Synthesis and some octahedral complexes of a chiral triaza macrocycle

Abstract

The chiral and bulky tacn (1,4,7-triazacyclononane, L1) analogue chtacn (2,5,8-triazabicyclo[7.4.01,9]tridecane, L2), which has a cyclohexane ring fused to the tacn framework, has been synthesized commencing with (±), (+)- or (–)-trans-cyclohexane-1,2-diamine. Syntheses and properties of cobalt(III), nickel(II), chromium(III) and iron(III) complexes are described. In the complex bis(RR-2,5,8-triazabicyclo[7.4.01,9]tridecane)cobalt(III) chloride hexafluorophosphate the cyclohexane rings and pairs of adjacent secondary amines occupy an approximate plane around the cobalt ion, with the remaining secondary amines in each tridentate ligand in trans dispositions. A large positive Cotton effect occurs under the low energy absorption band in the circular dichroism spectrum of this cobalt(III) complex of the R,R-(–)-chtacn ligand. In the dinuclear complex aqua-di-µ-chloro-chlorobis(SS-2,5,8-triazabicyclo[7.4.01,9]tridecane)dinickel(II) perchlorate each nickel atom is bound to a tridentate macrocyclic ligand in different dispositions, with the distorted octahedron of each nickel completed by two bridging chloride ions and either a chloride ion or aqua molecule. For [M(Ln)2]n+ complexes, electronic maxima are shifted slightly to lower energy and reduction potentials slightly to more negative potential in the case of L2 compared with L1.