Gold complexes of an alicyclic indazole-derived N-heterocyclic carbene: Syntheses, characterizations, and ligand disproportionation

Abstract

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 [Au 3I 2(Indy) 4][Au 3I 4(Indy) 2] (3′) or [Au(Indy) 2][AuI 2] (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]BF 4 (4) and selective conversion of 3 to the gold(III) species [AuI 3(Indy)] (5). All complexes 1-5 have been fully characterized using multinuclei NMR spectroscopies, ESI mass spectrometry, and X-ray diffraction analysis. © 2012 American Chemical Society.