Gold(I)‐Catalysed Asymmetric Hydroamination of Alkenes: A Silver‐ and Solvent‐Dependent Enantiodivergent Reaction

Abstract

In the present study, we report the first silver-dependent enantiodivergent gold-catalysed reaction. The asymmetric intramolecular hydroamination of alkenes catalysed by the combination of a single chiral binuclear gold(I) chloride complex and silver perchlorate can afford both enantiomers of the products by a simple solvent change from toluene to methanol. Such an enantiodivergent reaction is strictly independent of the reaction temperature or of the nature of the catalyst anion and displays the same first-order kinetic rate law with respect to substrate concentration in both solvents. Beyond a simple solvent effect the enantioinversion is controlled by gold-silver chloride adducts which occur only in methanol and allow a dual activation of the reagent. While one single gold atom activates the alkene moiety, the other gold atom forms an oxophilic gold-silver chloride adduct which is likely to interact with the carbamate function. By comparison with toluene, which affords (S)-enantiomer, this proximal and bimetallic activation would allow an opposite stereodifferentiation of the two diastereomeric intermediates during the final protodeauration step and lead therefore to the (R)-enantiomer.

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

“…Many more synthetic efforts have been made in this area with gold(I)-phosphine complexes. Michon and Agbossou-Niedercorn investigated intramolecular hydroamination of alkenes in details, and better enantioselectivity were obtained in the case of bisphosphine ligand 170 [115,119,120]. The authors also observed a rare dependence of configuration of newly formed stereogenic center on the presence of silver salt [120].…”

Origin of Enantioselectivity Reversal in Lewis Acid-Catalyzed Michael Additions Relying on the Same Chiral Source

“…29 However, these specific substrate-metal complex interactions have not been observed to result in a complete reversal of enantioselectivity depending on the choice of metal catalyst. While a number of previous reports [6][7][8][9][14][15] have observed metal-dependent enantiodivergence, reliance on an additional Lewis basic site of the reactive substrate has not previously been suggested as a rationale for such a reversal. In this system, the choice of metal influences the coordination environment of the metal-ligand complex while the active participation of a Lewis basic site in the substrate is critical to induce the observed reversal of enantioselectivity.…”

“…Several reports observing a reversal in enantioselectivity with the same chiral source exist, including the use of distinct metals, 6 counterions, 7 the introduction of subtle structural modifications of the catalyst system, 8 or simply changes in solvent or temperature. 9 Nevertheless, the design of effective and general catalytic asymmetric methods to induce complete reversals in enantioselectivity continues to be a challenge. 5e,f Importantly, often only one of the two enantiomers is obtained in high enantiomeric excess since it is difficult to induce large energy differences between transition states that lead to the competing products required for effective enantiodivergence.…”

Reactivity Studies of Cationic Au(III) Difluorides Supported by N-Ligands

“…The chemistry of organometallic and coordination complexes containing an Au-F bond is underdeveloped, with only 8 unique compounds for Au( I) [1][2][3][4][5][6] and 15 for Au(III) [7][8][9][10][11][12][13][14][15][16] as well as a single Au(II) complex 17 having been characterized by X-ray crystallography. The first was described in 2005, with most examples being reported in the past 5 years as interest in the area increases.…”