Marcetta Darensbourg has pioneered the understanding of hydrogenase mimics by investigating first, second, and outer coordination sphere interactions. Her work has inspired others to reveal mechanistic details of hydrogenase mimics, and more broadly, of fundamental principles of redox catalysis. This talk will focus on the interconversion of H2 and protons enabled by amino acid and peptide based outer coordination spheres. The [Ni(PCy2NAmino acid2)2]2+ (CyAA) has been used as a well-understood catalytic core upon which an amino acid based outer coordination sphere had been added to enhance catalytic activity and understand the resulting features attributed to the outer coordination sphere. Adding amino acids and peptides has enabled faster rates, lower overpotentials, and water solubility. Most recently, attaching the amino acid phenylalanine has resulted in fully reversible H2 production/oxidation at room temperature, a feature reminiscent of enzymes. The addition of a second amino acid produces synergistic effects in some cases. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site, and that these subtle cooperative interactions are essential to catalytic performance. Equally subtle interactions can inhibit reversibility. While the rules governing these interactions are still being developed, the importance of the outer coordination sphere for synthetic molecular electrocatalysts is clear, the idea of which was first explored by “out of the active-site” thinkers like Marcetta Darensbourg.

Effect of the outer coordination sphere on molecular catalysts: A tribute to Marcetta, the hydrogenase whisperer

253rd National Meeting (2017)

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