1851-93-0Relevant articles and documents
Ligand-free Guerbet-type reactions in air catalyzed by in situ formed complexes of base metal salt cobaltous chloride
Kumar, Akshai,Kumar, Pradhuman,Nandi, Pran Gobinda
, p. 1100 - 1108 (2022/03/02)
Inexpensive, earth-abundant and environmentally benign cobaltous chloride efficiently accomplishes the catalytic β-alkylation of alcohols in air at 140 °C. At higher loadings of cobaltous chloride (1 mol%) in the presence of 2.5 mol% NaOtBu, 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 sodium t-butoxide along with a non-linear dependence on the concentration of 1-phenyl ethanol and benzyl alcohol.
RETRACTED ARTICLE: The Manganese(I)-Catalyzed Asymmetric Transfer Hydrogenation of Ketones: Disclosing the Macrocylic Privilege
Passera, Alessandro,Mezzetti, Antonio
supporting information, p. 187 - 191 (2019/12/11)
The bis(carbonyl) manganese(I) complex [Mn(CO)2(1)]Br (2) with a chiral (NH)2P2 macrocyclic ligand (1) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.
Controlling the selectivity and efficiency of the hydrogen borrowing reaction by switching between rhodium and iridium catalysts
Wang, Danfeng,McBurney, Roy T.,Pernik, Indrek,Messerle, Barbara A.
supporting information, p. 13989 - 13999 (2019/10/01)
The catalytic alkylation of ketones with alcohols via the hydrogen borrowing methodology (HB) has the potential to be a highly efficient approach for forming new carbon-carbon bonds. However, this transformation can result in more than one product being formed. The work reported here utilises bidentate triazole-carbene ligated iridium and rhodium complexes as catalysts for the selective formation of alkylated ketone or alcohol products. Switching from an iridium centre to a rhodium centre in the complex resulted in significant changes in product selectivity. Other factors-base, base loading, solvent and reaction temperature-were also investigated to tune the selectivity further. The optimised conditions were used to demonstrate the scope of the reaction across 17 ketones and 14 alcohols containing a variety of functional groups. A series of mechanistic investigations were performed to probe the reasons behind the product selectivity, including kinetic and deuterium studies.