620-94-0Relevant articles and documents
Relaxation processes of some aromatic sulfides, sulfoxides, and sulfones in a polystyrene matrix
Desando, M. A.,Walker, S.,Baarschers, W.H.
, p. 3460 - 3466 (1980)
Dielectric absorption studies have been made of a number of aromatic sulfides, sulfoxides, and sulfones in a polystyrene matrix at a variety of temperatures in the frequency range of 102-105 Hz, and in three cases between 104-107 Hz.One compound, bis (4-pyridyl) sulfide, was also examined as a pure compressed solid in the frequency range of 104-107 Hz.The Eyring parameters have been determined and used to characterize the relaxation processes.Low enthalpies of activation (ca.15 kJ mol-1) have been estimated for an intramolecular relaxation process of diphenyl, bis (4-tolyl) and bis (4-pyridyl) sulfide, and rotation about the C-S bond in these symmetrical aromatic sulfides would, thus, be expected to occur quite readily.These low barriers are to be contrasted with those for the molecular relaxation values of 60-78 kJ mol-1 for diphenyl, bis(4-tolyl) and bis(4-chlorophenyl) sulfoxides and sulfones.The enthalpies of activation (ca.39 kJ mol-1) for the molecular relaxation of the disklike molecules, dibenzothiophene and its oxides, are also lower than those for the corresponding nonplanar diphenyl sulfur oxides.
A Visible-Light-Harvesting Covalent Organic Framework Bearing Single Nickel Sites as a Highly Efficient Sulfur–Carbon Cross-Coupling Dual Catalyst
Chen, Hui,Liu, Wanlu,Laemont, Andreas,Krishnaraj, Chidharth,Feng, Xiao,Rohman, Fadli,Meledina, Maria,Zhang, Qiqi,Van Deun, Rik,Leus, Karen,Van Der Voort, Pascal
supporting information, p. 10820 - 10827 (2021/04/09)
Covalent Organic Frameworks (COFs) have recently emerged as light-harvesting devices, as well as elegant heterogeneous catalysts. The combination of these two properties into a dual catalyst has not yet been explored. We report a new photosensitive triazine-based COF, decorated with single Ni sites to form a dual catalyst. This crystalline and highly porous catalyst shows excellent catalytic performance in the visible-light-driven catalytic sulfur–carbon cross-coupling reaction. Incorporation of single transition metal sites in a photosensitive COF scaffold with two-component synergistic catalyst in organic transformation is demonstrated for the first time.
Photoredox Nickel-Catalyzed C-S Cross-Coupling: Mechanism, Kinetics, and Generalization
Qin, Yangzhong,Sun, Rui,Gianoulis, Nikolas P.,Nocera, Daniel G.
supporting information, p. 2005 - 2015 (2021/02/06)
Photoredox-mediated nickel-catalyzed cross-couplings have evolved as a new effective strategy to forge carbon-heteroatom bonds that are difficult to access with traditional methods. Experimental mechanistic studies are challenging because these reactions involve multiple highly reactive intermediates and perplexing reaction pathways, engendering competing, but unverified, proposals for substrate conversions. Here, we report a comprehensive mechanistic study of photoredox nickel-catalyzed C-S cross-coupling based on time-resolved transient absorption spectroscopy, Stern-Volmer quenching, and quantum yield measurements. We have (i) discovered a self-sustained productive Ni(I/III) cycle leading to a quantum yield φ > 1; (ii) found that pyridinium iodide, formed in situ, serves as the dominant quencher for the excited state photocatalyst and a critical redox mediator to facilitate the formation of the active Ni(I) catalyst; and (iii) observed critical intermediates and determined the rate constants associated with their reactivity. Not only do the findings reveal a complete reaction cycle for C-S cross-coupling, but the mechanistic insights have also allowed for the reaction efficiency to be optimized and the substrate scope to be expanded from aryl iodides to include aryl bromides, thus broadening the applicability of photoredox C-S cross-coupling chemistry.
