3665-72-3Relevant articles and documents
Ultrafast Observation of a Photoredox Reaction Mechanism: Photoinitiation in Organocatalyzed Atom-Transfer Radical Polymerization
Koyama, Daisuke,Dale, Harvey J. A.,Orr-Ewing, Andrew J.
, p. 1285 - 1293 (2018)
Photoredox catalysis has driven a revolution in the field of organic chemistry, but direct mechanistic insights into reactions of genuine synthetic utility remain relatively scarce. Herein we report ultrafast time-resolved spectroscopic observation of a bimolecular organocatalyzed photoredox reaction, from catalyst photoexcitation through to photoinduced electron transfer (PET) and intermediate formation, using transient vibrational and electronic absorption spectroscopy with sub-picosecond time resolution. Specifically, the photochemical dynamics of initiation in organocatalyzed atom-transfer radical polymerization (O-ATRP) are elucidated for two complementary photoredox organocatalysts (N,N-diaryl-5,10-dihydrophenazines). Following photoexcitation, a dissociative bimolecular electron transfer is observed from the first excited singlet state of both photocatalysts to methyl 2-bromopropionate in dichloromethane, toluene, and dimethylformamide. The photocatalyst excited donor state, ground state, and radical cation are tracked in real time alongside the debrominated radical fragment. Our work challenges previously proposed mechanisms of initiation in O-ATRP and indicates that PET from short-lived excited singlet states can exert control of polymer molecular weight and dispersity by suppressing the steady-state concentration of the reactive debrominated radical. More broadly, we aim to demonstrate the potential of ultrafast absorption spectroscopy to observe directly transient, open-shell intermediates in mechanistic studies of photoredox catalysis.
Ligand-Free Iron-Catalyzed C-F Amination of Diarylamines: A One-Pot Regioselective Synthesis of Diaryl Dihydrophenazines
Aoki, Yuma,O'Brien, Harry M.,Kawasaki, Hiroto,Takaya, Hikaru,Nakamura, Masaharu
, (2019/01/21)
A one-pot synthesis of various 5,10-diaryl-5,10-dihydrophenazines (DADHPs) from diarylamines has been achieved by using an iron-catalyzed C-F amination. Homodimerization of magnesium diarylamides, followed by defluorinative intramolecular cyclization (dou
Aerobic Oxidative Homo- and Cross-Coupling of Amines Catalyzed by Phenazine Radical Cations
Bri?ar, Rok,Unglaube, Felix,Hollmann, Dirk,Jiao, Haijun,Mejía, Esteban
, p. 13481 - 13490 (2018/11/02)
Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.
