A Proton-Switchable Bifunctional Ruthenium Complex That Catalyzes Nitrile Hydroboration

A new bifunctional pincer ligand framework bearing pendent proton-responsive hydroxyl groups was prepared and metalated with Ru­(II) and subsequently isolated in four discrete protonation states. Stoichiometric reactions with H₂ and HBPin showed facile E–H (E = H or BPin) activation across a Ru­(II)–O bond, providing access to unusual Ru–H species with strong interactions with neighboring proton and boron atoms. These complexes were found to promote the catalytic hydroboration of ketones and nitriles under mild conditions, and the activity was highly dependent on the ligand’s protonation state. Mechanistic experiments revealed a crucial role of the pendent hydroxyl groups for catalytic activity

Recyclable Trifluoromethylation Reagents from Fluoroform

We present a strategy to rationally prepare CF₃^– transfer reagents at ambient temperature from HCF_3. We demonstrate that a highly reactive CF₃^– adduct can be synthesized from alkali metal hydride, HCF₃, and borazine Lewis acids in quantitative yield at room temperature. These nucleophilic reagents transfer CF₃^– to substrates without additional chemical activation, and after CF₃ transfer, the free borazine is quantitatively regenerated. These features enable syntheses of popular nucleophilic, radical, and electrophilic trifluoromethylation reagents with complete recycling of the borazine Lewis acid

A Proton-Switchable Bifunctional Ruthenium Complex That Catalyzes Nitrile Hydroboration

A new bifunctional pincer ligand framework bearing pendent proton-responsive hydroxyl groups was prepared and metalated with Ru­(II) and subsequently isolated in four discrete protonation states. Stoichiometric reactions with H₂ and HBPin showed facile E–H (E = H or BPin) activation across a Ru­(II)–O bond, providing access to unusual Ru–H species with strong interactions with neighboring proton and boron atoms. These complexes were found to promote the catalytic hydroboration of ketones and nitriles under mild conditions, and the activity was highly dependent on the ligand’s protonation state. Mechanistic experiments revealed a crucial role of the pendent hydroxyl groups for catalytic activity

Recyclable Trifluoromethylation Reagents from Fluoroform

We present a strategy to rationally prepare CF₃^– transfer reagents at ambient temperature from HCF_3. We demonstrate that a highly reactive CF₃^– adduct can be synthesized from alkali metal hydride, HCF₃, and borazine Lewis acids in quantitative yield at room temperature. These nucleophilic reagents transfer CF₃^– to substrates without additional chemical activation, and after CF₃ transfer, the free borazine is quantitatively regenerated. These features enable syntheses of popular nucleophilic, radical, and electrophilic trifluoromethylation reagents with complete recycling of the borazine Lewis acid

Stereoretentive Deuteration of α‑Chiral Amines with D₂O

We present the direct and stereoretentive deuteration of primary amines using Ru-bMepi (bMepi = 1,3-(6′-methyl-2′-pyridyl­imino)­isoindolate) complexes and D₂O. High deuterium incorporation occurs at the α-carbon (70–99%). For α-chiral amines, complete retention of stereochemistry is achieved when using an electron-deficient Ru catalyst. The retention of enantiomeric purity is attributed to a high binding affinity of an imine intermediate with ruthenium, as well as to a fast H/D exchange relative to ligand dissociation

A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding

A frustrated Lewis pair accessory functionality is positioned in the secondary coordination sphere of a terpyridine ligand (Tpy^BN = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic acid pinacol ester) to promote directed Lewis acid/base interactions. Following metalation with VCl₃, the utility of the metal Lewis acid/base triad (LABT) is highlighted with N₂H₄ as a cooperatively coordinated substrate, affording the first η²-[N₂H₃]⁻ vanadium complex

A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding

A frustrated Lewis pair accessory functionality is positioned in the secondary coordination sphere of a terpyridine ligand (Tpy^BN = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic acid pinacol ester) to promote directed Lewis acid/base interactions. Following metalation with VCl₃, the utility of the metal Lewis acid/base triad (LABT) is highlighted with N₂H₄ as a cooperatively coordinated substrate, affording the first η²-[N₂H₃]⁻ vanadium complex

A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding

A frustrated Lewis pair accessory functionality is positioned in the secondary coordination sphere of a terpyridine ligand (Tpy^BN = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic acid pinacol ester) to promote directed Lewis acid/base interactions. Following metalation with VCl₃, the utility of the metal Lewis acid/base triad (LABT) is highlighted with N₂H₄ as a cooperatively coordinated substrate, affording the first η²-[N₂H₃]⁻ vanadium complex

A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding

A frustrated Lewis pair accessory functionality is positioned in the secondary coordination sphere of a terpyridine ligand (Tpy^BN = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic acid pinacol ester) to promote directed Lewis acid/base interactions. Following metalation with VCl₃, the utility of the metal Lewis acid/base triad (LABT) is highlighted with N₂H₄ as a cooperatively coordinated substrate, affording the first η²-[N₂H₃]⁻ vanadium complex

Simple Ligand Modifications with Pendent OH Groups Dramatically Impact the Activity and Selectivity of Ruthenium Catalysts for Transfer Hydrogenation: The Importance of Alkali Metals

Remarkable differences in selectivity and activity for ruthenium-catalyzed transfer hydrogenation are described that are imparted by pendent OH groups. Kinetic experiments, as well as the study of control complexes devoid of OH groups, reveal that the pendent OH groups serve to orient the ketone substrate through ion pairing with an alkali metal under basic conditions. The deprotonation of the OH groups was found to modulate the electronics at the metal center, providing a more electron rich ruthenium center. The effects of the ion pairing between alkali metals and the pendent alkoxide groups were highlighted by demonstrating chemoselective transfer hydrogenation of ketones in the presence of olefins. The results illustrate that a simple ligand modification (installation of OH groups) imparts dramatic changes to catalysis. Pendent OH groups turn on catalysis through electronic perturbations at the metal site under basic conditions and can also change the mechanism of catalysis, the latter of which can be used to promote chemoselective reductions