Markus Drees

Electrocatalytic hydrogenation of 1‐octene as non‐activated model substrate with neutral water as H‐donor is reported, using [(^tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a k_obs of 87 s⁻¹. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl⁻ and afford the highly reactive anionic Ir(I) hydride complex [(^tBuPCP)Ir(H)]⁻ (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(^tBuPCP)Ir(H)₂] (3) in 88 % FE from the reaction of 2 with H₂O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro‐hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H₂ formation. Even in strongly alkaline conditions (Bu₄NOH added), the electro‐hydrogenation of 1‐octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H₂O activation, reminiscent to transfer hydrogenation pathways, instead of classical H⁺ reduction. DFT calculations confirmed oxidative addition of H₂O as a key step in this context.

Electrocatalytic hydrogenation of 1‐octene as non‐activated model substrate with neutral water as H‐donor is reported, using [(^tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a k_obs of 87 s⁻¹. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl⁻ and afford the highly reactive anionic Ir(I) hydride complex [(^tBuPCP)Ir(H)]⁻ (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(^tBuPCP)Ir(H)₂] (3) in 88 % FE from the reaction of 2 with H₂O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro‐hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H₂ formation. Even in strongly alkaline conditions (Bu₄NOH added), the electro‐hydrogenation of 1‐octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H₂O activation, reminiscent to transfer hydrogenation pathways, instead of classical H⁺ reduction. DFT calculations confirmed oxidative addition of H₂O as a key step in this context.

Molecular perovskites are important materials in the area of barocalorics, improper ferroelectrics and ferroelastics, where the search for principles that link composition, structure and mechanical properties is a key challenge. Herein, we report the synthesis of a new series of dicyanamide-based molecular perovskites [A]Ni(C2N3)3, where A+ is a range of alkylated piperidinium cations. We use this new family to explore how A+ cations determine their mechanical response by measuring the bulk modulus (B) – using high-pressure powder X-ray diffraction. Within the series, we find a positive correlation between the network distortions of the pseudocubic [Ni(C2N3)3]– network and B. Furthermore, we show that we can tune framework distortions, and therefore B, by synthesising A-site solid solutions. The applied methodology is a blueprint for linking framework distortions and mechanical properties in network materials and guides us toward principles for designing macroscopic properties via systematic compositional changes in molecular perovskites.

With the aim to design new water-soluble organometallic Ru(II) complexes acting as anticancer agents catalysing transfer hydrogenation (TH) reactions with biomolecules, we have synthesized four Ru(II) monocarbonyl complexes (1-4) featuring the 1,4-bis(diphenylphosphino)butane (dppb) ligand and different bidentate nitrogen (N^N) ligands, of general formula [Ru(OAc)CO(dppb)(N^N)]n (n = +1, 0; OAc = acetate). The compounds have been characterised by different methods, including 1H and 31P NMR spectroscopy, electrochemistry as well as single crystals X-ray diffraction in the case of 1 and 4. The compounds have also been studied for their hydrolysis in aqueous environment, and for the catalytic regioselective reduction of NAD+ to 1,4-NADH in aqueous solution with sodium formate as hydride source. Moreover, the stoichiometric and catalytic oxidation of 1,4-NADH have also been investigated by UV-Visible spectrophotometry and NMR spectroscopy. Overall, initial structure-activity relationships could be inferred which point towards the influence of the extension of the aromatic N^N ligand in the cationic complexes 1-3 on the TH in both reduction/oxidation processes. The neutral complex 4, featuring a picolinamidate N^N ligand, stands out as the most active catalyst for the reduction of NAD+, while being completely inactive towards NADH oxidation. The compound can also convert pyruvate into lactate in the presence of formate, albeit with scarce efficiency. In any case, for all compounds, Ru(II) hydride intermediates could be observed and even isolated in the case of complexes 1-3. Together, insight from the kinetic and electrochemical characterization suggests that, in the case of Ru(II) complexes 1-3, catalytic NADH oxidation sees the H-transfer from 1,4-NADH as the rate limiting step, whereas for NAD+ hydrogenation with formate as the H-donor, the rate limiting step is the transfer of the ruthenium hydride to the NAD+ substrate. The latter is further modulated by the presence of di-cationic aquo- or mono-cationic hydroxo-species of complexes 1-3. Instead, compound 4, stable with respect to hydrolysis in aqueous solution, appears to operate via a different mechanism. Finally, the anticancer activity and ability to form reactive oxygen species (ROS) of complexes 1-3 have been studied in cancerous and non-tumorigenic cells in vitro. Noteworthy, the conversion of aldehydes to alcohols could be achieved by the three Ru(II) catalysts in living cells, as assessed by fluorescence microscopy. Furthermore, the formation of Ru(II) hydride intermediate upon treatment of cancer cell extracts with complex 3 has been detected by 1H NMR spectroscopy. Overall, this study paves the way to the application of non-arene based organometallic complexes as TH catalysts in biological environment.

We propose that chemical interactions in the coordination compound Pd(acac)₂ can be mapped on a wine-rack network, explaining linear negative thermal expansion in a classic coordination compound based on concepts known from network materials.

Mixed precious-group metal–organic frameworks [Ru _x Rh _3−x (BTC) ₂ ] of the HKUST-1-type were synthesized and characterized (PXRD, BET, IR, Raman, XPS, TGA, SS-UV/VIS, EA, and HR-TEM).

Unlike different types of Lewis pairs as polymerization catalysts for acrylic monomers, organometallic aluminum(III) compounds are reported that show a surprisingly high polymerization activity even without an additional Lewis base. DFT calculations, end group analysis and kinetic investigations clearly suggest a main group element (MGE) group transfer polymerization (GTP) mechanism analogous to the known metal‐mediated GTP mechanism. The novel catalysts perform a precision polymerization of a broad variety of monomers, ranging from 2‐isopropenyl‐2‐oxazoline to tert‐butylmethacrylate and N,N‐dimethylacrylamide. Additionally, extended Michael‐type structures like 4‐vinyl pyridine are accessible. Especially the Al(III) half‐metallocenes show an almost quantitative initiator efficiency, and, combined with the living character of the polymerization reactions, they enable the synthesis of block copolymers, even with unconventional monomers like vinyl phosphonates.