Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

Abstract

We recently reported the first example of a monomeric stibine oxide. Herein, we assess the Brønsted basicity of a series of monomeric pnictine oxides (Dipp3PnO; Pn = P, As, and Sb).

A Sterically Accessible Monomeric Stibine Oxide Activates Organotetrel(IV) Halides, Including C–F and Si–F Bonds

“…The Dipp substituents are sufficiently sterically demanding to kinetically stabilize a monomeric, bench-stable species that can engage in H-bonding, Bro̷nsted base chemistry, coordination chemistry, and O atom transfer. The Bro̷nsted basicity of Dipp 3 SbO is dramatically enhanced over that of the lighter congeners, and our molecular orbital calculations suggested that Dipp 3 SbO enjoys a similarly privileged Lewis acidity . Access to the Lewis acidic Sb atom is, however, largely precluded by the steric shielding of the Dipp substituents.…”

“…Phosphine oxides and arsine oxides are commonly used as Lewis bases, and in our earlier work we studied the interaction between Dipp 3 SbO and transition-metal centers . This coordination chemistry, in combination with the dramatically enhanced Bro̷nsted basicity of Dipp 3 SbO relative to its lighter congeners, led us to anticipate that the stibine oxide would readily form stable Lewis adducts with a wide variety of main-group Lewis acids. As an initial test of this capability, we investigated its reaction with PbMe 3 Cl, which features a sterically unencumbered Pb atom capable of expanding its coordination sphere and a low-lying Pb–Cl σ* orbital into which it can accept electron donation.…”

“…We have previously demonstrated that, for the Dipp 3 PnO series, this variation in electronic structure manifests as comparatively enhanced basicity for the stibine oxide. 57 The LUMO of Mes 3 SbO, although highly delocalized across the stiboryl unit and the aryl groups, nonetheless exhibits significant Sb−O σ* character with a pronounced lobe opposite the Sb−O bond (Figure 2C). The low-lying LUMO of Mes 3 SbO relative to its lighter congeners suggests that there will be enhanced Lewis acidity at the Sb center, as well as enhanced biphilic reactivity across the polar unsaturated stiboryl group.…”

Chemical Structure Elucidation in the Development of Inorganic Drugs: Evidence from Ru‐, Au‐, As‐, and Sb‐based Medicines

“…Among the first to be prepared was the antimony analog of arsanilic acid, which was described as "para-aminophenylstibinic acid" (although it would now be called para-aminophenylstibonic acid) and given the moniker stibamine. [139] Although the compound was initially described as a monomeric stibonic acid, it is now known that, like arylstibine oxides, [101][102][103][140][141][142] arylstibonic acids can self-associate into higher-nuclearity structures. [143][144][145][146] In the absence of oligomerization, they may also remain monomeric but expand their coordination sphere, possibly with ligand exchange occurring.…”

Recent advances in the stabilization of monomeric stibinidene chalcogenides and stibine chalcogenides

“…The relative Brønsted basicity of Dipp 3 PnO (Pn = P, As, Sb) was probed. 96 Based on the theoretical analyses described above, we hypothesized that the Lewis basicity at the O atom would increase from Dipp 3 PO < Dipp 3 AsO < Dipp 3 SbO. Treatment of Dipp 3 PnO with triflic acid afforded the corresponding [Dipp 3 PnOH][CF 3 SO 3 ] salt in all cases.…”