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

Abstract

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 [AuI (L1)]SbF6 complex is a more active catalyst compared to neutral L2- and L3-AuI 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 AuI 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 AuI2 -L intermediates, isolation of which lends support to the proposed double A3 coupling mechanism.