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- ItemLigand-Controlled Palladium-Catalyzed Carbonylation of Alkynols : Highly Selective Synthesis of α-Methylene-β-Lactones(Weinheim : Wiley-VCH, 2020) Ge, Yao; Ye, Fei; Liu, Jiawang; Yang, Ji; Spannenberg, Anke; Jiao, Haijun; Jackstell, Ralf; Beller, MatthiasThe first general and regioselective Pd-catalyzed cyclocarbonylation to give α-methylene-β-lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N-arylated imidazole (L11) in the presence of Pd(MeCN)2Cl2 as pre-catalyst. A variety of easily available alkynols provide under additive-free conditions the corresponding α-methylene-β-lactones in moderate to good yields with excellent regio- and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemCobalt-Catalyzed Aqueous Dehydrogenation of Formic Acid(Weinheim : Wiley-VCH, 2019) Zhou, Wei; Wei, Zhihong; Spannenberg, Anke; Jiao, Haijun; Junge, Kathrin; Junge, Henrik; Beller, MatthiasAmong the known liquid organic hydrogen carriers, formic acid attracts increasing interest in the context of safe and reversible storage of hydrogen. Here, the first molecularly defined cobalt pincer complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial for catalytic activity is the use of the specific complex 3. Compared to related ruthenium and manganese complexes 7 and 8, this optimal cobalt complex showed improved performance. DFT computations support an innocent non-classical bifunctional outer-sphere mechanism on the triplet state potential energy surface. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemCooperative catalytic methoxycarbonylation of alkenes: Uncovering the role of palladium complexes with hemilabile ligands(Cambridge : RSC, 2018) Dong, Kaiwu; Sang, Rui; Wei, Zhihong; Liu, Jie; Dühren, Ricarda; Spannenberg, Anke; Jiao, Haijun; Neumann, Helfried; Jackstell, Ralf; Franke, Robert; Beller, MatthiasMechanistic studies of the catalyst [Pd2(dba)3/1,1′-bis(tert-butyl(pyridin-2-yl)phosphanyl)ferrocene, L2] for olefin alkoxycarbonylation reactions are described. X-ray crystallography reveals the coordination of the pyridyl nitrogen atom in L2 to the palladium center of the catalytic intermediates. DFT calculations on the elementary steps of the industrially relevant carbonylation of ethylene (the Lucite α-process) indicate that the protonated pyridyl moiety is formed immediately, which facilitates the formation of the active palladium hydride complex. The insertion of ethylene and CO into this intermediate leads to the corresponding palladium acyl species, which is kinetically reversible. Notably, this key species is stabilized by the hemilabile coordination of the pyridyl nitrogen atom in L2. The rate-determining alcoholysis of the acyl palladium complex is substantially facilitated by metal-ligand cooperation. Specifically, the deprotonation of the alcohol by the built-in base of the ligand allows a facile intramolecular nucleophilic attack on the acyl palladium species concertedly. Kinetic measurements support this mechanistic proposal and show that the rate of the carbonylation step is zero-order dependent on ethylene and CO. Comparing CH3OD and CH3OH as nucleophiles suggests the involvement of (de)protonation in the rate-determining step.
- ItemHomogeneous cobalt-catalyzed reductive amination for synthesis of functionalized primary amines([London] : Nature Publishing Group UK, 2019) Murugesan, Kathiravan; Wei, Zhihong; Chandrashekhar, Vishwas G.; Neumann, Helfried; Spannenberg, Anke; Jiao, Haijun; Beller, Matthias; Jagadeesh, Rajenahally V.The development of earth abundant 3d metal-based catalysts continues to be an important goal of chemical research. In particular, the design of base metal complexes for reductive amination to produce primary amines remains as challenging. Here, we report the combination of cobalt and linear-triphos (bis(2-diphenylphosphinoethyl)phenylphosphine) as the molecularly-defined non-noble metal catalyst for the synthesis of linear and branched benzylic, heterocyclic and aliphatic primary amines from carbonyl compounds, gaseous ammonia and hydrogen in good to excellent yields. Noteworthy, this cobalt catalyst exhibits high selectivity and as a result the -NH2 moiety is introduced in functionalized and structurally diverse molecules. An inner-sphere mechanism on the basis of the mono-cationic [triphos-CoH]+ complex as active catalyst is proposed and supported with density functional theory computation on the doublet state potential free energy surface and H2 metathesis is found as the rate-determining step.
- 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