Constanze Neumann

• Doctor of Philosophy
• Group Leader at Max Planck Institute für Kohlenforschung

The precision with which atoms can be positioned in 3D space through reticular chemistry imbues metal‐organic frameworks (MOFs) with the potential to access catalytic performance beyond what is possible with classical heterogeneous manifolds. In this paper, we highlight illustrative examples in which MOF‐based catalysts integrate adsorption and cat...

Transition-metal-catalyzed cleavage of the Si–H bond in silanes to yield silyl radicals requires substantial amounts of energy, which is commonly supplied by photons. For Rh(II) porphyrins, efficient hydrosilylation catalysis only becomes accessible upon site isolation in a MOF, and the formation of free silyl radicals likewise requires irradiation...

The preparation of regioisomers of small molecules is routine, but an analogous concept of positional isomerism is absent for extended materials. Crystalline frameworks such as zeolites and metal-organic frameworks (MOFs) can furnish well-defined active sites for heterogeneous catalysis, but their arrangement cannot be tuned in isolation. Here we s...

Metal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation...

Metal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation...

Rh(II) porphyrin complexes display pronounced metal‐centered radical character and the ability to activate small molecules under mild conditions, but catalysis with Rh(II) porphyrins is extremely rare. In addition to facile dimerization, Rh(II) porphyrins readily engage in kinetically and thermodynamically facile reactions involving two Rh(II) cent...

Rh(II) porphyrin complexes display pronounced metal‐centered radical character and the ability to activate small molecules under mild conditions, but catalysis with Rh(II) porphyrins is extremely rare. In addition to facile dimerization, Rh(II) porphyrins readily engage in kinetically and thermodynamically facile reactions involving two Rh(II) cent...

Radical reactions have recently experienced a resurgence in organic chemistry after many decades of being considered to be too unselective to offer a viable solution for complex synthetic problems. Radical intermediates often have a number of different reaction pathways available to them that are all associated with insubstantial reaction barriers...

The challenge of forming C-18F bonds is often a bottleneck in the development of new 18F-labeled tracer molecules for noninvasive functional imaging studies using positron emission tomography (PET). Nucleophilic aromatic substitution is the most widely employed reaction to functionalize aromatic substrates with the radioactive fluorine-18 but its s...

Acknowledging the crucial role of stereochemistry in fields as diverse as total synthesis, synthetic methodology, spectroscopy, and the study of the origin of life, the 56th SCS Conference on Stereochemistry, better known as the BÃ1/4rgenstock Conference, brought together a diverse range of chemistry expertise in Brunnen, Switzerland. image

Rh(II) porphyrin complexes display pronounced metal-centered radical character and the ability to activate small molecules under mild conditions, but catalysis with Rh(II) porphyrins is extremely rare. In addition to facile dimerization, Rh(II) porphyrins readily engage in kinetically and thermodynamically facile reactions involving two Rh(II) cent...

This critical review discusses the synthesis of alcohols via hydrogenation of carboxylic acids promoted by heterogeneous metal catalysis. The introductory chapter rationalizes the comparative reactivity of carboxylic acid derivatives, which is proceeded by a description of different mechanisms for carboxylic acid hydrogenation. Reaction pathways ar...

The fine‐tuning of metal‐phosphine‐catalyzed reactions relies largely on accessing ever more precisely tuned phosphine ligands by de‐novo synthesis. Late‐stage C−H functionalization and diversification of commercial phosphines offers rapid access to entire libraries of derivatives based on privileged scaffolds. But existing routes, relying on phosp...

Due to the high affinity of phosphines for transition metals, C−H functionalization of aryl phosphines is dominated by phosphorous‐directed reactions. Here we pair a sterically controlled borylation reaction of unprotected phosphines with phosphine self‐assisted Suzuki‐Miyaura reactions to grant ready access to libraries of functionalized phosphine...

We report synthetic strategies for installing platinum group metals (PGMs: Pd, Rh, Ir, and Pt) on a scorpionate-derived linker (TpmC*) within a metal-organic framework (MOF), both by room-temperature postsynthetic metalation and by direct solvothermal synthesis, with a wide range of metal loadings relevant for fundamental studies and catalysis. In-...

The number and diversity of methods for installing carbon–fluorine bonds have substantially expanded over the past two decades, enabling enantioselective fluorinations, reactions with complex substrates, and the use of ever simpler reaction precursors. Fluorination chemistry was long held back by unreactive alkali fluoride salts and highly reactive...

