Tetradecacobalt(II)‐Containing 36‐Niobate [Co14(OH)16(H2O)8Nb36O106]20− and Its Photocatalytic H2 Evolution Activity

A gigantic Co₁₄‐containing 36‐niobate, Na₁₂K₈[Co₁₄(OH)₁₆(H₂O)₈Nb₃₆O₁₀₆] ? 71H₂O ( 1 ), has been prepared by the hydrothermal method and structurally characterized. Polyanion [Co₁₄(OH)₁₆(H₂O)₈Nb₃₆O₁₀₆]^20? ( 1 a ) comprises a central Co₇ core, surrounded by another seven isolated Co²⁺ ions and six Lindqvist‐type (Nb₆O₁₉) hexaniobate fragments. This is the first example of a high‐nuclear cobalt‐cluster‐containing polyoxoniobate. The photocatalytic H₂ evolution activity of Pt‐loaded 1 was observed in methanol solution under irradiation using a 300 W Xe lamp.     

Synthesis of tri-substituted biaryl based trianglimines: formation of C3-symmetrical and non-symmetrical regioisomers

2-Functionalised aromatic monoaldehydes were synthesised in good to excellent yields by reacting 4-bromo-2-fluorobenzaldehyde with different secondary amines and phenol. The Suzuki-coupling reaction of the newly functionalised aromatic monoaldehydes with 4-formylphenylboronic acid afforded the corresponding 2-functionalised-4,4'-biphenyldialdehydes in good yields (47-85%). The [3+3]-cyclocondensation reactions of the 2-functionalised-4,4'-biphenyldialdehydes with (1R,2R)-1,2-diaminocyclohexane afforded a mixture of regioisomeric C(3)-symmetrical and non-symmetrical trianglimines. Reduction of the C(3)-symmetrical and the non-symmetrical trianglimines with NaBH(4) in a mixture of THF and MeOH afforded the corresponding trianglamines in high yields.     

Noncovalent Bifunctional Organocatalysts: Powerful Tools for Contiguous Quaternary‐Tertiary Stereogenic Carbon Formation,Scope, and Origin of Enantioselectivity

Relying on the assembly of commercially available catalyst building blocks, highly stereocontrolled quaternary carbon (all carbon substituted) formation has been achieved with unmatched substrate diversity. For example, the in situ assembly of a tricomponent catalyst system allows α‐branched aldehyde addition to nitroalkene or maleimide electrophiles (Michael products), while addition to an α‐iminoester affords Mannich reaction products. Very good yields are observed and for fifteen of the eighteen examples 96–99 % ee is observed. Using racemic α‐branched aldehydes, two contiguous (quaternary–tertiary) stereogenic centers can be formed in high diastereo‐ and enantiomeric excess (eight examples) via an efficient in situ dynamic kinetic resolution, solving a known shortcoming for maleimide electrophiles in particular. The method is of practical value, requiring only 1.2 equiv of the aldehyde, a 5.0 mol % loading of each catalyst component, for example, O‐tBu‐L ‐threonine (O‐tBu‐L ‐Thr), sulfamide, DMAP or O‐tBu‐L ‐Thr, KOH, and room temperature reactions. As a highlight, the first demonstration of ethylisovaleraldehyde ( 7 ) addition is disclosed, providing the most congested quaternary stereogenic carbon containing succinimide product ( 8 ) known to date. Finally, mechanistic insight, via DFT calculations, support a noncovalent assembly of the catalyst components into a bifunctional catalyst, correctly predict two levels of product stereoselectivity, and suggest the origin of the tricomponent catalyst system’s exceptionality: an alternative hydrogen bond motif for the donor‐acceptor pair than currently suggested for non‐assembled catalysts.     

Noncovalent bifunctional organocatalysts: powerful tools for contiguous quaternary-tertiary stereogenic carbon formation, scope, and origin of enantioselectivity

Relying on the assembly of commercially available catalyst building blocks, highly stereocontrolled quaternary carbon (all carbon substituted) formation has been achieved with unmatched substrate diversity. For example, the in situ assembly of a tricomponent catalyst system allows α-branched aldehyde addition to nitroalkene or maleimide electrophiles (Michael products), while addition to an α-iminoester affords Mannich reaction products. Very good yields are observed and for fifteen of the eighteen examples 96-99?% ee is observed. Using racemic α-branched aldehydes, two contiguous (quaternary-tertiary) stereogenic centers can be formed in high diastereo- and enantiomeric excess (eight examples) via an efficient in situ dynamic kinetic resolution, solving a known shortcoming for maleimide electrophiles in particular. The method is of practical value, requiring only 1.2?equiv of the aldehyde, a 5.0?mol?% loading of each catalyst component, for example, O-tBu-L-threonine (O-tBu-L-Thr), sulfamide, DMAP or O-tBu-L-Thr, KOH, and room temperature reactions. As a highlight, the first demonstration of ethylisovaleraldehyde (7) addition is disclosed, providing the most congested quaternary stereogenic carbon containing succinimide product (8) known to date. Finally, mechanistic insight, via DFT calculations, support a noncovalent assembly of the catalyst components into a bifunctional catalyst, correctly predict two levels of product stereoselectivity, and suggest the origin of the tricomponent catalyst system's exceptionality: an alternative hydrogen bond motif for the donor-acceptor pair than currently suggested for non-assembled catalysts.     

