Gold(I) and\nGold(III) Complexes of Expanded-Ring N‑Heterocyclic\nCarbenes: Structure, Reactivity, and Catalytic Applications

Abstract

The oxidative addition of bromine to homo- and heterobis­(carbene)\ngold­(I) complexes <b>1–6</b> containing expanded-ring\nN-heterocyclic carbene (erNHC) ligands was explored to prepare the\nfirst examples of gold­(III) erNHC complexes. The use of stoichiometric\namounts of bromine consistently gave clean gold-centered oxidations\nleading to the isolation of monocarbene and mixed carbene complexes\nof the type [AuBr₃(erNHC)] (<b>7–9</b>) and <i>trans</i>-[AuBr₂(^<i>i</i>Pr₂-bimy)­(erNHC)]­BF₄ (<b>13–15</b>),\nrespectively. The use of excess bromine additionally led to ligand\nbrominations in the monocarbene series affording [AuBr₃(erNHC^Br2)] complexes (<b>10–12</b>), while\nin the case of the heterobis­(carbene) series, tribromide complexes\nof the type <i>trans</i>-[AuBr₂(^<i>i</i>Pr₂-bimy)­(erNHC)]­Br₃ (<b>16–18</b>) were obtained instead. Comparison of the catalytic\nactivities of all complexes in the hydroamination of alkynes revealed\nthe superior performance of mono-erNHC complexes in all cases.