Apolar media solvation

Coordination of the anions to the cationic palladium center may strongly depend on the polarity of the reaction medium. Solvation of the ion-pair by protic solvent molecules, such as methanol, is expected to facilitate cation-anion dissociation and therefore render the metal center more electrophilic and more easily accessible for substrate molecules. In relatively apolar solvents, close-contact ion-pairs are generally expected to exist. Anion displacement by substrate molecules may then require the use of noncoordinating anions, such as certain tetraaryl borates [19], with a relatively strong affinity for interaction with the solvent molecules. This will lead to a reduced barrier for displacement of these anions by monomer molecules. 

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