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- ItemHydrolysis Stability of Bidentate Phosphites Utilized as Modifying Ligands in the Rh-Catalyzed n-Regioselective Hydroformylation of Olefins(Washington, DC : ACS, 2016) Zhang, Baoxin; Jiao, Haijun; Michalik, Dirk; Kloß, Svenja; Deter, Lisa Marie; Selent, Detlef; Spannenberg, Anke; Franke, Robert; Börner, ArminThe stability of ligands and catalysts is an almost neglected issue in homogeneous catalysis, but it is crucial for successful application of this methodology in technical scale. We have studied the effect of water on phosphites, which are the most applied cocatalysts in the n-regioselective homogeneous Rh-catalyzed hydroformylation of olefins. The stability of the bidentate nonsymmetrical diphosphite L1, as well as its two monophosphite constituents L2 and L3, toward hydrolysis was investigated by means of in situ NMR spectroscopy under similar conditions as applied in industry. Hydrolysis pathways, intermediates, and kinetics were clarified. DFT calculations were used to support the experimentally found data. The acylphosphite unit L2, which reacts with water in an unselective manner, was proven to be much less stable than the phenolphosphite L3. The stability of the bidentate ligand L1 can be therefore mainly attributed to its phenolphosphite moiety. With an excess of water, the hydrolysis of L1 and L2 as well as their Rh-complexes is first-order with respect to the phosphite. Surprisingly, coordination to Rh significantly stabilizes the monodentate ligand L2, while in strong contrast, the bidentate ligand L1 decomposes faster in the Rh complex. NMR spectroscopy provided evidence for the existence of species from decomposition of phosphites, which can likewise coordinate as ligands to the metal. Electron-withdrawing groups in the periphery of the acylphosphite moiety decrease the stability of L1, whereas 3,5-disubstituted salicylic acid derivatives with bulky groups showed superior stability. These modifications of L1 also give rise to different catalytic performances in the n-regioselective hydroformylation of n-octenes and 2-pentene, from which the 3,5-di-t-butyl-substituted ligand offered a higher n-regioselectivity accompanied by a lowering of the reaction rate in comparison to the parent ligand L1.
- ItemA General Regioselective Synthesis of Alcohols by Cobalt-Catalyzed Hydrogenation of Epoxides(Weinheim : Wiley-VCH, 2020) Liu, Weiping; Leischner, Thomas; Li, Wu; Junge, Kathrin; Beller, MatthiasA straightforward methodology for the synthesis of anti-Markovnikov-type alcohols is presented. By using a specific cobalt triphos complex in the presence of Zn(OTf)2 as an additive, the hydrogenation of epoxides proceeds with high yields and selectivities. The described protocol shows a broad substrate scope, including multi-substituted internal and terminal epoxides, as well as a good functional-group tolerance. Various natural-product derivatives, including steroids, terpenoids, and sesquiterpenoids, gave access to the corresponding alcohols in moderate-to-excellent yields. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemA Stable Manganese Pincer Catalyst for the Selective Dehydrogenation of Methanol(Weinheim : Wiley-VCH, 2016-12-2) Andérez-Fernández, María; Vogt, Lydia K.; Fischer, Steffen; Zhou, Wei; Jiao, Haijun; Garbe, Marcel; Elangovan, Saravanakumar; Junge, Kathrin; Junge, Henrik; Ludwig, Ralf; Beller, MatthiasFor the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long-term stability was demonstrated for the Mn-PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.
- ItemTowards a methanol economy based on homogeneous catalysis: methanol to H2 and CO2 to methanol(Cambridge : Soc., 2015) Alberico, E.; Nielsen, M.The possibility to implement both the exhaustive dehydrogenation of aqueous methanol to hydrogen and CO2 and the reverse reaction, the hydrogenation of CO2 to methanol and water, may pave the way to a methanol based economy as part of a promising renewable energy system. Recently, homogeneous catalytic systems have been reported which are able to promote either one or the other of the two reactions under mild conditions. Here, we review and discuss these developments.
