Complexes of a porphyrin-like N4-donor Schiff-base macrocycle

Abstract

A metal-free 16-membered N4-donor [1 + 1] Schiff-base macrocycle was isolated as HLPr·2acid, by 1:1 condensation of diphenylamine-2,2′-dicarboxaldehyde (1), dipropylene triamine and an excess of either acetic or formic acid, or as HLPr·(tosylic acid) when just one equivalent of tosylic acid was employed. Interestingly, the acid-free synthesis employed for the 14-membered analogue HLEt failed to generate pure HLPr macrocycle, but nevertheless the crude product obtained was able to be used in subsequent complexation reactions to form five mononuclear complexes: ZnIILPr(BF4) ·H2O·0.5IPA (where IPA is isopropylalcohol), [Cu IILPr](BF4), [NiIIL Pr](BF4), [CoIILPr](BF 4)·0.5H2O, [FeIIILPr(NCS) 2]·1.5H2O. Crystal structure determinations show that, like the HLEt analogues, [NiIILPr] (BF4) features a square planar N4 coordinated Ni II centre and [FeIIILPr(NCS) 2]·0.15MeOH·0.2H2O features an octahedral N6 coordinated FeIII centre (two NCS anions bound axially). In both cases the N4-donor macrocycle is bound equatorially to the metal ion. Cyclic voltammograms of the BF4 complexes were carried out in MeCN vs. 0.01 mol L-1 AgNO3/Ag and revealed multiple redox processes. The ZnII complex exhibits multiple ligand-centered redox processes. Interestingly, [NiIIL Pr](BF4) has two reversible redox processes, at E m = +0.38 (ΔE = 0.06 V) and -1.7 V (ΔE = 0.06 V), whereas the previously reported analogue [NiIILEt](BF 4) had a process at Epc = +0.59 V with only a weak return wave. Likewise, [CuIILPr](BF4) has a reversible process, at Em = -1.17 V (ΔE = 0.06 V) plus a process at Epc = +0.45 V, whereas previously reported [CuIIL Et](BF4) only featured irreversible processes, with the oxidation occurring at Epc = +0.50 V. © 2013 The Royal Society of Chemistry.