By combining NOE NMR measurements and accurate theoretical modeling, we have discovered that the coun- terion in olefin-Au(I) catalysts resides mainly far away from the gold site, the latter carrying only a small fraction of the positive charge. The preferential position of the counterion is tunable through the choice of the ancillary ligand, and this opens the way to greater control over the properties and activity of these catalysts. In our specific case, an interesting structure/reactivity correlation can be sketched. The position of the counterion determined for 1BF4 is apt to interfere with the nucleophile attacking the coordinated olefin. On the contrary, electronic (interactions with H9) and steric (hindered 2,6-diisopropyl aryls) confinement of the counterion make strong counterion effects in 2BF4 unlikely. In nice agreement, counterion effects in Au(I) catalyzed activation of unsaturated substrates are much more frequent when phosphines4,6,7 are used as ancillary ligands instead of NHCs.
Ion Pairing in Cationic Olefin-Gold(I) Complexes
ZUCCACCIA, DANIELE;BELPASSI, LEONARDO;TARANTELLI, Francesco;MACCHIONI, Alceo
2009
Abstract
By combining NOE NMR measurements and accurate theoretical modeling, we have discovered that the coun- terion in olefin-Au(I) catalysts resides mainly far away from the gold site, the latter carrying only a small fraction of the positive charge. The preferential position of the counterion is tunable through the choice of the ancillary ligand, and this opens the way to greater control over the properties and activity of these catalysts. In our specific case, an interesting structure/reactivity correlation can be sketched. The position of the counterion determined for 1BF4 is apt to interfere with the nucleophile attacking the coordinated olefin. On the contrary, electronic (interactions with H9) and steric (hindered 2,6-diisopropyl aryls) confinement of the counterion make strong counterion effects in 2BF4 unlikely. In nice agreement, counterion effects in Au(I) catalyzed activation of unsaturated substrates are much more frequent when phosphines4,6,7 are used as ancillary ligands instead of NHCs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
