- Synthesis and characterization of Mn/Co/Ti LDH and its utilization as a photocatalyst in visible light assisted degradation of aqueous Rhodamine B
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Luminescent Mn/Co/Ti LDH, synthesized by a single step hydrothermal route, has been found to be optically responsive for utilization as a highly efficient photocatalyst in destruction of the cationic dye Rhodamine B, in aqueous solution under visible light irradiation. The material has been found to be better than the commercial catalysts like MnO, CoO, TiO2 and Degussa P25. Multiple techniques like XRD, XPS, FT-IR, EIS, TG, UV-visible DRS, PL, TRES, N2-sorption-desorption, dynamic light scattering, TEM-EDS and AFM analyses were used to characterize the LDH. The results indicated Mn/Co/Ti LDH to have a multilayered crystalline structure with hexagonal morphology that carries metal ions in mixed valences, oxygen vacancies, defect states, thermal stability, narrow band gap, high surface area, and electrostatic surface charge variation with pH. The photocatalytic activity of the LDH could be co-related with the structural aspects such as oxidation states, narrow band gap, high surface area and existence of defects. The active species responsible for photocatalysis have been evaluated with EPR, terephthalic acid fluorescence probe and indirect radical-hole trapping experiments. The photodegradation mechanism involves electron and hole hopping across the material and also photosensitization of the dye. Ex situ1H-NMR and GC-MS analyses of the colorless end products of Rhodamine B destruction provide further insight into the reaction mechanism. The complete mineralization of the decolorized end product of degradation was evaluated with TOC analysis. The results indicate the potential for using multi metal incorporated LDH in destroying dyes and their degradation products in industrial wastewater.
- Chowdhury, Priyadarshi Roy,Bhattacharyya, Krishna G.
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p. 112016 - 112034
(2016)
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Read Online
- Reaction of lithium eneselenolates derived from selenoamides with ketones: A highly diastereoselective synthetic route to β,β-disubstituted β-hydroxy selenoamides
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The reaction of lithium eneselenolates generated from selenoamides with a variety of ketones proceeded smoothly at -78°C to give the corresponding β,β-disubstituted β-hydroxy selenoamides in moderate to good yields. The reaction showed high diastereoselectivity. The products obtained were converted to the corresponding amides by reacting them with cyclohexene oxide.
- Murai, Toshiaki,Ishizuka, Masato,Suzuki, Akiko,Kato, Shinzi
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Read Online
- Discovery and Redesign of a Family VIII Carboxylesterase with High (S)-Selectivity toward Chiral sec-Alcohols
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Highly enantioselective lipase has been widely utilized in the preparation of versatile enantiopure chiral sec-alcohols through kinetic or dynamic kinetic resolution. Lipase is intrinsically (R)-selective, and it is difficult to obtain (S)-selective lipase. Recent crystal structures of a family VIII carboxylesterase have revealed that the spatial array of its catalytic triad is the mirror image of that of lipase but with a catalytic triad that is distinct from lipase. We, therefore, hypothesized that the family VIII carboxylesterase may exhibit (S)-enantioselectivity toward sec-alcohols similar to (S)-selective serine protease, whose catalytic triad is also spatially arrayed as its mirror image. In this study, a homologous enzyme (carboxylesterase from Proteobacteria bacterium SG_bin9, PBE) of a known family VIII carboxylesterase (pdb code: 4IVK) was prepared, which showed not only moderate (S)-selectivity toward sec-alcohols such as 3-butyn-2-ol and 1-phenylethyl alcohol but also (R)-selectivity toward particular sec-alcohols among the substrates explored. Furthermore, the (S)-selectivity of PBE has been significantly improved by rational redesign based on molecular modeling. Molecular modeling identified a binding pocket composed of Ser381, Ala383, and Arg408 for the methyl substituent of (R)-1-phenylethyl acetate and suggested that larger residues may increase the enantioselectivity by interfering with the binding of the slow-reacting enantiomer. As predicted, substituting Ser381with larger residues (Phe, Tyr, and Trp) significantly improved the (S)-selectivity of PBE toward all sec-alcohols explored, even the substrates toward which the wild-type PBE exhibits (R)-selectivity. For instance, the enantioselectivity toward 3-butyn-2-ol and 1-phenylethyl alcohol was improved from E = 5.5 and 36.1 to E = 2001 and 882, respectively, by single mutagenesis (S381F).
- Park, Areum,Park, Seongsoon
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p. 2397 - 2402
(2022/02/17)
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- Conformationally Controlled Linear and Helical Hydrocarbons Bearing Extended Side Chains
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Conformationally controlled flexible molecules are ideal for applications in medicine and materials, where shape matters but an ability to adapt to multiple and changing environments is often required. The conformation of flexible hydrocarbon chains bearing contiguous methyl substituents is controlled through the avoidance of syn-pentane interactions: alternating syn-anti isomers adopt a linear conformation while all-syn isomers adopt a helical conformation. From a simple diamond lattice analysis, larger substituents, which would be required for most potential applications, result in significant and unavoidable syn-pentane interactions, suggesting substantially reduced conformational control. Through a combination of computation, synthesis, and NMR analysis, we have identified a selection of substitution patterns that allow large groups to be incorporated on conformationally controlled linear and helical hydrocarbon chains. Surprisingly, when the methyl substituents of alternating syn-anti hydrocarbons are replaced with acetoxyethyl groups, the main chain of almost 95% of the population of molecules adopt a linear conformation. Here, the side chains adopt nonideal eclipsed conformations with the main chain, thus minimizing syn-pentane interactions. In the case of all-syn hydrocarbons, concurrent removal of some methyl groups on the main chain adjacent to the large substituents is required to maintain a high population of molecules adopting a helical conformation. This information can now be used to design flexible hydrocarbon chains displaying functional groups in a defined relative orientation for multivalent binding or cooperative reactivity, for example, in targeting the interfaces defined by disease-relevant protein-protein interactions.
- Aggarwal, Varinder K.,Butts, Craig P.,Davy, Matthew,Dutton, Oliver J.,Guo, Lin,Kucukdisli, Murat,Myers, Eddie L.,Wagnières, Olivier
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supporting information
p. 16682 - 16692
(2021/10/21)
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- A Cobalt(II) Complex Bearing the Amine(imine)diphosphine PN(H)NP Ligand for Asymmetric Transfer Hydrogenation of Ketones
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Novel chiral cobalt complex a containing amine(imine)diphosphine PN(H)NP ligand and complex b containing bis(amine)diphosphine PN(H)N(H)P ligand were synthesized. The structures of two complexes were characterized by X-ray crystallography and high resolution mass spectrometry. The catalytic performances of cobalt complexes a and b for asymmetric transfer hydrogenation (ATH) of ketones under mild conditions were evaluated using 2-propanolisopropanol as solvent and hydrogen source after being activated by 8 equivalents of base. Complex a showed a good reactivity for reduction of ketones, with a turnover number (TON) of up to 555, and a maximum enantiomeric excess (ee) value of up to 91 %. Complex b exhibited inertness for hydrogenation of ketones. Electronic structure studies on a and b were conducted to account for the function of ligands on the catalytic performances.
