Au(I) and Au(III) complexes of a sterically bulky benzimidazole-derived N-heterocyclic carbene

The reaction of [AuCl(SMe2)] with in situ generated [AgCl(iPr2-bimy)] (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene), which in turn was obtained by the reaction of Ag2O with 1,3-diisopropylbenzimidazolium bromide (iPr2-bimyH+Br−, A), afforded the monocarbene Au(I) complex [AuCl(iPr2-bimy)] (1). Subsequent reaction of 1 and the ligand precursor iPr2-bimyH+BF4−, (B) in acetone in the presence of K2CO3 yielded the bis(carbene) complex [Au(iPr2-bimy)2]BF4 (2) as a white powder in 80% yield. The oxidative addition of elemental iodine to complex 2 gave the bis(carbene) Au(III) complex trans-[AuI2(iPr2-bimy)2]BF4 (3) as an orange-red powder in 92% yield. All complexes 1–3 have been fully characterized by multinuclear NMR spectroscopies, ESI mass spectrometry, elemental analysis, and X-ray single crystal diffraction. Complexes 1 and 2 adopt a linear geometry around metal centers as expected for d10 metals. The geometry around the Au(III) metal center in 3 is essentially square-planar with two carbene ligands in trans-position to each other. Complex 3 shows absorption and photoluminescence properties owing to a ligand to metal charge transfer.