Abstract
Density functional theory calculations have been used to investigate the activation steps involving three of the most used alkylidene groups in Ru-catalysts for olefins metathesis. Specifically, we compared the benzylidene, the indenylidene and a phosphonium alkylidene groups. Calculations reveal that the benzylidene and the indenylidene groups behave rather similarly, despite their structural differences. The phosphonium alkylidene group seems to have the most favourable activation pathway.