Torsten Beweries

Biradical(oid)s are key intermediates in the formation and cleavage of chemical bonds, and their application as molecular switches is of particular interest. In contrast, tetraradical(oid)s remain far less explored, although they may, for example, consist of two biradical(oid) units. Herein, we report the synthesis of phosphorus-centered bi- and tetraradicaloids coordinated to group 4 metallocene fragments of titanium and zirconium. The target compounds were obtained via ring-expansion reactions of metallocene-substituted isonitriles with one or two equivalents of the biradicaloid [P(μ-NTer)]2, affording group 4 metallocene complexes bearing one or two bridged P-centered, five-membered heterocyclic biradicaloid units. These systems function as mono- and double-molecular switches, respectively, each based on a biradicaloid motif. Upon irradiation with light (638 nm), the biradicaloid heterocycles undergo transannular bond formation in one or both five-membered heterocyclic biradicaloid units, resulting in the generation of housane-type species. The photoinduced switching behavior as well as CO2 activation were investigated in solution by NMR and UV/Vis spectroscopy. Quantum-chemical calculations were further performed to examine the design of the isonitrile ligands, the mechanism of their insertion reactions, and the electronic structure and photoswitching behavior, supporting the experimental findings.

Formation of the sodium salt of phenol systematically lowers the hydrogenation enthalpy from sodium phenoxide to sodium cyclohexanolate, establishing a tunable thermodynamic pathway for hydrogen storage. Graphical abstract created with Perplexity AI, minor refinements made with GPT-5.6 Sol, OpenAI.

Without a vanadium alkylidyne, and using a dianionic allene bound to vanadium, we demonstrate how vanadatetrahedranes and vanadacyclobutadienes can be accessed and how these species can interconvert.

Plastic waste poses a major environmental challenge, yet it also represents a valuable feedstock to produce high‐value chemicals. In this work, we report an ecofriendly and efficient mechanochemical strategy for upcycling of bio‐ and fossil‐based polyesters under mild conditions into synthetically useful building blocks. Bio‐based polyethylene furanoate (PEF), polybutylene furanoate (PBF), and polylactic acid (PLA), as well as fossil‐derived polyethylene terephthalate (PET), were successfully transformed into their corresponding transesterification and amidation products in excellent yields using sodium methoxide as a catalyst. These reactions generate the corresponding diol, methanol, and sodium chloride as byproducts, which can be recovered and reused. Furthermore, using the same protocol, PEF was converted into bio‐based plasticizers, including diethylhexyl furanate (DEHF) and diisoamyl furanoate (DIAF) in excellent yields. Importantly, the method is not limited to pure polymers but is also effective for commercially available PET‐ and PLA‐based packaging materials. The products were isolated by simple aqueous workup and characterized using NMR, IR, HRMS, and XRD techniques. Overall, this mechanochemical route offers a sustainable, cost‐effective, and versatile approach for polyester waste valorization, contributing significantly to a circular plastic economy.

The understanding of the nature of catalyst–substrate complexes is key for the optimization of catalytic transformations such as asymmetric hydrogenation of prochiral olefins. We present a crystallographic and NMR spectroscopic study of coordination of the prochiral olefin α‐methyl‐β‐amidoitaconate to two [Rh(diphosphine)] ⁺ fragments under varying pH conditions. While under neutral conditions substrate coordination is observed, yielding the expected Rh(I)–substrate complexes, the coordination under basic conditions results in the deprotonation of the amide group, giving neutral Rh(I) complexes that possess covalent Rh–N linkages. At low pH, oxidative addition of the acid induces 1,2‐insertion of the olefin functional group into the Rh hydride, resulting in the formation of Rh(III) alkyl complexes that are commonly regarded as catalytically inactive species for hydrogenation. The NMR spectroscopic aspects of these rare transformations are investigated using a combination of low‐field flow and high‐field NMR spectroscopy. Finally, the relevance of these observations for asymmetric hydrogenation of α‐methyl‐β‐amidoitaconate is discussed.

