Fourier Transform Infrared Spectroscopic Characterization of Olefin Complexation by Silver Salts in Solution

Complex formation between 1-hexene and silver salts in chloroform solution has been characterized using Fourier transform infrared spectroscopy. Silver tetrafluoroborate, AgBF4, and silver triflate, AgCF3SO3, form 1:2 Ag+:1-hexene complexes in solution. The olefinic CC vibrational stretching frequency at 1640 cm-1 in 1-hexene shifts to approximately 1580 cm-1 upon complexation with these silver salts. Silver trifluoroacetate, AgCF3CO2, exhibits limited complexation and silver nitrate, AgNO3, exhibits no measurable complexation. Salts with the larger BF4- and CF3SO3- anions have a much stronger tendency to form complexes than those with the smaller NO3- and CF3CO2- anions. The tendency of these salts to form complexes in solution was most strongly correlated with anion size and was not well-correlated with measures of anion-donor electron density or softness parameter. The effect of ether-containing compounds, such as triethylene glycol (TEG) and poly(ethylene glycol) (PEG), on the silver−olefin interaction in chloroform solution was also studied. The formation of a silver ion−ether oxygen−olefin complex is consistent with the data. For TEG added to a solution of AgBF4 and 1-hexene in chloroform, there are approximately 2.5 oxygens per silver ion in the complex. For PEG added to a solution of silver triflate and 1-hexene in chloroform, there are approximately 1.8 oxygens per silver ion.