Exploring Mechanistic Pathway of C-F Bond Activation to C-C Bond Formation with Grignard Reagents by First Principles Simulations

Kansal, Dhwani and Mallik, Bhabani Shankar (2015) Exploring Mechanistic Pathway of C-F Bond Activation to C-C Bond Formation with Grignard Reagents by First Principles Simulations. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

Nucleophilic substitution reaction to form C-C bond from C-X bond with assistance of transition metal catalyst is one of the novel synthetic method for synthesis in organic chemistry. Recently, chemists have developed new synthetic methods for the formation of C-C bond from C-F bond with Grignard reagents without transition metal catalyst. Organofluorine compounds are of great importance and this proves to be a highly efficient method for the carrying out C-F activation to give C-C coupled product. The aim of this thesis is to predict the plausible mechanism for the pathway in going from C-F to C-C bond with nucleophilic Grignard reagents and to predict the transition state which is the highest point in the potential energy surface in going from reactant to product along the reaction coordinate. Here we present a computational study for the mechanistic pathway and the prediction of transition states for the reactions involving alkyl and aryl fluoride with aryl Grignard reagents. We have carried out ab-initio (HF/3-21G*) and density functional theory (DFT) calculations with hybrid functional B3LYP using 6-311+G (2d,p) basis set to study the reaction mechanism. Activation of both sp3 C-F bond and sp2C-F bond was investigated and it was observed that due to comparatively shorter bond length of aryl C-F bond the reaction requires some activating/directing groups in the latter case. The effect of halide and the mechanism with dimer of Grignard reagent was also examined. It was observed that the reaction goes via transition state in which the alkyl group becomes planar and magnesium is tetrahedrally coordinated. In case of sp3 C-F bond activation a cyclic four membered transition state is formed whereas in case of sp2C-F bond activation with directing groups a six membered transition state is formed.

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