Non‐emissive Ru^II Polypyridyl Complexes as Efficient and Selective Photosensitizers for the Photooxidation of Benzylamines

Abstract

Five new RuII polypyridyl complexes bearing N‐(arylsulfonyl)‐8‐amidoquinolate ligands and three of their biscyclometalated IrIII congeners have been prepared and employed as photocatalysts (PCs) in the photooxidation of benzylamines with O2. In particular, the new RuII complexes do not exhibit photoluminescence, rather they harvest visible light efficiently and are very stable in solution under irradiation with blue light. Their non‐emissive behavior has been related to the low electrochemical energy gaps and rationalized on the basis of theoretical calculations (DFT analysis) that predict low S0←T1 energy values. Moreover, the RuII complexes, despite being non‐emissive, display excellent activities in the selective photocatalytic transformation of benzylamines into the corresponding imines. The presence of an electron‐withdrawing group (‐CF3) on the arene ring of the N‐(arylsulfonyl)‐8‐amidoquinolate ligand improves the photocatalytic activity of the corresponding photocatalyst. Furthermore, all the experimental evidence, including transient absorption spectroscopy measurements suggest that singlet oxygen is the actual oxidant. The IrIII analogues are considerably more photosensitive and consequently less efficient photosensitizers (PSs).

Heteroleptic/Heterometallic Sierpiński Triangle with Room Temperature Fluorescence Emission and Photocatalytic Amine Oxidation Activity

“…Due to the critical role that imine plays as an essential synthetic intermediate in the fields of pharmaceuticals, agriculture, and biology, the oxidation of amine to imine is a significant chemical reaction. − It was decided to test the photocatalytic activity of the complexes S1 , S2 using the oxidation reaction of amine to imine. The catalytic reaction was carried out in an NMR sample tube under the illumination of a Xe lamp (λ > 420 nm, 300 W), with CD 3 CN serving as the solvent, benzylamine serving as the catalytic substrate, and tert -butyl hydroperoxide (TBHP) serving as the oxidizing agent.…”

Mechanism of the Visible-Light-Promoted C(sp3)–H Oxidation via Uranyl Photocatalysis

“…Quantum computational chemistry plays an important role in the mechanism research today and provides numerous constructive suggestions including the confirmation of target structures, methodology development, and catalyst design. − Density functional theory (DFT) is a well-established and popular first-principle method in quantum chemistry, which has been extensively employed to investigate the mechanism of organic synthesis reactions, especially metal-catalyzed reactions. DFT calculations have been demonstrated to be reliable in revealing detailed potential energy surfaces and the geometric and electronic properties of reactants, products, intermediates, and transition states in various catalytic reactions. − In contrast to that of transition metals (e.g., Ru­(bpy) 3 2+ (bpy = 2,2′-bipyridine), − [Rh III (dtbbpy) 2 (I) 2 ] + (dtbbpy = 4,4′-di tert -butyl-2,2′-bipyridine) , ) involved in photocatalytic reactions, the theoretical study on the mechanism of the uranyl photocatalytic reaction is rare, especially for the important oxidation reaction of alkylbenzenes, ,, for which the oxidation products are pivotal for the production of many industrial products such as petrochemicals, pharmaceuticals, fragrance compounds, agrochemicals, etc.…”