| 1. |
- Reinholdt, Anders, et al.
(författare)
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An Approach to Carbide-Centered Cluster Complexes
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:8, s. 4812-4819
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Csp(3)-H Activation without Chelation Assistance in an Iridium Pincer Complex Forming Cyclometallated Products
- 2017
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Ingår i: Chemistry - A European Journal. - : WILEY-V C H VERLAG GMBH. - 0947-6539 .- 1521-3765. ; 23:8, s. 1748-1751
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Ligand Control in Selective C–H Oxidative Functionalization Using Pd-PEPPSI-Type Complexes
- 2016
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X. ; 2016:20, s. 3395-3400
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Synthesis, spectroscopic characterization and catalytic activity of platinum(II) carbene complexes
- 2016
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Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693. ; 445, s. 129-133
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Acceptorless dehydrogenation of 4-methylpiperidine by supported pincer-ligated iridium catalysts in continuous flow
- 2023
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Ingår i: Catalysis Science and Technology. - 2044-4753. ; 13:17, s. 5113-5119
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Extraction with Water-in-Carbon Dioxide Microemulsions : A Case Study on Steviol Glycosides
- 2019
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Ingår i: Journal of Surfactants and Detergents. - : Wiley. - 1097-3958 .- 1558-9293. ; 22:6, s. 1505-1514
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 51:6, s. 2338-2345
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Efficient Conversion of Biomass Derived Levulinic Acid to γ-Valerolactone Using Hydrosilylation
- 2021
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; 2021:37, s. 5243-5247
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: ChemCatChem. - 1867-3880. ; 15:20
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Garg, Nitish K., et al.
(författare)
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Selective Valorization of Bio-derived Levulinic Acid and Its Derivatives into Hydrocarbons and Biochemicals by Using Hydrosilylation
- 2023
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 29:30
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Tidskriftsartikel (refereegranskat)abstract
- Herein we report an efficient hydrosilylation strategy to selectively defunctionalize biomass-derived levulinic acid into value-added chemicals such as pentane-1,4-diol, pentan-2-ol, 2-MTHF and C5 hydrocarbons by using cost-effective silanes and the commercially available catalyst B(C6F5)3 at room temperature. All reactions work well in chlorinated solvents but, as a greener alternative, most reactions can be run in toluene or solvent-less.
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| 12. |
- Johansson, Maria H., et al.
(författare)
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Chiral platinum(II) complexes. Crystal and molecular structures of cis-[PtPhCl((R,R)-CHIRAPHOS)] and cis-[PtCl2((R,R)-CHIRAPHOS)]
- 2001
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 316:1-2, s. 149-152
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Tidskriftsartikel (refereegranskat)abstract
- The reaction between trans-PtPhCl(SMe2)2 and (R,R)-CHIRAPHOS gives cis-[PtPhCl((R,R)-CHIRAPHOS)] (1). The crystals of which are monoclinic, space group P21 with a = 12.875(3), b = 18.012(4), c = 13.864(3) Å, β = 109.71(3)° and Z = 4. In CDCl3 1 reacts with Ph2P(C6H4)CH2N(Me)(COEt) to give cis[PtCl2((R,R)-CHIRAPHOS)] (2), the crystals of which are monoclinic, space group P21 with a = 7.8052(16), b = 17.679(4), c = 9.843(2) Å, β = 100.67(3)° and Z = 2.
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| 13. |
- Jonasson, Klara J., et al.
(författare)
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Synthesis and characterisation of POCsp3OP supported Ni(II) hydroxo, hydroxycarbonyl and carbonate complexes
- 2018
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Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387. ; 143, s. 132-137
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Tidskriftsartikel (refereegranskat)abstract
- A nickel(II) hydroxo complex (3) supported by a cyclohexyl based POCsp3OP pincer ligand (POCsp3OP = cis-1,3-Bis-(di-tert-butylphosphinito)cyclohexyl) is reported. Complex 3 reacts with CO to form the corresponding hydroxycarbonyl complex, (POCsp3OP)NiCOOH (4). Complex 3 is also reactive towards CO2, forming a bicarbonate species (5) that under reduced pressure loses 1/2 eq. of H2O and CO2 to give a binuclear, bridged carbonate complex (6). All compounds were characterized in the solid state by X-ray diffraction.
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| 14. |
- Karimzadeh-Younjali, Morteza, et al.
(författare)
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α- and β-Eliminations in Transition Metal Complexes : Strategies to Cleave Unstrained C−C and C−F Bonds
- 2021
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Ingår i: Helvetica Chimica Acta. - : Wiley. - 0018-019X .- 1522-2675. ; 104:11
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Forskningsöversikt (refereegranskat)abstract
- Oxidative addition is the standard process for single-bond activation in transition metal catalysis and it is known to operate for many types of bonds, but challenging σ-bonds e. g. C(sp3)−F and C(sp3)−C(sp3) bonds are the exceptions in this respect. This short review aims at demonstrating how both α- and β-eliminations may be better options for activation of unstrained C−F and C−C single bonds. Selected examples of such eliminations are presented with a mechanistic focus indicating how unstrained and unactivated C−C and C−F bonds can be broken by employing α- and β-eliminations in transition metal hydrocarbyl ligands. Our examples show that the reaction barrier in β-eliminations is controlled by the s-character of the participating bonds where a higher s-character gives a better overlap in the multi-center transition state thereby increasing the reactivity; still β-aryl eliminations can compete with the classical β-hydrogen eliminations in certain cases.
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| 15. |
- Kovalenko, Oleksandr O., et al.
(författare)
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An electron poor iridium pincer complex for catalytic alkane dehydrogenation
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:40, s. 15963-15969
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Tidskriftsartikel (refereegranskat)abstract
- A novel electron deficient 4,6-bis(trifluoromethyl)-1,3-phenylene diphosphinite ligand 4 was developed and synthesized. Reaction of Ir precursors with ligand 4 gave chloro(hydride) pincer complex 5, which demonstrated a higher TON in alkane dehydrogenation reactions compared to similar phosphinite based pre-catalysts. The formation of cyclooctene (COE) and tert-butylethylene adducts of the 14e catalysts was also studied and the COE adduct is implicated as the resting state of the catalyst. All compounds were characterized by NMR spectroscopy and, in addition, the molecular structures of key complexes were confirmed by X-ray analysis.
