Alkoxycarbonylations are important and versatile reactions that result in the formation of a new C-C bond. Herein, we report on a new and halide-free alkoxycarbonylation reaction that does not require the application of an external carbon monoxide atmosphere. Instead, manganese carbonyl complexes and organo(alkoxy)borate salts react to form an ester product containing the target C-C bond. The required organo(alkoxy)borate salts are conveniently generated from the stoichiometric reaction of an organoborane and an alkoxide salt and can be telescoped without purification. The protocol leads to the formation of both aromatic and aliphatic esters and gives complete control over the ester's substitution (e.g., OMe, OtBu, OPh). A reaction mechanism was proposed on the basis of stoichiometric reactivity studies, spectroscopy, and DFT calculations. The new chemistry is particularly relevant for the field of Mn(I) catalysis and clearly points to a potential pathway toward irreversible catalyst deactivation.

Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC-pincer complexes (Ru-CNC's) were prepared. Depending on the synthetic procedure, normal (1, 2) or mixed normal/abnormal NHC-complexes (3) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds 4-6. Nitrile adduct 4 shows reactivity toward strong bases to yield dearomatized complex 7, which heterolytically activates H₂ to form the bis-hydrido complex 8. Finally, these Ru-CNC's are active in catalytic hydrogenation of CO₂ to formate salts, and unlike the phosphine-containing Ru-PNP counterpart, they also catalyze the selective hydrogenation of esters to alcohols.

The metal-ligand cooperative activation of CO₂ with pyridine-based ruthenium PNP pincer catalysts leads to pronounced inhibition of the activity in the catalytic CO₂ hydrogenation to formic acid. The addition of water restores catalytic performance by activating alternative reaction pathways and leads to unprecedented Ru-catalyzed CO₂ hydrogenation activity. The mechanism of the underlying chemical transformations is proposed on the basis of DFT calculations, kinetic experiments, and NMR reactivity studies.