A computational study of the mechanism of palladium insertion into alkynyl and aryl carbon-fluorine bonds

An ab initio molecular orbital study using both gas-phase and B3LYP/DZVP-COSMO solvation models of the mechanism of palladium insertion into alkyne and aryl carbon-halogen bonds suggests that the mechanism of palladium insertion into alkyne species can proceed via a concerted oxidative addition across the carbon-halogen bond. A stepwise mechanism via a sigma-complex is favoured when a nitro group is introduced onto the alkyne. The palladium insertion into variously substituted aryl fluorides was again found to proceed via a single-step concerted mechanism, and although a sigma-complex can be located when 2,4-dinitro and 2-nitro substitution is present, the energy of this stepwise route is very similar to the concerted pathway and no clear decision on the pathway can be made. No intermediate sigma-complex could be located for eta(6)-tricarbonylchromium-complexed fluorobenzene, and only a concerted pathway was identified.