On the reactivity of the electrogenerated cobalt(I) species towards aryl halides in the presence of allylethers

Unexpected stabilization of a simple cobalt(I) salt in acetonitrile at a glassy carbon electrode

“…In the absence of a nitrogen-containing ligand or co-solvent (e.g., bipyridine or pyridine), known for their stabilizing properties towards Co I , R 1 remains irreversible at high scan rates. By analogy with our previous results [12,[27][28][29][30], the reduction of Co II (BF 4 ) 2 can be related to an EC type mechanism in which the electrogenerated cobalt(I) would undergo a very fast disproportionation leading to a deposit of solid cobalt, Co (s) , at the electrode surface along with regeneration of half the starting cobalt(II) salt (Scheme 1). Under these conditions, X corresponds to the anodic redissolution of Co (s) , and the number of electrons involved at R 1 is close to two.…”

“…On the other hand, we have discovered that some carbon-carbon bond syntheses involving allylic [8] or vinylic [5] derivatives and aromatic halides can be achieved in one step, in the absence of a zinc salt, but in the presence of pyridine. Under these conditions, the stabilization of Co I is essentially ensured by the allylic or vinylic derivative via the formation of p complexes [27][28][29][30].…”

A new bipyridyl cobalt complex for reductive dechlorination of pesticides

“…More recently, it was reported that CoBr2 in the presence of a single equivalent of 2,2'-bipyridine or pyridine exhibits a high catalytic activity toward the reduction of aromatic halides [41,42]. In an aqueous solution containing a surfactant, the reduced tris-complex was stabilized in the micelle and a mild kinetic enhancement was reported in the catalytic reduction of allyl halides by the Co(bpy)3 + complex.…”

CoI‐ and Co0‐Bipyridine Complexes Obtained by Reduction of CoBr2bpy: Electrochemical Behaviour and Investigation of Their Reactions with Aromatic Halides and Vinylic Acetates

“…In fact, Ar-Y is formed only when the potential is set at À1.4 V (plots D and E), which is a value corresponding to the plateau of wave R 2 . As already discussed in our previous papers, [8,9,11,22] ArH most likely arises from the decomposition of intermediate arylcobalt species in a radical ArC, which abstracts an hydrogen atom from the solvent. The mechanism of the formation of Ar-Ar is not yet elucidated, and the Ar-Ar/Ar-H ratio strongly depends on the conditions (ligand, solvent, potential applied).…”

“…[5] In that context, the quest for reactive low-valent cobalt complexes within the scope of CÀC bond formation has become a major topic in our group. Over the past five years, we have focused on cobalt-centered catalytic systems based on the association of a cobalt(ii) halide with weak labile complexing agents such as pyridine, [8] allyl ethers [9] or acetates, [10] vinyl acetates, [11] ZnBr 2 salts, [12] or mixtures of them. These systems have found applications in both the chemical and electrochemical conversion of aromatic halides into the corresponding arylzinc species, [13,14] or their coupling with aromatic halides, [15] olefins, [16] vinylic acetates.…”