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| 16. |
- Lukato, Simon, et al.
(författare)
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Selective oxidation of benzyl alcohols with molecular oxygen as the oxidant using Ag-Cu catalysts supported on polyoxometalates
- 2021
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Ingår i: Results in Chemistry. - : Elsevier BV. - 2211-7156. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- We report an efficient process for the oxidation of benzyl alcohols using molecular oxygen as the oxidant catalyzed by Ag-Cu catalysts supported on polyoxometalates (Ag-Cu/POM). The Ag-Cu/POM catalyst was prepared by galvanic displacement in the presence of polyvinyl pyrrolidone and polyethylene glycol. The catalysts were characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), powder X-ray diffraction (PXRD), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET) surface analysis, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA). The oxidation reaction was carried out using a Schlenk– line setup, under ambient atmospheric pressure. Reaction products were identified by GC–MS and quantified with GC using an internal standard method. The Ag-Cu/POM catalyst gave close to 100% benzyl alcohol conversion in 5 h with >99% selectivity to benzaldehyde. When tested on various benzyl alcohol derivatives the Ag-Cu catalysts showed good conversions and >99% selectivity to the corresponding aldehydes. The Ag-Cu catalysts supported on the POM are highly stable, and don't show tendency to leach or deactivate. The catalysts are heterogeneous in nature and easy to recover after reactions, and could be reused at least 5 times without significant loss in activity and selectivity.
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| 17. |
- Majeed, Maitham H., et al.
(författare)
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A PdII Carbene Complex with Anthracene Side-Arms for π-Stacking on Reduced Graphene Oxide (rGO) : Activity towards Undirected C–H Oxygenation of Arenes
- 2018
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-0682. ; 2018:43, s. 4742-4746
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Tidskriftsartikel (refereegranskat)abstract
- An N-heterocyclic carbene palladium(II) complex containing two anthracene side arms was immobilized on the surface of reduced graphene oxide (rGO) by π-stacking. The activity of the homogeneous analogue and the supported complex in undirected C–H acetoxylation reaction of arenes was studied. The results show that the catalytic efficiency in acetoxylation of benzene is improved in the immobilized materials compared to the homogeneous analogue. According to XPS analysis, the immobilized catalyst maintains the original oxidation state of PdII after the catalytic reaction.
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| 18. |
- Majeed, Maitham H, et al.
(författare)
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Directed C-H Halogenation Reactions Catalysed by PdII Supported on Polymers under Batch and Continuous Flow Conditions
- 2019
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 25:59, s. 13591-13597
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Tidskriftsartikel (refereegranskat)abstract
- A new generation of N-heterocyclic carbene palladium(II) complexes containing vinyl groups in different positions in the backbone of the N-heterocycle have been developed. The fully characterised monomers were copolymerised with divinylbenzene to fabricate robust polymer supported NHC-PdII complexes and these polymers were applied as heterogeneous catalysts in directed C-H halogenation of arenes with a pyridine-type directing group. The catalysts demonstrated medium-high catalytic activity with up to 90 % conversion and 100 % selectivity in chlorination. They are heterogeneous and recyclable (at least six times) with no significant leaching of palladium in batch mode catalysis. The best catalyst was also applied under continuous flow conditions where it disclosed an exceptional activity (90 % conversion) and 100 % selectivity for the mono-halogenated product for at least six days, with no leaching of palladium, no loss of activity and an ability to maintain the original oxidation state of PdII .
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| 19. |
- Majeed, Maitham H., et al.
(författare)
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Polymer-Supported Palladium(II) Carbene Complexes : Catalytic Activity, Recyclability, and Selectivity in C-H Acetoxylation of Arenes
- 2017
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 23:35, s. 8457-8465
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Tidskriftsartikel (refereegranskat)abstract
- Heterogeneous catalysts for selective oxidation of C-H bonds were synthesized by co-polymerization of new N-heterocyclic carbene-palladium(II) (NHC-PdII) monomers with divinylbenzene. The polymer-supported NHC-PdII-catalysed undirected C-H acetoxylation of simple and methylated arenes as well as polyarenes, with similar or superior efficiency compared to their homogeneous analogues. In particular, the regioselectivity has been improved in the acetoxylation of biphenyl and naphthalene compared to the best homogeneous catalysts. The new polymer-supported catalysts maintain the original oxidation state of PdII after repeated catalytic reactions, and exhibit no significant leaching of palladium. In addition, the new catalysts have been successfully recovered and reused without loss of activity over several cycles of reactions.
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| 20. |
- Majeed, Maitham H., et al.
(författare)
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Synthesis and crystal structure of trans-dichlorido- [3-methyl-1-(4-vinylbenzyl)-1H-imidazol-3-ium-2- yl-kC2](4-phenylpyridine-kN)palladium(II)
- 2016
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Ingår i: Acta crystallographica. Section E: Crystallographic communications. - 2056-9890. ; 72, s. 534-537
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, [PdCl2(C11H9N)(C13H14N2)], represents a new class of palladium-based polymerizable monomer which could give a potentially catalytically active polymer. It was synthesized via transmetallation from the corresponding silver complex. The PdII ion coordinates two Cl anions, one C atom from the N-heterocyclic carbene (NHC) ligand and one N atom from the 4-phenylpyridine ligand, displaying a slightly distorted square-planar geometry. The dihedral angle between the imidazole ring and the pyridine ring is 34.53 (8)-. The Pd-C bond length between the NHC ligand and the PdII ion is 1.9532 (16) A ° . In the crystal, weak non-classical C-H Cl hydrogen bonds link the molecules into a tape structure along [101]. A weak -- interaction is also observed [centroid-centroid distance = 3.9117 (11) A ° ].
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| 21. |
- Manojveer, Seetharaman, et al.
(författare)
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Ru-Catalyzed Cross-Dehydrogenative Coupling between Primary Alcohols to Guerbet Alcohol Derivatives : With Relevance for Fragrance Synthesis
- 2018
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 83:18, s. 10864-10870
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Tidskriftsartikel (refereegranskat)abstract
- A simple method has been developed for the cross dehydrogenative coupling between two different primary alcohols using readily available RuCl2(PPh3)3 as a precatalyst through the borrowing-hydrogen approach. The present methodology is applicable to a large variety of alcohol derivatives including long chain aliphatic alcohols and heteroaryl alcohols. In addition, the methodology was applied in a straightforward protocol to synthesize commercially available fragrances such as Rosaphen and Cyclamenaldehyde in good yields.
