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ACS catalysis 13, 3356 - 3369 (2023). doi:10.1021/acscatal.2c05704, Heterogeneously catalyzed gas–solid-phase reactions generally suffered from diffusion limitations in large-scale processes or in academic studies when zeolites were used as catalysts or supports. Here, we elucidated the effects of diffusion of reactants/products in nonoxidative propane (PDH) and isobutane dehydrogenation (iBDH) reactions on the performance of catalysts possessing differently structured ZnO$_x$ species on (S-1), dealuminated beta (deAl beta), and ZrO$_2$. The catalysts were prepared through physically mixing ZnO and the support. Force-field molecular dynamics simulations revealed that the effectiveness factor $η$ is larger than 0.99 in the PDH reaction over all catalysts and in the iBDH reaction over the ZnO-deAl beta catalyst, thus suggesting that mass transport limitations do not play any significant role. However, the iBDH reaction over S-1-based catalysts suffers from some diffusion limitations (0.35 < $η$ < 0.9). Such conditions are favorable for cracking reactions responsible for isobutene selectivity loss. To compare intrinsic catalyst activity in the PDH and iBDH reactions over the ZnO$_x$/S-1 catalyst, molecular-level insights into individual reaction pathways were derived from density functional theory calculations. The nature of active ZnOx sites was investigated by X-ray absorption spectroscopy and was established to depend on the kind of support material. Binuclear ZnO$_x$ species are formed inside small S-1 pores or on the surface of ZrO$_2$, while three-dimensional multinuclear ZnO$_x$ clusters are generated in the $β$ zeolite with larger pores. The latter show higher Zn-related activity in the PDH reaction under conditions free of any diffusion constraints. The developed ZnO–deAl beta showed the space–time yield of propene or isobutene formation of 2 kgC$_3$H$_6$ kg$_{cat}$ $^{–1}$ h$^{–1}$ or 6.3 kg$_{i-C_{4}}$H$_8$ kg$_{cat} $^{–1}$ h$^{–1}$ at 550 °C and about 70–80% equilibrium alkane conversion with an olefin selectivity of about 90%. The activity values are higher than those reported for the state-of-the-art non-noble metal oxide catalysts tested at the same or even higher temperatures., Published by ACS, Washington, DC

Using titanocene synthon [Cp2Ti(Me3SiC2SiMe3)] the selective conversion of aryl-substituted triphosphiranes P3Ar3 into Cp2TiP2Ar2 complexes was achieved., Triphosphiranes are three-membered phosphorus cycles and their fundamental reactivity has been studied in recent decades. We recently developed a high-yielding, selective synthesis for various aryl-substituted triphosphiranes. Variation of the reaction conditions in combination with theoretical studies helped to rationalize the formation of these homoleptic phosphorus ring systems and highly reactive intermediates could be isolated. In addition we showed that a titanocene synthon [Cp2Ti(btmsa)] facilitates the selective conversion of these triphosphiranes into titanocene diphosphene complexes. This unexpected reactivity mode was further studied theoretically and experimental evidence is presented for the proposed reaction mechanism.

The Co^II-catalyzed [2+2+2] cycloaddition of functionalized diynes and phosphaalkynes resulting in the formation of an array of structurally interesting phosphinines is reported. A combination of 1,2-bis(diphenylphosphino)benzene (dppbenz) and CoI_2 turned out to be the most suitable and active catalyst system under microwave reaction conditions. Chemoselective cyclizations of phosphaalkynes in the presence of nitriles have been observed, and a number of carbonyl functionalities are tolerated as well. The reaction can successfully be conducted with a 1:1 ratio of phosphaalkyne/diyne substrate. Model reactions with benzonitrile and diyne demonstrated that Co^II catalysts in the presence of bisphosphines prefer carbocyclization, while reduction to lower oxidation states promotes heterocyclization to the corresponding pyridine. A reaction mechanism comprising a Co^II oxidation state for the cyclotrimerization process is proposed and rationalized based on control experiments and theoretical calculations. Version of record

