CATALYSIS OF ETHYLENE DIMERIZATION BY COMPLEXATION WITH METAL RADICAL CATIONS - AN ABINITIO STUDY

The 2s + 2s cycloaddition of ethylene, a forbidden Woodward-Hoffmann type closed-shell reaction, is illustrated by ab initio calculations to be catalyzed by complexation with Be.+. The reaction path calculated proceeds via a metallacyclopentane radical cation intermediate and two successive 1,2-hydrogen shifts to form the isomeric butenes. The possible reaction to cyclobutane by formation of a second carbon-carbon bond from the metallacyclopentane has also been examined. The complexed dimerization reaction is found to be exothermic for all products (26.3 kcal mol-1 for 1-butene, 27.9 kcal mol-1 for cis-2-butene, 29.5 kcal mol-1 for trans-2-butene, and 21.3 kcal mol-1 for cyclobutane) with no point on any of the reaction paths higher in energy than the starting point, Be.+ + 2C2H4. Remarkable parallels to transition-metal-catalyzed dimerizations are found.