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| 22. |
- Margarita, Cristiana, et al.
(författare)
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Dissipative Cyclic Reaction Networks : Mechanistic Insights into a Minor Enantiomer Recycling Process
- 2024
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Ingår i: ChemSystemsChem. - 2570-4206. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- An analysis of an out-of-equilibrium cyclic reaction network which continuously converts a minor undesired product enantiomer to the desired major enantiomer by irreversible addition of chemical fuel and irreversible elimination of spent fuel is presented. The reaction network is maintained as long as fuel is added; interrupted fuel addition drives the system towards equilibrium, but the cyclic process restarts upon resumed fuel addition, as demonstrated by three consecutive fuel cycles. The process is powered by the hydrolysis of methyl cyanoformate to HCN and monomethyl carbonic acid, which decomposes to CO2 and MeOH. The time it takes to reach steady state depends on the rate of conversion of the fuel and decreases with increased conversion rate. Three catalysts, one metal catalyst and two enzymes, together constitute an efficient regulation system allowing control of the forward, backward and waste-forming steps, thereby assuring the production of high yields of products with high enantiopurity.
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| 23. |
- Mbabazi, Ruth, et al.
(författare)
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Advances in carbon dioxide and propylene oxide copolymerization to form poly(propylene carbonate) over heterogeneous catalysts
- 2022
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Ingår i: Results in Chemistry. - : Elsevier BV. - 2211-7156. ; 4
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Forskningsöversikt (refereegranskat)abstract
- Chemical conversion of carbon dioxide (CO2) into value-added products is an attractive industrial process because it offers several economic and environmental advantages. This review presents advances and challenges in the CO2 and propylene oxide (PO) co-polymerization using heterogeneous catalysts to form poly (propylene carbonate) (PPC), an environmentally friendly polymer with several applications. In the co-polymerization process, CO2 is employed as a green carbon source, an alternative to the toxic phosgene which has numerous negative environmental impacts. However, this route of polycarbonate production, is hindered by the chemical inertness of CO2, and to overcome this, various catalysts have been developed. A number of heterogeneous catalysts including carboxylates, double metal cyanides and composites, have achieved varying success in activating CO2 in the production of polycarbonates. The effect of different reaction conditions including pressure, temperature and solvent has been explored. The limitations faced by various heterogeneous catalysts and improvements made over the past decades have been highlighted. Mechanistic insights for the production of PPC from CO2 and PO have been presented and the differences in both the regioselectivity and stereochemistry of the resultant polymers discussed.
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| 24. |
- Mbabazi, Ruth, et al.
(författare)
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Highly efficient CO2 and propylene oxide co-polymerization using Zn glutarate/Zn-Cr double metal cyanide composite catalyst
- 2024
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Ingår i: Sustainable Chemistry for Climate Action. - 2772-8269. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- A highly active zinc glutarate-double metal cyanide (DMC) composite catalyst (ZnGA/Zn-CrDMC) was designed for the carbon dioxide (CO2) and propylene oxide (PO) copolymerization reaction. The composite catalyst was synthesized in a rheological phase reaction and characterized using Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The synthesized composite catalysed the solvent free reactions of PO and CO2 to afford biodegradable polypropylene carbonate (PPC) copolymer. 1H NMR,13C NMR, FT-IR and ESI-TOF mass spectrometry measurements were employed to confirm the characteristics of the PPC produced. Under optimal reaction conditions (50 bar CO2, 70 °C, 24 h), the ZnGA-Zn3[Cr(CN)6]2 composite displayed higher catalytic activities in the copolymerization reactions than the individual catalysts. The ZnGA:Zn3[Cr(CN)6]2 ratio of 15:1 gave PPC yield of 47.9 g polymer/g cat compared to ZnGA that produced 42.6 g polymer/ g cat in 24 h. In addition, the PPC produced from the composite catalyst displayed higher carbonate linkage content (Fc = 85.4 %) compared to the value of Fc = 33.9 %. obtained using the Zn3[Cr(CN)6]2 catalyst. Similaly, the composite catalsyt produced PPC with molecular weight of 4200 g/mol and narrow polydispersity index of 2.2. The resultant PPC copolymer displayed good thermal stability, exhibiting a high degradation temperatures (TGA-10%) of 229 °C and complete decomposition at 350 °C.
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| 25. |
- Mousa, Abdelrazek H., et al.
(författare)
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Aromatic PCN pincer palladium complexes : Forming and breaking CC bonds
- 2017
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Ingår i: Journal of Organometallic Chemistry. - : Elsevier BV. - 0022-328X. ; 845, s. 157-164
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Tidskriftsartikel (refereegranskat)abstract
- Through a salt metathesis reaction, ( t-BuPCN)Pd-ONO2 (2) was prepared and used as a precursor for producing ( t-BuPCN)Pd-OH (3) and ( t-BuPCN)Pd-aryl acetylide complexes 4 (phenyl acetylide) and 5 (p-tolyl acetylide). The aryl acetylide complexes could also be prepared through another synthetic route: by condensation of 3 with the corresponding aryl acetylene. The reactivity of complexes 3 and 4 toward carbon dioxide was studied and it was found that both reactions give the hydrogen carbonate complex (6). The low reactivity of the Pd-acetylide bond was further confirmed by the fact that the propiolate complex undergoes decarboxylation to give 4. PCN palladium complexes are good catalysts for the decarboxylative cross coupling reactions between acetylene carboxylic acids and aryl halides. The yield of the cross coupling product was improved by adding a catalytic amount of CuI.
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| 26. |
- Mousa, Abdelrazek H., et al.