- Huo, Shangfei,Chen, Hong,Zuo, Weiwei
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supporting information
p. 37 - 42
(2020/10/21)
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- London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
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The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
- Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
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p. 4823 - 4832
(2021/02/01)
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- Chromium-Catalyzed Production of Diols From Olefins
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Processes for converting an olefin reactant into a diol compound are disclosed, and these processes include the steps of contacting the olefin reactant and a supported chromium catalyst comprising chromium in a hexavalent oxidation state to reduce at least a portion of the supported chromium catalyst to form a reduced chromium catalyst, and hydrolyzing the reduced chromium catalyst to form a reaction product comprising the diol compound. While being contacted, the olefin reactant and the supported chromium catalyst can be irradiated with a light beam at a wavelength in the UV-visible spectrum. Optionally, these processes can further comprise a step of calcining at least a portion of the reduced chromium catalyst to regenerate the supported chromium catalyst.
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Paragraph 0111
(2021/03/19)
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- Porous Organic Frameworks Featured by Distinct Confining Fields for the Selective Hydrogenation of Biomass-Derived Ketones
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The asymmetric hydrogenation of biomass-derived molecules for the preparation of single enantiomer compounds is an effective method to reduce the rapid consumption of fossil resources. Porous organic frameworks (POFs) with pure organic surfaces may provide unusual confinement effects for organic substrates in chiral catalysis. Here, a series of POF catalysts are designed with chiral active centers decorated into sharply defined one-dimensional channels with diameters in the range of 1.2–2.9 nm. Due to the synergistic effect originating from the conjugated inner wall, the POF material (aperture size 2.4 nm) concentrates over 90% of aromatic species into the porous architecture, and its affinity is one or two orders of magnitude higher than those of classical porous solids. As determined by PBE+D3 calculation, the phenyl fragment reveals strong π–π interaction for steric hindrance around the metal active site to achieve stronger asymmetric induction. Therefore, this POF catalyst achieves high conversion (>99% yield) and enantioselectivity (>99% ee) for various substrates. The advantages of using the POF platform as a chiral catalyst can provide new perspectives on POF-based solid-state host–guest chemistry and asymmetric heterogeneous catalysis.
- Yang, Yajie,Deng, Dan,Zhang, Shenli,Meng, Qinghao,Li, Zhangnan,Wang, Zeyu,Sha, Haoyan,Faller, Roland,Bian, Zheng,Zou, Xiaoqin,Zhu, Guangshan,Yuan, Ye
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- Synthesis of cis-1,2-diol-type chiral ligands and their dioxaborinane derivatives: Application for the asymmetric transfer hydrogenation of various ketones and biological evaluation
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Two cis-1,2-diol-type chiral ligands (T1 and T2) and their tri-coordinated chiral dioxaborinane (T(1–2)B(1–2)) and four-coordinated chiral dioxaborinane adducts with 4-tert-butyl pyridine sustained by N → B dati
- Kilic, Ahmet,Balci, Tu?ba Ersayan,Arslan, Nevin,Aydemir, Murat,Durap, Feyyaz,Okumu?, Veysi,Tekin, Recep
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- Boron containing chiral Schiff bases: Synthesis and catalytic activity in asymmetric transfer hydrogenation (ATH) of ketones
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Asymmetric Transfer Hydrogenation (ATH) has been an attractive way for the reduction of ketones to chiral alcohols. A great number of novel and valuable synthetic pathways have been achived by the combination usage of organometallic and coordination chemistry for the production of important class of compounds and particularly optically active molecules. For this aim, four boron containing Schiff bases were synthesized by the reaction of 4-formylphenylboronic acid with chiral amines. The boron containing structures have been found as stable compounds due to the presence of covalent B–O bonds and thus could be handled in laboratory environment. They were characterized by 1H NMR and FT-IR spectroscopy and elemental analysis and they were used as catalyst in the transfer hydrogenation of ketones to the related alcohol derivatives with high conversions (up to 99%) and low enantioselectivities (up to 22% ee).
- Pa?a, Salih,Arslan, Nevin,Meri??, Nermin,Kayan, Cezmi,Bingül, Murat,Durap, Feyyaz,Aydemir, Murat
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- Enantioselective transfer hydrogenation of pro-chiral ketones catalyzed by novel ruthenium and iridium complexes of well-designed phosphinite ligand
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The interaction of [Ru(η6-arene)(μ-Cl)Cl]2 and Ir(η5-C5Me5)(μ-Cl)Cl]2 with a new Ionic Liquid-based phosphinite ligand, [(Ph2PO)-C6H9N2Ph]Cl, (2) gave [Ru((Ph2PO)-C6H9N2Ph)(η6-p-cymene)Cl2]Cl (3), [Ru((Ph2PO)-C6H9N2Ph)(benzene)Cl2]Cl (4) and [Ir((Ph2PO)-C6H9N2Ph)(C5Me5)Cl2]Cl (5), complexes. All the compounds were characterized by a combination of multinuclear NMR and IR spectroscopy as well as elemental analysis. Furthermore, the Ru(II) and Ir(III) catalysts were applied to asymmetric transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with good activity (up to 55% ee and 99% conversion) under mild conditions. Notably, [Ir((Ph2PO)-C6H9N2Ph)(C5Me5)Cl2]Cl (5) is more active than the other analogous complexes in the transfer hydrogenation (up to 81% ee).
- Arslan, Nevin
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p. 628 - 637
(2020/01/02)
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- Chiral Imidazo[1,5- a]pyridine-Oxazolines: A Versatile Family of NHC Ligands for the Highly Enantioselective Hydrosilylation of Ketones
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Herein we report the synthesis and application of a versatile class of N-heterocyclic carbene ligands based on an imidazo[1,5-a]pyridine-3-ylidine backbone that is fused to a chiral oxazoline auxiliary. The key step in the synthesis of these ligands involves the installation of the oxazoline functionality via a microwave-assisted condensation of a cyano-azolium salt with a wide variety of 2-amino alcohols. The resulting chiral bidentate NHC-oxazoline ligands form stable complexes with rhodium(I) that are efficient catalysts for the enantioselective hydrosilylation of structurally diverse ketones. The corresponding secondary alcohols are isolated in good yields (typically >90%) with good to excellent enantioselectivities (80-93% ee). The reported hydrosilylation occurs at ambient temperatures (40 °C), with excellent functional group tolerability. Even ketones bearing heterocyclic substituents (e.g., pyridine or thiophene) or complex organic architectures are hydrosilylated efficiently, which is discussed further in this report.
- Chinna Ayya Swamy,Varenikov, Andrii,Ruiter, Graham De
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supporting information
p. 247 - 257
(2020/02/04)
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- Diastereoselective Synthesis of P-Chirogenic and Atropisomeric 2,2′-Bisphosphino-1,1′-binaphthyls Enabled by Internal Phosphine Oxide Directing Groups
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Diphosphine ligands that merge both axial and P-centered chirality may exhibit superior or unique properties. Herein we report the diastereoselective introduction of P-centered chirality at the 2-position of the axially chiral 2′-(phosphine oxide)-1,1′-binaphthyl scaffold. A lithium–bromide exchange reaction of a 2-bromo-2′-(phosphine oxide)-1,1′-binaphthyl and treatment with dichlorophosphines followed by a nucleophilic organometallic reagent afforded unsymmetrical 2-phosphino-2′-(phosphine oxide)-1,1′-binaphthyls with binaphthyl axial chirality and one or two phosphorus stereocenters with a variety of P substituents. The final diastereomerically pure 2,2′-bisphosphino-1,1′-binaphthyls were obtained by reduction of the phosphine oxide directing group. Preliminary results demonstrated that a ligand with this hybrid chirality could induce higher stereoselectivity in the metal-complex-catalyzed asymmetric hydrogenation of a dialkyl ketone.
