Gold(I) Complexes Stabilized by Nine‐ and Ten‐Membered N‐Heterocyclic Carbene Ligands

• Published in: Chemistry : a European journal 2019-09, Vol.25 (50), p.11745-11757
• Main Authors: Cervantes‐Reyes, Alejandro, Rominger, Frank, Rudolph, Matthias, Hashmi, A. Stephen K.
• Format: Article
• Language: English
• Subjects: Anion exchange; Anion exchanging; carbenes; Catalysis; Catalysts; Catalytic activity; Chemistry; Gold; Isomerization; Ligands; N-heterocyclic carbenes; Steric hindrance
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.201902458

Nine‐ and ten‐membered N‐heterocyclic carbene (NHC) ligands have been developed and for the first time their gold(I) complexes were synthesized. The protonated NHC pro‐ligands 2 a–h were prepared by the reaction of readily available N,N′‐diarylformamidines with bis‐electrophilic building blocks, followed by anion exchange. In situ deprotonation of the tetrafluoroborates 2 a–h with tBuOK in the presence of AuCl(SMe2) provided fast access to NHC‐gold(I) complexes 3–10. These new NHC‐gold(I) complexes show very good catalytic activity in a cycloisomerization reaction (0.1 mol % catalyst loading, up to 100 % conversion) and their solid‐state structures reveal high steric hindrance around the metal atom (%Vbur up to 53.0) which is caused by their expanded‐ring architecture. Meet the new members of the golden family: A new series of N‐heterocyclic carbene ligands bearing a rigid expanded‐ring backbone, supply unique stability to the gold(I) complex, and provide a high steric hindrance towards the metal center, which results in an excellent catalytic activity.