Researchers develop light-driven method to generate reactive hydrogen atoms for metal-free chemical synthesis

Researchers have developed a light-driven method to generate highly reactive hydrogen atoms for chemical synthesis. The technique produces individual hydrogen atoms under mild conditions, solving a long-standing challenge in preparing and using these reactive particles. Individual hydrogen atoms were first produced a century ago by Nobel laureate Irving Langmuir, but because they react rapidly with other substances, they have been difficult to harness. Researchers at Germany's Max Planck Institute of Colloids and Interfaces, University College London, and Imperial College London used these generated atoms to reduce organic molecules without metals, providing a potential method for chemical transformations under milder conditions.

This technology enables researchers to produce highly reactive individual hydrogen atoms under mild conditions and use them to reduce organic molecules. The method helps chemists study the unusual reactivity of atomic hydrogen and explore its potential in other chemical reactions. Hydrogen is the simplest element in the periodic table, with one proton and one electron. However, its behavior changes when it exists as individual atoms or molecules. In the laboratory, hydrogen typically appears as H₂, a stable molecule formed by two bonded hydrogen atoms. Individual hydrogen atoms, denoted as H•, exhibit higher reactivity and are difficult to prepare and control.

Its high reactivity makes it difficult to utilize in chemical synthesis.

New method generates hydrogen atoms

Nils J. Floehr, lead author at the Max Planck Institute of Colloids and Interfaces, said: "From a chemical perspective, the hydrogen atom is very simple, but its reactivity is extremely intense." Therefore, researchers sought a method to generate atomic hydrogen under conditions that could direct its reactivity toward specific chemical transformations. The new method combines hydrazine and a thiophenol derivative, then exposes the mixture to light. The light provides the energy needed to trigger electron transfer between the two molecules. Notably, the research shows this process generates a short-lived intermediate belonging to a class of compounds known as Rydberg radicals.

This intermediate exists for about 13 picoseconds, or 13 trillionths of a second. As the Rydberg molecule decays, it releases a hydrogen radical that can participate in chemical reactions.

Applications of hydrogen radicals

The team used hydrogen radicals generated through the light-driven process to reduce several organic molecules without metals under mild conditions. Tested compounds included highly functionalized alkenes and halogenated compounds. According to the researchers, reduction reactions are very important in organic chemistry because they enable chemists to modify molecules by adding hydrogen or changing the molecule's electronic structure. Generating reactive hydrogen under controlled conditions can provide another tool for these transformations. Peter H. Seeberger, director of the Department of Biomolecular Systems at the Max Planck Institute of Colloids and Interfaces, said: "For organic chemistry, the discovery of new chemical intermediates opens up new possibilities.

As this work advances, atomic hydrogen becomes a practical tool for synthetic chemists."

The researchers view this method as a starting point for further research, rather than a solution limited to the demonstrated reduction reactions. The unusual reactivity of atomic hydrogen may also have potential application value in other areas of organic chemistry and biological sciences. Further research will be needed to determine how broad the application scope of this technology is.

Impact of light-driven technology on chemical synthesis

The development of this light-driven technology marks an important advance in the field of chemical synthesis. The generated reactive hydrogen atoms can reduce organic molecules without metals, which not only solves the previous challenges of preparing and controlling hydrogen atoms but also provides a new tool for chemical transformations. Hydrogen's high reactivity gives it potential in chemical synthesis, particularly in organic chemistry and biological sciences. With further research, this technology may expand to broader applications, driving development in related fields.