Controlled synthesis and reversible oxidation of a thiolate-bridged macrocyclic dinickel(II) complex

Abstract

The synthesis of S-(2,6-Diformyl-4-methylphenyl) dimethylthiocarbamate, a valuable thiolate-containing ligand precursor, is reported in detail for the first time. This precursor has considerable potential in biosite modelling studies. A macrocycle L and a related acyclic ligand L′ have been prepared, as complexes, from the precursor and 1,3-diaminopropane. The macrocycle was successfully templated by both zinc(II) and nickel(II) ions yielding [Zn₂L(H₂O)₂][O₃SCF₃]₂·H₂O 1 and the diamagnetic complex [Ni₂L][ClO₄]₂2, respectively. A single-crystal X-ray analysis of 1 showed the zinc ions to have trigonal-bipyramidal environments and the macrocycle to have a stepped conformation. In contrast, the structure determination of 2 revealed square-planar N₂S₂ co-ordination for Ni^II and a bowed macrocycle conformation which results in much shorter metal–metal and sulfur–sulfur separations than the stepped conformation adopted in the case of Zn^II[average Zn ⋯ Zn 3.351(1), S ⋯ S 3.363(3) for 1vs. Ni ⋯ Ni 3.146(2), S ⋯ S 2.839(5)Å for 2]. Two one-electron oxidations, the first reversible and the second quasi-reversible, were observed for the dinickel(II) complex, whereas one irreversible two-electron oxidation was observed for the dizinc(II) complex. An acetal forms in the presence of ethanol and leads to the isolation of the acyclic trinickel(II) complex [Ni₂L′₂Ni][ClO₄]₂3.