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. Silve r tetrafluoroborate, AgBF4, and silver triflate, AgCF3SO3, form 1:2 Ag+:1-h exene complexes in solution. The olefinic C = C vibrational stretching freq uency at 1640 cm(-1) in 1-hexene shifts to approximately 1580 cm(-1) upon c omplexation with these silver salts. Silver trifuoroacetate, AgCF3CO2, exhi bits limited complexation and silver nitrate, AgNO3, exhibits no measurable complexation. Salts with the larger BF4- and CF3SO3- anions have a much st ronger tendency to form complexes than those with the smaller NO3- and CF3C O2- anions. The tendency of these salts to form complexes in solution was m ost strongly correlated with anion size and was not well-correlated with me asures of anion-donor electron density or softness parameter. The effect of ether-containing compounds, such as triethylene glycol (TEG) and poly(ethy lene glycol) (PEG), on the silver-olefin interaction in chloroform solution was also studied. The formation of a silver ion-ether oxygen-olefin comple x is consistent with the data. For TEG added to a solution of AgBF4 and 1-h exene 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.