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

A metal-free 16-membered N-4-donor [1 + 1] Schiff-base macrocycle was isolated as HLPr center dot 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 center dot(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: (ZnLPr)-L-II(BF4)center dot H2O center dot 0.5IPA (where IPA is isopropyl-alcohol), [(CuLPr)-L-II](BF4), [(NiLPr)-L-II](BF4), [(CoLPr)-L-II](BF4)center dot 0.5H(2)O, [(FeLPr)-L-III(NCS)(2)]center dot 1.5H(2)O. Crystal structure determinations show that, like the HLEt analogues, [(NiLPr)-L-II](BF4) features a square planar N-4 coordinated Ni-II centre and [(FeLPr)-L-III(NCS)(2)]center dot 0.15MeOH center dot 0.2H(2)O features an octahedral N-6 coordinated Fe-III centre (two NCS anions bound axially). In both cases the N-4-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 Zn-II complex exhibits multiple ligand-centered redox processes. Interestingly, [(NiLPr)-L-II](BF4) has two reversible redox processes, at E-m = + 0.38 (Delta E = 0.06 V) and -1.7 V (Delta E = 0.06 V), whereas the previously reported analogue [(NiLEt)-L-II](BF4) had a process at E-pc = +0.59 V with only a weak return wave. Likewise, [(CuLPr)-L-II](BF4) has a reversible process, at E-m = -1.17 V (Delta E = 0.06 V) plus a process at E-pc = +0.45 V, whereas previously reported [(CuLEt)-L-II](BF4) only featured irreversible processes, with the oxidation occurring at E-pc = +0.50 V.