Chromium(III) complexes of 1,4,8,12-tetraazacyclopentadecane

Abstract

The reaction of [CrCl₃(dmf)₃](dmf =N,N-dimethylformamide) with 1,4,8,12-tetraazacyclopentadecane ([15]aneN₄) in dmf solution gives trans-[Cr([15]aneN₄)Cl₂]Cl in high yield. Using the dichloro complex as a precursor, a variety of Cr^III complexes of formula trans-[Cr([15]aneN₄)X₂]⁺ have been prepared and characterised (X = Br, N₃, OH or NCS). The cis-oxalato complex cis-[Cr([15]aneN₄)(ox)]⁺ has also been characterised as the perchlorate salt. This complex on treatment with concentrated hydrochloric acid gives a dichloro complex which appears to be identical to that prepared by the dmf route. Complexes of [15]aneN₄ can occur in six diastereoisomeric forms due to the four chiral secondary NH centres. The trans-VI conformer with three chair six-membered chelate rings and an eclipsed five-membered ring (CCCe) appears to be favoured. Infrared and visible spectra are reported and the detailed sterochemistry of the complexes discussed.