Finding the mechanism of a reaction is a difficult task for complex processes. In particular, it is usually necessary to take into account the effect of the environment and of the temperature as it might change the reaction path and the intermediates geometries. From a theoretical point of view, the search for a mechanism consists in finding the most probable path connecting reactants to products which usually correspond to the Minimum Energy Path (MEP) linking the reactants to the products. In practice, one starts from an initial path and tries to optimize it down to the MEP. Studying the reactivity of such systems is difficult because they possess many conformations that introduce spurious transition states and spoil the main pathway optimization. Moreover, when studying chemical reactivity quantum methods are needed to describe bond breaking/formation leading to costly calculations. In this communication, we will present the method that we have developed to study complex reactions mechanisms and that is freely available in the Opt'n Path code[1,2] The originality of our approach is to use different sets of coordinates to describe the reactive moities and the spectator groups to produce good initial paths.With this method, we can focus on the main reactive process with no a priori: we are free to find any path connecting the reactants to the products. The presentation will be illustrated with mechanistical studies of organic and organometallic reactions in which our method has been successully used such as the multicomponent Ugi reaction or the indole formation catalyzed by Palladium.[3] [1] a) P. Dayal, J. Garrec, N. Chéron, R. Ramozzi, R. Grüber, P. Fleurat-Lessard to be submitted; b) N. Chéron, J.-F. Le Maréchal, P. Fleurat-Lessard Actualité Chimique 2013, 375-376, 91. [2] Opt'n Path v1.50, P. Fleurat-Lessard, P. Dayal, Freely available at http://perso.ens-lyon.fr/paul.fleurat-lessard/ReactionPath.html. [3] a) R. Grüber, P. Fleurat-Lessard Organometallics 2014, 33, 1996; b) Chéron, N.; Ramozzi, R.; El Kaim, L.; Grimaud, L.; Fleurat-Lessard, P. J. Org. Chem., 2012, 77, 1351; c) Ramozzi, R.; Chéron, N.; El Kaim, L.; Grimaud, L.; Fleurat-Lessard, P. Chem. Eur. J. 2014, 20, 9094.

Chemist view on reaction pathways

249th National Meeting (2015)

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