Reduced Phenalenyl in Catalytic Dehalogenative Deuteration and Hydrodehalogenation of Aryl Halides

Abstract

Dehalogenative deuteration reactions are generally performed through metal-mediated processes. This report demonstrates a mild protocol for hydrodehalogenation and dehalogenative deuteration of aryl/heteroaryl halides (39 examples) using a reduced odd alternant hydrocarbon phenalenyl under transition metal-free conditions and has been employed successfully for the incorporation of deuterium in various biologically active compounds. The combined approach of experimental and theoretical studies revealed a single electron transfer-based mechanism.

Tuning Redox States of Phenalenyl-Based Molecules by Consecutive Reduction toward Transition Metal-Free Heck-Type C–C Cross-Coupling

“…These studies have driven us to tune the redox state of phenalenyl species by utilizing the doubly reduced anionic phenalenyl molecule for the Mizoroki–Heck-type coupling. It is noteworthy that very recently, we have been successful in activating carbon–halogen bonds under transition metal-free C–H arylation and dehalogenative deuteration using a doubly reduced phenalenyl-based species. To the best of our knowledge, for Mizoroki–Heck-type coupling, there is no report available at room temperature without the influence of any external stimuli that can catalyze the reaction under transition metal-free conditions.…”

“…Parallelly, we developed the concept of using in situ generated phenalenyl-based radicals to design single-electron transfer (SET)-based catalysts in hydrosilylation, , preparation of cathode materials for a single-compartment H 2 O 2 fuel cell, and recently for the N -alkylation of anilines . Moreover, various transition metal-free catalytic C–C cross-coupling reactions have been reported using the SET process from monoreduced phenalenyl-based radicals. − Very recently, we have deployed the doubly reduced anionic closed-shell state of the phenalenyl-based molecule to perform catalytic C–H arylation and dehalogenative deuteriation …”

“…The importance of the present work lies in the fact that the current protocol avoids the use of any metal for Matsuda–Heck-type coupling and can accomplish Mizorki–Heck-type coupling without a transition metal under ambient conditions (avoiding any external stimulation such as heat or light). Phenalenyl molecules, although applied previously for various catalytic transformations, − were not employed in a Heck-type coupling reaction to date. Thus, in the current study, the exploitation of all possible redox states of phenalenyl-based molecules was accomplished in designing the catalytic Heck-type reaction.…”

“…20−23 Very recently, we have deployed the doubly reduced anionic closed-shell state of the phenalenyl-based molecule to perform catalytic C−H arylation 24 and dehalogenative deuteriation. 25 Herein, we demonstrate the utilization of both the radical and anionic states of PLY-based ligands in accomplishing the transition metal-free catalytic Heck-type coupling reactions. The cyclic voltammetric study of a typical cationic phenalneyl (PLY) molecule 26 exhibits two reversible reduction waves at ∼ −0.9 V vs saturated calomel electrode (SCE) generating a monoreduced PLY radical and another at ∼ −1.8 V vs SCE, which is attributed to the generation of a doubly reduced PLY anion.…”

A Convenient and Stable Heterogeneous Nickel Catalyst for Hydrodehalogenation of Aryl Halides Using Molecular Hydrogen

“…[16] Dehalogenations of organohalides can be accomplished using (over)stoichiometric amounts of transfer hydrogenation reagents such as alcohols, [17] formic acid (or its salts), [18] metal hydride reducing agents, [19] Grignard reagents, [20] and others. [21] However, molecular hydrogen is a more attractive hydrogen donor, with wide adoption in the chemical industry, due to its considerably lower cost and higher atom efficiency than the above alternatives.…”