Synthesis of the cage penta-azamacrobicycloalkane 12,1 7-dimethyl-1,5,9,1 2,17-penta-azabicyclo[7.5.5]nonadecane, its basicity, and metal complex formation. Crystal structure of the copper(II) perchlorate complex

Abstract

The synthesis and characterisation of the new penta-azamacrobicycloalkane 12,17-dimethyll,5,9,12,17-penta-azabicyclo[7.5.5]nonadecane (L) are described. Its basicity in aqueous solution has been investigated by potentiometric and spectroscopic (¹H, ¹³C n.m.r.) techniques. The macrocycle L can take up three protons. It behaves as a very strong base (proton sponge) in the first protonation step, as a moderate base in the second step (log K₂= 8.41), and as very weak base in the last step (log K₃ < 2). The ¹H n.m.r. spectrum of the monoprotonated species HL⁺ in CD₃CN shows a broad signal attributable to two deshielded NH protons, which are rapidly exchanged with acidic hydrogens on the n.m.r. time-scale. pH–¹³C N.m.r. studies have been carried out and a tentative structure for HL⁺, in accord with the n.m.r. features, is proposed. A number of metal ions were tested for complex formation with L. According to ¹³C n.m.r. spectroscopy, there was no evidence of metal co-ordination with Na⁺, K⁺, Be²⁺, and Al³⁺, whereas some weak interaction occurs for Mg²⁺ A lithium complex is formed at high pH. With the other metal ions, solid complexes were isolated from the reaction of the appropriate metal perchlorate and [HL] Br in boiling methanol. The molecular structure of the complex [CuL][ClO₄]₂·H₂O has been determined by single-crystal X-ray analysis. The compound crystallises in an orthorhombic unit cell (space group P2₁2₁2₁) with lattice constants a= 17.332(5), b= 15.448(5), c= 9.066(4)Å, with Z= 4. Least-squares refinement converged at R= 0.058 for 1 865 observed reflections. The copper ion is wholly enclosed by the macrobicycle and is five-co-ordinated. The co-ordination geometry is a distorted square pyramid with the secondary nitrogen atom in the apical position. The electronic spectra of the copper, cobalt, and nickel complexes show essentially the same features in the solid state and in solution, and are diagnostic of a distorted square-pyramidal structure.