Cobalt-Catalyzed Formation of Grignard Reagents via C–O or C–S Bond Activation

Abstract

C­(aryl)–OMe bond functionalization catalyzed by cobalt­(II) chloride in combination with a nacnac-type ligand and magnesium as a reductant is reported. Borylation and benzoylation of aryl methoxides are demonstrated, and C­(aryl)–SMe bond borylation can be achieved under similar conditions. This is the first example of achieving these transformations using cobalt catalysis. Mechanistic studies suggest that a Grignard reagent is generated as an intermediate in a rare example of a magnesiation via a C–O bond activation reaction. Indeed, an organomagnesium species could be directly observed by electrospray ionization mass spectroscopic analysis. Kinetic experiments indicate that a heterogeneous cobalt catalyst performs the C–O bond activation.

Nickel-Catalyzed Cross-Coupling Reaction of Aryl Methyl Sulfides with Aryl Bromides

“…C–S electrophiles (e.g., thiols, sulfides, sulfoxides, sulfones, and sulfonium salts) have recently become a complementary alternative to halides within the cross-coupling arena, as the bond dissociation energy (BDE) of C–S bond of various sulfur-containing molecules is lower than that of C–F, C–O, and C–N bonds of relative analogues . Aryl sulfides are found widely in nature as well as useful synthetic intermediates and final products, and thus they may be regarded as surrogates and as nucleophilic partners in the cross-coupling reactions (Scheme a) .…”

Coupling of Heteroarene and Arenol via Nickel‐Catalyzed C−H/C−OH Activation

“…[8] The key success of this reaction is the facile CÀ O cleavage enabled by the coordination of Al onto O atoms of CÀ O. Lee also reported cobalt-catalyzed functionalization of aryl ether assisted by Lewis acidic of Mg reagent. [9] Our group has developed a series of Ni-mediated coupling reactions with aryl methyl ether in recent years using reactive coupling partners like trialkylaluminum, [10] Grignard reagents, [11] and Grignardassisted tandem CÀ H/CÀ O activation reactions. [12] The drawback of this catalytic manifold based on strong Lewis acid is the functional intolerance, reducing the utility of the reaction to wider scope.…”