Enecarbamates as selective substrates in oxidations: chiral-auxiliary-controlled mode selectivity and diastereoselectivity in the [2+2] cycloaddition and ene reaction of singlet oxygen and in the epoxidation by DMD and mCPBA

The stereochemical course of the oxidation of chiral oxazolidinone-substituted enecarbamates has been studied for singlet oxygen ((1)O(2)), dimethyldioxirane (DMD), and m-chloroperbenzoic acid (mCPBA) by examining of the special structural and stereoelectronic features of the enecarbamates. Valuable mechanistic insight into these selective oxidations is gained. Whereas the R(1) substituent on the chiral auxiliary is responsible for the steric shielding of the double bond and determines the sense of the pi-facial diastereoselectivity, structural characteristic such as the Z/E configuration and the nature of the R(2) group on the double bond are responsible for the extent of the diastereoselectivity. Stereoelectronic steering by the vinylic nitrogen functionality controls the mode selectivity (ene reaction vs [2+2] cycloaddition) in the case of (1)O(2).     

On the origin of regio- and stereoselectivity in singlet oxygen addition to enecarbamates

The reactions of excited state singlet molecular oxygen ((1)Δ(g),(1)O(2)) continue to witness interesting new developments. In the most recent manifestation, (1)O(2) is tamed to react with enecarbamates in a stereoselective manner, which is remarkable, in view of its inherently high reactivity (Acc. Chem. Res. 2008, 41, 387). Herein, we employed the CAS-MP2(8,7)/6-31G* as well as the CAS-MP2(10,8)/6-31G* computations to unravel the origin of (i) diastereoselectivities in dioxetane or hydroperoxide formation and (ii) regioselectivity leading to a [2 + 2] cycloadduct or an ene product when (1)O(2) reacts with an oxazolidinone tethered 2-phenyl-1-propenyl system. The computed Gibbs free energy profiles for E- and Z-isomers when (1)O(2) approaches through the hindered and nonhindered diastereotopic faces (by virtue of chiral oxazolidinone) of the enecarbamates exhibit distinct differences. In the case of E-isomer, the relative energies of the transition structures responsible for hydroperoxide (ene product) are lower than that for dioxetane formation. On the other hand, the ene pathway is predicted to involve higher barriers as compared to the corresponding dioxetane pathway for Z-isomer. The energy difference between the rate-determining diastereomeric transition structures involved in the most favored ene reaction for E-enecarbamate suggests high diastereoselectivity. In contrast, the corresponding energy difference for Z-enecarbamate in the ene pathway is found to be diminishingly close, implying low diastereoselectivity. However, the dioxetane formation from Z-enecarbamate is predicted to exhibit high diastereoselectivity. The application of activation strain model as well as the differences in stereoelectronic effects in the stereocontrolling transition structures is found to be effective toward rationalizing the origin of selectivities reported herein. These predictions are found to be in excellent agreement with the experimental observations.     

Probing the stereoselectivity of the Heck arylation of endocyclic enecarbamates with diazonium salts. Concise syntheses of (2S,5R)-phenylproline methyl ester and Schramm's C-azanucleoside

[reaction: see text] The diastereoselectivity of the Heck arylation of several chiral, nonracemic, five-membered endocyclic enecarbamates with aryldiazonium tetrafluoroborates was evaluated. The cis selectivity observed for some enecarbamates bearing coordinating groups was explored in the concise synthesis of the (2S,5R)-(+)-phenylproline methyl ester, a scaffold for the nonpeptide cholecystokinin antagonist (+)-RP 66803, and in the synthesis of Schramm's potent antiprotozoan C-azanucleoside.     

Enecarbamates as imine surrogates: nucleophilic addition of 1,3-dicarbonyl compounds to enecarbamates

[reaction: see text] Novel Mannich-type reactions of 1,3-dicarbonyl compounds with enecarbamates have been developed. Stable and storable enecarbamates work as surrogates of aliphatic aldehyde-derived imines, which are known to be difficult to isolate and store.     