- Huo, Shangfei,Li, Jianli,Wang, Tingyi,Wang, Zeming,Xue, Qingquan,Zhu, Meifang,Zuo, Weiwei
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supporting information
p. 8153 - 8159
(2020/04/24)
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- Chemoselective Oxidation of Equatorial Alcohols with N-Ligated λ3-Iodanes
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The site-selective and chemoselective functionalization of alcohols in complex polyols remains a formidable synthetic challenge. Whereas significant advancements have been made in selective derivatization at the oxygen center, chemoselective oxidation to the corresponding carbonyls is less developed. In cyclic systems, whereas the selective oxidation of axial alcohols is well known, a complementary equatorial selective process has not yet been reported. Herein we report the utility of nitrogen-ligated (bis)cationic λ3-iodanes (N-HVIs) for alcohol oxidation and their unprecedented levels of selectivity for the oxidation of equatorial over axial alcohols. The conditions are mild, and the simple pyridine-ligated reagent (Py-HVI) is readily synthesized from commercial PhI(OAc)2 and can be either isolated or generated in situ. Conformational selectivity is demonstrated in both flexible 1,2-substituted cyclohexanols and rigid polyol scaffolds, providing chemists with a novel tool for chemoselective oxidation.
- Mikhael, Myriam,Adler, Sophia A.,Wengryniuk, Sarah E.
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supporting information
p. 5889 - 5893
(2019/08/26)
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- Transfer hydrogenation of ketones catalyzed by a trinuclear Ni(II) complex of a Schiff base functionalized N-heterocyclic carbene ligand
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A new Schiff base-functionalized N-heterocyclic carbene ligand precursor 3-benzyl-1-[2-((2-hydroxy-benzylidene)-amino]-ethyl-3H-imidazol-1-ium bromide (3), and its trinuclear Ni(II) complex [LNiL-Ni-LNiL].2Br (4) where L = 2-[2-(3-benzylimidazol-1-yl) ethyliminomethyl]phenol, were synthesized via the solventless and free carbene routes respectively. Both compounds were characterized by spectroscopic and X-ray diffraction techniques. Single crystal XRD analysis of 4 showed that it is composed of a central square planar Ni(II) ion symmetrically linked to two distorted square planar Ni(II) ions via two bridging ligands. The central Ni(II) ion is only bound to the Schiff base moieties of the bridging ligands via the phenolate oxygen donor (O1) and imine nitrogen donor (N1) atoms in a trans [N^O^(Ni2+)^N^O] mode, whilst the carbene moieties of each bridging ligand and a tridentate L are coordinated in a distorted square planar CNHC-(Ni2+)^N^O^CNHC mode to stabilise each of the terminal Ni(II) ions. Complex 4 showed significant activity as a catalyst in the transfer hydrogenation of a range of aliphatic and aromatic ketones, at a catalyst concentration of 0.1 mol%. An excellent conversion up to 100% was achieved for aromatic ketones after 4 h.
- Abubakar, Samaila,Ibrahim, Halliru,Bala, Muhammad D.
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p. 276 - 282
(2018/10/02)
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- Task-Dependent Coordination Levels of SmI2
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Ligation plays a multifaceted role in the chemistry of SmI2. Depending on the ligand, two of its major effects are increasing the reduction potential of SmI2, and in the case of a ligand, which is also a proton donor, it may also enhance the reaction by protonation of the radical anion generated in the preceding step. It turns out that the number of ligand molecules that are needed to maximize the reduction potential of SmI2 is significantly smaller than the number of ligand molecules needed for a maximal enhancement of the protonation rate. In addition to the economical use of the ligand, this information can also be utilized as a diagnostic tool for the reaction mechanism in differentiating between single and multistep processes. The possible pitfalls in applying this diagnostic tool to PCET and cyclization reactions are discussed.
- Maity, Sandeepan,Nimkar, Amey,Hoz, Shmaryahu
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supporting information
p. 1994 - 1998
(2019/05/16)
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- Iridium-catalyzed asymmetric hydrogenation method for the preparation of chiral alcohols
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The present invention provides one kind of iridium-catalyzed asymmetric hydrogenation method for the preparation of chiral alcohols, the method specifically is: in the glove box filled with nitrogen, the [Ir (COD) Cl]2 With a chiral P, N, N ligand soluble in methanol, stir at room temperature 1 hour, [...] catalyst. Adding substrate alkone and alkali additive, is placed on the high-pressure in the reactor, for a certain reaction under the pressure of the hydrogenation reaction. Slowly release hydrogen, silica gel to remove the solvent and separate the product after the alcohol. The invention states iridium catalyzed alkone asymmetric hydrogenation for the preparation of chiral reaction has mild condition, easy to operate, and the product of the enantioselectivity and the like.
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Paragraph 0095-0100; 0103; 0104
(2019/06/07)
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- Enantioselective Hydrogenation of Ketones using Different Metal Complexes with a Chiral PNP Pincer Ligand
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The synthesis of different metal pincer complexes coordinating to the chiral PNP ligand bis(2-((2R,5R)-2,5-dimethyl-phospholanoethyl))amine is described in detail. The characterized complexes with Mn, Fe, Re and Ru as metal centers showed good activities regarding the reduction of several prochiral ketones. Comparing these catalysts, the non-noble metal complexes produced best selectivities not only for aromatic substrates, but also for different kinds of aliphatic ones leading to enantioselectivities up to 99% ee. Theoretical investigations elucidated the mechanism and rationalized the selectivity. (Figure presented.).
- Garbe, Marcel,Wei, Zhihong,Tannert, Bianca,Spannenberg, Anke,Jiao, Haijun,Bachmann, Stephan,Scalone, Michelangelo,Junge, Kathrin,Beller, Matthias
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supporting information
p. 1913 - 1920
(2019/03/13)
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- Catalysts for the asymmetric transfer hydrogenation of various ketones from [3-[(2S)-2-[(diphenylphosphanyl)oxy]-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride] and [Ru(η6-arene)(μ-Cl)Cl]2, Ir(η5-C5Me5)(μ-Cl)Cl]2 or [Rh(μ-Cl)(cod)]2
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The combination of [3-[(2S)-2-[(diphenylphosphanyl)oxy]-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride] with [Ru(η6-arene)(μ-Cl)Cl]2, Ir(η5-C5Me5)(μ-Cl)Cl]2 or [Rh(μ-Cl)(cod)]2, in the presence of KOH/isoPrOH, has been found to generate catalysts that are capable of enantioselectively reducing alkyl, aryl ketones to the corresponding (R)-alcohols. Under optimized conditions, when the catalysts were applied to the asymmetric transfer hydrogenation, we obtained the secondary alcohol products in high conversions and enantioselectivities using only 0.5 mol% catalyst loading. In addition, [3-[(2S)-2-{[(chloro(?4-1,5-cyclooctadiene)rhodium)diphenyl phosphanyl] oxy}-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride], (6) complex is much more active than the other analogous complexes in the transfer hydrogenation. Catalyst 6 acts as excellent catalysts, giving the corresponding (R)-1-phenyl ethanol in 99% conversion in 30 min (TOF ≤ 396 h?1) and in high enantioselectivity (92% ee).
