Behavior of Group 6 Fischer Aminocarbene Complexes in a Supercharged Medium: A Single Electron Transfer−H Atom Transfer Process

The ESI-MS study of the ionization of a series of aryl, alkenyl, and alkynyl (Fischer) aminocarbene complexes is described. The process requires the initial capture of one electron from the ESI source, followed by the transfer of a hydrogen atom to the additive (TTF or Cs2CO3). Regardless of their structure, both NH and N,N-disubstituted aminocarbenes can effectively ionize under ESI-MS conditions, as long as they have abstractable H atoms. Overall, the process can be envisaged as a single electron transfer−H atom transfer process. The experimental findings are supported by DFT calculations. The ESI-MS ionization of bis-alkynylaminocarbene complexes follows the same patterns. However, the [M − H]− ions evolve by arylacetylene extrusion together with the usual sequence of CO loss. The process requires the presence of a free NH group and occurs by intramolecular hydrogen transfer from the NH to the metal center. Bis-aminocarbenes having rigid tethers between the nitrogen atoms or lacking free NH groups do not produce this fragmentation.