Maik Weidauer

Zinc-catalyzed depolymerization of artificial polyethers.

Recycling polymers: In the present study, the efficient zinc-catalyzed depolymerization of a variety of artificial polyethers has been investigated. Chloroesters were obtained as the depolymerization products, which are suitable precursors for new polymers. By using straightforward zinc salts, extraordinary catalyst activities and selectivities were feasible (see scheme).

Low‐Temperature Iron‐Catalyzed Depolymerization of Polyethers

Iron will: The iron-catalyzed depolymerization of a range of polyethers is studied. The products of the depolymerization reactions are chloroesters, which can be used as starting materials for new polymers. In the presence of simple iron salts extraordinary catalyst activities and selectivities are feasible at low temperature.

Nickel-catalyzed C(sp 2 )–C(sp 2 ) Cross Coupling Reactions of Sulfur-Functionalities and Grignard Reagents

In the present study, the nickel-catalyzed carbon carbon bond formation of a range of sulfur containing substrates with Grignard reagents via desulfurization has been explored. After investigation of different reaction parameters with a well-defined nickel complex an excellent and easy-accessible pre-catalyst was found. The obtained system was capable to convert a broad scope of substrates under mild reaction conditions.Graphical Abstract

Synthesis of δ- and ε-Cyanoesters by Zinc-Catalyzed Ring-Opening of Cyclic Ethers with Acid Chlorides and Subsequent Cyanation

In the present study, the zinc-catalyzed cleavage of cyclic ethers with acid halides as nucleophiles to yield chloroesters with different chain length has been investigated in detail. In the presence of straightforward and commercially available zinc salts as pre-catalysts excellent yields and selectivities were feasible. After studying the reaction conditions and the scope of the method, several efforts were carried out to understand the reaction mechanism. The obtained chloroesters were subsequently converted to δ- and ε-cyano esters, which are useful precursors in natural product synthesis.Graphical Abstract

Nitrous Oxide-dependent Iron-catalyzed Coupling Reactions of Grignard Reagents.

The formation of carbon-carbon bonds is one of the fundamental transformations in chemistry. In this regard the application of palladium-based catalysts has been extensively investigated during recent years, but nowadays research focuses on iron catalysis, due to sustainability, costs and toxicity issues; hence numerous examples for iron-catalyzed cross-coupling reactions have been established, based on the coupling of electrophiles (R(1)-X, X = halide) with nucleophiles (R(2)-MgX). Only a small number of protocols deals with the iron-catalyzed oxidative coupling of nucleophiles (R(1)-MgX + R(2)-MgX) with the aid of oxidants (1,2-dihaloethanes). However, some issues arise with these oxidants; hence more recently the potential of the industrial waste product nitrous oxide (N(2)O) was investigated, because the unproblematic side product N(2) is formed. Based on that, we demonstrate the catalytic potential of easily accessible iron complexes in the oxidative coupling of Grignard reagents. Importantly, nitrous oxide was essential to obtain yields up to >99% at mild conditions (e.g. 1 atm, ambient temperature) and low catalyst loadings (0.1 mol%) Excellent catalyst performance is realized with turnover numbers of up to 1000 and turnover frequencies of up to 12000 h(-1). Moreover, a good functional group tolerance is observed (e.g. amide, ester, nitrile, alkene, alkyne). Afterwards the reaction of different Grignard reagents revealed interesting results with respect to the selectivity of cross-coupling product formation.