- Meri?, Nermin,Arslan, Nevin,Kayan, Cezmi,Rafikova, Khadichakhan,Zazybin, Alexey,Kerimkulova, Aygul,Aydemir, Murat
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p. 108 - 118
(2019/04/17)
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- Chiral C2-symmetric η6-p-cymene-Ru(II)-phosphinite complexes: Synthesis and catalytic activity in asymmetric reduction of aromatic, methyl alkyl and alkyl/aryl ketones
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Chiral C2-symmetric bis(phosphinite) ligands and their binuclear ruthenium(II) complexes have been synthesized and used as catalysts in the ruthenium-catalyzed asymmetric transfer hydrogenation of aromatic, methyl alkyl and alkyl/aryl ketones using 2-propanol as both the hydrogen source and solvent in the presence of KOH. Under optimized conditions, all complexes showed high catalytic activity as catalysts in the reduction of various ketones to corresponding chiral secondary alcohols. Products were obtained with high conversions (99%) and moderate to good enantioselectivities (82% ee). Furthermore, C2-symmetric bis(phosphinite) ligands and their binuclear ruthenium(II) complexes were characterized by multinuclear NMR spectroscopy, FT-IR spectroscopy, LC/MS-MS and elemental analysis.
- Karaka?, Duygu Elma,Aydemir, Murat,Durap, Feyyaz,Baysal, Ak?n
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p. 430 - 439
(2017/12/06)
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- Lanthanide aryloxides catalyzed hydroboration of aldehydes and ketones
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The lanthanide aryloxides Ln(OAr)3(THF)2 (Ar = Ar1 = 2,6-tBu2-4-MeC6H2, Ln = Yb (1), Y (2); Ar = Ar2 = 2,6-iPr2C6H3, Ln = Y (3); Ar = Ar3 = 2,6-Me2C6H3, Ln = Y (4); Ar = Ar1, Ln = Sm (5), Nd (6)) could be served as highly efficient catalysts for the hydroboration of aldehydes and ketones with good functional group tolerance and excellent chemoselectivity. Computational studies were carried out to probe a feasible mechanism of the Ln-aryloxides catalyzed hydroboration of aldehydes/ketones.
- Zhu, Zhangye,Dai, Ping,Wu, Zhenjie,Xue, Mingqiang,Yao, Yingming,Shen, Qi,Bao, Xiaoguang
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- Application of Ni(II) complexes of air stable Schiff base functionalized N-heterocyclic carbene ligands as catalysts for the transfer hydrogenation of aliphatic ketones
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New air stable N-heterocyclic carbene functionalized Schiff base ligands (L) of the type 2-[-2-[3-(R)imidazol-1-yl]ethyliminomethyl]phenol [R = methyl (2), 2-pyridylmethyl (3)] were synthesized and characterized by NMR, IR, MS, and CHN analysis. Single crystal X-ray structural analysis of their Ni(II) complexes revealed square planar arrangement of the chelating ligands coordinated in tridentate (2, C^N^O) and tetradentate (3, N^C^N^O) modes around the metal. The three new isolated and fully characterized complexes were utilized as catalysts for the catalytic transfer hydrogenation of aliphatic ketones in 2-propanol as solvent and source of hydrogen. Based on 0.2 mol% catalyst concentration, the complexes showed activity for aliphatic ketones and 100% conversion (turnover number of 500) for cyclohexanone and all the aromatic ketones tested.
- Abubakar, Samaila,Bala, Muhammad D.
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p. 2913 - 2923
(2018/09/27)
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- Biocatalytic Racemization Employing TeSADH: Substrate Scope and Organic Solvent Compatibility for Dynamic Kinetic Resolution
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Racemization in combination with a kinetic resolution is the base for a dynamic kinetic resolution (DKR). Biocatalytic racemization was successfully performed for a broad scope of sec-alcohols by employing a single alcohol dehydrogenase (ADH) variant from Thermoanaerobacter pseudoethanolicus (formerly T. ethanolicus; TeSADH W110A I86A C295A). The catalyst employed as a lyophilized whole cell preparation or cell free extract, which tolerated various non-water miscible organic solvents under micro-aqueous or two-phase conditions, whereby cyclohexane and n-hexane suited best. Various concepts for combining the enzymatic racemization with an enzymatic kinetic resolution to achieve overall a bis-enzymatic DKR were evaluated. A proof of concept showed a successful DKR with racemization in aqueous phase combined with acylation in the organic phase.
- Pop?oński, Jaros?aw,Reiter, Tamara,Kroutil, Wolfgang
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p. 763 - 768
(2018/02/27)
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- A new class of well-defined ruthenium catalysts for enantioselective transfer hydrogenation of various ketones
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A pair of novel optically pure phosphinite ligands were synthesized by ring opening reaction of chiral amines with (R)-styrene oxide or (S)-glycidyl phenyl ether oxide using a straightforward method in high yields and their ruthenium complexes were described in detail. The ruthenium complexes proved to be highly efficient catalysts for the enantioselective hydrogenation of ketones, affording products up to 99% ee. The results showed that the corresponding chiral alcohols could be obtained with high activity and excellent enantioselectivities at the desired temperature. (2S)-1-{benzyl[(1S)-1-(naphthalen-1-yl)ethyl]amino}-3-phenoxypropan-2-yl diphenylphosphinito[dichloro(η6-benzene)ruthenium (II)] acts an excellent catalyst in the reduction of ketones, giving the corresponding alcohol up to 99% ee.
- Kayan, Cezmi,Meri?, Nermin,Rafikova, Khadichakhan,Zazybin, Alexey,Gürbüz, Nevin,Karakaplan, Mehmet,Aydemir, Murat
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- CHIRAL METAL COMPLEX COMPOUNDS
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The invention comprises novel chiral metal complex compounds of the formula (I) wherein M, PR2, R3 and R4 are outlined in the description, its stereoisomers, in the form as a neutral complex or a complex cation with a suitable counter ion. The chiral metal complex compounds can be used in asymmetric reactions, particularly in asymmetric reductions of ketones, imines or oximes.
