UC Santa Cruz

Phosphine oxides and arsine oxides are common laboratory reagents with diverse applications that stem from the chemistry exhibited by these monomeric species. Stibine oxides are, in contrast, generally dimeric or oligomeric species because of the reactivity-quenching self-association of the highly polarized stiboryl (Sb=O/Sb⁺-O^-) group. We recently isolated Dipp₃SbO (Dipp = 2,6-diisopropylphenyl), the first example of a kinetically stabilized monomeric stibine oxide, which exists as a bench-stable solid and bears an unperturbed stiboryl group. Herein, we report the isolation of Mes₃SbO (Mes = mesityl), in which the less bulky substituents maintain the monomeric nature of the compound but unlock access to a wider range of reactivity at the unperturbed stiboryl group relative to Dipp₃SbO. Mes₃SbO was found to be a potent Lewis base in the formation of adducts with the main-group Lewis acids PbMe₃Cl and SnMe₃Cl. The accessible Lewis acidity at the Sb atom results in a change in the reactivity with GeMe₃Cl, SiMe₃Cl, and CPh₃Cl. With these species, Mes₃SbO formally adds the E-Cl (E = Ge, Si, C) bond across the unsaturated stiboryl group to form a 5-coordinate stiborane. The biphilicity of Mes₃SbO is sufficiently potent to activate even the C-F and Si-F bonds of C(p-MeOPh)₃F and SiEt₃F, respectively. These results mark a significant contribution to an increasingly rich literature on the reactivity of polar, unsaturated main-group motifs. Furthermore, these results highlight the utility of a kinetic stabilization approach to access unusual bonding motifs with unquenched reactivity that can be leveraged for small-molecule activation.