Bridging Lewis acidic antimony centers with electron-withdrawing carborane cages

While fluorinated carbon-based electron withdrawing substituent groups are commonly employed when strengthening the Lewis acidity of group 15 organometallic compounds, we exploit an alternative approach by leveraging the electron-withdrawing properties of the carbon vertices of three-dimensional icosahedral boron clusters, known as carboranes. Here, we report the synthesis of C-bound ortho-carborane bridged antimony(iii) species, which can be conveniently oxidized to their antimony(v) counterparts using o-chloranil. The corresponding antimony(v) species have proven to strongly bind to small molecules showing that with the aid of bulky C-bound carborane groups, antimony(v) centers have enhanced Lewis acidic properties. This improved Lewis acidity is confirmed via binding studies and computational analysis, which together highlight the reactivity of accepting σ* orbitals, commonly referred to as sigma holes.