Interactions of Organozinc Compounds with Crown Ethers and Cryptands: Formation of R2Zn(18-crown-6) Rotaxanes

Several pieces of evidence indicate that R 2 Zn(18-crown-6) rotaxanes are components of solutions prepared from some R 2 Zn (R = alkyl or aryl) compounds and 18-crown-6, and crystal structures show that Et 2 Zn(18-crown-6) and Ph 2 Zn(18-crown-6) solids that precipitate from such solutions have rotaxane structures. By contrast, the R 2 Zn compounds do not form rotaxanes with 15-crown-5 or its nitrogen equivalent, 1,4,7,10,13-pentamethyl-1,4,7,10,13-pentaazacyclopentadecane. Disproportionation of R 2 Zn by macrocycles to form coordinated RZn + cations and R 3 Zn - anions is less favorable than the corresponding reaction with R 2 Mg, although Tol 2 Zn (Tol = p -methylphenyl) and 2,1,1-cryptand do form TolZn(2,1,1-cryptand) + Tol 3 Zn - .