Chiral-auxiliary-controlled diastereoselectivity in the epoxidation of enecarbamates with DMD and mCPBA

[structure: see text] Chiral oxazolidinone-substituted enecarbamates 1 are epoxidized in a diastereoselectivity up to 93:7 for both DMD and mCPBA. The diastereofacial differentiation depends on the steric interaction between the R(1) substituent on the oxazolidinone ring and the incoming electrophile. The stereochemical course of epoxidation was assessed by chemical correlation with the known optically active diols.     

Formal Asymmetric Organocatalytic [3+2] Cyclization between Enecarbamates and 3‐Indolylmethanols: Rapid Access to 3‐Aminocyclopenta[b]indoles

A highly enantio‐ and diastereoselective synthesis of 3‐aminocyclopenta[b]indoles has been developed through formal [3+2] cycloaddition reaction of enecarbamates and 3‐indolylmethanols. This transformation is catalyzed by a chiral phosphoric acid that achieves simultaneous activation of both partners of the cycloaddition. Mechanistic data are also presented that suggest that the reaction occurs through a stepwise pathway.     

Asymmetric lithiation-substitution sequences of substituted allylamines

[reaction: see text] (-)-Sparteine-mediated asymmetric lithiation-substitution sequences of 2- and 3-substituted N-(Boc)-N-(p-methoxyphenyl) allylic amines with electrophiles have been investigated. Asymmetric lithiation-substitutions of N-(Boc)-N-(p-methoxyphenyl) allylic amines 11, 12, 13, 14, and 15 provide highly enantioenriched enecarbamates in good yields. Further transformations to give aldehydes, acids, ketones, and a Diels-Alder adduct are reported. The 1,4-addition products from reactions of the lithiated allylic amines from 14 and 15 with conjugated activated alkenes gives enecarbamates with two and three stereogenic centers in good yields with high diastereomeric and enantiomeric ratios. Synthetic transformation of these products by acid hydrolysis and subsequent cyclization provide stereoselective access to bicyclic compounds containing four and five stereogenic centers with high diastereoselectivity and enantioselectivity. It is suggested that allyllithium complexes generated by asymmetric deprotonation react with most electrophiles with inversion of configuration.     

Asymmetric carbon-carbon bond formations by conjugate additions of lithiated N-boc allylic amines to nitroalkenes: enantioselective synthesis of functionalized cyclopentanoids

[reaction: see text] Allylic organolithiums generated by enantioselective deprotonation of N-Boc-N-(p-methoxyphenyl) allylic amines undergo conjugate additions with nitroalkenes to provide enecarbamates containing two contiguous stereogenic centers in good yields with high diastereoselectivities and enantioselectivities. Further elaboration of these adducts to enantioenriched substituted cyclopentanones and aminocyclopentanes is reported.     

Organocatalytic cycloaddition–elimination cascade for atroposelective construction of heterobiaryls

The first chiral phosphoric acid (CPA) catalyzed cycloaddition–elimination cascade reaction of 2-naphthol- and phenol-derived enecarbamates with azonaphthalenes has been established, providing a highly atroposelective route to an array of axially chiral aryl-C3-benzoindoles in excellent yields with excellent enantioselectivities. The success of this strategy derives from the stepwise process involving CPA-catalyzed asymmetric formal [3 + 2] cycloaddition and subsequent central-to-axial chirality conversion by elimination of a carbamate. In addition, the practicality of this reaction had been verified by varieties of transformations towards functionalized atropisomers.

An organocatalytic asymmetric cycloaddition–elimination cascade reaction of aryl enecarbamates with azonaphthalenes has been developed to access axially chiral heterobiaryls in excellent yields and enantioselectivities.     

