| 1. |
- Reinholdt, Anders, et al.
(author)
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An Approach to Carbide-Centered Cluster Complexes
- 2019
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:8, s. 4812-4819
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Journal article (peer-reviewed)abstract
- We report the first examples of the carbide ligand in (Cy 3 P) 2 Cl 2 Ru≡C (RuC) developing into a μ 3 ligand toward metal centers. Conventionally, sterics exclude this coordination mode, but Fe 2 (CO) 9 and Co 2 (CO) 8 expel bridging CO ligands upon reaction with RuC to form trimetallic (Cy 3 P) 2 Cl 2 Ru=CFe 2 (CO) 8 (RuCFe 2 ) and (Cy 3 P) 2 Cl 2 Ru=CCo 2 (CO) 7 (RuCCo 2 ) complexes. Thus, the proximity offered by metal-metal associations in bimetallic carbonyl complexes allows the formation of trinuclear carbide complexes as verified by NMR, Mössbauer, and X-ray spectroscopic techniques.
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| 2. |
- Ahlstrand, David A., et al.
(author)
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Csp(3)-H Activation without Chelation Assistance in an Iridium Pincer Complex Forming Cyclometallated Products
- 2017
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In: Chemistry - A European Journal. - : WILEY-V C H VERLAG GMBH. - 0947-6539 .- 1521-3765. ; 23:8, s. 1748-1751
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Journal article (peer-reviewed)abstract
- Cyclometallation of 8-methylquinoline and 2-(dimethylamino)-pyridine in an iridium-based pincer complex is described. The C-H activation of 2-(dimethylamino) pyridine is not chelation assisted, which has not been described before for Csp(3)-H bonds in cyclometallation reactions. The mechanism of the cyclometallation of 2-(dimethylamino) pyridine was studied by DFT calculations and kinetic measurements.
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| 3. |
- Bolbat, Ekaterina, et al.
(author)
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Ligand Control in Selective C–H Oxidative Functionalization Using Pd-PEPPSI-Type Complexes
- 2016
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In: European Journal of Organic Chemistry. - : Wiley. - 1434-193X. ; 2016:20, s. 3395-3400
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Journal article (peer-reviewed)abstract
- To achieve high selectivity in directed C–H activation, an NHC ligand was introduced to a palladium catalyst. A range of Pd-PEPPSI complexes were applied in the direct acetoxylation of 2-phenylpyridine. The best catalyst was found to be the one based on a diisopropylphenyl-substituted NHC ligand, and this was successfully used for the functionalization of sp2as well as more challenging sp3bonds for a broad variety of substrates. The explored method showed a highly improved selectivity compared to previously reported results with up to 96 % yield for the monoacetoxylated product. Kinetic studies show that sterics of the catalyst is less important in dictating conversion and selectivity; despite an induction period, it was shown that the catalyst is molecular in nature.
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| 4. |
- Bolbat, Ekaterina, et al.
(author)
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Synthesis, spectroscopic characterization and catalytic activity of platinum(II) carbene complexes
- 2016
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In: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693. ; 445, s. 129-133
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Journal article (peer-reviewed)abstract
- A novel platinum complex with 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidenyl ligand has been synthesized and characterized on the basis of elemental analysis, MS, 1H and 13C NMR spectroscopy, X-ray Absorption Spectroscopy and single crystal X-ray diffraction studies. The XRD determination of the complex (monoclinic, C2/c) revealed a structure in which the platinum (II) centre coordinates two chlorides, a carbon atom of the N-heterocyclic carbene (NHC) and is stabilized by coordinating the nitrogen atom of a 3-chloropyridine molecule, forming an over-all square planar geometry. By prolonging the time of the reaction, it was possible to obtain the trans-dichloridobis(3-chloropyridine) platinum(II) complex under the same reaction conditions. The electronic and molecular properties of both complexes were investigated and compared by means of Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS), supported by numerical simulations. The platinum carbene complex obtained was tested in a series of C-H activation and hydrosilylation reactions.
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| 5. |
- Chakrabarti, Kaushik, et al.
(author)
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Acceptorless dehydrogenation of 4-methylpiperidine by supported pincer-ligated iridium catalysts in continuous flow
- 2023
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In: Catalysis Science and Technology. - 2044-4753. ; 13:17, s. 5113-5119
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Journal article (peer-reviewed)abstract
- Finding alternative and sustainable ways to produce, store and convert energy is key for reducing fossil fuel-based CO2 emissions. In this transformation, hydrogen for energy storage and hydrogen-powered fuel cells for energy conversion can play important roles. However, storage of hydrogen itself is difficult and the concept of reversible liquid organic hydrogen carriers (LOHCs) has been proposed given the advantages of using liquid storage materials. A key part in the adaption of LOHCs is the catalyst design for efficient dehydrogenation of these hydrogen-carrying species. In this study, the use of silica- and alumina-supported POCOP-Ir systems for gas phase acceptorless dehydrogenation of 4-methylpiperidine (an LOHC with 6.1 wt% hydrogen) is investigated in a continuous-flow system with a high TON. To increase stability and reactivity, a new POCOP-Ir complex with two anchors was designed and found to be highly active in the dehydrogenation of 4-methylpiperidine with ∼91 000 turnovers in 45 h. In addition, this catalyst showed a maintained activity with a TOF of 1684 h−1 after 45 h.
