Facile oxidation of NHC-Au(i) to NHC-Au(iii) complexes by CsBr₃

Abstract

CsBr3 was investigated as a new and convenient oxidant for NHC-Au(I) complexes (NHC = imidazo[1,5-a]pyridin-3-ylidene) for the preparation of the respective Au(III) complexes. The Au(I) complexes were synthesized by the silver salt method using [(NHC)2Ag]PF6 and (tht)AuBr. Unexpectedly, the reactions yielded both neutral (NHC)AuBr and ionic [(NHC)2Au]PF6, depending on the N-substituent of the NHC ligand. Oxidation with CsBr3 gave the complexes (NHC)AuBr3 and [(NHC)2AuBr2]PF6 in high yields and purity, which proves the suitability of this reagent. The complexes were further characterised by X-ray diffraction and electronic absorption and emission spectroscopy. The Au(I) complexes exhibit a dual emission attributable to intraligand fluorescence and phosphorescence at both room temperature and 77 K. Upon irradiation with polychromatic light (λ > 305 nm), the Au(III) complexes are cleanly photo-reduced to the Au(I) congener.

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

“…[8][9][10][11][12] Not surprisingly, the most common synthetic pathway to Au III -NHC complexes involves oxidative addition of halogens or halogen equivalents to Au I -NHC precursor complexes. 8,9,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Other procedures, such as carbene transfer between Ag I and Au III , 8 or reaction of imidazolium ions with Au III in the presence of base, 9,10 are usually complicated by reduction of Au III to Au I . However, Lu et al synthesized the Au III -tetracarbene complex 1 by treatment of HAuCl 4 with an Ag I -NHC complex.…”

Reactivity of Mononuclear and Dinuclear Gold(I) Amidinate Complexes with CS2 and CsBr3

“…For reference, the Au-S bond distances in (IPr)Au(S2CNEt2) and (IPr)Au[S2CN(CH2Ph)2], IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, are 2.314(5) and 2.2999(12) Å, respectively [27], and 2.312(3) Å in Ph3PAu(indazol-1-yldithiocarbamate) [28]. With the recent use of CsBr3 to oxidize Au(I) to Au(III), we attempted a similar reaction with 1 [29]. Indeed, reaction of 1 with CsBr3 is accompanied by a color change to red-brown; however, upon workup the 1 H NMR spectrum revealed the presence of the dinuclear Au(I) amidinate, Au2[(2,6-Me2C6H3N)2C(H)]2, 3, as well as resonances consistent with Ph3PBr2, Equation (4).…”

“…NaN(SiMe3)2, anhydrous carbon disulfide (Aldrich, Milwaukee, WI, USA) and Ph3PAuCl (Strem, Newportbury, MA, USA) were used as received. The amidine ligand, [4], and CsBr3 [29] were prepared as previously described. Benzene-d6 and chloroform-d1 (Cambridge Isotope Laboratories, Tewksbury, MA, USA) were dried over molecular sieves and degassed with three freeze-evacuatethaw cycles.…”

Aggregation of Au(i)-complexes on amorphous substrates governed by aurophilicity

“…Such dual emission composed of fluorescence and phosphorescence is typical for gold-tagged aromatic systems. [44][45][46][47][48] Also bromine substituted naphthalene derivatives show comparable dual luminescence behaviour in nitrogen purged solutions with phosphorescence caused by intersystem crossing processes facilitated by the presence of heavy atoms. 49 Accordingly, the iodido species features a more intense phosphorescence band in relation to the fluorescence band than the bromido complex due to the enhanced heavy atom effect.…”