Universität Stuttgart
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Item Open Access Tetra-μ3-iodido-tetrakis[(tri-n-butylphosphane-κP)copper(I)](2014) Klenk, Simon; Frey, Wolfgang; Bubrin, Martina; Laschat, SabineTetrameric phosphane complexes of copper(I) halides are extensively used as reagents for copper-mediated conjugate additions. Furthermore, theoretical interest stems from the fact that all group 11 elements in the oxidation state +1 are prone to form clusters with potential metal-metal distances. Thus, theoretical work on such complexes (XCuPR3)4 has been carried out to study structures and stabilities in detail. However, the plethora of structural information on these compounds came from X-ray crystal structure analyses. Although the known tri-n-butyl phosphane complex [n-Bu3PCuI]4 had already been characterized by using X-ray crystallography, no atomic coordinates, bond lengths or bond angles were reported. Thus, we reinvestigated the crystal structure of [n-Bu3PCuI]4. We were able to confirm the previously postulated tetrameric complex with a distorted heterocubane structure similar to the AsEt3 derivative.Item Open Access Precursor molecules for 1,2-diamidobenzene containing cobalt(ii), nickel(ii) and zinc(ii) complexes : synthesis and magnetic properties(2024) Hunger, David; Suhr, Simon; Bayer, Valentin; Albold, Uta; Frey, Wolfgang; Sarkar, Biprajit; Slageren, Joris vanMolecular magnetic materials based on 1,2-diamidobenzenes are well known and have been intensively studied both experimentally and computationally. They possess interesting magnetic properties as well as redox activity. In this work, we present the synthesis and investigation of potent synthons for constructing discrete metal-organic architectures featuring 1,2-diamidobenzene-coordinated metal centres. The synthons feature weakly bound dimethoxyethane (dme) ligands in addition to the 1,2-diamidobenzene. We characterize these complexes and investigate their magnetic properties by means of static and dynamic magnetometry and high-field electron paramagnetic resonance (HFEPR). Interestingly, the magnetic and magnetic resonance data strongly suggest a dimeric formulation of these complexes, viz. [MII(bmsab)(dme)]2 (bmsab = 1,2-bis(methanesulfonamido)benzene; dme = dimethoxyethane) with M = Co, Ni, Zn. A large negative D-value of -60 cm-1 was found for the Co(ii) synthon and an equally large negative D of -50 cm-1 for the Ni(ii) synthon. For Co(ii), the sign of the D-value is the same as that found for the known bis-diamidobenzene complexes of this ion. In contrast, the negative D-value for the Ni(ii) complex is unexpected, which we explain in terms of a change in coordination number. The heteroleptic Co(ii) complex presented here does not feature slow relaxation of the magnetization, in contrast to the homoleptic Co(ii) 1,2-diamidobenzene complex.Item Open Access Cooperative Lewis acid‐1,2,3‐triazolium‐aryloxide catalysis : pyrazolone addition to nitroolefins as entry to diaminoamides(2023) Wanner, Daniel M.; Becker, Patrick M.; Suhr, Simon; Wannenmacher, Nick; Ziegler, Slava; Herrmann, Justin; Willig, Felix; Gabler, Julia; Jangid, Khushbu; Schmid, Juliane; Hans, Andreas C.; Frey, Wolfgang; Sarkar, Biprajit; Kästner, Johannes; Peters, RenéPyrazolones represent an important structural motif in active pharmaceutical ingredients. Their asymmetric synthesis is thus widely studied. Still, a generally highly enantio- and diastereoselective 1,4-addition to nitroolefins providing products with adjacent stereocenters is elusive. In this article, a new polyfunctional CuII-1,2,3-triazolium-aryloxide catalyst is presented which enables this reaction type with high stereocontrol. DFT studies revealed that the triazolium stabilizes the transition state by hydrogen bonding between C(5)-H and the nitroolefin and verify a cooperative mode of activation. Moreover, they show that the catalyst adopts a rigid chiral cage/pore structure by intramolecular hydrogen bonding, by which stereocontrol is achieved. Control catalyst systems confirm the crucial role of the triazolium, aryloxide and CuII, requiring a sophisticated structural orchestration for high efficiency. The addition products were used to form pyrazolidinones by chemoselective C=N reduction. These heterocycles are shown to be valuable precursors toward β,γ’-diaminoamides by chemoselective nitro and N-N bond reductions. Morphological profiling using the Cell painting assay identified biological activities for the pyrazolidinones and suggest modulation of DNA synthesis as a potential mode of action. One product showed biological similarity to Camptothecin, a lead structure for cancer therapy.Item Open Access A practical and robust zwitterionic cooperative Lewis acid/acetate/benzimidazolium catalyst for direct 1,4‐additions(2023) Hans, Andreas C.; Becker, Patrick M.; Haußmann, Johanna; Suhr, Simon; Wanner, Daniel M.; Lederer, Vera; Willig, Felix; Frey, Wolfgang; Sarkar, Biprajit; Kästner, Johannes; Peters, RenéA catalyst type is disclosed allowing for exceptional efficiency in direct 1,4‐additions. The catalyst is a zwitterionic entity, in which acetate binds to CuII, which is formally negatively charged and serving as counterion for benzimidazolium. All 3 functionalities are involved in the catalytic activation. For maleimides productivity was increased by a factor >300 compared to literature (TONs up to 6700). High stereoselectivity and productivity was attained for a broad range of other Michael acceptors as well. The polyfunctional catalyst is accessible in only 4 steps from N‐Ph‐benzimidazole with an overall yield of 96 % and robust during catalysis. This allowed to reuse the same catalyst multiple times with nearly constant efficiency. Mechanistic studies, in particular by DFT, give a detailed picture how the catalyst operates. The benzimidazolium unit stabilizes the coordinated enolate nucleophile and prevents that acetate/acetic acid dissociate from the catalyst.