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closo-Borate aryliodonium zwitterions: Convenient intermediates for functional closo-borane derivatives and molecular materials.
Abstract
Zwitterionic aryliodonium derivatives of closo-borates are attractive intermediates in regioselective functionalization of anionic boron clusters through nucleophilic substitution with halides, and N-, O-, and C-centered reagents. They are easily available in high yields by highly regioselective direct aryliodination of the closo-borate anions with ArI(II) species, typically PhI(OAc)2, and undergo four types of transformations: substitution through a rearrangement of a 10-I-3 species, dissociation to boronium ylides and trapping with the solvent, SET and homolysis of the 9-I-2 species to B–I products, and iodoaryl slippage to cage arylation byproducts. These zwitterions exhibit moderate and well-balanced thermal stability, which, in most cases, is sufficient for their isolation and synthetic applications. It depends on the closo-borane, position of the aryliodonium substituent, the presence of other substituents, and finally the nature of the aryl group. The two-step process, aryliodination and substitution, can be regarded as a regioselective activation of the B–H bond for nucleophilic substitution. This review summarizes the formation, structure, stability and reactions of zwitterionic derivatives of 10- and 12-vertex closo-borate anions accumulated in the literature in the past decade.
CH25006 Accepted 12 April 2025
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