Abstract
Herein, we synthesized and characterized through NMR and X-ray techniques a new set of [(NHC)-Au-X] complexes (NHC = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene), differing in the counterion X– (X– = OMs–, NO3–, ClO4–, 2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoroheptanoate (PFHp–)). All of these complexes, together with those already known having NTf2– and phthalimide (ptm–) as counterions, were tested as catalysts in the methoxylation of 3-hexyne. The results were analyzed together with those obtained previously. The values of activation parameters (ΔH⧧ and ΔS⧧) for different anions are also reported. The overall catalytic and kinetic evidence, together with an extensive computational work, confirm the general mechanistic picture given recently in which the anion plays an active role in all steps of the reaction mechanism: pre-equilibrium, nucleophilic attack, and protodeauration. Medium-coordinating anions (OMs–, OTs–) containing a highly symmetric anchoring group give the best catalytic performances. ...
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