Ruthenium-Sulfonamid-Komplexe als Katalysatoren für Carbenübertragungsreaktionen

Ruthenium(I) complexes are a less costly alternative to the established rhodium catalysts in carbene transfer reactions. This type of ruthenium catalysts shows a particularly high Z-selective cyclopropanation of trisubstituted alkenes with diazoacetates. In this work, cyclic N-sulfonyl-carboxamido ligands, like saccharin and derivatives, acesulfame and a sulfahydantoin were synthesized and employed to create two-core Ru(I) complexes (like [Ru2(CO)4(µ-L)2]). As a possible solution for the problem of relative facile isomerization (head-head or head-tail constitution) of the complexes, two of the saccharin molecules were connected by a terphenyl bridge. To study the selectivity and activity of these complexes in cyclopropanation reactions, they were used as catalysts, for example in the reaction between an olefin (styrene, cyclohexene, 2-methyl-2-butene) and methyl diazoacetate. In spite of the isomerization of these complexes, a certain stereoselectivity was observable. This is expressed in higher yields of Z-cyclopropanes in case of catalysts with initially head-tail arranged ligands (especially with 6-bromosaccharin as ligand)