(författare)
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Carboxylation of the Ni-Me Bond in an Electron-Rich Unsymmetrical PCN Pincer Nickel Complex
- 2020
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Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 39:9, s. 1553-1560
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a new unsymmetrical PCN ligand bearing tert-butyl groups on the phosphorus atom and isopropyl groups on the nitrogen donor atom is presented. It reacts with the commercially available Ni(DME)Br2 precursor to offer the corresponding t-BuPCNi-Pr pincer nickel bromide complex 1 together with a paramagnetic species, which was characterized as a tetrahedral nickel complex. Complex 1 reacts with MeMgCl to give the corresponding methyl complex 3. Carboxylation of complex 3 using 4 atm of CO2 gave the PCN nickel acetate complex 4 under mild reaction conditions comparable to those for the corresponding palladium complexes with PCP ligands.
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| 27. |
- Mousa, Abdelrazek H., et al.
(författare)
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Enhancing the Stability of Aromatic PCN Pincer Nickel Complexes by Incorporation of Pyridine as the Nitrogen Side Arm
- 2020
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-0682. ; 2020:45, s. 4270-4277
-
Tidskriftsartikel (refereegranskat)abstract
- New PCNPy pincer nickel complexes have been synthesized through a short synthetic route. Incorporating pyridine as the nitrogen side arm facilitated the C–H activation in the PCN ligand and allowed the cyclometallation with nickel to take place at room temperature. Pyridine also enhanced the stability of β-hydrogen-containing alkyl complexes. Also, the symmetric NCN nickel complex with pyridine side arms was successfully obtained giving a rare example of such type of complexes to be prepared through direct C–H activation. Furthermore, preliminary results showed that the (PCNPy)Ni–Br is active in Kumada coupling reactions particularly the coupling of aryl halides with aryl Grignard reagents.
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| 28. |
- Mousa, Abdelrazek H., et al.
(författare)
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Synthesis, Characterization, and Reactivity of PCN Pincer Nickel Complexes
- 2018
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 37:15, s. 2581-2593
-
Tidskriftsartikel (refereegranskat)abstract
- New diamagnetic nickel(II) complexes based on an unsymmetrical (1-(3-((ditert-butylphosphino)methyl)phenyl)-N,N-dimethyl-methanamine) (PCN) pincer ligand were synthesized and characterized by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy. Their molecular structures were confirmed by X-ray diffraction. Oxidation to high-valent paramagnetic Ni(III) dihalide complexes was achieved through straightforward reaction of the corresponding diamagnetic halide complexes with anhydrous CuX2 (X = Cl, Br). In agreement with this, the complexes are active in Kharasch addition of CCl4 to olefins. The reaction of the hydroxo complex (8) and the amido complex (11) with CO2 produced the hydrogen carbonate and carbamate complexes, respectively. The hydrogen carbonate complex was converted to the dinuclear nickel carbonate complex (10). The methyl (13), phenyl (14), and p-tolylacetylide (15) complexes are also described in the current study providing the first example of the hydrocarbyl nickel complexes based on an unsymmetric aromatic pincer ligand. Furthermore, the reactivity of the methyl complex toward different electrophiles has been investigated, showing that C-C bond formation is possible with aryl halides, whereas the reaction with CO2 is sluggish.
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| 29. |
- Munshi, Sandip, et al.
(författare)
-
Hydrogen-atom and oxygen-atom transfer reactivities of iron(
- 2022
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 51:3, s. 870-884
-
Tidskriftsartikel (refereegranskat)abstract
- A series of iron(ii) complexes with the general formula [FeII(L2-Qn)(L)]n+ (n = 1, L = F−, Cl−; n = 2, L = NCMe, H2O) have been isolated and characterized. The X-ray crystallographic data reveals that metal–ligand bond distances vary with varying ligand field strengths of the sixth ligand. While the complexes with fluoride, chloride and water as axial ligand are high spin, the acetonitrile-coordinated complex is in a mixed spin state. The steric bulk of the quinoline moieties forces the axial ligands to deviate from the Fe–Naxial axis. A higher deviation/tilt is noted for the high spin complexes, while the acetonitrile coordinated complex displays least deviation. This deviation from linearity is slightly less in the analogous low-spin iron(ii) complex [FeII(L1-Qn)(NCMe)]2+ of the related asymmetric ligand L1-Qn due to the presence of only one sterically demanding quinoline moiety. The two iron(ii)-acetonitrile complexes [FeII(L2-Qn)(NCMe)]2+ and [FeII(L1-Qn)(NCMe)]2+ generate the corresponding iron(iv)-oxo species with higher thermal stability of the species supported by the L1-Qn ligand. The crystallographic and spectroscopic data for [FeIV(O)(L1-Qn)](ClO4)2 bear resemblance to other crystallographically characterized S = 1 iron(iv)-oxo complexes. The hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reactivities of both the iron(iv)-oxo complexes were investigated, and a Box–Behnken multivariate optimization of the parameters for catalytic oxidation of cyclohexane by [FeII(L2-Qn)(NCMe)]2+ using hydrogen peroxide as the terminal oxidant is presented. An increase in the average Fe–N bond length in [FeII(L1-Qn)(NCMe)]2+ is also manifested in higher HAT and OAT rates relative to the other reported complexes of ligands based on the N4Py framework. The results reported here confirm that the steric influence of the ligand environment is of critical importance for the reactivity of iron(iv)-oxo complexes, but additional electronic factors must influence the reactivity of iron-oxo complexes of N4Py derivatives.
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| 30. |
- Nakibuule, Fiona, et al.
(författare)
-
Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by talc and other phyllosilicates
- 2020
-
Ingår i: BMC Chemistry. - : Springer Science and Business Media LLC. - 2661-801X. ; 14:1
-
Tidskriftsartikel (refereegranskat)abstract
- Naturally occurring phyllosilicate minerals such as talc and vermiculite in conjunction with n-tetra butyl ammonium bromide (TBAB) co-catalyst were found to be efficient in the coupling of CO2 with epoxides to form cyclic carbonates. The reaction was carried out in a pressurized autoclave reactor at moderate pressures of 10–35 bars and temperatures of 100–150 °C. The optimized catalyst system exhibited > 90% conversion of the epoxides and > 90% selectivity for the desired cyclic carbonates, in the presence or absence of a solvent. The selectivity of the catalytic system could be improved with heat pre-treatment of the phyllosilicates albeit this resulted in slightly lower epoxide conversion. The results obtained using the heat treated phyllosilicates strongly support the hydrogen bond assisted mechanism for the cycloaddition of epoxides and CO2. The cycloaddition reaction could also be carried out in the absence of TBAB, although lower cyclic carbonate yields were observed. The phyllosilicate part of the catalyst system is heterogeneous, easy to separate after completion of reactions and reusable a number of runs without loss of activity.
