Terminal acetylene-silver trifluoromethanesulfonate π complexes. Synthesis, stoichiometry, and activation of the terminal carbon---hydrogen bond

Terminal acetylene---silver(I) trifluoromethanesulfonate π complexes have been isolated. They are of 1 : 1 stoichiometry in the solid state and solution with all carbon---carbon triple bonds coordinated to silver ion. Their stability constants as measured by proton NMR are strongly solvent dependent and decrease in the order 1,5-hexadiyne> 1,7-octadiyne> 1-hexyne, 3-methyl-1-pentyne> 3,3-dimethyl-1-butyne. IR and NMR analysis indicates weakening and polarization of the terminal carbon---hydrogen bond upon silver ion coordination. In solution terminal acetylenes π coordinated to silver ion undergo deuterium exchange approximately 10⁵ times faster than uncoordinated acetylenes. The mechanism of deuterium exchange does not involve silver acetylides as intermediates.