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Page/Page column 18; 19; 23; 24; 27
(2018/11/10)
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- Half-Sandwich Osmium(II) Complexes with Bidentate N,N-Chelating Ligands and Their Use in the Transfer Hydrogenation of Ketones
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The reaction of appropriate N,N-bidentate ligands with the [(η6-p-cymene)Os(μ-Cl)Cl]2dimer (p-cymene = C10H14), followed by metathesis reaction with NH4PF6, gave the new osmium(II) arene complex salts [(η6-p-cymene)OsCl(C5H4N-2-CH=N–R)]PF6, where [R = tert-butyl (1), isopropyl (2), 2,6-dimethylphenyl (3), or 2,6-diisopropylphenyl (4)]. The dimer was also reacted with the N,N′-bidentate ligands di-(2-pyridyl)amine (5), 4-phenyl-3,6-di(2-pyridyl)pyridazine (6), 4,4′-di-tert-butyl-2, 2′-bipyridine (7), and 5,5′-dimethyl-2,2′-bipyridine (8). In addition, the reaction of the precursor [(η6-C6H6)Os(μ-Cl)Cl]2with the N,N′-bidentate ligands gave [(η6-C6H6)OsCl(N,N)]2where N,N = 4,4′-di-tert-butyl-2,2′-bipyridine (9), 5,5′-dimethyl-2,2′-bipyridine (10), 3,6-bis(2-pyridyl)-4-phenyl pyridazine (11), or di-(2-pyridyl)amine (12). The compounds were characterized by using1H and13C NMR, UV/Vis, FTIR spectroscopy and elemental analysis. The single-crystal X-ray structures for compounds 1, 4, 8, 10, 11, and 12 showed that the osmium(II) complexes adopted the classical three-legged piano stool geometry. These osmium(II) compounds were found to be effective catalysts for the transfer hydrogenation of ketones into alcohols with NaOH as base and 2-propanol as the solvent and hydrogen source. A range of cyclic, aromatic, and aliphatic ketones was studied and good turnover numbers achieved.
- Gichumbi, Joel M.,Omondi, Bernard,Friedrich, Holger B.
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p. 915 - 924
(2017/02/15)
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- Chiral phosphinites as efficient ligands for enantioselective Ru(II), Rh(I) and Ir(III)-catalyzed transfer hydrogenation reactions
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Abstract: Metal-catalyzed enantioselective transfer reduction of ketones to enantiomerically enriched chiral alcohols has recently attracted attention. Therefore, a series of methyl alkyl or alkyl/aryl ketones have been reduced by using Ru(II), Rh(I) and Ir(III) catalysts based on C2-symmetric chiral ferrocenyl phosphinite ligands. The corresponding optically active secondary alcohols were obtained in excellent conversions and moderate-to-good enantioselectivities. The best results were obtained with an iridium catalyst, giving up to 98% conversion and 80% ee.
- Baysal, Ak?n,Elma Karaka?, Duygu,Meri?, Nermin,Ak, Bünyamin,Aydemir, Murat,Durap, Feyyaz
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p. 365 - 372
(2017/04/18)
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- Unsymmetrical Iron P-NH-P′ Catalysts for the Asymmetric Pressure Hydrogenation of Aryl Ketones
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The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure β-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P′. Four new ligands PR2CH2CH2NHCHR′CHR′′PPh2 (R=iPr, Cy, R′=Ph, CH(CH3)2, R′′=Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2(CO)(P-NH-P′) and mer-FeCl(H)(CO)(P-NH-P′). The hydride complex with the rigid ligand with R′=R′′=Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst. Prochiral aryl ketones are reduced under mild conditions (THF, 0.1 mol % catalyst, 1 mol % KOtBu, 5–10 bar, 50 °C) to the (S)-alcohols, usually in enantiomeric excess (ee) greater than 90 %. DFT calculations provided transition-state structures for the enantiodetermining hydride-transfer step.
- Smith, Samantha A. M.,Lagaditis, Paraskevi O.,Lüpke, Anne,Lough, Alan J.,Morris, Robert H.
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p. 7212 - 7216
(2017/05/31)
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- Manganese(I)-Catalyzed Enantioselective Hydrogenation of Ketones Using a Defined Chiral PNP Pincer Ligand
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A new chiral manganese PNP pincer complex is described. The asymmetric hydrogenation of several prochiral ketones with molecular hydrogen in the presence of this complex proceeds under mild conditions (30–40 °C, 4 h, 30 bar H2). Besides high catalytic activity for aromatic substrates, aliphatic ketones are hydrogenated with remarkable selectivity (e.r. up to 92:8). DFT calculations support an outer sphere hydrogenation mechanism as well as the experimentally determined stereochemistry.
- Garbe, Marcel,Junge, Kathrin,Walker, Svenja,Wei, Zhihong,Jiao, Haijun,Spannenberg, Anke,Bachmann, Stephan,Scalone, Michelangelo,Beller, Matthias
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supporting information
p. 11237 - 11241
(2017/09/02)
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- Half-sandwich ruthenium catalyst bearing an enantiopure primary amine tethered to an N-heterocyclic carbene for ketone hydrogenation
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By using a copper transmetalation reagent [Cu-(Kaibene)2]I, the NHC ligand (S,S)-MeNC3H2NCHPhCHPhNH2 "Kaibene" was transferred to ruthenium to make a precatalyst [RuCp?(Kaibene)(MeCN)](PF6) (Cp? = 1,2,3,4,5-pentamethylcyclopentadienyl), 7, in high yield as a mixture of two diastereomers. Under relatively mild conditions (0.02 mol % Ru, 0.16 mol % KOtBu, iPrOH, 50 °C, 25 bar of H2), this compound catalyzes the hydrogenation of aryl ketones and one alkyl ketone effectively with excellent activity and productivity (TOF up to 48 s-1, TON up to 104). At higher hydrogenation pressure (46 bar), the catalytic hydrogenation of N-phenyl-benzylimine to the corresponding amine is efficiently achieved. The hydrogenation of prochiral ketones resulted in low ee (35% for 4-chloroacetophenone). NMR spectroscopy was used to observe diastereomeric hydrides RuCp?(Kaibene)(H) 13-R/S that were generated by reaction of 7 with H2 and base in THF-d8. Complementary DFT studies suggest that either the heterolytic splitting of dihydrogen to form 13-R/S or the hydride transfer to the substrate can be rate-determining depending on the substrate. Experimental and computational results support mechanisms that involve the heterolytic splitting of dihydrogen to the nitrogen of the amide-ligated form of Kaibene in THF or the heterolytic splitting to an outer-sphere alkoxide derived from the product alcohol or 2-PrOH solvent. An unusual feature is the rapid drop in ee of the product alcohol from as high as 60% (R) to 0% in some cases; this might be due to racemization of the Kaibene ligand in THF caused by the strong base or competitive inhibition of one diastereomer of the catalyst by reaction with the product (R)-alcohol.
- Wan, Kai Y.,Sung, Molly M. H.,Lough, Alan J.,Morris, Robert H.
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p. 6827 - 6842
(2017/11/06)
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- Highly Enantioselective Hydrosilylation of Ketones Catalyzed by a Chiral Oxazaborolidinium Ion
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A highly enantioselective hydrosilylation of ketones was developed for the synthesis of a variety of chiral secondary alcohols. In the presence of a chiral oxazaborolidinium ion (COBI) catalyst, the reaction proceeded with good yields (up to 99%) with excellent enantioselectivities (up to 99% ee).
