| 1. |
- Abbasi, Alireza, et al.
(author)
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Highly hydrated cations : Deficiency, mobility and coordination of water in crystalline nonahydrated scandium(III), yttrium(III) and lanthanoid(III) trifluoromethanesulfonate
- 2005
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 11:14, s. 4065-4077
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Journal article (peer-reviewed)abstract
- Trivalent lanthanide-like metal ions coordinate nine water oxygen atoms, which form a tricapped trigonal prism in a large number of crystalline hydrates. Water deficiency, randomly distributed over the capping positions, was found for the smallest metal ions in the isomorphous nonahydrated trifluoromethanesulfonates, [M(H2O)(n)]CF3SO3)(3), in which M=Sc-III, Lu-III, Yb-III, Tm-III or Er-III. The hydration number n increases (n=8.0(1), 8.4(1), 8.7(1), 8.8(1) and 8.96(5), respectively) with increasing ionic size. Deuterium (H-2) solid-state NMR spectroscopy revealed fast positional exchange between the coordinated capping and prism water molecules; this exchange started at temperatures higher than about 280 K for lutetium(m) and below 268 K for scandium(m). Similar positional exchange for the fully nonahydrated yttrium(m) and lanthanum(m) compounds started at higher temperatures, over about 330 and 360 K, respectively. An exchange mechanism is proposed that can exchange equatorial and capping water molecules within the restrictions of the crystal lattice, even for fully hydrated lanthanoid(III) ions. Phase transitions occurred for all the water-deficient compounds at; 185 K. The hydrated scandium(III) trifluoromethanesulfonate transforms reversibly (Delta H degrees= -0.80(1) kJ mol(-1) on cooling) to a trigonal unit cell that is almost nine times larger, with the scandium ion surrounded by seven fully occupied and two partly occupied oxygen atom positions in a distorted capped trigonal prism. The hydrogen bonding to the trifluoromethanesulfonate anions stabilises the trigonal prism of water ligands, even for the crowded hydration sphere of the smallest metal ions in the series. Implications for the Lewis acid catalytic activity of the hydrated scandium(III) and lanthanoid(III) trifluoromethanesulfonates for organic syntheses performed in aqueous media are discussed.
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| 2. |
- Abdi, Zahra, et al.
(author)
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In Situ Synthesis of Manganese Oxide as an Oxygen-Evolving Catalyst : A New Strategy
- 2021
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In: Chemistry - A European Journal. - : John Wiley & Sons. - 0947-6539 .- 1521-3765. ; 27:4, s. 1330-1336
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Journal article (peer-reviewed)abstract
- All studies on oxygen-evolution reaction by Mn oxides in the presence of cerium(IV) ammonium nitrate (CAN) have been so far carried out by synthesizing Mn oxides in the first step. And then, followed by the investigation of the Mn oxides in the presence of oxidants for oxygen-evolution reaction (OER). This paper presents a case study of a new and promising strategy for in situ catalyst synthesis by the adding Mn-II to either CAN or KMnO4/CAN solution, resulting in the formation of Mn-based catalysts for OER. The catalysts were characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both compounds contained nano-sized particles that catalyzed OER in the presence of CAN. The turnover frequencies for both catalysts were 0.02 (mmolO2 /mol(Mn).
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| 3. |
- Abujubara, Helal, et al.
(author)
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Ionic Liquid-Mediated Approach for the Synthesis of Site-Specific Thioether Conjugates
- 2023
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In: Chemistry-a European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 29:28
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Journal article (peer-reviewed)abstract
- Site-specific conjugation approaches are of great importance in drug discovery, notably for the synthesis of biochemical probes or molecular conjugates for targeted delivery. Herein, we report a mild ionic liquid (IL)-mediated thiolation technique that relies on the use of 1,3-ethyl-methyl imidazolium acetate, [C(2)mim][OAc] as a solvent and precursor to generate activated IL, as well as a solvent for the conjugation reaction. First, a focused library of active ILs was prepared for functionalizing/conjugating cysteine-containing small molecules and unprotected peptides. Interestingly, a bifunctional active IL could also be successfully employed as a linker for the conjugation of peptides lacking Cys. This study sets the ground for further investigation of the use of active ILs for modifying, labeling or conjugating larger and more complex therapeutic modalities such as proteins and antibodies.
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| 4. |
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| 5. |
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| 6. |
- Afewerki, Samson, et al.
