Trifluoromethylation of [AuF3 (SIMes)]: Preparation and Characterization of [Au(CF3 )x F3-x (SIMes)] (x=1-3) Complexes.

Marlon Winter,Simon Steinhauer,Niklas Limberg,Alberto Pérez‐Bitrián,Mathias A Ellwanger,Sebastian Riedel,Karsten Sonnenberg

doi:10.1002/chem.202002940

Marlon Winter, Simon Steinhauer + Show 5 more

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https://doi.org/10.1002/chem.202002940

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Abstract

Trifluoromethylation of [AuF3(SIMes)] with the Ruppert–Prakash reagent TMSCF3 in the presence of CsF yields the product series [Au(CF3)xF3−x(SIMes)] (x=1–3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19F NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans‐[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13C NMR spectrum reveals that trans‐[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au−Ccarbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13C NMR spectrum is presented.

Highlights

Fluorido organo gold complexes are highly reactive species which take part in a large variety of gold-catalyzed or -mediated reactions.[1,2] Their reactivity derives from the relatively low AuÀF bond dissociation energy compared to many other known EÀF (E = element) bonds.[3]
The molecular structure of [AuF3(SIMes)] in the solid state reveals that the AuÀF bond with the fluorido ligand in trans position to the SIMes ligand is about 5 pm longer than those to the cis-fluorido ligands.[14]
When TMSCF3 is condensed into a DCM solution of [AuF3(SIMes)] at À80 8C in the presence of the nucleophilic fluoride source CsF, compound 1 is formed. 19F NMR spectroscopy investigations show that first only compound 1 is formed, but during the consumption of [AuF3(SIMes)], a second substitution reaction of a fluorido ligand by a trifluoromethyl group is observed, forming cis-[Au(CF3)2F(SIMes)] (2) in solution

Summary

Introduction

N-Heterocyclic carbene (NHC) ligands have attracted increasing attention for the stabilization of highly reactive compounds, for example, complexes that contain transition metals in high oxidation states, due to their steric demand and strong s-donating properties.[13] Recently, our group reported on the stabilization of AuF3 using the SIMes (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) ligand.[14] The resulting complex [AuF3(SIMes)] contains the highly Lewis acidic AuF3 unit in monomeric form and is stable in common organic solvents such as dichloromethane. This is contrary to AuF3, which is a fluorine-bridged polymer in the solid state and reacts unselectively and sometimes violently with most organic solvents.[15]. Overview of the preparation of the four literature-known, isolated fluorido trifluoromethyl gold complexes.[9,10,12]

Results and Discussion

Conclusions

Conflict of interest