For the first time, chemists at the University of Bonn and Lehigh University in Bethlehem (USA) have developed a titanium catalyst that makes light usable for selective chemical reactions. It provides a cost-effective and non-toxic alternative to the ruthenium and iridium catalysts used so far, which are based on very expensive and toxic metals. The new catalyst can be used to produce highly selective chemical products that can provide the basis for antiviral drugs or luminescent dyes, for example. The results have been published in the international edition of the journal "Angewandte Chemie".
The electrons in chemical molecules are reluctant to lead a single life; they usually occur in pairs. Then they are particularly stable and do not tend to forge new partnerships in the form of new bonds.
However, if some of the electrons are brought to a higher energy level with the help of light (photons), things begin to look different when it comes to this "monogamy":
In such an excited state, the molecules like to donate or to accept an electron. This creates so-called "radicals", that have electrons, are highly reactive and can be used to form new bonds.
Irradiation with green light
The new catalyst is based on this principle: At its core is titanium, which is connected to a carbon ring in which the electrons are particularly mobile and can be easily excited. Green light is sufficient to use the catalyst for electron transfer to produce reactive organic intermediates that are otherwise not easily obtainable.
"In the laboratory, we irradiated a reaction flask containing the titanium catalyst that can be viewed as a ‘red dye’ with green light," reports Prof. Dr. Andreas Gansäuer from the Kekulé Institute of Organic Chemistry and Biochemistry at the University of Bonn.
"And it worked right away." The mixture generates radicals from organic molecules that initiate many reaction cycles from which a wide variety of chemical products can be produced.
A key factor in reactions with this photo redox catalyst is the wavelength of the light used for irradiation. "Ultraviolet radiation is unsuitable because it is far too energy-rich and would destroy the organic compounds," says Gansäuer. Green light from LED lamps is both mild and energy-rich enough to trigger the reaction.
Catalysts are substances that increase the speed of chemical reactions and reduce the activation energy without being consumed themselves. This means that they are available continuously and can trigger reactions that would otherwise not occur in this form. The catalyst can be tailored to the desired products depending on the organic molecule with which the titanium is bonded.
Building blocks for antiviral drugs or luminescent dyes
The new titanium catalyst facilitates the reactions of epoxides, a group of chemicals from which epoxy resin are made. These are used as an adhesive or for composites. However, the scientists are not aiming for this mass product, but for the synthesis of much more valuable fine chemicals.
"The titanium-based, tailor-made photo redox catalysts can for instance be used to produce building blocks for antiviral drugs or luminescent dyes," says Gansäuer. He is confident that these new catalysts provide a cost-effective and more sustainable alternative to the ruthenium and iridium catalysts used so far, which are based on very expensive and toxic metals.
The development is an international collaborative effort by Zhenhua Zhang, Tobias Hilche, Daniel Slak, Niels Rietdijk and Andreas Gansäuer from the University of Bonn and Ugochinyere N. Oloyede and Robert A.
Flowers II from Lehigh University (USA). While the scientists from the University of Bonn investigated how the desired compounds could best be synthesized with the new catalyst, their colleagues from the USA carried out measurements to prove the reaction pathways.
"The luminescence phenomenon really opens up interesting space to consider the design of new sustainable reactions that proceed through free radical intermediates," says Prof. Robert Flowers from the Lehigh University.
Prof. Dr. Andreas Gansäuer
Kekulé Institute of Organic Chemistry and Biochemistry
University of Bonn
Zhenhua Zhang, Tobias Hilche, Daniel Slak, Niels Rietdijk, Ugochinyere N. Oloyede, Robert A. Flowers II and Andreas Gansäuer: Titanocenes as Photoredox Catalysts Using Green-Light Irradiation, international edition of the journal "Angewandte Chemie", DOI: 10.1002/anie.202001508
Johannes Seiler | idw - Informationsdienst Wissenschaft
Turning carbon dioxide into liquid fuel
06.08.2020 | DOE/Argonne National Laboratory
Tellurium makes the difference
06.08.2020 | Friedrich-Schiller-Universität Jena
Scientists at the Fraunhofer Institute for Laser Technology ILT have come up with a striking new addition to contact stamping technologies in the ERDF research project ScanCut. In collaboration with industry partners from North Rhine-Westphalia, the Aachen-based team of researchers developed a hybrid manufacturing process for the laser cutting of thin-walled metal strips. This new process makes it possible to fabricate even the tiniest details of contact parts in an eco-friendly, high-precision and efficient manner.
Plug connectors are tiny and, at first glance, unremarkable – yet modern vehicles would be unable to function without them. Several thousand plug connectors...
An international research team has found a new approach that may be able to reduce bone loss in osteoporosis and maintain bone health.
Osteoporosis is the most common age-related bone disease which affects hundreds of millions of individuals worldwide. It is estimated that one in three women...
Traditional single-cell sequencing methods help to reveal insights about cellular differences and functions - but they do this with static snapshots only...
“Core-shell” clusters pave the way for new efficient nanomaterials that make catalysts, magnetic and laser sensors or measuring devices for detecting electromagnetic radiation more efficient.
Whether in innovative high-tech materials, more powerful computer chips, pharmaceuticals or in the field of renewable energies, nanoparticles – smallest...
An international research team with Prof. Cornelia Denz from the Institute of Applied Physics at the University of Münster develop for the first time light fields using caustics that do not change during propagation. With the new method, the physicists cleverly exploit light structures that can be seen in rainbows or when light is transmitted through drinking glasses.
Modern applications as high resolution microsopy or micro- or nanoscale material processing require customized laser beams that do not change during...
23.07.2020 | Event News
21.07.2020 | Event News
07.07.2020 | Event News
06.08.2020 | Earth Sciences
06.08.2020 | Power and Electrical Engineering
06.08.2020 | Life Sciences