Chemistry of thiocarboxylates: synthesis and structures of neutral copper(I) thiocarboxylates with triphenylphosphine

The reactions of Na+ R[O]CS- (R = Me, Ph) with mixtures of CuCl and PPh3 in stoichiometric ratios yielded the compounds [Cu4(SC[O]Me)4(PPh3)4] (1), [Cu4(SC[O]Ph)4(PPh3)3] (2), [Cu2(SC[O]Me)2(PPh3)4] (3), [Cu(SC[O]Ph)(PPh3)2] (4), and [Cu2(SC[O]Ph)2(PPh3)3] (5) quantitatively. Compound 2 was also obtained from mixtures of CuCl, PPh3, and NaSC[O]Ph in the ratio 1:1:1. The analogous thioacetate compound similar to 2 and the thiobenzoate analogue of 1 could not be obtained. Attempts to prepare the unsymmetrical dimer of a thioacetate compound similar to 5 gave a mixture of 1 and 3. The structures of 1-4 have been determined by single-crystal X-ray diffraction methods. Crystal data for 1: triclinic space group Pl, a = 11.5844(3) A, b = 13.2459(3) A, c = 14.3433(3) A, alpha = 64.019(1) degrees, beta = 79.297(1) degrees, gamma = 69.426(1) degrees, V = 1850.98(7) A3, Z = 1, Dcalcd = 1.439 g.cm-3. Crystal data for 2.0.5CH2Cl2.H2O: triclinic space group P1, a = 12.4413(1) A, b = 15.5443(1) A, c = 20.4637(3) A, alpha = 94.974(1) degrees, beta = 95.976(1) degrees, gamma = 100.450(1) degrees, V = 3848.09(7) A3, Z = 2, Dcalcd = 1.416 g.cm-3. Single-crystal data for 3: monoclinic space group P2(1)/n, a = 15.2746(2) A, b = 23.2947(2) A, c = 19.0518(3) A, beta = 96.713(1) degrees, V = 6732.5(2) A3, Z = 4, Dcalcd = 1.309 g.cm-3. Crystal data for 4: triclinic space group P1, a = 10.2524(3) A, b = 12.9826(4) A, c = 14.5340(4) A, alpha = 87.723(1) degrees, beta = 75.322(1) degrees, gamma = 75.978(1) degrees, V = 1815.14(9) A3, Z = 2, Dcalcd = 1.327 g.cm-3. Compound 1, [mu 3-SC[O]Me-S)2(mu-SC[O]Me-S)2(CuPPh3)4], is a tetramer with a distorted stepladder structure in which two copper atoms are trigonally coordinated and the other two are tetrahedrally coordinated. Two bonding modes, namely, mu 3-S and mu 2-S, were observed for the Me[O]CS- anion. The structure of 2 may be described as a highly distorted cubanoid structure and formulated as [(mu 3-SC[O]Ph-S3)(mu 3-SC[O]Ph-S2,O)3(Cu)(CuPPh3)3]. In 2, three copper atoms have tetrahedral coordination geometry and one copper atom is trigonally coordinated. Unprecedented bonding modes, namely, mu 3-S, have been observed for the R[O]CS- anions, in 1 and 2 and mu 3-S2,O in 2. Compound 3, [(mu-SC[O]MeS)(mu-SC[O]Me-S,O)[Cu(PPh3)2]2] is a dimer with mu 2-S and mu 2-S,O bonding modes of Me[O]CS- ligands. Monomeric structure was found in 4 in which the copper atom has trigonal planar geometry with a very weak intramolecular interaction with O. Variable temperature 31P NMR studies in solution show the presence of various species in equilibria.     

Coordination modes between copper(II) and N-acetylneuraminic (sialic) acid from a 2D-simulation analysis of EPR spectra. Implications for copper mediation of sialoglycoconjugate chemistry relevant to human biology

