Gold(III) Bis(di‑N‑heterocyclic carbene) Square Planar Trication with Axial Ligand Interactions with Bromides from Ag/Br Counteranion Assemblies

• Published in: Organometallics 2017-06, Vol.36 (12), p.2285-2292
• Main Authors: Baron, Marco, Tubaro, Cristina, Cairoli, Maddalena L. C, Orian, Laura, Bogialli, Sara, Basato, Marino, Natile, Marta M, Graiff, Claudia
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.7b00163

The mononuclear tricationic bis­(di-N-heterocyclic carbene) gold­(III) complex 13+ of formula [Au­(MeImCH2ImMe)2]3+ (Im = imidazol-2-ylidene) was successfully synthesized by transmetalation of the di­(N-heterocyclic carbene) ligand from the corresponding silver­(I) complex to KAuBr4. The counteranion of the gold­(III) cationic complex depends on the synthetic procedure. The crude product, isolated by the transmetalation reaction, consists of infinite (Ag4Br7 3–) n ribbons. By adding a stoichiometric amount of AgPF6, the complete precipitation of AgBr is achieved, and the counteranions are PF6 –. If substoichiometric amounts of silver salts are added, then the (Ag4Br7 3–) n ribbon breaks, and silverbromides anionic aggregates of lower nuclearity are obtained, for example, Ag2Br6 4–. The X-ray crystal structures of 1-Ag 4 Br 7 , 1-PF 6 , and 1-Br,(Ag 2 Br 6 ) 0.5 were determined. The complexes with any type of bromide present interactions between the Au center and two bromides of the counteranions so that the geometry around gold is pseudo-octahedral. The gold-bromide interaction has been investigated via DFT calculations and is mainly electrostatic.