The Chemical Problem of Energy Change: Multi-Electron Processes

Abstract

This special issue is focussed on arguably the most important fundamental question in contemporary chemical research: how to efficiently and economically convert abundant and thermodynamically stable molecules, such as H 2 O, CO 2 , and N 2 into useable fuel and food sources. The 3 billion year evolutionary experiment of nature has provided a blueprint for the answer: multi-electron catalysis. However, unlike one-electron transfer, we have no refined theories for multi-electron processes. This is despite its centrality to much of chemistry, particularly in catalysis and biology. In this article we highlight recent research developments relevant to this theme with emphasis on the key physical concepts and premises: (i) multi-electron processes as stepwise single-electron transfer events; (ii) proton-coupled electron transfer; (iii) stimulated, concerted, and co-operative phenomena; (iv) feedback mechanisms that may enhance electron transfer rates by minimizing activation barriers; and (v) non-linearity and far-from-equilibrium considerations. The aim of our discussion is to provide inspiration for new directions in chemical research, in the context of an urgent contemporary issue.

Copper Chloride Catalysis: Do μ4-Oxido Copper Clusters Play a Significant Role?

“…Copper complexes are also widely used as catalysts in oxidation reactions in combination with noninnocent ligand systems. , Another possibility to employ effective copper-based catalysts is the combination of multiple copper centers within one molecule, which ensures the electron transfer as a “multielectron package” as required for this reaction type. , Progress in the latter regard has been made in the activation of CH bonds by the use of multinuclear catalysts such as cubane − and μ 4 -oxido clusters. − The electron transfer for both catalyst types can be explained by reasonable mechanisms; however, none of these reaction pathways can be assigned to simple copper salts such as CuCl 2 ·2H 2 O. Better understanding of these catalytic systems not only would provide more insight into catalytic redox reactions in general but furthermore should allow the design and synthesis of second-generation copper catalysts.…”

“…3,6 Another possibility to employ effective copper-based catalysts is the combination of multiple copper centers within one molecule, which ensures the electron transfer as a "multielectron package" as required for this reaction type. 7,8 Progress in the latter regard has been made in the activation of CH bonds by the use of multinuclear catalysts such as cubane 9−12 and μ 4 -oxido clusters. 13−17 The electron transfer for both catalyst types can be explained by reasonable mechanisms; however, none of these reaction pathways can be assigned to simple copper salts such as CuCl 2 •2H 2 O.…”

Towards Global Artificial Photosynthesis (Global Solar Fuels): Energy, Nanochemistry, and Governance

“…The authors generalise that new avenues of chemistry research leading to inexpensive, smallscale, portable solar-to-fuel energy devices will open up through evaluation of the hypothesis that if the energy barrier producing stepwise single electron transfer intermediate states is sufficiently greater than another reaction pathway that involves the simultaneous or cooperative transfer of two electrons, then the latter will be preferred. [18] Elucidating Fine Structure The significance to artificial photosynthetic constructions of the paper by GAP presenter Nobuo Kamiya and others on the cubane configuration of the OEC in PSII to a level of 1.9 Å has already been highlighted. [19] In this edition, Ron Pace and Rob Stranger of the ANU ('The Biomimetic Inspiration for Renewable Hydrogen Fuel Production from Water Oxidation within Artificial Photosynthesis') detail how their high-level computational chemical analyses of this structure reveal that one region of the Mn 4 /Ca cluster is dominantly involved in substrate water binding, while a separate Mn is principally responsible for the redox accumulation function, acting as a 'battery', and so is capable of being replaced by another constant voltage electron sink (i.e.…”