[Cu(bcp)(DPEphos)]+: A Versatile and Efficient Copper-Based Photoredox Catalyst and Photosensitizer

Abstract

The development of photoredox catalysis has recently enabled the design of remarkably powerful synthetic tools now commonly used in a wide array of chemical transformations, and notably for the generation of radical species under mild, safe and environmentally friendly conditions. This field is largely dominated by ruthenium and iridium complexes, the main alternative to the use of these photocatalysts mostly relying on the use of organic dyes, which poses problems not only in terms of cost - therefore strongly limiting synthetic applications of photocatalysis - but also, more importantly, for the design of new light-mediated transformations. Much less attention has been devoted to the use of copper complexes in photoredox catalysis, despite their strong potential not only as cheaper catalysts but also for the activation of a broader range of substrates. Most copper complexes are indeed known to be poor photocatalysts, mostly due to their short-lived excited states and low redox potentials. Over the last decade, one copper-based copper complex has however emerged as a remarkably efficient and general photoredox catalyst, which is at the core of this Spotlight that highlights its applications as a photosensitizer and its potential.

Copper-(Photo)Catalyzed Radical Reactions with Organic Halides

“…The identification of a photoactive copper(I) complex that could activate a broad variety of non-activated organic halides together with displaying good photophysical and electrochemical properties thus became our primary objective and to do so, the reduction of unactivated aryl and alkyl halides was envisioned. A broad set of homoleptic and heteroleptic copper complexes was evaluated and [Cu(bcp)(DPEphos)]PF 6 , 42 a complex whose efficiency as a photosensitizer for the photocatalytic reduction of water 43 and carbon dioxide 44 had been previously demonstrated, turned out to be, by far, the most efficient. Using catalytic amounts of this complex combined with Hunig’s base as the sacrificial reductant in acetonitrile under irradiation with blue LEDs in acetonitrile overnight enabled the smooth activation of a variety of organic halides 21 , as shown in Scheme 8 , thus paving the way for the use of such substrates in more complex transformations.…”

Quantifying flattening distortion on the thermodynamics and kinetics of electron transfers of Cu(i) photoredox catalysts

“…22 Ru(II) polypyridyl complexes (e.g., [Ru(bpy) 3 ] 2+ , (bpy = 2,2′bipyridine)) and Ir(III) phenylpyridine ( ppy) complexes (e.g., Ir ( ppy) 3 ) still dominate the field given their notable photophysical and photochemical properties. 2,23 Nevertheless, their scarcity and high cost have become a hurdle to adopting this technology in large-scale industrial applications. 24,25 This aspect has revitalized the exploration of first-row transition metal complexes as alternatives to traditional photosensitizers, given their economic advantages and availability.…”

“…[25][26][27] In the last decade, luminescent Cu(I) complexes (e.g., [Cu(dmp) 2 ] + , dmp = 2,9-dimethyl-1,10-phenanthroline) have emerged as alternatives to traditional Ru-and Ir-photoredox catalysts. 23,27 The outer-sphere electron transfer mechanism of Cu(I) photoredox catalysts is summarized in Fig. 1.…”

Ultrafast relaxation processes in photoactive heteroleptic copper(I) complexes: insights into the interplay between excited states.

“…In this study, we combine state of the art femtosecond time-resolved transient absorption (TA) and fluorescence up conversion (FUC) spectroscopy with Time Dependent Density Functional Theory (TD DFT) computations to yield an in-depth description of the photophysical behavior of [Cu(bcp)(Xantphos)] + and [Cu(bcp)(DPEphos)] + . These two complexes are amongst the most used heteroleptic copper(I) complexes in photoredox catalysis [33][34][35][36][37][38][39][40][41][42] or solar energy conversion [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] . Since they are often used as model for this class of complexes, having the most refined description of their excited state dynamics is crucial to further enhance the properties of new derivatives.…”