Non-aromatic 1,3-Disilapyrroles: a class of stable organosilicon-based triplet diradicals

Abstract Open-shell molecules with unpaired electrons and a high-spin S ≥ 1 configuration are of fundamental importance in chemistry, biology and towards molecular electronics. Among metal-free systems, carbon- and silicon-based triplet diradicals with two unpaired electrons and strong ferromagnetic coupling are proposed as key intermediates in many organic and elementorganic transformations but their isolation remains challenging due to their very high reactivity. Herein, we report the facile synthesis of the first isolable 1,3-disilapyrroles which represent organosilicon-based delocalized triplet diradicals. They result from click chemistry of two divalent silicon atoms in a 1,1-bis(silylenyl)aniline to the carbon-carbon triple bond of diphenylacetylenes. Remarkably, the spin-density distribution of these triplet diradicals exhibits an asymmetric delocalization due to steric congestion. The unpaired electrons in the 1,3-disilapyrroles enable an unprecedented reactivity, including cyclotetramerization and complete cleavage of the carbon-oxygen triple bond of CO at ambient temperature with subsequent C(sp3)-H bond activation to give a new bicyclic product.