Finally, the most common S-H bond in nature has been broken.

Finally, the most common S-H bond in nature has been broken.

The carbon-hydrogen bond (C-H) is most common chemical bond. For example, in oil and plastics, two-thirds of chemical bonds are carbon-hydrogen bonds. The close bond between these carbons and hydrogens has long thwarted attempts by chemists to uncouple them, making it difficult to add new additional features to carbon-based molecules.

Reactions that add C-H bonds are known as C-H bond activation. This has been a longstanding problem for chemists since C-H bonds are inactive part and if this can be done successfully it will be a joy to many chemical researchers.

While both organic and inorganic chemistry have come a long way over past few decades, there are still no reagents or catalysts that allow chemists to cram anything into strongest carbon-hydrogen bonds.

Now, after almost 25 years of work, a group of chemists at University of California at Berkeley have succeeded in completely breaking down various types of carbon-hydrogen bonds, opening door to synthesis of many new organic molecules.

Finally, the most common S-H bond in nature has been broken.

Rivalry with carbon-hydrogen bonds is a "good tradition" at UC Berkeley. In 1982, chemistry professor Robert Bergman was first to demonstrate that an iridium (Ir) atom can break carbon-hydrogen bonds in organic molecules by being placed between carbon and hydrogen. and attach a ligand between carbon and hydrogen.

Finally, the most common S-H bond in nature has been broken. Finally, the most common S-H bond in nature has been broken.

Robert Bergman is professor (retired) in Department of Chemistry at University of California, Berkeley. | Image Source: UC Berkeley

However, Bergman's discovery is not practical because it requires presence of an iridium atom for each broken carbon-hydrogen bond. A decade later, other researchers found a way to use iridium and other transition metals such as tungsten as catalysts to break millions of carbon-hydrogen bonds with a single atom.

In late 1980s, John Hartwig, now a professor of organic chemistry at UC Berkeley, was Bergman's graduate student and also studied inactive carbon-hydrogen bonds. In 2000, he published an article in journal Science describing how to use a rhodium (Rh) metal catalyst to insert >boron (B). The advantage of this approach is that once boron has been successfully introduced, it can be easily replaced by other compounds.

After that, researchers continued to improve reaction, and metal involved in reaction was changed from rhodium to iridium. This catalytic reaction has also been used by some pharmaceutical companies to synthesize drugs by modifying various types of carbon-hydrogen bonds.

However, problem still exists when carbon-hydrogen bond at end of carbon chain is methyl (-CH3), reaction efficiency is very low. For example, converting methane (CHâ‚„) to methanol (CH3OH) was a pipe dream.

The carbon in methyl group is attached to three hydrogens, and this group is usually found at end of molecular chain. C-H bonds in methyl groups are strongest C-H bonds, they contain fewest electrons and are least reactive.

On May 15, Hartwig and his team once again published their latest findings in journal Science. They developed a new catalyst and finally broke "strongest" carbon-hydrogen bond.

Finally, the most common S-H bond in nature has been broken. Finally, the most common S-H bond in nature has been broken.

John Hartwig is professor of chemistry at the University of California, Berkeley. | Image Source: UC Berkeley

Finally, the most common S-H bond in nature has been broken.

The new study uses a new iridium-based catalyst. In reaction, iridium can break one of three carbon-hydrogen bonds in terminal methyl group, in other words, it can cut off terminal hydrogen atom and then insert a boron compound, which is easy to replace with other more complex chemical groups replaced.

Finally, the most common S-H bond in nature has been broken. Finally, the most common S-H bond in nature has been broken.

The black spheres represent carbon atoms and center shows an iridium-based catalyst (blue) that converts a hydrogen atom (white) from a methyl group (yellow) at end of molecule into cut, add last boron compound (pink and red) . This compound can be replaced by more complex chemical groups. The upper part of diagram shows reactions that take place in simple hydrocarbon chains, and lower part shows reactions that take place in more complex carbon compounds. | Image courtesy of John Hartwig / UC Berkeley.

This new catalyst is very easy to handle and provides a catalytic reaction that can almost attach various chemicals to any type of carbon-hydrogen bond, and reaction efficiency is 50-80 times higher than previous catalysts< /strong>. With a catalyst in hand, chemists can make molecules faster that they didn't want to make before. It's not that these molecules couldn't have been created in past, it's just that they might have taken too long to create or required too much research.

To demonstrate practicality of new catalytic reaction, in experiments, researchers used method of adding a boron compound to 63 terminal carbon atoms with different molecular structures. Next, boron compound was replaced by any number of chemical groups. The results showed that while this is a reaction that specifically targets C-H bond at end, it can also affect C-H bond at other positions where there is no C-H bond at end of molecule.

Finally, the most common S-H bond in nature has been broken.

This technology can bring big dividends. Hydrocarbons are key components of many industrial processes, with nearly 1 billion pounds of hydrocarbons annually used in industry to produce solvents, refrigerants, flame retardants, pharmaceutical synthesis and more.

With this new type of catalyst, chemists can modify or enhance certain biological activities by making small structural adjustments to complex natural structures that have a specific biological activity. One of its potential applications is modification of natural compounds of plants and animals that have certain special effects in order to improve certain properties of these compounds. Among other things, this method will also allow chemists to add new chemical groups to ends of organic molecules, polymerizing them into unprecedentedly long chains.

Hartwig said current results are preliminary. Since yield of final reaction product is not consistent, Hartwig believes there is still a lot of room for improvement, meaning they need to keep making better catalysts.

Link source:

https://news.berkeley.edu/2020/05/21/scientists-finally-crack-natures-most-common-chemical-bond/

https://science.sciencemag.org/content/368/6492/736

Cover source: MasterTux / Pixabay

Source: Principle

Related