New zirconocene-coupling route to large, functionalized macrocycles

The development of a new macrocyclization reagent, Rosenthal's Cp2Zr(pyr)(M e3SiC drop CSiMe3), has allowed the preparation of two large, functionalize d macrocycles. The diyne 5,5'-bis(4-trimethylsilylphenyl)-2,2'-bipyridine w as trimerized to the bipyridine-containing macrocycle 5, and 1,4-bis(4-(tri methylsilyl)ethynylphenyl)-2,3-diphenyl-1,4-diazabuta-1,3-diene was dimeriz ed to macrocycle 6. Both zirconocene-containing macrocycles were characteri zed by single-crystal X-ray diffraction. Macrocycle 5, which is cleanly con verted to air-stable cyclophane 7 with benzoic acid, has a cavity of van de r Waals radius 6.03 Angstrom. In general, the Cp2Zr(pyr)(Me3SiC drop CSiMe3 ) reagent gives higher yields of macrocycles via the coupling of diynes tha n does the reagent generated by addition of n-BuLi to Cp2ZrCl2.