The equilibrium distribution of species formed between Cu(II) and N-acetylneuraminic (sialic) acid (I, LH) at 298 K has been determined using a two-dimensional (2D) simulation analysis of electron paramagnetic resonance (EPR) spectra. In acidic solutions (pH values < 4), the major species present are Cu(2+), [CuL]+ [logbeta = 1.64(4)], and [CuL2] [logbeta = 2.77(5)]. At intermediate pH values (4.0 < pH < 7.5), [CuL2H-1]- [logbeta = -2.72(7)] and two isomers of [CuLH-1] [logbeta (overall) = -3.37(2)] are present. At alkaline pH values (7.5 < pH < 11), the major species present is [CuL2H-2]2-, modeled as three isomers with unique giso and Aiso values [logbeta (overall) = -8.68(3)]. Two further species ([CuLH-3]2- and [CuL2H-3]3-) appear at pH values > 11. It is proposed that [CuL]+ most likely features I coordinated via the deprotonated carboxylic acid group (O1) and the endocyclic oxygen atom (OR) forming a five-membered chelate ring. Select Cu(II)-I species of the form [CuLH-1] may feature I acting as a dianionic tridentate chelate, via oxygen atoms derived from O1, OR, and one deprotonated hydroxy group (O7 or O8) from the glycerol tail. Alternatively, I may coordinate Cu(II) in a bidentate fashion as the tert-2-hydroxycarboxylato (O1,O2) dianion. Spectra predicted for Cu(II)-I complexes in which I is coordinated in either a O1,OR {I1-} or O1,O2 {I2-} bidentate fashion {e.g., [CuL]+ (O1,O R), [CuL2] (bis-O1,O R), [CuLH-1] (isomer: O1, O2), [CuL2H-1]- (O1, O R; O1, O2), and [CuL2H-2]2- (isomer: bis-O1, O2)} have "irregular" EPR spectra that are ascribed to the existence of Cu(II)-I(monomer) <==> Cu(II)-I(polymer) equilibria. The formation of polymeric Cu(II)-I species will be favored in these complexes because the glycerol-derived hydroxyl groups at the complex periphery (O, 7O, 8O9) are available for further Cu(II) binding. The presence of polymeric Cu(II)-I species is supported by EPR spectral data from solutions of Cu(II) and the homopolymer of I, colominic acid (Ipoly). Conversely, spectra predicted for Cu(II)-I complexes where I is coordinated in a {I2-} tridentate {e.g., [CuLH-1] (isomer: O1, O R, O7, or O8) and [CuL2H-2]2- (isomer: bis-O1,O R,O7, or O8)} or tetradentate fashion {I3-} {e.g., [CuLH-3]2- (O1, O R, O, 8O9)} are typical for mononuclear tetragonally elongated Cu(II) octahedra. In this latter series of complexes, the tendency toward the formation of polymeric Cu(II)-I analogues is small because the polydentate I effectively wraps up the mononuclear Cu(II) center. This work shows that Cu(II) could potentially mediate the chemistry of sialoglycoconjugate-containing proteins in human biology, such as the sialylated amyloid precursor protein of relevance to Alzheimer's disease.     

High turnover frequency observed in catalytic enantioselective additions of enecarbamates and enamides to iminophosphonates

[Structure: see text] In addition reactions of enecarbamates and enamides, extremely high turnover frequency of the catalyst was observed in comparison with that of silicon enolate addition reactions. This is presumably due to fast transfer of the proton that locates on the nucleophiles.     

Electrochemical synthesis and structural and physical characterization of one- and two-electron-reduced forms of [SMo12O40]2-

Isolation of a soluble [NHex4]+ salt has allowed a detailed electrochemical study of the anion alpha-[SMo12O40]2- to be undertaken. Four reversible one-electron-reduction processes are observed in CH2Cl2 solution. Controlled potential electrolysis led to isolation of tetraalkylammonium salts of the one-electron-reduced anion alpha-[SMo12O40]3- and the two-electron-reduced anion alpha-[SMo12O40].4- [SMo12O40]3- is stable to disproportionation in dry solvents (Kdis = 10(-7.4). EPR and magnetic susceptibility data indicate that [SMo12O40]3- is a simple paramagnet (S = 1/2) while [SMo12O40]4- is paramagnetic with the mu eff values decreasing at low temperatures. Solutions of the two-electron-reduced species are EPR silent, but microcrystalline powders show very weak signals. The crystal structure of alpha-[NBu4]3[SMo12O40] has been determined (triclinic P1; a = 13.840(3) A; b = 15.587(4) A; c = 19.370(3) A; alpha = 94.82(2) degrees; beta = 93.10(1) degrees; gamma = 91.05(2) degrees; Z = 2). There is disorder around the C2 axis of the central SO4(2-) tetrahedron. In the presence of aqueous HClO4 (0.045 M) in thf/H2O or MeCN/H2O (98/2 v/v), [SMo12O40]2- exhibits five two-electron-reduction processes. Under these conditions, [SMo12O40]3- protonates and disproportionates into [SMo12O40]2- and the (2e-, 2H+)-reduced anion [H2SMo12O40]2-.     

