Beattie, Jeffrey W., and Jonathan E. Stevens
Often reactions are catalyzed by the presence of metal ions. The role of copper in catalyzing the Sonagashira reactions1,2,3, a multistep coupling reaction which results in the linking of a terminal alkyne to an organic halide, is not completely understood. Researchers speculate that it proceeds with the deprotonation of a terminal alkyne, which is theoretically facilitated by the copper (I) cation.
This work uses ab initio molecular orbital and density functional calculations to understand the impact of complexation of Cu+ with acetylene and phenylacetylene. Modeling is done in the gas phase and in organic solvents. Results suggest that the resulting complex, which forms through coordination of π electrons to the Cu+ ion, is stable. The energy required to deprotonate the complex is reduced compared to that of the alkyne alone, hence increasing the acidity.
1. Chinchilla, R.; Nájera, C. The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry. Chem. Rev. 2007, 107, 874-922.
2. Stephens, R. D.; Castro, C. E. The Substitution of Aryl Iodides with Cuprous Acetylides. A Synthesis of Tolanes and Heterocyclics. J. Org. Chem. 1963, 28, 3313-3315.
3. M. J. Mio, private communication