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We explore the interfaces of recently-emerging synthetic and processing technologies in organic synthesis. Our goals are to:

1) unearth new chemistry for formation of Carbon-Carbon or Carbon-Heteroatom bonds

2) tame high-energy, reactive intermediates for use in oxidation or reduction reactions

3) develop sustainable, safer and scalable methods as alternatives for existing chemical transformations.

 

Synthetic Photoelectrochemistry

Single Electron Transfer (SET) chemistry gives rise to unconventional modes of reactivity and intermediates, thus serving as a platform for innovative bond constructions, deconstructions and functional group transformations. A surge of recent interest in SET chemistry is associated with the rise of two key vehicles for conducting SET, namely: 1) visible light photoredox catalysis (PRC) and 2) synthetic organic electrochemistry (SOE). Both methods offer phenomenal capabilities to synthetic chemists and are already changing the landscape of small molecule synthesis. However, both methods suffer from fundamental drawbacks. In visible light PRC, the 'redox energy' is constrained by the energy of visible light photons. Sacrificial oxidants/reductants are needed for net-oxidative/reductive processes, which may interfere with downstream chemistry. In SOE, high applied potentials often required encourage unselective, deleterious redox processes. 

PRC and SOE are often regarded as competing technologies and their fusion has been largely overlooked. The Barham Lab aims to harness the synergy of PRC and SOE: "Synthetic Photoelectrochemistry" (PEC), thereby overcoming the drawbacks of each parent technology.

 PRC vs SOE

We explore three different strategies for this synergy:

1) electrochemically-mediated PhotoRedox Catalysis - "e-PRC"

Here, electrochemistry is directly involved in the photocatalytic cycle. Electrochemistry builds up a base layer of energy that is 'topped-up' by visible light energy, thereby generating "super-redox" agents in a transient fashion:

ePRC concept

Moreover, sacrificial reductants/oxidants in visible light PRC can be replaced by cathodic/anodic current, increasing atom economy and removing interfering by-products:

ePRC concept2

2) decoupled PhotoElectroChemistry - "iPEC"

Here, electrochemistry and photochemistry are decoupled and handle different steps in the mechanism.

***Coming Soon***

3) interfacial PhotoElectroChemistry - "dPEC"

Here, photon energy is transferred to an electrode "photoelectrode" which engages substrates in electrochemistry in a mild fashion, offsetting the high applied potentials otherwise required with light energy. This mirrors the concept of a photoelectrochemical cell, but for use with organic substrates instead of oxidation of H2O:

iPEC concept

 

 

Flow Photo-, Electro- and Photoelectrochemistry

Both PRC and SOE suffer upon scale-up due to the physical constraints governing transfer of photons/electrons to (or from) the reaction. Both benefit from processing in continuous flow (CF) which offers short path lengths for light transmission and small interelectrode distances.

The Barham Lab intends to leverage CF for enabling and scaling photochemical, electrochemical and photoelectrochemical reactions.

Flow PEC

Flow Microwave Chemistry

***Coming Soon***

  1. Fakulty of Chemistry and Pharmacy
  2. Institute of Organic Chemistry

Dr.
Joshua Barham

Joshua-Philip.Barham[at]ur.de

Contact

Sofja Kovalevskaja Group Leader

Office: CH 23.2.80

Phone +49 (0)941 943-4373
E-mail