Amides and sulfonamides: efficient molecular padlocks for the template synthesis of azacyclam (1,3,5,8,12-pentaazacyclotetradecane) macrocycles

Abstract

Amides and sulfonamides, both aliphatic and aromatic, acted as efficient locking fragments, in the presence of formaldehyde and base (triethylamine), in closing the open-chain tetramine 1,9-diamino-3,7-diazanonane around labile metal centres prone to a square type of co-ordination, i.e. Ni^II and Cu^II, to give a pentaazamacrocyclic complex of the azacyclam family. The product of the copper(II) template reaction involving methanesulfonamide as a locking fragment (3-methanesulfonyl-1,3,5,8,12-pentaazacyclo-tetradecane)dinitratocopper(II), was obtained in crystalline form and its crystal and molecular structure determined from single-crystal X-ray diffraction data, collected with the use of Cu-Kα radiation: trigonal, space group R3c, a=b=c= 14.997(3)Å, α=β=γ= 98.48(2)°, Z= 6. Only the four secondary amine nitrogen atoms of the macrocycle are bound to the Cu^II, giving a regular square stereochemistry. The tertiary nitrogen atom N(1), which presents distinct sp² structural features, is not involved in the co-ordination. The axial positions of the elongated octahedron are occupied by oxygen atoms of the nitrate ions. A kinetic investigation was carried out on the copper(II) template reactions involving diprotic acids as locking fragments, including amides, amines and carbon acids, such as nitroethane and diethyl malonate: for the systems investigated the rate of the template reaction seems to be related to the strength of the diprotic acid. This suggests that the monodeprotonated form of the acid is present in the rate-determining step of the cyclisation process.