Digging the Sigma‐Hole of Organoantimony Lewis Acids by Oxidation

Abstract

The development of group 15 Lewis acids is an area of active investigation that has led to numerous advances in anion sensing and catalysis. While phosphorus has drawn considerable attention, emerging research shows that organoantimony(III) reagents may also act as potent Lewis acids. Comparison of the properties of SbPh3, Sb(C6F5)3, and SbArF3 with those of their tetrachlorocatecholate analogues SbPh3Cat, Sb(C6F5)3Cat, and SbArF3Cat (Cat=o‐O2C6Cl4, ArF=3,5‐(CF3)2C6H3) demonstrates that the Lewis acidity of electron deficient organoantimony(III) reagents can be readily enhanced by oxidation to the +V state—as verified by binding studies, organic reaction catalysis, and computational studies. The results are rationalized by explaining that oxidation of the antimony center leads to a lowering of the accepting σ* orbital and a deeper carving of the associated σ‐hole.

121/123Sb Nuclear Quadrupole Resonance Spectroscopy: Characterization of Non-Covalent Pnictogen Bonds and NQR Crystallography

“…52 Very recently, Yang et al have shown how to "dig" a deeper σ-hole by oxidizing antimony(III) to the +V state. 53 Historical work has been reported on the interaction of SbF 3 with Lewis bases; however, the resulting compounds have very rarely been examined in the context of noncovalent PnB. A recent review by Scilabra et al inventories the relevant published structures and discusses them anew in this context.…”

Anion Chelation via Double Chalcogen Bonding: The Case of a Bis-telluronium Dication and Its Application in Electrophilic Catalysis via Metal–Chloride Bond Activation

“…17 The high Lewis acidity of [3] 2+ also comes to light using Ph 3 PO as a probe. 18 Indeed, 31 P NMR measurements in CH 2 Cl 2 show a larger deshielding of the phosphorus resonance upon addition of [3][BArF 24 ] 2 to Ph 3 PO (Δδ = 7.9 ppm for a 6 mM 1:1 mixture) than with [2][BArF 24 ] (Δδ = 6.1 ppm for a 6 mM 1:1 mixture).…”

Bis-4-hydroxycoumarin Synthesis: A Simple Laboratory Experiment for Undergraduate Students

“…The expected mechanistic pathway for the synthesis of bis-4-hydroxycoumarins is shown in Scheme 2. SbPh 3 has no such significant strong Lewis acid activity, 22 but the catalyst is so effective that a very small amount (0.02 g) of SbPh 3 is adequate for successful completion of the reaction.…”