Extending the coordination chemistry of cobalt with the metalloligand [Pt2(μ-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives

• Published in: Inorganica Chimica Acta 2011-10, Vol.376 (1), p.446-455
• Main Authors: Clarke, Hannah M., Henderson, William, Nicholson, Brian K.
• Format: Article
• Language: English
• Subjects: Cobalt complexes; Electrospray ionisation mass spectrometry; Platinum complexes; X-ray crystal structure
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2011.07.006

The first examples of cobalt(III) adducts of [Pt2(μ-S)2(PPh3)4] have been synthesised by air oxidation of cobalt(II) adducts containing the ligands dithiocarbamate or the anion of 8-hydroxyquinoline (Q); the X-ray structure of [Pt2(μ-S)2(PPh3)4CoQ2]PF6 is reported and is the first of a true six-coordinate adduct of [Pt2(μ-S)2(PPh3)4]. An ESI MS study indicates fragmentation of [Pt2(μ-S)2(PPh3)4CoQ2]+ to the radical cation [Pt2(μ-S)2(PPh3)4]+, which can be independently generated mass spectrometrically from [Pt2(μ-S)2(PPh3)4] in alkaline solution. [Display omitted] ► Series of new cobalt(II) and cobalt(III) adducts of [Pt2(μ-S)2(PPh3)4] prepared. ► 8-Hydroxyquinolinate (Q), picolinate and dithiocarbamate promote oxidation of Co(II) to Co(III). ► ESI MS study indicates fragmentation of [Pt2(μ-S)2(PPh3)4CoQ2]+ to [Pt2(μ-S)2(PPh3)4]+. ► [Pt2(μ-S)2(PPh3)4]+ observed in ESI MS analysis of [Pt2(μ-S)2(PPh3)4] in alkaline solution. ► Structure of [Pt2(μ-S)2(PPh3)4CoQ2]PF6 is the first of a true six-coordinate adduct of this type. The coordination chemistry of the metalloligand [Pt2(μ-S)2(PPh3)4] towards cobalt(II) and cobalt(III) centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed methodology. Reaction of [Pt2(μ-S)2(PPh3)4] with CoCl2·6H2O in methanol gave a green-yellow suspension of the known adduct [Pt2(μ-S)2(PPh3)4CoCl2], and the CoBr2 adduct could be similarly prepared. When in situ-generated [Pt2(μ-S)2(PPh3)4CoCl2] is reacted with 8-hydroxyquinoline (HQ) and base, the initial product is the cobalt(II) adduct [Pt2(μ-S)2(PPh3)4CoQ]+, which is then converted in air to the cobalt(III) adduct [Pt2(μ-S)2(PPh3)4CoQ2]+, isolated as its hexafluorophosphate salt. The corresponding picolinate (Pic) derivative [Pt2(μ-S)2(PPh3)4Co(Pic)2]+ was similarly prepared, however reaction of [Pt2(μ-S)2(PPh3)4], CoCl2·6H2O and 8-(tosylamino)quinoline (HTQ) produced only the cobalt(II) adduct [Pt2(μ-S)2(PPh3)4CoTQ]+. Reactions of [Pt2(μ-S)2(PPh3)4], CoCl2·6H2O and dithiocarbamates gave cobalt(III) complexes [Pt2(μ-S)2(PPh3)4Co(S2CNR2)2]+ [R=Et or R2=(CH2)4], and proceeded much more rapidly, consistent with the known ability of the dithiocarbamate ligand to stabilize cobalt in higher oxidation states. A study of the fragmentation of cobalt(III) adducts by positive-ion ESI mass spectrometry indicated that [Pt2(μ-S)2(PPh3)4CoQ2]+ fragments to form the radical cation [Pt2(μ-S)2(PPh3)4]+, which could also be generated by ESI MS analysis of [Pt2(μ