Stable Au^III complexes with four N-heterocyclic carbene groups can be prepared in high yield directly from KAuCl₄

Abstract

Gold(iii) N-heterocyclic carbene (NHC) complexes of form [Au(NHC)Cl]Cl were synthesized by reaction of KAuCl with bis- and tetrakis(imidazolium) salts in the presence of a mild base. Treatment of these complexes with KPF afforded four-coordinate Au complexes of form [Au(NHC)](PF). X-Ray crystallography showed the [Au(NHC)] cations in the hexafluorophosphate salts to have a square planar Au(NHC) moiety [AuC 2.024(4)-2.082(7) Å]. In the [Au(NHC)Cl] cations in the chloride salts, coordination about Au was tetragonally-distorted octahedral, the axial Au-Cl bonds being substantially longer [AuCl 3.148(2)-3.693(1) Å] than the equatorial Au-C bonds [AuC 2.024(4)-2.082(7) Å]. NMR and conductance studies suggested that the structures of the complexes seen in the solid state persisted in DMSO solution, except in one case where a chlorido ligand dissociated from [Au(NHC)Cl] to form [Au(NHC)Cl]. The Au(NHC) unit was surprisingly robust. An Au complex was found to undergo H/D exchange reactions in DO solution at 100 °C with no signs of decomposition detectable by H NMR spectroscopy.H NMR studies showed that various complexes containing Au(NHC) moieties underwent little or no decomposition when heated at 120 °C in DMSO-d for extended periods.

A bench stable formal Cu(iii) N-heterocyclic carbene accessible from simple copper(ii) acetate

“…It is close to the chemical shifts of Au( iii )–C signals in similar Au( iii )-tetra(NHC) complexes, commonly observed between 147 and 145 ppm. 35 This might indicate a close relationship between the electronic structure of 1 and those relatively widespread compounds. 35 , 36 The backbone resonance at 123.2 ppm and the CH 2 bridges at 62.4 ppm are also very close to those of Au( iii )-tetra(NHC) complexes at about 124 and 63 ppm, respectively.…”

“… 35 This might indicate a close relationship between the electronic structure of 1 and those relatively widespread compounds. 35 , 36 The backbone resonance at 123.2 ppm and the CH 2 bridges at 62.4 ppm are also very close to those of Au( iii )-tetra(NHC) complexes at about 124 and 63 ppm, respectively. The elemental analysis of isolated 1 is in excellent accordance with the calculated composition derived from SC-XRD.…”

Coinage Metal N‐Heterocyclic Carbene Complexes: Recent Synthetic Strategies and Medicinal Applications

“…The proton NMR studies have shown that the compound underwent H/D exchange reactions in D 2 O solution at 100 °C without decomposition (Scheme 46). [90] …”

“…[89] In underwent H/D exchange reactions in D 2 O solution at 100°C without decomposition (Scheme 46). [90] Cucciolito et al prepared Au I À NHC complexes with a sugar moiety (198 and 199) by using sugar incorporated imidazolium precursor 196 as starting material. Treatment of imidazolium precursor 196 with the silver oxide in acetone produced the target Ag I À NHC complex 197.…”

Stepwise Synthesis of Tetra-imidazolium Macrocycles and Their N-Heterocyclic Carbene Metal Complexes

“…Polyimidazolium linked macrocycles have also been utilized as precursors for N -heterocyclic carbene metal complexes and previously the Au(III) complex IV (Figure 2) was prepared the reaction of KAuCl 4 with a macrocyclic tetra -imidazolium salt II (Mageed et al, 2017). Additionally, dinuclear Au(II) and mixed valence Au(I)/Au(III) complexes of have been prepared by the oxidation of dinuclear Au(I) complexes of macrocyclic NHC ligands (Mageed et al, 2018).…”