2017, Sherborne, Grant J., Adomeit, Sven, Menzel, Robert, Rabeah, Jabor, Brückner, Angelika, Fielding, Mark R., Willans, Charlotte E., Nguyen, Bao N.

A mechanistic investigation of Ullmann-Goldberg reactions using soluble and partially soluble bases led to the identification of various pathways for catalyst deactivation through (i) product inhibition with amine products, (ii) by-product inhibition with inorganic halide salts, and (iii) ligand exchange by soluble carboxylate bases. The reactions using partially soluble inorganic bases showed variable induction periods, which are responsible for the reproducibility issues in these reactions. Surprisingly, more finely milled Cs2CO3 resulted in a longer induction period due to the higher concentration of the deprotonated amine/amide, leading to suppressed catalytic activity. These results have significant implications on future ligand development for the Ullmann-Goldberg reaction and on the solid form of the inorganic base as an important variable with mechanistic ramifications in many catalytic reactions.

2020, Włodarczyk-Biegun, M.K., Paez, J.I., Villiou, M., Feng, J., Del Campo, A.

In this paper we explore the printability of reversible networks formed by catechol functionalized PEG solutions and metal cations (Al3+, Fe3+ or V3+). The printability and shape fidelity were dependent on the ink composition (metal ion type, pH, PEG molecular weight) and printing parameters (extrusion pressure and printing speed). The relaxation time, recovery rate and viscosity of the inks were analyzed in rheology studies and correlated with thermodynamic and ligand exchange kinetic constants of the dynamic bonds and the printing performance (i.e. shape fidelity of the printed structures). The relevance of the relaxation time and ligand exchange kinetics for printability was demonstrated. Cells seeded on the materials crosslinked with Al3+, Fe3+ ions were viable and revealed well-spread morphologies during 7 day culture, indicating the potential of the formulations to be used as inks for cell encapsulation. The proposed dynamic ink design offers significant flexibility for 3D bioprinting, and enables straightforward adjustment of the printable formulation to meet application-specific needs.

2019, Bläsing, Kevin, Labbow, Rene, Michalik, Dirk, Reiß, Fabian, Schul, Axel, Villinger, Alexander, Walker, Svenja

Attempts have been made to prepare salts with the labile tris(trimethylsilyl)chalconium ions, [(Me3Si)3E]+ (E=O, S), by reacting [Me3Si-H-SiMe3][B(C6F5)4] and Me3Si[CB] (CB−=carborate=[CHB11H5Cl6]−, [CHB11Cl11]−) with Me3Si-E-SiMe3. In the reaction of Me3Si-O-SiMe3 with [Me3Si-H-SiMe3][B(C6F5)4], a ligand exchange was observed in the [Me3Si-H-SiMe3]+ cation leading to the surprising formation of the persilylated [(Me3Si)2(Me2(H)Si)O]+ oxonium ion in a formal [Me2(H)Si]+ instead of the desired [Me3Si]+ transfer reaction. In contrast, the expected homoleptic persilylated [(Me3Si)3S]+ ion was formed and isolated as [B(C6F5)4]− and [CB]− salt, when Me3Si-S-SiMe3 was treated with either [Me3Si-H-SiMe3][B(C6F5)4] or Me3Si[CB]. However, the addition of Me3Si[CB] to Me3Si-O-SiMe3 unexpectedly led to the release of Me4Si with simultaneous formation of a cyclic dioxonium dication of the type [Me3Si-μO-SiMe2]2[CB]2 in an anion-mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me3Si)3E]+ and [(Me3Si)2(Me2(H)Si)E]+ ion formation are presented as well as mechanistic investigations on the template-driven transformation of the [(Me3Si)3E]+ ion into a cyclic dichalconium dication [Me3Si-μE-SiMe2]22+. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

2020, Fischer, Fabian, Pientka, Tobias, Jiao, Haijun, Spannenberg, Anke, Hapke, Marko

The efficient synthesis and structural characterisation of a series of novel CpCo(i)-olefin-phosphite/phosphoramidite complexes and their evaluation in catalytic cyclotrimerisation reactions are reported. The protocol for precatalyst synthesis is widely applicable to different P-containing ligands, especially phosphites and phosphoramidites, as well as acyclic and cyclic olefins. A selection of the prepared complexes was investigated towards their catalytic performance in [2 + 2 + 2] cycloaddition reactions of diynes and nitriles, as well as triynes. While revealing significant differences in reactivity, the most reactive precatalysts work even already at 75 °C. One of these precatalysts also proved its potential in exemplary (co)cyclotrimerisations towards functionalised pyridines and benzenes. The energetics of complex formation and exemplary ligand exchange with a substrate diyne were elucidated by theoretical calculations and compared with the catalytic reactivity. © 2020 The Royal Society of Chemistry.