Palladium catalysts can do it

October 09, 2020

Palladium catalysts help synthesize key chemicals for many industries. However, direct reaction of two basic reagents, aryl halides and alkyllithium compounds, remains a challenge. Now, a team of scientists have found that a catalyst containing YPhos-type ligands can mediate this reaction even at room temperature. This discovery may contribute to the development of more sustainable processes in the chemical industry, the authors write in the journal Angewandte Chemie.

Palladium-catalyzed chemical processes are very useful. Palladium catalysts help to couple simple carbon-containing compounds to form more complicated chemical structures. However, they have yet failed to couple two common reagents in chemical synthesis, aryl halides and alkyllithium compounds. Among the aryl halides, aryl chlorides are common synthesis reagents that react variably during palladium-catalyzed reactions to produce side products.

For coupling reactions with aryl halides and alkyllithium compounds, chemists usually take "detours" by adding intermediate synthesis steps. Unfortunately, every extra synthesis step produces chemical waste and adds costs.

This problem led Viktoria Daeschlein-Gessner and her team from Ruhr University Bochum to investigate new palladium catalysts. They thought that a functional catalyst would ease many chemical syntheses. "The coupling of aryl chloride and alkyllithium reagents represents one of the most challenging reactions and--if being successful--promises a broad applicability," the authors explain.

After testing various existing catalysts, the authors identified a promising candidate. This catalyst was based on a class of ylide-substituted phosphines called YPhos.

Chemists use YPhos-containing palladium catalysts for difficult coupling reactions. The YPhos ligands combine a negatively charged carbon center and a positively charged phosphonium group (the ylide) with a phosphine-type ligand--phosphines are typical ligands in palladium catalysis. This ylide-phosphine ligand setup results in special electronic properties. The scientists observed that the ligand electronics helped to activate aryl halides, which is a crucial step in the reaction between aryl halides and alkyllithium compounds.

One of the YPhos class of ligands, a ligand called joYPhos, was shown to have the most favorable architecture. Its combination of electronic properties and a space-filling architecture suppressed the many side reactions otherwise occurring in the coupling.

The authors remark that precatalysts containing the YPhos ligands also performed extraordinarily well. Precatalysts have their ligands and a palladium source prearranged in separate compounds. Like two-component adhesives, they assemble in the reaction mixture to form the effective catalyst. This prearrangement makes their handling user-friendly and the compounds are more stable than the free ligands, according to the authors.

In a scale-up of the reaction, the scientists synthesized a building block of lesinurad, a drug used for treating gout. They also showed that the catalyst performed well for many variations of the aryl halide and alkyllithium reagents. These results led to the conclusion that this transformation is generally applicable. This new palladium catalyst may thus help to avoid costly "detours" in future organic syntheses.
About the Author

Professor Viktoria H. Daeschlein-Gessner holds a chair of inorganic chemistry at the Ruhr-Universität Bochum, Germany. Her research group investigates carbanionic and ylidic compounds and their use in the chemistry of main group elements and transition metals, focusing on an advanced understanding of the electronic structures. With this knowledge, the group develops new synthetic strategies, catalysts, and catalytic transformations.


Related Palladium Articles from Brightsurf:

Well oriented
Polypropylene (PP) is one of the most widely used plastics in the world.

Palladium catalysts can do it
Palladium catalysts help synthesize key chemicals for many industries. However, direct reaction of two basic reagents, aryl halides and alkyllithium compounds, remains a challenge.

Scientists got one step closer to solving a major problem of hydrogen energy
A team of scientists from Far Eastern Federal University (FEFU) together with their colleagues from Austria, Turkey, Slovakia, Russia (MISIS, MSU), and the UK found a way to hydrogenate thin metallic glass layers at room temperature.

A chemist from RUDN developed a green catalyst for pharmaceutical and industrial chemistry
Many production facilities (e.g. plastic manufacturers, pharma companies, and others) use nanocatalysts that contain palladium--an expensive component that is not sustainably produced.

A new synthesis method for three-dimensional nanocarbons
A Nagoya University team has developed a new method of synthesis for three-dimensional nanocarbons, utilizing a catalytic reaction to connect benzene rings and create an eight-membered ring structure.

To make or to break: Novel reversible technique produces acyl fluoride using rare metal
Acyl fluorides are organic compounds that contain a fluorine atom in their structure.

Teaching old transition metals new tricks: Chemists activate palladium catalysis by light
In the production of compounds, chemists have the goal of finding strategies that are most selective and avoid waste products.

Manipulating ligands
Chemists at TU Dresden succeeded in fabricating surface-clean noble metal aerogels boosting the electrocatalysis performance by revisiting ligand chemistry.

A milestone in ultrafast gel fabrication
Alexander von Humboldt research fellow Ran Du opens up new space for both fundamental and application-orientated studies for noble metal gels and other systems at TU Dresden.

CCNY chemists develop safer hydrogenation processes
Safe and environmentally-friendly hydrogen gas on demand could be on the horizon following a new 'hydrogenation' chemical process in development at The City College of New York.

Read More: Palladium News and Palladium Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to