One Collision – Two Heteroatoms: Gas‐Phase Preparation of Azasilabenzenes

Abstract Nature has long favored cyclic, particularly heterocyclic, molecules in the synthesis of key biomolecules. Silicon‐substituted hydrocarbons have gained increasing attention due to their unique chemical bonding and electronic structure compared to their iso‐valent carbon counterparts. However, the synthesis of silicon‐containing heterocyclic molecules remains a significant challenge. In this work, we investigate the reaction mechanism leading to a sparsely explored class of silicon‐ and nitrogen‐containing aromatic heterocycles, in which silicon and nitrogen atoms are positioned adjacently within an aromatic, six‐membered ring: azasilabenzenes. This is achieved through the reaction of the silicon nitride (SiN) radical with 1,3‐butadiene (C 4 H 6 ) via single collision conditions, exploiting a crossed molecular beam experiment combined with electronic structure calculations and statistical analysis. Our results reveal the formation of two novel cyclic products: 1‐aza‐2‐silacyclohexa‐3,5‐dien‐2‐ylidene and 1‐aza‐2‐silabenzene. Interestingly, this reaction contrasts with the iso‐valent system involving the cyano radical (CN) and 1,3‐butadiene (C 4 H 6 ), which predominantly yields an acyclic product (1‐cyano‐1,3‐butadiene) via a simple addition–elimination pathway. In addition to elucidating the reaction pathways, this study also provides insights into the nature of bonding and atomic interactions in the resulting products, offering a deeper understanding of structure–stability relationships in silicon–nitrogen heterocycles and the counterintuitive concept of iso‐valency.