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| 31. |
- Nermark, Fiona M., et al.
(författare)
-
Desulfurization of Morupule Coal with Subcritical Aqueous Ethanol Extraction
- 2022
-
Ingår i: ChemistryOpen. - : Wiley. - 2191-1363. ; 11:11
-
Tidskriftsartikel (refereegranskat)abstract
- Coal combustion greatly contributes to global emissions of toxic gases into the atmosphere, with sulfur emissions as one of the prominent pollutants in addition to carbon dioxide. Nevertheless, Botswana utilizes Morupule's sub-bituminous coal with average sulfur and ash contents, as determined in this study being 1.9 and 24.4 % by weight with an average calorific value of 22 MJ Kg−1 to generate electricity. We report an optimized extraction method for reducing total sulfur in Morupule coal from 1.9±0.2 to 0.43±0.02 wt.% at optimum conditions of ethanol/water (90/10, v/v %) at 129 °C (105 bars) in 10 minutes. A Box–Behnken experimental design was employed to select the optimal conditions of temperature (100–180 °C), water proportion in ethanol (10–90, v/v %) and extraction time (10–30 minutes), thus reducing the total sulfur under these mild conditions compared to conventional extraction. The optimized conditions were however not efficient in removing ash.
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| 32. |
- Nermark, Fiona M., et al.
(författare)
-
Optimization of coal desulfurization method by sub/supercritical fluid extraction with binary mixtures of carbon dioxide and ethyl lactate as a solvent
- 2024
-
Ingår i: Green Analytical Chemistry. - 2772-5774. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Coal combustion for energy results in the emission of air pollutants such as NOx and SOx, which negatively affect human health and the environment. Reducing toxic gas emissions and ash production is needed to achieve cleaner coal. This study aimed to develop an extraction method for desulfurizing coal with non-toxic solvents before combustion. Mixtures of sub/supercritical carbon dioxide and ethyl lactate (EL) were used at temperatures of 60–80 °C and extraction times of 15–45 min. Box-Behnken design (BBD) was used to assess the influence of the extraction parameters and to optimize the extraction method. The results show that higher temperatures and lower EL content significantly increased desulfurization. The optimal conditions for desulfurization were CO2/EL (95:5, v/v) at 80 °C, 300 bar and 15 min, reducing total sulfur in coal from 1.90 to 0.13% by weight. The extraction was efficient for removing organic sulfur, sulfones and sulfates, whereas there were still traces of sulfoxides and sulfides remaining in the coal after extraction. Moreover, the ash content slightly decreased while the calorific value increased by 8% and 3% by weight, respectively. The use of a temperature less than 100 °C and an extraction time of 15 min make this method "greener" in comparison to other proposed "green" methods, which use temperatures above 200 °C. Thus, the method has the potential to produce clean coal.
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| 33. |
- Njogu, Rachael E.N., et al.
(författare)
-
Electronically Divergent Triscyclometalated Iridium(III) 2-(1-naphthyl)pyridine Complexes and Their Application in Three-Component Methoxytrifluoromethylation of Styrene
- 2019
-
Ingår i: Synlett. - : Georg Thieme Verlag KG. - 0936-5214 .- 1437-2096. ; 30:7, s. 792-798
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic study of the photophysical and electrochemical properties of triscyclometalated homoleptic iridium(III) complexes based on 2-(1-naphthyl)pyridine (npy) ligands is presented. A systematic investigation of ligand substitution patterns showed an influence on the lifetime of the excited state, with slight changes in the absorption and emission spectral features. Specifically, the emission lifetime of a complex of an npy ligand substituted with a strongly electron-withdrawing trifluoromethyl group was longer than that of the corresponding complex with the electronically nonperturbed ligand (3.7 μs versus 1.5 μ s). Electronically complementary ligands and complexes with orthogonal configurations showed slightly shorter excited state lifetimes compared with unsubstituted npy (1.4-3.0 μs). All complexes displayed reversible or quasireversible redox-couple processes, with the complex of the trifluoromethylated ligand showing the highest ground-state oxidation potential E 1/2 ox [Ir(III)/Ir(IV) = 0.95 V vs. SCE in CH 2 Cl 2 ]. This study showed that these complexes can be used as efficient photoredox catalysts, as demonstrated by their application in a regioselective methoxytrifluoromethylation in which the npy complexes showed equal or better performance compared with the archetypical photo redox catalyst tris[2-phenylpyridinato]iridium(III).
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| 34. |
- Odhiambo, Ruth A., et al.
(författare)
-
Synthesis, characterisation and ion-binding properties of oxathiacrown ethers appended to [Ru(bpy)2]2+. Selectivity towards Hg2+, Cd2+ and Pb2
- 2018
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 8:7, s. 3663-3672
-
Tidskriftsartikel (refereegranskat)abstract
- A series of complexes with oxathiacrown ethers appended to a [Ru(bpy)2]2+ moiety have been synthesized and characterised using 1H NMR, 13C NMR, IR, electronic absorption and emission spectroscopies, mass spectrometry and elemental analyses. The complexes exhibit strong MLCT luminescence bands in the range 608-611 nm and one reversible metal centred oxidation potential in the range 1.00-1.02 V. Their selectivity and sensitivity towards Hg2+, Cd2+ and Pb2+ metal ions have been investigated using electronic absorption, luminescence, cyclic and differential pulse voltammetry titrations. Their responses towards selected cations and anions have also been investigated using electronic absorption and luminescence. While the complexes are selective towards Hg2+ and Cd2+ ions, none of them is selective towards Pb2+ ions. In particular, complex 2 gives a selective change in the UV/Vis absorbance with Hg2+ making it possible to detect mercury down to a detection limit of 68 ppm. The binding constants and limits of detection of the complexes have been calculated, with values ranging from 4.37 to 5.38 and 1.4 × 10-3 to 6.8 × 10-5 for log Ks and LOD respectively.
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| 35. |
- Polukeev, Alexey V., et al.
