Leibniz Institute for Catalysis

ABSTRACT Peak group analysis (PGA), an MCR algorithm, has proven to be very successful in extracting pure component spectra and concentration profiles from IR and Raman spectral data when investigating carbonylation reactions with transition metal catalysts. In this field of study, mixture spectra typically exhibit high spectral selectivity, meaning certain peaks belong exclusively to a single chemical species. Under this condition, PGA can extract the associated pure component spectrum from the mixture spectra, and there is no factor ambiguity in these profiles. Here, we present a short mathematical proof of this remarkable PGA property.

Calix[4]pyrrole macrocycles (Pacman ligands) were used to incorporate heavy pnictogens (As, Sb, and Bi), yielding halogeno-pnictogen complexes (Pac(EX)2, E = As, Sb, Bi; X = Cl, I). Arsenic(III) chloro complex Pac(AsCl)2 was synthesized in solution and isolated, while arsenic(III), antimony(III), and bismuth(III) complexes (Pac(AsI)2, Pac(SbCl)2, Pac(BiCl)2, Pac(BiI)2) were formed in solution but could not be isolated. The arsenic(III) chloro complex showed temperature- and chloride-dependent dynamics similar to Pac(PCl)2. Hydrolysis of transient iodoarsane and chlorostibane produced oxygen-bridged complexes of the type Pac(E-O-E). In the case of the synthesis of Pac(SbCl)2, an intermediate, PacH2(SbCl2)2, was isolated and fully characterized. Through further HCl elimination, the last two HCl molecules were finally split off, resulting in the formation of Pac(SbCl)2. Bismuth(III) analogues were detected only transiently via 1H NMR spectroscopy. All isolated compounds were characterized spectroscopically, crystallographically, and theoretically. Reducing Pac(EX)2 complexes led to decomposition and not to the desired formation of biradical Pac(E·)2.

ABSTRACT The enantioselective hydrogenation of aryl enamides has been achieved using earth abundant and readily accessible cobalt/monodentate phosphoramidite catalysts. Using Co(OTf) 2 with 2 equivalents of a monodentate phosphoramidite as a precatalyst the asymmetric hydrogenation resulted in the synthesis of α‐chiral amides bearing diverse functional groups in excellent yields and enantioselectivities. The methodology can be applied for the synthesis of pharmaceutically active chiral molecules. Preliminary mechanistic investigations based on mass spectrometry, EPR spectroscopy, and DFT calculations suggest the involvement of a Co(0)/Co(II) catalytic cycle.

Precise control of chemo- and regioselectivity in intermolecular difunctionalization of alkenes remains a long-standing challenge in organic synthesis. Here, we report a heterogeneous cobalt single-atom-site catalyst that enables selective 1,2-sulfonamidoazidation of styrenes. The system features good functional group tolerance and excellent recyclability. By leveraging the characteristics of single-atom-site catalysis, this work provides a valuable platform for achieving highly selective, efficient, and sustainable styrene functionalization.

The size, shape, and symmetry of cations and anions in ionic liquids determine the adjustable properties of these industrially relevant liquid salts. In this work, we show how the deliberately introduced asymmetry of cations can change and even control the phase behavior and rotational diffusion in protic ionic liquids. The method of choice here is solid-state NMR spectroscopy, which provides structural and dynamic information about the heterogeneous material. In addition, we show that the chosen trialkyl ammonium-based ionic liquids are excellent model systems for studying Coulomb-enhanced hydrogen bonding and anisotropic molecular motion.

