Synthesis of new palladium complexes containing a sulfonamide ligand and their catalytic evaluation in carbene chemistry

Since their first synthesis, sulfonamides and their derivatives have attracted the
interest of many biochemists’ due to their importance in medicinal chemistry.
Afterward, the development of organometallic chemistry gave new interest to
sulfonamide compounds. Metal complexes containing sulfonamides ligands
represent interesting organometallics molecules due to their different catalytic
proprieties. Here we present the first result of the optimised way to prepare
palladium complexes containing sulfonamides ligands, their crystals structures
and catalytic activity in cyclopropanation reaction of styrene.The new complexes were prepared quantitatively by reacting Pd(PPh3)4 and 2-halogenobenzenesulfonamides. In the case of the iodide, the reaction
proceeded at room temperature for 4 hours. The precipitate is filtered after 4 h on a Buchner funnel, washed with toluene and pentane. For the complexes
containing bromides, the reaction was carried out at 70 °C for 12 hours. All these complexes were characterized by various NMR methods. . In 31P NMR, all
the complexes show two doublets and one singlet. The analysis reveals that the singlet can be assigned easily to the trans isomer and the two speared
doublet for the cis one. The trans isomer is obtain as a major product. the high steric hindrance of the mesithyl (Mes) group leads to more formation of the
cis isomer. The catalytic activity of the four complexes are evaluated in cyclopropanation reaction of styrene with EtDA (of ethyl diazoacetate). To enhance selectivity for
the cyclopropane, EtDA was added slowly via a pump syringe to a solution of styrene and catalyst. The yields are determined by GC based on EtDA. Results
show that independently of the mixture of cis and trans isomers, ester cyclopropane is obtained in good yield. In all instances, the trans cyclopropane was the
major product.In conclusion, we have shown an easy way to prepare novel palladium complexes bearing sulfonamide ligand. The sulfonamide substituent in ortho position
of the phenyl linked to the palladium leads to the formation of the cis and trans complexes isomer. The structures of the trans complexes were confirmed by
X-ray crystallographic analysis. The catalytic activity of all the complexes in cyclopropanation of styrene leads to good yield with selectivity for the trans
cyclopropane.