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Tunable Multisite Proton-Coupled Electron Transfer Mediators: Distinct Pathways for Substrate Reduction Versus

John M Ovian1, Joseph Derosa1, Mengdi Li1

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Summary
This summary is machine-generated.

This study investigates proton-coupled electron transfer (PCET) mediators, revealing a multisite PCET pathway for substrate reduction and a distinct Cp-ring protonation pathway for hydrogen evolution. This offers flexibility in designing new PCET catalysts.

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Area of Science:

  • Organometallic Chemistry
  • Catalysis
  • Organic Synthesis

Background:

  • Proton-coupled electron transfer (PCET) reagents facilitate H atom transfer from weak X-H bonds.
  • PCET reagent tunability (redox, pKa) allows selective reductions, but modular catalyst design is limited.
  • Cobaltocene-based PCET mediators offer tunable properties for organic transformations.

Purpose of the Study:

  • Elucidate the mechanism of a dimethylaniline-appended cobaltocene PCET mediator.
  • Determine the protonation site in the reactive Co(II, NH)+ intermediate.
  • Investigate whether substrate reduction and hydrogen evolution reaction (HER) share a common pathway.

Main Methods:

  • Kinetic analysis
  • Spectroscopic characterization
  • Mechanistic studies using N-aryl imine substrates

Main Results:

  • Identified a multisite PCET (MS-PCET) pathway for substrate reduction.
  • Characterized the protonation site in the reduced, protonated mediator.
  • Established a distinct Cp-ring protonation pathway for competing HER.

Conclusions:

  • PCET mediator reactivity and selectivity are dictated by redox, acid-base, and structural properties.
  • Substrate compatibility can be tuned by mediator design.
  • Findings enable flexible design of reductive PCET mediators.