- Kang, Byung Chul,Shin, Sung Ho,Yun, Jaesook,Ryu, Do Hyun
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supporting information
p. 6316 - 6319
(2017/12/08)
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- New functional chiral P-based ligands and application in ruthenium-catalyzed enantioselective transfer hydrogenation of ketones
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Metal-catalyzed asymmetric transfer hydrogenation is a powerful and practical method for the reduction of ketones to produce the corresponding secondary alcohols, which are valuable building blocks in the pharmaceutical, perfume, and agrochemical industries. Hence, a series of novel chiral β-amino alcohols were synthesized by chiral amines with regioselective ring opening of (S)-propylene oxide or reaction with (S)-(+)-2-hydroxypropyl p-toluenesulfonate by a straightforward method. The chiral ruthenium catalytic systems generated from [Ru(arene)(μ-Cl)Cl]2 complexes and chiral phosphinite ligands based on amino alcohol derivatives were employed in asymmetric transfer hydrogenation of ketones to give the corresponding optically active alcohols; (2S)-1-{[(2S)-2-[(diphenylphosphanyl)oxy]propyl][(1R)-1-phenylethyl]amino}propan-2-yldiphenylphosphinitobis[dichol-oro(η6-benzene)ruthenium(II)] acts an excellent catalyst in the reduction of α-naphthyl methyl ketone, giving the corresponding alcohol with up to 99% ee. The substituents on the backbone of the ligands were found to have a remarkable effect on both the conversion and enantioselectivity of the catalysts. Furthermore, this transfer hydrogenation is characterized by low reversibility under these conditions.
- Meri?, Nermin,Kayan, Cezmi,Gürbüz, Nevin,Karakaplan, Mehmet,Binbay, Nil Ertekin,Aydemir, Murat
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p. 1739 - 1749
(2017/10/26)
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- Asymmetric Transfer Hydrogenation of Ketones Using New Iron(II) (P-NH-N-P′) Catalysts: Changing the Steric and Electronic Properties at Phosphorus P′
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The asymmetric transfer hydrogenation (ATH) of ketones is an efficient method for producing enantio-enriched alcohols which are used as intermediates in a variety of industrial processes. Here we report the synthesis of new iron ATH precatalysts (S,S)-[FeBr(CO)(Ph2PCH2CH2NHCHPhCHPhNC=CHCH2PR′2)][BPh4] (R′=Et, and ortho-tolyl (o-Tol)) where one of the phosphine groups is modified with small alkyl and large aryl substituents to probe the effect of this change on the activity and selectivity of the catalytic system. A simple reversible equilibrium kinetic model is used to obtain the initial TOF and the inherent enantioselectivity S=kR/kS of these catalysts along with those for the previously reported catalysts with R′=Ph and Cy for the ATH of acetophenone. With an increase in the size of the PR′2 group, the TOF goes through a maximum at PPh2 while the S value goes through a maximum of 510 at R′=Cy. The complex with R′=o-Tol starts with a high S value of 200 but is rapidly changed to a second catalyst with an S value of 28. For the reduction of acetophenone to (R)-1-phenylethanol, turnover numbers of up to 5200 and ee up to 98 % were achieved. The chemotherapeutic pharmaceutical precursor (R)-(3′,5′-bis(trifluoromethyl))-1-phenylethanol is synthesized in up to 95 % ee. Several other alcohols can be prepared in greater than 90 % ee by choosing the precatalyst with the correctly matched steric properties. A hydride complex derived from the catalyst with R′=Cy is characterized by NMR spectroscopy. It is proposed that low concentration trans-hydride carbonyl complexes with the FeH parallel to the NH of the ligand are the active catalysts in all of these systems.
- Smith, Samantha A. M.,Prokopchuk, Demyan E.,Morris, Robert H.
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p. 1204 - 1215
(2017/09/06)
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- Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones
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A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η6-arene)Ru(μ-Cl)Cl]2 with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η6-arene)RuCl(C5H4N-2-CH=N-R)]PF6, with arene?=?C6H6, R?=?iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene?=?p-cymene, R?=?iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by 1H NMR and 13C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100?%.
- Gichumbi, Joel M.,Friedrich, Holger B.,Omondi, Bernard
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p. 867 - 877
(2016/10/25)
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- Vapour phase transfer hydrogenation of α,β-unsaturated carbonyl compounds. Thermodynamic and experimental studies
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This paper presents the first systematic thermodynamic study of the vapour phase transfer hydrogenation of α,β-unsaturated carbonyl compounds at temperatures: 423.15-723.15 K. Calculations were made for four compounds, namely: acrolein, α-methylacrolein, β-methylacrolein and methyl vinyl ketone. The Gibbs free energies and equilibrium mole fractions (EMFs) were calculated for transfer hydrogenation with ethanol and 2-propanol as hydrogen donors. It was noted that for transfer hydrogenation and hydrogenation with hydrogen the formation of the unsaturated alcohol (UOL) is the least thermodynamically favoured reaction and that saturated alcohol (SOL) and saturated aldehyde or ketone (SAL or SON) are the main products. A set of eight carbonyl compounds have been transfer hydrogenated with ethanol and 2-propanol in the presence of MgO as the catalyst. The main conclusions are that: (a) the reduction of a carbonyl group into a carbinol group occurs with a very high selectivity, (b) for almost all carbonyl compounds, except acrolein, the reactivity of 2-propanol highly exceeded that shown by ethanol and (c) the high chemoselectivity of transfer hydrogenation of acrolein with alcohols resulted from the kinetic control caused by the presence of magnesium oxide.
- Gliński, Marek,Ulkowska, Urszula
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p. 131 - 140
(2015/12/18)
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- Synthesis, characterization and reactivity of iron- and cobalt-pincer complexes
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The tBuPONOP (2,6-bis(di-tert-butyl-phosphinito)pyridine) complexes of iron and cobalt, (tBuPONOP)FeCl2 (1) and (tBuPONOP)CoCl2 (2)) have been prepared. Both complexes are paramagnetic and the solid-state structures of 1 and 2 were determined by single crystal X-ray diffraction studies. Analogous Fe and Co complexes of the tBuPNP (2,6-bis(di-tert-butyl-phosphinomethyl)pyridine) ligand (3 and 4, respectively) were prepared to allow comparison between the closely related pincer ligands in the hydrosilylation of carbonyl moieties. All four complexes were found to be catalytically active when treated with NaBEt3H, which was assumed to generate a metal-hydride species in-situ.
- Smith, Ashleigh D.,Saini, Anu,Singer, Laci M.,Phadke, Neha,Findlater, Michael
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p. 286 - 291
(2016/07/06)
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- Application of arene ruthenium(II) complexes with pyridine-2-carboxaldimine ligands in the transfer hydrogenation of ketones
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The reaction of various pyridine-2-carboxaldimine ligands with the [(η6-arene)Ru(μ-Cl)Cl]2 dimer followed by a metathesis reaction with ammonium hexaflourophosphate, yielded the ruthenium(II) arene complex salts [(η6-arene)RuCl(C5H4[Formula presented]6; where (arene?=?C6H6 (1), p-cymene (2), Ar?=?3, 5-dimethyl phenyl (a), 2,3-dimethyl phenyl (b), 2,5-dimethyl phenyl (c), 3,4-dimethyl phenyl (d)). The compounds were characterized by elemental analysis, FT- IR, UV–vis and 1H and 13C NMR. Single crystal X-ray structures for compounds 1a, 1d and 2e were also determined and showed that the ruthenium(II) centre has a pseudo-octahedral geometry and the molecule adopted a three legged piano stool geometry in which the arene ring occupies the apex and the nitrogen atoms of the N,N′-bidentate ligand and the chloride atom the base of the stool. The Ru(II) complex salts were active for the catalytic transfer hydrogenation of ketones into alcohols in the presence of NaOH using 2-propanol as the hydrogen source at 82?°C. The complexes were suitable for a wide range of aliphatic, cyclic and aromatic ketones giving good turn over numbers.
