MOLECULAR-ORBITAL INVESTIGATION OF THE OXIDATION OF OLEFINS BY CIS-RUTHENIUM(IV) AND TRANS-RUTHENIUM(VI)-DIOXO COMPLEXES

The INDO/1 semi-empirical molecular orbital model is employed to analyze the reaction between olefins and cis-and trans-Ru(VI)-dioxo complexes. Interesting differences in the reactivity of these seemingly similar complexes toward olefins exist. For the cis-RuVIO2 system, products formed from the cleavage of the C=C double bond (i.e. carbonyls) are obtained. The trans isomer is selective for epoxidations. Three distinct pathways for interaction between the cis-RuO2 complex and ethylene were considered—[1 + 2], [2 + 2], and [3 + 2] cycloaddition—as were the intermediates derived from these pathways. The dioxometallacycle is formed from the [3 + 2] pathway. INDO/1 calculations show that the dioxometallacycle is the global minimum for the interaction of ethylene and the cis-RuO22+ complex. Conversion of the dioxometallacycle to epoxide products is energetically unfavorable. For the trans-RuVIO2 complex no dioxometallacycle forms and only epoxides (by a nonconcerted [1+2] pathway) are formed. © 1990, American Chemical Society. All rights reserved.