RuNi nanoparticles supported on a metal-organic framework (RuNi@MOF) and formed in situ from a ruthenium complex enclosed inside a nickel-based MOF act as a highly active catalyst for the Guerbet reaction of ethanol to 1-butanol, providing turnover numbers up to 725 000 Ru-1. Negligible activity of the RuNi@MOF ethanol upgrading catalyst system tow...

Late-stage fluorination reactions aim to reduce the synthetic limitations of conventional organofluorine chemistry with respect to substrate scope and functional group tolerance. C–F bond formation is commonly thermodynamically favorable but almost universally associated with high kinetic barriers. Apart from PhenoFluor chemistry, most modern aroma...

A practical transition-metal-assisted ¹⁸F-deoxyfluorination of phenols with large substrate scope empowers the production of radiotracers appropriate for positron emission tomography imaging.

Introducing C–F bonds into organic molecules is a challenging task, particularly through C–H activation methods. Now, a uranium-based photocatalyst turns traditional selectivity rules on their heads and fluorinates unfunctionalized alkane Csp3–H bonds, even in the presence of C–H bonds that are typically more reactive.

Nucleophilic aromatic substitution (SNAr) is widely used by organic chemists to functionalize aromatic molecules, and it is the most commonly used method to generate arenes that contain (18)F for use in positron-emission tomography (PET) imaging. A wide range of nucleophiles exhibit SNAr reactivity, and the operational simplicity of the reaction me...

We report an aromatic C-H hydroxylation protocol in which the arene is activated through η6-coordination to an iridium(III) complex. η6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η5-cyclohexadienyl a...

Starting from aliphatic alcohols or phenols the title reaction has been elaborated providing challenging alkylaryl ethers which are difficult to access by conventional Mitsunobu conditions.

An alkyl aryl ether bond formation reaction between phenols and primary and secondary alcohols with PhenoFluor has been developed. The reaction features a broad substrate scope and tolerates many functional groups, and substrates that are challenging for more conventional ether bond forming processes may be coupled. A preliminary mechanistic study...

An alkyl aryl ether bond formation reaction between phenols and primary and secondary alcohols with PhenoFluor has been developed. The reaction features a broad substrate scope and tolerates many functional groups, and substrates that are challenging for more conventional ether bond forming processes may be coupled. A preliminary mechanistic study...

Charming fluorine: This Essay examines the recent surge in late-stage fluorination reactions and outlines challenges that need to be overcome to increase the impact of modern fluorination methods on the synthesis of complex organofluorine compounds. It is outlined how an improved understanding of the bonding interactions of fluoride could lead to a...

Verzauberndes Fluor: Dieser Essay schildert die jüngsten Erfolge bei Fluorierungen im späten Synthesestadium und identifiziert die noch zu nehmenden Hürden zur Etablierung solcher Methoden in der Synthese komplexer Organofluoride. Ansätze werden beschrieben, wie ein vermehrtes Verständnis der Bindungswechselwirkungen des Fluors zu einer neuen Klass...

Over the past decade, the most significant, conceptual advances in the field of fluorination were enabled most prominently by organo- and transition-metal catalysis. The most challenging transformation remains the formation of the parent CF bond, primarily as a consequence of the high hydration energy of fluoride, strong metal-fluorine bonds, and...

Die wichtigsten konzeptionellen Fortschritt auf dem Gebiet der Fluorierungen der letzten zehn Jahre wurden durch die Organo- und Übergangsmetallkatalyse ermöglicht. Die schwierigste Umwandlung ist weiterhin die Bildung der C-F-Stammbindung, was in erster Linie eine Folge der hohen Hydratationsenergie von Fluorid, starker Metall-Fluor-Bindungen und...

New chemistry methods for the synthesis of radiolabeled small molecules have the potential to impact clinical positron emission tomography (PET) imaging, if they can be successfully translated. However, progression of modern reactions from the stage of synthetic chemistry development to the preparation of radiotracer doses ready for use in human PE...

Contains details on materials and methods, experimental data for chemistry and radiochemistry, and spectroscopic data. (PDF)

The unnatural isotope fluorine-18 (18F) is used as a positron emitter in molecular imaging. Currently, many potentially useful 18F-labeled probe molecules are inaccessible for imaging because no fluorination chemistry is available to make them. The 110-minute half-life of 18F requires rapid syntheses for which [18F]fluoride is the preferred source...