Density functional theory calculations for simple oxametallacycles: Trends across the periodic table

Density functional theory (DFT) was used to calculate the structures of simple oxametallacycles, generated by inserting one or two metal atoms in the C-O bond of the ethylene oxide molecule, for 14 different transition metals (groups VIIIa-c, Ib, IIb). The calculated energetic stability of these complexes generally decreases from left to right of the periodic table and from top to bottom of each group of metals. Silver, which is unique among these metals in catalyzing selective ethylene epoxidation, gives an oxametallacycle intermediate that is more stable than ethylene oxide by ca. 10 kcal/mol. The modest stability of this intermediate may explain the formation of the less energetically favorable C2H4O isomer, ethylene oxide, on silver catalysts. The calculated relative stabilities of oxametallacycles versus acetaldehyde on various metal surfaces are consistent with previous experimental observations that an oxametallacycle is the preferred intermediate in ethanol decarbonylation on the Rh(111) surface, whereas eta(2)-CH3CHO is preferred on the Pd(111) surface.