- Gichumbi, Joel M.,Friedrich, Holger B.,Omondi, Bernard
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- Asymmetric transfer hydrogenation of alkyl/aryl or alkyl/methyl ketones catalyzed by known C2-symmetric ferrocenyl-based chiral bis(phosphinite)-Ru(II), Rh(I) and Ir(III) complexes
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Known Ru(II), Rh(I) and Ir(III) complexes of C2-symmetric ferrocenyl based chiral bis(phoshinite) ligands were catalyzed the asymmetric transfer hydrogenation of alkyl/aryl or alkyl methyl ketones. Corresponding secondary alcohols were obtained with high enantioselectivities up to 98% ee and reactivities using iso-propanol as the hydrogen source.
- Durap, Feyyaz,Karaka?, Duygu Elma,Ak, Bünyamin,Baysal, Akin,Aydemir, Murat
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- Enantioselective transfer hydrogenation of various ketones with novel efficient iridium(III) ferrocenyl-phosphinite catalysts
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The asymmetric reduction of prochiral ketones is a pivotal reaction for the preparation of chiral alcohols which form an extremely important class of intermediates for fine chemicals and pharmaceuticals. Especially, iridium-based asymmetric reduction of ketones to enantiomerically enriched alcohols has recently attracted important attention by a number of research groups and interest in this area is growing. Therefore, a series of novel neutral mononuclear iridium(III) ferrocenyl-phosphinite complexes have been prepared and applied in the iridium(III)-catalyzed asymmetric transfer hydrogenation (ATH) of ketones to give corresponding secondary alcohols with outstanding enantioselectivities and reactivities using 2-propanol as the hydrogen source (up to 99% ee and 99% conversion). It was seen that the substituents on the backbone of the ligands resulted in a significant effect on both the activity and % enantioselectivity. Furthermore, the structural elucidation of the complexes was carried out by elemental analysis, IR and multi-nuclear NMR spectroscopic data.
- Meri?, Nermin,Aydemir, Murat
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p. 120 - 128
(2016/07/13)
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- Iron(II)/(NH)2P2 Macrocycles: Modular, Highly Enantioselective Transfer Hydrogenation Catalysts
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A generalized protocol for the synthesis of chiral (NH)2P2 macrocycles allows changing the linker between the phosphines and gives access to a family of such ligands, as demonstrated for the propane-1,3-diyl analogue. The corresponding complexes based on earth-abundant and nontoxic iron were applied as catalysts in the asymmetric transfer hydrogenation of polar double bonds. Thanks to the ligand modularity and to the use of tunable isonitriles as ancillary ligands, the catalyst system can be individually optimized for each substrate to give high enantioselectivity (up to 99.9% conversion and 99.6% ee, TOF up to >3950 h-1) for a broad scope of 26 substrates.
- Bigler, Raphael,Huber, Raffael,St?ckli, Marco,Mezzetti, Antonio
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p. 6455 - 6464
(2016/10/18)
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- IRON(II) CATALYSTS CONTAINING TRIDENTATE PNP LIGANDS, THEIR SYNTHESIS, AND USE THEREOF
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The application describes catalytic materials for hydrogenation or asymmetric hydrogenation. In particular, the application describes iron(ll) complexes containing tridentate diphosphine PNP ligands useful for catalytic hydrogenation.
- -
-
Paragraph 0263
(2016/11/28)
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- 16-Electron pentadienyl- and cyclopentadienyl-ruthenium half-sandwich complexes with bis(imidazol-2-imine) ligands and their use in catalytic transfer hydrogenation
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Bis(η5-2,4-dimethylpentadienyl)ruthenium(ii), [(η5-C7H11)2Ru] (1, "open ruthenocene"), which has become accessible in high yield and large quantities via an isoprene-derived diallyl ruthenium(iv) complex, can be converted into the protonated open ruthenocene 2 by treatment with HBF4 and subsequently into the protonated half-open ruthenocene 3 by reaction with cyclopentadiene. The electronic structure of 3 was studied by DFT methods, revealing that the CH-agostic complex [(η5-C5H5)Ru{(1-4η)-C7H12-η2-C5,H5}]BF4 (A) represents the global minimum, which is 3.7 kcal mol-1 lower in energy than the hydride complex [(η5-C5H5)RuH(η5-C7H11)]BF4 (B). 2 and 3 were treated with the ligands N,N′-bis(1,3,4,5-tetramethylimidazolin-2-ylidene)-1,2-ethanediamine (BLMe) and N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,2-ethanediamine (BLiPr) to afford the cationic 16-electron pentadienyl and cyclopentadienyl complexes [(η5-C7H11)Ru(BLR)]BF4 (4a, R = Me; 4b, R = iPr) and [(η5-C5H5)Ru(BLR)]BF4 (5a, R = Me; 5b, R = iPr). All complexes catalyse the transfer hydrogenation of acetophenone in isopropanol, and the most active complex 4a in this reaction was employed for the hydrogenation of a broader range of aliphatic and aromatic ketones.
- Gl?ge, Thomas,Jess, Kristof,Bannenberg, Thomas,Jones, Peter G.,Langenscheidt-Dabringhausen, Nadine,Salzer, Albrecht,Tamm, Matthias
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p. 11717 - 11724
(2015/06/30)
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- Facile Protocol for Catalytic Frustrated Lewis Pair Hydrogenation and Reductive Deoxygenation of Ketones and Aldehydes
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A series of ketones and aldehydes are reduced in toluene under H2 in the presence of 5 mol % B(C6F5)3 and either cyclodextrin or molecular sieves affording a facile metal-free protocol for reduction to alcohols. Similar treatment of aryl ketones resulted in metal-free deoxygenation yielding aromatic hydrocarbons.
- Mahdi, Tayseer,Stephan, Douglas W.
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supporting information
p. 8511 - 8514
(2015/11/27)
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- Deciphering a 20-Year-Old Conundrum: The Mechanisms of Reduction by the Water/Amine/SmI2 Mixture
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The reaction of SmI2 with the substrates 3-methyl-2-butanone, benzyl chloride, p-cyanobenzyl chloride, and anthracene were studied in the presence of water and an amine. In all cases, the water content versus rate profile shows a maximum at around 0.2 M H2O. The rate versus amine content profile shows in all cases, except for benzyl chloride, saturation behavior, which is typical of a change in the identity of the rate-determining step. The mechanism that is in agreement with the observed data is that electron transfer occurs in the first step. With substrates that are not very electrophilic, the intermediate radical anions lose the added electron back to samarium(III) relatively quickly and the reaction cannot progress efficiently. However, in a mixture of water/amine, the amine deprotonates a molecule of water coordinated to samarium(III). The negatively charged hydroxide, which is coordinated to samarium(III), reduces its electrophilicity, and therefore, lowers the rate of back electron transfer, which allows the reaction to progress. In the case of benzyl chloride, in which electron transfer is rate determining, deprotonation by the amine is coupled to the electron-transfer step.