The heterodinuclear zirconocene/titanocene complexes, [Cp ₂ Zr(μ‐Me)(μ‐C ₂ R)(TiCp ₂ )] where R = SiMe ₃ and R = Ph, were prepared using the previously reported comproportion reaction of the zirconocene alkynyl methyl complex with Rosenthal's zirconocene source. Examination of the molecular structure revealed alkynyl group migration from Zr to Ti, as confirmed by single‐crystal x‐ray analysis, nuclear magnetic resonance spectroscopy, and quantum chemical calculations. The homodinuclear (Zr/Zr) and heterodinuclear (Ti/Zr) complexes were activated with [Ph ₃ C][B(C ₆ F ₅ ) ₄ ], B(C ₆ F ₅ ) ₃ , and a mixture of B(C ₆ F ₅ ) ₃ with excess Et ₃ SiH (SiHB system) as aluminium‐free activators and tested in ethylene polymerization. Depending on the type of activator, unique reactivity was observed, resulting in either electron or methyl abstraction and the formation of cationic species. The catalytically active species are proposed to have dinuclear character, forming linear polyethylenes with unsaturated groups predominantly on the Zr cationic center. In contrast, the Ti cationic center generated by a SiHB system only in dichloromethane produced silicon‐terminated polyethylenes.

The catalytic dehydrocoupling of amine boranes produces well‐defined BN compounds and polymers that are isovalent electronic to hydrocarbon analogs. In this study, the synthesis and characterization of a set of Rh, Ir, and Ru complexes with tridentate imidazolylphosphine PN(H)N ligands of the type (imidazolyl)CH ₂ N(H)CH ₂ CH ₂ PR ₂ ( R = i Pr, t Bu) are presented. These complexes potentially engage in metal–ligand cooperative dehydrogenation of amine boranes, followed by BN coupling. All complexes show facial coordination of the PN(H)N ligands to the metal centers with pronounced hydrogen bonding to an outer‐sphere chloride ligand. All Rh and Ir complexes are active catalysts for the dehydrogenation of H ₃ B·NMeH ₂ and H ₃ B·NMe ₂ H, producing mainly linear and cyclic BN oligomers. Only the Ru complex [Ru(PN(H)N)(PPh ₃ )(CO)(H)]Cl ( 8 ) produces low‐molecular‐weight poly(aminoboranes) from H ₃ B·NMeH ₂ with high activity after activation with KO t Bu, supporting metal‐ligand cooperativity during activation of the amine borane substrates.

Knowledge of the potential degradation products of active pharmaceutical ingredients (APIs) is of major interest for the development and approval of new drugs. Therefore, methodologies for the time-efficient and precise prediction of degradation products and pathways are of great importance. Traditional degradation assessments typically involve solution-based forced degradations under acidic, basic, thermal, or photolytic conditions. However, such conditions often fail to accurately replicate degradation pathways relevant to solid-state formulations. A promising addition to the established solvent-based approaches are forced degradation processes in the solid-state using mechanochemistry. The newly developed methodologies enable a time-efficient and accurate simulation of degradation pathways under mild reaction conditions in the solid-state. Herein, the general principles of forced mechanochemical degradations will be discussed on the basis of published case studies involving marketed drugs.

Phosphaalkkenes are an underrepresented class of phosphorus-based ligands that hold great potential for the stabilisation of low-valent transition metal and main group fragments. We present the synthesis of a monoanionic PNP type bis-phosphaalkene ligand and its reactions with [Rh(cod)(Cl)]2 which furnish two unique dinuclear Rh(I) complexes. These complexes show C-H activation of the Mes* groups of the PNP ligand and the presence of three different phosphaalkene coordination modes, respectively. Computational analyses suggests the presence of a unique Rh−Rh donor-acceptor interaction in the C-H activated complex. Stabilisation of the desired tricoordinate PNP supported Rh(I) species is possible in presence of the strongly donating CO ligand, yielding a mononuclear square-planar complex of the type [(PNP)Rh(CO)].

The challenge of producing new environmentally friendly and fossil-free polyesters has strongly encouraged the development of bio-based alternatives such as poly(ethylene furanoate) (PEF) and polybutylene furanoate (PBF) as alternatives to commodity plastics such as poly(ethylene terephthalate) (PET) for everyday applications. In this contribution we report the mechanochemical depolymerisation of these polymers using NaOH in the presence of NaCl as an additive along with the synthesis of high-molecular weight PEF and PBF. Efficient depolymerisation, producing 2,5-furandicarboxylic acid (FDCA) and the corresponding diols in quantitative yields after aqueous acidic workup, is possible within 30 minutes milling time. Using sligthly modified reaction conditions, transesterification with MeOH produces the 2,5-furandicarboxylic acid dimethyl ester (FuMe2), which can potentially be reused for polymer synthesis. Notably, the furan ring remains stable under the mechanochemical conditions used. The applicability of these straight-forward, environmentally friendly protocols on large scale is demonstrated in reactions on multigram scale.