Identification of a Self-Photosensitizing Hydrogen Atom Transfer Organocatalyst System

Abstract

We developed organocatalyst systems to promote the cleavage of stable C−H bonds, such as formyl, α-hydroxy, and benzylic C−H bonds, through a hydrogen atom transfer (HAT) process without the use of exogenous photosensitizers. An electronically tuned thiophosphoric acid, 7,7'-OMe-TPA, was assembled with substrate or co-catalyst N-heteroaromatics through hydrogen bonding and π−π interactions to form electron donor−acceptor (EDA) complexes. Photoirradiation of the EDA complex induced stepwise, sequential single-electron transfer (SET) processes to generate a HAT-active thiyl radical. The first SET was from the electron-rich naphthyl group of 7,7'-OMe-TPA to the protonated Nheteroaromatics and the second proton-coupled SET (PCET) from the thiophosphoric acid moiety of 7,7'-OMe-TPA to the resulting naphthyl radical cation. Spectroscopic studies and theoretical calculations characterized the stepwise SET process mediated by short-lived intermediates. This organocatalytic HAT system was applied to four different carbon−hydrogen (C−H) functionalization reactions, hydroxyalkylation and alkylation of N-heteroaromatics, acceptorless dehydrogenation of alcohols, and benzylation of imines, with high functional group tolerance.

Electron donor–acceptor complex-catalyzed photoredox reactions mediated by DIPEA and inorganic carbonates

“…4 In the meantime, the catalytic potential of the EDA complex has also been demonstrated by organocatalyzed EDA complex-mediated reactions. 3 a ,5 Since 2019, the EDA catalysis strategy, i.e. EDA complex-mediated radical generation with catalytic amounts of electron donors 6–9 or acceptors, 10 has emerged as a rapidly growing subfield.…”

Site-Selective α-Alkylation of 1,3-Butanediol Using a Thiophosphoric Acid Hydrogen Atom Transfer Catalyst

“…14) Therefore, we focused on the linear 1,3-diol moiety, a common structure in biologically active molecules, to perform regioselective C-H functionalization reactions. In this work, we achieved secondary-alcohol-selective C-H functionalization of linear 1,3-diol by using a thiophosphoric acid HAT catalyst [22][23][24][25][26][27][28] (Chart 1b). This is the first example of regioselective α-hydroxy C-H functionalization of linear 1,3-diols via HAT process.…”

Photocatalyst‐free Light‐driven Dehydrogenation of Alcohols into Carbonyl Compounds under Mild Conditions

“…[8] Recently, the same group also developed organocatalyst systems to promote the cleavage of stable CÀ H bonds through a hydrogen atom transfer process and realized series different carbon-hydrogen (CÀ H) functionalization reactions including dehydrogenation of alcohols. [9] Chen's group employed binuclear platinum(II) diphosphite complexes as a single complex catalyst and realized dehydrogenation of alcohols to aldehydes and ketones in moderated to excellent yields. [10] Lately, Liu's group constructed a platinum nanocluster/graphitic carbon nitride (Pt/gÀ C 3 N 4 ) composite as a photocatalyst and achieved selective transformation of alcohols to ketones under sunlight irradiation at room temperature.…”

“…Kanai's group reported the first dehydrogenation of aliphatic secondary alcohols to ketones at room temperature by utilizing a ternary hybrid catalyst system comprising the photoredox catalyst (Mes−Acr), thiophosphate organocatalyst and a Ni(II) catalyst [8] . Recently, the same group also developed organocatalyst systems to promote the cleavage of stable C−H bonds through a hydrogen atom transfer process and realized series different carbon‐hydrogen (C−H) functionalization reactions including dehydrogenation of alcohols [9] . Chen's group employed binuclear platinum(II) diphosphite complexes as a single complex catalyst and realized dehydrogenation of alcohols to aldehydes and ketones in moderated to excellent yields [10] .…”