Hydrogenation and dehydrogenation of N-heterocycles under Cp*Co(III)-catalysis.

To realize the goal of a carbon-free energy economy, it is crucial to discover reactions that utilize sustainable resources as alternatives to fossil feedstocks. In this study, a well-defined, air-stable Cp*Co(III)-catalyst for transfer hydrogenation of quinoline derivatives and oxidative dehydrogenation of cyclic amines in water is developed. While the former reaction is promoted by formic acid as a transfer hydrogenation reagent, the latter is mediated by molecular oxygen as the sole oxidant. These processes provide new avenues for the investigation of air-stable cobalt catalysts for environmentally benign hydrogenation and dehydrogenation reactions.

Methanol as a hydrogen source: room-temperature highly-selective transfer hydrogenation of α,ß-unsaturated ketones.

The described system offers an ideal, user-friendly protocol for the chemoselective homogeneous hydrogenation of α,ß-unsaturated ketones at room temperature using methanol as a liquid organic hydrogen carrier. Excellent yields were achieved with an in situ-prepared phosphine-free Cp*Ir(III)/bipyridonate complex. Chemoselective reduction with other reducible functionalities and late-stage functionalization were also explored.

Iron-Catalyzed α-Methylation of Ketones Using Methanol as the C1 Source under Photoirradiation.

A mild, environmentally benign approach for α-methylation of ketones utilizing methanol as the C1 source under visible light has been developed. The reaction conditions were favorable for a wide range of ketones with both aromatic and aliphatic backbones, allowing for good-to-excellent yields of the respective products. The tentative mechanism is postulated after preliminary mechanistic and kinetic experiments.

C-H and N-H bond annulation of aryl amides with unactivated olefins by merging cobalt(iii) and photoredox catalysis.

A mild, environment-friendly protocol has been developed to carry out the [4+2] annulation of aryl amides with unactivated olefins. A range of sterically and electronically diverse aryl amides and unactivated olefins were successfully employed under the developed conditions to get a variety of dihydroisoquinolinones in good-to-excellent yields.

Cp*CoIII -Catalyzed Efficient Dehydrogenation of Secondary Alcohols.

A novel, well-defined molecular Cp*CoIII complex was isolated and structurally characterized for the first time. The efficiency of this cobalt catalyst was demonstrated in the alcohol dehydrogenation and dehydrative coupling of secondary alcohols under mild conditions into ketones and ethers, respectively.

Dehydrative Cp*Co(III)-Catalyzed C-H Bond Allenylation.

An efficient, unprecedented reactivity of Cp*Co(III) for the synthesis of tetrasubstituted allenes under mild conditions is disclosed. Electron-rich and highly nucleophilic cobalt facilitates the dehydrative C-H bond allenylation directly from propargylic alcohols without any derivatization. The reaction proceeds via reversible cyclometalation followed by alcohol-directed regioselective alkyne insertion and ß-hydroxy elimination to provide the tetrasubstituted allenes.