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 O 2 , 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)](PF 6 ) [where pqaet is 2-((2-phenylquinolin-8-yl)thio)ethan-1amine] 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 H 2 O 2 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 O 2 .

Template Synthesis of Cyclometalated Macrocycle Iridium(III) Complexes Based on Photoinduced C–N Cross-Coupling Reactions In Situ

“…Additionally, the 13 C NMR spectra revealed resonance peaks at 43.47, 43.44, 48.90, and 51.58, and 43.48 ppm for complexes 1a , 2a , 3a , and 4a , respectively. These findings are in agreement with previous observations reported for [Ir(pq) 2 (en)](PF 6 ) complex …”

“…Each L1a ligand anchors to an Ir(III) ion in a C-shape conformation, with the quinoline arms positioned trans to each other, denoted by a bond angle of N1–Ir1–N2 at 173.5(4)°. Other details align with those reported in previous studies …”

“…The cyclization of [Ir­(La)­(en)]­(PF 6 ) complexes was conducted leveraging our previously developed in situ interligand C–N cross-coupling under visible light irradiation, , as depicted in Scheme . Complex 1a served as a prototype to refine the photoreaction conditions and analyze spectral changes.…”

“…Prior investigations from our group have established a robust protocol for the amination of coordinated 2-phenylquinoline (pq) complexes at the C8 position through in situ interligand C–N cross-coupling under visible light irradiation in an oxygen-rich environment. , Mechanistic explorations revealed that metal aminyl radicals play a pivotal role in forming new C–N bond. , These findings offer a new pathway for the in situ generation of new multidentate complexes. The efficacy and mildness of the reaction conditions for this in situ interligand cross-coupling prompted us to extend this methodology to the synthesis of cyclometalated macrocycle complexes.…”

In Situ Synthesis of Hexadentate Cyclometalated Ir(III) Complexes as Photocatalysts for the Oxidation of Sulfides into Sulfoxides in Water

“…Building on our group's previous work, we have established a robust protocol for the amination of coordinated 2-phenylquinoline (pq) complexes at the C8 position via in situ inter-ligand C-N cross-coupling in the presence of O 2 under visible light irradiation [24,25]. Mechanistic studies suggest that metal aminyl radicals are instrumental in new C-N bond formation [26,27], paving the way for the in situ synthesis of new multidentate complexes and inspiring the development of new stable Ir(III) photosensitizers under mild conditions. In this paper, we report the synthesis of four new hexadentate cyclometalated Ir(III) complexes [Ir(bfpqen)](PF 6 ) (1), [Ir(btqen)](PF 6 ) (2), [Ir(bmpqen)](PF 6 ) (3), and [Ir(bnqen)](PF 6 ) (4) (where bfpqen is N,N ′ -bis(2-(4-fluorophenyl)quinolin-8-yl)ethane-1,2diamine, btqen is N,N ′ -bis(2-(4-tolyl)quinolin-8-yl)ethane-1,2-diamine, bmpqen is N,N ′bis(2-(4-methoxyphenyl)quinolin-8-yl)ethane-1,2-diamine, and bnqen is N,N ′ -bis(2naphthylquinolin-8-yl)ethane-1,2-diamine) through in situ inter-ligand C-N cross-coupling under benign conditions.…”