Interaction charge transfer-induced electrostatic

When the protonated amine-arm does not participate in the reaction (TS1-I ), the reaction is very endothermic. However, the activation barrier decreases to 2.6 kcal/mol and the endothermicity of the reaction becomes very small (only 0.2 kcal/mol), if the protonated amine-arm participates in the reaction (TS1-II). In this transition state the O-H distance is 1.709A, typical of a hydrogen bond. The origin of the acceleration was explained in terms of the enhancement of polarization of CO2 induced by the protonated amine arm, which increases the positive charge in the carbon atom. This polarization favors the electrostatic interaction between hydride and C02, and since this polarization increases the contribution of the C p orbital in the it orbital of C02, it favors also the charge-transfer from the H ligand to the 71 orbital of C02. In other paths starting with direct interaction between C02 and Ru the effect of the protonated amine was much smaller. 

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