Waldemar Maximilian Czaplik

Practical iron-catalyzed dehalogenation of aryl halides

An operationally simple iron-catalyzed hydrodehalogenation of aryl halides has been developed with 1 mol% Fe(acac)(3) and commercial t-BuMgCl as reductant. The mild reaction conditions (THF, 0 degrees C, 1.5 h) effect rapid chemoselective dehalogenation of (hetero)aryl halides (I, Br, Cl) and tolerate F, Cl, OR, SR, CN, CO(2)R, and vinyl groups.

Iron‐Catalyzed Reductive Aryl–Alkenyl Cross‐Coupling Reactions

Transition metal-catalyzed cross-coupling reactions constitute one of the most versatile methods for carbon–carbon bond formation. Apart from the established palladium and nickel catalyst systems, recent years have witnessed the development of new methods based upon economically and environmentally attractive iron catalysis. Iron-catalyzed cross-coupling reactions boast great operational simplicity, low costs, and high reactivity : The employed precatalysts are cheap and nontoxic iron salts; no addition of high-molecular-weight and airsensitive ligands is required; unactivated substrates (organochlorides) are reactive; the mild reaction conditions tolerate various functional groups. Metal-catalyzed cross-coupling methods, including Heck reactions, are also among the mostused systems for the synthesis of substituted styrenes, which are ubiquitous structural motifs in biological molecules and valuable intermediates of fine chemicals, agrochemicals, pharmaceuticals, and materials. 5] Whereas such reactions are dominated by palladium and nickel catalysts, only a handful of iron-catalyzed alkenylations of pre-formed arylmetal reagents have been reported, with mostly moderate yields of the crosscoupling product. The development of a direct crosscoupling between two sp electrophiles, an alkenyl halide and an aryl halide under in situ reductive conditions would shun the use of pre-formed organometallics but instead exploit the much cheaper and less hazardous organohalides. However, a stereoelectronic differentiation between both sp-hybridized electrophiles (aryl X, alkenyl Y) is key to a selective crosscoupling reaction. We recently demonstrated the concept of a sustainable domino iron catalysis in the context of direct sp sp cross-coupling reactions between aryl bromides and alkyl bromides via in situ formation of the organomagnesium species. Herein, we report our recent study of iron-catalyzed cross-coupling reactions of arylmagnesium bromides and alkenyl bromides and the direct reductive cross-coupling between aryl bromides and alkenyl bromides with the simple precatalyst FeCl3/TMEDA (TMEDA = N,N,N’,N’-tetramethylethylenediamine; Scheme 1). An initial investigation of electrophile/nucleophile combinations in the cross-coupling of phenyl and vinyl moieties resulted in the exclusive formation of styrene (3 a) from the reaction of phenylmagnesium bromide and vinyl bromide with a FeCl3/TMEDA (1:4) catalyst system. The electronically inverse reaction of bromobenzene and vinylmagnesium bromide led to no conversion under identical reaction conditions (Scheme 2). The high substrate selectivity is also reflected in the direct reductive cross-coupling of bromobenzene (1 a) and vinyl bromide (2 a). Unlike metal–halogen exchange based on expensive isopropylmagnesium chloride for the generation of the Grignard species, we rather resorted to a more sustainable strategy utilizing magnesium ribbons (Table 1).

On the quantitative recycling of Raney–Nickel catalysts on a lab-scale

An efficient protocol for the selective hydrogenation of heteroarenes and olefins has been developed exhibiting quantitative and hazard-free recycling of the Raney–Nickel catalyst.