SYNTHESIS AND CHARACTERIZATION OF THE AZA-CAGE 4-BENZYL-10,15-DIMETHYL-1,4,7,10,15-PENTAAZABICYCLO[5.5.5]HEPTADECANE (L) - ITS PROTON-TRANSFER PROPERTIES AND LITHIUM COMPLEX - THE CRYSTAL-STRUCTURE OF THE MONOPROTONATED SALT (HL) (BPH4)

The synthesis and characterization of the small, new benzyl aza-cage 4-benzyl-10,15-dimethyl-1,4,7,10,15-pentaazabicyclo[5.5.5]heptadecane (L) are reported. The basicity constants have been determined in aqueous solution by potentiometry (25-degrees-C, [NaCl] 0.15 mol dm-3). L behaves as a biprotic base: log K1 = 11.8, log K2 = 8.3. The crystal structure of the monoprotonated salt [HL][BPh4] has been determined by single-crystal X-ray analysis. The compound crystallizes in an orthorhombic unit cell (space group Pc2(1)n, Z = 4) with lattice constants a = 11.400(4), b = 16.893(3), c = 20.537(6) angstrom. Least-squares refinement converged at R = 0.078 (R(w) = 0.056) for 1290 unique reflections with l > 3-sigma(l). The structure of [HL]+ shows the five nitrogens atoms in an endo configuration, indicating that the proton is inside the cage cavity. The cage L encapsulate Li+ and the complex formation equilibrium for [LiL]+ has been investigated by potentiometry [log K = 3.0(1)] and Li-7 NMR techniques.