Effect of counteranion X on the spin crossover properties of a family of diiron(II) triazole complexes [Fe(II)2(PMAT)2](X)4

Seven diiron(II) complexes, [Fe(II)(2)(PMAT)(2)](X)(4), varying only in the anion X, have been prepared, where PMAT is 4-amino-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole and X = BF(4)(-) (1), Cl(-) (2), PF(6)(-) (3), SbF(6)(-) (4), CF(3)SO(3)(-) (5), B(PhF)(4)(-) (6), and C(16)H(33)SO(3)(-) (7). Most were isolated as solvates, and the microcrystalline ([3], [4]·2H(2)O, [5]·H(2)O, and [6]·?MeCN) or powder ([2]·4H(2)O, and [7]·2H(2)O) samples obtained were studied by variable-temperature magnetic susceptibility and Mo?ssbauer methods. A structure determination on a crystal of [2]·2MeOH·H(2)O, revealed it to be a [LS-HS] mixed low spin (LS)-high spin (HS) state dinuclear complex at 90 K, but fully high spin, [HS-HS], at 293 K. In contrast, structures of both [5]·?IPA·H(2)O and [7]·1.6MeOH·0.4H(2)O showed them to be [HS-HS] at 90 K, whereas magnetic and M?ssbauer studies on [5]·H(2)O and [7]·2H(2)O revealed a different spin state, [LS-HS], at 90 K, presumably because of the difference in solvation. None of these complexes undergo thermal spin crossover (SCO) to the fully LS form, [LS-LS]. The PF(6)(-) and SbF(6)(-) complexes, 3 and [4]·2H(2)O, appear to be a mixture of [HS-LS] and [HS-HS] at low temperature, and undergo gradual SCO to [HS-HS] on warming. The CF(3)SO(3)(-) complex [5]·H(2)O undergoes gradual, partial SCO from [HS-LS] to a mixture of [HS-LS] and [HS-HS] at T(1/2) ≈ 180 K. The B(PhF)(4)(-) and C(16)H(33)SO(3)(-) complexes, [6]·(1)/(2)MeCN and [7]·2H(2)O, are approximately [LS-HS] at all temperatures, with an onset of gradual SCO with T(1/2) > 300 K.     

Molecular and supramolecular features of oxo-peroxovanadium complexes containing O3N, O2N2 and ON3 donor sets

The complexes [VO(O2)Hbpa]+ (1a), [VO(O2)bpa] (1b, Hbpa = bis(picolyl)-beta-alanine), [VO(O2)heida]- (2, H2heida =N-(2-hydroxyethyl)iminodiacetic acid), [VO(O2)(3OH-pic)2]- (3a), [VO(O2)(3OH-pic)2]-/[V(O2)2(3OH-pic)2]- (3b, 3OH-pic = 3-hydroxypicolinic acid), [VO(O2)(3OH-pa)2] (6, 3OH-pa = 3-hydroxypicolylamide), [VO2(3OH-pic)2]- (4), [VO(tBuO2)(3OH-pic)2] (5) and [VO(tBuO2)(3OH-pa)2]2+ (7) have been characterised. The structures of 21a[ClO4].1b.2.25H2O, K.2H2O, [NH4].H2O and [nBu4]3b are reported. Supramolecular patterns arise from intermolecular hydrogen bonds, the relevance of which for the peroxo/hydroperoxo intermediates in oxo transfer reactions catalysed by vanadate-dependent haloperoxidases is addressed. Specific solution patterns have been analysed by 51V and 17O NMR.     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.     

