Carbazole-based N₄-donor Schiff base macrocycles: obtained metal free and as Cu(<scp>ii</scp>) and Ni(<scp>ii</scp>) complexes

Abstract

The very different multi-step routes to the closely related pair of diformyl-carbazole head units, 1,8-diformyl-3,6-di-tert-butyl-9H-carbazole (1tBu) and 1,8-diformyl-9H-carbazole (1H), are detailed and compared. The first examples of Schiff base macrocycles derived from diformyl-carbazole head units are reported. Specifically, the direct cyclisation of 1tBu or 1H with diethylenetriamine gives the two metal-free [1 + 1] Schiff base macrocycles HLH and HLtBu in high yields. Four carbazole-based macrocyclic complexes, [Cu^IIL(OH₂)]OAc and [Ni^IIL]OAc, where L = LH or LtBu, were accessed either by metallation of these macrocycles, or by metal templated reaction of the macrocycle components. [Cu^IILtBu(OH₂)]OAc·0.5(Ether) and [NiLH]OAc·EtOH, were structurally characterised, confirming the nickel(ii) complexes are square planar (both show diamagnetic NMR spectra) and that the copper(ii) complexes are square pyramidal with a water molecule bound in the axial site. Like porphyrins, both of these N₄-donor macrocycles, which differ only in the R group present at the 3 and 6 positions (H or tBu), impose a strong ligand field.