Gold Complexes of an Alicyclic Indazole-Derived N-Heterocyclic Carbene: Syntheses, Characterizations, and Ligand Disproportionation

A gold­(I) NHC complex bearing a heteroalicyclic indazolin-3-ylidene ligand, [AuCl­(Indy)] (<b>1</b>) (Indy = 6,7,8,9-tetrahydropyridazino­[1,2-<i>a</i>]­indazolin-3-ylidene), has been synthesized via the silver–carbene transfer method. Conversion of complex <b>1</b> to its heavier halido analogues [AuBr­(Indy)] (<b>2</b>) and [AuI­(Indy)] (<b>3</b>) was achieved by metathesis reactions involving LiBr and NaI in acetone, respectively. In contrast to <b>1</b> and <b>2</b>, complex <b>3</b> undergoes ligand disproportionation/autoionization upon crystallization, forming the solid complex salts [Au₃I₂(Indy)₄]­[Au₃I₄(Indy)₂] (<b>3</b>′) or [Au­(Indy)₂]­[AuI₂] (<b>3</b>″) depending on the solvent used. This reversible process assisted by aurophilic interactions, and only occurring in the iodido complex <b>3</b>, has been studied further by spectroscopic comparison with [Au­(Indy)₂]­BF₄ (<b>4</b>) and selective conversion of <b>3</b> to the gold­(III) species [AuI₃(Indy)] (<b>5</b>). All complexes <b>1</b>–<b>5</b> have been fully characterized using multinuclei NMR spectroscopies, ESI mass spectrometry, and X-ray diffraction analysis