Reactions of urea with Cu+ in the gas phase: An experimental and theoretical study

The gas-phase reactions between Cu+ and urea have been investigated by mean s of mass spectrometry techniques. The primary products formed in the ion s ource correspond to [urea-Cu](+), [(urea)(2)-Cu](+), and [Cu+,C,N-2,H-2] co mplexes. The MIKE spectrum of [urea-Cu](+) complex shows several spontaneou s losses, namely, NH3 and HNCO. A very weak peak corresponding to the loss of H2O is also observed, as well as a minor fragmentation of the adduct ion to yield Cu+. The structures and bonding characteristics of the different complexes involved in the urea-Cu+ potential energy surface (PES) were inve stigated using density functional theory (DFT) at the B3LYP level of theory and a valence triple-xi. Attachment of Cu+ takes place preferentially at t he carbonyl oxygen atom, while attachment at the amino group is 12.4 kcal/m ol less exothermic. Insertion of the metal cation into the C-N bonds of the neutral is predicted to be slightly exothermic, in contrast with what was found for formamide and guanidine. The estimated urea-Cu+ binding energy (6 2.3 kcal/mol) is 6.0 kcal/mol greater than that of formamide. The explorati on of the PES indicates that there are several reaction paths leading to th e loss of ammonia yielding as product ions HNCOCu+ complexes where the meta l cation is attached either to the oxygen or the nitrogen of the HNCO speci es. Also several reaction paths can be envisaged for the loss of HNCO, in w hich bisligated [HNCO-Cu-NW3](+) and [OC(NH)-Cu-NH3](+) complexes play an i mportant role.