Electrospray ionization and liquid secondary ion mass spectrometric study of N-heterocyclic carbenes and their 1, 2, 4-triazolium salt precursors

摘要

N-Heterocyclic carbenes and their 1,2,4-triazolium salt precursors were analyzed by electrospray ionization (ESI) and liquid secondary ion mass spectrometry (LSIMS). It was found that under applied conditions the C5 carbene center is formed from [M + ClO_4]~+ ion, were M corresponds to the 1,2,4-triazolium dicationic system, by loss of HClO_4 molecule. Further decomposition of formed carbene ions, namely [M - H]~+ ion, consist in the breaking of triazolium ring and loss bulky substituents form N1 and N4 atoms through the hydrogen transfer to the carbene center. This is in contrast to the [M]~(2+) carbene precursor ions for which only the loss of N1 substituent occurred as a simple heterolytic bond cleavage.