Chlorocobalt(III) and chlorochromium(III) complexes of a new chiral quinquedentate polyamine based on RR-trans-cyclohexane-1,2-diamine

Abstract

The potentially quinquedentate ligand RR,RR-1,3-bis(2′-aminocyclohexylamino)-2-methylpropan-2-amine (L³) readily forms both chloropentaaminecobalt(III) and chloropentaaminechromium(III) complex cations. The [Co(L³)Cl]Cl[ClO₄]·2H₂O compound crystallized in the orthorhombic space group P2₁2₁2₁, a= 10.414(2), b= 12.789(3), c= 18.869(4)Å, with the co-ordinated chloride in a trans disposition relative to the central primary amine in the ligand, the two pairs of nitrogen donors from the cyclohexane-1,2-diamine residues being coplanar with the cobalt ion. The –NH–CH₂–C(CH₃)(NH₂)–CH₂–NH– core of the ligand necessarily occupies an octahedral face. Metal–nitrogen distances (Co–N 1.944–1.971 Å) are slightly longer than in the 5-methyl-3,7-diazanonane-1,5,9-triamine analogue although still relatively short for cobalt(III)–amine bonds, whereas Co–Cl (2.241 Å) is also short. Chiroptical properties of the complexes are reported. Base hydrolysis reactions of the chloro–cobalt(III) and –chromium(III) complexes both exhibit two steps, assigned to chloride hydrolysis and trans–cis isomerization reactions.