Red Light–Blue Light Chromoselective C(sp²)–X Bond Activation by Organic Helicenium-Based Photocatalysis

Abstract

Chromoselective bond activation has been achieved in organic helicenium ( n Pr-DMQA + )-based photoredox catalysis. Consequently, control over chromoselective C(sp 2 )−X bond activation in multihalogenated aromatics has been demonstrated. n Pr-DMQA + can only initiate the halogen atom transfer (XAT) pathway under red light irradiation to activate low-energy-accessible C(sp 2 )−I bonds. In contrast, blue light irradiation initiates consecutive photoinduced electron transfer (conPET) to activate more challenging C(sp 2 )−Br bonds. Comparative reaction outcomes have been demonstrated in the α-arylation of cyclic ketones with red and blue lights. Furthermore, red-light-mediated selective C(sp 2 )−I bonds have been activated in iodobromoarenes to keep the bromo functional handle untouched. Finally, the strength of the chromoselective catalysis has been highlighted with two-fold functionalization using both photo-to-transition metal and photo-to-photocatalyzed transformations.

Triaryl Carbenium Ion Pair Mediated Electrocatalytic Benzylic C−H Oxygenation in Air

“…[49] The CV curves revealed that the introduction of 1 (Figure 2F [B(C 6 F 5 ) 4 ] À was more readily reduced than oxygen in air. [50][51][52] Based on precedent literatures [11-12,53À 59] and our preliminary studies, [45][46][47][48] we proposed the mechanism for ion pair mediated benzylic CÀ H oxygenation under electronic catalytic conditions (Figure 2G). First, the deprotonation occurred by [B(C 6 F 5 ) 4 ] À anion at the benzylic position to generate a benzylic anion I, following a single-electron oxidation by the anode to form the benzylic radical II.…”

Ultrafast Dynamics of a Red-Light-Activated Organic Photocatalyst in the Oxidative Hydroxylation of Phenylboronic Acid

“…counter ion was synthesized according to a previously reported method. 43 For all optical measurements, solutions were prepared by dissolving 2.5 mg of n Pr-DMQA + in 5 mL of N,N-dimethylformamide (DMF). 0.5 mmol of phenylboronic acid and 1 https://doi.org/10.26434/chemrxiv-2024-cnc9w ORCID: https://orcid.org/0000-0001-9692-5312 Content not peer-reviewed by ChemRxiv.…”

“…[33][34][35][36][37][38] The benefits of red-light photocatalysis include its lower energy requirement, reduced side reactions, minimized health risks, and its greater penetration through scattering media. [39][40][41][42][43] This work investigates the ultrafast dynamics of the organic N,N′-di-n-propyl-1,13dimethoxyquinacridinium ( n Pr-DMQA + ) red-light photocatalyst to understand its mechanism in the aerobic oxidative hydroxylation of phenylboronic acid. n Pr-DMQA + , shown in Figure 1 inset, is a member of the helicene family characterized by a condensed aromatic structure, with fused rings arranged in a nonplanar fashion to alleviate steric hindrances.…”

“…Electron transfer from DIPEA ( i Pr2NEt/ i Pr2NEt •+ = +0.72 V vs SCE in DMF) to an excited triplet state (E1/2(C + */C • ) = +1.18 V vs SCE in DMF)43,[69][70][71][72][73] can then lead to the formation of the ground state neutral n Pr-DMQA radical which can subsequently reduce oxygen to superoxide radical anion under aerobic conditions 75. Alternatively an oxidative pathway is also viable if the excited triplet state of the cationic n Pr-DMQA (E1/2 (C •++ /C + *) = −0.62 V vs SCE in DMF) is oxidized under aerobic condition (O2/O2 •-= −0.57 V vs SCE in DMF43 ) generating dicationic radical species of the n Pr-DMQA and the superoxide radical anion. Both pathways are thermodynamically feasible.…”