Switching between borrowing hydrogen and acceptorless dehydrogenative coupling by base transition-metal catalysts

Ruthenium Complexes with NNN-Pincer Ligands for N-Methylation of Amines Using Methanol

A series of ruthenium complexes (Ru1-Ru4) bearing new NNN-pincer ligands were synthesized in 58-78% yields. All of the complexes are air and moisture stable and were characterized by IR, NMR, and high-resolution mass spectra (HRMS). In addition, the structures of Ru1-Ru3 were confirmed by X-ray crystallographic analysis. These Ru(II) complexes exhibited high catalytic efficiency and broad functional group tolerance in the N-methylation reaction of amines using CH3OH as both the C1 source and solvent. Experimental results indicated that the electronic effect of the substituents on the ligands considerably affects the catalytic reactivity of the complexes in which Ru3 bearing an electron-donating OMe group showed the highest activity. Deuterium labeling and control experiments suggested that the dehydrogenation of methanol to generate ruthenium hydride species was the rate-determining step in the reaction. Furthermore, this protocol also provided a ready approach to versatile trideuterated N-methylamines under mild conditions using CD3OD as a deuterated methylating agent.

NNN manganese complex-catalyzed α-alkylation of methyl ketones using alcohols: an experimental and computational study

We present here a phosphine-free, quinoline-based pincer Mn catalyst for α-alkylation of methyl ketones using primary alcohols as alkyl surrogates. The C-C bond formation reaction proceeds via a hydrogen auto-transfer methodology. The sole by-product formed is water, rendering the protocol atom efficient. Electronic structure theory studies corroborated the proposed mechanism.

Nickel-Catalyzed Chemodivergent Coupling of Alcohols: Efficient Routes to Access α,α-Disubstituted Ketones and α-Substituted Chalcones

Chemodivergent (de)hydrogenative coupling of primary and secondary alcohols is achieved utilizing an inexpensive nickel catalyst, (6-OH-bpy)NiCl2 . This protocol demonstrates the synthesis of branched carbonyl compounds, α,α-disubstituted ketones, and α-substituted chalcones via borrowing hydrogen strategy and acceptorless dehydrogenative coupling, respectively. A wide range of aryl-based secondary alcohols are coupled with various primary alcohols in this tandem dehydrogenation/hydrogenation reaction. The nickel catalyst, along with KOt Bu or K2 CO3 , governed the selectivity for the formation of branched saturated ketones or chalcones. A preliminary mechanistic investigation confirms the reversible dehydrogenation of alcohols to carbonyls via metal-ligand cooperation (MLC) and the involvement of radical intermediates during the reaction.

Chemoselective α-Alkylation and α-Olefination of Arylacetonitriles with Alcohols via Iron-Catalyzed Borrowing Hydrogen and Dehydrogenative Coupling

α-Alkyl and α-olefin nitriles are very important for organic synthesis and medicinal chemistry. However, different types of catalysts are employed to achieve either α-alkylation of nitriles by borrowing hydrogen or α-olefination by dehydrogenative coupling methods. Designing and developing high-performance earth-abundant catalysts that can procure different products from the same starting materials remain a great challenge. Herein, we report an iron(0) catalyst system that achieves chemoselectivity between borrowing hydrogen and dehydrogenative coupling protocols by simply changing the base. A broad range of nitriles and alcohols, including benzylic, linear aliphatic, cycloaliphatic, heterocyclic, and allylic alcohols, were selectively and efficiently converted to the corresponding products. Mechanistic studies reveal that the reaction mechanism proceeds through a dehydrogenative pathway. This iron catalytic protocol is environmentally benign and atom-efficient with the liberation of H₂ and H₂O as green byproducts.