Transition-metal complexes of the macrocyclic ligand C-meso-5,12-dimethyl-1,4,8,11-tetra-azacyclotetradecane

Abstract

Reduction of 5,12-dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene dihydroperchlorate with Na[BH₄] in methanol–water solution gives predominantly the title ligand (L_M). The metal(II) complexes [CuL_M][ClO₄]₂, [NiL_M][ClO₄]₂, [PbL_M][NO₃]₂·1.5H₂O, and [ZnL_M][ClO₄]₂ has been prepared. In aqueous solution, spectroscopic measurements show that a planar–octahedral equilibrium [NiL_M]²⁺+ 2H₂O ⇌[NiL_M(OH₂)₂]²⁺ occurs with the nickel(II) derivative. The octahedral nickel(II) complexes [NiCl₂L_M], [Ni(NCS)₂L_M], and [NIL_M(OSMe₂)₂][ClO₄]₂ have been characterised. The cobalt(III) complexes trans-[CoCl₂L_M]Cl·2H₂O, trans-[Co(N₃)₂L_M][N₃], trans-[CoBr₂L_M]Br·H₂O, and trans-[Co(NO₂)₂L_M][ClO₄] have also been prepared. X-Ray crystallography on the azido-complex conflrms that it has the trans-(III) or cyclam structure. Ligand folding can occur as indicated by the preparation of cis-[RhCl₂L_M]Cl. N-Methylation of L_M with formic acid–formaldehyde gives the NN′N″N‴-tetramethyl ligand and complexes of this ligand with Zn^II and Cu^II have been prepared. The co-ordination chemistry of L_M is discussed and i.r. and d–d electronic spectra reported.