Theoretical study of ethylene addition to O=W(=CH₂)(CH ₃)₂

Quantum chemical calculations using density functional theory at the B3LYP level of theory were carried out to investigate the reaction pathways for the addition of ethylene to WO(CH₃)₂(CH₂) (W1). The results are compared to those of previous theoretical studies of the ethylene addition to OsO₃(CH₂) (Os1) and ReO₂(CH ₃)(CH₂) (Re1). The theoretically predicted reactions pathways exhibit significant differences. The energetically most favourable reaction of the tungsten system W1 is the [2+2]_W,C addition across the W=C double bond yielding the metallacyclobutane W3a which then rearranges to the slightly more stable isomer W3b. The [2+2]_Re,C addition of the rhenium compound yielding the metallacyclobutane Re3a has the lowest activation barrier for the ethylene addition to the rhenium system, but the reaction is endothermic while the exothermic formation of the more stable isomer Re3b has a much higher activation barrier. The [3+2]_C,O addition Os1 + C ₂H₄ → Os2 is the thermodynamically most favorable reaction of the osmium compound.