Preparation and molecular structure of bridged tetra-aza macrocyclic ligands

Abstract

Three derivatives of geometric isomers of 1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradecane have been prepared by coupling (a) the meso-isomer with formaldehyde and formic acid and (b) the meso- and racemic isomers with glyoxal. Their crystal structures have been determined from four-circle diffractometer data: 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azatricyclo[9.3.1.1]hexadecane (3) is triclinic, P, with a= 5.977(1), b= 11.276(2), c= 8.964(2)Å, α= 112.85(1), β= 115.54(1), γ= 91.28(1)°, R= 0.043 for 1 339 observed reflections [I > 3σ(I)]; meso-1,1,3,6,6,8-hexamethyl-3a,5a,8a,10a-tetra-azaperhydropyrene, isomer (4), is triclinic, P, with a= 6.219(2), b= 8.412(3), c= 19.397(7)Å, α= 94.62(3), β= 87.65(3), γ= 118.50(3)°, R= 0.049 for 1 371 observed reflections; and the racemic isomer (5) is monoclinic, P2₁/c, with a= 11.507(2), b= 11.964(2), c= 13.885(2)Å, β= 107.94(1)°, R= 0.041 for 2 128 observed reflections. The structures show that none have four aligned lone pairs, and thus are unlikely to function as quadridentate ligands to one metal ion. The conformation of (3) is standard, but (4) and (5) have cis-fusion at three of five junctions in their fused decalin system. This can be attributed to steric hindrance at an intermediate stage in the formation process.