Lewis Superacids

Abstract

Abstract Lewis acids (LAs) play a prominent role in all domains of chemistry. The present contribution deals with a “super” class of LAs. As a starting point for a meaningful discussion, a more general treatise of the concept of Lewis acidity is required. Lewis acidity is a multi‐dimensional property that depends on a delicate interplay of steric and electronic factors during the interaction with a reference Lewis base or a substrate. Accordingly, various methods that gauge the strength and effectiveness of LAs on various grounds have been developed, as will be discussed in the first part of this work. Different scaling methods do not necessarily show the same trend. In turn, there is no reason to believe that one single parameter is sufficient to describe the full character of a LA. Based on the nature of the Lewis acidity scaling methods and the factors that cause the computed or measured output, a classification into “global”, “effective”, and “intrinsic” groups is made. With this framework in mind, the fluoride ion affinity (FIA) is chosen as a firm “global” parameter to discuss a broad range of LAs within the second part of this contribution. LAs that exceed the FIA of SbF 5 are termed Lewis superacids (LSAs). Accordingly, LAs that reach or exceed this threshold are collected and discussed. The clear focus is on neutral LAs of the p‐block elements, but reference will also be given for cationic Lewis acidic compounds. The majority of those compounds can be found in group 13 and for the heavier group 15 elements. Beyond, this summary touches strong Lewis acidity of d‐block metals and Lewis acidity in alternative media.