Computational Analysis of the Effect on Sonogashira Coupling by Copper (I) Mixed-Ligand Chelation of 4,7-Disubstituted-1,10-Phenanthrolines: Towards Improving Substitution Chemistry in 1, 10-Phenanthrolines

When copper (I) is used to bind the nitrogen atoms of 1,10-phenanthroline through chelation, the reactivity at the 4 and 7 positions of the ligand is dramatically enhanced. Previous studies have demonstrated that yields can be increased through copper coordination from 5% to 90-95% for 4,7-substitution (distal side) of phenanthroline.1-3 DFT calculations have been performed on the pure 1,10-phenanthroline ligand, the ligand bound to copper with exogeneous coordinating groups, 4,7-dichloro-1,10-phenanthroline, and 4,7-dichloro-1,10-phenanthroline bound to copper in an attempt to determine the motivation for the profound change in substitution reactivity observed. In the case of the chloro-substituted ligand, chelation by copper (I) substantially reduces the heterolytic bond dissociation energy at the 4 and 7 positions, rendering the molecule susceptible to substitution. This is the computational code that was used, including the geometry units of the molecules.