(författare)
-
Combined Experimental and Computational Study of the Mechanism of Acceptorless Alcohol Dehydrogenation by POCOP Iridium Pincer Complexes
- 2022
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 41:7, s. 859-873
-
Tidskriftsartikel (refereegranskat)abstract
- Iridium pincer complexes of the type (POCOP)Ir (POCOP = 2,6-(tBu2PO)2C6H3) are very productive catalysts for dehydrogenation of secondary alcohols. To our surprise, we found that turnover frequencies demonstrated by (POCOP)IrH2 (IrH2) are higher in more dilute solutions of the catalyst, which triggered a mechanistic study of alcohol dehydrogenation by IrH2. Here, we provide strong evidence that acceleration by dilution is related to the rate-limiting mass transfer of hydrogen, which, so far, has not received much attention in the literature. Using experimental and computational methods, we show that dehydrogenation has two high-barrier steps, namely the reaction of IrH2 with alcohol to give (POCOP)IrH(OR) (IrH(OR)) and subsequent β-elimination in the latter. Depending on the alcohol and reaction conditions, IrH(OR) can be formed via an associative pathway that includes proton transfer to the hydride or a dissociative mechanism that involves hydrogen elimination from IrH2 to give a 14e (POCOP)Ir species. Rapid re-hydrogenation of IrH(OR) or the 14e (POCOP)Ir by dissolved hydrogen is responsible for the rate retardation in more concentrated solutions of the catalyst. The suggested mechanism gives a satisfactory quantitative description of the catalytic cycle, such that kinetic curves and reaction orders in the catalyst can be reproduced.
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| 36. |
- Polukeev, Alexey V., et al.
(författare)
-
Cyclohexane-Based Phosphinite Iridium Pincer Complexes : Synthesis, Characterization, Carbene Formation, and Catalytic Activity in Dehydrogenation Reactions
- 2017
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 36:3, s. 639-649
-
Tidskriftsartikel (refereegranskat)abstract
- Metalation of two cyclohexane-based phosphinite pincer ligands, cis-POCyPO (4) and trans-POCyPO (5) (POCyPO = {1,3-bis-[(di-tert-butylphosphinito]cyclohexane}−), is reported. In line with previously published results (Dalton Trans. 2009, 8626, DOI: 10.1039/B910798C), ligand 4 undergoes aromatization to give benzene-based complex (POCOP)IrHCl (3) at high temperatures in the presence of [Ir(COD)Cl]2. However, here we present the isolation of carbene complex (POCyOP)IrCl (6) which is an intermediate in the aromatization process; upon reaction with H2, 6 can be readily transformed to the corresponding hydrido-chloride 8. Metalation of trans-POCyOP ligand 5 gives hydrido-chloride 13 which only upon further heating can be converted to the corresponding carbene 14. A mechanistic study of hydrogenation of carbene 6 is reported, as well as interesting ambient temperature CO-induced C-H activation in β-position of 6, a process that under other circumstances takes place around 200 °C. The cis complex (POCyOP)IrHCl (8), upon activation with base, revealed moderate activity in transfer dehydrogenation of cyclooctane (144 turnover numbers (TON)), while the performance of trans analog 13 was much better (up to 1684 TON). Carbene complex 6 and in situ generated 14 demonstrated promising activity in acceptorless dehydrogenation of alcohols, presumably operating via a novel metal-ligand cooperation type mechanism. Some of the alcohol dehydrogenations generated large amounts of polystyrene.
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| 37. |
- Polukeev, Alexey V., et al.
(författare)
-
Iridium Catalyzed Dehydrogenation in a Continuous Flow Reactor as a Tool Towards Practical On-Board Hydrogen Generation From LOHCs
- 2022
-
Ingår i: ChemSusChem. - : Wiley. - 1864-564X .- 1864-5631. ; 15:8
-
Tidskriftsartikel (refereegranskat)abstract
- To enable the large-scale use of hydrogen fuel cells for mobility applications, convenient methods for on-board hydrogen storage and release need to be developed. A promising approach is liquid organic hydrogen carriers (LOHCs), since these are safe, available on a large scale and compatible with existing re-fuelling infrastructure. Usually, LOHC dehydrogenation is carried out in batch-type reactors by transition metals and their complexes and suffers from slow H 2 release kinetics and/or inability to reach high energy density by weight due to low conversion or the need to dilute the reaction mixture. Here we report the use of a continuous flow reactor in combination with a heterogenized iridium pincer complex, which enables a tremendous increase in LOHC dehydrogenation rates. Thus, dehydrogenation of isopropanol is performed in a regime that in terms of gravimetric energy density, hydrogen generation rate and precious metal content is potentially compatible with applications in a fuel-cell powered car.
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| 38. |
- Polukeev, Alexey V., et al.
(författare)
-
Iridium complexes with aliphatic, non-innocent pincer ligands
- 2018
-
Ingår i: Journal of Organometallic Chemistry. - : Elsevier BV. - 0022-328X. ; 867, s. 33-50
-
Tidskriftsartikel (refereegranskat)abstract
- Pincer complexes attract considerable attention both as interesting objects for fundamental studies and efficient catalysts. This review describes a relatively new offshoot of the field - namely, the chemistry of iridium complexes with aliphatic PCsp3P non-innocent pincer ligands. High flexibility, often combined with possibility to activate internal C-H bonds, offers several new patterns of metal-ligand cooperation; some of them were successfully used in catalysis of acceptorless alcohol dehydrogenation, olefin hydroformylation and deuterium exchange, others opened up for remarkable stoichiometric reactions.
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| 39. |
- Polukeev, Alexey V., et al.
(författare)
-
Iridium Hydride Complexes with Cyclohexyl-Based Pincer Ligands : Fluxionality and Deuterium Exchange
- 2016
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 35:16, s. 2600-2608
-
Tidskriftsartikel (refereegranskat)abstract
- Two hydride compounds with aliphatic pincer ligands, (PCyP)IrH2 (PCyP = {cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane}(-) (1) and (PCyP)IrH4 (2), have been studied, with emphasis on features where such systems differ from arene-based analogues. Both compounds reveal relatively rapid exchange between alpha-C-H and Ir-H, which can occur via formation of carbene or through demetalation, with nearly equal barriers. This observation is confirmed by deuterium incorporation into the alpha-C-H position. Complex 1 can reversibly add an N-2 molecule, which competes with the alpha-agostic bond for a coordination site at iridium. The hydrogen binding mode in tetrahydride 2 is discussed on the basis of NMR and IR spectra, as well as DFT calculations. While the interpretation of the data is somewhat ambiguous, the best model seems to be a tetrahydride with minor contribution from a dihydrido-dihydrogen complex. In addition, the catalytic activity of 1 in deuterium exchange using benzene-d(6) as a deuterium source is presented.
