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