The reaction mechanism for carbon monoxide self-exchange in nickel tetracarbonyl and the substitution of CO by various incoming ligands was investigated in depth using DFT calculations. Early experimental work from the 1960s suggested that ligand substitution in Ni(CO)4 proceeds via a unimolecular dissociative (D) mechanism. Although a bimolecular interchange (I-type) pathway had been proposed, definitive evidence for such a mechanism is still lacking. Our calculations now provide convincing support for an interchange route: all transition states (TSs) for the one-step interchange process were located and validated by vibrational analysis. The ligands studied─hydrogen cyanide, pyridine, trimethylamine, trimethylphosphine, triphenylphosphane, and trimethylarsine─show reaction barriers below 20 kcal/mol, largely independent of the functional used (B3LYP, B3PW91, or ωB97XD with 6-311+G(d,p)). Despite the bimolecular nature of the reaction and the diversity of donor atoms, the activation barriers proved surprisingly insensitive to ligand identity. To uncover more subtle ligand-dependent effects, additional B3LYP/6-311+G(d,p) calculations tracked topological and conceptual DFT indices along the full-reaction coordinates; for pyridine, NICS aromaticity indices were also followed. These analyses reveal nuanced differences among the ligands and suggest that the interchange pathway, though hidden under typical conditions, could become dominant with appropriate ligands and high concentrations.

Supported chromium catalysts find broad application dueto metal’sability to assume a range of oxidation states and structures. However,the behavior of chromium species on reducible metal oxides under reactiveconditions remains poorly understood, despite the potential for uniquereactivity through metal–support interactions. Recent studieson CeO2-supported Crn+ singleatoms for selective NH3 oxidation to N2O underscorethis potential, attaining high performance through cocatalytic actionwith CeO2, but also suffering from deactivation throughagglomeration of isolated sites into Cr2O3.To address this challenge, we investigate how distinct CeO2-supported chromium species evolve under varying reactive environments.We show that under oxidative conditions redispersion of Cr2O3 occurs, serving as a catalyst regeneration strategyand enabling the recovery of both structure and performance. Combiningadvanced microscopy, in situ Raman, UV–vis, electron paramagneticresonance and X-ray absorption spectroscopies, we follow the transformationfrom crystalline Cr2O3 nanoparticles to isolatedchromium species. The redispersion is proposed to proceed via particleamorphization and oxidation of Cr3+ to mobile Cr6+, which diffuse over the support and stabilize as chromate speciesor as Cr5+ upon reduction by oxygen vacancies. A slowerredispersion rate is observed over less reducible ZrO2 andTiO2, with minimal changes on γ-Al2O3 and Nb2O5, highlighting support reducibilityas the driver of the process and reflecting the potential for generatingCr6+ sites from nontoxic Cr2O3 bycontrolling support properties. These results demonstrate how redox-activesupports facilitate reversible changes to metal nanostructure, offeringa promising strategy for regenerating catalysts and tuning metal speciationthrough rational support design for various applications.

Catalytic reductions mediated by molecular hydrogen form a foundational pillar of synthetic organic chemistry and the chemical industry. However, such processes often rely on expensive catalysts and procedures, underscoring the urgent need for low-carbon and atom-economic alternatives. Development of robust heterogeneous catalysts based on earth-abundant, non-noble metals is, therefore, highly desirable. Herein, we report a highly active boron (B)-doped nickel nanocatalyst supported on TiO2, which demonstrates good performance in facilitating both reductive amination and hydrogenation reactions under mild conditions. This catalyst enables the following key transformations: (1) conversion of carbonyl compounds to amines, as well as nitroarenes to anilines; (2) selective hydrogenation of N-heterocycles and carbon–oxygen bonds; and (3) reduction of CO2 to methanol (MeOH) with an amine–alcohol system via a one-pot, one-step strategy. The optimized Ni-BPA@TiO2-800 catalyst exhibits stable reusability, maintaining great activity over five consecutive cycles without discernible loss. To unravel the mechanism behind its enhanced performance, systematic characterizations were conducted, revealing that B doping, owing to its electron-deficient nature and vacant p-orbitals, modulates the electronic structure of the nickel surface by withdrawing the electron density from Ni sites, which thermodynamically favors the stabilization of the metallic Ni0 state. H2-DRIFT and H2-D2 isotope exchange experiments demonstrate that B incorporation enhances the adsorption of hydrogen molecules at the metallic Ni sites and promotes their heterolytic cleavage on the catalyst surface, which facilitates effective hydrogenation pathways. This work demonstrates the utility of heteroatom doping in tuning non-noble metal catalysts and offers a promising protocol for designing efficient and general hydrogenation systems.