Controlling Proton Delivery through Catalyst Structural Dynamics.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Bioinorganic Chemistry

Background:

• Synthetic molecular catalysts for hydrogen (H2) production often mimic hydrogenase enzymes.
• The role of dynamic structural changes in enzyme function is well-known but often overlooked in synthetic catalyst design.

Purpose of the Study:

• To investigate the impact of controlling structural dynamics on H2 production rates in synthetic nickel catalysts.
• To explore how ligand modifications influence catalyst performance by affecting dynamic processes.

Main Methods:

• Synthesis and characterization of [Ni(P^Ph2 N^C6H4R2)2]2+ catalysts with varying R groups (alkyl and cycloalkyl).
• Measurement of H2 production turnover frequencies.
• Analysis of the correlation between catalytic rates and ligand structural dynamics (chair-boat ring inversion).

Main Results:

• Catalyst turnover frequencies showed an inverse correlation with the rates of ligand chair-boat ring inversion.
• The rate of ring inversion was identified as a key factor governing protonation at productive or non-productive catalytic sites.
• Modification of the outer coordination sphere effectively controlled dynamic processes involved in proton delivery.

Conclusions:

• Controlling structural dynamics is a crucial design parameter for enhancing synthetic H2 production catalysts.
• This approach, analogous to protein architecture in enzymes, can increase H2 production rates significantly (up to three orders of magnitude) with minimal overpotential increase.
• Ligand design can be used to tune catalyst dynamics for improved proton delivery and overall efficiency.