New Zirconocene-Coupling Route to Large, Functionalized Macrocycles

The development of a new macrocyclization reagent, Rosenthal's Cp2Zr(pyr)(Me3SiC⋮CSiMe3), has allowed the preparation of two large, functionalized macrocycles. The diyne 5,5'-bis(4-trimethylsilylphenyl)-2,2'-bipyridine was trimerized to the bipyridine-containing macrocycle 5, and 1,4-bis(4-(trimethylsilyl)ethynyl-phenyl)-2,3-diphenyl-1,4-diazabuta-1,3-diene was dimerized to macrocycle 6. Both zirconocene-containing macrocycles were characterized by single-crystal X-ray diffraction. Macrocycle 5, which is cleanly converted to air-stable cyclophane 7 with benzoic acid, has a cavity of van der Waals radius 6.03 Å. In general, the Cp2Zr(pyr)(Me3SiC⋮CSiMe3) reagent gives higher yields of macrocycles via the coupling of diynes than does the reagent generated by addition of n-BuLi to Cp2ZrCl2.