Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers.

Jong-Hwa Shon,Thomas S Teets,Jimmie Weaver,Dooyoung Kim,Steven Sittel,Manjula D Rathnayake

doi:10.1039/d0sc06306a

Abstract

Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylation via radical-mediated pathways, with optimized conditions that only require the photocatalyst and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.

Highlights

Visible-light photoredox catalysis has emerged as a powerful, versatile, and increasingly important methodology in organic synthesis.[1]
We have demonstrated that bis-cyclometalated iridium complexes with b-diketiminate ancillary ligands are versatile photosensitizers for a variety of photoredox transformations
The highly reducing nature of their excited state permits an expansion of the substrate scope to challenging organobromide and organochloride substrates, which traditionally are inert to photoredox catalysis or require forcing, complex reaction conditions to activate

Summary

Introduction

Visible-light photoredox catalysis has emerged as a powerful, versatile, and increasingly important methodology in organic synthesis.[1]. Replacing TMEDA with BIH as the sacri cial reagent allows further optimization of the conditions for aryl bromide hydrodebromination and an expansion of the substrate scope, summarized in Scheme 1.

Results

Conclusion