Chlorine anion encapsulation by molecular capsules based on cucurbit[5]uril and decamethylcucurbit[5]uril

Three barrel-shaped artificial molecular capsules 1-3, based on normal cucurbit[5]uril (Q[5]) and decamethylcucurbit[5]uril (Me10Q[5]), were synthesized and structurally characterized by single-crystal X-ray diffraction. Encapsulation of a chlorine anion in the cavity of a Q[5] or Me10Q[5] to form closed a molecular capsule with the coordinated metal ions or coordinated metal ions and water molecules in the crystal structures of these compounds is common. The three complexes [Pr2(C30H30N20O10)Cl3(H2O)13]3+ 3 Cl- x 5 H2O (1), [Sr2(C40H50N20O10)(H2O)4Cl]3+ 3 Cl- x 2 (HCl) 19 H2O (2) and [K(C40H50N20O10)(H2O)Cl] x [Zn(H2O)2Cl2] x [ZnCl4]2- x 2 (H3O)+ x 8 H2O (3) all crystallize as isolated molecular capsules.     

Influence of hydrogen bonding on the assembly of six-membered vanadium borophosphate cluster anions: synthesis and structures of (NH4)2(C2H10N2)6[Sr(H2O)5]2[V2P2BO12](6)10H2O, (NH4)2(C3H12N2)6[Sr(H2O)4]2[V2P2BO12](6)17H2O, and (NH4)3(C4H14N2)4 5[Sr(H2O)5]2[Sr(H2O)4][V2P2BO12]6 10H2O

Three new strontium vanadium borophosphate compounds, (NH4)2(C2H10N2)6[Sr(H2O)5]2[V2P2BO12]6 10H2O (Sr-VBPO1) (1), (NH4)2(C3H12N2)6[Sr(H2O)4]2[V2P2BO12]6 17H2O (Sr-VBPO2) (2), and (NH4)3(C4H14N2)4.5[Sr(H2O)5]2[Sr(H2O)4][V2P2BO12]6 10H2O (Sr-VBPO3) (3) have been synthesized by interdiffusion methods in the presence of diprotonated ethylenediamine, 1,3-diaminopropane, and 1,4-diaminobutane. Compound 1 has a chain structure, whereas 2 and 3 have layered structures with different arrangements of [(NH4) [symbol: see text] [V2P2BO12]6] cluster anions within the layers. Crystal data: (NH4)2(C2H10N2)6[Sr(H2O)5]2[V2P2BO12]6 10H2O, monoclinic, space group C2/c (no. 15), a = 21.552(1) A, b = 27.694(2) A, c = 20.552(1) A, beta = 113.650(1) degrees, Z = 4; (NH4)2(C3H12N2)6[Sr(H2O)4]2[V2P2BO12]6 17H2O, monoclinic, space group I2/m (no. 12), a = 15.7618(9) A, b = 16.4821(9) A, c = 21.112(1) A, beta = 107.473(1) degrees, Z = 2; (NH4)3(C4H14N2)4.5[Sr(H2O)5]2[Sr(H2O)4] [V2P2BO12]6 10H2O, monoclinic, space group C2/c (no. 15), a = 39.364(2) A, b = 14.0924(7) A, c = 25.342(1) A, beta = 121.259(1) degrees, Z = 4. The differences in the three structures arise from the different steric requirements of the amines that lead to different amine-cluster hydrogen bonds.     