Coherent manipulation of electron spins in the {Cu3} spin triangle complex impregnated in nanoporous silicon

We report on coherent manipulation of electron spins in an antiferromagnetically coupled spin triangle {Cu3-X} (X=As, Sb) impregnated in freestanding nanoporous silicon (NS) by using 240 GHz microwave pulses. Rabi oscillations are observed and the spin coherence time is found to be T(2)=1066 ns at 1.5 K. This demonstrates that the {Cu3-X}:NS hybrid material provides a promising scheme for implementing spin-based quantum gates. By measuring the spin relaxation times of samples with different symmetries and environments we give evidence that a spin chirality is the main decoherence source of spin triangle molecules.     

Transition metal containing decatungstosilicate dimer [M(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (M = Mn(2+), Co(2+), Ni(2+))

The new, monometal substituted silicotungstates [Mn(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (1), [Co(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (2) and [Ni(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (3) have been synthesized and isolated as the potassium salts K(10)[Mn(H(2)O)(2)(gamma-SiW(10)O(35))(2)] x 8.25 H(2)O (K-1), K(10)[Co(H(2)O0(2)(gamma-SiW(10)O(35))(2)] x 8.25 H(2)O (K-2) and K(10)[Ni(H(2)O)(2)(gamma-SiW(10)O(35))(2)] x 13.5 H(2)O (K-3), which have been characterized by IR spectroscopy, single crystal X-ray diffraction, elemental analysis and cyclic voltammetry. Polyanions 1-3 are composed of two (gamma-SiW(10)O(36)) units fused on one side via two W-O-W' bridges and on the other side by an octahedrally coordinated trans-MO(4)(OH(2))(2) transition metal fragment, resulting in a structure with C(2v) point group symmetry. Anions 1-3 were synthesized by reaction of the dilacunary precursor [gamma-SiW(10)O(36)](8-) with Mn(2+), Co(2+) and Ni(2+) ions, respectively, in 1 M KCl solution at pH 4.5. The electrochemical properties of 1-3 were studied by cyclic voltammetry and controlled potential coulometry in a pH 5 buffer medium. The waves associated with the W-centers are compared with each other and with those of the parent lacunary precursor [gamma-SiW(10)O(36)](8-) in the same medium. They appear to be dominated by the acid-base properties of the intermediate reduced species. A facile merging of the waves for 3 is observed while those for 1 and 2 remain split. Controlled potential coulometry of the single wave of 3 or the combined waves of 1 and 2 is accompanied by catalysis of the hydrogen evolution reaction. No redox activity was detected for the Ni(2+) center in 3, whereas the Co(2+) center in 2 shows a one-electron redox process. The two-electron, chemically reversible process of the Mn(2+) center in 1 is accompanied by a film deposition on the electrode surface.     

On the sol–gel synthesis and catalytic activity of Ce1−xAxO2−δ (A = Pr, Sm, Gd) SOFCs anode materials for reforming of methane

A sol–gel route to synthesize nanocrystalline praseodymium-, samarium- and gadolinium-doped ceria powders for solid oxides fuel Cells SOFCs is presented. The method involves metal nitrates with propionic acid (both as chelating ligand and solvent), gel formation, liquid nitrogen quenching, drying at 150 °C/24 h, and finally decomposition at 450 °C in nitrogen followed by calcination at 650 °C in air. TG–DTA, BET, XRD, FTIR, UV–vis and catalytic tests were used to characterize the samples. Ce_0.8Pr_0.2O_2?δ sample exhibited the best catalytic performance in methane steam reforming under water deficient conditions, closely followed by Ce_0.9Gd_0.1O_2?δ, Ce_0.8Sm_0.2O_2?δ and Ce_0.8Gd_0.2O_2?δ catalysts. The superior catalytic performance of Ce_0.8Pr_0.2O_2?δ sample was attributed to the existence of praseodymium species (Pr⁴⁺/Pr³⁺) strongly interacting with ceria. The two systems act synergistically in the catalytic steam reforming of methane.