A general and atom-economical synthesis of 1,1-diborylalkanes from alkenes and a borane without the need for an additional H2 acceptor is reported for the first time. The key to our success is the use of an earth-abundant zirconium-based catalyst, which allows a balance of self-contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H2 acceptor, which was required in other reported systems. Furthermore, substrates such as simple long-chain aliphatic alkenes that did not react before also underwent 1,1-diboration in our system. Significantly, the unprecedented 1,1-diboration of internal alkenes enabled the preparation of 1,1-diborylalkanes. �� 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Non-metal catalysed heterodehydrocoupling of primary and secondary phosphines (R1R2PH, R2 = H or R1) with hydrosilanes (R1’R2’R3’SiH, R2’, R3’ = H or R1’) to produce synthetically useful silylphosphanes (R1R2P-SiR1’R2’R3’) has been achieved using B(C6F5)3 as the catalyst (10 mol%, 100 oC). Kinetic studies demonstrated that the reaction is first-order in silane and B(C6F5)3 but zero-order in phosphine. Control experiments, DFT calculations as well as DOSY NMR studies suggest that a R1R2HP•B(C6F5)3 adduct is initially formed and which subsequently undergoes partial dissociation to form an “encounter complex” held together via weak secondary interactions. The latter mediates Frustrated Lewis Pair-type Si-H bond activation of the silane substrates. We also found that B(C6F5)3 catalyses the homodehydrocoupling of primary phosphines to form cyclic phosphine rings and the first example of catalytic hydrosilylation of P-P bonds to produce silylphosphanes (R1R2P-SiR1’R2’R3’). Moreover, the introduction of PhCN to the reactions involving secondary phosphines with hydrosilanes allowed the heterodehydrocoupling reaction to proceed efficiently under much milder conditions (1.0 mol% B(C6F5)3 at 25 °C). Mechanistic studies, as well as DFT calculations, revealed that PhCN plays a key mechanistic role in facilitating the dehydrocoupling reactions rather than simply functioning as H2-acceptor.

Manganese-catalyzed hydrogenation reactions have aroused widespread interest in recent years. Among the catalytic systems described, especially PNP- and NNP-Mn pincer catalysts have been reported for the hydrogenation of aldehydes, ketones, nitriles, aldimines and esters. Furthermore, NNP-Mn pincer compounds are efficient catalysts for the hydrogenolysis of less reactive amides, ureas, carbonates, and carbamates. Herein, the synthesis and application of specific imidazolylaminophosphine ligands and the corresponding Mn pincer complexes are described. These new catalysts have been characterized and studied by a combination of experimental and theoretical investigations, and their catalytic activities have been tested in several hydrogenation reactions with good to excellent performance. Especially, the reduction of N-heterocycles can be performed under very mild conditions.

Der zentrale Punkt dieser Dissertation ist eine theoretische Untersuchung der Struktur, Stabilität und Aktivität von Übergangsmetallen (Fe, Co, Ni, Cu, Pd und Pt), die auf den unterschiedlichen Oberflächen der hexagonalen ß-Mo2C und kubischen-δ-MoC Phasen abgelagert sind. Es zeigt sich, dass Struktur und Stabilität von Trägerkatalysatoren durch die Eigenschiften der Übergangsmetalle und deren Wechselwirkung mit den Carbidoberflächen bestimmt werden und von der Metallbeladung abhängig sind; und dies wiederum bestimmt die Aktivität der katalytischen Reaktionen., The central point of this dissertation is a computational investigation into the structure, stability, and activity of transition metals (Fe, Co, Ni, Cu, Pd and Pt) supported on the different terminations of the hexagonal ß-Mo2C and cubic-δ-MoC phases. It is found that the structure and stability of supported catalysts are determined by the nature of the transition metals and their interaction with the carbide surfaces and are dependent on the metal loading; and this in turn determines the activity of the catalytic reactions.