Efficient access to hexaaryl-substituted borazines in batch and continuous-flow

Abstract

Borazine-doped π-conjugated frameworks have significantly contributed to advancing the application of boron–nitrogen-doped organic materials. However, the challenging synthetic procedure has imposed limits on progress. In the case of hexaaryl-substituted borazines (HABs), the instability of B,B′,B′′-trichloro-N,N′,N′′-triarylborazine (TCB) due to the high reactivity of the boron site necessitates the synthesis and nucleophilic substitution of the chlorinated borazine under strict avoidance of moisture and oxygen to obtain HABs. Moving toward an ideal more sustainable synthesis, the first continuous flow process for the synthesis of HABs has been developed, enabling fast and safe boron arylation. The new process facilitates the neutralization and cleanup of the TCB solution from acidic by-products by utilizing an inorganic scavenger. BY making use of bio-derived 2-MeTHF as reaction medium, the common wasteful isolation procedure of HABs can be avoided, thus allowing not only simplifying the preparation of substituted borazines in high yields but also minimizing its environmental impact and improving its safety profile.