酸正丁醇和乙二醇为原料,采用溶剂热法合成了钛乙二醇盐(TG)前躯体,在高压汞灯照射下制备出无定形TiO2。利用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)、紫外-可见吸收光谱(UV-Vis)、表面光电压谱(SPS)、N2吸附-脱附对所得材料进行了结构和性能的表征。借助X射线吸收精细结构(XAFS)对无定形TiO2的形成机制进行了分析,并通过硝基苯的还原反应考察了材料的光催化性能。结果表明:在紫外光驱动无定形TiO2的形成过程中,中心元素Ti4+的配位环境发生变化,由八面体结构转变为四面体结构;由于特殊的孔道结构使得多孔无定形TiO2显示出较好的光催化活性。