Chemically Separable Ruthenium Hydride Isomers with Distinct Hydride Transfer Properties

Area of Science:

• Catalysis
• Organometallic Chemistry
• Reaction Mechanisms

Background:

• Transition metal hydrides are crucial in catalysis, requiring precise control over their reactivity.
• Hydricity, the hydride donor ability, is a key parameter for optimizing catalytic processes.

Purpose of the Study:

• To synthesize and characterize isomeric ruthenium hydrides with varying ligands.
• To investigate the effect of these ligands on hydricity and reactivity towards hydride acceptors.
• To elucidate the mechanism of hydride transfer reactions.

Main Methods:

• Synthesis of ruthenium hydride complexes with N-heterocyclic carbene and pyridine ligands.
• Thermodynamic measurements of hydricity.
• Kinetic studies using stopped-flow experiments.
• Isotopic labeling and computational modeling (DFT).

Main Results:

• Ligands trans to the Ru-H bond modulated hydricity by up to 8 kcal mol-1.
• Distinct reactivity observed towards CO2 and organic hydride acceptors.
• Outer-sphere hydride transfer mechanism confirmed.
• Disruption of conventional scaling relationships by strong trans effects.

Conclusions:

• Ligand design is a powerful strategy to tune hydricity and reactivity in transition metal hydrides.
• Understanding trans effects is key to developing novel hydride transfer reactivity.
• This work provides a platform for designing advanced catalysts for challenging transformations.