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- ItemA chemical reaction controlled by light-activated molecular switches based on heterocyclopentanediyls(Cambridge : RSC, 2019) Bresien, Jonas; Kröger-Badge, Thomas; Lochbrunner, Stefan; Michalik, Dirk; Müller, Henrik; Schulz, Axel; Zander, EdgarMolecular switches are molecules that can reversibly be shifted between at least two stable states with different physical and chemical properties, making them interesting for application as chemical sensors or molecular machines. We recently discovered that five-membered, cyclic biradicals based on group 15 elements are efficient and robust photochemical switches that can be activated by red light. The quantum yield of the photo-isomerization is as high as 24.6%, and the thermal equilibration of the photo-activation product proceeds rapidly at ambient temperature. The fully reversible process was studied by experimental and high-level ab initio techniques. We could further demonstrate that the biradical character could be completely turned on and off, so the system could be applied to control chemical equilibria that involve activation products of the cyclic biradicals. © 2019 The Royal Society of Chemistry.
- ItemZwitterionic and biradicaloid heteroatomic cyclopentane derivatives containing different group 15 elements(Cambridge : RSC, 2015) Hinz, Alexander; Schulz, Axel; Villinger, AlexanderThe formal cyclopentane-1,3-diyl derivatives [E1(μ-NTer)2({E2C} = NDmp)] (Ter = 2,6-dimesityl-phenyl, Dmp = 2,6-dimethylphenyl) were prepared by 1,1-insertion of CNDmp into the N–E2 bond of [E1(μ-NTer)2E2] (E1 = N, P; E2 = P, As). The insertion does not occur for E1 = E2 = As or E2 = Sb. Dependent on the choice of formal radical centres E, either a biradicaloid or a zwitterion was obtained. The biradicaloid features a P and an As radical center and its biradical character was established by computations as well as characteristic reactivity with respect to the formation of a housane derivative and the activation of molecules bearing multiple bonds, which was demonstrated using the example of PCtBu. In contrast, the formally N,As- and N,P-centered biradicaloids are better regarded as zwitterionic species in accord with computations and diminished reactivity, as neither housane formation nor activation of multiple bonds could be observed.
- ItemParahydrogen-induced polarization with a metal-free P–P biradicaloid(Cambridge : RSC Publ., 2019) Zhivonitko, Vladimir V.; Bresien, Jonas; Schulz, Axel; Koptyug, Igor V.Metal-free H2 activations are unusual but interesting for catalytic transformations, particularly in parahydrogen-based nuclear spin hyperpolarization techniques. We demonstrate that metal-free singlet phosphorus biradicaloid, [P(μ-NTer)]2, provides pronounced 1H and 31P hyperpolarization while activating the parahydrogen molecules. A brief analysis of the resulting NMR signals and the important kinetic parameters are presented.