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

Abstract

Electrospray ionization mass spectrometry of copper(II) nitrate solution in the presence of phenanthroline (phen) leads to the generation of the monocation (phen)Cu(NO 3 ) + from which NO 2 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 massselected 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.

On-line electrogeneration of copper-peptide complexes in microspray mass spectrometry

“…When copper salts are used, Cu ϩ ions are produced either by specific preparation of a copper(I) salt [18,19] or by gas-phase reactions using a copper(II) salt. In ESI-MS studies, Cu ϩ ions are produced by reduction of Cu 2ϩ during the ionization process [20 -22] [24].…”

Electrochemical generation of Cu(I) complexes in aqueous solutions studied by on-line mass spectrometry

“…Cu 2+ reduction can be favored by increasing the nozzle-skimmer voltages or the source voltage. Schrö der et al have also observed this phenomenon by increasing the cone voltage tension [25]. Gianelli et al have reported the effect of the presence of solvents on Cu 2+ reduction and correlated the production of Cu + with the ionization energy of alcohols [26].…”

“…This massto-charge ratio corresponds to a ligated copper oxide cation: [BCP + CuO] + . Schrö der et al have characterized this kind of complex with phenanthroline using copper(II) nitrate [25]. This compound stems from a Cu 2+ complex in solution coordinated with nitrate and reduced in gasphase.…”

About the Electrospray Ionization Source in Mass Spectrometry: Electrochemistry and On-chip Reactions

“…Another peak corresponding to [BCP + CuO] + (1:1 complex) was present at a relative abundance of 18% and stemmed from a copper(ii) complex in solution. [24,28] This small quantity of copper(ii) ions can be released in solution from the oxidation of uncomplexed copper(i) ions. On the other hand, when the experiments were performed in presence of a copper(ii) salt and with a Pt electrode the 1:1 complex was much higher (81% of relative abundance), but the 2:1 complex was still the most abundant.…”

“…This formation of copper(i) complexes from a copper(ii) salt can be explained by the reduction of Cu 2+ to Cu + in gas phase. [28,29] Cu + ions formed in gas phase were able to react with ligands offering a better affinity. However, UV-vis experiments carried out after electrodissolution of copper in the spray solution containing BCP corroborated the formation of Cu + complexes in solution.…”