Transition-metal complexes of the macrocyclic ligand 5,6,12,13-tetramethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene

Abstract

The title macrocyclic ligand (L) has been prepared as its dihydroperchlorate salt by the reaction of 3-methylbut-3-en-2-one with ethylenediamine monohydroperchlorate in methanol solution. The reaction gives the trans-di-imine and a ca. 7 : 3 mixture of the C-meso and C-rac diastereoisomers. Fractional crystallisation of [NiL][ClO₄]₂ from aqueous solution gives three isomers [(a)–(c)] identified by ¹H n.m.r. spectroscopy. X-Ray crystallography confirms that isomer (b) is the centrosymmetric N-meso-C-meso diastereoisomer and isomer (c) is the N-rac-C-rac diastereoisomer. Equilibration of (a) and (b) in Me₂SO–K[OH] gives isomer (d) which is the other member of the C-meso series. N.m.r. studies confirm that the reaction proceeds via the steps (b)→(a)→(d). Isomer (b) has a diequatorial arrangement of the ring methyls. A number of other metal(II) complexes (M = Cu, Zn, or Hg) have been charecterised as their perchlorate salts. In addition a series of octahedral cobalt(III) complexes of the general type trans-[CoX₂L]ⁿ⁺[X₂= Cl₂, Br₂, (NO₂)₂, (NCS)₂, (N₃)₂, (NH₃)₂, (O₂CMe)₂, or Cl(NO₂)] and trans-[RhCl₂][ClO₄]₂ have been synthesised, as has cis-[Co(CO₃)L][ClO₄]·2H₂O. Infrared and d–d spectra are reported.