Dimetallic thiolate-bridged complexes: synthesis and rich electrochemistryof dinickel(II) and dizinc(II) monothiolate complexes

The synthesis of the two-armed amine precursor 2,6-di[N-(3'-aminopropyl)ami nomethyl]-4-methylphenol (1) is detailed. Zinc(II) and nickel(II) templated Schiff base condensation reactions of 1 and 2.6-diformyl-4-methylthiopheno late (obtained by base hydrolysis of S-(2,6-diformyl-4-methylphenyl)dimethy lthiocarbamate (2)), in IPA, yield the macrocyclic complexes Zn(2)L1(CH3CO2 )(2)(H2O)(2) (3) and [Ni(2)L1(MeCN)(2)](ClO4)(2) (4), respectively. Additio n of two equivalents of NaNCS to 4, in DMF, gives the complex [Ni(2)L1(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-met hylthiophenolate, pyrazole and two equivalents of 2-(2-aminoethyl)pyridine. Single crystal X-ray diffraction studies of 4 and 5 revealed differing env ironments for the nickel(II) ions within the macrocycle: in the case of 4 o ne 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 othe r is octahedral. In contrast, the structure determination carried out on 6 shows that both of the nickel ions are square planar. H-1 and C-13 NMR stud ies show that the diamagnetic compounds Zn(2)L1(CH3CO2)(H2O)(2) (3) and [Ni (2)L2(C3H3N2)](CF3SO3)(2) (6) remain intact in MeNO2-d(3) solution. In MeCN -d(3) solution the dizinc complex 3 again retains its integrity. In contras t, the dinickel complex 6 has some tendency to coordinate MeCN in the other wise vacant axial sites leading to traces of paramagnetic species in soluti on and to very broad signals in the H-1 NMR spectrum. Electrochemical studi es, in MeCN, on the soluble dinickel(II) complexes 4 and 6, revealed a seri es of one electron processes (- 1.23(QR), + 0.65(I) and + 1.00(R) V versus 0.01 M AgNO3-Ag for 4; - 1.46(I), - 0.96(R), + 1.03(I) and + 1.50(I) V vers us 0.01 M AgNO3-Ag for 6; where R, reversible; I, irreversible; QR, quasire versible), in contrast to the dizinc(II) complex 3 which is redox inactive over this range. (C) 2000 Elsevier Science Ltd. All rights reserved.