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

• Published in: Inorganica Chimica Acta Vol. 363; no. 12; pp. 2702 - 2714
• Main Authors: Sproules, Stephen, Kapre, Ruta R., Roy, Nabarun, Weyhermüller, Thomas, Wieghardt, Karl
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.10.2010
• Subjects: Aminobenzenethiolate; Cobalt; DFT; Electronic structure; Noninnocent ligands; Aminobenzenethiolate; Electronic structure; Noninnocent ligands; DFT; Cobalt
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2010.03.042

Monoanionic 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. 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.