First synthesis, experimental and theoretical vibrational spectra of an oxametallacycle on a metal surface
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abstract
High-resolution electron energy loss spectroscopy (HREELS) studies were performed to examine the reactions of 2-iodoethanol (ICH2CH2OH) on the Ag(110) surface. The goal of these experiments was to isolate and spectroscopically characterize a stable surface oxametallacycle, an intermediate previously proposed but never isolated in the chemistry of a variety of oxygenates, including epoxides. The hydroxyethyl intermediate (- CH2CH2OH), formed from initial carbon-iodine bond scission, decomposed at 263 K to yield a variety of volatile products as well as a surface oxametallacycle (-CH2CH2O-). The oxametallacycle intermediate, formed at 263 K, remained intact until 340 K, permitting spectroscopic characterization by HREELS. Density Functional Theory (DFT) calculations were employed to determine the fully optimized structure for the oxametallacycle on silver and to predict the infrared spectrum and molecular motions for that structure. The excellent agreement between the infrared spectrum predicted for an oxametallacycle incorporating two silver atoms and the experimental HREEL spectrum conclusively identifies the surface oxametallacycle. The principal reaction channel for this intermediate in temperature programmed desorption (TPD) experiments is coupling of two oxametallacycles to form the cyclic product -butyrolactone, rather than the anticipated ring closure: pathway to form ethylene oxide. However, one of the vibrational modes predicted by DFT appears to be a possible reaction coordinate for the conversion of oxametallacycles to ethylene oxide.
