Solvent-Induced Umpolung Reaction from Dioxygenation to C-S Coupling in Bis(2-phenylquinoline) Iridium(III) Thiolate Complexes.

Abstract

The construction of C-S bonds is of great importance in the field of synthetic and medicinal chemistry. Herein, solvent-induced umpolung reactions from dioxygenation to interligand C-S cross-coupling in bis(cyclometalated) Ir(III) thiolate complexes are reported in good to excellent yields at room temperature. Specifically, the reaction of rac-[Ir(pq)2(aet)] (where pq is 2-phenylquinoline and aet is 2-aminoethanethiolate) can be selectively switched to dioxygenation in acetonitrile solution in the presence of O2, resulting in the formation of a sulfinato complex rac-[Ir(pq)2(aes)] (where aes is 2-aminoethanesulfinato). Alternatively, the reaction in trifluoroethanol solution leads to interligand C-S cross-coupling, affording a rac-[Ir(pq)(pqaet)](PF6) [where pqaet is 2-((2-phenylquinolin-8-yl)thio)ethan-1-amine] complex, which generates a new tetradentate ligand in situ. Mechanistically, the formation of electrophilic metal thiyl radicals is proposed as a key intermediate in the interligand C-S coupling reaction. Furthermore, the sequential oxidation of a thioether complex into a sulfoxide complex is also observed at room temperature using H2O2 as an oxidant. Additionally, a new approach for the synthesis of a hexadentate ligand is developed through sequential C-S and C-N interligand coupling of metal thiolate complexes in situ under visible light irradiation in the presence of O2.