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| 40. |
- Polukeev, Alexey V., et al.
(författare)
-
Unravelling strong temperature-dependence of JHD in transition metal hydrides : solvation and non-covalent interactions versus temperature-elastic H-H bonds
- 2023
-
Ingår i: Chemical Science. - 2041-6520. ; 14:43, s. 12308-12320
-
Tidskriftsartikel (refereegranskat)abstract
- A number of transition metal hydrides reveal intriguing temperature-dependent JHD in their deuterated derivatives and possibly the temperature dependent hydrogen-hydrogen distance (r(H-H)) as well. Previously, theoretical studies rationalized JHD and r(H-H) changes in such compounds through a “temperature-elastic” structure model with a significant population of vibrational states in an anharmonic potential. Based on the first variable temperature neutron diffraction study of a relevant complex, (p-H-POCOP)IrH2, observation of its elusive counterpart with longer r(H-H), crystallized as an adduct with C6F5I, and thorough spectroscopic and computational study, we argue that the model involving isomeric species in solution at least in some cases is more relevant. The existence of such isomers is enabled or enhanced by solvation and weak non-covalent interactions with solvent, such as halogen or dihydrogen bonds. “Non-classical” hydrides with r(H-H) ≈ 1.0-1.6 Å are especially sensitive to the above-mentioned factors.
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| 41. |
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| 42. |
- Sjövall, Sven, et al.
(författare)
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Cyclometalation reactions on rhodium(I). Evidence for a chelate effect and competing C-H and C-O oxidative additions
- 2001
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 20:23, s. 4919-4926
-
Tidskriftsartikel (refereegranskat)abstract
- The ligand Ph2PC6H4(CH2N(Me)CO(Et)) reacts with (bis(diphenylphosphino)butane) (2,5-norbornadiene)rhodium tetrafluoroborate (2a) and (bis(diphenylphosphino)ethane)(2,5-norbornadiene) rhodium tetrafluoroborate (2b) at room temperature in the presence of hydrogen to displace the norbornadiene and give the chelate complexes 3a,b, in which the phosphorus and the oxygen atoms are coordinated to give an eight-membered ring. At elevated temperatures these complexes are converted into cyclometalated Rh(III) benzyl hydride complexes. Rate law, activation parameters, and reactivity trends of this latter transformation indicate that displacement of one of the phosphine functionalities of the bis-chelating phosphine takes place before the C-H activation. Complex 3b was characterized by X-ray crystallography. On the other hand, under ambient conditions the ligand (±)-Ph2PC6H4(CH(Me)O(CO)Et) undergoes activation of either the benzylic C-O or C-H bond, depending on the nature of the Rh precursor used. Thus, 2b gives overall elimination of propionic acid to result in a styrene complex, which was characterized by X-ray crystallography, whereas bis(2,5-norbornadiene)rhodium tetrafluoroborate gives a mixture of Rh(III) benzyl hydride stereoisomers. The difference in reactivity is discussed in terms of different mechanisms for the two processes.
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| 43. |
- Sjövall, Sven, et al.
(författare)
-
Synthesis, characterisation and crystal structures of the palladium(II) phosphite complexes cis-[PdI2{cis-(iPr2PO)2C 6H10}] and trans-[Pd2I4{cis-(iPr2PO) 2C6H10}2]
- 2001
-
Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 325:1-2, s. 182-186
-
Tidskriftsartikel (refereegranskat)abstract
- Treatment of 2 equiv. of a mixture of the diphosphite cis, trans-1,3-(iPr2PO)2C6H 10 with [Pd(CO2CF3)2] and sequential addition of an excess of NaI gives the binuclear 16-atom ring chelate complex trans-[Pd2I4{cis-(iPr2PO) 2C6H10}2] (1) and the mononuclear complex cis-[PdI2{cis-(iPr2PO)2C 6H10}] (2) exclusively. NMR spectroscopy and X-ray crystallography have unambiguously determined the structures of both complexes in solution and in the solid state. The cyclohexane ring orients its 1,3-substituents in a diaxial manner in 2, while the same ring-substituents in 1 are diequatorially oriented.
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| 44. |
- Suman, Sigridur G., et al.
(författare)
-
Synthesis of mixed salts of the [Mo2O2(μ-S)2(SCN)6-n(L)n](4+n)− anion (n = 0–2); structures of [Mo2O2(μ-S)2(SCN)5(CH3CN)]3−, [Mo2O2(μ-S)2(CN)5]3−, and [Mo2O2(μ-S)2(CN)2(O)]2−, and probing the ligand exchange of thiocyanate and cyanide
- 2021
-
Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387. ; 209
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous coordination of cyanide and verification of the composition of the resulting coordination compound is important to ensure confidence in its coordination. Isothiocyanato compounds 1–7 were synthesized employing different synthetic routes and the complex, [Mo2O2(μ-S)2(SCN)5(CH3CN)]3−, 4, was structurally characterized. Ligand exchange reaction of 4 with cyanide forms 8, a cyano complex. Complex 8 was isolated as an organosoluble salt and fully characterized and confirmed as the major product formed in the aqueous ligand exchange reaction of 4–7 with cyanide. The crystal structure of 8 revealed the unusual [Mo2O2(μ-S)2(CN)5]3− anion where the two molybdenum(V) centers are unsymmetrically coordinated. A second unsymmetric cyano complex [Mo2O3(μ-S)2(CN)2]2− 9, presumed hydrolysis product from an aqueous reaction, was isolated and structurally characterized revealing one square pyramidal Mo center and one tetrahedral Mo center in the binuclear core. Attempts to quantify the first order dissociative ligand substitution rate of thiocyanate in 4 to form 8 using the stopped-flow method gave an estimated minimum rate constant of 70 s−1. This confirms that the exchange reaction is sufficiently fast to be useful in aqueous coordination of cyanide.
