National University of Singapore (NUS) scientists have demonstrated that stepwise customised functionalisation of multihydrosilanes to access fully substituted silicon compounds can be realised using neutral eosin Y, an inexpensive dye molecule.
The development of a unified catalytic platform for stepwise and programmable functionalisation of multihydrosilanes is highly challenging. However, having this platform will facilitate the rational design of organosilanes with predictable functions, in which bespoke silane molecules are required. Three specific requirements need to be simultaneously realised through a single catalytic system: (i) the selective and preferable hydrogen atom abstraction of silicon-hydrogen (Si-H) bonds in the presence of various activated carbon-hydrogen (C-H) bonds; (ii) a diverse range of Si-H functionalisations; and (iii) highly selective monofunctionalisation of di- and trihydrosilanes.
In a recent paper, Associate Professor Jie WU and his colleagues from the Department of Chemistry, NUS, have developed a new method for synthesising organosilanes, a family of chemical compounds which have a variety of applications from organic and polymer synthesis, materials science, medicinal chemistry, to agriculture. The researchers used eosin Y, a low-cost, readily available dye molecule, as a photocatalyst to selectively remove hydrogen atoms from hydrosilanes. This enables different functional chemical groups to be attached to the silicon atom in a step by step manner, potentially creating a wide variety of useful silicon compounds. An amount of energy of approximately 90 kcal/mol is required to break a Si-H bond, and the uniqueness of this catalyst is that it uses much lower energy (~63 kcal/mol) to break the Si-H bond. Also, unlike other photocatalysts, eosin Y is able to selectively break the Si-H bonds rather than some more reactive C-H bonds. More than eight different new chemical transformations have been realised by the research team using various commodity feedstocks as the starting materials to react with hydrosilanes.
These findings were published in the journal Nature Chemistry on 9 March 2023.
The researchers also used a continuous microflow reactor for the monofunctionalisation of di- and trihydrosilanes, which resulted in high selectivity and yield. Unlike conventional bath reactors, the continuous microflow reactor allows for high mixing efficiency and precise residence time control. Also, this process is highly scalable. The use of eosin Y with microflow reactor offers a convenient strategy for stepwise decoration of silicon atoms to access silanes with four different substituents in a programmable and on-demand manner.
The research team plans to extend the strategy to generate chiral silicon reagents, and to apply this method to materials/polymers containing Si-H bonds for post-functionalisation purposes. They are also working towards fully automating the on-demand synthesis of multifunctional silanes.
Assoc Prof Wu said, "We would like to establish a general and sustainable strategy to synthesize functional organosilanes in an efficient, on-demand, and fully automated fashion. With this method, the preparation of desired silicon reagents will be more easily accessible, and in future, chemists can focus their energies on the design and development of functional silicon molecules limited only by their imagination."
