[en] This work presents a density functional theory study of the norbornene ROMP metathesis reactions. The energies have been calculated in a Grubbs catalyst model Cl₂(PH₃)₂Ru=CH₂. The geometries and energy profile are similar to the Grubbs methylidene (Cl₂(PCy₃)₂Ru=CH₂ real model. It was found that the metathesis reaction proceeds via associative mechanism (catalyst-norbornene) followed by dissociative substitution of a phosphine ligand with norbornene, giving a monophosphine complex. The results are in reasonable agreement with the available experimental data. The dissociation energy of the phosphines is predicted to be 23.2 kcal mol^-1. (author)