Density Functional Study on the Hydrido Migration to CO2 and CS2 of the (η5-C5H4(CH2)3NH3+)MH(H2PCH2PH2) (M = Fe, Ru, and Os) Complexes Promoted by the Protonated Amine Arm. Which Path Does the Reaction Take, Abstraction or Insertion?

Abstract

We have performed theoretical calculations for the hydrido migration to the CO2 and CS2 carbon of the Fe, Ru, and Os complexes which have an intramolecular N−H···H−M H-bond by the hybrid density functional method (B3LYP) using the model complexes (η5-C5H4(CH2)3NH3+)MH(H2PCH2PH2) (M = Fe, Ru, and Os). In the previous study (Matsubara, T. Organometallics 2001, 20, 19−24), we investigated the reaction mechanism for the Ru complex assuming the two considered pathways, i.e., (a) the abstraction of the hydrido ligand by an incoming CO2 without direct coordination of CO2 to the Ru atom, and (b) the insertion of CO2 to the Ru−H bond with the η2-CO precoordination of CO2 to the Ru atom, and found a quite interesting fact that the generally unlikely path a due to its energetical difficulty is more favorable than path b, which has been considered in most cases. This is because the protonated amine arm effectively functions to promote only the electrophilic attack of CO2 in path a and remarkably stabilizes the product to make the potential energy surface of the reaction quite smooth. In the present study, we have further examined the effects of the metal and solvent on the reactivity and the mechanism and also the hydrido migration to CS2, which is completely different from CO2 in the charge distribution, to search the other significant factors that determine the reactivity and the reaction path.