Photoinduced Ligand-to-Metal Charge Transfer Enables Photocatalyst-Independent Light-Gated Activation of Co(II)

Abstract

Photoredox catalysis can be used to manipulate the redox state of a transition metal complex leading to the desired reactivity. While powerful, obviating the role of the second catalyst would be attractive from the perspective of simplifying the protocol and using visible light to uncover unexpected, enabling reactivity. Herein we report that Co-acetylides, formed in situ, are photoactive complexes that undergo ligand-to-metal charge transfer using visible light. The net transformation uses air-stable Co­(II) complexes as precatalysts and induces Co­(I) chemistry. The acetylide is an electron reservoir forming the Co­(I) but accepting the electron back at the end of the catalytic cycle. The electronic nature of the acetylide leads to either on–off behavior or simply initiates catalysis, depending on electronics.

Spin-Forbidden Excitation Enables Infrared Photoredox Catalysis

“…After the celite was loaded onto a column and eluted with an ethyl acetate:hexane gradient from 0-20%. The product matched literature values 2 . To a 1 dram vial equipped with a stir bar was added N-vinyl carbazole (0.80 mmol ,1 equiv.).…”

“…The characterization of this compound matched literature values2 .In a 250 mL round bottom flask containing a stir-bar, aldehyde, ethanol, KOH, 2-acetylarene, and aqueous ammonia (28% ammonia in water) were added in that order under open atmosphere. The reaction was stirred for 12 hours and a precipitate formed.…”

“…Benjamin D. Ravetz,1 Nicholas E. S. Tay, 1 Candice L. Joe, 2 * Melda Sezen-Edmonds, 2 Michael A. Schmidt, 2 Yichen Tan, 2 Jacob M. Janey, 2 Martin D. Eastgate, 2 Tomislav Rovis 1 * Os(II) polypyridyl complexes ( Fig. 1b) display significant S0→T1 excitation in the DR and NIR regions (660-800 nm) 13 which is typically attributed to strong SOC induced by Os.…”

Visible‐Light Controlled Divergent Catalysis Using a Bench‐Stable Cobalt(I) Hydride Complex

“…These modes of action mean that the vast majority of reactions reside in the area of radical transformations. However, interest in the direct visible‐light promotion of transition‐metal catalysed processes is growing . Clearly, visible light, as a widely‐available, cheap, sustainable and non‐invasive method of energy delivery, can exert precise spatial and temporal control over a chemical process.…”

Photocatalyst-Independent Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides: Stereocontrol and Mechanism

“…25,26 The utilization of earthabundant metals as visible-light photocatalysts has recently gained great interest in order to develop sustainable photocatalysts. 27 Recent reported light-induced metal catalysts include Cu, [28][29][30][31] Co, [32][33][34][35] Ni, 26,[36][37][38] Mn, [39][40][41] Ce [42][43][44][45] and Fe 46,47 complexes. Such metal complexes usually involve photoinduced single-electron transfer (SET) between substrate and catalyst, and allow for reactions that occur directly from their photoexcited states, without the assistance of exogenous photocatalysts that harvest light to transfer electron or energy.…”