The molecular and electronic structures of monomeric cobalt complexes containing redox noninnocent o-aminobenzenethiolate ligands

Dark blue [PPh4][CoIII(2L)] (2), where (2L)2− represents the closed-shell dianion of 4,6-di-tert-butyl-2-[(pentafluorophenyl)amino]benzenethiol, has been synthesized from the reaction of H2(2L) and CoCl2 (2:1) in acetonitrile with excess NEt3, brief exposure of the solution to air, and addition of [PPh4]Br. The oxidation of 2 with one equivalent of iodine produces the neutral species [CoIII(2L)2I]0 (3), where (2L)1− represents the one-electron oxidized π radical anion of (2L)2−. Crystalline [CoIII(4L)] (4), where (4L)3− is the π radical monoanion of bis-2,2′-(1,2-diphenylethylenediimine)-benzenethiolate, was precipitated from a toluene reflux of [CoII(3L)2], where (3L)2− is the closed-shell monoanion of 2-(phenylmethylamino)benzenethiol. The reduction of 4 with CoCp2 under anaerobic conditions yielded dark violet crystals of [CoCp2][CoIII(4L)] (5). The reaction of Zn(CH3CO2)2 with 2-phenylbenzothiazoline in methanol resulted in the formation of [ZnII(3L)2]0 (6). The two monoanions 2, and 5, along with [N(n-Bu)4][Co(abt)2] (1) (abt2− = o-aminobenzenethiolate), and neutral 4 have all been shown by X-ray crystallography to be square planar. A tetrahedral geometry was adopted by 6. From temperature dependent (3–300 K) magnetic susceptibility measurements, it was established the monoanions have a triplet ground state characterized by a large zero field splitting. EPR measurements of 4, and electrochemically oxidized 1 and 2 reveal distinctly different spin Hamiltonian parameters that are interpreted with the aid of density function theoretical (DFT) calculations. It is shown that oxidation states describing a d6 Co(III) or d7 Co(II) cannot be unambiguously assigned for these neutral and monoanionic species.

Graphical abstractMonoanionic cobalt complexes with two bidentate or one tetradentate o-aminobenzenethiolate ligands have been prepared and structurally characterized. The one-electron oxidation to the neutral compound is a ligand-centered event. The oxidation state of the cobalt ion is ambiguous, as it is more reduced than typical Co(III) and more oxidized than typical Co(II) complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide