Computational studies, mechanism cross-coupling

The groups of Hu and You reported a remarkable palladium-catalyzed oxidative cross-coupling of Af-containing heteroarenes 62 with diversely substituted thiophenes 47 to afford products 63A-D (Scheme 10.19). The Af-containing heteroarenes included electron-rich heterocycles such as xanthines and azoles as weU as electron-poor heterocycles such as pyridine IV-oxides. In cases where heteroarenes demonstrated sluggish reactivity, CuBr was used as an additive to assist C—H bond activation. A computational study provided support for a two-fold C—H activation pathway via a CMD mechanism. 

The main objective of this thesis is to apply computational methods to the study of Pd-catalyzed cross-coupling reactions with the aim of determining and/or better understanding their reaction mechanisms. In particular, three different Pd-catalyzed cross-coupling reactions have been investigated. A brief summary of the reasons that prompted us to study these reactions and the particular objectives established for each these studies are summarized next. 

Overall, theoretical calculations have been used in this thesis to determine, elucidate, and propose reaction mechanisms for Pd-catalyzed cross-coupling reactions. In particular, they have allowed the characterization of reaction intermediates and transition states involved in these processes. Hence, we can conclude that the results presented in this thesis prove that the use of computational methods, namely DFT calculations, is a very useful tool for the study of reaction mechanisms of homogeneous catalytic reactions. 

The laws of physics needed to answer the question are well known. Since the potential energy surface is given, one knows the masses of the colliders and so one only needs to solve the SchrUdinger equation. The problem of course is that the number of coupled equations that need to be solved is enormous and not yet within reach of present day computers. Necessarily then the theorist is restricted to studying model systems and construction of approximations. One type of approximation is to solve the exact classical mechanical equations of motion. One selects initial conditions which correspond to the experimental initial state, integrates the equations of motion forward in time till the process is over and then obtains cross sections, product distributions etc. In essence, Hamilton s equations of motion serve as a black box , whose structure is determined by the masses and the potential energy surface. This black box provides the necessary transformation from initial conditions to final conditions. 

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