Copper(I) complexes of dinucleating macrocyclic bis(dithiadiimine) ligands

Abstract

The 34- and 36-membered macrocyclic bis(dithiadiimine) Schiff bases 3,17,26,40-tetrathia-6,14,29,37-tetraazapentacyclo[40.4.1^8,12.1^31,35.0.0^19,24]octatetraconta-6,8,10,12(47),13,19,21,23,29,31,33,35(48),36,42,44,46-hexadecaene (L³) and 3,16,25,38-tetrathia-6,13,28,35-tetraazapentacyclo[38.4.2^8,11.2^30,33.0.0^18,23]octatetraconta-6,8,10,12,18,20,22,28,30,32,34,40,42,44,45(46),47(48)-hexadecaene (L²) have been synthesized in high yield by a 2 + 2 condensation of isophthalaldehyde and terephthalaldehyde with 2,2′-o-phenylenebis(methylenethio)bis(ethanamine) (L¹) in acetonitrile. Air-stable dicopper(I) complexes of L² and L³ were obtained from complexation reactions with [Cu(CH₃CN)₄]ClO₄ in CH₃CN solution, with the structure of [Cu₂L²][ClO₄]₂· 0.5CH₃OH·2.5H₂O confirmed by a crystal structure analysis. The complex consists of two N₂S₂ donor sets each tetrahedrally co-ordinated to the copper(I) ions with two para-substituted phenyl rings bridging the two N₂S₂ ‘compartments’ π-stacked parallel (separation 3.5 Å), and a double helical arrangement of the ligand backbone clearly evident. Electrochemical studies of the dinuclear complexes revealed quasi-reversible Cu^I–Cu^II couples above +1 V (versus NHE), with reversibility influenced by the presence of ferrocene, which acts as a surface modifier for electron transfer.