- ItemPNPN-H in Comparison to other PNP, PNPN and NPNPN Ligands for the Chromium Catalyzed Selective Ethylene Oligomerization(Weinheim : Wiley-VCH Verlag, 2019) Rosenthal, UweMany examples exist for the chromium catalyzed selective ethylene oligomerization in which the influence of ligands is essential for the formation of products. Regarding the tri- and tetramerization to 1-hexene or 1-octene mostly PNP ligands are responsible for the tetra- and some of such modified ligands for the trimerization. A very special case in these reactions are PNPN−H ligands, showing in most cases highly selective trimerization of ethylene to 1-hexene. In this review all existing published information about these PNPN−H ligands is accumulated and compared to some other related PNP, PNPN and NPNPN ligands in the chromium catalyzed selective ethylene oligomerization with respect to the switch from tetra- to trimerization and back by different substituent pattern of PNP ligand. Mechanistic information and arguments are collected to explain the switch from tetra- to trimerization and back by substitution of functional groups in classical PNP to PNPN−H ligands as a result of mono- and dinuclear catalytic species. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemRecycling and Separation of Homogeneous Catalyst from Aqueous Multicomponent Mixture by Organic Solvent Nanofiltration(Basel : MDPI, 2021) Schnoor, J.-Kilian; Bettmer, Jens; Kamp, Johannes; Wessling, Matthias; Liauw, Marcel A.Organic solvent nanofiltration (OSN) has evolved to an established recycling method for homogeneous catalysts. However, commercial availability has not circumvented the need for classification and the scoping of possible applications for specific solvent mixtures. Therefore, Evonik’s DuraMem® 300 was assessed for the recycling of magnesium triflate at two transmembrane pressures from a mixture of ethanol, ethyl acetate and water. Catalyst retention up to 98% and permeability of up to 4.44·10−1∙L∙bar−1∙m−2∙h−1 were possible when less than 25% ethyl acetate was in the mixture. The retention of some of the components in the ternary mixture was observed while others were enriched, making the membrane also suitable for fractioning thereof.
- ItemNon-Pincer-Type Manganese Complexes as Efficient Catalysts for the Hydrogenation of Esters(Weinheim : Wiley-VCH, 2017-4-21) van Putten, Robbert; Uslamin, Evgeny A.; Garbe, Marcel; Liu, Chong; Gonzalez-de-Castro, Angela; Lutz, Martin; Junge, Kathrin; Hensen, Emiel J. M.; Beller, Matthias; Lefort, Laurent; Pidko, Evgeny A.Catalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub-stoichiometric amounts of KOtBu base.
- ItemZirconium-Catalyzed Atom-Economical Synthesis of 1,1-Diborylalkanes from Terminal and Internal Alkenes(Weinheim : Wiley-VCH, 2020) Wang, Xianjin; Cui, Xin; Li, Sida; Wang, Yue; Xia, Chungu; Jiao, Haijun; Wu, LipengA general and atom-economical synthesis of 1,1-diborylalkanes from alkenes and a borane without the need for an additional H2 acceptor is reported for the first time. The key to our success is the use of an earth-abundant zirconium-based catalyst, which allows a balance of self-contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H2 acceptor, which was required in other reported systems. Furthermore, substrates such as simple long-chain aliphatic alkenes that did not react before also underwent 1,1-diboration in our system. Significantly, the unprecedented 1,1-diboration of internal alkenes enabled the preparation of 1,1-diborylalkanes. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemPalladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds(Weinheim : Wiley-VCH, 2021) Ge, Yao; Ye, Fei; Yang, Ji; Spannenberg, Anke; Jiao, Haijun; Jackstell, Ralf; Beller, MatthiasA direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon–carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
- ItemCatalytic, Kinetic, and Mechanistic Insights into the Fixation of CO2 with Epoxides Catalyzed by Phenol-Functionalized Phosphonium Salts(Weinheim : Wiley-VCH, 2021) Hu, Yuya; Wei, Zhihong; Frey, Anna; Kubis, Christoph; Ren, Chang-Yue; Spannenberg, Anke; Jiao, Haijun; Werner, ThomasA series of hydroxy-functionalized phosphonium salts were studied as bifunctional catalysts for the conversion of CO2 with epoxides under mild and solvent-free conditions. The reaction in the presence of a phenol-based phosphonium iodide proceeded via a first order rection kinetic with respect to the substrate. Notably, in contrast to the aliphatic analogue, the phenol-based catalyst showed no product inhibition. The temperature dependence of the reaction rate was investigated, and the activation energy for the model reaction was determined from an Arrhenius-plot (Ea =39.6 kJ mol-1 ). The substrate scope was also evaluated. Under the optimized reaction conditions, 20 terminal epoxides were converted at room temperature to the corresponding cyclic carbonates, which were isolated in yields up to 99 %. The reaction is easily scalable and was performed on a scale up to 50 g substrate. Moreover, this method was applied in the synthesis of the antitussive agent dropropizine starting from epichlorohydrin and phenylpiperazine. Furthermore, DFT calculations were performed to rationalize the mechanism and the high efficiency of the phenol-based phosphonium iodide catalyst. The calculation confirmed the activation of the epoxide via hydrogen bonding for the iodide salt, which facilitates the ring-opening step. Notably, the effective Gibbs energy barrier regarding this step is 97 kJ mol-1 for the bromide and 72 kJ mol-1 for the iodide salt, which explains the difference in activity.