A visible-light-mediated photocatalyzed protocol utilizing copper−phenanthroline-based catalysts has been developed that can convert a large number of olefins into their chlorosulfonylated products. Besides the Cu(I) complex [Cu(dap) 2 ]Cl, now well-established in photo-ATRA processes, the corresponding Cu(II) complex [Cu(dap)Cl 2 ] proved to be often even more efficient in the title reaction, being advantageous from an economic point of view but also opening up new avenues for photoredox catalysis. Moreover, the copper complexes outperformed commonly used ruthenium, iridium, or organic dye based photocatalysts, owing to their ability to stabilize or interact with transient radicals by inner sphere mechanisms. The use of stoichiometric Na 2 CO 3 in combination with the copper photocatalysts was found to be essential to convert unactivated olefins to the desired products, in contrast to activated olefins for which no additive was required. As suggested by appropriate control experiments, the role of Na 2 CO 3 is attributed to prevention of poisoning of the catalyst.

The CuII complex [CuII(dmp)2Cl]Cl (dmp = 2,9‐dimethyl‐1,10‐phenanthroline) is evaluated as an oxidation stable precursor for visible‐light‐mediated CuI‐photoredox catalysis, being efficient and considerable more cost‐effective compared to previously established copper(I) photocatalysts. Its performance and efficiency are demonstrated within a broad scope of atom transfer radical addition (ATRA) reactions, allowing the 1,2‐difunctionalization of alkenes, as well as for decarboxylative coupling and an Appel reaction. Moreover, the utility of the complex is shown by various gram‐scale functionalizations of styrene, thus suggesting [CuII(dmp)2Cl]Cl to be a low‐priced alternative precatalyst for processes run on scale. Furthermore, this study provides UV/Vis evidence on the mechanism for the visible light activation of CuII complexes.

Developments in the field of photoredox catalysis that leveraged the long-lived excited states of Ir­(III) and Ru­(II) photosensitizers to enable radical coupling processes paved the way for explorations of synthetic transformations that would otherwise remain unrealized. While first row transition metal photocatalysts have not been as extensively investigated, valuable synthetic transformations covering broad scopes of olefin functionalization have been recently reported featuring photoactivated chlorobis­(phenanthroline) Cu­(II) complexes. In this study, the photochemical processes underpinning the catalytic activity of [Cu­(dmp)2Cl]Cl (dmp = 2,9-dimethyl-1,10-phenanthroline) were studied. The combined results from static spectroscopic measurements and conventional photochemistry, ultrafast transient absorption, and electron paramagnetic resonance spin trapping experiments strongly support blue light (λex = 427 or 470 nm)-induced Cu–Cl homolytic bond cleavage in [Cu­(dmp)2Cl]+ occurring in <100 fs. On the basis of electronic structure calculations, this bond-breaking photochemistry corresponds to the Cl → Cu­(II) ligand-to-metal charge transfer transition, unmasking a Cu­(I) species [Cu­(dmp)2]+ and a Cl atom, thereby serving as a departure point for both Cu­(I)- or Cu­(II)-based photoredox transformations. No net photochemistry was observed through direct excitation of the ligand-field transitions in the red (λex = 785 or 800 nm), and all combined experiments indicated no evidence of Cu–Cl bond cleavage under these conditions. The underlying visible light-induced homolysis of a metal–ligand bond yielding a one-electron-reduced photosensitizer and a radical species may form the basis for novel transformations initiated by photoinduced homolysis featuring in situ-formed metal–substrate adducts utilizing first row transition metal complexes.

Herein, we report a visible light-mediated coppercatalyzed protocol enabling the highly economic, vicinal difunctionalization of olefins utilizing the readily available bulk chemical iodoform. This protocol is characterized by high yields under environmentally benign reaction conditions and allows the regioselective and chemoselective functionalization of activated double bonds. Besides the synthetic utility of the shown transformation, this study undergirds the exclusive role of copper in photoredox catalysis as the title transformation is not possible via the most commonly employed ruthenium, iridium, or organic dye-based photocatalysts owing to the ability of copper to stabilize and interact with radical intermediates in its coordination sphere. Furthermore, the protocol can be smoothly scaled to gram quantities of the product, which offers manifold possibilities for further transformations, for example, heterocycle synthesis or intramolecular cyclopropanation.

This review summarizes the different applications and underlying concepts that are applied for the Cu(i)- or Cu(ii)-photocatalyzed difunctionalizations of alkenes.