Reactivity of CO2 towards Mo[N(R)Ph)3]

The Laplaza/Cummins L3Mo (L = N(R)Ar) system is a very important complex for activating small molecules such as N2. Previous experimental work has shown that CS2 binds to the L3Mo system and forms an Mo-CS-Mo intermediate, while the environmentally important CO2 molecule is unreactive. The aim of this paper is to explain why there is this contrast in reactivity. We have used density functional methods to show that at first glance the reaction of 3L3Mo + CO2 should proceed smoothly to give L3Mo-O + L3Mo-CO-MoL 3. However initial coordination of the CO2 molecule to L3Mo does not take place because of the bending of CO2, the energy required to cross from the doublet to the quartet state, and the lower metal-CO2 binding energy compared to metal-CS2. The subsequent formation of the L3Mo-CO-MoL3 intermediate is similarly unfeasible due to steric and entropic effects. We have provided a molecular orbital rationalization for these effects and have also shown that it is important to take account of steric factors in order to get an accurate understanding of the energetic picture. © 2009 The Royal Society of Chemistry.