Radical Additions of Carbyne to Achieve Metalla-aromatic Radicals

Transition metal-carbynes are efficient catalysts or key intermediates in a variety of chemical transformations. Significant research has focused on exploring their reactivity, aiming to understand the bonding characters and develop new applications. However, the radical addition reactions of metal-carbynes remain unknown, mainly due to the high polarity of metal-carbyne bonds, which is prone to electrophilic or nucleophilic additions. In this study, we report for the first time the radical addition reaction of metal-carbyne through the reactions of an osmium-carbyne located in aromatic ring with various radicals. The delocalized electronic structure and substantially steric hindrance of metallacycle provide sufficient stability for spectroscopic and/or structural characterizations of the radical addition intermediates, and endow high selectivity for the subsequent transformations. Notably, through this newly developed reaction, a spin-delocalized metalla-aromatic radical was achieved, which represents the first example of metal d-orbital participating in spin delocalization of open-shell π conjugated molecules, although considerable efforts have been dedicated to this field. This work not only opens up an avenue for the radical chemistry of metal-carbynes, but also provides a conceptually new strategy for preparing metal-contained open-shell π conjugated molecules in material science.