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

摘要

Dark blue [PPh_4][Co~(III)(~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 H_2(~2L) and CoCl_2 (2:1) in acetonitrile with excess NEt_3, brief exposure of the solution to air, and addition of [PPh_4]Br. The oxidation of 2 with one equivalent of iodine produces the neutral species [Co~(III)(~2L) _2I]~0 (3), where (~2L~(1-) represents the one-electron oxidized π radical anion of (~2L)~(2-). Crystalline [Co~(III)(~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 [Co~(II)(~3L)_2], where (~3L) ~(2-) is the closed-shell monoanion of 2-(phenylmethylamino) benzenethiol. The reduction of 4 with CoCp_2 under anaerobic conditions yielded dark violet crystals of [CoCp_2][Co ~(III)(~4L)] (5). The reaction of Zn(CH_3CO _2)_2 with 2-phenylbenzothiazoline in methanol resulted in the formation of [Zn~(II)(~3L)_2]~0 (6). The two monoanions 2, and 5, along with [N(n-Bu)_4][Co(abt) _2] (1) (abt~(2-) = 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 d~6 Co(III) or d~7 Co(II) cannot be unambiguously assigned for these neutral and monoanionic species.