Photoredox catalysis enables unique and broadly applicable chemical reactions but controlling their selectivity has proven to be difficult. The pursuit of enantioselectivity is a particularly daunting challenge, arguably due to the high energy of the activated radical (ion) intermediates, and previous approaches have invariably required pairing of the photoredox catalytic cycle with an additional activation mode for asymmetric induction. A potential solution for photoredox reactions proceeding via radical ions would be catalytic pairing with enantiopure counterions. However, while attempts toward this approach have been described, high selectivity has not yet been accomplished. Here we report a potentially general solution to radical cation-based asymmetric photoredox catalysis. We describe organic salts, featuring confined IDPi counteranions that catalyze highly enantioselective [2+2]-cross cycloadditions of styrenes.

Coordination compounds of earth-abundant 3d transition metals are among the most effective catalysts for the electrochemical reduction of carbon dioxide (CO 2 ). While the properties of the metal center are crucial for the ability of the complexes to electrochemically activate CO 2 , systematic variations of the metal within an identical, redox-innocent ligand backbone remain insufficiently investigated. Here, we report on the synthesis, structural and spectroscopic characterization, and electrochemical investigation of a series of 3d transition-metal complexes [M = Mn(I), Fe(II), Co(II), Ni(II), Cu(I), and Zn(II)] coordinated by a new redox-innocent PNP pincer ligand system. Only the Fe, Co, and Ni complexes reveal distinct metal-centered electrochemical reductions from M(II) down to M(0) and show indications for interaction with CO 2 in their reduced states. The Ni(0) d 10 species associates with CO 2 to form a putative Aresta-type Ni-η 2 -CO 2 complex, where electron transfer to CO 2 through back-bonding is insufficient to enable electrocatalytic activity. By contrast, the Co(0) d 9 intermediate binding CO 2 can undergo additional electron uptake into a formal cobalt(I) metallacarboxylate complex able to promote turnover. Our data, together with the few literature precedents, single out that an unsaturated coordination sphere (coordination number = 4 or 5) and a d 7 -to-d 9 configuration in the reduced low oxidation state (+I or 0) are characteristics that foster electrochemical CO 2 activation for complexes based on redox-innocent ligands.