Deconvolution of the Mechanism of Homogeneous Gold-Catalyzed Reactions

Abstract

The role of chiral counterions in gold-catalyzed asymmetric intramolecular hydroamination/hydroalkoxylation reactions of allenes and the oxidation state of the gold catalyst in the benzannulation of 2-carbonylphenylalkynes have been investigated using XAFS at the L3 edge of gold. Fitting of experimental data indicated a bond between cationic gold and a BINOL-phosphate anion in solution. 31 P NMR confirmed that this phosphate group is likely not to be labile and may stay bonded to the gold catalyst during the catalytic cycle. In the benzannulation reaction, XAFS analysis suggested the majority of gold species obtained from reacting starting material with AuCl 3 to be Au(III) complexes. NMR and mass spectrometry characterization led to the previously unobserved intermediate 10. gem-Diaurate complexes, which have been previously proposed as possible intermediates, were not detected.

Intermolecular Mono‐ and Dihydroamination of Activated Alkenes Using a Recoverable Gold Catalyst

“…Finally, the mechanism of gold‐catalyzed asymmetric intramolecular hydroamination/hydroalkoxylation of allenes was recently investigated by Nguyen et al using a chiral phosphate counterion. The latter was shown to act as a ligand phosphate counterion was shown to act as a ligand for the gold species during all reactions 14. These, and other findings, support the idea that achieving a deep understanding of gold catalyst activity in hydroamination reactions remains a challenging endeavor.…”

Gold(III)‐Mediated Contraction of Benzene to Cyclopentadiene: From p‐Benziporphyrin to Gold(III) True Tetraarylcarbaporphyrin

“…The detected contraction adds an unprecedented route to numerous organic transformations of aromatic compounds catalyzed by simple gold-(III) compounds. [17,18,21] At present, relatively little is understood considering the real active catalytic species, [18][19][20] but, herein, a gold(III) p-bonding interaction is instrumental for contraction, an interaction that is frequently postulated as an essential step. [18,22,23] Although the present work has allowed the first Scheme 5.…”

“…The choice of metal cation is strongly motivated by the rising interest in reactions catalyzed by gold nanoparticles and gold(I) or gold(III) compounds. [16][17][18][19][20][21][22][23] Herein, we report on the formation and characterization of gold(III) 21-carbaporphyrin, in which the CNNN coordination cavity comprises four trigonally hybridized donor atoms.…”

Insights into the mechanism for gold catalysis: behaviour of gold(i) amide complexes in solution

“…8 For all the evidence for complexes which, in the solid state, display coordination numbers for gold that exceed two, the rationalisation of gold catalysis in solution rarely invokes species with coordination numbers that exceed two unless they are hypothesised in transition states of complex-induced activation reactions. 5,7,8,[22][23][24] Despite the ever-growing database of transformations catalysed by gold(I) and the proposed cationic nature of the complex in these transformations, little experimental information is available regarding the existence in solution of a tricoordinate gold species and the general nature of gold complexes in solution.…”