Steric Selection of Anion Binding Sites by Organoantimony(V) Pnictogen Bond Donors: An Experimental and Computational Study.

Catecholatostiboranes have emerged as useful Lewis acids in several applications. To better understand the factors that control the properties of these species, we examined the Lewis acidities of (-CClO)Sb(-Tol) (, Tol = tolyl) and (-CClO)Sb(-Tol) (), two triarylcatecholatostiboranes that differ by the nature of the aryl substituent. Fluoride anion binding studies indicate that is more Lewis acidic than , a factor readily assigned to the steric crowding around antimony in the case of the -tolyl derivative. But, while binds F trans to a Sb-C bond as is typical of catecholatostiboranes, prefers binding trans to a Sb-O bond. Computational analyses of and reveal the existence of several σ holes, and an activation strain analysis is employed to elucidate the origin of these stiboranes' anion-binding geometry preferences.