03 Fakultät Chemie

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4

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Author: search.filters.author.Allgaier, AlexanderSubject: search.filters.subject.540

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    Hydrogen spillover through hydride transfer : the reaction of ZnO and ZrO2 with strong hydride donors
    (2024) Benz, Michael; Bunjaku, Osman; Nowakowski, Michal; Allgaier, Alexander; Biswas, Indro; Slageren, Joris van; Bauer, Matthias; Estes, Deven P.
    Hydrogen spillover, transfer of H2 from a metal surface to a support (often metal oxides), is pivotal for many heterogeneous catalytic processes, including Cu/ZnO and Cu/ZrO2 catalyzed methanol synthesis. Little is known about hydrogen spillover on ZnO or ZrO2, due to the high complexity of the metal-metal oxide interface. Here, we model hydrogen spillover on ZnO and ZrO2 by reacting them with molecular metal hydrides to see how the properties of the hydrides affect hydrogen spillover. While the good H· donors HV(CO)4dppe (1) and CpCr(CO)3H (2) do not react with the metal oxide surfaces, the strong hydride donors iBu2AlH (3), Cp2ZrHCl (4), and [HCu(PPh3)]6 (5) do reduce ZnO and ZrO2 to give defect sites with the same EPR signatures as obtained via hydrogen spillover. We also observe new M-O bonds to the surface using X-ray absorption spectroscopy (XAS). We propose that these metal oxides undergo hydrogen spillover via initial hydride transfer followed by tautomerization of the surface hydride, giving reduced sites and OH bonds. This mechanism is in contrast to the traditional spillover mechanism involving discrete proton- and electron transfer steps. We also observe that ZnO is easier to reduce than ZrO2, explaining the difficulty observing spillover on Cu/ZrO2.
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    Visible‐light activation of diorganyl bis(pyridylimino) isoindolide aluminum(III) complexes and their organometallic radical reactivity
    (2024) Wenzel, Jonas O.; Werner, Johannes; Allgaier, Alexander; Slageren, Joris van; Fernández, Israel; Unterreiner, Andreas‐Neil; Breher, Frank
    We report on the synthesis and characterization of a series of (mostly) air‐stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible‐light excitation. The redox non‐innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon‐centered radicals. The photo‐induced homolytic cleavage of the Al-C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin‐free Giese‐type reactions and carbonyl alkylations under ambient conditions, which both indicated radical‐polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench‐stable aluminum organometallics.