A Proton-Switchable Bifunctional Ruthenium Complex That Catalyzes Nitrile Hydroboration

Area of Science:

• Organometallic Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Development of novel ligand frameworks for transition metal catalysis is crucial.
• Pincer ligands offer unique stability and reactivity profiles in metal complexes.
• Proton-responsive functional groups can modulate catalytic activity.

Purpose of the Study:

• To synthesize and characterize a new bifunctional pincer ligand framework with pendent hydroxyl groups.
• To investigate the reactivity of the corresponding Ruthenium(II) complexes with H2 and HBPin.
• To explore the catalytic application of these complexes in hydroboration reactions.

Main Methods:

• Synthesis of a novel bifunctional pincer ligand.
• Metalation with Ruthenium(II) and isolation of four protonation states.
• Stoichiometric reactions with H2 and HBPin, catalytic hydroboration assays, and mechanistic studies.

Main Results:

• Facile E-H (E = H or BPin) activation across a Ru(II)-O bond was achieved.
• Unusual Ru-H species with strong interactions with neighboring proton and boron atoms were formed.
• The Ruthenium complexes catalyzed hydroboration of ketones and nitriles under mild conditions.
• Catalytic activity was highly dependent on the ligand's protonation state.
• Mechanistic studies highlighted the critical role of the pendent hydroxyl groups.

Conclusions:

• A new class of Ruthenium(II) pincer complexes with tunable protonation states was successfully prepared.
• These complexes exhibit efficient catalytic activity in hydroboration, modulated by ligand protonation.
• The pendent hydroxyl groups are essential for the observed catalytic performance, demonstrating a cooperative effect.