Trifluoromethylation of [AuF₃(SIMes)]: Preparation and Characterization of [Au(CF₃)_xF_3−x(SIMes)] (x=1–3) Complexes

Abstract

Trifluoromethylation of [AuF 3 (SIMes)] with the Ruppert-Prakash reagent TMSCF 3 in the presence of CsF yields the product series [Au(CF 3) x F 3Àx (SIMes)](x = 1-3). The degree of trifluoromethylation is solvent dependenta nd the ratio of the speciesc an be controlled by varying the stoichiometry of the reaction, as evidenced from the 19 FNMR spectra of the correspondingr eactionm ixtures.T he molecular structures in the solid state of trans-[Au(CF 3)F 2 (SIMes)] and [Au(CF 3) 3 (SIMes)] are presented, together with as elective route for the synthesis of the latter complex.C orrelation of the calculated SIMes affinity with the carbene carbon chemical shifti nt he 13 CNMR spectrum reveals that trans-[Au(CF 3)F 2 (SIMes)] and [Au(CF 3) 3 (SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, an ew correlation between the AuÀC carbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13 CNMR spectrum is presented.

Reactivity of [AuF3(SIMes)]: Pathway to Unprecedented Structural Motifs

“…The only other known reaction of [AuF 3 (SIMes)] that led to manifold substitutions of fluorido ligands is the one with Me 3 SiCF 3 (see Scheme 1, bottom left). [17] However, in the case of the reaction with Me 3 SiCF 3 , also the two times substituted product was observed by NMR spectroscopy, contrary to the reaction with Me 3 SiX (X = CN, N 3 ) presented herein, in which none of the cis-[AuFX 2 (SIMes)] products are observed at any point.…”

“…Monitoring the reaction mixture by multinuclear NMR spectroscopy, the formation of 2 was confirmed (see Table 1 and Scheme 2, bottom). In the 13 C{ 1 H} NMR spectrum, 1 and 2 also have similar chemical shifts for the carbene carbon atom at 185.3 and 186.4 ppm, respectively, which is particularly sensitive to the nature of the Lewis acidic moiety bound to the Au atom (see below) [16,17,32,63] …”

“…Comparison of the perfluoroalkoxido gold complexes revealed that the stability of the complex decreases with Correlation between the calculated SIMes affinity (À Δ r G diss ) and the chemical shift of the carbene carbon atom in the 13 C{ 1 H} NMR spectrum (δ( 13 C carbene )) of compounds 1-10 (green: alkynido complexes, orange: cyanido complexes, red: azido complexes, blue: perfluoroalkoxido complexes) and related, literature-known compounds (black). [14,16,17,65] The 13 C chemical shift of uncoordinated SIMes, which is plotted at a SIMes affinity of 0 kJ • mol À 1 , is also included. [66] smaller perfluorinated moieties bound to the central gold atom, as also supported by quantum-chemical calculations.…”

“…The solid state structure of [AuF 3 (SIMes)] reveals that the Au−F bond length of the fluorido ligand trans to the NHC is about 5 pm longer than those of the fluorido ligands in cis position [14] . Subsequent studies on the substitution of the fluorido ligand in trans position were performed by our group to selectively introduce a chloride, [16] pentafluoroorthotellurate, [16] and trifluoromethyl [17] group via trimethylsilyl reagents (Scheme 1, left). Interestingly, in the reaction with Me 3 SiCF 3 , also a second and third substitution can be observed, with their ratios depending on the reaction conditions [17] …”

“… Overview of the literature‐known reactivity of [AuF 3 (SIMes)] towards Me 3 SiX (X=Cl, [16] OTeF 5 , [16] CF 3 [17] ) reagents (left, blue) and the reactivity of [AuF 3 (SIMes)] investigated in this work towards trimethylsilyl compounds and perfluorinated carbonyl‐bearing molecules (right, green).…”