The coupling of organic groups by the electrochemical reduction of organic halides: Catalysis by 2,2′-bipyridinenickel complexes

Merging Photoredox and Nickel Catalysis: The Direct Synthesis of Ketones by the Decarboxylative Arylation of α‐Oxo Acids

“…[13] Ad etailed mechanism for the proposed metallaphotoredox aryl cross-coupling with a-oxo acids is shown in Scheme 1. It is well established that photoredox catalyst [Ir{dF(CF 3 )ppy} 2 {dtbbpy}] + + 1 [14] readily absorbs photons upon visible-light irradiation to generate the oxidizing excited state *[Ir{dF(CF 3 )ppy} 2 [13d] by the excited photocatalyst 2 should generate the reduced photocatalyst 4 and ac orresponding carboxyl radical species.Atthis stage,wepresumed that this open-shell dicarbonyl intermediate would rapidly extrude CO 2 to deliver the critical acyl radical species 5.W ithin the same time frame,the second catalytic cycle would be initiated by oxidative addition of the Ni 0 catalyst 6 [16] into the aryl halide (e.g., 4-iodotoluene (7), as shown) to generate Ni II aryl complex 8.T he resulting electrophilic metal species 8 would then rapidly trap the nucleophilic acyl radical 5 to produce nickel acyl complex 9.A tt his stage,r eductive elimination from this Ni III complex would be expected to forge the requisite C sp 2 À C sp 2 bond of compound 10,w hile expelling the corresponding Ni I complex 11.F inally,s ingle-electron transfer (SET) from the photocatalyst, Ir II species 4,t ot he Ni I -dtbbpy complex 11 would return the metal catalyst to the required Ni 0 oxidation state in an exergonic process.I ndeed, the thermodynamic requirements of the two-electron reduction of Ni II to Ni 0 are favorable (E 1/2 II/0 = À1.2 Vv s. SCE in DMF), [17] given the corresponding reduction potential of Ir II complex 4 (E 1/2 III/II = À1.37 Vvs. SCE in CH 3 CN).…”

“…Finally, single-electron transfer (SET) from the photocatalyst Ir II species 4 to the Ni I -dtbbpy complex 11 would return the metal catalyst to the required Ni 0 oxidation state in an exergonic process. Indeed, the thermodynamic requirements of the two electron reduction of Ni II to Ni 0 are favorable ( E 1/2 II/0 = −1.2 V vs. SCE in DMF) [17] given the corresponding reduction potential of the Ir II complex 4 ( E 1/2 III/II = −1.37 V vs. SCE in CH 3 CN). [15] It should be noted that this second photoredox-mediated SET event regenerates the ground state Ir III catalyst 1 while reconstituting the requisite Ni 0 complex 6 , completing the photoredox and nickel cycles simultaneously.…”

5,5’-Biindole

“…Among several methods available for the synthesis of biindole compounds [44][45][46][47], the use of the Madelung´s indole reaction was found suitable for the cyclization of , '-bis-formyl-o-tolidine to produce 5,5'-biindole.…”

Carbon−Carbon Bond Formation with Electrogenerated Nickel and Palladium Complexes

“…[59] The mechanism of this dimerisation has been studied. [60] Scheme 5. a) e Ϫ , [NiBr 2 (bipy)] (10 mol %), DMF, one-compartment cell, Mg anode, 20°C…”