Activation of carbon dioxide: nickel-catalyzed electrochemical carboxylation of diynes

The simultaneous activation of carbon dioxide and diyness by electrogenerated LNi(O) complexes (L = bpy, pentamethyldiethylenetriamine: PMDTA) enables the selective incorporation of one molecule of CO[sub 2] into the unsaturated systems and the preparative-scale electrosyntheses of carboxylic acids. A series of nonconjugated diynes afforded selectively linear or cyclic adducts depending on the ligand. Diynes bearing both a terminal and an internal triple bond gave exclusive CO[sub 2] incorporation into the terminal alkynyl group, regioselectively at the 2-position. The electrocarboxylation of 1,3-diynes with the Ni-PMDTA catalytic system yielded, regio- and stereoselectively, (E)-2-vinylidene-3-yne carboxylic acids in one step. The electrosyntheses were carried out in single-compartment cells fitted with a consumable magnesium anode, and utilized a catalytic amount of an air-stable Ni(II) complex as the catalyst precursor. Cyclic voltammetry studies revealed that both carbon dioxide and the diynes are able to coordinate to LNi(O)-generated species in DMF. 39 refs., 3 figs., 5 tabs.