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Issue 22, 2013
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Complexes of a porphyrin-like N4-donor Schiff-base macrocycle

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A metal-free 16-membered N4-donor [1 + 1] Schiff-base macrocycle was isolated as HLPrPrPr·2acid, by 1 : 1 condensation of diphenylamine-2,2′-dicarboxaldehyde (1), dipropylene triamine and an excess of either acetic or formic acid, or as HLPrPrPr·(tosylic acid) when just one equivalent of tosylic acid was employed. Interestingly, the acid-free synthesis employed for the 14-membered analogue HLEtEt failed to generate pure HLPrPrPr macrocycle, but nevertheless the crude product obtained was able to be used in subsequent complexation reactions to form five mononuclear complexes: ZnIILPrPrPr(BF4)·H2O·0.5IPA (where IPA is isopropylalcohol), [CuIILPrPrPr](BF4), [NiIILPrPrPr](BF4), [CoIILPrPrPr](BF4)·0.5H2O, [FeIIILPrPrPr(NCS)2]·1.5H2O. Crystal structure determinations show that, like the HLEtEt analogues, [NiIILPrPrPr](BF4) features a square planar N4 coordinated NiII centre and [FeIIILPrPrPr(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, [NiIILPrPrPr](BF4) has two reversible redox processes, at Em = +0.38 (ΔE = 0.06 V) and −1.7 V (ΔE = 0.06 V), whereas the previously reported analogue [NiIILEtEt](BF4) had a process at Epc = +0.59 V with only a weak return wave. Likewise, [CuIILPrPrPr](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 [CuIILEtEt](BF4) only featured irreversible processes, with the oxidation occurring at Epc = +0.50 V.

Graphical abstract: Complexes of a porphyrin-like N4-donor Schiff-base macrocycle

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The article was received on 20 Dec 2012, accepted on 28 Jan 2013 and first published on 29 Jan 2013

Article type: Paper
DOI: 10.1039/C3DT33057E
Citation: Dalton Trans., 2013,42, 7913-7923
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    Complexes of a porphyrin-like N4-donor Schiff-base macrocycle

    R. K. Wilson (née Sanyal) and S. Brooker, Dalton Trans., 2013, 42, 7913
    DOI: 10.1039/C3DT33057E

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