(author)
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Direct Regiospecific and Highly Enantioselective Intermolecular α-Allylic Alkylation of Aldehydes by a Combination of Transition-Metal and Chiral Amine Catalysts
- 2012
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:10, s. 2972-2977
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Journal article (peer-reviewed)abstract
- The first direct intermolecular regiospecific and highly enantioselective a-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd0 complexes and simple chiral amines as co-catalysts is disclosed. The co-catalytic asymmetric chemoselective and regiospecific a-allylic alkylation reaction is linked in tandem with in situ reduction to give the corresponding 2-alkyl alcohols with high enantiomeric ratios (up to 98:2 e.r.; e.r.=enantiomeric ratio). It is also an expeditious entry to valuable 2-alkyl substituted hemiacetals, 2-alkyl-butane-1,4-diols, and amines. The concise co-catalytic asymmetric total syntheses of biologically active natural products (e.g., Arundic acid) are disclosed.
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| 7. |
- Agarwala, Hemlata
(author)
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Correspondence of RuIIIRuII and RuIVRuIII Mixed Valent States in a SmallDinuclear Complex
- 2012
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18, s. 5667-5675
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Journal article (peer-reviewed)abstract
- The dirutheniumACHTUNGTRENUNG(III) compound[(m-oxa){RuACHTUNGTRENUNG(acac)2}2] [1, oxa2=oxamidato(2), acac=2,4-pentanedionato]exhibits an S=1 ground statewith antiferromagnetic spin-spin coupling(J=40 cm1). The molecularstructure in the crystal of 1·2C7H8 revealedan intramolecular metal–metaldistance of 5.433 and a notableasymmetry within the bridging ligand.Cyclic voltammetry and spectroelectrochemistry(EPR, UV/Vis/NIR) of thetwo-step reduction and of the two-stepoxidation (irreversible second step)produced monocation and monoanionintermediates (Kc=105.9) with broadNIR absorption bands (e ca.2000m1cm1) and maxima at 1800 (1)and 1500 nm (1+). TD-DFT calculationssupport a RuIIIRuII formulationfor 1 with a doublet ground state. The1+ ion (RuIVRuIII) was calculated withan S=3/2 ground state and the doubletstate higher in energy (DE=694.6 cm1). The Mulliken spin densitycalculations showed little participationof the ligand bridge in the spin accommodationfor all paramagnetic species[(m-oxa){RuACHTUNGTRENUNG(acac)2}2]n, n=+1, 0, 1,and, accordingly, the NIR absorptionswere identified as metal-to-metal (intervalence)charge transfers. Whereasonly one such NIR band was observedfor the RuIIIRuII (4d5/4d6) system 1,the RuIVRuIII (4d4/4d5) form 1+ exhibitedextended absorbance over the UV/Vis/NIR range.
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| 8. |
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| 9. |
- Ahlberg, P., et al.
(author)
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Solvated CH5+ in liquid superacid
- 2001
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In: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 7:12, s. 2501-2510
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Journal article (peer-reviewed)
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| 10. |
- Ahlford, Katrin, et al.
(author)
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Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Amino Acid Derived Rhodium Complexes : On the Origin of Enantioselectivity and Enantioswitchability
- 2009
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 15:42, s. 11197-11209
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Journal article (peer-reviewed)abstract
- Amino acid based thioamides, hydroxamic acids, and hydrazides have been evaluated as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of ketones in 2-propanol. Catalysts containing thioamide ligands derived from L-valine were found to selectively generate the product with an R configuration (95 % ee), whereas the corresponding L-valine-based hydroxamic acids or hydrazides facilitated the formation of the (S)-alcohols (97 and 91 % ee, respectively). The catalytic reduction was examined by performing a structure–activity correlation investigation with differently functionalized or substituted ligands and the results obtained indicate that the major difference between the thioamide and hydroxamic acid based catalysts is the coordination mode of the ligands. Kinetic experiments were performed and the rate constants for the reduction reactions were determined by using rhodium–arene catalysts derived from amino acid thioamide and hydroxamic acid ligands. The data obtained show that the thioamide-based catalyst systems demonstrate a pseudo-first-order dependence on the substrate, whereas pseudo-zero-order dependence was observed for the hydroxamic acid containing catalysts. Furthermore, the kinetic experiments revealed that the rate-limiting steps of the two catalytic systems differ. From the data obtained in the structure–activity correlation investigation and along with the kinetic investigation it was concluded that the enantioswitchable nature of the catalysts studied originates from different ligand coordination, which affects the rate-limiting step of the catalytic reduction reaction.
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