A class of non-aromatic 1,3-disilapyrroles acting as stable organosilicon-based triplet diradicals

Open-shell molecules with unpaired electrons and a high-spin S >= 1 configuration are of fundamental importance in chemistry, biology and 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 organometallic transformations but their isolation remains challenging due to their very high reactivity. Here we report the facile synthesis of isolable 1,3-disilapyrroles which act as organosilicon-based delocalized triplet diradicals. The 1,3-disilapyrroles result from cycloaddition reactions of two divalent silicon atoms in a N,N-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 show unprecedented reactivity, including cyclotetramerization and cleavage of the carbon-oxygen triple bond of CO at ambient temperature with subsequent C(sp3)-H bond activation to give a polycyclic product. Carbon- and silicon-based triplet diradicals with two unpaired electrons are proposed as intermediates in organic and organometallic reactions but their isolation is challenging. Now, isolable 1,3-disilapyrroles are reported to act as organosilicon-based delocalized triplet diradicals and mediate the cleavage of the CO triple bond and C(sp3)-H bond activation.