Add time:07/26/2019         Source:sciencedirect.com

The synthesis of the two-armed amine precursor 2,6-di[N-(3′-aminopropyl)aminomethyl]-4-methylphenol (1) is detailed. Zinc(II) and nickel(II) templated Schiff base condensation reactions of 1 and 2,6-diformyl-4-methylthiophenolate (obtained by base hydrolysis of S-(2,6-diformyl-4-methylphenyl)dimethylthiocarbamate (2)), in IPA, yield the macrocyclic complexes Zn2L1(CH3CO2)2(H2O)2 (3) and [Ni2L1(MeCN)2](ClO4)2 (4), respectively. Addition of two equivalents of NaNCS to 4, in DMF, gives the complex [Ni2L1(NCS)2(DMF)] (5). An acyclic complex, [Ni2L2(C3H3N2)](CF3SO3)2 (6), is formed by reaction of two equivalents of nickel(II) ions with 2,6-diformyl-4-methylthiophenolate, pyrazole and two equivalents of 2-(2-aminoethyl)pyridine. Single crystal X-ray diffraction studies of 4 and 5 revealed differing environments for the nickel(II) ions within the macrocycle: in the case of 4 one nickel ion is square planar whilst the other is octahedral, whereas in 5 both nickel ions are high spin but one is square pyramidal whilst the other is octahedral. In contrast, the structure determination carried out on 6 shows that both of the nickel ions are square planar. 1H and 13C NMR studies show that the diamagnetic compounds Zn2L1(CH3CO2)2(H2O)2 (3) and [Ni2L2(C3H3N2)](CF3SO3)2 (6) remain intact in MeNO2-d3 solution. In MeCN-d3 solution the dizinc complex 3 again retains its integrity. In contrast, the dinickel complex 6 has some tendency to coordinate MeCN in the otherwise vacant axial sites leading to traces of paramagnetic species in solution and to very broad signals in the 1H NMR spectrum. Electrochemical studies, in MeCN, on the soluble dinickel(II) complexes 4 and 6, revealed a series of one electron processes (−1.23QR, +0.65I and +1.00R V versus 0.01 M AgNO3–Ag for 4; −1.46I, −0.96R, +1.03I and +1.50I V versus 0.01 M AgNO3–Ag for 6; where R, reversible; I, irreversible; QR, quasireversible), in contrast to the dizinc(II) complex 3 which is redox inactive over this range.

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