Synthesis and X‐ray Structures of the Polycyclic Dimers {[PhB(μ‐NtBu)₂AsN(tBu)H]LiI}₂ and [PhB(μ‐NtBu)₂AsN(tBu)Li]₂

Abstract

The metathesis of [PhB(μ-NtBu) 2 ]AsCl and tBuN(H)Li in 1:1 molar ratio in diethyl ether produced the amido derivative [PhB(μ-NtBu) 2 AsN(tBu)H] (1) in good yield. The lithiation of 1 with one equivalent of nBuLi afforded the lithium salt [PhB(μ-NtBu) 2 AsN(tBu)Li] (2a). Both 1 and 2a were characterized by multinuclear NMR spectroscopy. The crystal structure of 2a is comprised of a U-shaped, centrosymmetric dimer in which the monomeric [PhB(μ-NtBu) 2 AsN(tBu)] Ϫ Li ϩ units are linked by 875 Li-N interactions to give a six-rung ladder. Oxidation of 2a with one-half equivalent of I 2 in diethyl ether resulted in hydrogen abstraction from the solvent to give the dimeric lithium iodide adduct {[PhB(μ-NtBu) 2 AsN(tBu)H]LiI} 2 (1 · LiI) with a central Li 2 I 2 ring.

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“…This radical is unstable in solution above 0 °C, which is in stark contrast to the neutral Al and Ga spirocyclic radicals M­[PhB­(μ-N t Bu) 2 ] 2 ] • (M = Al and Ga; 105 and 106 ), which are stable in the solid state at room temperature . Attempts to extend this synthetic strategy to yield a stable As radical, [As­[PhB­(μ-N t Bu) 2 ] 2 ] • , led to the formation of a zwitterionic spirocycle wherein chloride transfer from SO 2 Cl 2 to one boron atom transpired ( 107 ; Scheme ) . In an attempt to form a stable N -heterocyclic silylene featuring a NBN backbone, Cui and co-workers combined the hydrochloride Si­(IV) precursor [PhB­(μ-NDipp) 2 Si­(H)­Cl] ( 108 ) with the carbene Im t Bu (Im t Bu = [(HCN t Bu) 2 C:]); a clean reaction transpired to afford the disilane product 109 from the formal insertion of the putative silylene :Si­[PhB­(μ-NDipp) 2 ] into the Si–Cl bond of unreacted 108 (Scheme ) .…”