Facial and Meridional PNN-Ruthenium Pincer Complexes in Base-Free Nitrile Hydration with Concurrent Ligand Backbone...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Coordination Chemistry

Background:

• Ruthenium complexes are versatile catalysts in organic synthesis.
• Pincer ligands offer unique coordination environments for metal centers.
• Developing efficient catalysts for nitrile hydration is crucial for amide synthesis.

Purpose of the Study:

• To synthesize and characterize novel ruthenium pincer complexes using a tridentate amide-pyridine-monophosphine ligand.
• To investigate the catalytic activity of these complexes in nitrile hydration reactions.
• To elucidate the mechanism of nitrile hydration catalyzed by the ruthenium complexes.

Main Methods:

• Synthesis of a tridentate amide-pyridine-monophosphine ligand (1).
• Reaction of ligand 1 with various ruthenium precursors to form pincer complexes (2-8).
• Catalytic evaluation of complexes 4 and 5 in nitrile hydration.
• Mechanistic studies including spectroscopic analysis and computational modeling.

Main Results:

• Successfully synthesized a series of Ru(II) and Ru(III) pincer complexes incorporating the novel ligand.
• Demonstrated base- and additive-free benzylic C-H oxidation under aerobic conditions at room temperature.
• Complexes 4 and 5 effectively catalyzed the hydration of various nitriles to amides at low catalyst loadings.
• Mechanistic studies revealed a [Ru-H] active species and a dihydrogen bond intermediate facilitating water activation.

Conclusions:

• The synthesized ruthenium pincer complexes are highly effective catalysts for nitrile hydration.
• The catalytic system operates under mild conditions and tolerates a wide range of nitrile substrates.
• The mechanistic insights provide a foundation for designing improved catalysts for amide synthesis.