Ru-Catalyzed Selective C–H Bond Hydroxylation of Cyclic Imides

We report on cyclic imides as weak directing groups for selective monohydroxylation reactions using ruthenium catalysis. Whereas acyclic amides are known to promote the hydroxylation of the C­(sp²)–H bond enabling five-membered ring ruthenacycle intermediates, the cyclic imides studied herein enabled the hydroxylation of the C­(sp²)–H bond via larger six-membered ruthenacycle intermediates. Furthermore, monohydroxylated products were exclusively obtained (even in the presence of overstoichiometric amounts of reagents), which was rationalized by the difficulty to accommodate coplanar intermediates once the first hydroxyl group was introduced into the substrate. The same reactivity was observed in the presence of palladium catalysts

Ruthenium(II)-Catalyzed C–H (Hetero)Arylation of Alkenylic 1,<i>n</i>‑Diazines (<i>n</i> = 2, 3, and 4): Scope, Mechanism, and Application in Tandem Hydrogenations

A general ruthenium­(II)-catalyzed methodology enabling the (hetero)­arylation of alkenylic C–H bonds utilizing a series of synthetically appealing diazines as directing groups is presented. Despite the presence of additional nitrogen lone pairs remote from the C–H bond activation site, which could eventually poison the catalyst, the reaction times are short (3 h), thus being suitable for selective double C–H bond arylation. Mixtures of <i>E</i>:<i>Z</i> isomeric products were observed in some cases, which were further hydrogenated in a tandem manner in the presence of the remaining ruthenium catalyst from the first step, representing an alternative approach to more difficult C­(sp³)–H bond functionalization. According to mechanistic studies, the unexpected <i>E</i>:<i>Z</i> product formation seems to occur by thermal CC bond isomerization after the reductive elimination step

Efficient Hydrogen Production at pH 7 in Water with a Heterogeneous Electrocatalyst Based on a Neutral Dimeric Cobalt-Dithiolene Complex

The development of efficient hydrogen production technologies is fundamental for replacing fossil-fuel-based energies. As such, electrocatalysts derived from Earth-abundant metal complexes are appealing, and interesting performances have typically been disclosed under acidic conditions in organic solvents. However, their applicability under relevant pH-neutral conditions has been underexplored. Herein, we demonstrate that nonionic, dimeric cobalt-dithiolene complexes supported on a multiwalled carbon nanotube (MWCNT)/carbon paper (CP) electrode are powerful electrocatalysts for hydrogen production in aqueous media at pH 7. The high turnover numbers encountered (TON up to 50980) after long reaction times (up to 16 h) are explained by the increased electroactive cobalt concentration on the modified electrode, which is ca. 4 times higher than that of a state-of-the-art cobalt porphyrin electrocatalyst. These findings point out that immobilizing well-defined, multinuclear, low-cost metal complexes on carbon material is a promising strategy to design highly electroactive electrodes enabling production of green energies