Radical-Like Activation of Alkanes by the Ligated Copper Oxide Cation (Phenanthroline)CuO

Electrospray ionization mass spectrometry of copper(II) nitrate solution in the presence of phenanthroline (phen) leads to the generation of the monocation (phen)Cu(NO3)+ from which NO2 is lost at elevated collision energy concomitant with formation of the ligated copper oxide cation (phen)CuO+. This structural assignment is based on the characteristic loss of atomic oxygen upon collision-induced dissociation (CID) of the mass-selected ion. In addition, loss of carbon monoxide is observed to occur upon CID, which is assigned to a transfer of the oxygen atom from the copper to the ligand to presumably afford phenanthrolinone/Cu+ followed by decarbonylation. Mass-selected (phen)CuO+ is found to react with alkanes larger than ethane. With propane, (phen)CuOH+ and (phen)Cu+ are formed as ionic products corresponding to hydrogen-atom abstraction and oxygen-atom transfer, respectively. Deuterium labeling reveals a moderate preference for the activation of secondary C−H bonds, which resemble the reactions of propane with chlorine atoms. Several minimum structures of relevant species have been optimized by density-functional calculations (B3LYP/TZVP) to obtain some thermochemical information on key intermediates along the reaction pathways. From the results, a qualitative potential-energy surface for alkane activation is suggested. With the unsaturated hydrocarbons ethene, propene, and benzene, almost exclusive oxygen-atom transfer is observed.