C-C bond formation is the pivotal step in synthetic chemistry. Catalytic methods that bring about the formation of C–C bonds find wide synthetic utility and lead to valuable fuel chemicals, pharmaceuticals, fine chemicals, agrochemicals, and natural products. Well explored approaches towards greener and sustainable C–C bond forming reactions involve catalytic C–X (X = H, Cl, Br, I) activation and subsequent cross coupling either involving radical mechanisms or purely organometallic mechanisms. Inexpensive, earth-abundant and environmentally benign cobaltous chloride efficiently accomplishes the catalytic β-alkylation of alcohol in air in presence of 2.5 mol% NaOtBu and 0.01 mol% of CoCl2 at 140 °C. In the presence of 2.5 mol% NaOtBu, at higher loadings of cobaltous chloride (1 mol%) there is a rapid formation of heterogeneous Co nanoparticles (NPs) which are apparently sensitive to air and result in poor yields (ca. 25%) of β-alkylated products. In contrast, performing the reaction in an argon atmosphere under otherwise identical conditions leads to higher yields (ca. 44%). The heterogenization and eventual loss of activity in air could be delayed by operating at a lower (0.01 mol%) CoCl2 loading in the presence of 2.5 mol% NaOtBu at 140 °C. Under these conditions, the catalytic β-alkylation of alcohols proceeded with high yields (up to 89%) and unprecedented turnovers (ca. 8900). Mechanistic studies are indicative of the involvement of catalysts based on in-situ generated molecular Co complexes of alcohols. Labelling studies provide key evidence for the involvement of C–H activation in the cobaltous chloride catalyzed β-alkylation with a KIE of 1.61. Kinetic studies indicate linear dependence of the rate on the concentration of cobaltous chloride and NaOtBu along with a non-linear dependence on the concentration of 1-phenyl ethanol and benzyl alcohol. These studies could open up several related reactivity with substrates that are capable of forming in-situ complexes with CoCl2.

Ligand-free Guerbet-type reactions in air catalyzed by in situ formed complexes of base metal salt cobaltous chloride

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