Preparation of Tremorine and Gemini Surfactant Precursors with Cationic Ethynyl-Bridged Digold Catalysts

Tremorine and precursors of gemini Surfactants were synthesised in a one-pot, three-step, double-catalytic A³ coupling reaction and characterised by structural and spectroscopic methods. The cationic [Au^I (L1)]SbF₆ complex is a more active catalyst compared to neutral L2- and L3-Au^I bis(trifluoromethanesulfonyl)imidate complexes (L1, L2=Buchwald-type biaryl phosphane; L3=triphenylphosphine) in promoting the double A³ coupling of ethynyltrimethylsilane, secondary amines (cyclic, aliphatic, or aromatic) and formaldehyde. The solvent influences the catalytic performance by desilylation of silyl acetylene or deactivation of the catalyst by a halide anion. Acetylide-bridged cationic digold(I) L1 and L2 complexes were isolated and characterised by means of single-crystal X-ray structure analysis and their spectroscopic properties. Iodine in the acetylene reagent deactivates the Au^I catalyst by formation of the less active iodido-bridged cationic digold(I) L1 complex, which was fully characterised by single-crystal X-ray crystal structure analysis and spectroscopy. The nature of the phosphine ligand of the gold complexes used as catalyst affects the stability and activity of the formed cationic ethynyl-bridged Au^I₂ -L intermediates, isolation of which lends support to the proposed double A³ coupling mechanism.

alkyne ligands; gold; homogeneous catalysis; multicomponent reactions; phosphane ligands.