Figure . Reactions of p-substituted benzeneboronic acids with [B12H11I] 2-: Correlation between Hammett constant and suitable solvent. For electron-poor benzeneboronic acids, NMP is better than CD3CN, for electron-rich benzeneboronic acids, CD3CN is better. Data for σ are from . Figure presents the interplay between the different possibilities which can occur upon oxidative addition (reaction A) of the B-I bond: Reaction B is the desired transmetallation (exchange of iodide by an anionic carbon) and reductive elimination to the desired product. D is the displacement of the iodide by a solvent molecule, preventing further reactions. With CH3CN, we found in mass spectrometry the formation of side products where the B-N coupling of the solvent with the cluster had occurred (to which in part water had added) (see SI), and which we assume was formed from the complex of Pd with dodecaborate and CH3CN.