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.