Bimacrocyclic NHC transition metal complexes

The preparation of seven concave NHC metal complexes derived from bimacrocyclic imidazolinium salt 1 is reported. The silver complex 2, obtained in 86% yield by reacting 1 with silver(I) oxide, was used to give copper complex 3, rhodium complex 5 and iridium complex 6 by transmetalation in good yields. Palladium complex 4 was obtained by reaction of the azolium salt 1 with palladium dichloride in 3-chloropyridine. The rhodium and iridium dicarbonyl complexes 7 and 8 were prepared via ligand exchange from the COD complexes 5 and 6. Silver complex 2, copper complex 3 and palladium complex 4 were characterized by single-crystal X-ray analysis. Silver complex 2 and copper complex 3 were tested in the cyclopropanation of styrene and indene with EDA (ethyl diazoacetate), where good results were obtained with 3, while low conversion and catalyst decomposition was observed with 2.

Graphical abstractSeven bimacrocyclic metal complexes bearing a concave NHC ligand have been prepared and characterized. The structures of silver complex 2, copper complex 3 and palladium complex 4 were elucidated by X-ray analysis. Silver complex 2 and copper complex 3 were tested as catalysts for the cyclopropanation of styrene and indene with EDA (ethyl diazoacetate).Figure optionsDownload full-size imageDownload as PowerPoint slide