Deconvolution of the Mechanism of Homogeneous Gold-Catalyzed Reactions

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-carbonylphenylallcynes 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. P-31 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 AuCl3 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.