New zirconocene-coupling route to large, functionalized macrocycles

The development of a new macrocyclization reagent, Rosenthal's Cp2Zr(pyr)(Me3SiC drop 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)ethynylphenyl)-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 Angstrom. In general, the Cp2Zr(pyr)(Me3SiC drop CSiMe3) reagent gives higher yields of macrocycles via the coupling of diynes than does the reagent generated by addition of n-BuLi to Cp2ZrCl2.