Synthesis, characterization and DFT studies of the cobalt(iii) complex of a tetrapodal pentadentate N4S donor ligand

Abstract

The synthesis of the pentadentate ligand 2,6-bis(3,3-dimethyl-2,4-dioxocyclohexanyl)-4-thiaheptane (N₄Samp) is described. The synthetic pathway involves the coupling of two 1,3-(dimethylenedioxy)-2-methyl-2-(methylene-p-toluenesulfonyl)propane moieties with sodium sulfide and subsequent synthetic elaboration to prepare the final N₄S donor system. The cobalt(III) complex [Co(N₄Samp)Cl]²⁺ has been prepared and subsequently crystallized as the tetrachlorozincate salt. The X-ray structure analysis confirms the pentadentate nature of the ligand and shows the thioether donor occupying one apex with four equivalent amine donors effectively occupying the equatorial plane of the molecule. The sixth coordination site is occupied by a chloro ligand. The electronic absorption and ¹³C NMR spectra have been studied. DFT calculations have been employed to explore structural and mechanistic comparisons between [Co(N₄Samp)Cl]²⁺ and an analogous pentaaamine complex.