Herein, we report on a facile and
selective one-pot synthetic route
to silicon–boron radicals. Reduction of Br2BTip
(Tip = 2,4,6-
i
PrC6H2) with KC8 in the presence of LSi-R affords LSi(
t
Bu)-B(Br)Tip (1) and LSi(N(TMS)2)-B(Br)Tip (2) [L = PhC(N
t
Bu)2]. These first examples of silicon–boron
isolated radical species feature spin density on the silicon and boron
atoms. 1 and 2 exhibit extraordinary stability
to high temperatures under inert conditions in solution and air stability
in the solid state. Both radicals have been isolated and fully characterized
by electron paramagnetic resonance spectroscopy, SQUID magnetometry,
mass spectrometry, cyclic voltammetry, single-crystal X-ray structure
analysis, and density functional theory calculations. Moreover, compound 1 exhibits one-electron transfer when treated with 1 equiv
of AgSO3CF3 and [Ph3C]+[B(C6F5)4]−, respectively,
resulting in the corresponding cations [LSi(
t
Bu)-B(Br)Tip]+[CF3SO3]− (3) and [LSi(
t
Bu)-B(Br)Tip]+[B(C6F5)4]− (4). Compounds 3 and 4 have been characterized with multinuclear NMR and mass spectrometry.
Two silylene molecules oxidatively react under formal [1 + 2 + 1]-cycloaddition to the CN bond of nitriles to yield5)). The strongly folded bicyclic SiCNSi cores in 2−5 feature inverted bridgehead carbon atoms and superelongated C−N bonds [1.745(12) to 1.801(2) Å], exceeding the lengths of C−N single bonds in known silaaziridines by up to 23%. Detailed bonding analysis discloses C−N bonding interactions, sharing far-reaching similarities with the central C−C bond in [1.1.1]propellane.
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