An Isolable Diboron‐Centered Diradical with a Triplet Ground State

Abstract

Two new diboranes, 2,6-bis(BMes )mesitylene (1) and 3,3'-bis(BMes )bimesitylene (3), were synthesized. Two-electron reduction of 1 with elemental potassium afforded the C-H activation product [(18-c-6)K(THF) ] ⋅2 bearing a BC four-membered ring as colorless crystals, whereas the reduction of 3 with potassium led to the isolation of [(18-c-6)K(THF) ] ⋅3 as dark blue crystals. Both reduction products were characterized by structural and spectroscopic methods. Electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations revealed that the electron spin density of 3 mainly resides on the two boron nuclei and features a triplet ground state, which was confirmed by superconducting quantum interference device (SQUID) measurements as well as theoretical calculations. 3 represents the first structurally characterized boron-centered diradical with a triplet ground state. In addition, the reactivity of [(18-c-6)K(THF) ] ⋅3 toward PhSeSePh and nBu SnH was investigated, which is consistent with its radical character.

Reversible Self‐Assembling of Boryl Radical Anions to Their Diradicals with Tunable Singlet Ground States

“…All of them were formed by covalent bonding (Scheme ). The two boron radical centers in the four‐membered B 2 P 2 singlet diradical were coupled through space ( A ), while all others have the two boryl radical centers coupled by π ‐conjugated bridges ( B – H ) –. Despite the fact that several boryl radical anions have been isolated, no formation of boryl diradicals through a self‐assembling approach has been observed.…”

Sequential Oxidation and C−H Bond Activation at a Gallium(I) Center

“…Wang et al. reported that reduction of the phenylene‐bridged diborane 4 affords proton abstraction and B−H and C−B bond formations by a radical pathway . The known Al I compounds 5 and 6 react with the activated C−H bond of Cp*H to furnish Cp* hydride derivatives but do not react with C(sp 2 )−H bonds .…”

A redox-active diborane platform performs C(sp3)–H activation and nucleophilic substitution reactions

“… 19 (2) Wang et al observed hydrogen-atom abstraction from a H 3 C group with concomitant formation of B–H and B–C bonds when they reduced 2,6-bis(BMes 2 )mesitylene to its diradical state. 20 (3) Fontaine exploited an intramolecular deprotonation step on an FLP platform to establish an NCH 2 –B bond; subsequent H 2 liberation provided the necessary thermodynamic driving force. 21 …”