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| 45. |
- Tebandeke, Emmanuel, et al.
(författare)
-
One pot synthesis of styrene carbonate from carbon dioxide and styrene in water catalyzed by nano-silver modified polyoxometalates
- 2023
-
Ingår i: Sustainable Chemistry for the Environment. - 2949-8392. ; 2
-
Tidskriftsartikel (refereegranskat)abstract
- Herein is reported an efficient catalytic system for the direct synthesis of styrene carbonate from styrene and CO2. The preparation and characterization of the catalyst using FTIR, TEM, EDX, XPS, and PXRD is presented. The catalyst comprised of nano-silver modified polyoxometalates (Agx/POM) and n-tetra butyl ammonium bromide (TBAB) was employed in the oxidative carboxylation of styrene with CO2 in water as the solvent using H2O2 oxidant. The catalysed reaction was performed in a stainless steel autoclave reactor and the products were analysed using GC-MS and GC-FID. The oxidative carboxylation process was carried out in a one pot set up without need for subsequent work-up and isolation of the styrene oxide formed from the epoxidation process. The process led to 64.6% styrene conversion in 6 h with 96.9% selectivity towards styrene carbonate at 50 ⁰C and 25 bar CO2. The Agx/POM catalyst and TBAB co-catalyst were both beneficial for the reaction and no cyclic carbonate was formed without the catalyst system. When tested on selected styrene derivatives, the catalyst system showed> 90% conversion and> 90% selectivity to the desired cyclic carbonates. The Agx/POM catalyst could be recovered at the end of the reaction and reused with a fresh amount of TBAB without significant loss in activity.
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| 46. |
- Wendt, Ola, et al.
(författare)
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Acetonitrile and Propionitrile Exchange at Palladium(II) and Platinum(II)
- 1997
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Ingår i: Journal of the Chemical Society. Dalton Transactions. - 1472-7773. ; 1997:24, s. 4733-4737
-
Tidskriftsartikel (refereegranskat)abstract
- Ligand exchange at square-planar [Pd(MeCN)4]2+ and [Pd(EtCN)4]2+ has been studied by 1H NMR line broadening and at [Pt(MeCN)4]2+ and [Pt(EtCN)4]2+ by isotopic labelling using 1H NMR spectroscopy in deuteriated nitromethane. Exchange takes place via two-term rate laws Rex/4 = (k1 + k2[RCN])cM with well defined k1 paths. Rate constants per co-ordination site k1298/s–1, k2298/kg mol–1 s–1 are 6.9 ± 1.6, 34 ± 3; 0.59 ± 0.12, 34 ± 3; 10.7 ± 1.8, 35 ± 4; (5.1 ± 2.3) × 10–6, (2.8 ± 0.2) × 10–5 and (5.5 ± 1.0) × 10–6, (3.3 ± 0.2) × 10–5 for [Pd(MeCN)4][CF3SO3]2, [Pd(MeCN)4][BF4]2, [Pd(EtCN)4][CF3SO3]2, [Pt(MeCN)4][CF3SO3]2 and [Pt(EtCN)4][CF3SO3]2, respectively. For [Pd(MeCN)4]2+ the k1 path is much larger for triflate than for tetrafluoroborate as counter ion. Changing the tetrafluoroborate concentration has no effect on the exchange rate of acetonitrile at [Pd(MeCN)4]2+. In this case the k1 path is ascribed to an attack by solvent at the metal centre. For triflate saturation kinetics is observed. This can be rationalized in terms of ion-pair formation followed by reversible intramolecular exchange of nitrile for triflate within the ion pair, with an equilibrium constant Kip300 = 8 ± 2 kg mol–1 and a rate constant k300 = 12.5 ± 1.3 s–1. All activation entropies are negative, indicating associative activation. A new, simple one-step synthesis of the substrate complexes as their triflate salts, using [M(acac)2] (acac = acetylacetonate) as starting material, and of [Pd(MeCN)4][BF4]2 using palladium(II) acetate, is described.
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| 47. |
- Wendt, Ola F.
(författare)
-
Transition metal pincer complexes with a central sp 3 -hybridized carbon atom
- 2018
-
Ingår i: Pincer Compounds : Chemistry and Applications - Chemistry and Applications. - 9780128129319 - 9780128129326 ; , s. 237-250
-
Bokkapitel (refereegranskat)abstract
- This chapter covers transition metal complexes with phosphorus-based pincer ligands with a central sp3-hybridization. It primarily focusses on progress in the last 4 years. The ligand types covered in this chapter include those based on straight alkyl chains but also complexes based on cyclohexane, dibenzobarrelene, cycloheptatriene, and diarylmethane scaffolds.
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| 48. |
- Yuan, Ning, et al.
(författare)
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In situ XAS study of the local structure and oxidation state evolution of palladium in a reduced graphene oxide supported Pd(ii) carbene complex during an undirected C-H acetoxylation reaction
- 2019
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:8, s. 2025-2031
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Tidskriftsartikel (refereegranskat)abstract
- In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(ii) catalyzed undirected C-H acetoxylation reaction in the presence of an oxidant. A Pd(ii) N-heterocyclic carbene complex π-stacked onto reduced graphene oxide (rGO) was used as the catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(ii) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(ii) are replaced by other ligands with a mean bond distance to Pd matching Pd-C/N/O. Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(iv) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(iv) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(ii)-Pd(iv)-Pd(ii) reaction mechanism.
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| 49. |
- Yuan, Ning, et al.
(författare)
-
In Situ XAS Study of the Local Structure and Oxidation State Evolutions of Palladium in a Reduced Graphene Oxide Supported Pd(II) Carbene Complex during an Undirected C−H Acetoxylation Reaction
- 2019
-
Ingår i: Catalysis Science & Technology. - 2044-4753 .- 2044-4761. ; 9:8, s. 2025-2031
-
Tidskriftsartikel (refereegranskat)abstract
- In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(II) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant. A Pd(II) N-heterocyclic carbene complex p-stacked onto reduced graphene oxide (rGO) was used as catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(II) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(II) are replaced by other ligands with a bond distance to Pd corresponding to carbon, nitrogen and/or oxygen (L). Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(IV) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(IV) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(II)-Pd(IV)-Pd(II) reaction mechanism.
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