Researchers at the Karlsruhe Institute of Technology (KIT) have introduced an innovative method for activating and catalytically transferring ammonia, utilizing main group elements as the basis for catalysis.
Ammonia (NH3), a compound comprising nitrogen and hydrogen, ranks among the most widely manufactured chemicals on a global scale. Its significance lies in its pivotal role in the synthesis of various nitrogen-based compounds. The prospect of producing amines through the direct addition of ammonia to unsaturated hydrocarbons represents a groundbreaking development in the field of chemistry. Amines, which are organic derivatives of ammonia, are in high demand across diverse industries.
Amines serve as foundational components in the production of agricultural and pharmaceutical chemicals, as well as detergents, dyes, lubricants, and coatings. Furthermore, amines find application as catalysts in the manufacturing of polyurethanes and play a crucial role in gas scrubbing processes at refineries and power plants.
The key challenge lies in breaking the robust bond between nitrogen and hydrogen in ammonia, known as activation, to theoretically enable its transfer to other molecules, such as unsaturated hydrocarbons. For instance, the transfer of ammonia to ethylene, a vital substance in the chemical industry, would yield ethylamine. This process is referred to as hydroamination by chemists. However, ammonia and ethylene do not readily react with each other; a catalyst is imperative for the reaction to proceed. Traditional catalysts based on transition metals, unfortunately, react with ammonia and subsequently lose their catalytic activity.
Professor Frank Breher, the head of a research group at the Division of Molecular Chemistry within KIT’s Institute for Inorganic Chemistry (AOC), emphasizes that “Hydroamination of non-activated alkenes with ammonia is considered a significant challenge, often regarded as the holy grail of catalysis.”
In collaboration with researchers from Paderborn University and Complutense University of Madrid, Professor Frank Breher and Dr. Felix Krämer from AOC have made substantial progress toward this formidable objective. They have devised a system for ammonia activation that does not rely on transition metals but rather on main group elements. This “atom-economic” activation process, followed by the transfer of ammonia, generates no waste, making it particularly appealing from a sustainability perspective. Their work has been published in Nature Chemistry.
The team developed a “frustrated Lewis pair” (FLP), comprising an acid as an electron pair acceptor and a base as an electron pair donor. Typically, these components react to form an adduct. However, by preventing or limiting adduct formation, a state of frustration is induced, prompting the molecule to readily interact with small molecules such as ammonia.
Breher highlights the importance of dampening reactivity to achieve reversibility when reacting with small molecules. This critical achievement enables the use of FLP in catalysis. The FLP demonstrated the ability to react effortlessly with non-aqueous ammonia in a thermoneutral manner and to reversibly break the nitrogen-hydrogen bond of ammonia at room temperature.
For the first time, researchers have presented NH3 transfer reactions catalyzed by a catalyst based on main group elements. While they have thus far only converted activated substrates and not unsaturated hydrocarbons, they are closer than ever to realizing their ultimate goal. Breher anticipates that their initial proof of concept will inspire further exploration of N-H-activated ammonia as an easily accessible and sustainable nitrogen source.
Reference: “A crystalline aluminium–carbon-based ambiphile capable of activation and catalytic transfer of ammonia in non-aqueous media” by Felix Krämer, Jan Paradies, Israel Fernández, and Frank Breher, 28 September 2023, Nature Chemistry.
DOI: 10.1038/s41557-023-01340-9
Table of Contents
Frequently Asked Questions (FAQs) about Catalytic Ammonia Activation
What is the significance of ammonia in chemistry?
Ammonia (NH3) is a vital chemical compound due to its role in producing various nitrogen-based compounds, such as amines.
What are amines, and why are they important?
Amines are organic derivatives of ammonia and find extensive use in industries for manufacturing agricultural and pharmaceutical chemicals, detergents, dyes, lubricants, coatings, and even as catalysts in polyurethane production.
What is the challenge in using ammonia for hydroamination?
Ammonia and substances like ethylene do not readily react, necessitating a catalyst. However, conventional transition metal-based catalysts tend to become inactive when exposed to ammonia.
How has this challenge been addressed in the study?
Researchers have developed a novel approach using main group elements as catalysts, avoiding the limitations of transition metals. This sustainable method enables ammonia activation without generating waste.
What is a “frustrated Lewis pair,” and how does it contribute to the process?
A frustrated Lewis pair (FLP) consists of an acid and a base that would typically react to form an adduct. By preventing adduct formation, a state of frustration is induced, allowing the molecule to interact with small molecules like ammonia.
What is the significance of achieving reversibility in ammonia reactions?
Reversible reactions with small molecules, like ammonia, are crucial for catalysis. The research team successfully achieved reversibility, making it possible to use ammonia as a substrate for further reactions.
What are the potential applications of this research?
While the study focused on activated substrates rather than unsaturated hydrocarbons, it marks a significant step towards using N-H-activated ammonia as a sustainable source of nitrogen, with potential applications in various industries.
1 comment
Ammonia is super imp in chemistry, amirite? Amines r big deals 4 real. Transition metal probs solved by main group elements, no waste! Frustrated Lewis pair = cool. Reversibility = key. N-H ammonia, future nitrogen src!