紫外/TiO2/芬顿复合工艺增强在近中性pH值下对布洛芬的降解能力

药品及个人护理品(PPCPs)造成的潜在环境污染已引起广泛关注. 布洛芬(IBP, 2-(4-异丁基苯基)丙酸)作为苯丙酸类非甾体抗炎药物, 是一种在水环境中广泛检测到的PPCPs类物质. 水环境中的IBP主要来自制药企业排放和人体代谢物, 因IBP具有不易挥发、物理性质稳定、半衰期较长和不易被生物吸收等特点, 其在环境的残留浓度较高且污染风险大. 目前,传统的水处理工艺并不能有效治理水中的IBP, 比如: 混凝剂和絮凝剂对IBP的去除效率低, 吸附和膜处理运行成本过高且不能矿化IBP. 近年兴起的光催化技术利用·OH和O2·-等强氧化性活性物种降解水中有机污染物, 将其彻底矿化, 实现污染物的无害处理. 光催化技术适用于常温、常压和中性pH环境, 该环境特点与污水环境十分匹配, 适合应用. 但异质光催化通常发生在催化剂表面, 有效反应活性位少, 反应速率不够高. 相比而言, 同质芬顿反应能够均匀、快速地在整个溶液中发生反应, 但芬顿反应必须在酸性条件下才可以进行.本文整合了异相光催化和均相光-芬顿反应的优点, 设计了紫外/TiO2/芬顿(PCF)复合工艺, 评估了在中性pH下对典型的PPCPs布洛芬的降解效果. 对比实验结果表明, PCF复合工艺对IBP的降解速率比传统的UV, UV/H2O2, Fenton, 光-Fenton和光催化快得多. 动力学分析发现, IBP的降解遵循两阶段的一级反应动力学, 且速率常数k1> k2. 本研究进一步优化了运行参数, 确定IBP降解的最佳条件为: pH = 4.2, [Fe2+]0= 0.20 mmol/L, [Fe2+]0/[H2O2]0= 1/40, [TiO2]0= 1.0 g/L. pH值的增加造成IBP降解速率略微降低, 但在30 min反应时间内, 中性pH (6.0-8.0)与最佳pH条件下的降解效率完全相同, 证明PCF在中性pH下进行水处理切实可行. 数据分析发现, lnk1和lnk2均与1/pH0, [IBP]0, [H2O2]0, [H2O2]0/[Fe2+]0和ln[TiO2]0线性相关, 据此建立了IBP去除效率的数学预测模型, 通过验证发现, 动力学模型曲线与实验数据高度契合, 表明模型的有效性高.     

Polyoxometalate-supported transition metal complexes and their charge complementarity: synthesis and characterization of [M(OH)6Mo6O18[Cu(Phen)(H2O)2]2][M(OH)6Mo6O18[Cu(Phen)(H2O)Cl]2].5H2O (M = Al(+, Cr3+)

Two Anderson-type heteropolyanion-supported copper phenanthroline complexes, [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2]1+ (1c) and [Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2]1- (1a) complement their charges in one of the title compounds [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2][Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5H2O [1c][1a].5 H2O 1. Similar charge complementarity exists in the chromium analogue, [Cr(OH)6Mo6O18[Cu(phen)(H2O)2]2][Cr(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5 H2O [2c][2a].5 H2O 2. The chloride coordination to copper centers of 1a and 2a makes the charge difference. In both compounds, the geometries around copper centers are distorted square pyramidal and those around aluminum/chromium centers are distorted octahedral. Three lattice waters, from the formation of intermolecular O-H.....O hydrogen bonds, have been shown to self-assemble into an "acyclic water trimer" in the crystals of both 1 and 2. The title compounds have been synthesized in a simple one pot aqueous wet-synthesis consisting of aluminum/chromium chloride, sodium molybdate, copper nitrate, phenanthroline, and hydrochloric acid, and characterized by elemental analyses, EDAX, IR, diffuse reflectance, EPR, TGA, and single-crystal X-ray diffraction. Both compounds crystallize in the triclinic space group P. Crystal data for 1: a = 10.7618(6), b = 15.0238(8), c = 15.6648(8) angstroms, alpha = 65.4570(10), beta = 83.4420(10), gamma = 71.3230(10), V = 2182.1(2) angstroms3. Crystal data for 2: a = 10.8867(5), b = 15.2504(7), c = 15.7022(7) angstroms, alpha = 64.9850(10), beta = 83.0430(10), gamma = 71.1570(10), V = 2235.47(18) angstroms3. In the electronic reflectance spectra, compounds 1 and 2 exhibit a broad d-d band at approximately 700 nm, which is a considerable shift with respect to the value of 650-660 nm for a square-pyramidal [Cu(phen)2L] complex, indicating the coordination of [M(OH)6Mo6O18]3- POM anions (as a ligand) to the monophenanthroline copper complexes to form POM-supported copper complexes 1c, 1a, 2c, and 2a. The ESR spectrum of compound 1 shows a typical axial signal for a Cu2+ (d9) system, and that of compound 2, containing both chromium(III) and copper(II) ions, may reveal a zero-field-splitting of the central Cr3+ ion of the Anderson anion, [Cr(OH)6Mo6O18]3-, with an intense peak for the Cu2+ ion.