Dinuclear Cp Cobalt Complexes of the 1,2,4,5-Benzenetetrathiolate Bischelating Ligand

• Published in: Inorganic chemistry 2008-02, Vol.47 (4), p.1301-1312
• Main Authors: Nomura, Mitsushiro, Fourmigué, Marc
• Format: Article
• Language: English
• Subjects: Chemical Physics; Chemical Sciences; Material chemistry; Physics
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic700778b

The dinuclear Cp*Co dithiolene complex [Cp*Co(btt)CoCp*] (1) is prepared in high yield from the reaction of the bis(dibutyltin) complex of 1,2,4,5-benzenetetrathiolate (btt) with 2 equiv of [Cp*Co(CO)I2]. Mononuclear complexes are also obtained from 1,2,4,5-tetrakis(isopropylthio)benzene (2) and sodium in pyridine, from benzo[1,2-d;4,5-d ′]bis(1,3-dithiolane-2,6-dione) (3) and t BuOK in tetrahydrofuran, or from benzo[d]-1,3-dithiolane-2-one (7) and t BuOK to afford respectively 4a, 4b, and [Cp*Co(bdt)] (6), while [Cp*Co(dmit)] (8) is obtained by literature methods. The X-ray structures of the dinuclear complex 1 and the mononuclear complexes 4a and 6 were determined. They are all characterized by Cp* · · · btt face-to-face intermolecular interactions, leading to a recurrent 4-fold symmetry motif. The cyclic voltammograms of the [Cp*Co(dithiolene)] complexes performed in CH2Cl2 show reversible CoIII to CoII reduction but irreversible oxidation waves. The large potential difference between the two reduction waves of the bimetallic complex 1 (269 mV) indicates a stable mixed-valence CoIII–CoII state for the reduced [Cp*Co(btt)CoCp*]− anion. Upon trimethyl phosphite addition, the mono-P(OMe)3 adduct [1·P(OMe)3] exhibits a red shift of the low-energy absorption band to the IR region (856 nm, ϵ = 13 000 M−1·cm−1), while [8·P(OMe)3] exhibits a 150 nm blue shift. The stability constants of these P(OMe)3 adducts were determined from UV–vis spectroscopic titration experiments, with, for example, log(K/mol−1·dm3) values of 3.1 and 0.52 for the mono- and bis-adduct of 1, respectively. The electrochemical investigation of 1 and 8 in excess phosphite shows a strong current enhancement upon oxidation, attributable to the catalytic generation of the radical cation P(OMe)3 •+.