Stabilisierung von Lewis‐azidem AuF₃ mithilfe eines N‐heterocyclischen Carbens: Herstellung und Charakterisierung von [AuF₃(SIMes)]

Abstract

Zwei unterschiedliche Reaktionspfade zum Trifluoridoorganogold(III)-Komplex [AuF 3 (SIMes)] werden beschrieben. Die Verbindung enthält das N-heterocyclische Carben SIMes (1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-yliden) als Ligand an einer molekularen, Lewisaziden AuF 3 -Einheit und wurde sowohl durchN MR-Spektroskopie als auchm ittels Rçntgenstrukturanalyse charakterisiert. Außer der Verwendung eines [AuF 4 ] À -Salzesals Vorstufe ist auchder direkte Einsatz der stark oxidierenden Verbindung AuF 3 mçglich. Die Reaktion läuft sogar in organischen Lçsungsmitteln in Gegenwart von freiem SIMes als Ligandenvorstufe ab.H ierbei kçnnen Zersetzungsreaktionen mit dem Lçsungsmittel verhindert werden.

Trifluoromethylation of [AuF3(SIMes)]: Preparation and Characterization of [Au(CF3)xF3−x(SIMes)] (x=1–3) Complexes

“…The molecular structureo f[ AuF 3 (SIMes)] in the solid state reveals that the AuÀFb ond with the fluorido ligand in trans position to the SIMes ligand is about 5pml onger than those to the cis-fluorido ligands. [14] In accordance with this finding, as electives ubstitution of the trans-fluorido ligand by ac hlorido or ap entafluoridoorthotellurato (OTeF 5 )l igand was recently reportedb yu s. [43] Hence, the trifluoromethylation of [AuF 3 (SIMes)] is expectedt oy ield trans-[Au(CF 3 )F 2 (SIMes)] (1). Indeed, when TMSCF 3 is condensed into aD CM solution of [AuF 3 (SIMes)] at À80 8Ci nt he presence of the nucleophilic fluoride source CsF,c ompound 1 is formed.…”

“…HCF 3 and trans-[AuClF 2 (SIMes)] are formed as by-products,t he presence of the former being probably due to side reactions of the highly basic transient CF 3 À anion with any proton sources, for example, from the solvent, [44,45,46] while the latter is formed by a chlorine/fluorine exchange reactionb etween [AuF 3 (SIMes)] and DCM, possibly promoted by the fluoridea nions of CsF. [14] The amount of by-products depends on the stoichiometry.T he more TMSCF 3 is used, the more HCF 3 is formed, while less [AuClF 2 (SIMes)] is present( see Supporting Information, Figures S10, S13 and S15). Compounds 1 and 2 partially decompose in solution at room temperature within af ew days, leadingt o the formation of elemental gold.…”

“…The AuÀFb ond lengths (193.2(5) pm, 193.2(10)pm) are comparable to the corresponding AuÀFbond lengths in the starting compound [AuF 3 (SIMes)] (191.6(1) pm, 192.1(1) pm). [14] The AuÀCF 3 bond length (203.6(10)pm) is similar to those in the literature-known anion trans-[Au(CF 3 ) 2 F 2 ] À (205.5(5) pm, 205.3(5) pm) [12] and of the corresponding AuÀCF 3 bond in the neutral isocyanide complex [Au(CF 3 ) 3 (CNC(CH 3 ) 3 )] (205.8(5) pm). [42] The AuÀC carbene bond length (203.5(9) pm) is slightly elongated compared to trans-[AuClF 2 (SIMes)] (200.8(3)pm), [43] [AuF 3 (SIMes)] (197.3(1) pm) [14] and trans-[AuF 2 (OTeF 5 )(SIMes)] (196.9(5) pm).…”

“…[13] Recently,o ur group reported on the stabilization of AuF 3 using the SIMes (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) ligand. [14] The resulting complex [AuF 3 (SIMes)]c ontains the highlyL ewis acidic AuF 3 unit in monomeric form and is stable in common organic solvents such as dichloromethane. This is contrary to AuF 3 ,w hich is af luorine-bridged polymeri nt he solid state and reacts unselectively and sometimes violently with most organics olvents.…”

An Organogold(III) Difluoride with a trans Arrangement

“…Geometries of a) the square-planar and b) the linear trifluoromethyl gold(III) and trifluoromethyl gold(I) fluoride complexes [CF 3 AuF 3 ] À and [CF3 AuF] À optimized at the DFT/M06 level with relevant bond lengths [pm] indicated (see note added in proof) [28]. …”