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.

Synthesis, Reactivity, and Complexation with Fe(0) of a Tight‐bite Bis(N‐heterocyclic silylene)

“…Compound 1 (Figure 2) crystallized in the monoclinic space group C2/c with one molecule in the asymmetric unit (see SI: Table S1). [9] The SiÀ NÀ Si angle of 109.33 (8)°in 1 and the intramolecular Si II •••Si II distance in 1 amounts to 2.8864(9) Å, akin to that in Ph-NSi 2 (SiÀ NÀ Si angle: 109.4(1)°and Si II •••Si II distance 2.895(1) Å). [7] NÀ H bond activation is a crucial transformation in organic synthesis due to its significance in several industrial processes.…”

“…In contrast, diphenyl acetylene resulted in the formation of an unusual diradical (V) at 4 °C and an interesting cyclotetramer at room temperature. [8] With this knowledge, we hypothesized that bissilylenes with short Si•••Si distances might help activate the challenging bonds and might also afford the MÀ M bonded compounds upon treatments with suitable precursors. Herein we report bis(NHSi) 1 using ptoluidine as a spacer and its reactivity with p-toluidine and Fe(CO) 5 .…”