Carbazole-based N4-donor Schiff base macrocycles: obtained metal free and as Cu(II) and Ni(II) complexes

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 HLH and HLtBu in high yields. Four carbazole-based macrocyclic complexes, [(CuL)-L-parallel to(OH2)]OAc and [(NiL)-L-parallel to]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. [(CuLtBu)-L-parallel to(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 N-4-donor macrocycles, which differ only in the R group present at the 3 and 6 positions (H or tBu), impose a strong ligand field.