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Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
; Fax: +64 3 479 7906
; Tel: +64 3 4797919
Dalton Trans., 2013,42, 7913-7923
20 Dec 2012,
28 Jan 2013
First published online
29 Jan 2013
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), [CuIILPr](BF4), [NiIILPr](BF4), [CoIILPr](BF4)·0.5H2O, [FeIIILPr(NCS)2]·1.5H2O. Crystal structure determinations show that, like the HLEt analogues, [NiIILPr](BF4) features a square planar N4 coordinated NiII 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, [NiIILPr](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 [NiIILEt](BF4) 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 [CuIILEt](BF4) only featured irreversible processes, with the oxidation occurring at Epc = +0.50 V.
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