Cleaner and stronger: how 8-quinolinolate facilitates formation of Co(III)-thiolate from Co(II)-disulfide complexes.

The formation of Co(III)-thiolate complexes from Co(II)-disulfide complexes using the anionic ligand 8-quinolinolate (quin) has been studied experimentally and quantum chemically. Two Co(II)-disulfide complexes [Co(LSSL)(Cl)] ( = 1 or 2; LSSL = 2,2'-disulfanediylbis(,-bis(pyridin-2-ylmethyl)ethan-1-amine; LSSL = 2,2'-disulfanedylbis (-((6-methylpyridin-2-yl)methyl)--(pyridin-2-ylmethyl) ethan-1-amine) have been successfully converted with high yield to their corresponding Co(III)-thiolate complexes upon addition of the ligand 8-quinolinolate. Using density functional theory (DFT) computations the d-orbital splitting energies of the cobalt-thiolate compounds [Co(LS)(quin)] and [Co(LS)(quin)] were estimated to be 3.10 eV and 3.07 eV, indicating a slightly smaller ligand-field strength of ligand LSSL than of LSSL. Furthermore, the orientation of the quin ligand in the thiolate compounds determines the stability of the thiolate complex. DFT computations show that the thiolate structure benefits from more electrostatic attraction when the oxygen atom of the quin ligand is positioned to the sulfur atom of the [Co(LS)] fragment. Quin is the first auxiliary ligand with which it appeared possible to induce the redox-conversion reaction in cobalt(II) compounds of the relatively weak-field ligand LSSL.