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| 6. |
- Cui, Jingwen, et al.
(author)
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Extraction with Water-in-Carbon Dioxide Microemulsions : A Case Study on Steviol Glycosides
- 2019
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In: Journal of Surfactants and Detergents. - : Wiley. - 1097-3958 .- 1558-9293. ; 22:6, s. 1505-1514
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Journal article (peer-reviewed)abstract
- This work explores the use of water-in-supercritical carbon dioxide (scCO2) microemulsions for the extraction of polar metabolites from plants. Stevia rebaudiana Bertoni leaves and polyethylene glycol trimethylnonyl ether (TMN) surfactants were selected for a case study. A CO2-water-TMN 10 mixture at 35 °C and 30.0 MPa extracted 7 mg target analyte/g dry leaves. The extraction was proven to occur due to a water-surfactant liquid solution rather than a water-in-CO2 microemulsion. Using a modified extraction setup, the microemulsion was created prior to extraction. TMN 6 was able to dissolve enough water in CO2 to extract steviol glycosides, in detectable but very small amounts.
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| 7. |
- Garg, Nitish Kumar, et al.
(author)
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A mononuclear iron(iii) complex with unusual changes of color and magneto-structural properties with temperature : Synthesis, structure, magnetization, multi-frequency ESR and DFT study
- 2022
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In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 51:6, s. 2338-2345
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Journal article (peer-reviewed)abstract
- From the reaction of 2-hydroxy-6-methylpyridine (L) with iron(ii) tetrafluoroborate, a new mononuclear iron(iii) octahedral complex [FeL6](BF4)3 has been isolated. The color of the complex reversibly changed from red at room temperature to yellow-orange at the liquid nitrogen temperature. Magnetization measurements indicate that iron(iii) in [FeL6](BF4)3 is in a high-spin state S = 5/2, from room temperature to 1.8 K. The high-spin ground state of iron(iii) is also confirmed by DFT calculations. Although the spin-crossover of the complex is not observed, X-band and multifrequency high-field/high-frequency electron spin resonance (ESR) spectroscopy shows rather uncommon iron(iii) spectra at room temperature and an unusual change with cooling. Spectral simulations reveal that the S = 5/2 ground state multiplet of the complex can be characterized by the temperature independent axial zero-field splitting parameter of |D| = +2 GHz (0.067 cm-1) while the value of the rhombic parameter E of the order of some tenths MHz increases on lowering the temperature. Single crystal X-ray diffraction (SCXRD) shows that the iron(iii) coordination geometry does not change with temperature while supramolecular interactions are temperature dependent, influencing the iron(iii) rhombicity. Additionally, the DFT calculations show temperature variation of the HOMO-LUMO gap, in agreement with the changes of color and ESR-spectra of the iron(iii) complex with temperature.
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| 8. |
- Garg, Nitish K., et al.
(author)
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Efficient Conversion of Biomass Derived Levulinic Acid to γ-Valerolactone Using Hydrosilylation
- 2021
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In: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; 2021:37, s. 5243-5247
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Journal article (peer-reviewed)abstract
- Converting biomass into value-added chemicals is of significant interest and we report an efficient hydrosilylation to convert levulinic acid to γ-valerolactone using cost-effective silanes such as PMHS and TMDS with B(C6F5)3 as catalyst. This metal free methodology works at room temperature reaching TONs and TOFs up to 16000 and 2000 h−1. Insights into the reaction mechanism are reported.
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| 9. |
- Garg, Nitish K., et al.
(author)
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Highly Efficient Base Catalyzed N-alkylation of Amines with Alcohols and β-Alkylation of Secondary Alcohols with Primary Alcohols
- 2023
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In: ChemCatChem. - 1867-3880. ; 15:20
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Journal article (peer-reviewed)abstract
- Borrowing hydrogen (BH) reactions are very useful for the sustainable synthesis of C−C and C−N bonds. They generally operate with transition metal-based catalysts along with stoichiometric/catalytic amounts of added base. Here we report that two catalytic transformations, generally carried out with the BH methodology, i. e. N-alkylation of amines with alcohols and β-alkylation of secondary alcohols with primary alcohols, can be performed very effectively with just catalytic amounts of base under air without using any transition metal-based catalyst. The mechanism is proposed to be based on air oxidation of the alcohol to aldehyde followed by condensation to an unsaturated intermediate which undergoes transfer hydrogenation with alcohol to the product.
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| 10. |
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