Photocatalytic Water-Soluble Cationic Platinum(II) Complexes Bearing Quinolinate and Phosphine Ligands

Cationic Pt(II) complexes ([Pt(QO/S)(P Lambda P)]X), having 8-oxy or 8-thioquinolinate (QO/S) and seven different mono- or bidentate phosphines as ligands, have been synthesized and characterized. The photophysical, stability, and photocatalytic properties of those complexes were studied and compared to that of the parent [Pt(QO/S)(dmso)(Cl)]. The coordination of phosphines induced a red-shift in the absorption energy of the MLCT band, whereas the emission wavelength of the complexes only depended on the nature of the quinolinate ligand. Moreover, the photocatalytic activity of the Pt(II) complexes was evaluated in the oxidation of sulfides using atmospheric oxygen as an oxidant. All the complexes were active photocatalysts for that transformation, with [Pt(QO)(BINAP)]Cl and [Pt(QO)(SEGPHOS)]Cl (BINAP: 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, SEGPHOS: (4,4'-bibenzodioxole)-5,5'-diyldiphosphine) exhibiting high catalytic performance and stability. In addition, the enhanced water solubility of the complexes allowed performance of the photooxidation reaction under environmentally friendly conditions. In particular, the catalyst [Pt(QS)(dppe)]Cl, bearing 8-thioquinolinate and diphenylphosphinoethate (dppe) as ligands, successfully catalyzed the oxidation of a variety of sulfides using water as a solvent.