Katrin Marie Dyballa

Source of Selectivity in Oxidative Cross-Coupling of Aryls by Solvent Effect of 1,1,1,3,3,3-Hexafluoropropan-2-ol.

Solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with a high capacity for donating hydrogen bonds generate solvates that enter into selective cross-coupling reactions of aryls upon oxidation. When electric current is employed for oxidation, reagent effects can be excluded and a decoupling of nucleophilicity from oxidation potential can be achieved. The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions. The shift in the redox potentials depends on the substitution pattern of the substrate employed. The concept has been expanded from arene-phenol to phenol-phenol as well as phenol-aniline cross-coupling. This driving force for selectivity in oxidative coupling might also explain previous findings using HFIP and hypervalent iodine reagents.

Ligand‐Modified Rhodium Catalysts on Porous Silica in the Continuous Gas‐Phase Hydroformylation of Short‐Chain Alkenes–Catalytic Reaction in Liquid‐Supported Aldol Products

Ligand‐modified Rh complexes were physically adsorbed on the surface of porous silica. The resulting materials were subjected to the continuous gas‐phase hydroformylation of C2 and C4 alkenes. The ligands used for catalyst modification were bidentate phosphorus ligands known from the literature, namely, sulfoxantphos (1) and a benzopinacol‐based bulky diphosphite 2. The tested catalyst materials were active and, in particular, selective as in comparable homogeneous liquid‐phase experiments. Long‐term stability experiments over 1000 h on stream showed minor deactivation. A significant increase in the catalyst mass after the reaction was detected by weighing and thermogravimetric analysis. By using headspace‐GC–MS, the mass increase could be attributed to high‐boiling compounds, which are formed in situ during the catalytic reaction itself and accumulate inside the pores of the support. Evidence is given that the initially physisorbed catalyst complexes dissolve in the high‐boiling aldol side‐products, which are suitable solvents for the active catalyst species and provide a liquid‐phase environment held by capillary forces on the support.

Solvent-Dependent Facile Synthesis of Diaryl Selenides and Biphenols Employing Selenium Dioxide.

Abstract Biphenols are important structure motifs for ligand systems in organic catalysis and are therefore included in the category of so‐called “privileged ligands”. We have developed a new synthetic pathway to construct these structures by the use of selenium dioxide, a stable, powerful, and commercially available oxidizer. Our new, and easy to perform protocol gives rise to biphenols and diaryl selenides depending on the solvent employed. Oxidative treatment of phenols in acetic acid yields the corresponding biphenols, whereas conversion in pyridine results in the preferred formation of diaryl selenides. As a consequence, we were able to isolate a broad scope of novel diaryl selenides, which could act as pincer‐like ligands with further applications in organic synthesis or as ligands in transition metal catalysis.

Synthesis of C2-Symmetric Diphosphormonoamidites and Their Use as Ligands in Rh-Catalyzed Hydroformylation: Relationships between Activity and Hydrolysis Stability

Abstract A series of diphosphoramidites has been synthetized with a piperazine, homopiperazine, and an acyclic 1,2‐diamine unit in the backbone. New compounds were tested alongside related N‐acyl phosphoramidites as ligands in the Rh‐catalyzed hydroformylation of n‐octenes to investigate their influence on the activity and regioselectivity. A subsequent study of their hydrolysis stability revealed that the most stable ligands induced the highest activity in the catalytic reaction.