Air, a major component of our atmosphere, is abundant and cheap. However, nitrogen, a key element in air, is highly stable and generally unreactive under normal conditions. In nature, some nitrogen-fixing microorganisms can convert nitrogen gas into ammonia at room temperature and pressure. In industrial settings, the Haber-Bosch process is used to convert nitrogen gas into ammonia, a process that requires extremely harsh conditions: temperatures between 350 to 550 degrees Celsius and pressures between 150 to 350 atmospheres.
This process, which is the only industrial method for synthesizing ammonia from nitrogen gas, serves as the sole source of nitrogen for the production of almost all other nitrogen-containing compounds. However, the Haber-Bosch process is energy-intensive and results in significant carbon dioxide emissions. Therefore, developing a new method that can synthesize nitrogen-containing compounds under mild conditions using nitrogen gas as a nitrogen source is of great significance. Not only can this method bypass the Haber-Bosch process, but it can also achieve the green and sustainable synthesis of nitrogen-containing compounds.
Alkylamines, a class of important nitrogen-containing compounds, are widely used in pharmaceuticals, pesticides, and materials. Traditionally, alkylamines are synthesized by reacting ammonia or its derivatives with pre-functionalized electrophilic carbon reagents. Ammonia is produced via the Haber-Bosch process, while electrophilic carbon reagents are typically obtained through the functionalization of olefins.
Recently, a research team from RIKEN, Japan, has developed a new method for synthesizing alkylamines, opening up a new pathway for alkylamine synthesis. By allowing nitrogen gas to react directly with olefins, alkylamines can be produced under mild conditions. This process involves the use of non-activated olefins for nitrogenation to generate alkylamines. In fact, this is a new strategy that utilizes multi-metal complexes.
The research, published in Nature under the title Hydroamination of alkenes with dinitrogen and titanium polyhydrides, demonstrates that by using a trinuclear titanium hydride framework as a platform, alkylamines can be synthesized directly from nitrogen gas under mild conditions, bypassing the traditional high-energy-consuming methods that rely on ammonia as the nitrogen source.
Takanori Shima, from RIKEN, is the first author and co-corresponding author, with Qizheng Zhuo as a co-first author. The study was also co-authored by Professor Lugen Luo from Anhui University and Professor Zhaomin Hou from RIKEN.
The team’s journey with trinuclear titanium hydride clusters has been a decade-long one, marked by numerous unexpected discoveries. In 2013, they aimed to synthesize titanium hydrides but instead discovered nitrogen gas activation and hydrogenation products when hydrogenating titanium alkyl compounds in the presence of nitrogen. Without nitrogen, they isolated the trinuclear titanium hydride cluster in 2014 while performing nuclear magnetic resonance analysis with deuterated benzene as a solvent, finding that the trinuclear titanium hydride cluster could undergo ring-opening and rearrangement of the benzene ring at room temperature and pressure.
In the current study, the researchers initially assumed that high temperatures would promote the formation of carbon-nitrogen bonds. However, multiple experiments failed to produce the desired results. After careful analysis, they discovered that carbon-nitrogen bonds could be formed at room temperature, and high temperatures could instead cause the existing carbon-nitrogen bonds to break.
The researchers noted that activating and converting nitrogen gas, especially through catalytic conversion, remains a highly challenging problem. In the future, they plan to continue exploring nitrogen gas activation and functionalization systematically to contribute to the efficient and green synthesis of nitrogen-containing compounds.
This new method not only offers a sustainable alternative to the Haber-Bosch process but also opens up a new avenue for the green synthesis of alkylamines, a crucial class of nitrogen-containing compounds. By addressing the challenges of nitrogen activation and conversion, this breakthrough paves the way for more environmentally friendly chemical processes in the future.
References:
1. Shima, T., Zhuo, Q., Zhou, X.et al. Hydroamination of alkenes with dinitrogen and titanium polyhydrides. Nature 632, 307–312 (2024). https://doi.org/10.1038/s41586-024-07694-5
2. Science 2013, 340, 1549
3. Nature 2014, 512, 413
Views: 0