- Maity, Sandeepan,Hoz, Shmaryahu
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supporting information
p. 18394 - 18400
(2015/12/24)
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- An unsymmetrical iron catalyst for the asymmetric transfer hydrogenation of ketones
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A new iron(II)(Ph2P-NH-N-PCy2) complex with a dicyclohexylphosphino group trans to the NH group was found to catalyze the asymmetric transfer hydrogenation of a variety of ketones with high enantioselectivity.
- Smith, Samantha A.M.,Morris, Robert H.
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supporting information
p. 1775 - 1779
(2015/06/16)
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- Enabling catalytic ketone hydrogenation by frustrated lewis pairs
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Hydrogenation of alkyl and aryl ketones using H2 is catalytically achieved in 18 examples using 5 mol % B(C6F5)3 in an ethereal solvent. In these cases the borane and ether behave as a frustrated Lewis pair to activate H2 and effect the reduction.
- Mahdi, Tayseer,Stephan, Douglas W.
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supporting information
p. 15809 - 15812
(2015/02/19)
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- Novel half-sandwich η5-Cp *-rhodium(III) and η5-Cp *-ruthenium(II) complexes bearing bis(phosphino)amine ligands and their use in the transfer hydrogenation of aromatic ketones
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Two new half-sandwich η5-Cp*-rhodium(III) and η5-Cp*-ruthenium(II) complexes have been prepared from corresponding bis(phosphino)amine ligands, thiophene-2-(N,N- bis(diphenylphosphino)methylamine) or furfuryl-2-(N,N-bis(diphenylphosphino) amine). Structures of the new complexes have been elucidated by multinuclear one- and two-dimensional NMR spectroscopy, elemental analysis and IR spectroscopy. These Cp*-rhodium(III) and Cp*-ruthenium(II) complexes bearing bis(phosphino)amine ligands were successfully applied to transfer hydrogenation of various ketones by 2-propanol. Copyright
- Ok, Fatih,Aydemir, Murat,Durap, Feyyaz
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- Zincocene and dizincocene N-heterocyclic carbene complexes and catalytic hydrogenation of imines and ketones
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The N-heterocyclic carbene (NHC) adducts Zn(CpR) 2(NHC)] (CpR=C5HMe4, C 5H4SiMe3; NHC=ItBu, IDipp (Dipp=2,6- diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*2] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh2)2(aItBu)]2 was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated ZnI adducts [Zn2Cp* 2(NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of 13C NMR spectroscopic and X-ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp* 2] with H2 to give [Zn2Cp*2] is discussed.
- Jochmann, Phillip,Stephan, Douglas W.
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supporting information
p. 8370 - 8378
(2014/07/08)
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- A well-defined monomeric aluminum complex as an efficient and general catalyst in the Meerwein-Ponndorf-Verley reduction
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The metal-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction allows for the mild and sustainable reduction of aldehydes and ketones but has not found widespread application in organic synthesis due to the high catalyst loading often required to obtain satisfactory yields of the reduced product. We report here on the synthesis and structure of a sterically extremely overloaded siloxide-supported aluminum isopropoxide capable of catalytically reducing a wide range of aldehydes and ketones (52 examples) in excellent yields under mild conditions and with low catalyst loadings. The unseen activity of the developed catalyst system in MPV reductions is due to its unique monomeric nature and the neutral donor isopropanol weakly coordinating to the aluminum center. The present work implies that monomeric aluminum alkoxide catalysts may be attractive alternatives to transition-metalbased systems for the selective reduction of aldehydes and ketones to primary and secondary alcohols.
- McNerney, Brian,Whittlesey, Bruce,Cordes, David B.,Krempner, Clemens
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supporting information
p. 14959 - 14964
(2015/01/08)
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- Nonmetal catalyzed hydrogenation of carbonyl compounds
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Solutions of the Lewis acid B(C6F5)3 in 1,4-dioxane are found to effectively catalyze the hydrogenation of a variety of ketones and aldehydes. These reactions, the first to allow entirely metal-free catalytic hydrogenation of carbonyl groups under relatively mild reaction conditions, are found to proceed via a "frustrated Lewis pair" mechanism in which the solvent, a weak Bronsted base yet moderately strong donor, plays a pivotal role.
- Scott, Daniel J.,Fuchter, Matthew J.,Ashley, Andrew E.
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supporting information
p. 15813 - 15816
(2015/02/19)
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- Iron(II) complexes containing unsymmetrical P-N-P′ pincer ligands for the catalytic asymmetric hydrogenation of ketones and imines
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After their treatment with LiAlH4 and then alcohol, new iron dicarbonyl complexes mer-trans-[Fe(Br)(CO)2(P-CH=N-P′)][BF 4] (where P-CH=N-P′ = R2PCH2CH=NCH 2CH2PPh2 and R = Cy or iPr or P-CH=N-P′ = (S,S)- Cy2PCH2CH=NCH(Me)CH(Ph)PPh2) are catalysts for the hydrogenation of ketones in THF solvent with added KOtBu at 50 C and 5 atm H2. Complexes with R = Ph are not active. With the enantiopure complex, alcohols are produced with an enantiomeric excess of up to 85% (S) at TOF up to 2000 h-1, TON of up to 5000, for a range of ketones. An activated imine is hydrogenated to the amine in 90% ee at a TOF 20 h-1and TON 99. This is a significant advance in asymmetric pressure hydrogenation using iron. The complexes are prepared in two steps: (1) a one-pot reaction of phosphonium dimers ([cyclo-(PR2CH2CH(OH) -)2][Br]2), KOtBu, FeBr2, and Ph2PCH2CH2NH2 (or (S,S)-Ph 2PCH(Ph)CH(Me)NH2 for the enantiopure complex) in THF under a CO atmosphere to produce the complexes cis- and trans-[Fe(Br) 2(CO)(P-CH=N-P′)]; (2) the reaction of these with AgBF 4 under CO(g) to afford the dicarbonyl complexes in high yield (50-90%). NMR and DFT studies of the process of precatalyst activation show that the dicarbonyl complexes are converted first to hydride-aluminum hydride complexes where the imine of the P-CH=N-P′ ligand is reduced to an amide [P-CH2N-P′]- with aluminum hydrides still bound to the nitrogen. These hydride species react with alcohol to give monohydride amine iron compounds FeH(OR′)(CO)(P-CH2NH-P′), R′ = Me, CMe2Et as well as the iron(0) complex Fe(CO)2(P-CH 2NH-P′) under certain conditions.
- Lagaditis, Paraskevi O.,Sues, Peter E.,Sonnenberg, Jessica F.,Wan, Kai Yang,Lough, Alan J.,Morris, Robert H.
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supporting information
p. 1367 - 1380
(2014/02/14)
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