H2 Evolution from a Thiolate-Bound Ni(III) Hydride | JoVE Visualize

Area of Science:

Inorganic Chemistry
Catalysis
Bioinorganic Chemistry

Background:

Terminal nickel hydrides are crucial proposed intermediates in proton reduction reactions catalyzed by molecular electrocatalysts and metalloenzymes.
Well-defined examples of paramagnetic nickel hydride complexes are scarce, particularly those featuring terminal hydrides, with most known examples involving bridging hydrides.

Purpose of the Study:

To synthesize and characterize a well-defined, terminally bound thiolate-Ni(III)-H complex with S = 1/2.
To investigate the electronic structure and properties of the terminal hydride ligand using advanced spectroscopic and computational methods.
To explore the reactivity of the synthesized complex, specifically its propensity for hydrogen (H2) evolution.

Main Methods:

Synthesis of a novel thiolate-Ni(III)-H complex.
Characterization using vibrational spectroscopy and Electron Paramagnetic Resonance (EPR), including pulse EPR studies.
Density Functional Theory (DFT) calculations to analyze electronic structure and spin distribution.
Kinetic studies to monitor the bimolecular reductive elimination of H2.

Main Results:

Successful synthesis of a terminally bound thiolate-Ni(III)-H complex with S = 1/2.
Thorough characterization confirmed the presence and properties of the terminal hydride ligand, with EPR studies indicating spin leakage onto the thiolate ligand.
DFT calculations supported the experimental findings regarding electronic structure.
The complex was observed to undergo bimolecular reductive elimination of H2 upon warming, with kinetic studies providing data on this reaction.

Conclusions:

The study reports the first well-defined example of a paramagnetic, terminally bound thiolate-Ni(III)-H complex.
The characterized complex serves as a valuable model for proposed nickel hydride intermediates in catalytic proton reduction.
The observed H2 evolution via bimolecular reductive elimination provides mechanistic insights relevant to hydrogenase enzymes and synthetic catalysts.