CATALYSIS OF THE RING-OPENING AND ISOMERIZATION OF CYCLOPROPANE BY COMPLEXATION WITH METAL RADICAL CATIONS - AN ABINITIO STUDY

The ring opening and isomerization of cyclopropane are shown by ab initio calculations to be catalyzed by complexation with Be.+. The reactions proceed via a common metallacyclobutane radical cation intermediate formed in a reaction that is endothermic by 12.3 kcal mol-1 relative to the cyclopropane-Be.+ complex. From this intermediate, three alternative reaction paths were examined, two isomerizations to give a propene-Be.+ complex and a C-C bond cleavage forming a carbene-ethylene-Be.+ species. These reactions are found to be exothermic by 5.4 and 5.2 kcal mol-1 relative to the cyclopropane-Be.+ complex, respectively. The isomerization of cyclopropane to give propene is calculated to be exothermic by 8.0 kcal mol-1 (exptl 7.9 kcal mol-1). Remarkable parallels to transition-metal catalyzed reactions were found for all the reactions examined.