Carbazole-based N4-donor Schiff base macrocycles: obtained metal free and as Cu(ii) and Ni(ii) 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 (1^tBu) and 1,8-diformyl-9H-carbazole (1^H), are detailed and compared. The first examples of Schiff base macrocycles derived from diformyl-carbazole head units are reported. Specifically, the direct cyclisation of 1^tBu or 1^H with diethylenetriamine gives the two metal-free [1 + 1] Schiff base macrocycles HL^H and HL^tBu in high yields. Four carbazole-based macrocyclic complexes, [Cu^IIL(OH₂)]OAc and [Ni^IIL]OAc, where L = L^H or L^tBu, were accessed either by metallation of these macrocycles, or by metal templated reaction of the macrocycle components. [Cu^IIL^tBu(OH₂)]OAc·0.5(Ether) and [NiL^H]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.