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)][AuI] (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, diffraction analysis.